CO2-Sensitive Connexin Hemichannels in Neurons and Glia: Three Different Modes of Signalling?

The Tissue Response to Hypoxia: How Therapeutic Carbon Dioxide Moves the Response toward Homeostasis and Away from Instability

Sustained tissue hypoxia is associated with many pathophysiological conditions, including chronic inflammation, chronic wounds, slow-healing fractures, microvascular complications of diabetes, and metastatic spread of tumors. This extended deficiency of oxygen (O₂) in the tissue sets creates a microenvironment that supports inflammation and initiates cell survival paradigms. Elevating tissue carbon dioxide levels (CO₂) pushes the tissue environment toward "thrive mode," bringing increased blood flow, added O₂, reduced inflammation, and enhanced angiogenesis. This review presents the science supporting the clinical benefits observed with the administration of therapeutic CO₂. It also presents the current knowledge regarding the cellular and molecular mechanisms responsible for the biological effects of CO₂ therapy. The most notable findings of the review include (a) CO₂ activates angiogenesis not mediated by hypoxia-inducible factor 1a, (b) CO₂ is strongly anti-inflammatory, (c) CO₂ inhibits tumor growth and metastasis, and (d) CO₂ can stimulate the same pathways as exercise and thereby, acts as a critical mediator in the biological response of skeletal muscle to tissue hypoxia.

Wood smoke particulate matter (WSPM2.5) induces pyroptosis through both Caspase-1/IL-1β/IL-18 and ATP/P2Y-dependent mechanisms in human bronchial epithelial cells

Emerging evidences have linked the air pollution particulate matters, especially the fine particulate matter PM2.5, to the disease development of chronic obstructive pulmonary disease (COPD). Our previous studies reported that biofuel PM2.5 can induce devastated damage of human bronchial epithelial cells, this study aims to further investigate the underlying molecular mechanisms how biofuel PM2.5 induces bronchial epithelial cell death and dysfunction. In this study, biofuel PM2.5 extracted from wood smoke (WSPM2.5) was used according to our previous publication. A 16-HBE cell line was used as the cell model. Results showed that: Firstly, WSPM2.5 induced significant pyroptosis in 16-HBE cells, reflected by the typical changes including elevated release of lactate dehydrogenase release (LDH) and activated activity and expression of Caspase-1/IL-1β/IL-18 signaling pathway. Then, specific inhibitors for both Caspases (Z-VAD-FMK) and Caspase-1 (VX-765), as well as specific siRNA knockdown of IL-1β all effectively attenuated the WSPM2.5-induced upregulation of downstream inflammatory cytokines and chemokines (IL-6, IL-8, CXCL-1, CXCL-2, etc), respectively. Notably, WSPM2.5 caused a novel increase of intracellular-to-extracellular ATP secretion, which could also contribute to the WSPM2.5-induced pyroptosis and inflammation by activating the Caspase-1/IL-1β/IL-18 signaling pathway through possible autocrine and/or paracrine mechanisms. Antagonism of ATP (Apyrase) or specific siRNA knockdown against ATP receptors (P2Y2 and P2Y7) both significantly inhibited the WSPM2.5-induced pyroptosis and inflammation. These results add up to the current knowledge and bring up novel insights that WSPM2.5 could induce significant pyroptosis and inflammation of human bronchial epithelial cells, through both a classic NLRP3/Caspase-1/IL-1β-dependent and a novel ATP/P2Y-dependent mechanisms.