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Saturday, January 28, 2012

The phenotypic fate and functional role for bone marrow-derived stem cells in liver fibrosis

Journal of Hepatology
Article in Press

The phenotypic fate and functional role for bone marrow-derived stem cells in liver fibrosis

Tatiana Kisseleva
Affiliations
Corresponding author. Address: 9500 Gilman Drive # 0702, La Jolla, CA 92093, USA. Tel.: +1 858 822 5339., David A. Brenner Dept. of Medicine, University of California, San Diego, CA, USA

Received 5 April 2011; received in revised form 12 August 2011; accepted 4 September 2011. published online 14 December 2011.

Corrected Proof


Summary
Liver fibrosis is an outcome of chronic liver injury of any etiology. It is manifested by extensive deposition of extracellular matrix (ECM) proteins that produce a fibrous scar in the injured liver. Bone marrow (BM) cells may play an important role in pathogenesis and resolution of liver fibrosis. BM cells contribute to the inflammatory response by TGF-β1 secretion and activation of liver resident myofibroblasts. Moreover, BM itself can serve as a source of collagen expressing cells, e.g. BM-derived fibrocytes and mesenchymal progenitors, which in turn, have a potential to in situ differentiate into fibrogenic myofibroblasts and facilitate fibrosis. Finally, BM cells play an active part in resolution of liver fibrosis after cessation of fibrogenic stimuli. While natural killer (NK) cells are implicated in apoptosis of activated hepatic stellate cells/myofibroblasts, cells of myelo-monocitic lineage secrete matrix metalloproteinases to actively degrade the fibrous scar. The focus of this review is on the current understanding of the role of different subsets of BM cells in the onset, development and resolution of liver fibrosis.

Introduction 
Liver fibrosis is caused by chronic injury which triggers apoptosis of hepatocytes, damage of the endothelial barrier, recruitment of inflammatory cells, increased secretion of TGF-β1, and activation of myofibroblasts responsible for scar formation [10], [50]. However, the contribution of bone marrow (BM) cells to liver fibrosis remains controversial [44], [51]. At the onset of fibrosis, BM cells are recruited to the site of injury to facilitate inflammation. It is believed that monocytes and macrophages are the primary source of TGF-β1, the major fibrogenic cytokine that plays a critical role in activation of fibrogenic myofibroblasts.

Myofibroblasts express type I collagen and other extracellular matrix proteins that constitute the fibrous scar in liver fibrosis. Three sources of myofibroblasts have been identified: hepatic stellate cells (HSCs) in hepatotoxic liver injury [27], portal fibroblasts in cholestatic liver injury [18], and fibrocytes in any inflamed liver (Fig. 1). Most myofibroblasts retain the markers of being originally derived from either fibroblasts (such as Thy1 and elastin), HSCs (such as vitamin A droplets, GFAP, and desmin), or fibrocytes (CD45). Theoretically, myofibroblasts may also be derived directly from a precursor cell, unrelated to stellate cells, fibroblasts, or fibrocytes. Cell fate mapping studies in reporter mice have demonstrated that both hepatic stellate cells and fibroblasts are septum transversum mesenchymal cells that migrate from the mesothelium and submesothelium C [5].



  • Figure 1


    Possible origins of fibrogenic myofibroblasts.
    Hepatic myofibroblasts may originate from liver resident mesenchymal cells. These include hepatic stellate cells, which under physiological conditions reside in the space of Disse in a quiescent state, and in response to injury undergo activation into myofibroblasts. Portal fibroblasts may also be a source of myofibroblasts in the fibrotic liver. In addition, BM-derived hematopoietic and mesenchymal cells may contribute to the myofibroblast population. While the role of mesenchymal stem cells in liver fibrosis is not well characterized due to the lack of specific markers and difficulties with their isolation, hematopoietic stem cells contribute to hepatic fibrocytes in response to liver injury.
Cessation of the injury often causes resolution of liver fibrosis with resorption of the fibrous scar [40], [41]. Under these circumstances, activated myofibroblasts undergo senescence [53], [77], [80], apoptosis and disappear [42], [73]. It has been shown that NK (and NKT) cells facilitate aHSCs apoptosis during regression of fibrosis [72], while newly recruited monocytes actively degrade extracellular matrix proteins (ECM) [20] via upregulation and secretion of matrix metalloproteinases (e.g. MMP13) [95] and collagenases [43].

Stem cell biology has become one of the most intensely studied areas of biomedical research and there is great optimism among scientists and the lay public that stem cells will be used as novel therapies for many incurable chronic diseases. Many institutions, including the State of California, have committed billions of dollars specifically to promote stem cell research with the goal of developing new therapies within a few years. As a result of new insights into stem cells, there is a renewed interest in the role of the bone marrow and its stem cells in liver fibrosis. The information to date is very conflicted, with different studies showing either a contributing effect or a therapeutic effect of bone marrow-derived cells to liver fibrosis.

Many studies have raised the issue of whether liver myofibroblasts may be derived from bone marrow stem cells, either hematopoietic or mesenchymal stem cells. Due to their well defined cell lineage markers and methodology for hematopoietic stem cell transfer, the contribution of hematopoietic stem cells to the population of liver myofibroblasts may be readily assessed in experimental murine liver fibrosis.

This review will address three issues: (1) the role of BM-derived macrophage to liver fibrogenesis, (2) the contribution of BM cells to myofibroblasts in the fibrotic liver, and (3) the role of BM stem cells in the resolution of liver fibrosis.

Inflammation
Expression of collagen type I marks fibrogenic/hematopoietic cells

While the fibrogenic properties of fibrocytes will be discussed below, it is important to note that expression of collagen type I by hematopoietic cells has a critical role in the development and maturation of hematopoietic BM cells required to mediate injury-triggered immune responses [22], [78], [89]. First, activated macrophages upregulate collagen type I upon maturation and migration to the site of injury [67]. Surprisingly, the level of collagen expression in activated macrophages is similar to activated cultured fibrocytes or fibrocyte-like cells [67]. Second, upregulation of collagen type I is associated with maturation of hematopoietic stem cells [22], [78], [89]. It is unknown why collagen expression is required for the function of hematopoietic stem cells. A recent study suggested that collagen I regulates the self-renewal of mouse embryonic stem cells through α2β1 integrin- and DDR1-dependent Bmi-1 [89]. However, the level of collagen expression in activated macrophages and fibrocytes is relatively low compared to activated myofibroblasts [67], [79], so that these cells are not major sources of collagen, but most likely mediate cellular interaction [78] with extracellular matrix causing cytoskeletal rearrangement [17], [31], [86].




