Pulmonary hypertension (PH) is characterized by profound vascular remodeling and altered Ca 2+ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Magnesium ion (Mg 2+ ), a natural Ca 2+ antagonist and a cofactor for numerous enzymes, is crucial for regulating diverse cellular functions, but its roles in PH remains unclear. Here, we examined the roles of Mg 2+ and its transporters in PH development. Chronic hypoxia and monocrotaline induced significant PH in adult male rats. It was associated with a reduction of [Mg 2+ ] i in PASMCs, a significant increase in gene expressions of Cnnm2 , Hip14 , Hip14l , Magt1 , Mmgt1 , Mrs2 , Nipa1 , Nipa2 , Slc41a1 , Slc41a2 and Trpm7 ; upregulation of SLC41A1, SLC41A2, CNNM2, and TRPM7 proteins; and downregulation of SLC41A3 mRNA and protein. Mg 2+ supplement attenuated pulmonary arterial pressure, right heart hypertrophy, and medial wall thickening of pulmonary arteries, and reversed the changes in the expression of Mg 2+ transporters. Incubation of PASMCs with a high concentration of Mg 2+ markedly inhibited PASMC proliferation and migration, and increased apoptosis, whereas a low level of Mg 2+ produced the opposite effects. siRNA targeting Slc41a1/2, Cnnm2, and Trpm7 attenuated PASMC proliferation and migration, but promoted apoptosis; and Slc41a3 overexpression also caused similar effects. Moreover, siRNA targeting Slc41a1 or high [Mg 2+ ] incubation inhibited hypoxia-induced upregulation and nuclear translocation of NFATc3 in PASMCs. The results, for the first time, provide the supportive evidence that Mg 2+ transporters participate in the development of PH by modulating PASMC proliferation, migration, and apoptosis; and Mg 2+ supplementation attenuates PH through regulation of Mg 2+ transporters involving the NFATc3 signaling pathway.

No abstract

Pulmonary hypertension (PH) is characterized by enhanced vasoreactivity and sustained pulmonary vasoconstriction, arising from aberrant Ca homeostasis in pulmonary arterial (PA) smooth muscle cells. In addition to Ca , magnesium, the most abundant intracellular divalent cation, also plays crucial roles in many cellular processes that regulate cardiovascular function. Recent findings suggest that magnesium regulates vascular functions by altering the vascular responses to vasodilator and vasoactive agonists and affects endothelial function by modulating endothelium-dependent vasodilatation in hypertension. Administration of magnesium also decreased pulmonary arterial pressure and improved cardiac output in animal models of PH. However, the role of magnesium in the regulation of pulmonary vascular function related to PH has not been studied. In this study, we examined the effects of magnesium on endothelin-1 (ET-1)-induced vasoconstriction, ACh-induced vasodilatation and the generation of NO in PAs of normoxic mice and chronic hypoxia (CH)-treated mice. Our data showed that removal of extracellular magnesium suppressed vasoreactivity of PAs to both ET-1 and ACh. A high concentration of magnesium (4.8 mm) inhibited ET-1-induced vasoconstriction in endothelium-intact or endothelium-disrupted PAs of normoxic and CH-treated mice, and enhanced the ACh-induced production of NO in PAs of normoxic mice. Moreover, magnesium enhanced ACh-induced vasodilatation in PAs of normoxic mice, and the enhancement was completely abolished after exposure to CH. Hence, in this study we demonstrated that increasing the magnesium concentration can attenuate the ET-1-induced contractile response and improve vasodilatation via release of NO from the endothelium. We also demonstrated that chronic exposure to hypoxia can cause endothelial dysfunction resulting in suppression of the magnesium-dependent modulation of vasodilatation.

Pulmonary hypertension (PH) is characterized by profound vascular remodeling and alterations in Ca2+ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Members of multiple transient receptor potential subfamilies (TRPC, TRPV, and TRPM) have been identified in pulmonary vascular tissue. Our previous studies showed that the expression and functions of the store‐operated TRPC1, receptor‐operated TRPC6, and the mechanosensitive TRPV4 channels are augmented in PASMCs during PH, and their upregulation contribute to PH development. In contrast, TRPM8 is down‐regulated in PASMCs of rats PH models, and activation of TRPM8 with agonists causes relaxation of pulmonary arteries (PAs)(Liu et al., Cell Physiol Biochem 2013, 31:892–904). However, the mechanism of TRPM8‐induced PA relaxation has not been determined. In this study, we examined the possible interactions of TRPM8 activation and store‐operated Ca2+ entry (SOCE) in PAs and PASMCs of normoxic and chronic hypoxic pulmonary hypertensive (CHPH) rats. We found that TRPM8 expression was down‐regulated in PAs and the TRPM8‐mediated cation entry was reduced significantly in the PASMCs of rats after 3 weeks of hypoxia (10% O2) exposure. Activation of TRPM8 with icilin (0.1–100 μM) caused concentration‐dependent relaxation of cyclopiazonic acid (CPA) and ET‐1 pre‐contracted endothelium‐denuded PAs in the presence of nifedipine. The vasorelaxant effect of icilin was abolished in the presence of the SOCE antagonist Gd3+ at submicromolar concentration. Icilin suppressed the CPA‐induced cation entry in PASMCs determined by the Mn2+ quenching technique and by Ca2+ transient measurement. The inhibitory effect of icilin on SOCE‐induced PA relaxation and Ca2+ entry were abolished by the TRPM8 antagonist AMTB, indicating that the effect was mediated specifically by TRPM8 channels. Moreover, TRPM8‐mediated inhibitory effects on CPA‐induced contraction in PAs and SOCE in PASMCs were significantly augmented in CHPH rats, probably related to the enhanced SOCE caused by PH. These results demonstrate for the first time that TRPM8 activation can cause relaxation of PA through inhibition of SOCE. Since SOCE plays many important roles in pulmonary vascular functions and is crucial for the vascular remodeling and the enhanced vasoconstriction in PH, the downregulation of TRPM8 expression and activity in PASMCs during PH may minimized the TRPM8‐dependent inhibition of SOCE, and allow unimpeded SOCE activity for PH development. Support or Funding Information Supported by grants NSFC31571179, NSFC31371165, NSF of Fujian Province 2015J01313, and Fujian Province Hundred Experts Award. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.