Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Cell Biology, Peroxisomes, Mitochondrial DNA, Oxidative phosphorylation, Biogenesis, PPAR alpha, PGC-1 alpha, MEMBRANE-LIPID-COMPOSITION, LINKED MECHANICAL ACTIVITY, ZELLWEGER-SYNDROME, CEREBROHEPATORENAL SYNDROME, ULTRASTRUCTURAL BASES, CERAMIDE KINASE, BETA-OXIDATION, STEADY-STATE, BIOGENESIS, LIVER, PGC-1α, PPARα, Animals, Cell Compartmentation, Cell Proliferation, Cell Respiration, DNA, Mitochondrial, Electron Transport, Gene Deletion, Hepatocytes, Lipids, Membrane Fluidity, Mice, Knockout, Mitochondria, Oxidation-Reduction, Oxidative Phosphorylation, Oxidative Stress, Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha, Peroxisome-Targeting Signal 1 Receptor, Protein Subunits, Receptors, Cytoplasmic and Nuclear, Transcription Factors, 0601 Biochemistry and Cell Biology, 1108 Medical Microbiology, 3101 Biochemistry and cell biology

Abstract:

The tight interrelationship between peroxisomes and mitochondria is illustrated by their cooperation in lipid metabolism, antiviral innate immunity and shared use of proteins executing organellar fission. In addition, we previously reported that disruption of peroxisome biogenesis in hepatocytes severely impacts on mitochondrial integrity, primarily damaging the inner membrane. Here we investigated the molecular impairments of the dysfunctional mitochondria in hepatocyte selective Pex5 knockout mice. First, by using blue native electrophoresis and in-gel activity stainings we showed that the respiratory complexes were differentially affected with reduction of complexes I and III and incomplete assembly of complex V, whereas complexes II and IV were normally active. This resulted in impaired oxygen consumption in cultured Pex5(-/-) hepatocytes. Second, mitochondrial DNA was depleted causing an imbalance in the expression of mitochondrial- and nuclear-encoded subunits of the respiratory chain complexes. Third, mitochondrial membranes showed increased permeability and fluidity despite reduced content of the polyunsaturated fatty acid docosahexaenoic acid. Fourth, the affected mitochondria in peroxisome deficient hepatocytes displayed increased oxidative stress. Acute deletion of PEX5 in vivo using adeno-Cre virus phenocopied these effects, indicating that mitochondrial perturbations closely follow the loss of functional peroxisomes in time. Likely to compensate for the functional impairments, the volume of the mitochondrial compartment was increased several folds. This was not driven by PGC-1α but mediated by activation of PPARα, possibly through c-myc overexpression. In conclusion, loss of peroxisomal metabolism in hepatocytes perturbs the mitochondrial inner membrane, depletes mitochondrial DNA and causes mitochondrial biogenesis independent of PGC-1α.