Epigenetic reprogramming of mtDNA and its etiology in mitochondrial diseases

Mitochondrial functionality and its regulation are tightly controlled through a balanced crosstalk between the nuclear and mitochondrial DNA interactions. Epigenetic signatures like methylation, hydroxymethylation and miRNAs have been reported in mitochondria. In addition, epigenetic signatures encoded by nuclear DNA are also imported to mitochondria and regulate the gene expression dynamics of the mitochondrial genome. Alteration in the interplay of these epigenetic modifications results in the pathogenesis of various disorders like neurodegenerative, cardiovascular, metabolic disorders, cancer, aging and senescence. These modifications result in higher ROS production, increased mitochondrial copy number and disruption in the replication process. In addition, various miRNAs are associated with regulating and expressing important mitochondrial gene families like COX, OXPHOS, ND and DNMT. Epigenetic changes are reversible and therefore therapeutic interventions like changing the target modifications can be utilized to repair or prevent mitochondrial insufficiency by reversing the changed gene expression. Identifying these mitochondrial-specific epigenetic signatures has the potential for early diagnosis and treatment responses for many diseases caused by mitochondrial dysfunction. In the present review, different mitoepigenetic modifications have been discussed in association with the development of various diseases by focusing on alteration in gene expression and dysregulation of specific signaling pathways. However, this area is still in its infancy and future research is warranted to draw better conclusions.