Effect of hypoxia on TRPV1 and TRPV4 channels in rat pulmonary arterial smooth muscle cells

Abstract

Transient receptor potential (TRP) channels of the vanilloid subfamily, mainly TRPV1 and TRPV4, are expressed in pulmonary artery smooth muscle cells (PASMC) and implicated in the remodeling of pulmonary artery, a landmark of pulmonary hypertension (PH). Among a variety of PH subtypes, PH of group 3 are mostly related to a prolonged hypoxia exposure occurring in a variety of chronic lung diseases. In the present study, we thus investigated the role of hypoxia on TRPV1 and TRPV4 channels independently of the increased pulmonary arterial pressure that occurs during PH. We isolated PASMC from normoxic rat and cultured these cells under in vitro hypoxia. Using microspectrofluorimetry and the patch-clamp technique, we showed that hypoxia (1 % O2 for 48 h) significantly increased stretch- and TRPV4-induced calcium responses. qRT-PCR, Western blotting, and immunostaining experiments revealed that the expression of TRPV1 and TRPV4 was not enhanced under hypoxic conditions, but we observed a membrane translocation of TRPV1. Furthermore, hypoxia induced a reorganization of the F-actin cytoskeleton, the tubulin, and intermediate filament networks (immunostaining experiments), associated with an enhanced TRPV1- and TRPV4-induced migratory response (wound-healing assay). Finally, as assessed by immunostaining, exposure to in vitro hypoxia elicited a significant increase in NFATc4 nuclear localization. Cyclosporin A and BAPTA-AM inhibited NFATc4 translocation, indicating the activation of the Ca(2+)/calcineurin/NFAT pathway. In conclusion, these data point out the effect of hypoxia on TRPV1 and TRPV4 channels in rat PASMC, suggesting that these channels can act as direct signal transducers in the pathophysiology of PH.

TRPV4 channels: physiological and pathological role in cardiovascular system

“…Accordingly, the cross reactivity of ruthenium red with other targets may possibly contribute to several experimental artifacts. However, the scientists have affirmed the specific functional role of TRPV4 channels in the cardiovascular system using TRPV4 -/ -animals and employing specific TRPV4 antagonists/modulators including TRPV4siRNA, RN-1734, AB159908, HC067047, and GSK2193874 [1,7,10,63,95].…”

“…Apparently, mechanical stretch/osmotic swelling-induced activation of TRPV4 channels is via phospholipase A 2 -and cytochrome p450 epoxygenase-dependent pathway, but stimuli such as phorbol esters and heat activate these channels via distinct, phospholipase A 2 -and cytochrome P450 epoxygenase-independent pathway [82,92]. The majority of studies emphasizing the physiological or pathophysiological role of TRPV4 channels have employed ruthenium red as TRPV4 antagonist [7,8,63]. However, apart from TRPV4 blocking activity, ruthenium red also possesses the ability to block mitochondrial Ca 2?…”

“…On the contrary, activation of these channels is also documented in the pathophysiology of diseases including cardiac remodeling and pulmonary hypertension [10,29,63] suggesting the dual functionality of TRPV4 channels. However, there has not been any experimental study explaining the mechanisms involved in beneficial as well as deleterious effects of these channels.…”

“…The physiological role of TRPV4 channels in flow-induced vasodilation has been well established [4,7,8,39,47,53,102,104], and these channels play a crucial role in the development of collateral blood vessels and hypoxic preconditioning [71]. However, these channels are also critically involved in cardiac remodeling [1], pulmonary hypertension [63,95], regulation of blood pressure [14,58], and congestive heart failure [88] (Table 1). The present review encompasses the pivotal physiological and pathological role of TRPV4 channels in cardiovascular system along with possible mechanisms.…”

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

“…49 So NFATc1 seems to protect the MCTinduced PAH, which is similar to Chan's results. 47 The NFATc4 nuclear/cytoplasmic ratio increased by 39 % when PASMC was exposed to hypoxia (1% O 2 for 48 h), 50 which suggests that NFATc4 activation may be implicated the hypoxia-induced PAH.…”