Physiological and clinically attainable concentrations of 1,25-dihydroxyvitamin D3 suppress proliferation and extracellular matrix protein expression in mouse pancreatic stellate cells.

Abstract

Vitamin D is an antiproliferative and differentiation-promoting secosteroid hormone with pleiotropic homeostatic functions in bone and extraskeletal tissues. Signaling of vitamin D is mediated via its ubiquitously expressed nuclear receptor, the vitamin D receptor (VDR). Pancreatic stellate cells have recently been identified as targets of vitamin D action. Our aim was to elucidate the effectiveness of the most potent endogenous vitamin D metabolite, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the proliferation and extracellular matrix (ECM) protein expression in pancreatic stellate cells (PSCs) using concentrations of the compound from the physiological and clinically attainable range in humans. Culture-activated mouse PSCs were exposed to 1,25(OH)2D3 concentrations ranging from 0.1nM to 10nM for 7 days and subjected to colorimetric crystal violet assay for cell growth assessment and to Western blot and immunohistochemical analyses of VDR, fibronectin and collagen I using protein-specific antibodies. Immunohistochemical localization of VDR was performed on mouse pancreatic tissue and on a set of human specimens obtained at pancreatic surgery. A low basal level of VDR was detected in PSCs that was strongly induced in the presence of ligand. Cell growth was suppressed dose-dependently by 1,25(OH)2D3, the mean percentages of inhibition ranging from 24% at the physiological 0.1nM concentration to around 60% at 10nM. Significant 48% and 40% reductions in fibronectin expression were seen at 0.5nM and 1nM 1,25(OH)2D3. A minor decrease in collagen I expression was detected at 5nM. VDR was predominantly localized in the islets of Langerhans in mouse and human tissues. In the latter VDR was expressed also in the exocrine tissue showing individual variation in its cellular distribution. Mouse PSCs express VDR protein and are sensitive 1,25(OH)2D3 target cells with low levels of 1,25(OH)2D3 exerting antiproliferative and antifibrotic effects on activated PSCs invitro.