Mitochondrial Mutator-Phenotype May Be Related to Pathogenesis of Nonalcoholic Fatty Liver Disease: Insights from Deep Sequencing of Liver Mitochondrial Genomes

CARLOS JOSE PIROLA; ROMINA SCIAN; CRISTIAN ROHR; HERNAN DOPAZO; GUSTAVO O. CASTAÑO; SILVIA SOOKOIAN

San Francisco

Congreso; The 66th Annual Meeting of the American Association for the Study of Liver Diseases: The Liver Meeting 2015; 2015

American Association for the Study of Liver Diseases AASLD

Background: Mitochondrial (mt) dysfunction is involved in the development of NAFLD; normal activity of mitochondria critically determines fatty acid beta-oxidation, OXPHOS and insulin signaling. In addition, liver mitochondrial biogenesis is reduced in NAFLD. The mt-genome is highly polymorphic and variants in mtDNA affect mt function. A small proportion of mtDNA belongs to the control region involved in mtDNA duplication (D-loop).To understand the clinical implications of mtDNA-variation in the pathogenesis of NAFLD, we sequenced whole liver mtDNA-genomes of 28 individuals, including patients with NAFLD (n = 20) and age and sex-matched controls (n = 8). In addition, we sequenced the entire nuclear POLG and POLG2 genes, which are involved in mtDNA-replication. Methods: Liver mtDNA was first amplified by long-range PCR; deep next generation sequencing was further performed.Results: We achieved an average read depth >800 per individual; mtDNA sequencing revealed 689 variants, 525 (76%) of them were observed in NAFLD showing an enrichment of 1.28-fold mutation fraction compared to controls (p = 0.0056). Ten of 16 base positions containing heteroplasmic variants were highly polymorphic (>0.1) and were observed in NAFLD. The mutation fraction of liver mtDNA-genomes in controls compared with that in patients with simple steatosis (NAFL) shows no significant difference. Remarkably, patients with NASH compared with controls harbored a significant higher number of mutations in mitochondrially encoded ATP synthase 6 (p = 0.033), cytochrome b (MT-CYB) (p = 0.011), and members of the NADH-dehydrogenase complex (p = 4.5 E-5). The comparison of liver mtDNA-diversity among patients with NAFL and NASH showed that the disease severity was associated with increased number of variants in the NADH-complex (p = 7.4 E-3). For variants predicted to be deleterious, an allelic association analysis was further conducted; we found a nonsynonymous variant in MT-CYB (m.15326) and two mutations in D-loop (m.146 and m.16298) that were significantly associated with the disease severity. Overall, mutations located in the NADH-complex were significantly associated with liver-related phenotypes and arterial hypertension. The missense p.Gln1236His variant in POLG was associated with liver mtDNA-copy number (p = 0.01) and the POLG2- rs7223078 was associated with the degree of histological steatosis (p = 0.036). Conclusion: the burden of mutations in liver mt-genomes may contribute to the pathogenesis of NAFLD and metabolic syndrome-associated comorbidities explaining part of the ?missing heritability?. NASH development may be associated with an OXPHOS-negative phenotype.