BMP signaling controls PASMC K_V channel expression in vitro and in vivo

Abstract

Bone morphogenetic proteins (BMPs) have been implicated in the pathogenesis of familial pulmonary arterial hypertension. The type 2 receptor (BMPR2) is required for recognition of all BMPs. Transgenic mice with a smooth muscle cell-targeted mutation in this receptor (SM22-tet-BMPR2 delx4ϩ ) developed increased pulmonary artery pressure, associated with a modest increase in arterial muscularization, after 8 wk of transgene activation (West ). In the present study, we show that these transgenic mice developed increased right ventricular pressures after only 1 wk of transgene activation, without significant remodeling of the vasculature. We then tested the hypothesis that the increased pulmonary artery pressure due to loss of BMPR2 signaling was mediated by reduced K V channel expression. There was decreased expression of K V1.1, KV1.5, and KV4.3 mRNA isolated from whole lung. Western blot confirmed decreased K V1.5 protein in these lungs. Human pulmonary artery smooth muscle cells (PASMC) treated with recombinant BMP2 had increased K V1.5 protein and macroscopic KV current density, which was blocked by anti-KV1.5 antibody. In vivo, nifedipine, a selective L-type Ca 2ϩ channel blocker, reduced RV systolic pressure in these dominant-negative BMPR2 mice to levels seen in control animals. This suggests that activation of L-type Ca 2ϩ channels caused by reduced KV1.5 mediates increased pulmonary artery pressure in these animals. These studies suggest that BMP regulates K V channel expression and that loss of this signaling pathway in PASMC through a mutation in BMPR2 is sufficient to cause pulmonary artery vasoconstriction. pulmonary arterial hypertension; voltage-gated potassium channel 1.5; bone morphogenetic protein receptor type 2; vascular tone A POTENTIAL ROLE for bone morphogenetic protein (BMP) signaling in the pathogenesis of vascular disease was suggested by studies of hereditary pulmonary arterial hypertension (PAH), a disorder characterized by the pathological development of increased pressure and structural remodeling of the pulmonary circulation. Mutations in the BMP type 2 receptor (BMPR2) gene were found to be responsible for hereditary PAH (10, 17). Subsequently, sporadic cases of PAH were also found to be associated with mutations in BMPR2 (37).Transgenic mice have demonstrated a critical role for BMP signaling in development. BMPR2(Ϫ/Ϫ) mice die early in development, before gastrulation. BMPR2(ϩ/Ϫ) mice develop normally and were originally thought to have no cardiovascular phenotype (4). However, a recent report in BMPR2(ϩ/Ϫ) mice suggested that they may have modest pulmonary hypertension, though that finding was not verified by a second group (18). Our laboratory constructed a conditional transgenic mouse expressing a dominant-negative BMPR2 (dnBMPR2) selectively in smooth muscle cells (SM22-tet-BMPR2 delx4ϩ mice). When the mutation was activated for 2 mo immediately after birth, the mice developed increased pulmonary artery pressure associated with a modest increase in arterial muscularization (39)....

Potassium channels in pulmonary arterial hypertension

“…Consistently, transgenic mice expressing a dominant-negative Bmpr2 gene in smooth muscle cells (SM22-tet-BMPR2delx4+) develop increased pulmonary arterial pressure, associated with a modest increase in arterial muscularisation [47]. To test whether anomalies seen in SM22-tet-BMPR2delx4+ are mediated by reduced K V channel expression, YOUNG et al [48] investigated the expression levels of several K V channels and revealed a pronounced diminution of K V 1.5 protein expression in the lungs of transgenic mice. Consistent with this, treatment of PASMCs with recombinant BMP2 stimulates K V 1.5 expression and was accompanied by increased current density in these cells; a functional effect blocked by an anti-K V 1.5 antibody [48,49].…”

“…To test whether anomalies seen in SM22-tet-BMPR2delx4+ are mediated by reduced K V channel expression, YOUNG et al [48] investigated the expression levels of several K V channels and revealed a pronounced diminution of K V 1.5 protein expression in the lungs of transgenic mice. Consistent with this, treatment of PASMCs with recombinant BMP2 stimulates K V 1.5 expression and was accompanied by increased current density in these cells; a functional effect blocked by an anti-K V 1.5 antibody [48,49]. The mechanism of K V 1.5 regulation by BMP signalling is unclear.…”

Interplay Between Serotonin Transporter Signaling and Voltage-Gated Potassium Channel (Kv) 1.5 Expression

“…Low levels of Kv1.5 gene expression and channel activity are hallmarks of human and experimental PH, including the chronic-hypoxia and monocrotaline models (Yuan et al, 1998a;Yuan et al, 1998b;Reeve et al, 2001;McMurtry et al, 2004;McMurtry et al, 2005;Bonnet et al, 2006;Guignabert et al, 2006;Young et al, 2006;Remillard et al, 2007;Archer et al, 2008;Guignabert et al, 2009). However, the underlying mechanism of Kv1.5 in PH (Yu et al, 2001), a signal-transducing transcription factor of the AP-1 family, and nuclear factor of activated T cells (NFAT) (Remillard et al, 2007).…”

Dichloroacetate Inhibits Vascular Remodeling and Increases Voltage-gate K+ Expression in a High-altitude-induced Pulmonary Artery Hypertension Rat Model

“…[Ca 2+ ]i is determined in part by the influx of Ca 2+ through voltage-gated, L-type Ca 2+ channels, 5,6) which are gated based on the membrane potential (Em) of the SMCs. 3,7) In pulmonary arterial smooth muscle cells (PASMCs), the Em is partially regulated by voltagegate K + (Kv) channels, and blocking Kv channels causes increased [Ca 2+ ]i. 3,[7][8][9] Each Kv is composed of both pore-forming α-and β-subunits.…”

“…3,7) In pulmonary arterial smooth muscle cells (PASMCs), the Em is partially regulated by voltagegate K + (Kv) channels, and blocking Kv channels causes increased [Ca 2+ ]i. 3,[7][8][9] Each Kv is composed of both pore-forming α-and β-subunits. The Kv α-subunits, including Kv1.2, Kv1.5, Kv2.1, and Kv9.3, are O 2 -sensitive channels and are expressed in PASMCs.…”