Journal article

Publication year: 2014

Pages: L791-L799

Journal: American Journal of Physiology - Lung Cellular and Molecular Physiology

Volume number: 307

Issue number: 10

ISSN: 1040-0605

eISSN: 1522-1504

DOI Link: https://doi.org/10.1152/ajplung.00167.2014

Publisher: American Physiological Society

Abstract: 
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 1 alpha (HIF-1 alpha), and iron on HO-1 expression in cystic fibrosis (CF). Immunohistochemical analysis of TLR4, HO-1, ferritin, and HIF-1 alpha 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-1 alpha, 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-1 alpha 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-1 alpha, downregulate HO-1 expression in CFBE41o- cells.

Harvard Citation style: Chillappagari, S., Venkatesan, S., Garapati, V., Mahavadi, P., Munder, A., Seubert, A., et al. (2014) Impaired TLR4 and HIF expression in cystic fibrosis bronchial epithelial cells downregulates hemeoxygenase-1 and alters iron homeostasis in vitro, American Journal of Physiology - Lung Cellular and Molecular Physiology, 307(10), pp. L791-L799. https://doi.org/10.1152/ajplung.00167.2014

APA Citation style: Chillappagari, S., Venkatesan, S., Garapati, V., Mahavadi, P., Munder, A., Seubert, A., Sarode, G., Guenther, A., Schmeck, B., Tuemmler, B., & Henke, M. (2014). Impaired TLR4 and HIF expression in cystic fibrosis bronchial epithelial cells downregulates hemeoxygenase-1 and alters iron homeostasis in vitro. American Journal of Physiology - Lung Cellular and Molecular Physiology. 307(10), L791-L799. https://doi.org/10.1152/ajplung.00167.2014