Nitric oxide signaling in adipose triglyceride lipase-deficient microvascular endothelial cells

Abstract

Mice lacking adipose triglyceride lipase (ATGL) were previously described to suffer from lethal cardiac dysfuction that originates from defective peroxisome proliferator-activated receptor α (PPARα) signaling in the heart. Recently, we have demonstrated that endothelium-dependent micro- and macrovascular relaxation is severely blunted in those mice. The aim of the present study was to investigate this phenomenon on a cellular level. Therefore, microvascular endothelial cells were isolated from hearts of WT and ATGL(−/−) mice and immortalized to create WT-MyEnd and ATGL(−/−)-MyEnd cells, respectively. Cells were characterized in terms of PPARα and NO signaling. PPARα mRNA expression was reduced more than 50% in ATGL(−/−)-MyEnd cells, which reflects well the situation in ATGL-deficient hearts. By contrast, mRNA expression of peroxisome proliferator-activated receptor-γ coactivator (PGC-1α) was similar in WT and ATGL-deficient cells. Protein expression and activity of endothelial nitric oxide synthase (eNOS) was almost identical between WT-MyEnd and ATGL(−/−)-MyEnd cells. To investigate if accelerated breakdown of NO due to increased formation of reactive oxygen species (ROS) occurs in ATGL-deficient endothelial cells, we measured mRNA and protein expression of xanthine oxidase (XO) and NADPH oxidase isoforms NOX2 and NOX4. However, no differences in mRNA or protein expression were observed. Our results indicate that, albeit impaired PPARα expression, NO signaling and bioavailability are not compromised by ATGL deficiency in microvascular endothelial cells. The mechanisms underlying the observed endothelial dysfunction in ATGL(−/−) mice (for example consequence of cardiac dysfunction, role of perivascular adipose tissue or other yet unknown effects) are currently under intensive investigation in our laboratory.