Higher baseline levels of fatty acid esters of hydroxy fatty acids do not further enhance the stimulatory effect of regular exercise on insulin sensitivity in obese mice
BackgroundExercise is an effective way to improve metabolic health, and the modulation of adipose tissue (AT) secretory functions may play a significant role in this process. AT produces various lipokines, including fatty acid esters of hydroxy fatty acids (FAHFA), which increase insulin sensitivity and have anti-inflammatory effects. While factors such as sex, age, obesity, and genetics influence FAHFA levels, their impact on exercise-induced FAHFA regulation remains unclear. MethodsFirst, sex-specific responses to an acute bout of exercise were assessed in wild-type (WT) and ADTRP-deficient (ADTRP KO) mice. Fasted mice underwent acute treadmill exercise until exhaustion, followed by analysis of non-esterified fatty acids in plasma, ex vivo lipolysis in the presence or absence of a hormone-sensitive lipase (HSL) inhibitor, and FAHFA release from AT (measured by LC-MS). Second, obese male WT and ADTRP KO mice fed a high-fat diet underwent 7 weeks of regular treadmill exercise (5 days/week), after which parameters of glucose homeostasis, plasma and AT FAHFA levels, and AT lipid profiles were analyzed. ResultsAcute exercise-induced increases in plasma non-esterified fatty acid levels, AT lipolysis, and FAHFA release from AT explants were more pronounced in male mice of both genotypes. Conversely, pharmacological inhibition of HSL using BAY 59-9435 increased FAHFA release from AT explants only in females. In obese sedentary ADTRP KO mice, insulin sensitivity was improved compared with their WT counterparts. Although regular exercise suppressed weight gain in obese animals of both genotypes, insulin sensitivity improved only in WT mice. Chronic exercise generally had no effect on plasma FAHFA levels in mice fed ad libitum; however, in WT mice, it increased the levels of FAHFA-containing triacylglycerol estolides, which were associated with improved insulin sensitivity. ConclusionsAcute exercise revealed sex-specific differences in AT lipolysis and FAHFA metabolism, with HSL playing an important role in FAHFA hydrolysis. Chronic exercise in obesity increases insulin sensitivity and FAHFA storage in AT; however, this effect is absent in ADTRP KO mice, which exhibit elevated FAHFA levels in AT, a condition associated with improved insulin sensitivity even in non-exercising animals.