Abstract
Evaluation of: Moreno-Navarrete JM, Catalȥn V, Whyte L et al. The l–a–lysophosphatidylinositol/ GPR55 system and its potential role in human obesity. Diabetes 61(2), 281–291 (2012). GPR55, first identified as an orphan G?protein–coupled receptor, was initially suggested to be the ‘atypical’ cannabinoid receptor but later lysophosphatidylinositol (LPI) was recognized as its principal endogenous agonist. In the evaluated study,the LPI–GPR55 system in adipose tissue was examined. GPR55 is expressed in white adipose tissue and its expression is higher in visceral than in subcutaneous fat. GPR55 expression is higher in obese than in lean subjects, and in the obese group is greater in diabetic than in nondiabetic patients. In addition, plasma LPI concentration is increased in obese individuals. In vitro, LPI increases intracellular Ca2+ concentration and stimulates the expression of PPAR?g and genes involved in fatty acid synthesis. In contrast to human adipocytes, LPI has no effect on triglyceride accumulation in rodent adipocytes and adipose tissue GPR55 expression is downregulated in both leptin-deficient mice and rats made obese by a high-fat diet, indicating that the role of GPR55 in adipose tissue is species specific.
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