Increased intestinal permeability has a critical role in the pathogenesis of liver fibrosis [81], [104]. Recent studies have demonstrated that in addition to phagocytosis, neutrophils, macrophages, and fibrocytes may utilize an alternative pathway to combat bacteria, by releasing extracellular DNA-based traps enriched in histones and major antimicrobial enzymes, cathelescidin and myeoloperoxidase [12], [16], [97], [106]. It remains unclear why terminally differentiated cells with phagocytic capacity decide to intake or exterminate bacteria [16]. This mechanism is activated in Vegenar granulomatosus [46] and Lupus nephritis [34]. Although the significance of such phenomenon for liver fibrosis still has to be investigated, fibrocyte-like cells from the spleen (CD45+Collagen-α1(I)+ BM-derived cells) may form DNA traps following LPS- or CCl4-induced liver injury [52]. Thus, identification and classification of fibrocytes and fibrocyte-like cells recruited to the injured liver may provide new insights into the pathogenesis of liver fibrosis.

Recruited BM macrophages induce fibrosis
BM macrophages and Kupffer cells (liver resident macrophages) are the major source of TGF-β1 in liver fibrosis [81]. T and B lymphocytes are also recruited to the site of injury and further facilitate secretion of fibrogenic cytokines. Ablation of myolo-monocytic CD11b+ cells in mice at the onset of liver fibrosis attenuated activation of fibrogenic myofibroblasts and collagen deposition in liver and kidney fibrosis [20], [21], [45].

Bacterial flora and toll-like receptor (TLRs) signaling are critical in the activation of Kupffer cells/macrophages and TGF-β1 release [81]. For example, TLR4 mutant and knockout mice are resistant to fibrosis of different etiologies [38]. Moreover, genome wide analysis studies have demonstrated that individuals carrying a low efficiency polymorphism in TLR4 gene are less susceptible to HCV-induced liver fibrosis [56]. Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns (PAMP) such as lipopolysaccharide (LPS), bacterial cell wall component, peptideglycan, and bacteria-derived unmethylated CpG-DNA [38]. In addition, endogenous ligands (alarmins, e.g. HMGB-1, hyaluronan) can bind TLR4 in the presence of CD14 and LPS-binding protein [LBP) and transduce similar signals [105]. Upon activation of TLRs, recruited BM cells produce inflammatory cytokines, such as TNF-a, IL-6, IL-1, MCP-1, and RANTES [82]. Moreover, microbial products have a significant impact on fibrogenic progression [104], and LPS synergistically facilitates other fibrogenic factors such as TGFβ-1, oxidative stress, and mechanical injury [2]. TLR4 on BM cells is important in experimental alcoholic liver disease [39], and TL9 on BM cells is important in experimental non-alcoholic steatohepatitis [61].

Antifibrotic effects of macrophages 
Original experiments by Duffield et al. [20] and subsequent studies [60], [102] have demonstrated that, over a period of time, two functionally distinct types of macrophages are recruited to the injured liver. During the injury phase, pro-fibrogenic macrophages mediate recruitment of injury-associated macrophages that promote myofibroblast proliferation and apoptosis [32]. In contrast, during recovery from injury, a population of macrophages predominates that resembles classical macrophages and does not promote HSC survival but mediates matrix degradation. This macrophage population is present during resolution of injury and at a time when pro-fibrogenic and inflammatory mediator levels are decreasing [20]. These two functional phenotypes are separated chronologically in experimental liver fibrosis by several days, suggesting that they may represent different populations.
How do monocytes/macrophages promote matrix degradation? First of all, during the resolution phase, myelo-monocytic cells serve as a source of collagen degrading enzymes, such as collagenase and other matrix metalloproteinases (MMPs) [24], [36], [99]. Thus, increased secretion of MMP13 by hepatic macrophages is critical for dissolution of the fibrous scar in the recovering liver [24]. In addition, macrophages are responsible for clearance of apoptotic cells [10], [58], [69].

 

Fibrogenic myofibroblasts
Definition of myofibroblasts Myofibroblasts are characterized phenotypically by a stellate shape and expression of stress fibers, abundant pericellular matrix and fibrotic proteins (α-smooth muscle actin (α-SMA), non-muscle myosin, fibronectin, vimentin, and collagen type I) [23]. Ultrastructurally, myofibroblasts are defined by prominent rough endoplasmic reticulum (rER), a Golgi apparatus producing collagen, peripheral myofilaments, fibronexus (no lamina) and gap junctions [23]. Myofibroblasts are implicated in wound healing and fibroproliferative disorders [28], [57]. Myofibroblasts are produced in response to fibrogenic stimuli, such as TGF-β1 [65]. Classic myofibroblasts differentiate from a mesenchymal lineage and, therefore, lack expression of lymphoid markers such as CD45 or CD34. However, subsets of myofibroblasts can express Thy1.1 (CD90) or CD34. It remains unclear whether expression of these genes links (myo)fibroblasts to hematopoietic stem cells, or these antigens have a broader distribution than previously appreciated. Sustained injury may trigger (trans)differentiation of myofibroblasts from other cellular sources, including HSCs [10].
The question remains whether BM-derived cells are capable of giving rise to the functional myofibroblasts in liver fibrosis. Several BM cells have been implicated in fibrogenesis, such as fibrocytes and circulating mesenchymal cells, which could contribute to liver fibrosis.

 

The origin of fibrogenic myofibroblasts 
Although initial reports have suggested that BM may be a source of fibrogenic myofibroblasts [26], [75], most recent studies have reported that the majority of myofibroblasts activated in response to injury are from liver resident cells [37], [48], [49], [51], [81]. These findings are based on BM transplantation techniques in mice, in which the collagen-α1(I) or collagen-α2(I) promoters drive expression of the GFP reporter only in BM cells [37], [51]. Since collagen-α1(I) or collagen-α2(I) fibers are expressed in the same cells to form a triple helix [85], these reporter genes are expected to exhibit identical localization. Indeed, similar results were obtained in both mice in response to two models of liver fibrosis [37], [51], bile duct ligation and toxic liver injury induced by CCl4, demonstrating that activated myofibroblasts do not originate in the BM but emerge from the liver resident cells, e.g. HSCs and portal fibroblasts. Meanwhile, a small population of collagen type I expressing BM-derived cells, scattered in the liver and spleen of these mice, is composed of fibrocytes [37], [51]. Despite differences in experimental approaches and duration of injury, there was no evidence that BM contributes to replenishment of HSCs and portal fibroblasts or liver stem cells.

