The IL-4 receptor α has a critical role in bone marrow–derived fibroblast activation and renal fibrosis
Authors: Hua Liang, Zhengmao Zhang, Jingyin Yan, Yuguo Wang, Zhaoyong Hu, William E. Mitch, Yanlin Wang
Journal: Kidney International (2017)

Renal fibrosis is a common pathway leading to the progression of chronic kidney disease, and bone marrow–derived fibroblasts contribute significantly to the development of renal fibrosis. However, the signaling mechanisms underlying the activation of these fibroblasts are not completely understood. Here, we examined the role of IL-4 receptor α (IL-4Rα) in the activation of myeloid fibroblasts in two experimental models of renal fibrosis. Compared with wild-type mice, IL-4Rα knockout mice accumulated fewer bone marrow–derived fibroblasts and myofibroblasts in their kidneys. IL-4Rα deficiency suppressed the expression of α-smooth muscle actin, extracellular matrix proteins and the development of renal fibrosis. Furthermore, IL-4Rα deficiency inhibited the activation of signal transducer and activator of transcription 6 (STAT6) in the kidney. Moreover, wild-type mice engrafted with bone marrow cells from IL-4Rα knockout mice exhibited fewer myeloid fibroblasts in the kidney and displayed less severe renal fibrosis following ureteral obstructive injury compared with wild-type mice engrafted with wild-type bone marrow cells. In vitro, IL-4 activated STAT6 and stimulated expression of α-smooth muscle actin and fibronectin in mouse bone marrow monocytes. This was abolished in the absence of IL-4Rα. Thus, IL-4Rα plays an important role in bone marrow–derived fibroblast activation, resulting in extracellular matrix protein production and fibrosis development. Hence, the IL-4Rα/STAT6 signaling pathway may serve as a novel therapeutic target for chronic kidney disease. Renal fibrosis is a common pathway leading to the progression of chronic kidney disease, and bone marrow–derived fibroblasts contribute significantly to the development of renal fibrosis. However, the signaling mechanisms underlying the activation of these fibroblasts are not completely understood. Here, we examined the role of IL-4 receptor α (IL-4Rα) in the activation of myeloid fibroblasts in two experimental models of renal fibrosis. Compared with wild-type mice, IL-4Rα knockout mice accumulated fewer bone marrow–derived fibroblasts and myofibroblasts in their kidneys. IL-4Rα deficiency suppressed the expression of α-smooth muscle actin, extracellular matrix proteins and the development of renal fibrosis. Furthermore, IL-4Rα deficiency inhibited the activation of signal transducer and activator of transcription 6 (STAT6) in the kidney. Moreover, wild-type mice engrafted with bone marrow cells from IL-4Rα knockout mice exhibited fewer myeloid fibroblasts in the kidney and displayed less severe renal fibrosis following ureteral obstructive injury compared with wild-type mice engrafted with wild-type bone marrow cells. In vitro, IL-4 activated STAT6 and stimulated expression of α-smooth muscle actin and fibronectin in mouse bone marrow monocytes. This was abolished in the absence of IL-4Rα. Thus, IL-4Rα plays an important role in bone marrow–derived fibroblast activation, resulting in extracellular matrix protein production and fibrosis development. Hence, the IL-4Rα/STAT6 signaling pathway may serve as a novel therapeutic target for chronic kidney disease. Chronic kidney disease (CKD) is a leading cause of death and a serious global health challenge. The prevalence of CKD continues to increase worldwide.1Meguid El Nahas A. Bello A.K. Chronic kidney disease: the global challenge.Lancet. 