Regulation of Anion Channel LRRC8 Volume-Regulated Anion Channels in Transport of 2'3'-Cyclic GMP-AMP and Cisplatin under Steady State and Inflammation.

The recently identified anion channel LRRC8 volume-regulated anion channels (VRACs) are heteromeric hexamers constituted with the obligate LRRC8A subunit paired with at least one of the accessory LRRC8B to LRRC8E subunits. In addition to transport chloride, taurine, and glutamate, LRRC8 VRACs also transport the anticancer agent cisplatin and STING agonists 2'3'-cyclic GMP-AMP (cGAMP) and cyclic dinucleotides; hence, they are implicated in a variety of physiological and pathological processes, such as cell swelling, stroke, cancer, and viral infection. Although the subunit composition largely determines VRAC substrate specificity, the opening of various VRAC pores under physiological and pathological settings remains enigmatic. In this study, we demonstrated that VRACs comprising LRRC8A and LRRC8E (LRRC8A/E-containing VRACs), specialized in cGAMP transport, can be opened by a protein component present in serum under resting condition. Serum depletion ablated the tonic activity of LRRC8A/E-containing VRACs, decreasing cGAMP transport in various human and murine cells. Also, heating or proteinase K treatment abolished the ability of serum to activate VRAC. Genetic analyses revealed a crucial role for cGAMP synthase (cGAS) in serum/TNF-promoted VRAC activation. Notably, the presence of cGAS on the plasma membrane, rather than its DNA-binding or enzymatic activity, enabled VRAC activation. Moreover, phospholipid PIP2 seemed to be instrumental in the membrane localization of cGAS and its association with VRACs. Corroborating a role for LRRC8A/D-containing VRACs in cisplatin transport, serum and TNF markedly potentiated cisplatin uptake and killing of cancer cells derived from human or mouse. Together, these observations provide new insights into the complex regulation of VRAC activation and suggest a novel approach to enhance the efficacy of cGAMP and cisplatin in treating infection and cancer.

SnRNA-Seq analysis reveals ten hub genes associated with alveolar epithelial cell injury during pulmonary acute respiratory distress syndrome.

Background: Alveolar epithelial cell injury is a key factor in the occurrence and development of pulmonary acute respiratory distress syndrome (ARDSp). Yet the gene expression profile of alveolar epithelial cells of patients with ARDSp remains unclear. Methods: We analyzed single nuclear RNA sequencing (snRNA-Seq) data from autopsy lung tissues of both ARDSp patients and healthy donors. Sequence data for type 2 alveolar epithelizal cells (AT2) were extracted by the Seurat package. Differentially expressed genes (DEGs) in AT2 were identified by the criteria |log2FC| ≥ 0.25 and P < 0.05 with DESeq2. A protein interaction network was constructed using Search Tool for the Retrieval of Interacting Genes (STRING) and Cytoscape software to identify hub genes. We then constructed an ARDSp rat model through induction by lipopolysaccharide (LPS) airway instillation. Left lung RNA was extracted and sequenced via Illumina Hiseq platforms. Analysis of the rat RNA sequencing data was then used to verify hub genes. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed on the identified hub genes. Results: In AT2, a total of 289 genes were identified as differentially expressed between those from ARDSp patients and healthy donors, and these included 190 upregulated and 99 downregulated genes. Ten hub genes were further identified (RPS27A, ACTG1, CAV1, HSP90AA1, HSPA5, CCND1, ITGA3, B2M, NEDD4L, and SEMA5A). There was a similar expression trend of HSPA5 between rat RNA and snRNA sequencing data. Discussion: ARDSp altered the gene expression profile of AT2. The identified hub genes were enriched in biological processes mainly involved in cell growth and transformation. Relatedly, ferroptosis and autophagy are possibly involved in AT2 injury during ARDSp. These novel insights into ARDSp may aid the discovery of potential targets for the diagnosis and treatment of ARDSp.