Hypoxia-induced migration in pulmonary arterial smooth muscle cells requires calcium-dependent upregulation of aquaporin 1

Abstract

Pulmonary arterial smooth muscle cell (PASMC) migration is a key component of the vascular remodeling that occurs during the development of hypoxic pulmonary hypertension, although the mechanisms governing this phenomenon remain poorly understood. Aquaporin-1 (AQP1), an integral membrane water channel protein, has recently been shown to aid in migration of endothelial cells. Since AQP1 is expressed in certain types of vascular smooth muscle, we hypothesized that AQP1 would be expressed in PASMCs and would be required for migration in response to hypoxia. Using PCR and immunoblot techniques, we determined the expression of AQPs in pulmonary vascular smooth muscle and the effect of hypoxia on AQP levels, and we examined the role of AQP1 in hypoxia-induced migration in rat PASMCs using Transwell filter assays. Moreover, since the cytoplasmic tail of AQP1 contains a putative calcium binding site and an increase in intracellular calcium concentration ([Ca(2+)](i)) is a hallmark of hypoxic exposure in PASMCs, we also determined whether the responses were Ca(2+) dependent. Results were compared with those obtained in aortic smooth muscle cells (AoSMCs). We found that although AQP1 was abundant in both PASMCs and AoSMCs, hypoxia selectively increased AQP1 protein levels, [Ca(2+)](i), and migration in PASMCs. Blockade of Ca(2+) entry through voltage-dependent Ca(2+) or nonselective cation channels prevented the hypoxia-induced increase in PASMC [Ca(2+)](i), AQP1 levels, and migration. Silencing AQP1 via siRNA also prevented hypoxia-induced migration of PASMCs. Our results suggest that hypoxia induces a PASMC-specific increase in [Ca(2+)](i) that results in increased AQP1 protein levels and cell migration.

Pulmonary Vascular and Ventricular Dysfunction in the Susceptible Patient (2015 Grover Conference Series)

“…43 Direct effects of hypoxia on PASMCs are also likely to play a role in vascular remodeling. For example, cells exposed to hypoxia ex vivo or derived from chronically hypoxic animals exhibit increases in both migration and proliferation, [53][54][55][56] and both K + channel activity and [Ca 2+ ] i are likely to play a role. Agents that activate and/or increase expression of K + channels, including the steroid hormone dehydroepiandrosterone and the metabolic modulator dichloroacetate, reduced remodeling in chronically hypoxic rats, 46,57,58 likely because increased intracellular K + confers resistance to apoptosis.…”

Significance of oxygen transport through aquaporins

“…Therefore, the increase in NtPIP1 ; 3 transcript levels (Fig. 6) could be among important factors contributing to improved root aeration, similarly to the increased transcript levels of HsAQP1 in hypoxic human tissues2526. Clearly, the link between pore-mediated O 2 transport and hypoxia deserves further attention.…”

“…Since the reports of hypoxia-induced expression of HsAQP1 2526 suggest that aquaporin-mediated transport processes may be especially important under low-O 2 conditions, we examined transcript levels of N. tabacum plants subjected to flooding-induced hypoxia. Although the ATP levels showed some decline in well-aerated plants after 7 days compared with 2 days (Fig.…”

Vascular remodeling in pulmonary hypertension

“…Increased intracellular calcium concentration ([Ca 2+ ] i ) is required for PASMC growth [80, 81] and migration [82] and has been documented in cells from hypoxic [65] and MCT-treated [83] animals and patients with PAH [80, 84]. VGCCs do not appear to contribute to elevated basal PASMC [Ca 2+ ] i in PH [73–75], but can be activated by agonists [85, 86] and contribute to stimulated proliferation [87].…”

“…PASMC migration is also known to be induced by hypoxia [99, 100] and modulated by changes in [Ca 2+ ] i [101], [82], but even so, the exact mechanisms controlling PASMC migration in PH have yet to be deciphered. During hypoxia, Ca 2+ -dependent increases in the expression of aquaporin 1 (AQP1), a membrane water channel, are required for migration of PASMCs [82].…”