Background

Thermogenic mechanisms are a focus in increasing energy expenditure (EE) in obesity treatment. Skeletal muscle non-shivering thermogenesis (SkNST) may be superior to brown adipose tissue thermogenesis in humans for increasing EE. Sarcolipin (Sln) decreases Serca Ca2+ uptake efficiency, increasing ATP consumption and generating heat. We show that other elements of Ca2+ regulation beyond Sln-SERCA are altered in rat gastrocnemius with UCP-1 knockout and cold exposure.

Methods

CRISPR was used to generate global UCP-1 knockout (KO) rats, and were raised alongside wildtype (WT) controls. Rats were fed chow or high-fat, high-sucrose diet, and underwent body composition measurements, glucose and insulin tolerance testing, metabolic and feeding studies, and cold challenge (10°C, CC) versus room temperature (23°C, RT) studies. Muscle, adipose, and organ tissues were collected at 24-25 weeks.

Results

Gene expression in gastrocnemius is altered with either or both of CC and strain in HFHS diet. Sln significantly increased with CC in KO rats (p < 0.05) and in KO versus WT with CC (p < 0.05). Dworf significantly increased with CC in KO rats (p < 0.01) while Atp2a1 decreased significantly with CC in WT rats but not KO (p < 0.05). Casq1 significantly decreased in KO rats at RT (p < 0.05). In chow diet, Dworf significantly increases with CC in WT and KO (p < 0.01) as is Sln (p < 0.05). Casq1, Cacna1s, andAtp2a1 significantly decrease with chow diet in CC (p <0.001 for all). We also observed significant increases in body weight and fat mass with UCP-1 knockout (p< 0.05).

Conclusions

We show here that body composition and gene expression of calcium regulatory elements change with CC and strain, suggesting Sln-SERCA driven thermogenesis includes other elements. We also highlight an unexpected increase in Dworf expression, a competitor to Sln in SERCA interaction. We plan to follow up with additional validation of these changes, utilizing proteonomics and imaging.