Fibrocytes are implicated in fibrogenesis of parenchymal organs 
Fibrocytes are defined as spindle shaped “CD45 and collagen type I (Col+) expressing leukocytes that mediate tissue repair and are capable of antigen presentation to naive T cells” [13]. Due to their ability to differentiate into myofibroblasts, fibrocytes are implicated in the fibrogenesis of skin, lungs, kidneys, and the liver [1], [48], [87]. In addition to collagen type I, fibronectin and vimentin, fibrocytes express CD45, CD34, MHCII, MHCI, CD11b, Gr-1, and secrete growth factors (TGF-β1, MCP-1) that promote deposition of ECM [11], [70]. Upon injury or stress, fibrocytes proliferate in the BM and migrate to the injured organ [13], [70]. The reported number of recruited fibrocytes varies from 25% (lung fibrosis) [48], [88] to ∼3–5% (liver fibrosis, e.g. BDL and CCl4) [49] of the collagen expressing cells, suggesting that the magnitude of fibrocyte differentiation into myofibroblasts depends on the organ and the type of injury. Fibrocytes originate from hematopoietic cells and differentiate in the liver into typical myofibroblasts [79]. Mice treated with human serum amyloid protein (hSAP) [66], a natural inhibitor of fibrocyte differentiation and maturation, develop less fibrosis in response to injury. Our data and studies in other parenchymal organs [14], [63], [68] clearly demonstrate that fibrocytes play an important role in pathogenesis of many fibrogenic disorders, including lungs. Elevated levels of circulating fibrocytes in peripheral blood in patients with lung fibrosis have a poor prognostic value [62]. Moreover, hSAP has been successfully tested in limited clinical trials in patients with skin, kidney and lung fibrosis [14], [59], [63], [68].

BM mesenchymal stem cells (MSCs) 
MSCs are defined as self-renewable, multipotent progenitor cells with the capacity to differentiate into lineage specific cells that form bone, cartilage, fat, tendon and muscle tissue [44], [84]. Unlike hematopoietic stem cells, MSCs are radio- and chemoresistant [9] and do not express progenitor markers (CD45, CD34, 133 [44]) or myelo-monocytic markers (CD11b, MHCII, and F4/80). Hepatic myofibroblasts may arise from BM-derived mesenchymal progenitors [26], [75]. BM-derived mesenchymal progenitors can give rise to myofibroblasts in the injured liver [6], [19], [55]. BM-derived cells may populate fibrotic lungs [35] and the liver [75] and contribute to fibrosis by differentiating into tissue myofibroblasts [40], [48], [75]. By subfractionating the BM stem cell compartment, the hepatic BM-derived myofibroblast-like cells were reported to be of mesenchymal stem cell origin [44], [75]. Cultured mesenchymal stem cells have the potential to become myofibroblast-like cells when transplanted into mouse livers [6], [19].

Whether circulating mesenchymal progenitors significantly contribute to ECM deposition in the course of experimental liver fibrosis remains to be determined, but they most likely represent a population, distinct from hematopoietic-derived fibrocytes [51]. Unlike hematopoietic stem cells, the definitive markers for mesenchymal stem cells have not been identified, and ablative radiation protocols to establish donor cell transfer have not been standardized. Therefore, a definitive murine liver fibrosis experiment with documented transfer of all bone marrow constituents expressing a myofibroblast specific marker has not been reported. Although initial enthusiasm about the BM origin of myofibroblasts declined in the recent years, further studies are required to re-evaluate this phenomenon.

Liver fibrosis precedes development of hepatocellular carcinoma [10], [38]. Recruitment of BM-derived fibroblasts (including fibrocytes) has been implicated in the pathogenesis of liver cancer, and cancer of other organs [8]. Thus, using collagen-α1(I)-GFP and α-smooth muscle actin (SMA)-RFP mice, BM-derived myofibroblasts were shown to contribute to neoplasia in gut and intestine [71]. Since most liver injury models in mice develop within a short period of time, it is possible that these experimental conditions are too short for the recruitment of BM myofibroblasts, as seen in cancer during 8–9months of development.

Contribution of BM cells in genetically altered mice 
BM cells may have different roles in different mouse models of genetically-induced liver injury. Since these phenomena are usually not observed in the wild type mice, contribution of BM-derived cells to hepatic cells is discussed separately.

The classical example is FAH−/− mice, in which a mutation in fumaryl-aceto-acetate hydrolase (FAH) gene causes a metabolic disorder equivalent to hereditary tyrosinemia type 1. Withdrawal of the protective drug 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) from drinking water causes extensive apoptosis of FAH−/− hepatocytes in these mice. Transplantation of wild type BM into these mice results in rescue from fatal liver failure by FAH-deficient hepatocytes. Wild type BM myelo-monocytes cells fuse with damaged hepatocytes to give rise to colonies of functional hepatocytes [54], [98]. Moreover, infusion of myeloid cells alone is sufficient to give rise to functional hepatocytes [3], [92], [101]. However, fusion of hepatocytes with macrophages was only rarely observed in wild type mice in response to other types of liver injury (CCl4, BDL), suggesting that hematopoietic cells have a limited contribution to hepatocyte population under physiological conditions or in response to injury [3], [92].

Recruitment of fibrocytes into the injured liver representing a high percentage of myofibroblasts has been observed in Abcb4-deficient mice (Abcb4−/− mice), and has been shown to substantially ameliorate development of liver fibrosis [74]. However, only a modest contribution of fibrocytes to liver fibrosis (3–5% of fibrogenic myofibroblasts) has been observed in wild type mice in response to CCl4 and BDL [51], [79]. Although Abcb4-deficient mice provide a unique opportunity to study recruitment of fibrocytes in great detail, they do not reflect the fibrocyte contribution to the population of myofibroblasts in hepatotoxic or cholestatic injury.

