The objective of this study is to elucidate the molecular mechanisms by which mitochondrial DNA (mtDNA) mutations cause tissue-specific, progressive diseases. Two parameters are proposed to be important. The first parameter is the special sensitivity of striated and smooth muscle to mitochondrial oxidative phosphorylation (OXPHOS) defects, coincident with their high level of OXPHOS gene expression. Reduced ATP in striated muscle would limit contraction causing cardiac hypertrophy and muscle weakness. Increased NADH in vascular smooth muscle would stimulate mitochondria oxygen free radical production, inactivating the vasodilator, NO, and causing vascular spasms and stroke-like episodes. The second parameter is the selective amplification of mutant mtDNAs within post-mitotic cells. The mutant mitochondria is hypothesized to create a local increase in NADH. This is perceived by the local nuclei which attempt to compensate by inducing mitochondrial bioenenesis and mtDNA replication in the surrounding mitochondria. This preferentially replicates the adjacent mutant mtDNAs, ultimately leading to localized respiratory failure. To test this hypothesis, we will preform three sets of experiments. First, we will examine the distribution of cytochrome c oxidase (COX)-deficient cells in pathologic hearts and vascular smooth muscle, an correlate these with increased mutant mtDNAs and a parallel induction of OXPHOS gene expression. According to the hypothesis, OXPHOS gene induction should coincide with regions of COX-negativity and mtDNA proliferation. Second, we will clone and characterize the transcription factors which recognize the OXBOX and REBOX promoter elements. The OXBOX imparts muscle-specific expression to OXPHOS genes and the REBOX appears to modulate OXPHOS gene expression in relation to the redox state of the cell. Hence, these factors could be the mediators of the tissue-specificity and progression of mtDNA diseases. Finally, we will insertionally inactive the mouse adenine nucleotide translocator (ANT) isoform genes and examine the effect on organ function and OXPHOS gene expression. ANT1 is heart and muscle-specific and its inactivation should cause hypertrophic cardiomyopathy and OXPHOS induction in heart and muscle. ANT2 helps compensate for respiratory deficiency and its inactivation should increase sensitivity to ischemic events and accentuate OXPHOS induction during stress. ANT3 is systemic but preferentially expressed in kidney and smooth muscle. its inactivation could result in hypertension and strokes, and cause OXPHOS induction in kidney and smooth muscle.
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