Hepatic ischemia/reperfusion injury involves functional TLR4 signaling in nonparenchymal cells

Endogenous ligands from damaged cells, so-called damage-associated molecular pattern molecules, can activate innate immunity via TLR4 signaling. Hepatic warm ischemia and reperfusion (I/R) injury and inflammation is largely TLR4 dependent. We produced TLR4 chimeric mice to assess whether the TLR4-dependent injury required TLR4 expression on liver parenchymal or nonparenchymal cells. Chimeric mice were produced by adoptive transfer of donor bone marrow cells into irradiated recipient animals using reciprocal combinations of TLR4 wild-type (WT; C3H/HeOuj) and TLR4 mutant (C3H/HeJ) mouse bone marrow. Wild-type chimeric mice bearing TLR4 mutant hemopoietic cells and TLR4 mutant mice transplanted with their own bone marrow-derived cells were protected from hepatic I/R and exhibited decreased JNK and NF-kappaB activation compared with WT chimeric mice transplanted with their own bone marrow. In contrast, TLR4 mutant mice transplanted with TLR4 WT bone marrow were not protected from liver I/R and demonstrated pronounced increases in JNK and NF-kappaB activation when compared with autochthonous transplanted mutant mice. In addition, depletion of phagocytes taking up gadolinium chloride failed to provide any additional protection to TLR4 mutant mice, but substantially reduced damage in WT mice after hepatic I/R. Together, these results demonstrate that TLR4 engagement on actively phagocytic nonparenchymal cells such as Kupffer cells is required for warm I/R-induced injury and inflammation in the liver.     

Effect of human scavenger receptor class A overexpression in bone marrow-derived cells on lipoprotein metabolism and atherosclerosis in low density lipoprotein receptor knockout mice

Scavenger receptors, which include various classes, play an important role in atherogenesis by mediating the unrestricted uptake of modified lipoproteins, resulting in the massive accumulation of cholesteryl esters. Because macrophage-derived foam cells are considered to be an important feature in early atherogenesis, we investigated the role of scavenger receptor class A (SR-A) overexpression, especially on macrophages in lipoprotein metabolism and atherosclerosis. Bone marrow from human SR-A (MSR1)-overexpressing mice was transplanted into irradiated low density lipoprotein receptor knockout [LDLR(-/-)] mice. The transplantation resulted in an increase in total serum cholesterol (approximately 15 to 25%), especially in the VLDL fraction, when compared with LDLR(-/-) mice that were transplanted with bone marrow of wild-type littermates. Quantification of atherosclerotic lesions in the mice that were fed a "Western-type" diet for 3 months revealed that there were no differences in mean lesion area between LDLR(-/-) mice transplanted with MSR1 overexpressing and wild-type littermate bone marrow, despite increased scavenger receptor activity in vitro. The presence or absence of the LDLR in the transplanted bone marrow did not influence these results.In conclusion, introduction of MSR1-overexpressing bone marrow in LDLR(-/-) mice via bone marrow transplantation resulted in a slight increase in lipoprotein levels, but had no effect on the atherosclerotic lesion area, despite increased scavenger receptor activity in vitro.     

Differentiating Functional Roles of Gene Expression from Immune and Non-immune Cells in Mouse Colitis by Bone Marrow Transplantation

To understand the role of a gene in the development of colitis, we compared the responses of wild-type mice and gene-of-interest deficient knockout mice to colitis. If the gene-of-interest is expressed in both bone marrow derived cells and non-bone marrow derived cells of the host; however, it is possible to differentiate the role of a gene of interest in bone marrow derived cells and non- bone marrow derived cells by bone marrow transplantation technique. To change the bone marrow derived cell genotype of mice, the original bone marrow of recipient mice were destroyed by irradiation and then replaced by new donor bone marrow of different genotype. When wild-type mice donor bone marrow was transplanted to knockout mice, we could generate knockout mice with wild-type gene expression in bone marrow derived cells. Alternatively, when knockout mice donor bone marrow was transplanted to wild-type recipient mice, wild-type mice without gene-of-interest expressing from bone marrow derived cells were produced. However, bone marrow transplantation may not be 100% complete. Therefore, we utilized cluster of differentiation (CD) molecules (CD45.1 and CD45.2) as markers of donor and recipient cells to track the proportion of donor bone marrow derived cells in recipient mice and success of bone marrow transplantation. Wild-type mice with CD45.1 genotype and knockout mice with CD45.2 genotype were used. After irradiation of recipient mice, the donor bone marrow cells of different genotypes were infused into the recipient mice. When the new bone marrow regenerated to take over its immunity, the mice were challenged by chemical agent (dextran sodium sulfate, DSS 5%) to induce colitis. Here we also showed the method to induce colitis in mice and evaluate the role of the gene of interest expressed from bone-marrow derived cells. If the gene-of-interest from the bone derived cells plays an important role in the development of the disease (such as colitis), the phenotype of the recipient mice with bone marrow transplantation can be significantly altered. At the end of colitis experiments, the bone marrow derived cells in blood and bone marrow were labeled with antibodies against CD45.1 and CD45.2 and their quantitative ratio of existence could be used to evaluate the success of bone marrow transplantation by flow cytometry. Successful bone marrow transplantation should show a vast majority of donor genotype (in term of CD molecule marker) over recipient genotype in both the bone marrow and blood of recipient mice.     

