Vascular Autophagy Changes And The Role Of Autophagy In Endothelial Cells Dysfunction After Simulated Microgravity

Spaceflight can induce changes of many system functions, and even long-termaviation activities may cause pathological changes in human. For the purposes of thecardiovascular system, weightlessness (microgravity) can induce orthostatic intoleranceand exercise tolerance decrease, which may endanger the health of the astronauts. For thisquestion, researchers found hypovolemia, skeletal muscle contraction function, anddistribution of blood to the head, the disappearance of fluid venous pressure and vascularremodeling etc. involved in the occurrence of orthostatic intolerance after weightlessness.Endothelial cells, the body’s largest organ secretion, which are lining in the blood vesselwalls. The metabolism and function disorder of endothelial cells would produce a series ofpathophysiological reactions. In particular, endothelial cells are very sensitive to thechange of gravity, its metabolism and function under the conditions of weightlessness may play an important role in cardiovascular deconditioning.Recent studies showed that weightlessness or simulated weightlessness can induceEC morphological and secretory function changes, including EC proliferation, apoptosisand regulation of many signaling molecules. However, the effects of weightlessness on theEC function and the mechanisms underlying it have not been fully elucidated. Autophagyis a process that abnormal proteins or intracellular organelles are carried to lysosome, thenwere degraded by enzyme. It is clear that autophagy has a close relationship with celldevelopment, differentiation and metabolic stress et al. Our early studies showed thatsimulated weightlessness can induce autophagy activation.In this study, we used a2D-clinostat to simulate microgravity, and we observed tubeformation, migration and expression of Bcl-2interacting protein (Beclin1) andMicrotubules-associated protein1A light chain3(LC3) in human umbilical veinendothelial cells (HUVECs). Specific inhibitors of autophagy (3-Methyladenine,3-MA)were pretreated to the culture medium and microgravity-induced changes inthe pathways that mediate angiogenesis were investigated. Then we used tailsuspension to simulate weightlessness, and we explore the expression ofautophagy-related genes (Beclin1and LC3) on rat carotid and femoral arteries.The main findings of this study are listed as the followings:1.Autophagy induced by clinostation promote HUVECs migration and angiogenesis.The aim of the present study was to observe the relationship between angiogenesis andautophagy in HUVECs after simulated microgravity. HUVECs cultured in vitro wererandomly divided into four groups: cells exposed to normal gravity for24h (Con),stimulated microgravity for24h (MG), exposed to normal gravity pretreated with3-MA(Con+3-MA) and stimulated microgravity pretreated with3-MA (MG+3-MA).The resultsof Western blot have shown that, compared with control group, the proteins of Beclin1andLC3were both up-regulated significantly after exposure to simulated microgravity, and itcould be reversed by pretreated with3-MA (inhibitor of autophagy). Moreover, comparedwith control group, HUVECs tube formation and migration were significantly promotedafter24h clinostation, which were also reversed by pretreated with3-MA. These results have indicated that autophagy would promote HUVECs angiogenesis and migration afterexposure to stimulated microgravity.2. Tail suspension promote autophagy in femoral artery, but not carotid artery.Rats were randomly divided into two groups: control group exposed to normal gravityfor28day (Con), microgravity group were suspended tail for24h (MG).The resultsshowed that the expression of mRNA and protein of Beclin1and LC3were not changedin in carotid artery, while Beclin1and LC3expressions were significantly enhanced onthe femoral artery. The results suggest that simulated microgravity for28days stimulateautophagy in the femoral artery of rats, and not in carotid artery.In conclusion, we firstly investigated the effects of clinostation on the activation ofautophagy and its relationship with angiogenesis in HUVECs after exposure to simulatedmicrogravity via clinostat device. The results show that autophagy activation induced bystimulated microgravity promote HUVECs angiogenesis. In addition, we observedchanges of autophagic activity in rat femoral and carotid artery after28day tail suspension.The results show that28days tail suspended stimulate autophagy in the femoral artery,rather not in carotid artery. These results will deepen our knowledge of the impacts thatvascular endothelial cell function induced by microgravity, enriched the theory of thespecific structure and function of vascular remodeling caused by microgravity, andprovides a theoretical basis and new ideas to cardiovascular dysfunction protectioninduced by aerospace weightlessness.