FXYD3 facilitates Na+ and liquid absorption across human airway epithelia by increasing the transport capacity of the Na/K ATPase

Stimulated Raman Scattering Microscopy Facilitates the Discovery of Diacylglycerol O-Acyltransferase 2 as a Target to Enhance Iodine Uptake in Papillary Thyroid Carcinoma

Radioactive 131I therapy is a primary treatment for papillary thyroid carcinoma (PTC), with approximately 30% of patients developing iodine-refractory disease. There is an urgent clinical need to improve iodine uptake in PTC. Previous research suggested a connection between triglyceride (TG) accumulation and decreased iodine uptake in benign thyroid cells. Notably, TG accumulation has been found to be a marker of aggressive human PTC. Therefore, it is crucial to elucidate whether TG accumulation affects iodine uptake in PTC, which may lead to a new way for enhancement of iodine uptake. Here, by combining stimulated Raman scattering (SRS) microscopy and deuterated Raman tags, we first quantitatively analyzed the level of TG and its source in the K1 cell with low iodine uptake and the TPC-1 cell with high iodine uptake. It was found that K1 cells had significantly greater TG accumulation than TPC-1 cells, primarily due to an increased exogenous uptake of fatty acids. Further RNA-seq transcriptome experiments revealed that the underlying mechanism could be upregulation of lipid biosynthesis, uptake, and transport-related genes, along with down-regulation of fatty acid β-oxidation and lipolysis-related genes in K1 cells. Among the upregulated lipid biosynthesis genes, diacylglycerol O-acyltransferase 2 (DGAT2) is of great importance as the rate-limiting enzyme in TG biosynthesis. Notably, the inhibition of DGAT2 led to a significant increase in the expression of iodine uptake-related proteins, namely, sodium iodide symporter (NIS) and thyroglobulin (Tg), in K1 cells. Further Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses unraveled that DGAT2 inhibition could enhance thyroid hormone synthesis, for which iodine is an essential raw material, by alleviating endoplasmic reticulum stress and upregulating the pathways related to protein glycosylation and transmembrane transport. In summary, our study has shown that SRS microscopy facilitates the discovery of DGAT2 as a potential target to enhance iodine uptake in PTC, which holds promise for improving treatment outcome of iodine-refractory PTC.

Increased ENaC-mediated liquid absorption across vitamin-D deficient human airway epithelia

Vitamin D deficiency is a risk factor for exacerbation of obstructive airway disease, a hallmark of which is mucus dehydration and plugging. Calcitriol (the active form of vitamin D) deficiency in cultured human airway epithelia resulted in increased SCNN1G and ATP1B1 mRNAs encoding subunits of ENaC and the Na-K pump compared with supplemented epithelia. These drive the absorption of airway surface liquid. Consistently, calcitriol-deficient epithelia absorbed liquid faster than supplemented epithelia. Calcitriol deficiency also increased amiloride-sensitive Isc and Gt without altering Na-K pump activity, indicating the changes in amiloride-sensitivity arose from ENaC. ENaC activity can be regulated by trafficking, proteases, and channel abundance. We found the effect was likely not induced by changes to endocytosis of ENaC given that calcitriol did not affect the half-lives of amiloride-sensitive Isc and Gt. Furthermore, trypsin nominally increased Isc produced by epithelia ± calcitriol, suggesting calcitriol did not affect proteolytic activation of ENaC. Consistent with mRNA and functional data, calcitriol deficiency resulted in increased γENaC protein. These data indicate that the vitamin D receptor response controls ENaC function and subsequent liquid absorption, providing insight into the relationship between vitamin D deficiency and respiratory disease.NEW & NOTEWORTHY It is unknown why calcitriol (active vitamin D) deficiency worsens pulmonary disease outcomes. Results from mRNA, immunoblot, Ussing chamber, and absorption experiments indicate that calcitriol deficiency increases ENaC activity in human airway epithelia, decreasing apical hydration. Given that epithelial hydration is required for mucociliary transport and airway innate immune function, the increased ENaC activity observed in calcitriol-deficient epithelia may contribute to respiratory pathology observed in vitamin D deficiency.

A Monoclonal Human Alveolar Epithelial Cell Line ("Arlo") with Pronounced Barrier Function for Studying Drug Permeability and Viral Infections

In the development of orally inhaled drug products preclinical animal models regularly fail to predict pharmacological as well as toxicological responses in humans. Models based on human cells and tissues are potential alternatives to animal experimentation allowing for the isolation of essential processes of human biology and making them accessible in vitro. Here, the generation of a novel monoclonal cell line "Arlo," derived from the polyclonal human alveolar epithelium lentivirus immortalized cell line hAELVi via single-cell printing, and its characterization as a model for the human alveolar epithelium as well as a building block for future complex in vitro models is described. "Arlo" is systematically compared in vitro to primary human alveolar epithelial cells (hAEpCs) as well as to the polyclonal hAELVi cell line. "Arlo" cells show enhanced barrier properties with high transepithelial electrical resistance (TEER) of ≈3000 Ω cm2 and a potential difference (PD) of ≈30 mV under air-liquid interface (ALI) conditions, that can be modulated. The cells grow in a polarized monolayer and express genes relevant to barrier integrity as well as homeostasis as is observed in hAEpCs. Successful productive infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a proof-of-principle study offers an additional, attractive application of "Arlo" beyond biopharmaceutical experimentation.