Abstract
Mitochondria play various roles for biological maintenance in adipocytes. As for lipid metabolism, mitochondria have the opposite function of burning fatty acid by β-oxidation and supplying triglyceride (TAG) to lipid droplet. Recent study revealed that brown adipocytes (BA) contain cytoplasmic mitochondria (CM), which have high β-oxidation ability, and peridroplet mitochondria (PDM), which adhere lipid droplet, have high ability to generate ATP to synthesize and supply TAG to lipid droplet. On the other hand, Mitofusin 2 (Mfn2) and Mitoguardin 2 (MIGA2), and diacylglycerol acyltransferase 2 (DGAT2) are speculated to involved in interaction between mitochondria, endoplasmic reticulum and lipid droplet to promote TAG synthesis and expansion of lipid droplet. However, little is known about such mitochondrial fractions in white adipocytes (WA). In this study, we investigated whether WA isolated from mice adipose tissue may have mitochondria fractions corresponding to CM/PDM in BA. Cytoplasmic mitochondria and peridroplet mitochondria in WA (CMw/PDMw) were separated by centrifugation. Mitochondrial DNA, mitochondrial protein, incorporation of MitoTracker Red, and citrate synthase activity were detected in PDMw, as well as CMw. Electron microscopy showed larger size of mitochondria were observed in PDMw, than in CMw. Immunoblot analysis showed that Perilipin (Plin) 1 and Plin3 were detected in PDMw, but not in CMw. In addition, MIGA2 was detected in both CMw and PDMw, whereas Mfn2 and DGAT2 in PDMw. Immunoprecipitation study revealed that co-precipitation of Plin1/3 and MIGA2/Mfn2/DGAT2 was observed in the PDMw fraction. Our data indicated that mitochondria adhering lipid droplet was detected, which bind to Plin1/3. Moreover, the immunoprecipitation study suggested that mitochondria in the PDMw fraction may support TAG synthesis and expansion of lipid droplet. These results suggested that CMw and PDMw might play different roles in lipid metabolism in WA. Disclosure M.Fuwa: None. M.Asano: None. I.Mori: None. H.Morita: None. K.Kajita: None. T.Ishizuka: None.
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