Smad3 signaling activates bone marrow-derived fibroblasts in renal fibrosis

Abstract

Recent studies have demonstrated that bone marrow-derived fibroblasts contribute significantly to the pathogenesis of renal fibrosis. However, the signaling mechanisms underlying the activation of bone marrow-derived fibroblasts in the kidney are incompletely understood. Since TGF-β1/Smad3 signaling has been shown to play an important role in the pathogenesis of kidney fibrosis, we investigated the role of Smad3 in the activation of bone marrow-derived fibroblasts in the kidney following obstructive injury using Smad3 knockout mice and Smad3 null monocytes. Compared with wild-type mice, Smad3-knockout mice accumulated significantly fewer bone marrow-derived fibroblasts in the kidney after obstructive injury. Furthermore, Smad3 knockout mice exhibited less myofibroblast activation and expressed less α-SMA in the obstructed kidney. Consistent with these findings, genetic deletion of Smad3 reduced total collagen deposition and suppressed expression of extracellular matrix proteins. Moreover, wild-type mice engrafted with Smad3−/− bone marrow cells displayed fewer bone marrow-derived fibroblasts in the kidney with obstructive injury and showed less severe renal fibrosis compared with wild-type mice engrafted with Smad3+/+ bone marrow cells. In cultured monocytes, TGF-β1 induced phosphorylation of Smad3 and Smad3 deficiency abolished TGF-β1-induced expression of α-SMA and extracellular matrix proteins. Taken together, our results demonstrate that Smad3 signaling plays an essential role in the activation of bone marrow-derived fibroblasts in the kidney during the pathogenesis of renal fibrosis.

JAK3/STAT6 Stimulates Bone Marrow–Derived Fibroblast Activation in Renal Fibrosis

“…[6][7][8][9]17,20,21 Recruitment of these circulating fibroblast precursors depends on locally produced chemokines. We previously showed that chemokine CXCL16 and its receptor CXCR6 play a critical role in recruiting these cells from the circulation to the injured kidney after obstructive injury, ischemia-reperfusion, and angiotensin II-induced hypertension.…”

“…5,6,10,11 The activation of myeloid fibroblast precursors is regulated by locally produced cytokines. 7,8,17 Profibrotic cytokines IL-4 and IL-13 promote fibrocyte differentiation, whereas antifibrotic cytokines IFN-g and IL-12 inhibit its differentiation, suggesting that a complex interplay in the inflamed milieu determines the fate of bone marrow-derived fibroblast precursors. 14,15 Naive CD4 + T cells can differentiate into two major distinct phenotypes, Th1 and Th2 cells, which are characterized by specific cytokine expression patterns.…”

“…(B and D) Representative Western blots show the effect of CP690,550 on STAT6 phosphorylation. CP690,550 is given 30 minutes before IL-4 or IL -13Because TGF-b1 is an important profibrotic cytokine and plays an important role in activating bone marrow-derived fibroblasts, 17 we examined the effect of CP690,550 on TGFb1-induced a-SMA, fibronectin, and collagen I expression in normal rat kidney fibroblasts. Our results showed that CP690,550 did not affect TGF-b1-stimulated a-SMA, fibronectin, and collagen I expression (Supplemental Figure 1), indicating that the effect of CP690,550 is independent of TGF-b1 signaling.…”

“…6,7,17,42,43 Bone Marrow Transplantation Bone marrow transplantation was performed as previously described. 6,10,17,42,44 Briefly, bone marrow cells (5310 6 ) from WT or STAT6 KO mice were transferred to lethally irradiated WT mice. Chimeric mice were allowed to recuperate for 7-8 weeks before UUO surgery.…”

T Helper 2 Cytokine Signaling in Bone Marrow–Derived Fibroblasts

“…19 A recent study has revealed that the TGF-b1-Smad3 pathway induces the transition of monocytes to bone marrow-derived fibroblasts in the course of renal fibrosis. 20 Yan et al 17 showed in this study that TGF-b1-induced expression of aSMA, fibronectin, and COLI was not affected by the pretreatment with CP690550 in rat kidney fibroblasts. These results indicate that the effect of CP690550 on the transition of monocytes to bone marrow-derived fibroblasts could be independent of the TGF-b1-Smad3 pathway; however, an experiment using TGF-b1-treated bone marrow-derived monocytes and CP690550 will be required to clarify it.…”