2005; 365: 331-340Abstract Full Text Full Text PDF PubMed Scopus (889) Google Scholar Therefore, new strategies for the prevention and treatment of CKD are much needed to reduce its morbidity and mortality. Renal fibrosis is a pathologic hallmark of CKD, which is manifested by extensive fibroblast activation. Activated fibroblasts produce a large amount of extracellular matrix (ECM), leading to the destruction of renal parenchyma and progressive loss of kidney function.2Zeisberg M. Neilson E.G. Mechanisms of tubulointerstitial fibrosis.J Am Soc Nephrol. 2010; 21: 1819-1834Crossref PubMed Scopus (666) Google Scholar, 3Liu Y. Cellular and molecular mechanisms of renal fibrosis.Nat Rev Nephrol. 2011; 7: 684-696Crossref PubMed Scopus (922) Google Scholar, 4Nath K.A. Tubulointerstitial changes as a major determinant in the progression of renal damage.Am J Kidney Diseases. 1992; 20: 1-17Abstract Full Text PDF PubMed Scopus (860) Google Scholar Despite improvement in the knowledge regarding diverse CKD-related aspects, the cellular and molecular events leading to the development of renal fibrosis and eventually to renal failure are not completely understood. Therefore, a better understanding of the pathogenesis of renal fibrosis is essential for developing novel therapeutic strategies for treating chronic fibrotic kidney disease and preventing its progression. Traditionally, activated fibroblasts were considered to arise from resident fibroblasts.5Strutz F. Zeisberg M. Renal fibroblasts and myofibroblasts in chronic kidney disease.J Am Soc Nephrol. 2006; 17: 2992-2998Crossref PubMed Scopus (270) Google Scholar, 6Mack M. Yanagita M. Origin of myofibroblasts and cellular events triggering fibrosis.Kidney Int. 2015; 87: 297-307Abstract Full Text Full Text PDF PubMed Scopus (236) Google Scholar However, recent accumulating evidence indicates that bone marrow–derived fibroblast precursors significantly contribute to the population of activated fibroblasts and the development of renal fibrosis.7Sakai N. Wada T. T helper 2 cytokine signaling in bone marrow-derived fibroblasts: a target for renal fibrosis.J Am Soc Nephrol. 2015; 26: 2896-2898Crossref PubMed Scopus (9) Google Scholar, 8Dong Y. Yang M. Zhang J. et al.Depletion of CD8+ T cells exacerbates CD4+ T cell-induced monocyte-to-fibroblast transition in renal fibrosis.J Immunol. 2016; 196: 1874-1881Crossref PubMed Scopus (26) Google Scholar, 9Yang J. Lin S.C. Chen G. et al.Adiponectin promotes monocyte-to-fibroblast transition in renal fibrosis.J Am Soc Nephrol. 2013; 24: 1644-1659Crossref PubMed Scopus (86) Google Scholar, 10Niedermeier M. Reich B. Rodriguez Gomez M. et al.CD4+ T cells control the differentiation of Gr1+ monocytes into fibrocytes.Proc Natl Acad Sci U S A. 2009; 106: 17892-17897Crossref PubMed Scopus (182) Google Scholar Bone marrow–derived fibroblast precursors, termed as fibrocytes, are spindle-shaped cells that express hematopoietic markers, such as cluster of differentiation 45 (CD45) and CD11b, and mesenchymal markers, such as platelet-derived growth factor receptor-β (PDGFR-β) and vimentin.11Bucala R. Spiegel L.A. Chesney J. et al.Circulating fibrocytes define a new leukocyte subpopulation that mediates tissue repair.Mol Med. 1994; 1: 71-81Crossref PubMed Google Scholar, 12Herzog E.L. Bucala R. Fibrocytes in health and disease.Exp Hematol. 2010; 38: 548-556Abstract Full Text Full Text PDF PubMed Scopus (197) Google Scholar, 13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar Our previous studies have demonstrated that bone marrow–derived fibroblast precursors substantially contribute to the development of renal interstitial fibrosis.13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar, 14Chen G. Lin S.C. Chen J. et al.CXCL16 recruits bone marrow-derived fibroblast precursors in renal fibrosis.J Am Soc Nephrol. 