Pontin (Ruvbl1) overexpression protects the heart against metabolic stress by reducing lipid accumulation, apoptosis, and fibrosis

Obesity and abnormal lipid profile are components of metabolic syndrome that are known to increase the risk of heart failure and cardiomyopathy. Lipid accumulation in cardiomyocytes disrupts metabolism and may cause mitochondrial dysfunction, oxidative stress, and inflammation. This promotes apoptosis, fibrosis, remodeling, and impaired contractility, accelerating cardiomyopathy and heart failure.

We have identified Pontin (Ruvbl1) as a strong modulator of the development of cardiomyopathy and heart failure. Further transcriptomic analysis has revealed a possible association of Pontin with lipid metabolism and mitochondrial function prompting us to hypothesise that Pontin plays a major role in lipid homeostasis in the heart.

This study tests if Pontin overexpression mitigates lipid accumulation, apoptosis, and fibrosis under metabolic stress. It aims to reveal molecular mechanisms of Pontin’s role in lipid homeostasis and cell survival during high-fat diet (HFD) challenges.

We used H9c2 cardiomyoblasts and primary neonatal rat cardiomyocytes (NRCM) with Pontin overexpression to assess the effects of exposure to palmitic and oleic acids. In vivo, cardiomyocyte-specific Pontin transgenic (PontincTG) and wild-type (WT) mice were fed with HFD for 16 weeks and the cardiac phenotypes were evaluated.

We overexpressed Pontin using adenoviral system in H9c2 and NRCMs. In response to palmitic acid, Pontin overexpression reduced lipid droplets formation. Importantly, Pontin expression significantly reduced apoptosis level following palmitic acid treatment, indicating a protective role of Pontin against lipotoxicity.

In vivo, following HFD stimulation, we observed significant weight gain accompanied by a slight increase in blood pressure and impaired glucose tolerance in both WT and PontincTG mice, indicating metabolic syndrome. Serum cholesterol rose by 69.7% in WT and 80.4% in PontincTG mice, without major differences in cardiac tissue cholesterol and triglyceride levels. Importantly, when we analysed cardiac tissue sections, we found that PontincTG hearts displayed significantly fewer lipid droplets compared to WT mice (p<0.05). In addition, in PontincTG mice, we found that apoptosis levels were 35% lower than in WT mice, and fibrosis levels were 27% lower (both with p-values <0.05), indicating protection against metabolic stress. However, based on echocardiography analysis, we did not observe significant changes in cardiac function and morphology between PontincTG and WT controls.

In summary, Pontin overexpression confers protection against lipid-induced cardiac injury in vitro and in vivo, limiting cardiomyocyte apoptosis, fibrosis, and adverse remodeling under HFD-induced metabolic stress.