| First Author | Chillappagari S | Year | 2014 |
| Journal | Am J Physiol Lung Cell Mol Physiol | Volume | 307 |
| Issue | 10 | Pages | L791-9 |
| PubMed ID | 25239913 | Mgi Jnum | J:222194 |
| Mgi Id | MGI:5644111 | Doi | 10.1152/ajplung.00167.2014 |
| Citation | Chillappagari S, et al. (2014) Impaired TLR4 and HIF expression in cystic fibrosis bronchial epithelial cells downregulates hemeoxygenase-1 and alters iron homeostasis in vitro. Am J Physiol Lung Cell Mol Physiol 307(10):L791-9 |
| abstractText | Hemeoxygenase-1 (HO-1), an inducible heat shock protein, is upregulated in response to multiple cellular insults via oxidative stress, lipopolysaccharides (LPS), and hypoxia. In this study, we investigated in vitro the role of Toll-like receptor 4 (TLR4), hypoxia-inducible factor 1alpha (HIF-1alpha), and iron on HO-1 expression in cystic fibrosis (CF). Immunohistochemical analysis of TLR4, HO-1, ferritin, and HIF-1alpha were performed on lung sections of CFTR-/- and wild-type mice. CFBE41o- and 16HBE14o- cell lines were employed for in vitro analysis via immunoblotting, immunofluorescence, real-time PCR, luciferase reporter gene analysis, and iron quantification. We observed a reduced TLR4, HIF-1alpha, HO-1, and ferritin in CFBE41o- cell line and CF mice. Knockdown studies using TLR4-siRNA in 16HBE14o- revealed significant decrease of HO-1, confirming the role of TLR4 in HO-1 downregulation. Inhibition of HO-1 using tin protoporphyrin in 16HBE14o- cells resulted in increased iron levels, suggesting a probable role of HO-1 in iron accumulation. Additionally, sequestration of excess iron using iron chelators resulted in increased hypoxia response element response in CFBE41o- and 16HBE14o-, implicating a role of iron in HIF-1alpha stabilization and HO-1. To conclude, our in vitro results demonstrate that multiple regulatory factors, such as impaired TLR4 surface expression, increased intracellular iron, and decreased HIF-1alpha, downregulate HO-1 expression in CFBE41o- cells. |
