Guillermo-Celestino Cardoso-Saldaña

The mitochondrial DNA copy number (mtDNA-CN) is considered an indirect indicator of the number of mitochondria and of mitochondrial dysfunction; its decrease may indirectly reflect mitochondrial DNA (mtDNA) alterations. A reduction in mtDNA-CN is associated with the development of cardiovascular diseases, including coronary artery disease (CAD). The study evaluates the association of relative blood mtDNA-CN with premature CAD (pCAD) and cardiometabolic factors among Mexican individuals from the GEA (Genetics of Atherosclerotic Disease) Mexican cohort. Relative blood mtDNA-CN was quantified by real-time PCR in 835 patients with pCAD and 896 control subjects (defined as a coronary artery calcium score of zero, assessed by computed tomography). Associations were evaluated using logistic regression (odds ratio [95% confidence interval]) adjusted for potential confounders. Compared with controls, patients with pCAD exhibited significantly lower relative blood mtDNA-CN (5.6 [3.5–9.8] vs. 9.1 [5.1–13.2]. p < 0.001). Similar results were observed in the sex-stratified analysis. Specifically, relative blood mtDNA-CN in women (6.2 [3.8–9.9]) and men (5.5 [3.4–9.7]) with pCAD was lower than that in women (9.5 [6.3–13.7]) and men (8.2 [5.5–12.5]) from the control group (p < 0.001). After adjusting for age, sex, body mass index, smoking status, LDL-cholesterol, type 2 diabetes mellitus, hypertension and physical activity, higher relative blood mtDNA-CN showed a negative association with pCAD (0.903 [0.881–0.927], p = 4.96 × 10⁻¹⁵). This association remained significant in men (0.894 [0.866–0.922], p = 2.90 × 10⁻¹²) and women (0.917 [0.876–0.960], p = 2.1 × 10⁻⁴). Among patients with pCAD, an inverse correlation was observed between relative blood mtDNA-CN and total abdominal fat (p = 0.001), visceral fat (p = 0.015), and subcutaneous fat (p = 0.004). Overall, our results show that reduced relative blood mtDNA-CN is associated with pCAD, which could be indicative of mitochondrial alterations. Furthermore, the inverse correlation between relative blood mtDNA-CN and total, visceral, and subcutaneous abdominal fat suggests a link between mitochondrial dysfunction and abdominal adiposity in patients with pCAD. These findings support that decreased relative blood mtDNA-CN may serve as a marker associated with the presence of pCAD and for adipose tissue alterations in Mexican women and men.

Many factors related to obesity can impact how mitochondria produce ATP, such as the uncoupling of oxidative phosphorylation (OXPHOS) caused by proton leaks from built-up free fatty acids (FFA), the increased levels of uncoupling proteins (UCPs), and changes in the levels of ATPase inhibitory protein factors 1 (IF1). Therefore, the present study aimed to assess the rate of ATP synthesis in mitochondria isolated from skeletal and cardiac muscle from animal models of sucrose diet-induced obesity at different time periods. Short periods of sucrose intake (6 and 12 weeks) are sufficient to induce fat accumulation, hypertriglyceridemia, and high plasma FFA. However, a significant decline in the ATP synthesis rate starts to be obvious in mitochondria from skeletal muscle after 24 weeks of sucrose consumption. This impairment of ATP synthesis is associated with increased FFA in skeletal muscle homogenate. ATP synthesis rates in both skeletal and cardiac muscle were found to be sensitive to oleic acid and GDP, a physiological inhibitor of UCPs that has been shown to increase with aging. In addition, a sucrose diet increases the IF1 content in both skeletal and heart muscle, probably to avoid the hydrolytic activity of ATP synthase. In mitochondria from heart muscle, a decrease in the ATP synthesis rate was only observed according to the age in both groups of rats, and it was not affected by sucrose feeding. Our results suggest that the decline of the ATP synthesis rate in mitochondria from skeletal muscle can be due to the accumulation of FFA in skeletal muscle tissue as uncouplers, and the IF1 overexpression induced by the sucrose diet is a response mechanism to avoid the ATP hydrolysis and to save the energy charge reduced by FFA-uncoupling OXPHOS.

Several factors related to the obesity can affect mitochondrial ATP biosynthesis including the uncoupling of oxidative phosphorylation (OXPHOS) by proton leak induced by accumulated free fatty acids (FFA), the over-expression of uncoupling proteins (UCPs) and altered expression of ATPase inhibitory protein factors 1 (IF1). Therefore, the present work was aimed to evaluate the activity of ATP synthase in isolated mitochondria from skeletal and heart muscle of animal models of obesity induced by sucrose diet at different periods. Short periods of sucrose intake (6 and 12 weeks) are sufficient to induce fat accumulation, hypertriglyceridemia and high plasma FFA. However, a significant decline in the activity of the ATP synthase starts to be obvious in mitochondria from skeletal muscle after 24 weeks of sucrose consumption. This impairment of ATP synthase is associated with increased FFA in skeletal muscle homogenate. Both skeletal and heart muscle ATP synthase activity were found sensitive to oleic acid and to GDP, a physiological inhibitor of UCPs, found enhanced by aging. In addition, sucrose diet increases the IF1 content in both skeletal and heart muscle probably to avoid the hydrolysis activity of ATP synthase. In mitochondria from heart muscle a decrease in the ATP synthase activity was only observed according to the age in both groups of rats and it was not affected by sucrose feeding. Our results suggest that the decline of the ATP synthase activity in mitochondria from skeletal muscle can be due to the accumulation of FFA in skeletal muscle tissue as uncouplers, and the IF1 over-expression induced by sucrose diet is an adaptative mechanism to inhibit the ATP synthase hydrolysis activity.