Interdependent Regulation of Polycystin Expression Influences Starvation-Induced Autophagy and Cell Death

Abstract

Autosomal dominant polycystic kidney disease (ADPKD) is mainly caused by deficiency of polycystin-1 (PC1) or polycystin-2 (PC2). Altered autophagy has recently been implicated in ADPKD progression, but its exact regulation by PC1 and PC2 remains unclear. We therefore investigated cell death and survival during nutritional stress in mouse inner medullary collecting duct cells (mIMCDs), either wild-type (WT) or lacking PC1 (PC1KO) or PC2 (PC2KO), and human urine-derived proximal tubular epithelial cells (PTEC) from early-stage ADPKD patients with PC1 mutations versus healthy individuals. Basal autophagy was enhanced in PC1-deficient cells. Similarly, following starvation, autophagy was enhanced and cell death reduced when PC1 was reduced. Autophagy inhibition reduced cell death resistance in PC1KO mIMCDs to the WT level, implying that PC1 promotes autophagic cell survival. Although PC2 expression was increased in PC1KO mIMCDs, PC2 knockdown did not result in reduced autophagy. PC2KO mIMCDs displayed lower basal autophagy, but more autophagy and less cell death following chronic starvation. This could be reversed by overexpression of PC1 in PC2KO. Together, these findings indicate that PC1 levels are partially coupled to PC2 expression, and determine the transition from renal cell survival to death, leading to enhanced survival of ADPKD cells during nutritional stress.

Beneficial Effects of Bempedoic Acid Treatment in Polycystic Kidney Disease Cells and Mice

“…To assess whether cell lines that recapitulate ADPKD cystic disease ex vivo express ACLY, one of the targets of BA, we tested the expression of this enzyme by immunoblotting PT- and IMCD-derived model cell lines in cells grown in 2D. All four cell lines tested, parental PT-derived Pkd1 +/- (PH2) cells, PT-derived Pkd1 -/- (PN24) cells (Joly et al, 2006) and IMCD-derived WT-IMCD3 and ID1-3E5 Pkd1 -/- cells (Decuypere et al, 2021) express ACLY (total ACLY or tACLY; Figure 3A and C ). In addition, these cell lines also expressed an active form of ACLY phosphorylated at a target site of Akt (also known as Protein Kinase B; PKB) at Ser-455 (pS455 ACLY).…”

Beneficial effects of bempedoic acid treatment in polycystic kidney disease cells and mice

“…Mouse inner medullary collecting duct (IMCD) cell lines were also generously provided by Dr. Stefan Somlo. Wild-type (Wt)-IMCD3 (Cas9) is a control cell line for IMCD3-CRISPR-knockout cells (ID1-3E5 Pkd1 −/− ) ( Decuypere et al, 2021 ). Both cell lines were cultured in regular DMEM/F12 medium containing 5% FBS in a 37°C humidified 5% CO 2 -95% air incubator with medium changes every other day and passaged approximately twice weekly.…”

Molecular Mechanisms of Epigenetic Regulation, Inflammation, and Cell Death in ADPKD

“…In cpk mice and Han:SPRD rats, autophagy is increased as autophagosomes were found by electron microscopy in the tubular cells lining the cysts, and enhanced autophagy components LC3-II and beclin-1 were also observed ( Belibi et al, 2011 ). In PC1 deficient cells, basal autophagy was enhanced ( Decuypere et al, 2021 ). However, in Pkd1 mutant mice, the expression level of autophagy genes was decreased although LC3-II protein level showed no change ( Belibi et al, 2011 ; Chou et al, 2018 ).…”

“…In PC1 knockout mice, starvation-induced autophagic response is enhanced. Although knockdown of PC2 in PC1 knockout cells did not significantly alter autophagy level, PC2 knockout cells showed reduced protein level of PC1 and the PC1 band seemed to be at a lower molecular weight, suggesting that the stability of PC1 protein during starvation is dependent on PC2 expression ( Decuypere et al, 2021 ).…”