Calcitriol modifies tight junctions, improves barrier function, and reduces TNF‐α‐induced barrier leak in the human lung‐derived epithelial cell culture model, 16HBE 14o

• Published in: Physiological reports Vol. 11; no. 7; pp. e15592 - n/a
• Main Authors: Rybakovsky, Elizabeth, DiGuilio, Katherine M., Valenzano, Mary Carmen, Geagan, Sophie, Pham, Kaithlyn, Harty, Ronald N., Mullin, James M.
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 01-04-2023; John Wiley and Sons Inc; Wiley
• Subjects: 25-Hydroxyvitamin D; Calcitriol; Calcitriol - metabolism; Calcitriol - pharmacology; Caspase-3; Cell culture; Cell death; claudin; Claudin-2 - metabolism; Coronaviruses; COVID-19; COVID-19 - metabolism; Electrical resistivity; Epithelial cells; Epithelial Cells - metabolism; ERK; Humans; Infections; Infectious diseases; lung; Lung - metabolism; Mannitol; MAP kinase; micronutrient; Microorganisms; Original; Phosphatase; Physiology; Respiratory tract diseases; Retinoic acid; Severe acute respiratory syndrome coronavirus 2; Sharpe‐Strumia Research Foundation; tight junction; Tight junctions; Tight Junctions - metabolism; tumor necrosis factor; Tumor Necrosis Factor-alpha - metabolism; Tumor Necrosis Factor-alpha - pharmacology; Tumor necrosis factor-α; Vitamin A; Vitamin D; Vitamin deficiency; lung; tumor necrosis factor; calcitriol; micronutrient; Sharpe-Strumia Research Foundation; claudin; tight junction; ERK
• ISSN: 2051-817X
• DOI: 10.14814/phy2.15592

Using the 16HBE 14o‐ human airway epithelial cell culture model, calcitriol (Vitamin D) was shown to improve barrier function by two independent metrics – increased transepithelial electrical resistance (TER) and reduced transepithelial diffusion of 14C‐D‐mannitol (Jm). Both effects were concentration dependent and active out to 168 h post‐treatment. Barrier improvement associated with changes in the abundance of specific tight junctional (TJ) proteins in detergent‐soluble fractions, most notably decreased claudin‐2. TNF‐α‐induced compromise of barrier function could be attenuated by calcitriol with a concentration dependence similar to that observed for improvement of control barrier function. TNF‐α‐induced increases in claudin‐2 were partially reversed by calcitriol. The ERK 1,2 inhibitor, U0126, itself improved 16HBE barrier function indicating MAPK pathway regulation of 16HBE barrier function. Calcitriol's action was additive to the effect of U0126 in reducing TNF‐ α ‐induced barrier compromise, suggesting that calcitriol may be acting through a non‐ERK pathway in its blunting of TNF‐ α – induced barrier compromise. This was supported by calcitriol being without effect on pERK levels elevated by the action of TNF‐α. Lack of effect of TNF‐ α on the death marker, caspase‐3, and the inability of calcitriol to decrease the elevated LC3B II level caused by TNF‐α, suggest that calcitriol's barrier improvement does not involve a cell death pathway. Calcitriol's improvement of control barrier function was not additive to barrier improvement induced by retinoic acid (Vitamin A). Calcitriol improvement and protection of airway barrier function could in part explain Vitamin D's reported clinical efficacy in COVID‐19 and other airway diseases.
Vitamin D utility in COVID‐19 infection may be due in part to improvement of airway epithelial barrier function and support of airway epithelial barrier function in "cytokine storm" situations. Remodeling of tight junctions is part of this process. Although the ERK‐1,2 pathway is involved in regulation of airway barrier function, Vitamin D is seemingly acting through a non‐ERK‐1,2 pathway to achieve its epithelial barrier support here.