2011; 22: 1876-1886Crossref PubMed Scopus (96) Google Scholar, 15Xia Y. Jin X. Yan J. et al.CXCR6 plays a critical role in angiotensin II-induced renal injury and fibrosis.Arterioscler Thromb Vasc Biol. 2014; 34: 1422-1428Crossref PubMed Scopus (41) Google Scholar, 16Xia Y. Yan J. Jin X. et al.The chemokine receptor CXCR6 contributes to recruitment of bone marrow-derived fibroblast precursors in renal fibrosis.Kidney Int. 2014; 86: 327-337Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar However, the molecular mechanisms underlying the activation of these fibroblasts are not completely understood. The activation of myeloid fibroblasts is regulated by cytokines that are locally produced by T helper (Th) cells. Th1 cells produce antifibrotic cytokines, such as interferon–γ, that suppress myeloid fibroblast differentiation, whereas Th2 cells produce profibrotic cytokines such as, interleukin (IL)-4 and IL-13, that promote myeloid fibroblast differentiation.17Schurigt U. Pfirschke C. Irmler I.M. et al.Interactions of T helper cells with fibroblast-like synoviocytes: up-regulation of matrix metalloproteinases by macrophage migration inhibitory factor from both Th1 and Th2 cells.Arthritis Rheum. 2008; 58: 3030-3040Crossref PubMed Scopus (17) Google Scholar, 18Jenkins S.J. Ruckerl D. Cook P.C. et al.Local macrophage proliferation, rather than recruitment from the blood, is a signature of TH2 inflammation.Science. 2011; 332: 1284-1288Crossref PubMed Scopus (1011) Google Scholar, 19Monney L. Sabatos C.A. Gaglia J.L. et al.Th1-specific cell surface protein Tim-3 regulates macrophage activation and severity of an autoimmune disease.Nature. 2002; 415: 536-541Crossref PubMed Scopus (1189) Google Scholar IL-4 receptor α (IL-4Rα) is a key component of the Th2 cytokine receptor, which mediates Th2 cytokine–signal transducer and activator of transcription 6 (STAT6) signaling pathway transduction and subsequent effector functions.20Quentmeier H. Kolsdorf K. Zaborski M. Drexler H.G. IL-4R alpha and gamma chain expression in LPS- and IL-4-stimulated MONO-MAC-6 cells.Leukemia. 1995; 9: 336-340PubMed Google Scholar, 21Kohanbash G. McKaveney K. Sakaki M. et al.GM-CSF promotes the immunosuppressive activity of glioma-infiltrating myeloid cells through interleukin-4 receptor-alpha.Cancer Res. 2013; 73: 6413-6423Crossref PubMed Scopus (125) Google Scholar, 22Herbert D.R. Orekov T. Perkins C. et al.IL-4R alpha expression by bone marrow-derived cells is necessary and sufficient for host protection against acute schistosomiasis.J Immunol. 2008; 180: 4948-4955Crossref PubMed Scopus (31) Google Scholar We previously demonstrated that Th2 cytokines activate the Janus kinase 3 (JAK3)–STAT6 signaling pathway to stimulate the activation of myeloid fibroblasts, which play a crucial role in the development of renal fibrosis.13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar Therefore, we hypothesized that IL-4Rα mediates Th2 cytokine–STAT6 signaling transduction in myeloid fibroblast activation and renal fibrosis. Here, we investigated the role of IL-4Rα signaling in activating bone marrow–derived fibroblast precursors in murine models of renal fibrosis induced by folic acid (FA) or unilateral ureteral obstruction (UUO). Our results demonstrate that IL-4Rα deficiency inhibits the activation of bone marrow–derived fibroblasts and suppresses the development of renal fibrosis. Myeloid fibroblast precursors substantially contribute to the pathogenesis of renal fibrosis.6Mack M. Yanagita M. Origin of myofibroblasts and cellular events triggering fibrosis.Kidney Int. 2015; 87: 297-307Abstract Full Text Full Text PDF PubMed Scopus (236) Google Scholar, 13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar, 14Chen G. Lin S.C. Chen J. et al.CXCL16 recruits bone marrow-derived fibroblast precursors in renal fibrosis.J Am Soc Nephrol. 