Hypoxia and Stretch Regulate Intercellular Communication in Vascular Smooth Muscle Cells Through Reactive Oxygen Species Formation

Abstract

Objective-We hypothesized that the alterations in vasomotor tone and adaptive remodeling responses that occur in the circulation because of hypoxia were dependent on changes in cell to cell communication through regulation of gap junction protein expression and function. Consequently, we studied the amount, distribution, and permeability of the principal vascular smooth muscle cell (VSMC) gap junction protein, connexin43, in rat aortic cultures exposed to oxygen partial pressures of 150 or 15 mm Hg. Methods and Results-Immunohistochemical staining, immunoblot assays, and Northern blot analyses demonstrated that connexin43 expression was reversibly increased in hypoxic cultures. As a result, hypoxic cells exhibited greater intercellular communication as determined by fluorescence recovery after photobleaching experiments. Using a fluorogenic substrate, hypoxic VSMCs showed increased reactive oxygen species generation, which could be prevented by the glutathione peroxidase mimic ebselen and the mitochondrial complex I inhibitor rotenone but not with the redox-sensitive thiol pyrrolidine dithiocarbamate. The rise in connexin43 expression attributable to hypoxia could be attenuated by ebselen and rotenone treatment. Interestingly, the previously reported induction of connexin43 expression by tensile stretch was also contingent on oxidative activity. Key Words: gap junction Ⅲ reactive oxygen species Ⅲ hypoxia Ⅲ stretch Ⅲ smooth muscle cell T he coordination and propagation of motor responses in blood vessels are brought about by neurohormonal modulation, ion channel conductance, and intercellular communication. [1][2][3] Although acute vasomotion leads to circulatory homeostasis through the maintenance of local vessel tone, sustained motor responses initiate structural remodeling of the tissue. 2,4,5 Because vasomotor and arterial remodeling responses require extensive signaling between the endothelium and medial smooth muscle layers, as well as between adjacent smooth muscle cells, we have been studying cell to cell communication in the vasculature. 1,2 Conclusions-Hypoxia See page 1707 and coverThe structure of the arterial circulation can be adjusted in both the circumferential and radial direction, resulting in changes to vessel diameter or wall thickness. For instance, vascular tissue responds to variations in the mechanical forces imposed on it by blood pressure (ie, tensile stretch) and blood flow (ie, shear stress) with rapid adjustments to vasomotor tone and with changes in tissue geometry when alterations in these forces persist. 6 These responses are specific for the type of hemodynamic force that is imposed on the vessel wall. Whereas an increase in tensile stretch causes vasoconstriction in the short term and arterial thickening in the long term, an increase in blood flow induces acute vasodilation and chronic enlargement of arterial diameter when the time-averaged shear force is maintained. 4 Vascular remodeling can also result from exposure to low levels of environmental oxygen. Chronic hypoxia causes ...

Control and Coordination of Vasomotor Tone in the Microcirculation

“…In any case, the involvement of Cx43-based channels in the control of vasomotor tone is consistent with the finding that tensile stretch increased the expression of this connexin as well as gap junction intercellular communication in vascular smooth muscle cells (Cowan et al, 1998). Interestingly, this response was mediated by the formation of reactive oxygen species (Cowan et al, 1998;Cowan et al, 2003), which has been reported to contribute to the initiation of the myogenic constriction in mouse-tail arterioles (Nowicki et al, 2001). …”

Impaired Vasoconstriction and Nitric Oxide-Mediated Relaxation in Pulmonary Arteries of Hypoxia- and Monocrotaline-Induced Pulmonary Hypertensive Rats

“…In addition, the reduced ACh-induced relaxation in the pulmonary arteries of hypoxic and MCT-treated rats probably is not caused by decreased endothelial cholinergic receptors or NO synthase, because the pulmonary artery relaxation by the NO donor SNP was also reduced in PH rats. Although the reduced ACh relaxation in the PH rats could be due to increased oxidative stress and decreased NO bioavailability in hypoxic rats (Cowan et al, 2003), it cannot account for the reduced ACh relaxation in the MCT-treated rats. In addition, the enhanced PHE contraction in L-NAME-or ODQ-treated pulmonary arteries of hypoxic rats suggests that NO production/bioavailability was not significantly compromised.…”

Improved pulmonary vascular reactivity and decreased hypertrophic remodeling during nonhypercapnic acidosis in experimental pulmonary hypertension

“…This is unlikely the only mechanism, because blockers of NO-cGMP enhanced Phe contraction in pulmonary arteries of hypoxic and MCT rats with or without acidosis, suggesting possible compensatory activation of the NO-cGMP pathway in experimental PH. The reduced ACh relaxation in the PH rats and its improvement with acidosis is also unlikely due to decreased NO bioavailability due to increased oxidative stress in the setting of hypoxia (16), because ACh-induced relaxation was also reduced in the MCT model and improved during induction of acidosis in MCT rats. A plausible explanation for the reduced ACh relaxation in hypoxic and MCT-treated rats is possible structural changes in the pulmonary vascular wall and decreased responsiveness of pulmonary VSMCs to vasodilators.…”