The Effects of TNFα on Mitochondria Morphology are Mediated by Endoplasmic Reticulum Stress in Human Airway Smooth Muscle Cells

Abstract

Airway inflammation is a key trigger for asthma, and pro‐inflammatory cytokines such as TNFα mediate the airway hyperreactivity and remodeling characteristic of asthma. In various diseases, inflammation leads to an increase in mitochondrial fission, associated with decreased expression of mitochondrial fusion proteins, such as Mfn2. Mitochondrial fission is generally coupled with mitochondrial biogenesis and cell proliferation. Some studies in other cell types suggest that mitochondrial fission may be a result of the accumulation of unfolded or misfolded proteins i.e., endoplasmic reticulum (ER) stress. ER stress activates three intracellular pathways to induce a homeostatic response to restore normal ER function. The IRE1α pathway is activated by autophosphorylation and splices XBP1 mRNA. Previous studies have shown that the XBP1 has downstream effects on mitochondrial proteins. In this study we hypothesized that TNFα induces activation of the IRE1α pathway which leads to a decrease in Mfn2 expression. hASM cells were isolated from lung specimen incidental to patient surgery. The patients were normal as evaluated by the clinical pathologist (no history of asthma or COPD). hASM cells were stimulated with TNFα (20 ng/ml) for 1, 3, 6, 12 or 24 h. Expression of total and phosphorylated IRE1α, Mfn2 and cleaved and uncleaved XBP1 were evaluated by Western blot. RNAscope® was used to measure Mfn2 mRNA expression in hASM cells transfected with non‐phosphorylatable IREα (DeltaP‐IRE1α; GFP tagged) compared to non‐transfected cells. Results were analyzed by 2‐way ANOVA with Bonferroni analysis when justified. We found that exposure of hASM cells to TNFα activated the IRE1α/XBP1 pathway and decreased Mfn2 expression in a time dependent fashion. In addition we found that TNFα exposure in cells expressing the inactive DeltaP‐IRE1α did not lead to a significant decrease in Mfn2 expression. Our results suggest that the IRE1α/XBP1 pathway may be involved in the regulation of mitochondrial fission, mitochondrial biogenesis and cell proliferation.Support or Funding InformationSupported by NIH grant HL126451 (GCS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.