NFATc3 Mediates Chronic Hypoxia-induced Pulmonary Arterial Remodeling with α-Actin Up-regulation

Abstract

Physiological responses to chronic hypoxia include polycythemia, pulmonary arterial remodeling, and vasoconstriction. Chronic hypoxia causes pulmonary arterial hypertension leading to right ventricular hypertrophy and heart failure. During pulmonary hypertension, pulmonary arteries exhibit increased expression of smooth muscle-␣-actin and -myosin heavy chain. NFATc3 (nuclear factor of activated T cells isoform c3), which is a Ca 2؉ -dependent transcription factor, has been recently linked to smooth muscle phenotypic maintenance through the regulation of the expression of ␣-actin. The aim of this study was to determine if: (a) NFATc3 is expressed in murine pulmonary arteries, (b) hypoxia induces NFAT activation, (c) NFATc3 mediates the up-regulation of ␣-actin during chronic hypoxia, and (d) NFATc3 is involved in chronic hypoxia-induced pulmonary vascular remodeling. NFATc3 transcript and protein were found in pulmonary arteries. NFAT-luciferase reporter mice were exposed to normoxia (630 torr) or hypoxia (380 torr) for 2, 7, or 21 days. Exposure to hypoxia elicited a significant increase in luciferase activity and pulmonary arterial smooth muscle nuclear NFATc3 localization, demonstrating NFAT activation. Hypoxia induced up-regulation of ␣-actin and was prevented by the calcineurin/NFAT inhibitor, cyclosporin A (25 mg/kg/day s.c.). In addition, NFATc3 knock-out mice did not showed increased ␣-actin levels and arterial wall thickness after hypoxia. These results strongly suggest that NFATc3 plays a role in the chronic hypoxia-induced vascular changes that underlie pulmonary hypertension.As altitude increases, the barometric pressure and atmospheric oxygen partial pressure decrease. This decrease in barometric pressure is the basic cause of all hypoxia-related problems in high altitude pathophysiology. Similar levels of hypoxia are present in patients with chronic bronchitis, emphysema, cystic fibrosis, asthma, and severe restrictive lung diseases (1). Chronic hypoxia (CH) 2 causes pulmonary hypertension due to pulmonary vasoconstriction, arterial remodeling, and polycythemia, which ultimately results in right ventricular (RV) hypertrophy and often heart failure (2). Pulmonary vasoconstriction is thought to be caused by elevated vascular tone through increased pulmonary arterial smooth muscle cell (PASMC) intracellular Ca 2ϩ ([Ca 2ϩ ] i ) (3-8) and increased sensitivity of the contractile apparatus to Ca 2ϩ (9 -12).Regardless of the cause of pulmonary hypertension, the structural change that is thought to underlie the increased vascular resistance is remodeling of small pulmonary arteries. A prominent feature of this vascular remodeling is medial thickening. In proximal pulmonary vessels, medial enlargement is caused by hypertrophy and hyperplasia of the pre-existing smooth muscle cells (reviewed in Ref.

Enhancement of pulmonary vascular remodelling and inflammatory genes with VIP gene deletion

“…This transcription factor can trigger both inflammatory and vascular smooth muscle cell proliferation pathways, and its activation has recently been invoked as the principal mechanism of chronic hypoxia-induced pulmonary arterial remodelling [25] and many of the findings in idiopathic pulmonary hypertension [26]. Therefore, it is tempting to speculate that vasoactive intestinal peptide may exert its broad modulator influence, at least in part, by inhibiting the activation of the nuclear factor of activated T-cells.…”

The role of nuclear factor of activated T cells in pulmonary arterial hypertension

“…35 Constitutively activated NFATc3 promotes soluble guonylyl cyclase-a1 and upregulation of the SM hypertrophic marker SM-a-actin in PASMC. 36,37 By contrast, Kang et al reported that lentiviral overexpression NFATc3 alone in human PASMC decreased SM -a-actin expression. Co-transfecting an a-SMA promoter and NFATc1, NFATc2, or NFATc3 overexpression vector, increased the a-SMA promoter activity by about 30%.…”

NFATc3 is required for intermittent hypoxia-induced hypertension

“…Adult male 9ϫNFAT-luciferase reporter (NFAT-luc) background strain FVBN, NFATc3-knockout (NFATc3 KO), Balb/C wild-type (WT), and FVBN mice (25-30 g) were used. In addition, NFAT-luc mice were backcrossed with NFATc3 KO mice for at least two generations, and NFAT-luc/NFATc3 ϩ/ϩ (WT) and NFAT-luc/ NFATc3 Ϫ/Ϫ (KO) mice were used (11). NFAT-luc mice were provided by Dr. Jeffery D. Molkentin (Department of Pediatrics, Children's Hospital Medical Center, Cincinnati, OH) (7), and NFATc3 KO mice were kindly provided by Dr. Laurie Glimcher (Harvard University) (49).…”

“…NFAT activation is generally associated with an increase in gene expression (31). However, several reports have shown that NFAT may also function as a repressor of gene expression (3,29,45).Of the four members of the NFAT family, NFATc3 is specifically implicated in vascular development (28) and maintenance of the contractile phenotype in vascular smooth muscle cells (VSMC) through regulation of ␣-actin expression (11,26,59). NFATc3 also modulates VSMC contractility by regulating voltage-dependent and large-conductance K ϩ channel expression in cerebral arteries (3,45).…”

“…Of the four members of the NFAT family, NFATc3 is specifically implicated in vascular development (28) and maintenance of the contractile phenotype in vascular smooth muscle cells (VSMC) through regulation of ␣-actin expression (11,26,59). NFATc3 also modulates VSMC contractility by regulating voltage-dependent and large-conductance K ϩ channel expression in cerebral arteries (3,45).…”