Protection against pressure overload-induced right heart failure by uncoupling protein 2 silencing

Aims

The role of uncoupling protein 2 (UCP2) in cardiac adaptation to pressure overload remains unclear. In a classical model of left ventricular pressure overload genetic deletion of UCP2 (UCP2^−/−) protected against cardiac hypertrophy and failure. However, in UCP2^−/− mice increased proliferation of pulmonary arterial smooth muscle cells induces mild pulmonary hypertension, right ventricular (RV) hypertrophy, and reduced cardiac output. This suggests a different role for UCP2 in RV and left ventricular adaptation to pressure overload. To clarify this situation in more detail UCP2^−/− and wild-type mice were exposed to pulmonary arterial banding (PAB).

Methods and results

Mice were analysed (haemodynamics, morphometry, and echocardiography) 3 weeks after PAB or sham surgery. Myocytes and non-myocytes were isolated and analysed separately. Cell shortening of myocytes and fura-2 loading of cardiomyocytes were used to characterize their function. Brd assay was performed to study fibroblast proliferation. Isolated mitochondria were analysed to investigate the role of UCP2 for reactive oxygen species (ROS) production. UCP2 mRNA was 2.7-fold stronger expressed in RV myocytes than in left ventricular myocytes and stronger expressed in non-myocytes compared with myocytes. Three weeks after PAB, cardiac output was reduced in wild type but preserved in UCP2^−/− mice. UCP2^−/− had increased RV wall thickness, but lower RV internal diameters and displayed a significant stronger fibrosis. Cardiac fibroblasts from UCP2^−/− had reduced proliferation rates but higher collagen-1 expression. Myocytes isolated from mice after PAB banding showed preserved function that was further improved by UCP2^−/−. Mitochondrial ROS production and respiration was similar between UCP2^−/− or wild-type hearts.

Conclusion

Despite a mild pulmonary hypertension in UCP2^−/− mice, hearts from these mice are well preserved against additional pressure overload (severe pulmonary hypertension). This—at least in part—depends on different behaviour of non-myocytes (fibroblasts).

Knock out of the NADPH oxidase Nox4 has no impact on life span in mice

The free radical theory of aging suggests reactive oxygen species as a main reason for accumulation of damage events eventually leading to aging. Nox4, a member of the family of NADPH oxidases constitutively produces ROS and therefore has the potential to be a main driver of aging. Herein we analyzed the life span of Nox4 deficient mice and found no difference when compared to their wildtype littermates. Accordingly neither Tert expression nor telomere length was different in cells isolated from those animals. In fact, Nox4 mRNA expression in lungs of wildtype mice dropped with age. We conclude that Nox4 has no influence on lifespan of healthy mice.

The NADPH Oxidase Nox2 Mediates Vitamin D-Induced Vascular Regeneration in Male Mice

1α,25-dihydroxy-vitamin D3 (1,25D) exerts protective effects in the vascular system and promotes myeloid cell differentiation, which are important sources of reactive oxygen species. Given that myeloid cell reactive oxygen species derives from Nox-family NADPH oxidases, we hypothesized that this enzyme family contributes to the beneficial effects of 1,25D on vascular regeneration. The function of Nox enzymes in this context was studied in the murine carotid artery electric injury regeneration model. Male mice were treated with daily injections of 1,25D (100 ng/kg · d) for 5 days and carotid injury was induced after 3 days. After injury, 1,25D increased the expression of Nox2 in the carotid artery. As determined by Evans blue staining on day 6, 1,25D improved vascular regeneration in a Nox2-dependent manner. Healing was lost in mice knockout for Nox2, but not in Nox1 or Nox4, knockout mice. Tissue specific knockouts demonstrated that the myeloid, but not the endothelial Nox2, was required for this effect. Mechanistically, the combination of injury and 1,25D induced the mobilization of angiogenic myeloid cells (AMCs) and increased the vascular expression of the cytokine stem cell derived factor (SDF)1, which attracts AMCs to the site of injury. Vitamin D in a Nox2-dependent manner activated MAPKs, and these are known to contribute to SDF1 induction. Accordingly, SDF1 induction was lost after deletion of Nox2. By inducing SDF1 and enhancing the number of AMCs, VitD3 is a novel approach to promote vascular repair.