Resolution of liver fibrosis
Disappearance of myofibroblasts Reversal of fibrosis is associated with increased collagenase activity, activation of macrophages/Kupffer cells that secrete matrix metalloproteinases, e.g. MMP-13, and matrix degradation [24], [95]. Senescence and apoptosis of activated HSCs play a significant role in resolution of liver fibrosis by eliminating the cell type responsible for producing the fibrotic scar [41], [53]. Several mechanisms are implicated in the apoptosis of activated HSC: (1) activation of death receptor-mediated pathways (Fas or TNFR-1 receptors) and caspases 8 and 3; (2) upregulation of pro-apoptotic proteins (e.g., p53, Bax, caspase 9); and (3) decrease of pro-survival genes (e.g., Bcl-2) [50]. A population of liver-associated natural killer (NK) cells and NKT cells mediate apoptosis of activated HSCs [72]. Kupffer cells and BM macrophages actively participate in clearance of apoptotic cells and degradation of extracellular matrix proteins.

Studies in culture suggest that aHSCs, at least in part, can revert to a quiescent phenotype. Therefore, the disappearance of activated α-SMA+ Col+ HSCs in the course of fibrosis reversal may indicate that activated HSCs return to their quiescent state, which is associated with expression of lipogenic genes (Adfp, Adipor1, CREBP, PPAR-γ) [83] and storage of vitamin A in lipid droplets. Depletion of peroxisome proliferator-activated receptor gamma (PPAR-γ) constitutes a key molecular event for HSC activation, and ectopic over-expression of this nuclear receptor results in the phenotypic reversal of activated HSC to quiescent cells in culture [83]. The treatment of activated HSCs with an adipocyte differentiation cocktail, over-expression of SREBP-1c, or culturing on basement membrane-like ECM [29], [100] result in up-regulation of adipogenic transcription factors and cause morphologic and biochemical reversal of activated HSCs to quiescent cells [93], [94]. Although these results suggest that activated HSCs can revert to a quiescent state, these findings have only been documented in cultured cells.

Therapy
Many studies have demonstrated that transplantation of bone marrow cells reduces experimental liver fibrosis ([76], [90] and others). The mechanism is not trans-differentiation of bone marrow cells into hepatocytes. More likely, hematological stem cells may contribute to the reversal of liver fibrosis via macrophages that produce collagenases [91] and phagocytose dead parenchymal cells [69]. More unexpectedly, mesenchymal stem cells, even though they have the potential to become myofibroblasts, also have functions that may contribute to the reversal of fibrosis. Cultured mesenchymal stem cells secrete agonists that inhibit hepatocyte apoptosis, induce hepatocyte proliferation, and increase hepatocyte specific gene expression [96]. Also, mesenchymal stem cells may be induced in culture to become endothelial progenitor cells (EPCs). Transplantation of EPCs reverses hepatic fibrosis and improves survival in CCl4-induced cirrhosis in rats [64].

BM cells for anti-fibrotic therapy 
The improvement of liver function following transplantation of hematopoietic progenitors in mice and rats with injured livers provided the basis for clinical trials [25]. Clinical studies with adoptive transfer of autologous CD133+ BM cells in patients have been reported to stimulate liver regeneration [4]. Similar to that, autologous infusion of CD34+ blood cells, or even monocytes, improved biochemical parameters and stimulated liver regeneration [33]. Within the limits of these small, uncontrolled clinical trials, evidence is starting to accumulate that transplantation of hematopoietic progenitors may be beneficial in patients. However, the mechanism of their action remains to be defined. Such improvement may result from release of cytokines and growth factors by transplanted hematopoietic cells, or occur due to infusion of scar-resorbing monocytes. In concordance with these observations, treatment with granulocyte-colony stimulating factor (G-CSF) was used to mobilize the BM cells and demonstrated a positive histological effect in patients with alcoholic steatohepatitis [30].
Mesenchymal stem cells serve as another potential target for the liver stem cell therapy. In addition, mesenchymal cells are readily available (for example, from fat tissue) and relatively easy to expand in vitro. A recent study investigated the ability of purified hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), and mononuclear cells to engraft and contribute to liver regeneration in response to injury in mice [15]. However, only a low level of engraftment with the MSCs and reconstitution of the liver mass has been reported [7].

In concordance with this notion, injection of MSC-derived conditioning media into a liver-assist device decreased hepatocyte apoptosis and increased their proliferation [96], [103]. However, recent studies have raised a safety question on MSCs transplantation, demonstrating that MSCs can give rise to myofibroblasts in mice in response to liver injury. For example, BM-derived MSCs contributed to the development of liver fibrosis in chimeric mice that received bone marrow transplantation with an enriched BM mesenchymal fraction, and subjected to the CCl4-liver injury [75]. Taken together, both hematopoietic and mesenchymal stem cells demonstrate a limited, if any, contribution to hepatocyte replenishment, but may stimulate liver function by providing soluble growth factors or cytokines [3], [49], [92].
A few clinical trials have been performed in patients with end-stage liver disease caused by hepatitis B, hepatitis C, alcoholic liver disease, and cryptogenic fibrosis. These patients were transplanted with autologous MSCs harvested from the iliac crest. The tested parameters (albumin, creatinine) demonstrated a modest but significant improvement without severe adverse effects, suggesting that MSCs might be useful for the treatment of end-stage liver disease with satisfactory tolerability [47].

Conclusions 
The literature provides evidence that bone marrow cells might contribute to increase or to inhibit experimental liver fibrosis  Figure 2. Although there is clearly a need for additional, better defined studies, some conclusions can be made from our current information. Hematological stem cells are the source of monocytes, Kupffer cells and recruited macrophage. Overall, these cells contribute to the initial inflammation in the injured liver that progresses to liver fibrosis. However, recruited macrophages may also secrete agonists such as IL-10 that inhibit stellate cell activation as well as collagenases that cause regression of fibrosis. Hematological stem cells are also the source of fibrocytes, which are recruited to the injured liver and function in the innate immune response as well as differentiate into myofibroblasts. Mesenchymal stem cells have the capacity to become myofibroblasts, but studies to follow their cell fate in vivo are limited by the lack of specific markers.


