Hypoxia-induced pulmonary arterial smooth muscle cell proliferation is controlled by forkhead box M1.

Pulmonary arterial hypertension (PAH) is a devastating disease, and no effective treatments are available. Hypoxia-induced pulmonary artery remodeling, including smooth muscle cell proliferation, contributes to PAH, but the exact mechanisms underlying this abnormal process are largely undefined. The forkhead box M1 (FoxM1) transcription factor regulates cancer cell growth by modulating gene expression critical for cell cycle progression. Here, we report for the first time, to the best of our knowledge, a novel function of FoxM1 in the hypoxia-stimulated proliferation of human pulmonary artery smooth muscle cells (HPASMCs). Exposure to hypoxia caused a marked up-regulation of FoxM1 gene expression, mainly at the transcription level, and this induction correlated with HPASMC cell proliferation. The knockdown of FoxM1 inhibited the hypoxia-stimulated proliferation of HPASMCs. We found that the knockdown of HIF-2α, but not HIF-1α, diminished FoxM1 induction in response to hypoxia. However, the knockdown of FoxM1 did not alter expression levels of HIF-2α or HIF-1α, suggesting that HIF-2α is an upstream regulator of FoxM1. Furthermore, the knockdown of FoxM1 prevented the hypoxia-induced expression of aurora A kinase and cyclin D1. Collectively, our results suggest that hypoxia induces FoxM1 gene expression in an HIF-2α-dependent pathway, thereby promoting HPASMC proliferation.

Identification of adult hepatic progenitor cells capable of repopulating injured rat liver.

UNLABELLED: Oval cells appear and expand in the liver when hepatocyte proliferation is compromised. Many different markers have been attributed to these cells, but their nature still remains obscure. This study is a detailed gene expression analysis aimed at revealing their identity and repopulating in vivo capacity. Oval cells were activated in 2-acetylaminofluorene-treated rats subjected to partial hepatectomy or in D-galactosamine-treated rats. Two surface markers [epithelial cell adhesion molecule (EpCAM) and thymus cell antigen 1 (Thy-1)] were used for purification of freshly isolated cells. Their gene expression analysis was studied with Affymetrix Rat Expression Array 230 2.0, reverse-transcriptase polymerase chain reaction, and immunofluorescent microscopy. We found that EpCAM(+) and Thy-1(+) cells represent two different populations of cells in the oval cell niche. EpCAM(+) cells express the classical oval cell markers (alpha-fetoprotein, cytokeratin-19, OV-1 antigen, a6 integrin, and connexin 43), cell surface markers recently identified by us (CD44, CD24, EpCAM, aquaporin 5, claudin-4, secretin receptor, claudin-7, V-ros sarcoma virus oncogene homolog 1, cadherin 22, mucin-1, and CD133), and liver-enriched transcription factors (forkhead box q, forkhead box a2, onecut 1, and transcription factor 2). Oval cells do not express previously reported hematopoietic stem cell markers Thy-1, c-kit, and CD34 or the neuroepithelial marker neural cell adhesion molecule 1. However, oval cells express a number of mesenchymal markers including vimentin, mesothelin, bone morphogenetic protein 7, and Tweak receptor (tumor necrosis factor receptor superfamily, member 12A). A group of novel differentially expressed oval cell genes is also presented. It is shown that Thy-1(+) cells are mesenchymal cells with characteristics of myofibroblasts/activated stellate cells. Transplantation experiments reveal that EpCAM(+) cells are true progenitors capable of repopulating injured rat liver. CONCLUSION: We have shown that EpCAM(+) oval cells are bipotential adult hepatic epithelial progenitors. These cells display a mixed epithelial/mesenchymal phenotype that has not been recognized previously. They are valuable candidates for liver cell therapy.