Kidney Protection against Ischemia/Reperfusion Injury by Myofibrillogenesis Regulator-1

Abstract

Background/Aims: Ischemia/reperfusion (I/R) injury is characterized by cytoskeletal reorganization and loss of polarity in proximal tubule epithelial cells. Previously, we showed that myofibrillogenesis regulator (MR)-1 promoted actin organization in cardiomyocytes. MR-1 is also expressed in the kidney. Methods: In this study, we investigated MR-1 expression in acute renal failure induced by I/R in Sprague-Dawley rats. We determined the MR-1 expression and the ratio of fibrous actin (F-actin) to globular actin (G-actin). HK-2 cells were treated with or without hypoxia/reoxygenation (H/R), and MR-1 levels were increased by adenoviral overexpression or silenced by RNA interference. Results: I/R and H/R resulted in cellular injury and decreases of MR-1, the F-/G-actin ratio, and myosin light chain (MLC)-2. MR-1 overexpression attenuated H/R-induced cell injury and loss of surface membrane polarity of actin. MR-1 overexpression also increased the expression and phosphorylation of MLC-2 and MLC kinase, which were decreased in MR-1-silenced and H/R-treated cells. Conclusion: Together, these data show that MR-1 promoted actin polarity on the membrane surface and protected HK-2 cells from H/R injury. The mechanism might involve the rapid organization of F-actin through the upregulation and phosphorylation of MLC-2.

Myofibrillogenesis regulator-1 attenuates hypoxia/reoxygenation-induced injury by repairing microfilaments in neonatal rat cardiomyocytes

“…In addition, MR-1 also induced MLC-2 expression, which further increased MLC-2 total phosphorylation. When combined with our previous study that showed MR-1 interacted directly with MLC-2, and MLC-2 was critical for actin polymerization to form F-actin [23] and regulated by MLCK [13], these data demonstrate that MR-1 protects cardiomyocytes from H/R injury by attenuating damage of actin filaments and activating the MLCK/MLC-2 pathway.…”

“…Our previous studies showed that MR-1 interacted directly with MLC-2 and induced cardiomyocyte hypertrophy via sarcomere organization [8]. MR-1 overexpression promoted actin polarity through the MLC-2-mediated reorganization of actin filaments and protected HK-2 cells from H/R injury [13]. This further suggests that MR-1 might protect cells from H/R injury through attenuating H/R-induced damage of the actin filament.…”

“…proteins during early stages of H/R, which is compatible with myocardial injury during I/R [20]. MR-1 is a functional gene that is highly expressed in the myocardium, skeletal muscle, kidney and liver [8,12,13,21]. Our previous studies showed that overexpressing MR-1 attenuated H/R-induced apoptosis in cardiomyocytes [22].…”

“…Cardiomyocytes were identified by indirect immunofluorescence staining using anti-α-actinin mouse monoclonal antibody for 2 h at room temperature, followed by FITC green-conjugated donkey anti-mouse secondary antibody (1:400) for 1 h in the dark at room temperature. For F-actin detection, cardiomyocytes were stained in the dark at room temperature for 1 h with phalloidin-FITC at a final concentration of 0.33 μmol/L [8,13]. The coverslips were mounted on glass slides with mounting medium.…”

“…MR-1 overexpression up-regulated MLC-2 [8,13] while MR-1 knockdown down-regulated MLC-2 phosphorylation [13,14]. I/R and hypoxia injury also induced MLCK protein expression and MLC-2 phosphorylation as well as aggravated actin polymerization and depolymerization in the myocardium [10,15,16].…”