TRPC4 Inactivation Confers a Survival Benefit in Severe Pulmonary Arterial Hypertension

Abstract

Pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure with lumen-occluding neointimal and plexiform lesions. Activation of store-operated calcium entry channels promotes contraction and proliferation of lung vascular cells. TRPC4 is a ubiquitously expressed store-operated calcium entry channel, but its role in PAH is unknown. We tested the hypothesis that TRPC4 promotes pulmonary arterial constriction and occlusive remodeling, leading to right ventricular failure in severe PAH. Severe PAH was induced in Sprague-Dawley rats and in wild-type and TRPC4-knockout Fischer 344 rats by a single subcutaneous injection of SU5416 [SU (semaxanib)], followed by hypoxia exposure (Hx; 10% O2) for 3 weeks and then a return to normoxia (Nx; 21% O2) for 3 to 10 additional weeks (SU/Hx/Nx). Although rats of both backgrounds exhibited indistinguishable pulmonary hypertensive responses to SU/Hx/Nx, Fischer 344 rats died within 6 to 8 weeks. Normoxic and hypertensive TRPC4-knockout rats recorded hemodynamic parameters similar to those of their wild-type littermates. However, TRPC4 inactivation conferred a striking survival benefit, due in part to preservation of cardiac output. Histological grading of vascular lesions revealed a reduction in the density of severely occluded small pulmonary arteries and in the number of plexiform lesions in TRPC4-knockout rats. TRPC4 inactivation therefore provides a survival benefit in severe PAH, associated with a decrease in the magnitude of occlusive remodeling.

Transient Receptor Potential Channel 4 Encodes a Vascular Permeability Defect and High-Frequency Ca2+ Transients in Severe Pulmonary Arterial Hypertension

“…We used a model of severe hypertension in Fischer rats that uniquely recapitulates key features of the human PAH, including occlusive vascular lesions and early death because of right-sided heart failure. 29,33 Previously, we found that rats lacking TRPC4 exhibit a substantial survival benefit in PAH, associated with a reduction of both lesion number and density. 29 However, the role of TRPC4 as a functional store-operated Ca 2þ entry channel constituent in the regulation of arteriolar endothelial barrier function in PAH has remained unstudied.…”

“…29,33 Previously, we found that rats lacking TRPC4 exhibit a substantial survival benefit in PAH, associated with a reduction of both lesion number and density. 29 However, the role of TRPC4 as a functional store-operated Ca 2þ entry channel constituent in the regulation of arteriolar endothelial barrier function in PAH has remained unstudied. Herein, we identified a defect in lung vascular permeability in PAH mediated by TRPC4, and discovered specific endothelial Ca 2þ signals associated with this phenomenon.…”

“…Consistent with previous reports, both wild-type and TRPC4-knockout animals developed severe pulmonary arterial hypertension, with right ventricular hypertrophy. 29,33 Fulton index values computed as the weight of the right ventricle divided by the weight of the left ventricle and septum were 0.76 AE 0.04 for wild-type hypertensive and 0.71 AE 0.04 for TRPC4-knockout hypertensive groups, compared with 0.26 AE 0.02 for wild-type normotensive animals (P < 0.01) ( Figure 1A). Isolated perfused lungs were prepared as previously described and equilibrated so that a baseline isogravimetric period was established, where lung pressures and weight remained stable.…”

“…DNA was extracted from tail snips, as described previously, 29 and 2 mL of the resulting DNA solution was subjected to PCR analysis using three primers (primer A, Filtration coefficient (K f ) values were measured as previously described, using zone 3 conditions. 30 Baseline K f was calculated as the rate of weight gain obtained 13 to 15 minutes after a 10 cm H 2 O increase in pulmonary venous pressure, normalized per 100 g predicted wet lung weight.…”

“…29 This phenomenon is associated with a reduction of both vascular lesion density and number, 29 and maintenance of cardiac output. 29 We identified ongoing endothelial Ca 2þ transients in wild-type and TRPC4-deficient rats, and found that TRPC4 potentiates tissue-wide Ca 2þ responses to acetylcholine (ACh). Furthermore, we found that PAH impairs endothelialdependent vasodilation in response to ACh.…”