CM of these cells has significantly reduced effects on fibroblast proliferation and SMA expression (Figure 5g and h) compared to the CM of LPA-stimulated PTECs transfected with control siRNA

CM of these cells has significantly reduced effects on fibroblast proliferation and SMA expression (Figure 5g and h) compared to the CM of LPA-stimulated PTECs transfected with control siRNA. fibroblast proliferation and myofibroblast differentiation. Administration of an inhibitor of myocardin-related transcription factor/serum response factor suppressed obstruction-induced renal fibrosis. Thus, targeting LPA-LPA1signaling and/or myocardin-related transcription factor/serum response factor-induced transcription could be promising therapeutic strategies for renal fibrosis. Keywords: Fibrosis, fibroblast, LPA1, CTGF == INTRODUCTION == Fibrosis is a common pathological feature of diseases that result in end-stage organ failure, including all forms of chronic kidney disease (CKD). 1Renal fibrosis appears to result from abnormal wound-healing processes. 2, 3Wound-healing responses involve multiple cell types, including epithelial cells, endothelial cells, pericytes, leukocytes and AM-4668 AM-4668 fibroblasts. Theinteractionsbetween these cell types have been increasingly appreciated to be central to the pathogenesis of fibrosis, ultimately resulting in the expansion of fibroblasts and their activation into myofibroblasts. 4, 5The molecular mediators of cell-cell communication in the development of fibrosis, however , remain to be fully elucidated. We and others have implicated the bioactive lipid lysophosphatidic acid (LPA) in fibrosis of multiple organs, including the kidney. 610LPA signals through specific G protein-coupled receptors (GPCRs), of which at least six have been identified and designated as LPA16. 11We have demonstrated that LPA signaling specifically through LPA1has pro-fibrotic effects on multiple cell types, promoting epithelial cell apoptosis, loss of endothelial cell barrier function, and fibroblast migration. 7, 8We have recently found that LPA contributes to fibrosis in a model of peritoneal fibrosis by inducing pro-fibrotic mesothelial cell to fibroblast communication AM-4668 through connective tissue growth factor (CTGF/CCN2). 12We found that LPA induces fibroblast proliferation and activation in this modelindirectly, by inducing mesothelial cell CTGF expression, which in turn drives fibroblast proliferation and myofibroblast accumulation in the peritoneum. CTGF has been noted to stimulate fibroblast proliferation and production of extracellular matrix, 13, 14and its expression has been demonstrated to be increased in fibrotic disorders, including CKD. 1517Both the development of renal fibrosis and the renal CTGF expression have previously been found to require LPA-LPA1signaling in the UUO model. 10These investigators found that LPA induced CTGF expression in tubular epithelial cells by signaling through LPA1. 10In contrast, other investigators have shown that LPA induces tubular CTGF expression through LPA2, in a pathway involving activation of latent TGF- in AM-4668 an v6 integrin-dependent manner. 18These investigators found this integrin-TGF–CTGF pathway was required for renal fibrosis in an ischemia-reperfusion injury model. 18A third group of investigators had previously implicated LPA3in renal ischemia-reperfusion injury. 19 Although several signaling pathways can produce CTGF expression, including Smad, 20we previously found that LPA signaling through LPA1stimulates CTGF expression in mesothelial cells through a myocardin-related transcription factor (MRTF)-serum response factor (SRF) pathway. 12SRF is a MADS box transcription factor that induces CTGF by binding to a CArG box sequence [CC(A/T)6GG] in AM-4668 its promoter region. 2123MRTF-A and MRTF-B are transcriptional co-activators that are sequestered in the cytoplasm by binding to globular actin (G-actin) monomers. Polymerization of G-actin into filamentous actin (F-actin) liberates MRTFs from G-actin, allowing their translocation to the nucleus, where they augment SRF transcriptional activity. 2426We and others have demonstrated that targeting of the MRTF-SRF pathway protects mice from fibrosis in several organs, including the 12, 2730 kidney. In this study, we consequently investigated the hypothesis that LPA signaling specifically through LPA1contributes to LRP8 antibody renal fibrosis by inducing tubular CTGF through the MRTF-SRF pathway. We further hypothesized that this induction of CTGF mediates pro-fibrotic epithelial cell-to-fibroblast communication that drives fibroblast proliferation and myofibroblast differentiation. Here we report compelling evidence for these hypotheses in UUO-induced renal fibrosis model. 31Clarifying the mediators and signaling pathways responsible for the epithelial cell-to-fibroblast communication that results in the expansion and activation of the fibroblast pool is important not only for understanding renal fibrogenesis, but for the rational development of new therapeutic strategies to treat renal fibrosis. == RESULTS == == Renal LPA1expression increased in the course of UUO-induced renal fibrosis == To determine the profile of renal LPA receptor subtypes in the course of renal fibrosis, we examined LPA receptors (LPA1-6) mRNA expression in whole kidneys (Supplementary Figure S1). In control kidneys obtained from LPA1-sufficient (LPA1+/+) mice, LPA2and LPA6were most highly expressed, followed by LPA1and LPA3. Control kidneys in LPA1-deficient (LPA1/) mice did not express LPA1as expected, and their LPA1deficiency did not cause compensatory changes in their expression of other LPA receptors. In LPA1+/+ligated kidneys, LPA1was the most highly induced LPA receptor; LPA5and LPA6expression was significantly increased as well, where LPA3expression was significantly decreased. == Genetic deletion of LPA1attenuated UUO-induced renal fibrosis == To examine the impact of LPA1on fibroblast accumulation and renal.