Role of IL-17A in neutrophil recruitment and hepatic injury after warm ischemia-reperfusion mice

Recent evidence suggests that IL-17A regulates neutrophil-dependent organ injury. Accordingly, the purpose of this study was to determine the role of IL-17A in neutrophil recruitment after ischemia-reperfusion (I/R) and in subsequent liver injury. Two mouse models including wild-type and IL-17A knockout mice were evaluated for I/R injury. The medial largest lobe of the liver was clamped for 90 min. In another set of experiments, recombinant mouse (rm)IL-17A homodimer or rmIL-17A/F heterodimer were administered to knockout mice before I/R, and liver injury was investigated. Isolated Kupffer cells were incubated with rmIL-17A or rmIL-17F, and production of TNF-α was measured. Studies evaluating the extent of liver injury as measured by serum transaminase levels demonstrated similar levels in the acute phase (6 h) in these two models. In contrast, in the subacute phase (20 h) after I/R, both serum transaminase levels and percent of hepatic necrosis were significantly reduced in the knockout mice compared with the wild-type mice. This reduction in liver injury seen in the knockout mice was associated with suppression of chemokine and adhesion molecule expression and reduction in infiltration of neutrophils into the liver. Administration of rmIL-17A homodimer, but not IL-17A/F heterodimer, increased liver injury in the subacute phase of I/R in KO mice. TNF-α production by isolated Kupffer cells increased significantly in the cells incubated with rmIL-17A compared with rmIL-17F. These results indicate that IL-17A is a key regulator in initiating neutrophil-induced inflammatory responses and hepatic injury in the subacute phase after reperfusion.     

Extensive fusion of haematopoietic cells with Purkinje neurons in response to chronic inflammation

Transplanted bone marrow-derived cells (BMDCs) have been reported to fuse with cells of diverse tissues, but the extremely low frequency of fusion has led to the view that such events are biologically insignificant. Nonetheless, in mice with a lethal recessive liver disease (tyrosinaemia), transplantation of wild-type BMDCs restored liver function by cell fusion and prevented death, indicating that cell fusion can have beneficial effects. Here we report that chronic inflammation resulting from severe dermatitis or autoimmune encephalitis leads to robust fusion of BMDCs with Purkinje neurons and formation of hundreds of binucleate heterokaryons per cerebellum, a 10-100-fold higher frequency than previously reported. Single haematopoietic stem-cell transplants showed that the fusogenic cell is from the haematopoietic lineage and parabiosis experiments revealed that fusion can occur without irradiation. Transplantation of rat bone marrow into mice led to activation of dormant rat Purkinje neuron-specific genes in BMDC nuclei after fusion with mouse Purkinje neurons, consistent with nuclear reprogramming. The precise neurological role of these heterokaryons awaits elucidation, but their frequency in brain after inflammation is clearly much higher than previously appreciated.     