2011; 22: 1876-1886Crossref PubMed Scopus (96) Google Scholar, 23LeBleu V.S. Taduri G. O'Connell J. et al.Origin and function of myofibroblasts in kidney fibrosis.Nat Med. 2013; 19: 1047-1053Crossref PubMed Scopus (872) Google Scholar To investigate the role of IL-4Rα in the activation of bone marrow–derived fibroblasts, wild-type (WT) and IL-4Rα knockout (KO) mice were treated with the vehicle FA. Kidney sections were stained for both CD45, a hematopoietic marker, and PDGFR-β, a mesenchymal marker, to identify bone marrow–derived fibroblasts. The number of CD45+ and PDGFR-β+ cells was significantly increased in the kidneys of WT mice after FA treatment. In contrast, the number of CD45+ and PDGFR-β+ cells was markedly reduced in the kidneys of IL-4Rα KO mice after FA treatment (Figure 1a and b). These data indicate that IL-4Rα plays an important role in the activation of bone marrow–derived fibroblast precursors in the kidneys after FA treatment. The IL-4Rα signaling pathway plays an important role in M2 macrophage polarization.24Park S.J. Lee K.P. Kang S. et al.Sphingosine 1-phosphate induced anti-atherogenic and atheroprotective M2 macrophage polarization through IL-4.Cell Signal. 2014; 26: 2249-2258Crossref PubMed Scopus (54) Google Scholar We recently showed that myeloid fibroblasts are derived from monocytes through M2 macrophage polarization in a mouse model of renal fibrosis.9Yang J. Lin S.C. Chen G. et al.Adiponectin promotes monocyte-to-fibroblast transition in renal fibrosis.J Am Soc Nephrol. 2013; 24: 1644-1659Crossref PubMed Scopus (86) Google Scholar Therefore, we determined whether IL-4Rα regulates macrophage polarization and myeloid fibroblast formation in FA nephropathy. Kidney sections were stained for CD206, an M2 macrophage marker, and PDGFR-β. The number of CD206+ and PDGFR-β+ cells was substantially increased in the kidneys of WT mice after FA treatment. The number of CD206+ and PDGFR-β+ cells was significantly decreased in the kidneys of IL-4Rα KO mice after FA treatment (Figure 1c and d). These results indicate that bone marrow–derived fibroblasts originate from monocytes through M2 macrophage polarization; this process is driven by the IL-4Rα signaling pathway. We next examined if IL-4Rα signaling affects myofibroblast formation in the kidneys. Kidney sections were stained for α-smooth muscle actin (α-SMA). The number of α-SMA–positive myofibroblasts was markedly increased in the kidneys of WT mice after FA treatment. In contrast, the number of myofibroblasts was significantly reduced in the kidneys of IL-4Rα KO mice after FA treatment (Figure 2a and b). Consistent with these findings, the α-SMA protein levels were significantly decreased in the kidneys of IL-4Rα KO mice after FA treatment compared with those in the kidneys of WT mice (Figure 2c and d). These results indicate that IL-4Rα signaling stimulates myofibroblast transformation in the kidneys during the development of renal fibrosis. To examine the role of IL-4Rα in the development of renal fibrosis, sirius red staining was performed to detect total collagen deposition in the kidneys. FA-treated WT mice developed significant collagen deposition in the kidneys compared with vehicle-treated WT mice. The degree of collagen deposition was markedly reduced in the kidneys of IL-4Rα KO mice after FA treatment. These data suggest that IL-4Rα plays a crucial role in the pathogenesis of renal fibrosis (Figure 3a and b). To evaluate the effect of IL-4Rα deficiency on ECM protein expression, immunofluorescence staining was performed to detect levels of fibronectin and collagen I, 2 major ECM proteins. Fibronectin and collagen I protein levels were significantly increased in the kidneys of FA-treated WT mice. The protein levels of these ECM proteins were significantly reduced in the kidneys of IL-4Rα KO mice after FA treatment (Figure 3c–f). Consistent with immunofluorescence staining, Western blot analysis demonstrated that IL-4Rα deficiency inhibited fibronectin and collagen I expression levels in the kidneys after FA treatment (Figure 3g–h). These data indicate that IL-4Rα signaling significantly contributes to ECM protein expressions in the kidney