Adipocyte HSL is required for maintaining circulating vitamin A and RBP4 levels during fasting.

Vitamin A (retinol) is distributed via the blood bound to its specific carrier protein, retinol-binding protein 4 (RBP4). Retinol-loaded RBP4 is secreted into the circulation exclusively from hepatocytes, thereby mobilizing hepatic retinoid stores that represent the major vitamin A reserves in the body. The relevance of extrahepatic retinoid stores for circulating retinol and RBP4 levels that are usually kept within narrow physiological limits is unknown.

Adipose retinol saturase is regulated by β-adrenergic signaling and its deletion impairs lipolysis in adipocytes and acute cold tolerance in mice.

Objective: Retinol saturase (RetSat) is an endoplasmic reticulum-localized oxidoreductase highly expressed in organs involved in lipid metabolism such as white (WAT) and brown adipose tissue (BAT). Cold exposure was shown to increase RETSAT protein in BAT but its relevance for non-shivering thermogenesis, a process with beneficial effects on metabolic health, is unknown.

Methods: We analyzed the regulation of RetSat expression in white and brown adipocytes and different murine adipose tissue depots upon β-adrenergic stimulation and cold exposure.