Deficiency of the NHE1 gene prevents hypoxia-induced pulmonary hypertension and vascular remodeling

Heparin inhibits pulmonary artery smooth muscle cell proliferation through guanine nucleotide exchange factor-H1/RhoA/Rho kinase/p27

Ras homolog gene family member A (RhoA) through Rho kinase kinase (ROCK), one of its downstream effectors, regulates a wide range of cell physiological functions, including vascular smooth muscle cell (SMC) proliferation, by degrading cyclin-dependent kinase inhibitor, p27. Our previous studies found that heparin inhibition of pulmonary artery SMC (PASMC) proliferation and pulmonary hypertension was dependent on p27 up-regulation. To investigate whether ROCK, a regulator of p27, is involved in regulation of heparin inhibition of PASMC proliferation, we analyzed ROCK expression in the lungs from mice and from human PASMCs exposed to hypoxia, and investigated the effect of ROCK expression in vitro by RhoA cDNA transfection. We also investigated the effect of guanine nucleotide exchange factor (GEF)-H1, an upstream regulator of RhoA, on heparin inhibition of PASMC proliferation by GEF-H1 cDNA transfection. We found that: (1) hypoxia increased ROCK expression in mice and PASMCs; (2) overexpression of RhoA diminished the inhibitory effect of heparin on PASMC proliferation and down-regulated p27 expression; and (3) overexpression of GEF-H1 negated heparin inhibition of PASMC proliferation, which was accompanied by increased GTP-RhoA and decreased p27. This study demonstrates that the RhoA/ROCK pathway plays an important role in heparin inhibition on PASMC proliferation, and reveals that heparin inhibits PASMC proliferation through GEF-H1/RhoA/ROCK/p27 signaling pathway, by down-regulating GEF-H1, RhoA, and ROCK, and then up-regulating p27.

Contribution of CXCR4(+)/PDGFRbeta(+) progenitor cells in hypoxic alveolar arterioles muscularization: role of myocardin

AIMS

Bone marrow (BM) progenitor cells may contribute to vascular remodelling. The present study aimed to investigate the contribution of BM-derived CXCR4(+) (a CXC chemokine receptor) and PDGFRbeta(+) (platelet-derived growth factor receptor beta) progenitor cells in hypoxia-induced muscularization of alveolar arterioles.

METHODS AND RESULTS

Accumulation of GFP(+) (green fluorescent protein) cells was markedly increased in the pulmonary vasculature by the hypoxic (10% O(2,) 4 weeks) chimeric mice with transgenic GFP-tagged BM. After injection of BM-derived CXCR4(+)/PDGFRbeta(+) progenitor cells into C57BL/6J mice, followed by 6-week hypoxia, the cells were found to home to the alveolar arterioles and readily differentiated into smooth muscle cells (SMCs). Under the same hypoxic conditions, mice infused with myocardin lentiviral RNAi vector-transduced progenitor cells displayed lower myocardin expression in the muscularized alveolar arterioles, correlating with decreased pulmonary artery pressure and arteriole muscularization. In vitro experiments further confirmed that the differentiation of the progenitor cells into SMCs occurred under hypoxia (1% O(2)), and SMC differentiation could be suppressed when myocardin RNAi was administered.

CONCLUSION

Theses results suggest that myocardin may contribute to the differentiation of CXCR4(+)/PDGFRbeta(+) progenitor cells into SMCs induced by hypoxia, which leads to the muscularization of alveolar arterioles.

Ouabain stimulates Na-K-ATPase through a sodium/hydrogen exchanger-1 (NHE-1)-dependent mechanism in human kidney proximal tubule cells