after FA nephropathy. We recently demonstrated that STAT6 signaling regulates Th2 cytokines–induced myeloid fibroblast activation and fibrosis development.13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar We then investigated whether IL-4Rα mediates the activation of STAT6 signaling in the kidney. Kidney sections were stained with a phospho-STAT6 (Tyr641) antibody. Prominent nuclear staining of phosphorylated STAT6 was mainly detected in the interstitial cells of WT mice after FA treatment. IL-4Rα deficiency significantly inhibited phospho-STAT6 levels in the kidneys after FA treatment (Figure 4a and b). In agreement with these results, Western blot analysis showed that phospho-STAT6 protein levels in the kidneys of IL-4Rα KO mice were reduced markedly compared with those in the kidney of WT mice after FA treatment (Figure 4c and d). We demonstrated that IL-4Rα plays a key role in the activation of CD45+ and PDGFR-β+ myeloid fibroblasts in the kidney and in the development of renal fibrosis after FA nephropathy. We then examined whether IL-4Rα mediates bone marrow–derived fibroblast activation and fibrosis development in another model of UUO-induced renal fibrosis. Kidney sections were stained for CD45 and PDGFR-β to identify bone marrow–derived fibroblasts. After inducing UUO injury, significantly fewer CD45+ and PDGFR-β+ myeloid fibroblasts were accumulated in the kidneys of IL-4Rα KO mice than in those of WT mice (Figure 5a and b). We next examined if IL-4Rα signaling affects bone marrow–derived myofibroblast formation in the kidneys. Kidney sections were stained for CD45 and α-SMA and were examined using a confocal microscope. The number of CD45+ and α-SMA+ myofibroblasts was significantly increased in the kidneys of WT mice with UUO injury. In contrast, the number of CD45+ and α-SMA+ myofibroblasts was considerably reduced in the obstructed kidneys of IL-4Rα KO mice (Supplementary Figure S1). To further quantify the number of myeloid fibroblasts in the kidney, freshly isolated kidney cells were stained for CD45 and collagen I or CD45 and α-SMA and were examined using flow cytometry. IL-4Rα deficiency significantly reduced CD45+ and collagen I+ cell accumulation and CD45+ and α-SMA+ cell formation in obstructed kidneys of IL-4Rα KO mice compared with that in obstructed kidneys of WT mice (Supplementary Figure S2). Consistent with these findings, IL-4Rα deficiency attenuated interstitial collagen deposition in the kidneys in response to UUO (Figure 5c and d). There results indicate that IL-4Rα has a crucial role in myeloid fibroblast activation and renal fibrosis development in response to obstructive injury. To determine the role of IL-4Rα in bone marrow–derived cells in the development of renal fibrosis, we performed bone marrow transplantation of WT mice with IL-4Rα+/+ or IL-4Rα−/− bone marrow cells. Eight weeks after bone marrow transplantation, chimeric mice were subjected to UUO. The genotype of bone marrow–derived cells from chimeric mice was confirmed by polymerase chain reaction of DNA extracted from peripheral blood cells (Supplementary Figure S3). WT mice transplanted with IL-4Rα−/− bone marrow cells exhibited fewer CD45+ and PDGFR-β+ bone marrow–derived fibroblasts in the obstructed kidneys compared with WT mice transplanted with IL-4Rα+/+ bone marrow cells (Figure 6a and b). Furthermore, there was a significant decrease in the number of CD206+ and PDGFR-β+ fibroblasts in the obstructed kidneys of WT mice transplanted with IL-4Rα−/− bone marrow cells compared with WT mice transplanted with IL-4Rα+/+ bone marrow cells (Figure 6c and d). WT mice engrafted with IL-4Rα−/− bone marrow cells developed less severe interstitial fibrosis and produced much lower α-SMA and ECM protein levels in the kidneys (Figure 7a–d). These data indicate that IL-4Rα signaling in bone marrow–derived cells plays an important role