The role of Pdia3-dependent 1α,25-dihydroxy vitamin D3 signaling on IgE-mediated mast cell activation

Active 1,25(OH)2 Vitamin D3 (1,25D3) is most commonly known for its role in the regulation of bone metabolism. However, research has now indicated it is a potent immune regulator beyond its calcemic effects. Vitamin D deficiency has been implicated in the pathogenesis of allergic diseases including asthma and atopic dermatitis. 1,25D3 is known to signal through the canonical Vitamin D receptor (VDR) facilitating its anti-inflammatory properties and regulating over 100 genes. However, protein disulfide isomerase family A, member 3 (Pdia3), was recently shown to mediate rapid-membrane responses to 1,25D3. In this study, we show that upon IgE-mediated activation, VDR knockout mast cells display enhanced cytokine production. Additionally, 1,25D3 suppresses cytokine production independently of VDR supporting the possibility of an alternative receptor facilitating the suppressive properties of Vitamin D on mast cells. Pdia3 protein and mRNA levels were upregulated in response to 1,25D3 in both WT and VDR KO mast cells. Upon blocking Pdia3 signaling, VDR KO mast cells lost their suppressive response to Vitamin D. Prostaglandin E 2 , which is released during Pdia3-dependent 1,25D3 signaling, mimicked Vitamin D effects on WT and VDR KO mast cells. Suppressor of Cytokine Signaling 3 (SOCS3), which is known to be upregulated by PGE 2 , was induced by 1,25D3 in both WT and VDR KO mast cells. Interestingly, VDR KO mast cells showed an enhanced induction of SOCS3 in comparison to WT. Collectively, our data depict a novel signaling mechanism utilized by mast cells to respond to 1,25D3 that could be explored as a potential therapeutic target for the treatment of allergic and inflammatory diseases.