Recent investigations demonstrate increased Na/H exchanger-1 (NHE-1) activity and plasma levels of ouabain-like factor in spontaneously hypertensive rats. At nanomolar concentrations, ouabain increases Na-K-ATPase activity, induces cell proliferation, and activates complex signaling cascades. We hypothesize that the activity of NHE-1 and Na-K-ATPase are interdependent. To test whether treatment with picomolar ouabain regulates Na-K-ATPase through an NHE-1-dependent mechanism, we examined the role of NHE-1 in ouabain-mediated stimulation of Na-K-ATPase in kidney proximal tubule cell lines [opossum kidney (OK), HK-2, HKC-5, and HKC-11] and rat kidney basolateral membranes. Ouabain stimulated Na-K-ATPase activity and tyrosine phosphorylation in cells that express NHE-1 (OK, HKC-5, and HKC-11) but not in HK-2 cells that express very low levels of NHE-1. Inhibition of NHE-1 with 5 microM EIPA, a NHE-1-specific inhibitor, prevented ouabain-mediated stimulation of (86)Rb uptake and Na-K-ATPase phosphorylation in OK, HKC-5, and HKC-11 cells. Expression of wild-type NHE-1 in HK2 cells restored regulation of Na-K-ATPase by picomolar ouabain. Treatment with picomolar ouabain increased membrane expression of Na-K-ATPase and enhanced NHE-1-Na-K-ATPase alpha1-subunit association. Treatment with ouabain (1 microg x kg body wt(-1) x day(-1)) increased Na-K-ATPase activity, expression, phosphorylation, and association with NHE-1 increased in rat kidney cortical basolateral membranes. Eight days' treatment with ouabain (1 microg x kg body wt(-1) x day(-1)) resulted in increased blood pressure in these rats. These results suggest that the association of NHE-1 with Na-K-ATPase is critical for ouabain-mediated regulation of Na-K-ATPase and that these effects may play a role in cardioglycoside-stimulated hypertension.

Hypoxia-inducible factor-1-dependent mechanisms of vascularization and vascular remodelling

The vascular system delivers oxygen and nutrients to every cell in the vertebrate organism. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of hypoxic/ischaemic vascular responses, driving transcriptional activation of hundreds of genes involved in vascular reactivity, angiogenesis, arteriogenesis, and the mobilization and homing of bone marrow-derived angiogenic cells. This review will focus on the pivotal role of HIF-1 in vascular homeostasis, the involvement of HIF-1 in vascular diseases, and recent advances in targeting HIF-1 for therapy in preclinical models.

Hypoxic regulation of ion channels and transporters in pulmonary vascular smooth muscle

Exposure to prolonged alveolar hypoxia, as occurs with many chronic lung diseases or residence at high altitude, results in the development of pulmonary hypertension, significantly worsening patient prognosis. While the structural and functional changes that occur in the pulmonary vasculature in response to chronic hypoxia have been well characterized, less is known regarding the cellular mechanisms underlying this process. The use of animals models of hypoxic pulmonary hypertension have provided important insights into the changes that occur in the pulmonary vascular smooth muscle cells and some of the mediators involved. In this chapter, the effect of chronic hypoxia on various pulmonary arterial smooth muscle cell ion channels and transporters, and the role of the transcription factor, hypoxia-inducible factor 1, in regulating these changes, will be discussed.

Growth inhibition of bovine pulmonary artery smooth muscle cells following long-term heparin treatment

Heparin (HP) inhibits pulmonary artery smooth muscle cell (PASMC) growth in vitro and vascular remodeling in vivo. Bârzu et al. (1994) suggested that the antiproliferative effect of HP on rat aortic smooth muscle cell in vitro diminishes with prolonged exposure to heparin. We exposed cultured bovine PASMC (BPASMC) to prolonged pretreatment with 20 microg/ml of 0-hexanoylated HP from passages 3 to13 and compared them to control (no pretreatment) cultures of identical passages. The pretreated BPASMC and control groups were growth arrested for 48 h, followed by treatment of 0-hexanoylated HP at different doses. On day 5, the growth inhibition of BPASMC was determined. The percent inhibition by 1 microg/ml of 0-hexanoylated HP was 46 +/- 14% versus 62 +/- 13%, for control and pretreated BPASMC, respectively. At 10 microg/ml the inhibition was 62 +/- 7% versus 84 +/- 6%. For 100 microg/ml the inhibition increased to 92 +/- 5% versus 100% and at 200 microg/ml the inhibition was 95 +/- 3% versus 100%. BPASMC (with or without preexposure to 0-hexanoylated HP), at passage 13, were sensitive to the growth inhibitory effect of 0-hexanoylated HP with no significant difference among the groups (95 +/- 3% inhibition vs. 100% for pretreated BPASMC). We found that 0-hexanoylated HP-induced necrosis as shown by flow cytometry and only minor apoptosis. Caspase-3 and PARP detection was insignificant between the groups. In summary, no cell subpopulation at long-term treatment exhibited resistance to 0-hexanoylated HP. The HP antiproliferative effect on SMC is potentially important in defining new approaches to the treatment of the remodeled vasculature of pulmonary hypertension. Liss, Inc.