in the activation of myeloid fibroblasts and in the development of renal interstitial fibrosis. These results reinforce the notion that myeloid fibroblasts are derived from monocytes through M2 macrophage polarization, which is regulated by the IL-4Rα signaling pathway.Figure 7Interleukin-4 receptor α (IL-4Rα) deficiency in bone marrow–derived cells reduces renal fibrosis and extracellular matrix protein expression. (a) Representative photomicrographs of kidney sections from wild-type (WT)→WT and knockout (KO)→WT mice stained with sirius red for the evaluation of total collagen deposition in the kidneys at 10 days after vehicle or unilateral ureteral obstruction UUO treatment. Bar = 50 μm. (b) Quantitative analysis of renal interstitial collagen deposition in the kidneys. **P < 0.01 versus WT→WT-CON, #P < 0.05 versus WT→WT UUO, and +P < 0.05 versus KO→WT UUO; n = 6 in each group. (c) Representative Western blots show the protein expressions of fibronectin (FN), collagen I (COL I), and α-smooth muscle actin (α-SMA) in the kidneys. (d) Quantitative analysis of the protein levels of FN, COL I, and α-SMA in the kidneys. **P < 0.01 versus WT→WT-CON, #P < 0.05 versus WT→WT UUO, and +P < 0.05 versus KO→WT UUO; n = 6 in each group. CON, contralateral; GAPDH, glyceraldehyde 3-phosphate dehydrogenase. To optimize viewing of this image, please see the online version of this article at www.kidney-international.org.View Large Image Figure ViewerDownload Hi-res image Download (PPT) As IL-4Rα signaling regulates IL-4–induced STAT6 activation and STAT6 is involved in myeloid fibroblast activation,13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar, 25Vento-Tormo R. Company C. Rodriguez-Ubreva J. et al.IL-4 orchestrates STAT6-mediated DNA demethylation leading to dendritic cell differentiation.Genome Biol. 2016; 17: 4Crossref PubMed Scopus (76) Google Scholar we then explored whether IL-4Rα mediates IL-4–induced STAT6 activation in mouse bone marrow–derived monocytes. IL-4 treatment increased phosphorylated STAT6 levels in mouse bone marrow–derived monocytes. IL-4Rα deficiency abolished IL-4–induced STAT6 phosphorylation (Figure 8a and b). These data indicate that IL-4–induced STAT6 activation is mediated by IL-4Rα in bone marrow–derived monocytes. We next investigated if IL-4Rα deficiency affects IL-4–induced monocyte-to-fibroblast transition and ECM protein expression in mouse bone marrow–derived monocytes. Fibronectin and α-SMA protein levels of mouse bone marrow–derived monocytes were substantially increased after IL-4 treatment but were significantly reduced in the absence of IL-4Rα (Figure 8c and d). These results indicate that IL-4Rα signaling mediates IL-4–induced bone marrow–derived fibroblast activation and ECM protein production. Recent studies have demonstrated that bone marrow–derived fibroblast precursors substantially contribute to the development of renal fibrosis.6Mack M. Yanagita M. Origin of myofibroblasts and cellular events triggering fibrosis.Kidney Int. 2015; 87: 297-307Abstract Full Text Full Text PDF PubMed Scopus (236) Google Scholar, 9Yang J. Lin S.C. Chen G. et al.Adiponectin promotes monocyte-to-fibroblast transition in renal fibrosis.J Am Soc Nephrol. 2013; 24: 1644-1659Crossref PubMed Scopus (86) Google Scholar, 13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar, 14Chen G. Lin S.C. Chen J. et al.CXCL16 recruits bone marrow-derived fibroblast precursors in renal fibrosis.J Am Soc Nephrol. 