Adipose Triglyceride Lipase Knockout Increases Anticontractile Effects of Perivascular Adipose Tissue

BACKGROUND: Perivascular adipose tissue (PVAT) fine-tunes blood vessel contractility and vascular homeostasis. During obesity and atherosclerosis, PVAT becomes dysfunctional and loses its anticontractile potential. Previously, we reported that global knockout of adipose triglyceride lipase (ATGL), the major enzyme responsible for the breakdown of triglycerides, has the potential to modify PVAT functions. To address the causal relationship between PVAT lipolysis and blood vessel contractility, we analyzed ex vivo vasomotor function of mice with tissue-specific rescue/overexpression or knockout of ATGL in adipose tissue. METHODS: To generate mice lacking ATGL in all tissues except for adipose tissue (ATGL knockout with adipocyte-specific expression of ATGL [A+/AKO]), we crossed adipocyte ATGL-rescued (A+) mice with ATGL-deficient (ATGL knockout [AKO]) mice. Body weight, plasma levels of fatty acids, and blood glucose were compared between A+/AKO and AKO mice. Ex vivo vasoreactivity studies were performed in the absence and presence of PVAT to test for acute and chronic effects of PVAT on vascular function. RESULTS: Adipocyte-rescued AKO mice (A+/AKO) had significantly less amounts of PVAT than AKO controls while displaying moderate ATGL expression. A+/AKO aortas exhibited decreased anticontractile effects of PVAT compared with AKO aortas. This effect on contractile function was observed in an agonist-specific manner without affecting smooth muscle cell function or endothelium-dependent relaxation. Assessment of cardiac function using the Langendorff setup revealed that adipocyte ATGL selectively modulated vascular contractility without affecting systolic or diastolic performance. Studies using mice that express ATGL solely in cardiac muscle and adipocyte-specific ATGL knockout mice verified our findings in A+/AKO mice, revealing acute and chronic effects of adipocyte lipolysis on vasoreactivity. CONCLUSIONS: We provide the first evidence that changes in adipocyte lipolysis have the potential to regulate blood vessel contractility. Ablation of ATGL in adipocytes decreases vascular contractility and, thus, has the potential to prevent PVAT dysfunction in obesity and atherosclerosis.