A1 adenosine receptor allosteric enhancer PD-81723 protects against renal ischemia-reperfusion injury

Activation of A(1) adenosine receptors (ARs) protects against renal ischemia-reperfusion (I/R) injury by reducing necrosis, apoptosis, and inflammation. However, extrarenal side effects (bradycardia, hypotension, and sedation) may limit A(1)AR agonist therapy for ischemic acute kidney injury. Here, we hypothesized that an allosteric enhancer for A(1)AR (PD-81723) protects against renal I/R injury without the undesirable side effects of systemic A(1)AR activation by potentiating the cytoprotective effects of renal adenosine generated locally by ischemia. Pretreatment with PD-81723 produced dose-dependent protection against renal I/R injury in A(1)AR wild-type mice but not in A(1)AR-deficient mice. Significant reductions in renal tubular necrosis, neutrophil infiltration, and inflammation as well as tubular apoptosis were observed in A(1)AR wild-type mice treated with PD-81723. Furthermore, PD-81723 decreased apoptotic cell death in human proximal tubule (HK-2) cells in culture, which was attenuated by a specific A(1)AR antagonist (8-cyclopentyl-1,3-dipropylxanthine). Mechanistically, PD-81723 induced sphingosine kinase (SK)1 mRNA and protein expression in HK-2 cells and in the mouse kidney. Supporting a critical role of SK1 in A(1)AR allosteric enhancer-mediated renal protection against renal I/R injury, PD-81723 failed to protect SK1-deficient mice against renal I/R injury. Finally, proximal tubule sphingosine-1-phosphate type 1 receptors (S1P(1)Rs) are critical for PD-81723-induced renal protection, as mice selectively deficient in renal proximal tubule S1P(1)Rs (S1P(1)R(flox/flox) PEPCK(Cre/-) mice) were not protected against renal I/R injury with PD-81723 treatment. Taken together, our experiments demonstrate potent renal protection with PD-81723 against I/R injury by reducing necrosis, inflammation, and apoptosis through the induction of renal tubular SK1 and activation of proximal tubule S1P(1)Rs. Our findings imply that selectively enhancing A(1)AR activation by locally produced renal adenosine may be a clinically useful therapeutic option to attenuate ischemic acute kidney injury without systemic side effects.     

Genetic inactivation of the adenosine A(2A) receptor exacerbates brain damage in mice with experimental autoimmune encephalomyelitis

Studies with multiple sclerosis patients and animal models of experimental autoimmune encephalomyelitis (EAE) implicate adenosine and adenosine receptors in modulation of neuroinflammation and brain injury. Although the involvement of the A(1) receptor has been recently demonstrated, the role of the adenosine A(2A) receptor (A(2A) R) in development of EAE pathology is largely unknown. Using mice with genetic inactivation of the A(2A) receptor, we provide direct evidence that loss of the A(2A) R exacerbates EAE pathology in mice. Compared with wild-type mice, A(2A) R knockout mice injected with myelin oligodendroglia glycoprotein peptide had a higher incidence of EAE and exhibited higher neurological deficit scores and greater decrease in body weight. A(2A) R knockout mice displayed increased inflammatory cell infiltration and enhanced microglial cell activation in cortex, brainstem, and spinal cord. In addition, demyelination and axonal damage in brainstem were exacerbated, levels of Th1 cytokines increased, and Th2 cytokines decreased. Collectively, these findings suggest that extracellular adenosine acting at A(2A) Rs triggers an important neuroprotective mechanism. Thus, the A(2A) receptor is a potential target for therapeutic approaches to multiple sclerosis.     

Role of bone marrow-derived progenitor cells in the maintenance and regeneration of dental mesenchymal tissues

While dental mesenchymal stem cells are well-studied, the origin of these cells is still unclear. Bone marrow-derived cells (BMDCs) have the potential to engraft into several tissues after injury, but whether they can become dental tissue-specific progenitor cells under normal conditions and the relationship of these cells to the tissue-resident cells are unknown. Thus, we transplanted green fluorescent protein (GFP)-labeled BMDCs into irradiated wild-type mice. We found that the engraftment of BMDCs participated in the regeneration and differentiated into periodontal specific cells after injury. Under normal conditions, there were more BMDCs engrafting into the dental mesenchymal tissue than other organs, in which the expression of stromal cell-derived factor-1 (SDF-1) was significantly higher than in other organs, and the engraftment of cells increased with time. A small fraction of GFP+ cells maintained the mesenchymal stem cell phenotype positive for CD105, CD106, and CD90, which were significantly less than the tissue-resident stem cells; meanwhile, GFP+/CD45+ cells were rare. Isolation and characterization of the dental pulp cells showed that the number of GFP+/Ki67+ cells were greater than the GFP-/Ki67+ cells. In addition, some GFP+ cells differentiated into the dental-specific cells and expressed dental-specific proteins, and can be found in the odontoblast layer after implantation of the apical bud. In conclusion, these data suggest that bone marrow progenitor cells communicate with dental tissues and become tissue-specific mesenchymal progenitor cells to maintain tissue homeostasis.     

