Lipolysis is a metabolic process by which triglycerides (TGs) are hydrolyzed into free fatty acids (FFAs) and glycerol to serve as fuels during fasting or cold-induced nonshivering thermogenesis. Cytoplasmic lipases are thought to be the predominant mechanism of liberating FFA from lipid stores. However, lysosomes also contain lipolytic activity via lysosomal acid lipase (Lipa). In adipocytes, the primary lipid-storing cell in the body with significant involvement in metabolism, the roles of Lipa and lysosomal lipolysis are unclear. We found that Lipa expression increases in the adipose tissue of mice in response to fasting, cold exposure, and CL316,243 (CL) treatment, a mimic of cold-induced lipolysis. Similar results were obtained in cultured adipocytes with nutrient-depletion or isoproterenol treatment, mimicking fasting or cold, respectively. Treatment of C57BL/6J mice with Lalistat (Lali), a specific inhibitor of Lipa, impaired thermogenesis, as evidenced by suppression of cold- and fasting-enhanced increases in plasma FFAs levels during cold exposure or CL treatment. Lipolysis was inhibited by Lali treatment in cultured adipocytes and fresh adipose tissue of C57BL/6J mice under fasting- or cold-mimic conditions. To conduct more detailed in vivo studies, we developed adipose-specific Lipa knockout (A-Lipa) mice, which exhibited lower plasma FFAs when challenged with fasting, cold exposure, or CL treatment. Furthermore, A-Lipa mice were significantly thermogenesis-impaired with exposure to cold or treatment with CL. To determine whether autophagy is involved in these phenomena, adipose-specific Atg5 knockout (A-Atg5) mice were challenged with fasting, cold exposure, or CL treatment. As was found in A-Lipa mice, A-Atg5 mice had lower levels of plasma FFAs and obliteration of stress-induced thermogenesis. Overall, our data suggest a previously unrecognized contribution of lysosomal lipolysis in adipocytes, possibly involving autophagy-related lipophagy.


Y.Yeh: None. B.Razani: None.


American Heart Association (897628); National Institutes of Health (DK131188)

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