1,25-Dihydroxyvitamin D Enhances the Regenerative Function of Lgr5+ Intestinal Stem Cells In Vitro and In Vivo

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder in the intestines without a cure. Current therapies suppress inflammation to prevent further intestinal damage. However, healing already damaged intestinal epithelia is still an unmet medical need. Under physiological conditions, Lgr5⁺ intestinal stem cells (ISCs) in the intestinal crypts replenish the epithelia every 3-5 days. Therefore, understanding the regulation of Lgr5⁺ ISCs is essential. Previous data suggest vitamin D signaling is essential to maintain normal Lgr5⁺ ISC function in vivo. Our recent data indicate that to execute its functions in the intestines optimally, 1,25(OH)₂D requires high concentrations that, if present systemically, can cause hypercalcemia (i.e., blood calcium levels significantly higher than physiological levels), leading to severe consequences. Using 5-bromo-2'-deoxyuridine (BrdU) to label the actively proliferating ISCs, our previous data suggested that de novo synthesized locally high 1,25(OH)₂D concentrations effectively enhanced the migration and differentiation of ISCs without causing hypercalcemia. However, although sparse in the crypts, other proliferating cells other than Lgr5⁺ ISCs could also be labeled with BrdU. This current study used high-purity Lgr5⁺ ISC lines and a mouse strain, in which Lgr5⁺ ISCs and their progeny could be specifically tracked, to investigate the effects of de novo synthesized locally high 1,25(OH)₂D concentrations on Lgr5⁺ ISC function. Our data showed that 1,25(OH)₂D at concentrations significantly higher than physiological levels augmented Lgr5⁺ ISC differentiation in vitro. In vivo, de novo synthesized locally high 1,25(OH)₂D concentrations significantly elevated local 1α-hydroxylase expression, robustly suppressed experimental colitis, and promoted Lgr5⁺ ISC differentiation. For the first time, this study definitively demonstrated 1,25(OH)₂D's role in Lgr5⁺ ISCs, underpinning 1,25(OH)₂D's promise in IBD therapy.