Interestingly hSMC displayed a similar
Interestingly, hSMC displayed a similar morphological response to ET-1 as CHOETA. This dramatic lowering of normalized cell index in hSMC mimics ET-1 induced smooth muscle contraction. Earlier studies have shown that stress-fiber formations in CHOETA are mediated by Gq/PLC and G12 and in CHOETB by Gq/PLC and G13 , , . It is not clear whether this difference in G12 vs. G13 activation can account for the differences in short-term morphology between CHOETA and CHOETB in response to ET-1 treatment. As far as smooth muscle, ET-1 is known to induce contraction via two mechanisms: one is a calcium-dependent Gq/PLC phosphorylation of myosin light chain (MLC) and the second is a calcium-sensitization mechanism through RhoA/Rho-kinase inactivating MLC phosphatase . It is possible that ET-1 activates similar pathways leading to short-term cytoskeleton changes in CHOETA CORM-3 and as it does in hSMC contraction.
Of importance is the fact that ETB activation may transmit signals for more relaxed cell morphology. Presently, ETB is thought to regulate vasodilation by secretion of NO and prostacyclin from endothelial cells. However, it remains to be seen which downstream effectors of ETA and ETB are responsible for their opposing short-term morphologies. Currently, it is not clear whether ET-1 treated CHO ETB cells are secreting dilatory effectors or they are signaling dilation through direct intracellular signaling. Secretion of NO as a dilatory effector is possible because wild-type CHO have been shown to express endogenous NOS isoforms , , however NO was already ruled out as a contributor of growth inhibition. On the other hand, expression of prostacyclin receptors in CHO has been shown to be negligible, making the possibility of prostacyclin being the dilatory or anti-proliferative effector unlikely . Given the evidence, ET-1 activation of ETB likely leads to intracellular pathways, which directly and not through secreted effectors, cause both the dilatory and growth inhibitory effects of CHO ETB cells.
Acknowledgments This work was supported in part by the National Institutes of Health/National Lung, Heart, and Blood Institute GrantHL25776.
Introduction Autophagy is a highly conserved and dynamic process of self-digestion, during which malfunctioning organelles, denatured proteins and a variety of macromolecules are degraded and recycled for cellular renovation (Mizushima and Komatsu, 2011; Choi et al., 2013). It plays a pivotal regulatory role in cellular homeostasis. Accumulating evidence demonstrated that autophagy regulates the metabolism, survival, and function of numerous cell types, including those comprising the cardiovascular system (Salabei and Hill, 2015). The change of autophagy is implicated in various vascular disease, including hypertension (Long et al., 2013), vascular aging (La Rocca et al., 2012), atherosclerosis (Martinet and De Meyer, 2009), and restenosis (Grootaert et al., 2015). Imbalance of endothelin (ET) system consisting of ligands and their receptors plays an essential role in cardiovascular pathogenesis. Specifically, abnormal of ET receptor is a main cause dysfunction of ET system (Agapitov and Haynes, 2002). There are two ET receptor subtypes: endothelin subtype A (ETA) and endothelin and subtype B (ETB). ETA receptors are present on vascular smooth muscle cells (VSMCs), where they mediate muscle contraction and regulating blood pressure. ETB receptors are found on both endothelial and VSMCs. Normally, ETB receptors are situated on vascular endothelial cells, and mediate vasodilation via release of nitric oxide and prostacyclin (Brunner et al., 2006) and clearance of endothelin-1 (ET-1) from the circulation (Kelland et al., 2010). Under pathological conditions [such as stroke (Vikman et al., 2006), coronary ischemic heart disease (Wackenfors et al., 2004), hypertension (Nilsson et al., 2008), and atherosclerotic plaque (Iwasa et al., 1999)], ETB receptors are primarily located in VSMCs. ETB receptors in VSMCs may mediate vasoconstriction in cardiovascular diseases (CVDs) (Dimitrijevic et al., 2009). As yet, it is unclear how autophagy is involved in regulation of ETB receptors in VSMCs.