Diabetic kidney disease (DKD) is one of the major diabetic complications, the leading cause of the end stage renal disease, and recently autophagy was shown to regulate DKD. Previously we reported Fyn functions as a muscle mass regulator by suppressing autophagy. More recently, we demonstrated that Fyn also down-regulates autophagy in HK2 cells, an in vitro cell model of renal proximal tubular epithelial cells (RPTC). Phospho-proteomic analysis revealed that Fyn phosphorylates Transglutaminase 2 (Tgm2), a known autophagic inhibitor, on Y369 and Y617. Fyn dependent phosphorylation of Tgm2 regulates autophagy. Moreover, since Tgm2 was reported to make a complex with p53 and p62, known autophagy regulator/substrate to degrade p53 in autophagosome in cancer cells we examined it in HK2 cells and found that p53 expression was decreased in Tgm2 knock-downed HK2 cells indicating that Tgm2-p62-p53 complex modulating autophagy in RPTC. Those are biochemical studies with in vitro systems, we proceeded it in vivo. Since previously we showed that Fyn could be regulated by energy status, we first examined whether energy status could change the subcellular localization of those molecules in RPTC in vivo using the marker, Aquaporin 1. Confocal microscopic studies revealed that Ad libitum fed mice showed no punctate of p62 in those cells indicating suppressing autophagy. Fyn, Tgm2 and p53 shaped the dotted form mainly in basement membrane. Interestingly, all the molecules changed their localizations into cytoplasm in fasted state where p62 punctations observed indicating increased autophagy. Taken together, these data suggest that Energy status could regulates Fyn to not only phosphorylates 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.
R. Uehara: None. E. Yamada: None. Y. Nakajima: None. K. Horiguchi: None. E. Ishida: None. S. Matsumoto: None. S. Okada: None. C.C. Bastie: None. M. Yamada: None.