Circadian clock disruption and growth of kidney cysts in autosomal dominant polycystic kidney disease

Background

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 and PKD2 genes, and often progresses to kidney failure. ADPKD progression is not uniform among patients, suggesting that factors secondary to the PKD1/2 gene mutation could regulate the rate of disease progression. Here we tested the effect of circadian clock disruption on ADPKD progression. Circadian rhythms are regulated by cell-autonomous circadian clocks composed of clock proteins. BMAL1 is a core constituent of the circadian clock.

Methods

To disrupt the circadian clock, we deleted Bmal1 gene in the renal collecting ducts of the Pkd1 ^RC/RC (RC/RC) mouse model of ADPKD (RC/RC; Bmal1 ^f/f ; Pkhd1 ^cre , called DKO mice), and in Pkd1 knockout mouse inner medullary collecting duct cells ( Pkd1Bmal1 KO mIMCD3 cells). Only male mice were used.

Results

Human nephrectomy ADPKD kidneys and Pkd1 KO mIMCD3 cells showed reduced Bmal1 gene expression compared to normal controls. When compared to RC/RC kidneys, DKO kidneys showed significantly altered clock gene expression, increased cyst growth, cell proliferation, apoptosis and fibrosis. DKO kidneys also showed increased lipogenesis and cholesterol synthesis-related gene expression, and increased tissue triglyceride levels compared to RC/RC kidneys. Similarly, in vitro, Pkd1Bmal1 KO cells showed altered clock genes, increased lipogenesis and cholesterol synthesis-related genes, and reduced fatty-acid oxidation-related gene expression compared to Pkd1KO cells. The Pkd1Bmal1 KO cells showed increased cell proliferation compared to Pkd1KO cells, which was rescued by pharmacological inhibition of lipogenesis.

Conclusion

Renal collecting duct specific Bmal1 gene deletion disrupts the circadian clock and triggers accelerated ADPKD progression by altering lipid metabolism-related gene expression.

Key points

• Lack of BMAL1, a circadian clock protein in renal collecting ducts disrupted the clock and increased cyst growth and fibrosis in an ADPKD mouse model.

• BMAL1 gene deletion increased cell proliferation by increasing lipogenesis in kidney cells.

• Thus, circadian clock disruption could be a risk factor for accelerated disease progression in patients with ADPKD.