  • Figure 2
    Potential roles of BM-derived progenitor populations in liver injury. BM is the source of hematopoietic and mesenchymal stem cells, which may participate in the response to liver injury.
Most, but not all, studies using BM transplantation have demonstrated a beneficial effect on experimental liver fibrosis. The mechanism for this benefit is unclear, and in particular BM-derived cells do not constitute a significant source of hepatocytes in the injured liver. However, both mesenchymal stem cells and hematopoietic stem cells are reported to contribute to the regression of liver fibrosis. On the basis of these studies, small, mostly uncontrolled clinical studies have treated cirrhotic patients with autologous transplantation of BM derived cells. Although these studies have established the feasibility of this approach, the mechanism and long term benefit of transplantation of BM-derived cells in cirrhosis is unknown.

Conflict of interest
The authors declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. The underlying research reported in the study was funded by the NIH Institutes of Health.

References
  1. Abe R, Donnelly SC, Peng T, Bucala R, Metz CN. Peripheral blood fibrocytes: differentiation pathway and migration to wound sites. J Immunol. 2001;166:7556–7562
  2. Albillos A, de la Hera A, Gonzalez M, Moya JL, Calleja JL, Monserrat J, et al. Increased lipopolysaccharide binding protein in cirrhotic patients with marked immune and hemodynamic derangement. Hepatology. 2003;37:208–217
  3. Alison MR, Islam S, Lim S. Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly. J Pathol. 2009;217:282–298
  4. am Esch JS, Knoefel WT, Klein M, Ghodsizad A, Fuerst G, Poll LW, et al. Portal application of autologous CD133+ bone marrow cells to the liver: a novel concept to support hepatic regeneration. Stem Cells. 2005;23:463–470
  5. Asahina K, Tsai SY, Li P, Ishii M, Maxson RE, Sucov HM, et al. Mesenchymal origin of hepatic stellate cells, submesothelial cells, and perivascular mesenchymal cells during mouse liver development. Hepatology. 2009;49:998–1011
  6. Baertschiger RM, Serre-Beinier V, Morel P, Bosco D, Peyrou M, Clement S, et al. Fibrogenic potential of human multipotent mesenchymal stromal cells in injured liver. PLoS One. 2009;4:e6657
  7. Banas A, Teratani T, Yamamoto Y, Tokuhara M, Takeshita F, Osaki M, et al. Rapid hepatic fate specification of adipose-derived stem cells and their therapeutic potential for liver failure. J Gastroenterol Hepatol. 2009;24:70–77
  8. Barth PJ, Schenck zu Schweinsberg T, Ramaswamy A, Moll R. CD34+ fibrocytes, alpha-smooth muscle antigen-positive myofibroblasts, and CD117 expression in the stroma of invasive squamous cell carcinomas of the oral cavity, pharynx, and larynx. Virchows Arch. 2004;444:231–234
  9. Bartsch K, Al-Ali H, Reinhardt A, Franke C, Hudecek M, Kamprad M, et al. Mesenchymal stem cells remain host-derived independent of the source of the stem-cell graft and conditioning regimen used. Transplantation. 2009;87:217–221
  10. Bataller R, Brenner DA. Liver fibrosis. J Clin Invest. 2005;115:209–218
  11. Bellini A, Mattoli S. The role of the fibrocyte, a bone marrow-derived mesenchymal progenitor, in reactive and reparative fibroses. Lab Invest. 2007;87:858–870
  12. Brinkmann V, Reichard U, Goosmann C, Fauler B, Uhlemann Y, Weiss DS, et al. Neutrophil extracellular traps kill bacteria. Science. 2004;303:1532–1535
  13. Bucala R, Spiegel LA, Chesney J, Hogan M, Cerami A. Circulating fibrocytes define a new leukocyte subpopulation that mediates tissue repair. Mol Med. 1994;1:71–81
  14. Castano AP, Lin SL, Surowy T, Nowlin BT, Turlapati SA, Patel T, et al. Serum amyloid P inhibits fibrosis through Fc gamma R-dependent monocyte-macrophage regulation in vivo. Sci Transl Med. 2009;1:5ra13
  15. Cho KA, Ju SY, Cho SJ, Jung YJ, Woo SY, Seoh JY, et al. Mesenchymal stem cells showed the highest potential for the regeneration of injured liver tissue compared with other subpopulations of the bone marrow. Cell Biol Int. 2009;33:772–777
  16. Chow OA, von Kockritz-Blickwede M, Bright AT, Hensler ME, Zinkernagel AS, Cogen AL, et al. Statins enhance formation of phagocyte extracellular traps. Cell Host Microbe. 2010;8:445–454
  17. Corbin BD, Seeley EH, Raab A, Feldmann J, Miller MR, Torres VJ, et al. Metal chelation and inhibition of bacterial growth in tissue abscesses. Science. 2008;319:962–965
  18. Desmouliere A, Darby I, Costa AM, Raccurt M, Tuchweber B, Sommer P, et al. Extracellular matrix deposition, lysyl oxidase expression, and myofibroblastic differentiation during the initial stages of cholestatic fibrosis in the rat. Lab Invest. 1997;76:765–778
  19. di Bonzo LV, Ferrero I, Cravanzola C, Mareschi K, Rustichell D, Novo E, et al. Human mesenchymal stem cells as a two-edged sword in hepatic regenerative medicine: engraftment and hepatocyte differentiation versus profibrogenic potential. Gut. 2008;57:223–231
  20. Duffield JS, Forbes SJ, Constandinou CM, Clay S, Partolina M, Vuthoori S, et al. Selective depletion of macrophages reveals distinct, opposing roles during liver injury and repair. J Clin Invest. 2005;115:56–65
  21. Duffield JS, Tipping PG, Kipari T, Cailhier JF, Clay S, Lang R, et al. Conditional ablation of macrophages halts progression of crescentic glomerulonephritis. Am J Pathol. 2005;167:1207–1219
