Price, Alexis L.

Airway inflammation is the central driver behind the pathogenesis of respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), chronic bronchitis, and the very recent pandemic outbreak of COVID-19. Previous studies reported that proinflammatory cytokine TNFa plays a significant role in airway inflammation by inducing hyper-reactivity of airway smooth muscle (ASM) and airway remodeling. TNFa also increases ASM force generation and ATP hydrolysis that requires energy. The excess energy demand is met by an increase in the level of PGC1a protein, mitochondrial biogenesis and subsequently increased mitochondrial volume density. Based on these previous findings, we hypothesized that TNFa promotes CREB phosphorylation at a specific serine 133 residue (pCREBS133) thereby transcriptionally activating PGC1a expression leading to mitochondrial biogenesis and increased mitochondrial volume density. In the study, human ASM cells were dissociated from bronchiolar tissue samples collected during bronchiolar surgery from female and male donors (34 to 71 years of age) with no history of respiratory diseases or current smoking. The dissociated ASM cells were serum-deprived for 48 h before experimentation. The ASM cells from each donor were separated into two groups: 1) time-matched untreated controls, and 2) TNFa treated (20 ng/ml for 6 h). Expression of CREB, pCREBS133, PCG1a, VDAC (an indicator of mitochondrial volume), and downstream signaling molecules (NRFs, TFAM), which regulate transcription and replication of the mitochondrial genome, were determined by quantitative real-time PCR (qPCR) and/or Western blot analysis. The binding of pCREBS133 to the PGC1a promoter was confirmed by bioinformatics analysis and chromatin immunoprecipitation (ChIP) assay. Mitochondria within ASM cells were labeled using MitoTracker green and imaged by 3D confocal microscopy for the assessment of mitochondrial volume density. Mitochondrial biogenesis was quantified by mitochondrial DNA (mtDNA) copy number relative to nuclear DNA using qPCR. Results were analyzed by one-way analysis of variance (ANOVA). Human ASM cells treated with TNFa showed increased pCREBS133 phosphorylation without any significant change in total CREB. The ChIP assay using a CREB-specific antibody revealed that pCREBS133 binds to the promoter of PGC1a and TNFa treatment further increased the binding affinity. Consistent with these findings, TNFa treatment increased PCG1a expression in ASM cells, and subsequently activated its downstream signaling pathway revealed by increased expression of its target genes, NRF1, NRF2 and TFAM. TNFa-induced activation of the PCG1a signaling pathway in ASM cells resulted in increased mitochondrial biogenesis as indicated by increased mitochondrial DNA copy number and increased mitochondrial volume density. Supported by NIH grant HL157984 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Proinflammatory cytokines such as TNFα mediate airway inflammation. Previously, we showed that TNFα increases mitochondrial biogenesis in human ASM (hASM) cells, which is associated with increased PGC1α expression. We hypothesized that TNFα induces CREB and ATF1 phosphorylation (pCREBS133 and pATF1S63), which transcriptionally co-activate PGC1α expression. Primary hASM cells were dissociated from bronchiolar tissue obtained from patients undergoing lung resection, cultured (one–three passages), and then differentiated by serum deprivation (48 h). hASM cells from the same patient were divided into two groups: TNFα (20 ng/mL) treated for 6 h and untreated controls. Mitochondria were labeled using MitoTracker green and imaged using 3D confocal microscopy to determine mitochondrial volume density. Mitochondrial biogenesis was assessed based on relative mitochondrial DNA (mtDNA) copy number determined by quantitative real-time PCR (qPCR). Gene and/or protein expression of pCREBS133, pATF1S63, PCG1α, and downstream signaling molecules (NRFs, TFAM) that regulate transcription and replication of the mitochondrial genome, were determined by qPCR and/or Western blot. TNFα increased mitochondrial volume density and mitochondrial biogenesis in hASM cells, which was associated with an increase in pCREBS133, pATF1S63 and PCG1α expression, with downstream transcriptional activation of NRF1, NRF2, and TFAM. We conclude that TNFα increases mitochondrial volume density in hASM cells via a pCREBS133/pATF1S63/PCG1α-mediated pathway.