Yap, John Q.

Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNFα and IL‐13) enhance cytosolic Ca 2+ concentration ([Ca 2+ ] cyto ) triggering airway smooth muscle (ASM) hyperreactivity (enhanced contractile state). Airway inflammation also induces ASM proliferation and remodeling (enhanced ASM synthetic state). In various diseases inflammation induces sarcoplasmic/endoplasmic reticulum (SR/ER) stress, which decreases SR/ER‐mitochondria interactions, with downstream effects on Ca 2+ regulation. In vascular smooth muscle cells, SR/ER stress promotes smooth muscle contraction and proliferation by disrupting SR/ER‐mitochondrial coupling. We hypothesized that inflammation induces SR/ER stress in human ASM, thereby altering expression of mitochondrial fission/fusion proteins (dynamin‐related protein ‐ Drp1 and mitofusin ‐ Mfn2) with downstream impact on ASM Ca 2+ regulation and contractility as well as proliferation. Human ASM cells were isolated from lung specimen incidental to patient surgery and exposed to TNFα or IL‐13 for 24h. Expression of SR/ER stress markers including PERK (protein kinase‐like endoplasmic reticulum kinase), Bip (Binding immunoglobulin protein also known as 78 kDa glucose‐regulated protein), PDI (protein disulfide isomerase), and mitochondrial fission/fusion proteins Drp1 and Mfn2 were evaluated by Western blot. The expression of the spliced isoform of the transcription factor XBP1 was investigated by quantitative real‐time PCR (RT‐PCR). For mitochondrial morphology (fission/fusion), ASM cells were loaded with Mitotracker Green and images analyzed using ImageJ and Matlab to quantify mitochondrial Form Factor and Aspect Ratio. The effect of inflammation induced SR/ER stress on human ASM proliferation was evaluated using CyQUANT assay. We found that after 24 h exposure to TNFα and IL‐13: 1) expression of SR/ER stress protein markers (PERK, BiP and XBP1) increased; 2) Drp1 expression increased and Mfn2 expression decreased; 3) mitochondrial fragmentation increased; 4) [Ca 2+ ] cyt and [Ca 2+ ] mito responses to ACh stimulation were uncoupled; 5) net [Ca 2+ ] cyt increased; 6) contractility increased; and 7) ASM cell proliferation increased. Together these results suggest that inflammation induces SR/ER stress that leads to changes in Mfn2 and Drp1 expression, which alter mitochondrial dynamics and Ca 2+ regulation resulting in ASM hyperreactivity and remodeling. Support or Funding Information NIH grant HL126451 (GCS).

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 ( Delta P‐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 Delta P‐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 Information Supported 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 .

