MTOR pathway inhibition attenuates hypercapnia-induced autophagy arrest and dysfunctional myogenesis
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ABSTRACT: Hypercapnia exposure in mice leads to reduced skeletal muscle repair capacity and myogenic potential. Autophagy is also reduced in this context. Satellite cells from mice treated with hypercapnia were isolated and compared to satellite cells from normocapnia control mice. Cells were isolated by FACS using Pax7-GFP tamoxifen inducible reporter to ensure enrichment of Pax7 cells.
Project description:Chronic CO2 retention, or hypercapnia, occurs in pulmonary diseases and leads to skeletal muscle wasting. Muscle wasting and hypercapnia are independently associated with substantial mortality. While abnormal skeletal muscle stem -satellite- cells, contribute to impaired myogenesis in pulmonary diseases, no mechanistic data exists on hypercapnia-driven dysfunctional satellite cells and myogenesis in-vivo. Autophagy regulates satellite cell activation and myogenesis, and while elevated CO2 inhibits autophagy in inflammatory cells, it has never been evaluated in the context of hypercapnia-driven abnormal myogenesis. Using lineage tracing in pre- and post-stem cell transplantation experiments, we show that hypercapnia undermines both Pax7- and α-7 integrin-expressing satellite cells activation, replication and myogenesis. Satellite cells’ multi-omic analyses indicate that hypercapnia disrupts multiple pathways regulated by autophagy. Moreover, autophagy-specific LC3 fluorescence-reporting mouse and cellular data demonstrate that hypercapnia reduces expressions of AMPK and Ulk1, which critically participate in autophagosome formation, and has no effect on the antagonistic mTOR pathway including Ulk1 serine-757 phosphorylation. Moreover, Atg7 knockout-driven loss of autophagy function phenocopies the effects on hypercapnia. After rapamycin administration, the hypercapnia-induced myogenic deficit is corrected by a sharp AMPK activation leading to the autophagy-stimulatory Ulk1 phosphorylation at serine-555, autophagy acceleration, increased satellite cells replication and improved myogenesis post-satellite cells transplantation.
Project description:In monocytes we used RNA-sequencing to investigate the effect of 4hrs of exposure to buffered hypercapnia (10% CO2) compared to normocapnia (5% CO2) with and without the pro-inflammatory stimulus LPS (2.5ug/ml) for the final 2hrs. Buffered hypercapnia causes transcriptional changes associated with altered metabolic function in both the basal and stimulated states.
Project description:Skeletal muscle dysfunction and elevated CO2 in the blood, or hypercapnia, are both associated with higher mortality in acute and chronic pulmonary diseases. Hypercapnia causes accelerated protein degradation, reduced protein synthesis, and dysfunctional myogenesis. We have recently reported that hypercapnia-induced skeletal myogenic dysfunction persists after resolution of CO2 exposure, suggesting the existence of durable cellular aberrations in previously hypercapnic cells. No data on lingering myofiber atrophy after hypercapnia resolution currently exist. Hypercapnia and age-induced skeletal muscle loss phenotypically overlap, and myogenic progenitor cells from hypercapnic mice elicit senescence-associated transcriptional programs. While aging is characterized by unique DNA methylation and other epigenetic changes, the potential association of hypercapnia and age-related differential methylation have never been investigated. In the present study, we show that hypercapnic mice elicit protracted muscle deterioration even after returning to normocapnia and demonstrate aberrant DNA methylation in comparison to animals never exposed to elevated CO2. We also show that these DNA methylation changes do not overlap with age-induced alterations.
Project description:Addition of CO2 to the inspired gas can ameliorate lung injury during high tidal volume mechanical ventilation in animal models. Although some effects of hypercapnia on physiology and cell signaling have been characterized, we hypothesized that assessment of genome-wide gene expression patterns would reveal novel pathways of protection. We subjected male C57BL/6J mice to non-injurious low stretch (tidal vol = 10 mL/kg, PEEP = 2 cm H2O) or injurious high stretch (tidal volume approx 35 mL/kg, PEEP = 0 cm H2O) mechanical ventilation for 3 hours under normocapnia (FiCO2 = 0) or hypercapnia (FiCO2 = 0.12).
Project description:In wild type, NR4A2-deficient, and NR4A3-deficient monocytes we used RNA-sequencing to investigate the effect of 4hrs of exposure to buffered hypercapnia (10% CO2) compared to normocapnia (5% CO2) with and without the pro-inflammatory stimulus LPS (2.5ug/ml) for the final 2hrs. Buffered hypercapnia causes transcriptional changes associated with altered metabolic function in both the basal and stimulated states.
Project description:Hypercapnia, the elevation of CO2 in blood and tissues, commonly occurs in severe acute and chronic respiratory diseases, and is associated with increased risk of mortality. Recent studies have shown that hypercapnia adversely affects innate immunity, host defense, lung edema clearance, and cell proliferation. Airway epithelial dysfunction is a feature of advanced lung disease, but the effect of hypercapnia on airway epithelium is unknown. Thus, in the current study we examined the effect of normoxic hypercapnia (20% CO2 for 24 h) vs normocapnia (5% CO2), on global gene expression in differentiated normal human airway epithelial cells. Gene expression was assessed on Affymetrix microarrays, and subjected to gene ontology analysis for biological process and cluster-network representation. We found that hypercapnia downregulated the expression of 183 genes and upregulated 126. Among these, major gene clusters linked to immune responses and nucleosome assembly were largely downregulated, while lipid metabolism genes were largely upregulated. The overwhelming majority of these genes were not previously known to be regulated by CO2. These changes in gene expression indicate the potential for hypercapnia to impact bronchial epithelial cell function in ways that may contribute to poor clinical outcomes in patients with severe acute or advanced chronic lung diseases.
Project description:Skeletal muscle has remarkable capacity to regenerate upon injury due to the presence of satellite cells. The maintenance and function of satellite cells are regulated by circadian clock. Cryptocrhome 2 (CRY2) is a key component of the circadian clock and its role in skeletal muscle regeneration remains controversial. Here, we report that CRY2 is down-regulated during muscle regeneration. Using the satellite cell specific CRY2 knockout mice (CRY2scko), we show that deletion of CRY2 enhances muscle regeneration. Single myofiber analysis showed that deletion of CRY2 enhances satellite cell self-renewal. In the absence of CRY2, the ERK1/2 and JNK1/2 signaling pathways become activated, which phosphorylates the transcription factor ETS1, which in turn binds to the promoter of PAX7 to induce its transcription. CRY2 deficient myoblasts survived better in ischemic muscle. Deletion of CRY2 also alleviated myopathy in mdx mice. Therefore, CRY2 plays an essential role in regulating satellite cell function and skeletal muscle regeneration.
Project description:Zfhx3, human ortholog of the Drosophila Zfh2 and first known mediator of hypercapnic immune suppression in vivo, is expressed in human and mouse MØs and its myeloid deletion reversed the effects of hypercapnia in gene expression in murine alveolar macrophages and protects against influenza A virus proliferation, lung injury and mortality increased by hypercapnia in infected mice.