Bone marrow transplantation results in donor-derived hepatocytes in an animal model of inherited cholestatic liver disease

Cell transplantation is a potential therapy for acquired or inherited liver diseases. Donor-derived hepatocytes (DDH) have been found in humans and mice after bone marrow transplantation (BMT) but with highly variable frequencies in different disease models. To test the effect of liver repopulation after BMT in inherited cholestatic liver diseases, spgp (sister of P-glycoprotein, or bile salt export pump, abcb11) knockout mice, a model for human progressive intrahepatic cholestasis type 2 with defects in excreting bile salts across the hepatocyte canalicular membrane, were transplanted with bone marrow cells from enhanced green fluorescent protein (EGFP) transgenic donor mice after lethal irradiation. One to 6 months later, scattered EGFP-positive DDHs with positive spgp staining were observed in the liver. These hepatocytes had been incorporated into hepatic plates and stained positively with hepatocyte-specific marker albumin. RT-PCR for the spgp gene revealed positive expression in the liver of sgsp knockout mice that had received the transplant. Bile acid analysis of bile samples showed that these mice also had higher levels of total biliary bile acid and taurocholic acid concentration than knockout mice without transplantation, indicating that BMT partially improved biliary bile acid secretion. Our results indicate that bone marrow cells could serve as a potential source for restoration of hepatic functions in chronic metabolic liver disease.     

小鼠脑组织腺苷A2A受体缺失模型的建立与评价

制备了脑组织腺苷A2A受体基因缺失的小鼠模型并对该模型进行评价。在采用2次6.2 Gy X线间隔照射对敲除A2A受体基因的雌性C57BL/6小鼠进行清髓处理后, 将野生型雄性C57BL/6小鼠骨髓细胞移植到其体内, 使其脑组织的A2A受体仍保持缺失型。然后对移植效果进行鉴定, 并对模型的生理指标进行观察和评价。结果发现: 骨髓移植6周后, 受体小鼠的白细胞性染色体基因由雌性变为雄性; 骨髓中A2A受体阳性细胞率为94.85%, 而脑内A2A受体mRNA与A2A受体基因敲除小鼠比较, 无显著差异。模型小鼠除心率略低于野生型小鼠外, 在呼吸频率、脑含水量以及脑内谷氨酸含量等生理指标上均与野生型小鼠和A2A基因敲除小鼠无显著差异。     

小鼠脑组织腺苷A2A受体缺失模型的建立与评价

制备了脑组织腺苷A2A受体基因缺失的小鼠模型并对该模型进行评价。在采用2次6.2 Gy X线间隔照射对敲除A2A受体基因的雌性C57BL/6小鼠进行清髓处理后, 将野生型雄性C57BL/6小鼠骨髓细胞移植到其体内, 使其脑组织的A2A受体仍保持缺失型。然后对移植效果进行鉴定, 并对模型的生理指标进行观察和评价。结果发现: 骨髓移植6周后, 受体小鼠的白细胞性染色体基因由雌性变为雄性; 骨髓中A2A受体阳性细胞率为94.85%, 而脑内A2A受体mRNA与A2A受体基因敲除小鼠比较, 无显著差异。模型小鼠除心率略低于野生型小鼠外, 在呼吸频率、脑含水量以及脑内谷氨酸含量等生理指标上均与野生型小鼠和A2A基因敲除小鼠无显著差异。     

Bone marrow expression of poly(ADP-ribose) polymerase underlies diabetic neuropathy via hematopoietic-neuronal cell fusion

Diabetic neuropathy is the most common diabetic complication. The pathogenetic pathways include oxidative stress, advanced glycation end product (AGE) formation, protein kinase C, and NF-κB activation, as well as increased polyol flux. These metabolic perturbations affect neurons, Schwann cells, and vasa nervorum, which are held to be the primary cell types involved. We hypothesize that diabetes induces the appearance of abnormal bone marrow-derived cells (BMDCs) that fuse with neurons in the dorsal root ganglia (DRG) of mice, leading to diabetic neuropathy. Neuronal poly(ADP-ribose) polymerase-1 (PARP-1) activation in diabetes is known to generate free radical and oxidant-induced injury and poly(ADP-ribose) polymer formation, resulting in neuronal death and dysfunction, culminating in neuropathy. We further hypothesize that BM-specific PARP expression plays a determining role in disease pathogenesis. Here we show that bone marrow transplantation (BMT) of PARP-knockout (PARPKO) cells to wild-type mice protects against, whereas BMT of wild-type cells to PARPKO mice, which are normally "neuropathy-resistant," confers susceptibility to, diabetic neuropathy. The pathogenetic process involving hyperglycemia, BMDCs, and BMDC-neuron fusion can be recapitulated in vitro. Incubation in high, but not low, glucose confers fusogenicity to BMDCs, which are characterized by proinsulin (PI) and TNF-α coexpression; coincubation of isolated DRG neurons with PI-BMDCs in high glucose leads to spontaneous fusion between the 2 cell types, while the presence of a PARP inhibitor or use of PARPKO BMDCs in the incubation protects against BMDC-neuron fusion. These complementary in vivo and in vitro experiments indicate that BMDC-PARP expression promotes diabetic neuropathy via BMDC-neuron fusion.     

