Novel factors in the biogenesis of mitochondrial reticulum found from heart of juvenile visceral steatosis mouse

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Mice with juvenile visceral steatosis (JVS) develop remarkable cardiac hypertrophy and exhibit an increased number of mitochondria in their heart. However, the biochemical characteristics and physiological functions of these mitochondria cardiac are little known. We demonstrated that the respiratory activities at state 3 with glutamate plus malate or succinate in the heart mitochondria of JVS mice were greatly decreased compared with those of control mice. The contents of cytochromes a + a3, b, and c + c1 in the heart mitochondria of these mice were also decreased, to 51 % , 45 % , and 79 % , respectively, of those of the control mice, Oligomycin-sensitive ATPase activity in these mitochondria, however, was increased to about 2 times over that of the control mice. Surprisingly, the ATP-Pi exchange activity of the heart mitochondria of JVS mice was greatly decreased, to 35 % of that of control mice.Since the mitochondrial number in the cardiac cells of JVS mice is increased approximately three-fold compared with that of control mice, factors and their mRNAs which are related with the mitochondrial biogenesis, should dramatically be increased in the cells of JVS mice heart. To find such factors, the fluorescence differential display was performed using the highly purified poly(A) RNAs extracted from hearts of JVS mice and the control mice. We found novel six genes four of which were up-regulated in the hearts of JVS mice and the remain two genes were down-regulated. Furthermore, we established the method to observe mitochondrial reticulum labeled with fluorescence protein by transfecting pDsRed-Mito at high yield of 50-70 % into HeLa cells, and then succeeded to observe the morphological change of mitochondrial reticulum in the cell cycle of the cells by a time-laps deconvolution CCD-fluorescence microscope, which were synchronized at the G1/S boundary by the double thymidine block protocol.