Endothelial and Smooth Muscle Cell Interactions in the Pathobiology of Pulmonary Hypertension

Abstract

In the pulmonary vasculature, the endothelial and smooth muscle cells are two key cell types that play a major role in the pathobiology of pulmonary vascular disease and pulmonary hypertension. The normal interactions between these two cell types are important for the homeostasis of the pulmonary circulation, and any aberrant interaction between them may lead to various disease states including pulmonary vascular remodeling and pulmonary hypertension. It is well recognized that the endothelial cell can regulate the function of the underlying smooth muscle cell by releasing various bioactive agents such as nitric oxide and endothelin-1. In addition to such paracrine regulation, other mechanisms exist by which there is cross-talk between these two cell types, including communication via the myoendothelial injunctions and information transfer via extracellular vesicles. Emerging evidence suggests that these nonparacrine mechanisms play an important role in the regulation of pulmonary vascular tone and the determination of cell phenotype and that they are critically involved in the pathobiology of pulmonary hypertension.Keywords: paracrine; myoendothelial injunction; microvesicles; vasoconstriction; vascular remodelingIn the pulmonary vasculature, endothelial cells (ECs) and smooth muscle cells (SMCs) are the key cell types involved in the regulation of vessel diameter in most of the pulmonary vascular tree and thereby they regulate pulmonary arterial pressure and total vascular resistance. ECs, which are strategically located as the innermost layer of the blood vessel and are in contact with the circulating blood, exert a delicate and constant influence on the underlying vascular smooth muscle cells (VSMCs). It is well recognized that the regulation of pulmonary vasoreactivity by the endothelium is predominantly accomplished by paracrine signaling through the release of various vasoactive agents such as nitric oxide (NO), endothelin-1 (ET-1) (1-3), and others (4-8). However, there is increasing evidence that the relationship between the EC and the SMC is not a simple one-way interaction from the endothelium to the SMC; rather, there are complicated interactions between them (9-11). Moreover, the communication patterns are not limited to paracrine signaling; cross-talk through myoendothelial gap junctions (MEJs), extracellular vesicles (EVs), and other mechanisms is critically involved (12)(13)(14)(15)(16)(17)(18)(19)(20). These mechanisms operate in a complicated but co-ordinated manner to maintain the homeostasis of the pulmonary circulation. Under pathological conditions, the interaction between ECs and VSMCs may be chronically altered so that a sustained increase in vasocontractility and abnormal vascular proliferation develops, which leads to high pulmonary artery pressure, vascular remodeling, right ventricular hypertrophy, and the clinical condition, pulmonary hypertension (PH) (1,(21)(22)(23)(24). This article discusses the recent progress in our knowledge of the interactions between ECs and SMCs thr...

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