Role of autophagy in the cardiovascular system and implications for the development of age-related vascular pathologies

Recent evidence showed that autophagy, a catabolic cellular mechanism responsible for nutrient recycling, plays a major role in the physiology of vascular cells such as endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). Moreover, dysregulation of this process is associated with the development of age-related cardiovascular disorders including heart failure, atherosclerosis, hypertension and arterial stiffness. To increase the understanding about the role of autophagy on the vasculature, with implications for the development of age-related pathologies we investigated in this project the role of VSMC and EC autophagy on the vasculature using mouse models with a knockout of the essential autophagy gene Atg7 in VSMCs or ECs. First we focused on the role of VSMC autophagy on the vascular structure and its, reactivity and biomechanics using a traditional organ bath setup, wire myograph and an in-house developed Rodent Oscillatory Tension Set-up to study Arterial Compliance (ROTSAC). Vascular reactivity measurements at 2 months of age showed enhanced voltage gated calcium channel (VGCC)-mediated contraction in the aorta and femoral artery segments of mice with an VSMC autophagy defect, which resulted in increased sensitivity to depolarization induced contractions. In addition, femoral artery segments showed a large increase in IP3-mediated contraction at the age of 2 months while this was absent in the aorta. Surprisingly, deletion of Atg7 in VSMCs also affected the relaxing capacities of the aorta and the femoral artery. In aortic segments basal unstimulated nitric oxide (NO) release as well as stimulated NO release was enhanced, while femoral artery segments display increased VSMC sensitivity to exogenous NO. Aortic segments of mice with a VSMC autophagy defect also displayed attenuated compliance and higher arterial stiffness, which was more evident at higher distention pressures. At the age of 3.5 months, passive aortic wall remodeling, rather than differences in VSMC tone, was responsible for these phenomena, since differences in compliance and stiffness were more pronounced when VSMCs were completely relaxed by the addition of exogenous NO. These observations are supported by histological data showing extracellular matrix remodeling. Short-term adaptations in the aorta, measured at 2 months, also included changes in the active modulation of arterial stiffness since depolarization induced contraction significantly increased vascular stiffness more in aortic segments of mice with an VSMC autophagy defect. As an increase of the focal adhesion protein vinculin was observed, we speculate that the enhanced active component is possibly due to an increase in focal adhesion sites. Similar to VSMC autophagy, we also investigated the effect of an EC selective Atg7 deficiency on the aortic reactivity and biomechanical properties using a ROTSAC setup and a traditional isometric organ bath setup. Short-term as well as long-term consequences were evaluated by measurements at the age of 2 and 3 months and 1 year. Surprisingly, no differences were seen between the EC autophagy deficient mice and control mice at the age of 1 year. This was in contrast to younger mice where isometric tension measurements of EC-specific autophagy deficient aorta segments showed features of endothelial dysfunction such as decreased acetylcholine sensitivity. Moreover, isobaric measurements however, showed a decline in basal NO bioavailability, which was mostly pronounced at the age of 3 months. In addition, a higher stiffness was present in aortic segments of mice with an EC autophagy defect as compared to control mice in unstimulated conditions. Blocking of basal NO with the eNOS inhibitor L-NAME eliminated this difference indicating this effect of EC autophagy on arterial stiffness were solely dependent on effects on basal NO bioavailability. This was in contrast with stimulated conditions where aortic segments of mice with an EC autophagy defect showed increased stiffness, independent on the presence of L-NAME. Overall we can conclude that autophagy in VSMCs and ECs plays a major role in normal vascular function since both the contractile and relaxing capacities of large elastic arteries as well as the smaller muscular arteries in mice are affected by a selective Atg7 knockout. Moreover, disruption of this homeostatic process results in an increased development of arterial stiffness as measured by an ex-vivo experimental setup.

Jaar van publicatie:2020

Trefwoorden:Doctoral thesis

Toegankelijkheid:Closed