Circadian Regulation of Human Adipose Tissue Metabolism

This proposal will address 3 main aims: 1) Determine the impact of endogenous AT circadian rhythms on AT function independent of diurnal nutrient delivery in humans, 2) determine the impact of central obesity on adipocyte circadian clock, and 3) establish for the first-time in vivo human adipocyte specific cistrome of the core circadian clock transcription factors, BMAL1 and CLOCK. In order to understand whether adipocytes have intrinsic circadian clock entrainment that is separate from food entrainment, we will compare rhythmicity of AT of lean volunteers studied under continuous vs. intermittent feeding paradigms. 20 normal weight adults (M/F= 10/10, split evenly between feeding groups) will be randomized to receive either "continuous" (CONT) feedings via a nasogastric (NG) feeding tube or receive 3 meals a day for the "intermittent" (INTER) study, also delivered via NG tube. The screening prior to the inpatient study visit will include vital signs, height, weight, hip/waist/neck circumference, body composition (DEXA scan) plasma lipid profile and fasting glucose. Potential volunteers will fill out questionnaires to exclude sleep disorders and assure normal sleep habits. For 3 days prior to and during the inpatient study, volunteers will be required to wear an Actiwatch 24 h/day; which objectively measures 24-hour sleep quality and quantity. (see detailed methodology).

For the inpatient visit, volunteers will be admitted to Mayo Clinic Clinical Research and Trials Unit (CRTU) at 1500 h where an NG tube will be placed. After baseline blood samples, the CONT feeding group will start liquid feedings (Ensure Plus®) at 1800 and continue for the next ~37 hrs. This will provide 12 h of continuous feeding before the first abdominal AT biopsies; this duration of continuous feeding abolishes the wide fluctuations in plasma insulin that occurs with normal meals and will avoid the progressive lipolytic response that would occur if fasting were used as the experimental design. FFA during isocaloric, continuous feeding is well within normal intraday variability. Participants randomized to INTER will receive 1/3rd of their daily energy needs at each "meal" via NG tube. These feedings will be given at 1800 h and 3 separate meals the following day. Participants will undergo measures of resting energy expenditure following the overnight period to appropriately interpret FFA Ra data.

To avoid retrieving AT sample from previously disrupted biopsy sites, every participant will be limited to 4 abdominal adipose tissue biopsies (1 per abdominal quadrant). To ensure a full 24 hours of data, all participants will have biopsies at: 0600, 1800, and 0600 the next day, half of participants will have a biopsy at 1200 and the other half at 2400. This hybrid (linked-cross sectional) will allow us to sample in series from multiple people and then create sample group means to account for disparate biopsy numbers. We are sampling from abdominal adipose tissue as this is the primary source of circulating FFA in humans and thus is the most likely for us to ascertain regulation of lipolysis proteins.