Effects of mTOR inhibition on cardiac and adipose tissue pathology and glucose metabolism in rats with metabolic syndrome

The mammalian target of rapamycin (mTOR) is a regulator of metabolism and is implicated in pathological conditions such as obesity and diabetes. We aimed to investigate the role of mTOR in obesity. A new animal model of metabolic syndrome (MetS), named DahlS.Z-Leprfa /Leprfa (DS/obese) rats was established previously in our laboratory. In this study, we used this model to evaluate the effects of mTOR inhibition on cardiac and adipose tissue pathology and glucose metabolism. DS/obese rats were treated with the mTOR inhibitor, everolimus, (0.83 mg/kg per day, per os) for 4 weeks at 9 weeks of age. Age-matched homozygous lean (DahlS.Z-Lepr+ /Lepr+ or DS/lean) littermates of DS/obese rats were used as controls. Treatment with everolimus ameliorated hypertension, left ventricular (LV) hypertrophy and fibrosis, and LV diastolic dysfunction, and attenuated cardiac oxidative stress and inflammation in DS/obese rats, but had no effect on these parameters in DS/lean rats. Treatment with everolimus reduced Akt Thr308 phosphorylation in the heart of DS/obese rats. It also alleviated obesity, hyperphagia, adipocyte hypertrophy, and adipose tissue inflammation in DS/obese rats. Everolimus treatment exacerbated glucose intolerance, but did not affect Akt phosphorylation levels in the fat or liver in these rats. Pancreatic β-cell mass was increased in DS/obese rats compared with that in DS/lean rats and this effect was attenuated by everolimus. Activation of mTOR signaling contributes to the pathophysiology of MetS and its associated complications. And mTOR inhibition with everolimus ameliorated obesity as well as cardiac and adipose tissue pathology, but exacerbated glucose metabolism in rats with MetS.