The histidine triad nucleotide-binding protein 2 (HINT-2) positively regulates hepatocellular energy metabolism.

Rajasekaran, Raviprasadh; Felser, Andrea; Nuoffer, Jean-Marc; Dufour, Jean-François; St-Pierre, Marie (2018). The histidine triad nucleotide-binding protein 2 (HINT-2) positively regulates hepatocellular energy metabolism. FASEB journal, 32(9), pp. 5143-5161. Federation of American Societies for Experimental Biology 10.1096/fj.201701429R

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The histidine triad nucleotide-binding protein 2 (HINT-2) is a mitochondrial adenosine phosphoramidase expressed in hepatocytes. The phenotype of Hint2 knockout ( Hint2) mice includes progressive hepatic steatosis and lysine hyperacetylation of mitochondrial proteins, which are features of respiratory chain malfunctions. We postulated that the absence of HINT-2 induces a defect in mitochondria bioenergetics. Isolated Hint2 hepatocytes produced less ATP and generated a lower mitochondrial membrane potential than did Hint2 hepatocytes. In extracellular flux analyses with glucose, the basal, ATP-linked, and maximum oxygen consumption rates (OCRs) were decreased in Hint2 hepatocytes and in HepG2 cells lacking HINT-2. Conversely, in HINT-2 overexpressing SNU-449 and HepG2 cells, the basal, ATP-linked, and maximum OCRs were increased. Similarly, with palmitate, basal and maximum OCRs were decreased in Hint2 hepatocytes, but they were increased in HINT-2 overexpressing HepG2 cells. When assayed with radiolabeled substrate, palmitate oxidation was reduced by 25% in Hint2 mitochondria. In respirometry assays, complex I- and II-driven, coupled and uncoupled respirations and complex IV KCN-sensitive respiration were reduced in Hint2 mitochondria. Furthermore, HINT-2 associated with cardiolipin and glucose-regulated protein 75 kDa. Our study shows decreased electron transfer and oxidative phosphorylation capacity in the absence of HINT-2. The bioenergetics deficit accumulated over time in hepatocytes lacking HINT-2 likely leads to the secondary outcome of steatosis.-Rajasekaran, R., Felser, A., Nuoffer, J.-M., Dufour, J.-F., St-Pierre, M. V. The histidine triad nucleotide-binding protein 2 (HINT-2) positively regulates hepatocellular energy metabolism.

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