Investigation of the molecular mechanisms underlying left ventricular hypertrophy in the presence of Complex I deficiency-dependent mitochondrial dysfunction

Several studies have demonstrated that a dysfunction of the mitochondrial Complex I (CI) and of the sirtuins pathway is associated with the development of left ventricular hypertrophy (LVH). A deficiency of Ndufc2 (a subunit of NADH dehydrogenase [ubiquinone]) has been previously shown to cause an altered CI activity with severe mitochondrial dysfunction. We examined the role of Ndufc2 deficiency and of subsequent CI dysfunction on the development of cardiac hypertrophy both in an in-vitro model and in humans. We performed Ndufc2 gene silencing in H9c2 cardiomyocytes. We found that Ndufc2-silenced cardiomyocytes, compared to not silenced cells, showed a significant degree of hypertrophy by fluorescence microscopy (p<0.01), with a significant increase of the hypertrophy markers ANP and beta-myosin heavy chain (p<0.01). In parallel, sirtuin 3 and its downstream molecules (AMPK, phosphoAMPK, FOXO3a) were significantly reduced (p<0.05), with an increase of the mTOR pathway (p<0.05). The administration of nicotinamide, restoring CI function, was able to reduce the cellular volume and the gene expression level of both hypertrophy markers. We confirmed these results also in rat neonatal cardiomyocytes. With regard to the human study, we included 246 hypertensive subjects (147 male, 59.7%) with a mean age of 59 ± 15 years. Seventy-nine individuals (32%) presented LVH. Genomic DNA was isolated from venous peripheral blood by using the FlexiGene kit (Qiagen). We studied 2 tag SNPs in NDUFC2: rs641836 and rs11237379 The analysis of possible associations with echocardiographic parameters showed that hypertensive patients who were carriers of the mutant A allele at NDUFC2 rs641836 had a significantly increase in septal thickness (p=0.001), posterior wall thickness (p=0.001), relative wall thickness (RWT) (p=0.005), LV mass (p=0.001), LV mass/body surface area (BSA) (p=0.001) and LV mass/height2.7 (p=0.002) compared to wild-type homozygotes. To better separate out the genetic effect, a covariate ANOVA was performed for each cardiac variable, considering age, gender, body mass index (BMI), office blood pressure (BP), antihypertensive treatment with a combination of 2 or more drugs and the number of BP-lowering agents as covariates. The analysis results were significant for septal thickness (p=0.017), posterior wall thickness (p=0.011), LV mass (p=0.003), LV mass/BSA (p=0.002) and LV mass/height2.7 (p=0.010). With regard to the NDUFC2 rs11237379 polymorphism, hypertensive patients who were carriers of the TT genotype had a significantly increase in septal thickness (p=0.001), posterior wall thickness (p=0.003), RWT (p=0.01), LV mass/BSA (p=0.012) and LV mass/height2. (p=0.0033) compared to subjects who were carriers of both the CC genotype and CT genotype. After the adjustment for covariates, significant differences were maintained for septal thickness (p=0.07), posterior wall thickness (p=0.008), RWT (p=0.021) and LV mass/BSA (p=0.03).