  22. Evseenko D, Schenke-Layland K, Dravid G, Zhu Y, Hao QL, Scholes J, et al. Identification of the critical extracellular matrix proteins that promote human embryonic stem cell assembly. Stem Cells Dev. 2008;18:919–928
  23. Eyden B. The myofibroblast: phenotypic characterization as a prerequisite to understanding its functions in translational medicine. J Cell Mol Med. 2008;12:22–37
  24. Fallowfield JA, Mizuno M, Kendall TJ, Constandinou CM, Benyon RC, Duffield JS, et al. Scar-associated macrophages are a major source of hepatic matrix metalloproteinase-13 and facilitate the resolution of murine hepatic fibrosis. J Immunol. 2007;178:5288–5295
  25. Fitzpatrick E, Mitry RR, Dhawan A. Human hepatocyte transplantation: state of the art. J Intern Med. 2009;266:339–357
  26. Forbes SJ, Russo FP, Rey V, Burra P, Rugge M, Wright NA, et al. A significant proportion of myofibroblasts are of bone marrow origin in human liver fibrosis. Gastroenterology. 2004;126:955–963
  27. Friedman SL, Roll FJ, Boyles J, Bissell DM. Hepatic lipocytes: the principal collagen-producing cells of normal rat liver. Proc Natl Acad Sci USA. 1985;82:8681–8685
  28. Gabbiani G, Ryan GB, Majne G. Presence of modified fibroblasts in granulation tissue and their possible role in wound contraction. Experientia. 1971;27:549–550
  29. Gaca MD, Zhou X, Issa R, Kiriella K, Iredale JP, Benyon RC. Basement membrane-like matrix inhibits proliferation and collagen synthesis by activated rat hepatic stellate cells: evidence for matrix-dependent deactivation of stellate cells. Matrix Biol. 2003;22:229–239
  30. Gaia S, Smedile A, Omede P, Olivero A, Sanavio F, Balzola F, et al. Feasibility and safety of G-CSF administration to induce bone marrow-derived cells mobilization in patients with end stage liver disease. J Hepatol. 2006;45:13–19
  31. Gebhardt C, Nemeth J, Angel P, Hess J. S100A8 and S100A9 in inflammation and cancer. Biochem Pharmacol. 2006;72:1622–1631
  32. Goerdt S, Orfanos CE. Other functions, other genes: alternative activation of antigen-presenting cells. Immunity. 1999;10:137–142
  33. Gordon MY, Levicar N, Pai M, Bachellier P, Dimarakis I, Al-Allaf F, et al. Characterization and clinical application of human CD34+ stem/progenitor cell populations mobilized into the blood by granulocyte colony-stimulating factor. Stem Cells. 2006;24:1822–1830
  34. Hakkim A, Furnrohr BG, Amann K, Laube B, Abed UA, Brinkmann V, et al. Impairment of neutrophil extracellular trap degradation is associated with lupus nephritis. Proc Natl Acad Sci USA. 2010;107:9813–9818
  35. Hashimoto N, Jin H, Liu T, Chensue SW, Phan SH. Bone marrow-derived progenitor cells in pulmonary fibrosis. J Clin Invest. 2004;113:243–252
  36. Higashiyama R, Inagaki Y, Hong YY, Kushida M, Nakao S, Niioka M, et al. Bone marrow-derived cells express matrix metalloproteinases and contribute to regression of liver fibrosis in mice. Hepatology. 2007;45:213–222
  37. Higashiyama R, Moro T, Nakao S, Mikami K, Fukumitsu H, Ueda Y, et al. Negligible contribution of bone marrow-derived cells to collagen production during hepatic fibrogenesis in mice. Gastroenterology. 2009;137:1459–1466el
  38. Inokuchi S, Aoyama T, Miura K, Osterreicher CH, Kodama Y, Miyai K, et al. Disruption of TAK1 in hepatocytes causes hepatic injury, inflammation, fibrosis, and carcinogenesis. Proc Natl Acad Sci USA. 2010;107:844–849
  39. Inokuchi S, Tsukamoto H, Park E, Liu ZX, Brenner DA, Seki E. Toll-like receptor 4 mediates alcohol-induced steatohepatitis through bone marrow-derived and endogenous liver cells in mice. Alcohol Clin Exp Res. 2011;35:1509–1518
  40. Iredale JP. Models of liver fibrosis: exploring the dynamic nature of inflammation and repair in a solid organ. J Clin Invest. 2007;117:539–548
  41. Iredale JP, Benyon RC, Pickering J, McCullen M, Northrop M, Pawley S, et al. Mechanisms of spontaneous resolution of rat liver fibrosis. Hepatic stellate cell apoptosis and reduced hepatic expression of metalloproteinase inhibitors. J Clin Invest. 1998;102:538–549
  42. Issa R, Zhou X, Constandinou CM, Fallowfield J, Millward-Sadler H, Gaca MD, et al. Spontaneous recovery from micronodular cirrhosis: evidence for incomplete resolution associated with matrix cross-linking. Gastroenterology. 2004;126:1795–1808
  43. Issa R, Zhou X, Trim N, Millward-Sadler H, Krane S, Benyon C, et al. Mutation in collagen-1 that confers resistance to the action of collagenase results in failure of recovery from CCl4-induced liver fibrosis, persistence of activated hepatic stellate cells, and diminished hepatocyte regeneration. FASEB J. 2003;17:47–49
  44. Kallis YN, Forbes SJ. The bone marrow and liver fibrosis: friend or foe?. Gastroenterology. 2009;137:1218–1221
  45. Karlmark KR, Weiskirchen R, Zimmermann HW, Gassler N, Ginhoux F, Weber C, et al. Hepatic recruitment of the inflammatory Gr1+ monocyte subset upon liver injury promotes hepatic fibrosis. Hepatology. 2009;50:261–274
  46. Kessenbrock K, Krumbholz M, Schonermarck U, Back W, Gross WL, Werb Z, et al. Netting neutrophils in autoimmune small-vessel vasculitis. Nat Med. 2009;15:623–625
  47. Kharaziha P, Hellstrom PM, Noorinayer B, Farzaneh F, Aghajani K, Jafari F, et al. Improvement of liver function in liver cirrhosis patients after autologous mesenchymal stem cell injection: a phase I–II clinical trial. Eur J Gastroenterol Hepatol. 2009;21:1199–1205