Airway inflammation plays a key role in asthma. In various diseases, inflammation leads to an increase in reactive oxygen species (ROS) generation and is associated with accumulation of unfolded proteins leading to endoplasmic reticulum (ER) stress. In response to ER stress, a homeostatic signaling cascade is triggered to restore normal function by halting protein translation and activating protein degradation and expression of molecular chaperones involved in protein folding. Three ER stress protein markers located at the ER membrane are involved in this signaling cascade: protein kinase RNA‐like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6) and inositol‐requiring enzyme 1 (IRE1α). In particular, phosphorylation of IRE1α catalyzes the alternative splicing of XBP1 mRNA leading to expression of the active XBP1 transcription factor. In this study, we hypothesize that pro‐inflammatory cytokine TNFα induces ROS production triggering ER stress in human airway smooth muscle (hASM). hASM cells were isolated from lung specimen incidental to patient surgery and exposed to TNFα (20 ng/ml) for 1, 3, 6, 12 or 24 h. To measure ROS production, hASM cells were loaded with the general oxidative stress indicator CM‐H2DCFDA or with the mitochondrial superoxide indicator MitoSOX™ Red. The CM‐H2DCFDA and MitoSOX™ Red signals were visualized using a Nikon A1R confocal imaging system. Images were analyzed using ImageJ. Exposure of hASM to tunicamycin (2 μg/ml) was used as a positive control for ER stress. Expression of IRE1α and PERK were determined by Western blot. Phosphorylation of IRE1α was also evaluated by immunoprecipitation and Western blot (Wes Simple Western™ system). The expression of the spliced isoform of the transcription factor XBP1 was examined by quantitative real‐time PCR (RT‐PCR). We found that ROS production increased in hASM within 1 h of TNFα exposure, followed by an increase in IRE1α phosphorylation within 1–3 h. Finally after 3–6 h, there was an increase in alternative splicing of XBP1 mRNA. Together these results show that the pro‐inflammatory cytokine TNFα increases ROS generation in hASM cells and induces an ER stress response that includes an increase in IRE1α phosphorylation and splicing of XBP1. This ER stress response may affect many downstream targets, among which we believe Mfn2 is a major target which affects mitochondrial Ca 2+ buffering, with specific effects on hASM force and/or increased cell proliferation associated with asthma. Support or Funding Information NIH grant HL126451 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Airway inflammation is a key aspect of diseases such as asthma. Proinflammatory cytokines such as TNFα mediate the inflammatory response. In various diseases, inflammation leads to endoplasmic reticulum (ER) stress, the accumulation of unfolded proteins, which triggers homeostatic responses to restore normal cellular function. We hypothesized that TNFα triggers ER stress through an increase in reactive oxygen species generation in human airway smooth muscle (hASM) with a downstream effect on mitofusin 2 (Mfn2). In hASM cells isolated from lung specimens incidental to patient surgery, dose- and time-dependent effects of TNFα exposure were assessed. Exposure of hASM to tunicamycin was used as a positive control. Tempol (500 μM) was used as superoxide scavenger. Activation of three ER stress pathways were evaluated by Western blotting: 1) autophosphorylation of inositol-requiring enzyme1 (IRE1α) leading to splicing of X-box binding protein 1 (XBP1); 2) autophosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) leading to phosphorylation of eukaryotic initiation factor 2α; and 3) translocation and cleavage of activating transcription factor 6 (ATF6). We found that exposure of hASM cells to tunicamycin activated all three ER stress pathways. In contrast, TNFα selectively activated the IRE1α/XBP1 pathway in a dose- and time-dependent fashion. Our results indicate that TNFα does not activate the PERK and ATF6 pathways. Exposure of hASM cells to TNFα also decreased Mfn2 protein expression. Concurrent exposure to TNFα and tempol reversed the effect of TNFα on IRE1α phosphorylation and Mfn2 protein expression. Selective activation of the IRE1α/XBP1 pathway in hASM cells after exposure to TNFα may reflect a unique homeostatic role of this pathway in the inflammatory response of hASM cells.

Abstract Background This study aimed to evaluate short-term and long-term mortalities in a cohort of unselected hospitalized patients with serum sodium concentration ([Na+]) variations within and outside of reference range. Methods All adult patients admitted to the Mayo Clinic, Rochester, MN, USA from January 2011 to December 2013 (n = 147358) were retrospectively screened. Unique patients admitted during the study period were examined. The main exposure was serum [Na+] variation. Outcome measures were hospital and 1-year all-cause mortalities. Results A total of 60944 patients, mean age 63 ± 17 years, were studied. On admission, 17% (n = 10066) and 1.4% (n = 852) had hypo- and hypernatremia, respectively. During the hospital stay, 11044 and 4128 developed hypo- and hypernatremia, respectively, accounting for 52.3 and 82.9% of the total hypo- and hypernatremic patients. Serum [Na+] variations of ≥6 mEq/L occurred in 40.6% (n = 24 740) of the 60 944 patients and were significantly associated with hospital and 1-year mortalities after adjusting potential confounders (including demographics, comorbidities, estimated glomerular filtration rate, admission serum [Na+], number of [Na+] measurements and length of hospital stay). Adjusted odds ratios for hospital and 1-year mortalities increased with increasing [Na+] variations in a dose-dependent manner, from 1.47 to 5.48 (all 95% confidence intervals >1.0). Moreover, in fully adjusted models, [Na+] variations (≥6 mEq/L) within the reference range (135–145 mEq/L) or borderline hypo- or hypernatremia (133–137 and 143–147 mEq/L, respectively) compared with 138–142 mEq/L were associated with increased hospital and 1-year mortalities. Conclusion In hospitalized adults, [Na+] fluctuation (≥6 mEq/L) irrespective of admission [Na+] and borderline hypo- or hypernatremia are independent predictors of progressively increasing short- and long-term mortality burdens.