Minichromosome maintenance 6 protects against renal fibrogenesis by regulating DUSP6-mediated ERK/GSK-3β/Snail1 signaling

Abstract

Background Renal fibrosis is a major determinant of chronic kidney disease (CKD) and an inevitable outcome in all types of progressive CKD. Minichromosome maintenance 6 (MCM6) promotes the migration and invasive ability of tumor cells by regulating the epithelial-mesenchymal transition (EMT) cascade, but its exact biological function in kidney diseases remains unclear. In this study, we aim to explore the role and potential mechanism of MCM6 in renal fibrosis. Methods Two unrelated in vivo fibrotic models including unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury (UIRI), and two in vitro tubular epithelial cells (TECs) injury models including TGF-β1-induced injury and hypoxia/reoxygenation-induced injury, were established to detect the expression of MCM6 in fibrotic models. And two adeno-associated viruses harboring MCM6 were delivered into the mice kidney via intraparenchymal injection to knockdown or overexpress the expression of MCM6 in renal tubules prior to the establishment of the UUO or UIRI model in order to further explore the specific role of MCM6 in renal fibrosis. Hematoxylin and eosin, Masson’s trichrome, immunohistochemical and immunofluorescence staining, western blotting assay, and qRT-PCR were performed to identify the effect of MCM6 on tubular injury, partial EMT, and interstitial fibrosis. Results MCM6 was significantly upregulated in TECs during progressive renal fibrosis including in vivo fibrotic models and in vitro injury stimulations. Conditional gene silencing of MCM6 aggravated partial EMT, extracellular matrix accumulation, and myofibroblast activation in UUO- or UIRI-induced renal fibrosis. And overexpression of MCM6 promoted the recovery of E-cadherin and suppressed the deposition of fibrotic markers, thereby retarding UUO- or UIRI-induced renal fibrosis. Mechanistically, activation of ERK/GSK-3β/Snail1 signaling was associated with MCM6-induced partial EMT. Additionally, DUSP6 expression substantially decreased in fibrotic kidneys and that it could be involved in MCM6-induced renal fibrosis by regulating ERK phosphorylation. Conclusion Our results are the first to identify the upregulation of MCM6 in fibrotic kidneys and further provide direct evidence that MCM6 play an important role in maintaining the tubular epithelial phenotype and protecting against renal fibrosis. MCM6 may be a useful biomarker for renal fibrosis and a potential anti-fibrotic therapeutic target for patients with CKD.