  48. Kisseleva T, Brenner DA. Fibrogenesis of parenchymal organs. Proc Am Thorac Soc. 2008;5:338–342
  49. Kisseleva T, Brenner DA. Hepatic stellate cells and the reversal of fibrosis. J Gastroenterol Hepatol. 2006;21:S84–S87
  50. Kisseleva T, Brenner DA. Mechanisms of fibrogenesis. Exp Biol Med (Maywood). 2008;233:109–122
  51. Kisseleva T, Uchinami H, Feirt N, Quintana-Bustamante O, Segovia JC, Schwabe RF, et al. Bone marrow-derived fibrocytes participate in pathogenesis of liver fibrosis. J Hepatol. 2006;45:429–438
  52. Kisseleva T, von Kockritz-Blickwede M, Reichart D, McGillvray SM, Wingender G, Kronenberg M, et al. Fibrocyte-like cells recruited to the spleen support innate and adaptive immune responses to acute injury or infection. J Mol Med. 2011;89:997–1013
  53. Krizhanovsky V, Yon M, Dickins RA, Hearn S, Simon J, Miething C, et al. Senescence of activated stellate cells limits liver fibrosis. Cell. 2008;134:657–667
  54. Lagasse E, Connors H, Al-Dhalimy M, Reitsma M, Dohse M, Osborne L, et al. Purified hematopoietic stem cells can differentiate into hepatocytes in vivo. Nat Med. 2000;6:1229–1234
  55. Li C, Kong Y, Wang H, Wang S, Yu H, Liu X, et al. Homing of bone marrow mesenchymal stem cells mediated by sphingosine 1-phosphate contributes to liver fibrosis. J Hepatol. 2009;50:1174–1183
  56. Li Y, Chang M, Abar O, Garcia V, Rowland C, Catanese J, et al. Multiple variants in toll-like receptor 4 gene modulate risk of liver fibrosis in Caucasians with chronic hepatitis C infection. J Hepatol. 2009;51:750–757
  57. Majno G, Gabbiani G, Hirschel BJ, Ryan GB, Statkov PR. Contraction of granulation tissue in vitro: similarity to smooth muscle. Science. 1971;173:548–550
  58. Marra F, Aleffi S, Galastri S, Provenzano A. Mononuclear cells in liver fibrosis. Semin Immunopathol. 2009;31:345–358
  59. Mathai SK, Gulati M, Peng X, Russell TR, Shaw AC, Rubinowitz AN, et al. Circulating monocytes from systemic sclerosis patients with interstitial lung disease show an enhanced profibrotic phenotype. Lab Invest. 2010;90:812–823
  60. Mitchell C, Couton D, Couty JP, Anson M, Crain AM, Bizet V, et al. Dual role of CCR2 in the constitution and the resolution of liver fibrosis in mice. Am J Pathol. 2009;174:1766–1775
  61. Miura K, Kodama Y, Inokuchi S, Schnabl B, Aoyama T, Ohnishi H, et al. Toll-like receptor 9 promotes steatohepatitis by induction of interleukin-1beta in mice. Gastroenterology. 2010;139:323–334e327
  62. Moeller A, Gilpin SE, Ask K, Cox G, Cook D, Gauldie J, et al. Circulating fibrocytes are an indicator of poor prognosis in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med. 2009;179:588–594
  63. Murray LA, Rosada R, Moreira AP, Joshi A, Kramer MS, Hesson DP, et al. Serum amyloid P therapeutically attenuates murine bleomycin-induced pulmonary fibrosis via its effects on macrophages. PLoS One. 2010;5:e9683
  64. Nakamura T, Torimura T, Sakamoto M, Hashimoto O, Taniguchi E, Inoue K, et al. Significance and therapeutic potential of endothelial progenitor cell transplantation in a cirrhotic liver rat model. Gastroenterology. 2007;133:91–107e101
  65. Parola M, Marra F, Pinzani M. Myofibroblast-like cells and liver fibrogenesis: emerging concepts in a rapidly moving scenario. Mol Aspects Med. 2008;29:58–66
  66. Pilling D, Buckley CD, Salmon M, Gomer RH. Inhibition of fibrocyte differentiation by serum amyloid P. J Immunol. 2003;171:5537–5546
  67. Pilling D, Fan T, Huang D, Kaul B, Gomer RH. Identification of markers that distinguish monocyte-derived fibrocytes from monocytes, macrophages, and fibroblasts. PLoS ONE. 2009;4:e7475
  68. Pilling D, Roife D, Wang M, Ronkainen SD, Crawford JR, Travis EL, et al. Reduction of bleomycin-induced pulmonary fibrosis by serum amyloid P. J Immunol. 2007;179:4035–4044
  69. Popov Y, Sverdlov DY, Bhaskar KR, Sharma AK, Millonig G, Patsenker E, et al. Macrophage-mediated phagocytosis of apoptotic cholangiocytes contributes to reversal of experimental biliary fibrosis. Am J Physiol Gastrointest Liver Physiol. 2010;298:G323–G334
  70. Quan TE, Cowper S, Wu SP, Bockenstedt LK, Bucala R. Circulating fibrocytes: collagen-secreting cells of the peripheral blood. Int J Biochem Cell Biol. 2004;36:598–606
  71. Quante M, Tu SP, Tomita H, Gonda T, Wang SS, Takashi S, et al. Bone marrow-derived myofibroblasts contribute to the mesenchymal stem cell niche and promote tumor growth. Cancer Cell. 2011;19:257–272
  72. Radaeva S, Sun R, Jaruga B, Nguyen VT, Tian Z, Gao B. Natural killer cells ameliorate liver fibrosis by killing activated stellate cells in NKG2D-dependent and tumor necrosis factor-related apoptosis-inducing ligand-dependent manners. Gastroenterology. 2006;130:435–452
  73. Ramachandran P, Iredale JP. Reversibility of liver fibrosis. Ann Hepatol. 2009;8:283–291
  74. Roderfeld M, Rath T, Voswinckel R, Dierkes C, Dietrich H, Zahner D, et al. Bone marrow transplantation demonstrates medullar origin of CD34+ fibrocytes and ameliorates hepatic fibrosis in Abcb4−/− mice. Hepatology. 2010;51:267–276
  75. Russo FP, Alison MR, Bigger BW, Amofah E, Florou A, Amin F, et al. The bone marrow functionally contributes to liver fibrosis. Gastroenterology. 2006;130:1807–1821
  76. Sakaida I, Terai S, Yamamoto N, Aoyama K, Ishikawa T, Nishina H, et al. Transplantation of bone marrow cells reduces CCl4-induced liver fibrosis in mice. Hepatology. 2004;40:1304–1311