Brain-Derived Neurotrophic Factor from Bone Marrow-Derived Cells Promotes Post-Injury Repair of Peripheral Nerve

Brain-derived neurotrophic factor (BDNF) stimulates peripheral nerve regeneration. However, the origin of BNDF and its precise effect on nerve repair have not been clarified. In this study, we examined the role of BDNF from bone marrow-derived cells (BMDCs) in post-injury nerve repair. Control and heterozygote BDNF knockout mice (BDNF+/−) received a left sciatic nerve crush using a cerebral blood clip. Especially, for the evaluation of BDNF from BMDCs, studies with bone marrow transplantation (BMT) were performed before the injury. We evaluated nerve function using a rotarod test, sciatic function index (SFI), and motor nerve conduction velocity (MNCV) simultaneously with histological nerve analyses by immunohistochemistry before and after the nerve injury until 8 weeks. BDNF production was examined by immunohistochemistry and mRNA analyses. After the nerve crush, the controls showed severe nerve dysfunction evaluated at 1 week. However, nerve function was gradually restored and reached normal levels by 8 weeks. By immunohistochemistry, BDNF expression was very faint before injury, but was dramatically increased after injury at 1 week in the distal segment from the crush site. BDNF expression was mainly co-localized with CD45 in BMDCs, which was further confirmed by the appearance of GFP-positive cells in the BMT study. Variant analysis of BDNF mRNA also confirmed this finding. BDNF+/− mice showed a loss of function with delayed histological recovery and BDNF+/+→BDNF+/− BMT mice showed complete recovery both functionally and histologically. These results suggested that the attenuated recovery of the BDNF+/− mice was rescued by the transplantation of BMCs and that BDNF from BMDCs has an essential role in nerve repair.     

Renal ischemia-reperfusion injury and adenosine 2A receptor-mediated tissue protection: the role of CD4+ T cells and IFN-gamma

A(2A) adenosine receptor (A(2A)R)-expressing bone marrow (BM)-derived cells contribute to the renal protective effect of A(2A) agonists in renal ischemia-reperfusion injury (IRI). We performed IRI in mice lacking T and B cells to determine whether A(2A)R expressed in CD4+ cells mediate protection from IRI. Rag-1 knockout (KO) mice were protected in comparison to wild-type (WT) mice when subjected to IRI. ATL146e, a selective A(2A) agonist, did not confer additional protection. IFN-gamma is an important early signal in IRI and is thought to contribute to reperfusion injury. Because IFN-gamma is produced by kidney cells and T cells we performed IRI in BM chimeras in which the BM of WT mice was reconstituted with BM from IFN-gamma KO mice (IFN-gamma KO-->WT chimera). We observed marked reduction in IRI in comparison to WT-->WT chimeras providing additional indirect support for the role of T cells. To confirm the role of CD4+ A(2A)R in mediating protection from IRI, Rag-1 KO mice were subjected to ischemia-reperfusion. The protection observed in Rag-1 KO mice was reversed in Rag-1 KO mice that were adoptively transferred WT CD4+ cells (WT CD4+-->Rag-1 KO) or A(2A) KO CD4+ cells (A(2A) KO CD4+-->Rag-1 KO). ATL146e reduced injury in WT CD4+-->Rag-1 KO mice but not in A(2A) KO CD4+-->Rag-1 KO mice. Rag-1 KO mice reconstituted with CD4+ cells derived from IFN-gamma KO mice (IFN-gamma CD4+-->Rag-1 KO) were protected from IRI; ATL146e conferred no additional protection. These studies demonstrate that CD4+ IFN-gamma contributes to IRI and that A(2A) agonists mediate protection from IRI through action on CD4+ cells.     

