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Transforming growth factor β (TGF-β)/Smad3 signaling plays a role in tissue fibrosis. We report here that Erbb4-IR is a novel long non-coding RNA (lncRNA) responsible for TGF-β/Smad3-mediated renal fibrosis and is a specific therapeutic target for chronic kidney disease. Erbb4-IR was induced by TGF-β1 via a Smad3-dependent mechanism and was highly upregulated in the fibrotic kidney of mouse unilateral ureteral obstructive nephropathy (UUO). Silencing Erbb4-IR blocked TGF-β1-induced collagen I and alpha-smooth muscle actin (α-SMA) expressions in vitro and effectively attenuated renal fibrosis in the UUO kidney by blocking TGF-β/Smad3 signaling. Mechanistic studies revealed that Smad7, a downstream negative regulator of TGF-β/Smad signaling, is a target gene of Erbb4-IR because a binding site of Erbb4-IR was found on the 3' UTR of Smad7 gene. Mutation of this binding site prevented the suppressive effect of Erbb4-IR on the Smad7 reporter activity; in contrast, overexpression of Erbb4-IR largely inhibited Smad7 but increased collagen I and α-SMA transcriptions. Thus, kidney-specific silencing of Erbb4-IR upregulated renal Smad7 and thus blocked TGF-β/Smad3-mediated renal fibrosis in vivo and in vitro. In conclusion, the present study identified that Erbb4-IR is a novel lncRNA responsible for TGF-β/Smad3-mediated renal fibrosis by downregulating Smad7. Targeting Erbb4-IR may represent a precise therapeutic strategy for progressive renal fibrosis.

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C-reactive protein (CRP) is associated with progressive diabetic nephropathy in patients with type-2 diabetes (T2DN). However, role of CRP in T2DN remains unclear. We report here that CRP is pathogenic in T2DN in db/db mice that express human CRP (CRPtg-db/db). Compared to the littermate db/db mice, CRPtg-db/db developed more severe T2DN, showing higher levels of fasting blood glucose and microalbuminuria and more progressive renal inflammation and fibrosis. Enhanced T2DN in CRPtg-db/db mice were associated with over-activation of CRP-CD32b, NF-κB, TGF-β/Smad3, and mTOR signaling. Further studies in vitro defined that CRP activated Smad3 directly at 15 mins via the CD32b- ERK/p38 MAP kinase crosstalk pathway and indirectly at 24 hours through a TGF-β1-dependent mechanism. Importantly, CRP also activated mTOR signaling at 30 mins via a Smad3-dependent mechanism as Smad3 bound mTOR physically and CRP-induced mTOR signaling was abolished by a neutralizing CD32b antibody and a specific Smad3 inhibitor. Finally, we also found that CRP induced renal fibrosis through a CD32b-Smad3-mTOR pathway because blocking mTOR signaling with rapamycin inhibited CRP-induced CTGF and collagen I expression. Thus, CRP is pathogenic in T2DN. CRP may promote CD32b- NF-κB signaling to mediate renal inflammation; whereas, CRP may enhance renal fibrosis in T2DN via CD32b-Smad3-mTOR signaling.

Diabetic nephropathy (DN) is the most common chronic kidney disease. Accumulation of glucose and metabolites activates resident macrophages in kidneys. Resident macrophages play diverse roles on diabetic kidney injuries by releasing cytokines/chemokines, recruiting peripheral monocytes/macrophages, enhancing renal cell injuries (podocytes, mesangial cells, endothelial cells and tubular epithelial cells), and macrophage-myofibroblast transition. The differentiation and cross-talks of macrophages ultimately result renal inflammation and fibrosis in DN. Emerging evidence shows that targeting macrophages by suppressing macrophage activation/transition, and macrophages-cell interactions may be a promising approach to attenuate DN. In the review, we summarized the diverse roles of macrophages and the cross-talks to other cells in DN, and highlighted the therapeutic potentials by targeting macrophages.

Proteinuria is a common feature for almost all glomerular diseases and reflects the severity of the glomerular lesion. The presence of a large amount of proteins in tubular fluid, however, may also contribute to the development of RIF (renal interstitial fibrosis). Endocytosis of albumin in proximal tubular cells triggers PKC (protein kinase C)-dependent generation of reactive oxygen species and secretion of chemokines. As a family including 12 isozymes, which PKC isozymes participate in RIF is still unclear. EMT (epithelial-mesenchymal transdifferentiation) of RTECs (renal tubular epithelial cells) plays a crucial role in the progress of RIF induced by proteinuria. In the present study, we investigated the role of classical PKC isozymes in the proteinuria-induced EMT of RTECs. Employing immunochemical staining, we found that PKC-α, -βI and -βII were expressed in glomerulus and in RTECs in both normal and diseased renal tissues, while PKC-γ was only expressed in podocytes in the glomerulus. Treatment of HK-2 cells with extracted urinary proteins resulted in EMT, as evidenced by morphological changes, decreased E-cadherin expression, increased α-SMA (α-smooth muscle actin) expression, as well as production of type I collagen and fibronectin. Western blot analysis of PKC isozymes in the cytosolic compared with membrane fraction revealed translocation of PKC-α and -βI, but not PKC-βII, in HK-2 cells undergoing EMT. Pretreatment with selective PKC-α inhibitor G-6976 or PKC-β inhibitor significantly attenuated EMT induced by urinary proteins. In summary, the present study suggested that PKC-α and -βI play critical roles in the EMT of RTECs in response to urinary proteins.

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Introduction and Aims: Elevated plasma levels of C-reactive protein (CRP) are closely associated with progressive renal injury in patients with chronic kidney disease (CKD). Here, we tested a hypothesis that CRP may promote renal fibrosis and inflammation via a TGF-β/Smad3-dependent mechanism.Methods: Role and mechanisms of TGF-β/Smad3 in CRP-induced renal fibrosis and inflammation were examined in a mouse model of unilateral ureteral obstruction (UUO) induced in CRP Tg/Smad3 KO mice and in a rat tubular epithelial cell line in which Smad3 gene is stably knocked down (S3KD-NRK52E). Results: We found that mice overexpressing the human CRP gene were largely promoted renal inflammation and fibrosis as evidenced by increasing IL-1β, TNF-α, MCP-1 expression, F4/80 + macrophages infiltration, and marked accumulation of α-smooth muscle actin (α-SMA), collagen I and fibronectin in the UUO kidney, which were blunted when Smad3 gene was deleted in CRPtg-Smad3KO. Mechanistically, we found that the protection of renal inflammation and fibrosis in the UUO kidney of CRPtg-Smad3KO mice was associated with the inactivation of CD32-NF-κB and TGF-β/Smad3 signaling. Conclusion:In conclusion, Smad3 deficiency protects against CRP-mediated renal inflammation and fibrosis in the UUO kidney by inactivating CD32-NF-κB and TGF-β/Smad3 signaling.