Lysosome restoration to activate podocyte autophagy: a new therapeutic strategy for diabetic kidney disease

Abstract

Autophagy, the intracellular lysosomal degradation process plays a pivotal role in podocyte homeostasis in diabetic kidney disease (DKD). Lysosomal function, autophagic activity, and their actions were investigated in vitro and in vivo. We found that LC3-II- and p62-positive vacuoles accumulated in podocytes of patients with DKD. Moreover, we found that advanced glycation end products (AGEs) could increase the protein expression of LC3-II and p62 in a dose- and time-dependent manner in cultured podocytes. However, the mRNA expression of LC3B, Beclin-1 or ATG7, as well as the protein level of Beclin-1 or ATG7 did not change significantly in the AGE-treated cells compared with that in control groups, suggesting that AGEs did not induce autophagy. In addition, AGEs led to an increase in the number of autophagosomes but not autolysosomes, accompanied with a failure in lysosomal turnover of LC3-II or p62, indicating that the degradation of autophagic vacuoles was blocked. Furthermore, we observed a dramatic decrease in the enzymatic activities, and the degradation of DQ-ovalbumin was significantly suppressed after podocytes were treated with AGEs. Plasma-irregular lysosomal-associated membrane protein 1 granules accompanied with the diffusion of cathepsin D expression and acridine orange redistribution were observed in AGE-treated podocytes, indicating that the lysosomal membrane permeability was triggered. Interestingly, we also found that AGEs-induced autophagic inhibition and podocyte injury were mimicked by the specific lysosomotropic agent, l-leucyl-l-leucine methyl ester. The exacerbated apoptosis and Rac-1-dependent actin-cytoskeletal disorganization were alleviated by an improvement in the lysosomal-dependent autophagic pathway by resveratrol plus vitamin E treatment in AGE-treated podocytes. However, the rescued effects were reversed by the addition of leupeptin, a lysosomal inhibitor. It suggests that restoring lysosomal function to activate autophagy may contribute to the development of new therapeutic strategies for DKD.

Critical Role for AMPK in Metabolic Disease-Induced Chronic Kidney Disease

“…Obesity or diabetes can lead to impairment of autophagy flux in renal cells [153,154]. HFD/obesity-induced autophagy impairment has been described in rodent models and obese patients [27,155].…”

sPLA2‐IB and PLA2R mediate insufficient autophagy and contribute to podocyte injury in idiopathic membranous nephropathy by activation of the p38MAPK/mTOR/ULK1 ser757 signaling pathway

“…P62 is a selective substrate of autophagy, binding directly to LC3 region or ubiquitylated organelles or proteins and p62 expression decline upon autophagy induction. 17 In the study, a weaker LC3-I/II expression of podocytes was shown in IMN patients with higher levels of proteinuria (Proteinuria-H patients, ≥3.5 g/d) than in patients with low levels of proteinuria (<3.5 g/d) by IHC assay ( Figure 1A). In addition, the podocyte LC3B-II dots were decreased and p62 expression was increased in Proteinuria-H patients, in contrast to Proteinuria-L patients viewed by confocal microscopy ( Figure 1B).…”

Depletion of protein kinase STK25 ameliorates renal lipotoxicity and protects against diabetic kidney disease

“…The results of this study also reveal that autophagy was significantly induced by inhibition of STK25 signaling in human kidney cells, which we observed both in basal culture conditions and when cells were challenged by oleic acid. Autophagy has been demonstrated to play an essential role in protecting the renal cells against injury under diabetic conditions through removal of protein aggregates and damaged organelles as well as by promoting cell survival, and the activation of autophagy has recently been suggested as a potential new therapeutic strategy for DKD (26,(48)(49)(50)(51). Autophagy is thought to be especially important for maintaining the homeostasis of postmitotic cells, such as podocytes, which have only limited capacity for regeneration and display a high level of basal autophagy (27,(52)(53)(54).…”