Leukocyte-derived extracellular superoxide dismutase does not contribute to airspace EC-SOD after interstitial pulmonary injury

The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) is abundant in the lung and is known to limit inflammation and fibrosis following numerous pulmonary insults. Previous studies have reported a loss of full-length EC-SOD from the pulmonary parenchyma with accumulation of proteolyzed EC-SOD in the airspace after an interstitial lung injury. However, following airspace only inflammation, EC-SOD accumulates in the airspace without a loss from the interstitium, suggesting this antioxidant may be released from an extrapulmonary source. Because leukocytes are known to express EC-SOD and are prevalent in the bronchoalveolar lavage fluid (BALF) after injury, it was hypothesized that these cells may transport and release EC-SOD into airspaces. To test this hypothesis, C57BL/6 wild-type and EC-SOD knockout mice were irradiated and transplanted with bone marrow from either wild-type mice or EC-SOD knockout mice. Bone marrow chimeric mice were then intratracheally treated with asbestos and killed 3 and 7 days later. At both 3 and 7 days following asbestos injury, mice without pulmonary EC-SOD expression but with EC-SOD in infiltrating and resident leukocytes did not have detectable levels of EC-SOD in the airspaces. In addition, leukocyte-derived EC-SOD did not significantly lessen inflammation or early stage fibrosis that resulted from asbestos injury in the lungs. Although it is not influential in the asbestos-induced interstitial lung injury model, EC-SOD is still known to be present in leukocytes and may play an influential role in attenuating pneumonias and other inflammatory diseases.     

High-resolution in-vivo analysis of normal brain response to cranial irradiation

Radiation therapy (RT) is a widely accepted treatment strategy for many central nervous system (CNS) pathologies. However, despite recognized therapeutic success, significant negative consequences are associated with cranial irradiation (CR), which manifests months to years post-RT. The pathophysiology and molecular alterations that culminate in the long-term detrimental effects of CR are poorly understood, though it is thought that endothelial injury plays a pivotal role in triggering cranial injury. We therefore explored the contribution of bone marrow derived cells (BMDCs) in their capacity to repair and contribute to neo-vascularization following CR. Using high-resolution in vivo optical imaging we have studied, at single-cell resolution, the spatio-temporal response of BMDCs in normal brain following CR. We demonstrate that BMDCs are recruited specifically to the site of CR, in a radiation dose and temporal-spatial manner. We establish that BMDCs do not form endothelial cells but rather they differentiate predominantly into inflammatory cells and microglia. Most notably we provide evidence that more than 50% of the microglia in the irradiated region of the brain are not resident microglia but recruited from the bone marrow following CR. These results have invaluable therapeutic implications as BMDCs may be a primary therapeutic target to block acute and long-term inflammatory response following CR. Identifying the critical steps involved in the sustained recruitment and differentiation of BMDCs into microglia at the site of CR can provide new insights into the mechanisms of injury following CR offering potential therapeutic strategies to counteract the long-term adverse effects of CR.     

Proteinase Activated Receptor 1 Mediated Fibrosis in a Mouse Model of Liver Injury: A Role for Bone Marrow Derived Macrophages

Liver fibrosis results from the co-ordinated actions of myofibroblasts and macrophages, a proportion of which are of bone marrow origin. The functional effect of such bone marrow-derived cells on liver fibrosis is unclear. We examine whether changing bone marrow genotype can down-regulate the liver''s fibrotic response to injury and investigate mechanisms involved. Proteinase activated receptor 1 (PAR1) is up-regulated in fibrotic liver disease in humans, and deficiency of PAR1 is associated with reduced liver fibrosis in rodent models. In this study, recipient mice received bone marrow transplantation from PAR1-deficient or wild-type donors prior to carbon tetrachloride-induced liver fibrosis. Bone marrow transplantation alone from PAR1-deficient mice was able to confer significant reductions in hepatic collagen content and activated myofibroblast expansion on wild-type recipients. This effect was associated with a decrease in hepatic scar-associated macrophages and a reduction in macrophage recruitment from the bone marrow. In vitro, PAR1 signalling on bone marrow-derived macrophages directly induced their chemotaxis but did not stimulate proliferation. These data suggest that the bone marrow can modulate the fibrotic response of the liver to recurrent injury. PAR1 signalling can contribute to this response by mechanisms that include the regulation of macrophage recruitment.