Atg5-mediated autophagy deficiency in proximal tubules promotes cell cycle G₂/M arrest and renal fibrosis

Abstract

Macroautophagy/autophagy protects against cellular stress. Renal sublethal injury-triggered tubular epithelial cell cycle arrest at G 2 /M is associated with interstitial fibrosis. However, the role of autophagy in renal fibrosis is elusive. Here, we hypothesized that autophagy activity in tubular epithelial cells is pivotal for inhibition of cell cycle G 2 /M arrest and subsequent fibrogenic response. In both renal epithelial cells stimulated by angiotensin II (AGT II) and the murine kidney after unilateral ureteral obstruction (UUO), we observed that occurrence of autophagy preceded increased production of COL1 (collagen, type I). Pharmacological enhancement of autophagy by rapamycin suppressed COL1 accumulation and renal fibrosis. In contrast, genetic ablation of autophagy by proximal tubular epithelial cell-specific deletion of Atg5, with reduction of the LC3-II protein level and degradation of SQSTM1/p62, showed marked cell cycle arrest at the G 2 /M phase, robust COL1 deposition, and severe interstitial fibrosis in a UUO model, as compared with wild-type mice. In vitro, AGT II exposure triggered autophagy preferentially in the G 1 /S phase, and increased COL1 expression in the G 2 /M phase in renal epithelial cells. Stimulation of Atg5-deficient primary proximal tubular cells with AGT II also resulted in elevated G 2 /M arrest and COL1 production. Pharmacological or genetic inhibition of autophagy increased AGT II-mediated G 2 /M arrest. Enhanced expression of ATG5, but not the autophagy-deficient ATG5 mutant K130R, rescued the G 2 /M arrest, suggesting the regulation of cell cycle progression by ATG5 is autophagy dependent. In conclusion, Atg5-mediated autophagy in proximal epithelial cells is a critical host-defense mechanism that prevents renal fibrosis by blocking G 2 /M arrest.

Dendrobium nobile Lindl alkaloid, a novel autophagy inducer, protects against axonal degeneration induced by Aβ25‐35 in hippocampus neurons in vitro

“…The formation of autophagosome is a key point in the process of autophagy, and once autophagy is induced, isolation of double membrane emerges to coat cargo and then elongates and expands to form the autophagosome . Beclin1 and ATG5 are necessary autophagy‐related proteins for the formation of double membrane; the conversion of endogenous LC3 I to LC3 II and exogenous GFP‐LC3 puncta is typically characterized as an autophagosome marker . Here, we found that Beclin1 and ATG5 protein levels were upregulated, and conversion of endogenous LC3 I to LC3 II and GFP‐LC3 puncta significantly increased in hippocampus neurons treated with DNLA, suggesting strongly that DNLA promotes autophagosome formation.…”

Increased Autophagy-Related 5 Gene Expression Is Associated with Collagen Expression in the Airways of Refractory Asthmatics

“…On the one hand, it has been shown that in proximal epithelial cells, ATG5-mediated autophagy reduced type I collagen deposition by blocking the G 2 /M phase arrest (42), a cell cycle phase whose arrest would initiate DNA repair and synthesis of pro-fibrotic factors (43). Furthermore, bleomycin-induced pulmonary fibrosis in a mouse model led to increased autophagy activation in the lungs as revealed by upregulated ATG5 protein expression levels and increased autophagosome formation (44).…”

AKI on CKD: heightened injury, suppressed repair, and the underlying mechanisms

“…Consistently, Livingston et al showed that renal fibrosis in obstructed kidneys was ameliorated in renal proximal tubule Atg7-knockout mice and interesting, this was associated with decreased production of specific pro-fibrotic factors 130 . However, Li et al reported higher levels of renal fibrosis in obstructed kidneys of proximal tubule Atg5-knockout mice 131 . Thus, while the protective role of autophagy in AKI is well-established, it is inconclusive whether autophagy is beneficial or detrimental to kidney repair.…”