Fasting upregulates adipose triglyceride lipase and hormone-sensitive lipase levels and phosphorylation in mouse kidney

Abstract

Circulating non-esterified fatty acids (NEFA) rise during fasting and are taken up by the kidneys, either directly from the plasma or during re-uptake of albumin from glomerular filtrate, and are stored as triacylglycerol (TAG). Subsequent utilization of stored fatty acids requires their hydrolytic release from cellular lipid droplets, but relatively little is known about renal lipolysis. We found that total [(3)H]triolein hydrolase activity of kidney lysates was significantly increased by 15% in the fasted state. Adipose triglyceride lipase (Atgl) and hormone-sensitive lipase (Hsl) mRNA expression was time-dependently increased by fasting, along with other fatty acid metabolism genes (Pparα, Cd36, and Aox). ATGL and HSL protein levels were also significantly induced (by 239 ± 7% and 322 ± 8%, respectively). Concomitant with changes in total protein levels, there was an increase in ATGL phosphorylation at the AMPK-regulated serine 406 site in the 14-3-3 binding motif, and an increase in HSL phosphorylation at serines 565 and 660 that are regulated by AMPK and PKA, respectively. Using immunofluorescence, we further demonstrate nearly ubiquitous expression of ATGL in the renal cortex with a concentration on the apical/lumenal surface of some cortical tubules. Our findings suggest a role for ATGL and HSL in kidney lipolysis.

Kidney triglyceride accumulation in the fasted mouse is dependent upon serum free fatty acids

“…Intracellular lipases needed to utilize triglyceride stored in lipid droplets also increased; hormone sensitive lipase (Hsl/Lipe) mRNA increased 7-fold and adipose triglyceride lipase (Atgl/Pnpla2) 2-fold. Others have reported that, after a fast, both HSL and ATGL activation by phosphorylation increases in the kidney(33). Taken together, this gene expression profile suggests that, despite increased mRNA levels of genes regulating FAO and decreased mRNA levels of genes mediating de novo lipogenesis, the kidney stores excess fatty acids in lipid droplets during fasting.…”

The PNPLA3 variant associated with fatty liver disease (I148M) accumulates on lipid droplets by evading ubiquitylation

“…In the same experiment, we examined the effects of fasting on mRNA and protein levels of two other LD proteins: adipocyte TG lipase (ATGL), the major lipase in LDs, and perilipin 2 (PLIN2), an LD protein that increases with TG accumulation in hepatocytes . ATGL mRNA levels increased with fasting, as expected . Despite the increase in ATGL mRNA, protein levels did not show a concomitant increase over the same time period.…”

“…(24) ATGL mRNA levels increased with fasting, as expected. (25) Despite the increase in ATGL mRNA, protein levels did not show a concomitant increase over the same time period. No correlation was found between the amount of PNPLA3 and ATGL on LDs.…”

Data on hepatic lipolysis, adipose triglyceride lipase, and hormone-sensitive lipase in fasted and non-fasted C57BL/6J female mice

“…Standardized rodent diet (Research Diets #D12450H, New Brunswick, New Jersey, USA) and water were provided to the mice ad libitum for 9 days. Half of the mice were randomly chosen for a 16 h overnight fast from 5 pm to 9 am prior to cervical dislocation and tissue collection as we have previously described [1] . Protocols were approved by the Animal Care Committee at the University of Waterloo, with all procedures performed in accordance with the Canadian Council on Animal Care.…”