2011; 22: 1876-1886Crossref PubMed Scopus (96) Google Scholar, 15Xia Y. Jin X. Yan J. et al.CXCR6 plays a critical role in angiotensin II-induced renal injury and fibrosis.Arterioscler Thromb Vasc Biol. 2014; 34: 1422-1428Crossref PubMed Scopus (41) Google Scholar, 16Xia Y. Yan J. Jin X. et al.The chemokine receptor CXCR6 contributes to recruitment of bone marrow-derived fibroblast precursors in renal fibrosis.Kidney Int. 2014; 86: 327-337Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar, 23LeBleu V.S. Taduri G. O'Connell J. et al.Origin and function of myofibroblasts in kidney fibrosis.Nat Med. 2013; 19: 1047-1053Crossref PubMed Scopus (872) Google Scholar However, molecular mechanisms underlying the activation of myeloid fibroblasts during the development of renal fibrosis are not completely elucidated. We recently demonstrated that Th2 cytokines stimulate myeloid fibroblast activation via the JAK3–STAT6 signaling pathway.13Yan J. Zhang Z. Yang J. et al.JAK3/STAT6 stimulates bone marrow-derived fibroblast activation in renal fibrosis.J Am Soc Nephrol. 2015; 26: 3060-3071Crossref PubMed Scopus (70) Google Scholar Although it is well-established that the biological effects of Th2 cytokines are regulated by IL-4Rα signaling,17Schurigt U. Pfirschke C. Irmler I.M. et al.Interactions of T helper cells with fibroblast-like synoviocytes: up-regulation of matrix metalloproteinases by macrophage migration inhibitory factor from both Th1 and Th2 cells.Arthritis Rheum. 2008; 58: 3030-3040Crossref PubMed Scopus (17) Google Scholar, 18Jenkins S.J. Ruckerl D. Cook P.C. et al.Local macrophage proliferation, rather than recruitment from the blood, is a signature of TH2 inflammation.Science. 2011; 332: 1284-1288Crossref PubMed Scopus (1011) Google Scholar the precise role of IL-4Rα in activating myeloid fibroblasts and promoting renal fibrosis remains to be determined. In this study, we demonstrated that the genetic disruption of IL-4Rα inhibits bone marrow–derived fibroblast accumulation and myofibroblast formation in the kidney and reduces the development of renal fibrosis. In cultured bone marrow–derived monocytes, IL-4Rα deficiency inhibits STAT6 activation and monocyte-to-fibroblast transition and ECM protein production after IL-4 treatment. These results indicate that IL-4Rα signaling via STAT6 plays a critical role in bone marrow–derived fibroblast activation and renal fibrosis development. Th2 cytokines exert their biological functions by interacting with specific type I and type II receptors on the cell surface. Both type I and type II receptors contain the IL-4Rα chain. When IL-4 binds to IL-4Rα with high affinity, the IL-4Rα chain interacts with the common γ chain to form the type I IL-4R. The type II IL-4R comprises the IL-4Rα chain and IL-13Rα1 chain. IL-13 is only able to bind to the type II IL-4R, whereas both type I and type II IL-4Rs can bind to IL-4.26Shirey K.A. Pletneva L.M. 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Willenborg S. Brinckmann J. et al.Interleukin-4 receptor alpha signaling in myeloid cells controls collagen fibril assembly in skin repair.Immunity. 2015; 43: 803-816Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar In this study, we showed that IL-4Rα deficiency significantly suppresses bone marrow–derived fibroblast accumulation and myofibroblast formation in the kidney. It is widely accepted that activated fibroblasts are responsible for the production of excessive amounts of ECM proteins such as fibronectin and collagen, leading to renal interstitial fibrosis.2Zeisberg M. Neilson E.G. Mechanisms of tubulointerstitial fibrosis.J Am Soc Nephrol. 2010; 21: 1819-1834Crossref PubMed Scopus (666) Google Scholar Furthermore, we demonstrated that IL-4Rα deficiency markedly inhibits the expression of ECM proteins and the development of FA-induced renal fibrosis. Consistent with the results of murine models of renal fibrosis, the absence of IL-4Rα abolished IL-4–induced expression of ECM proteins and α-SMA in cultured bone marrow–derived monocytes. These data indicate that IL-4Rα plays an important role in the activation of bone marrow–derived fibroblasts and the development of renal fibrosis. Tissue damage leads to the activation of innate immunity, including the recruitment of monocytes. Cells of