Tgm2-p62-p53 Complex May Function as an Autophagic Regulator Through Fyn and Involve in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is one of the major diabetic complications and the leading cause of the end stage renal disease. Recently autophagy was shown to regulate DKD. Previously we reported that Fyn regulates muscle mass by suppressing autophagy through Fyn-STAT3-VPS34 signaling pathway. More recently, we demonstrated that Fyn also down-regulates autophagy in HK2 cells, an in vitrocell model of renal proximal tubular epithelial cells (RPTC). Phospho-proteomic analysis revealed that Fyn phosphorylates Transglutaminase 2 (Tgm2), a known autophagic inhibitor, at Y369 and Y617. Moreover, we found that Fyn-dependent phosphorylation of Tgm2 regulates autophagy. It has been reported that Tgm2 forms complexes with p53 and p62 (a known autophagy regulator) to mediate degradation of p53 at autophagosome in cancer cells and p53 functions as a DKD inducer. We found that p53 expression was decreased in Tgm2 knock-downed HK2 cells suggesting that Tgm2-p62-p53 complex also modulates autophagy in RPTC. We previously showed that Fyn and autophagy is regulated by energy status, therefore we next examined whether energy levels changed the subcellular localization of p53, p62 and Tgm2 in HK2 cells in vivousing the marker, Aquaporin 1. Confocal microscopic studies revealed that ad libitum-fed mice showed increased punctate of p62 in RPTC suggesting that autophagy was reduced. Fyn, Tgm2 and p53 shaped the dotted form mainly in the basement membrane of the cells. Interestingly, all these molecules moved to the cytoplasm in fasted state, where decreased p62 punctations were observed indicating increased autophagy. More importantly, in HFD fed mice, diet-induced rodent models of metabolic disorders, we found that protein expression of p53 was increased due to decreased levels of degradation with inhibition of autophagy implicated by decreased p62 punctations in RPTC. Taken together, these data suggest that the metabolic status may regulate Fyn to not only phosphorylate Tgm2 and modulates Tgm2-p62-p53 complex but also change their co-localizations of Fyn, p53 and Tgm2 in RPTC to regulate autophagy leading to pathogenesis of DKD.