Fengxin Zhu

GQ5 Hinders Renal Fibrosis in Obstructive Nephropathy by Selectively Inhibiting TGF-β–Induced Smad3 Phosphorylation

TGF-β1, via Smad-dependent or Smad-independent signaling, has a central role in the pathogenesis of renal fibrosis. This pathway has been recognized as a potential target for antifibrotic therapy. Here, we identified GQ5, a small molecular phenolic compound isolated from the dried resin of Toxicodendron vernicifluum, as a potent and selective inhibitor of TGF-β1-induced Smad3 phosphorylation. In TGF-β1-stimulated renal tubular epithelial cells and interstitial fibroblast cells, GQ5 inhibited the interaction of Smad3 with TGF-β type I receptor (TβRI) by blocking binding of Smad3 to SARA, suppressed subsequent phosphorylation of Smad3, reduced nuclear translocation of Smad2, Smad3, and Smad4, and downregulated the transcription of major fibrotic genes such as α-smooth muscle actin (α-SMA), collagen I, and fibronectin. Notably, intraperitoneal administration of GQ5 in rats immediately after unilateral ureteral obstruction (UUO) selectively inhibited Smad3 phosphorylation in UUO kidneys, suppressed renal expression of α-SMA, collagen I, and fibronectin, and resulted in impressive renal protection after obstructive injury. Late administration of GQ5 also effectively attenuated fibrotic lesions in obstructive nephropathy. In conclusion, our results suggest that GQ5 hinders renal fibrosis in rats by selective inhibition of TGF-β1-induced Smad3 phosphorylation.

Homocysteine Induces Collagen I Expression by Downregulating Histone Methyltransferase G9a.

Hyperhomocysteinemia (HHcy) leads to several clinical manifestations including hepatic fibrosis. Excess deposition of extracellular matrix (ECM) components including collagen is the eponymous lesion of liver fibrosis. In this study, we demonstrated that elevated concentration of Hcy induced the expression of collagen type I in cultured human liver cells as well as in liver tissue of HHcy mice. Meanwhile, Hcy inhibited the expression of histone methyltransferase G9a. Mechanistically, silencing endogenous G9a by siRNA enhanced the promoter activity of COL1A1 in LO2 cells. Conversely, overexpressing G9a inhibited the promoter activity of COL1A1. CHIP assay demonstrated that G9a binds to the neuron-restrictive silencer element (NRSE) on the promoter of COL1A1. Hcy treatment decreased the binding of G9a on NRSE, which in turn decreased the level of H3K9me2 on the promoter of COL1A1, led to upregulation of COL1A1. Taken together, these results provide a novel mechanism on explaining how HHcy promotes ECM production.

Numb contributes to renal fibrosis by promoting tubular epithelial cell cycle arrest at G2/M

Numb is a multifunctional protein involved in diverse cellular processes. However, the function of Numb in kidney remains unclear. Here, we reported that Numb is expressed in renal tubules and glomeruli in normal adult kidney. Numb expression was upregulated in fibrotic kidneys induced by unilateral ureteral obstruction (UUO) in mice as well as in human fibrotic kidney tissues. Numb overexpression in cultured proximal tubular cells increased the G2/M cell population and upregulated the expression of TGF-β1 and CTGF. Whereas, proximal tubule Numb knockout (PEPCK-Numb-KO) mice showed reduced G2/M arrest, decreased expression of TGF-β1 and CTGF, and attenuated fibrotic lesions due to either UUO or unilateral ischemia reperfusion nephropathy. Inhibiting p53 activity by pifithrin-β dramatically mitigated Numb-induced G2/M arrest, indicating that Numb potentiates G2/M arrest via stabilizing p53 protein. Together, these data suggest that Numb is a potential target for anti-fibrosis therapy.

Hyperhomocysteinemia Exacerbates Cisplatin-induced Acute Kidney Injury

Hyperhomocysteinemia (HHcy) has been linked to several clinical manifestations including chronic kidney disease. However, it is not known whether HHcy has a role in the development of acute kidney injury (AKI). In the present study, we reported that HHcy mice developed more severe renal injury after cisplatin injection and ischemia-reperfusion injury shown as more severe renal tubular damage and higher serum creatinine. In response to cisplatin, HHcy mice showed more prevalent tubular cell apoptosis and decreased tubular cell proliferation. Mechanistically, a heightened ER stress and a reduced Akt activity were observed in kidney tissues of HHcy mice after cisplatin injection. Stimulating cultured NRK-52E cells with Hcy significantly increased the fraction of cells in G2/M phase and cell apoptosis together with decreased Akt kinase activity. Akt agonist IGF-1 rescued HHcy-induced cell cycle arrest and cell apoptosis. In conclusion, the present study provides evidence that HHcy increases the sensitivity and severity of AKI.

QiShenYiQi Attenuates Renal Interstitial Fibrosis by Blocking the Activation of β-Catenin

Chronic kidney disease (CKD) is becoming a worldwide problem. However, current treatment options are limited. In the current study we showed that QiShenYiQi (QSYQ), a water-ethanol extract from several Chinese medicines, is a potent inhibitor of renal interstitial fibrosis. QSYQ inhibited transforming growth factor-β1 (TGF-β1)-responsive α-smooth muscle actin (α-SMA), collagen I, and fibronectin up-regulation in obstructive nephropathy and cultured cells. Administration of QSYQ also inhibited the established renal interstitial fibrosis in obstructive nephropathy. Interestingly, QSYQ selectively inhibited TGF-β1-induced β-catenin up-regulation and downstream gene transcription. Taken together, our study suggests that QSYQ selectively inhibits TGF-β1-induced β-catenin up-regulation and might have significant therapeutic potential for the treatment of renal fibrosis.