Molecular Regulation of Heme Oxygenase-1 Expression by E2F Transcription Factor 2 in Lung Fibroblast Cells: Relevance to Idiopathic Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a fatal chronic lung disease. Heme oxygenase-1 (HMOX1/HO-1) is an enzyme that catalyzes the degradation of heme. The role of HO-1 in the pathogenesis of IPF has been studied; however, the molecular regulation of HO-1 and its role in IPF are still unclear. In this study, we found that HO-1 protein levels significantly increased in lung myofibroblasts in IPF patients and in lungs in a murine model of bleomycin-induced lung fibrosis. In addition, we observed that administration of a E2F transcription factor inhibitor elevated HO-1 mRNA and protein levels in lung fibroblasts. Downregulation of E2F2 by siRNA transfection increased HO-1 mRNA and protein levels, while overexpression of E2F2 reduced HO-1 levels. However, overexpression of E2F2 did not alter hemin-induced HO-1 protein levels. Furthermore, modulation of HO-1 levels regulated TGF-β1-induced myofibroblast differentiation without altering the phosphorylation of Smad2/3 in lung fibroblast cells. Moreover, the phosphorylation of protein kinase B (Akt) was significantly upregulated in HO-1-depleted lung fibroblast cells. In summary, this study demonstrated that E2F2 regulates the baseline expression of HO-1, but has no effect on modulating HO-1 expression by hemin. Finally, elevated HO-1 expression contributes to the TGF-β1-induced lung myofibroblast differentiation through the activation of the serine/threonine kinase AKT pathway. Overall, our findings suggest that targeting E2F2/HO-1 might be a new therapeutic strategy to treat fibrotic diseases such as IPF.

特发性肺纤维化（IPF）是一种致命的慢性肺部疾病。血红素加氧酶 - 1（HMOX1/HO - 1）是一种催化血红素降解的酶。HO - 1在IPF发病机制中的作用已被研究；然而，HO - 1的分子调控及其在IPF中的作用仍不清楚。在本研究中，我们发现IPF患者的肺肌成纤维细胞以及博来霉素诱导的肺纤维化小鼠模型的肺中，HO - 1蛋白水平显著升高。此外，我们观察到给予一种E2F转录因子抑制剂可提高肺成纤维细胞中HO - 1的mRNA和蛋白水平。通过小干扰RNA转染下调E2F2可增加HO - 1的mRNA和蛋白水平，而E2F2的过表达则降低HO - 1水平。然而，E2F2的过表达并不改变氯化血红素诱导的HO - 1蛋白水平。此外，调节HO - 1水平可调控转化生长因子 - β1诱导的肌成纤维细胞分化，而不改变肺成纤维细胞中Smad2/3的磷酸化。而且，在HO - 1缺失的肺成纤维细胞中，蛋白激酶B（Akt）的磷酸化显著上调。总之，本研究表明E2F2调节HO - 1的基础表达，但对氯化血红素调节HO - 1的表达没有影响。最后，HO - 1表达升高通过激活丝氨酸/苏氨酸激酶AKT途径促进转化生长因子 - β1诱导的肺肌成纤维细胞分化。总体而言，我们的研究结果表明，靶向E2F2/HO - 1可能是治疗IPF等纤维化疾病的一种新的治疗策略。