Role of Lactate in Lipid Metabolism, Just Always Inhibiting Lipolysis?

I appreciate the mechanism underlying the role of lactate in lipid metabolism proposed by Liu et al. (1). They found that lactate suppresses lipolysis in adipose tissue through a direct activation of GPR81. However, the argument that lactate suppresses lipolysis might be worthy of further consideration. Several studies have shown that there exists a substrate cycle or futile cycle in skeletal muscle as well as in adipose tissue, which dissipates redundant energy as heat via the cycle of synthesis, hydrolysis, and oxidation of triglyceride (2, 3). Furthermore, Hagström-Toft et al. (4) found that hypoglycemia increases both lipid and lactate mobilization in skeletal muscle and adipose tissues. It is well known that hypoglycemia will promote lipid hydrolysis to release fatty acids for providing energy by oxidation. I also found that lactate concentration was positively correlated with glycerol concentration in skeletal muscle and adipose tissues (unpublished data). Therefore, it is possible that lactate produced by anaerobic glycolysis might relieve the inhibition of glucose aerobic oxidation on fatty acid oxidation or adjust intracellular redox state via lactate shuttle in skeletal muscle and adipose tissues and thus promote fatty acid oxidation.