Obestatin and Rosiglitazone Differentially Modulate Lipid Metabolism Through Peroxisome Proliferator-activated...

Obestatin is a 23-residue peptide, obtained after posttranslational modification of preproghrelin. It has been shown, in Swiss albino mice, to upregulate glycerolipid metabolism and PPARγ signaling. It was opined that the by-products of increased glycerolipid metabolism triggered PPARγ signaling. It was hypothesized that obestatin upon co-administration with a full agonist of PPARγ should reveal the comparative significance or possible synergy in PPARγ signaling. We postulated they would act synergistically by obestatin increasing PPARγ expression and rosiglitazone enhancing PPARγ activity. We evaluated the combination in DIO-C57BL/6 mice and observed that obestatin completely reversed the increase in subcutaneous fat brought about by rosiglitazone. To understand their role at the adipocyte level, 3T3-L1 cells were treated with a combination of obestatin and rosiglitazone during (1) initiation of differentiation and (2) after 14 days from initiation of differentiation when the adipocytes were mature. Interestingly, their influence was mainly adipogenic and showed double lipid accumulation when estimated 14 days after initiation of differentiation. There was an upregulation of Pparγ by fourfold, Hsl by eightfold, Glut4 by fourfold, Leptin by 2.7-fold, Atgl by sixfold, Fasn by sixfold, and Fabp4 by sevenfold at the mRNA level, whereas in mature adipocytes there was a significant decrease in fat accumulation by 20%. There was downregulation of Pparγ, Hsl, Lpl, and Fasn by 0.5-fold at the mRNA level. These results show that the combined influence of obestatin and rosiglitazone is significant and the outcome is dependent on the metabolic stage of the adipocyte.