Regulation of Adipose Triglyceride Lipase in vivo

In an effort to understand the in vivo coordination of proteins involved in lipolysis, a model of transient negative energy balance is critical. This experiment utilized lactating dairy cows to determine whether changes in abundance of key lipid droplet proteins and lipases are associated with altered lipolytic rates in vivo. Four adipose tissue biopsies were collected from 26 cows during positive energy balance (prior to calving and at 151–161 days of lactation) and during negative energy balance (5–9 and 21–31 days of lactation). Perilipin, hormone sensitive lipase (HSL), phospho‐HSL, and adipose triglyceride lipase (ATGL) were quantified by western blotting. Weekly blood samples were collected 3 weeks prior to parturition through 21–28 days of lactation and again at 151–161 days of lactation for analyses of serum metabolites. Elevated glycerol concentration (P<0.05) confirmed increased lipolysis during early lactation. Abundance of perilipin and HSL remained constant, but phospho‐HSL increased (P<0.03) at 5–9 days in lactation, consistent with stimulation of lipolysis via protein kinase A. In contrast, ATGL decreased during early lactation (P<0.01). Based on protein abundance, these results substantiate the emerging hypothesis that ATGL functions primarily under basal conditions. Supported by USDA‐CSREES, NRI project 2009‐35206‐05222.