  77. Schnabl B, Purbeck CA, Choi YH, Hagedorn CH, Brenner D. Replicative senescence of activated human hepatic stellate cells is accompanied by a pronounced inflammatory but less fibrogenic phenotype. Hepatology. 2003;37:653–664
  78. Schnoor M, Cullen P, Lorkowski J, Stolle K, Robenek H, Troyer D, et al. Production of type VI collagen by human macrophages: a new dimension in macrophage functional heterogeneity. J Immunol. 2008;180:5707–5719
  79. Scholten D, Reichart D, Paik YH, Lindert J, Bhattacharya J, Glass CK, et al. Migration of fibrocytes in fibrogenic liver injury. Am J Pathol. 2011;179:189–198
  80. Schrader J, Fallowfield J, Iredale JP. Senescence of activated stellate cells: not just early retirement. Hepatology. 2009;49:1045–1047
  81. Seki E, De Minicis S, Osterreicher CH, Kluwe J, Osawa Y, Brenner DA, et al. TLR4 enhances TGF-beta signaling and hepatic fibrosis. Nat Med. 2007;13:1324–1332
  82. Seki E, Uchinami H, Osawa Y, Brenner DA, Schwabe RF. TLR4 mediates inflammation and fibrogenesis after bile duct ligation. Hepatology. 2005;42:265A–266A
  83. She H, Xiong S, Hazra S, Tsukamoto H. Adipogenic transcriptional regulation of hepatic stellate cells. J Biol Chem. 2005;280:4959–4967
  84. Song L, Tuan RS. Transdifferentiation potential of human mesenchymal stem cells derived from bone marrow. FASEB J. 2004;18:980–982
  85. Stefanovic B, Brenner DA. 5′ stem-loop of collagen alpha 1(I) mRNA inhibits translation in vitro but is required for triple helical collagen synthesis in vivo. J Biol Chem. 2003;278:927–933
  86. Steinbakk M, Naess-Andresen CF, Lingaas E, Dale I, Brandtzaeg P, Fagerhol MK. Antimicrobial actions of calcium binding leucocyte L1 protein, calprotectin. Lancet. 1990;336:763–765
  87. Strieter RM, Gomperts BN, Keane MP. The role of CXC chemokines in pulmonary fibrosis. J Clin Invest. 2007;117:549–556
  88. Strieter RM, Keeley EC, Hughes MA, Burdick MD, Mehrad B. The role of circulating mesenchymal progenitor cells (fibrocytes) in the pathogenesis of pulmonary fibrosis. J Leukoc Biol. 2009;86:1111–1118
  89. Suh HN, Han HJ. Collagen I regulates the self-renewal of mouse embryonic stem cells through alpha2beta1 integrin- and DDR1-dependent Bmi-1. J Cell Physiol. 2011;226:3422–3432
  90. Sun CK, Chen CH, Kao YH, Yuen CM, Sheu JJ, Lee FY, et al. Bone marrow cells reduce fibrogenesis and enhance regeneration in fibrotic rat liver. J Surg Res. 2011;169:e15–e26
  91. Thomas JA, Pope C, Wojtacha D, Robson AJ, Gordon-Walker TT, Hartland S, et al. Macrophage therapy for murine liver fibrosis recruits host effector cells improving fibrosis, regeneration, and function. Hepatology. 2011;53:2003–2015
  92. Thorgeirsson SS, Grisham JW. Hematopoietic cells as hepatocyte stem cells: a critical review of the evidence. Hepatology. 2006;43:2–8
  93. Tsukamoto H. Adipogenic phenotype of hepatic stellate cells. Alcohol Clin Exp Res. 2005;29:132S–133S
  94. Tsukamoto H. Fat paradox in liver disease. Keio J Med. 2005;54:190–192
  95. Uchinami H, Seki E, Brenner DA, D’Armiento J. Loss of MMP 13 attenuates murine hepatic injury and fibrosis during cholestasis. Hepatology. 2006;44:420–429
  96. van Poll D, Parekkadan B, Cho CH, Berthiaume F, Nahmias Y, Tilles AW, et al. Mesenchymal stem cell-derived molecules directly modulate hepatocellular death and regeneration in vitro and in vivo. Hepatology. 2008;47:1634–1643
  97. von Kockritz-Blickwede M, Goldmann O, Thulin P, Heinemann K, Norrby-Teglund A, Rohde M, et al. Phagocytosis-independent antimicrobial activity of mast cells by means of extracellular trap formation. Blood. 2008;111:3070–3080
  98. Wang X, Willenbring H, Akkari Y, Torimaru Y, Foster M, Al-Dhalimy M, et al. Cell fusion is the principal source of bone-marrow-derived hepatocytes. Nature. 2003;422:897–901
  99. Watanabe T, Niioka M, Hozawa S, Kameyama K, Hayashi T, Arai M, et al. Gene expression of interstitial collagenase in both progressive and recovery phase of rat liver fibrosis induced by carbon tetrachloride. J Hepatol. 2000;33:224–235
  100. Wells RG. The role of matrix stiffness in regulating cell behavior. Hepatology. 2008;47:1394–1400
  101. Willenbring H, Bailey AS, Foster M, Akkari Y, Dorrell C, Olson S, et al. Myelomonocytic cells are sufficient for therapeutic cell fusion in liver. Nat Med. 2004;10:744–748
  102. Xidakis C, Ljumovic D, Manousou P, Notas G, Valatas V, Kolios G, et al. Production of pro- and anti-fibrotic agents by rat Kupffer cells; the effect of octreotide. Dig Dis Sci. 2005;50:935–941
  103. Yagi H, Parekkadan B, Suganuma K, Soto-Gutierrez A, Tompkins RG, Tilles AW, et al. Long-term superior performance of a stem cell/hepatocyte device for the treatment of acute liver failure. Tissue Eng Part A. 2009;15:3377–3388
  104. Yan AW, Fouts E, Brandl J, Starkel P, Torralba M, Schott E, et al. Enteric dysbiosis associated with a mouse model of alcoholic liver disease. Hepatology. 2011;53:96–105
  105. Yang D, Oppenheim JJ. Antimicrobial proteins act as “alarmins” in joint immune defense. Arthritis Rheum. 2004;50:3401–3403
  106. Yousefi S, Gold JA, Andina N, Lee JJ, Kelly AM, Kozlowski E, et al. Catapult-like release of mitochondrial DNA by eosinophils contributes to antibacterial defense. Nat Med. 2008;14:949–953
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