Impaired Vitamin D metabolism with low IL-6 and CCL-2 responsiveness to in-vitro Vitamin D treatment in autoimmune polyglandular syndrome type 2 (APS-2)

Introduction:

VD deficiency is associated with several endocrine autoimmune diseases including type 1 diabetes (T1D). Here we reasoned whether VD regulated immune markers like pro-inflammatory cytokine IL-6 and monocyte chemokine ligand 2 (CCL-2) are altered in high inflammatory T1D patients with multiple autoimmune disorders known as autoimmune-polyglandular syndrome type 2 (APS-2).

Methods:

CD14⁺ monocytes from APS-2 patients (T1D + autoimmune thyroiditis (n = 13)) and healthy controls (HC; n = 30) were cultured with VD +/- IL1β stimulation. Gene expression for VD metabolism (VD receptor (VDR) and 24-hydroxylase (CYP24A1)) and pro-inflammatory IL-6 and CCL-2 were analyzed using quantitative real-time PCR normalized to endogenous reference 18sRNA.

Results:

mRNA expression of VDR was reduced under VD treatment and correlated negatively with VD-induced CYP24A1 in patients and HC (r =-0.36, p = 0.02). However, VD-treated monocytes revealed impaired VD-metabolism, as shown by decreased CYP24A1 mRNA in APS-2 (p < 0.007). IL1β-induced IL-6 and CCL-2 were both inhibited through VD in APS-2 and HC respectively (IL-6_APS-2 p < 3 × 10^-3 and CCL-2_APS-2 p < 5 × 10^-4; IL-6_Co p < 10^-7 and CCL-2_Co p < 10^-7). VD-mediated IL-6 and CCL-2 reduction was less pronounced in APS-2 patients (IL6: p < 0.05; CCL-2: p = 0.005). Furthermore, basal CCL-2 expression was increased in APS-2 (p = 0.01).

Conclusion:

Induction of CYP24A1 and negative feedback regulation of VDR identify a normal paracrine regulation. However, poor CYP24A1 induction in APS-2 patients points to an impaired VD metabolism. Pro-inflammatory IL-6 and CCL-2 are less responsive to VD treatment in APS-2 patients, indicating a pro-inflammatory status. Basal raised CCL-2 suggests elevated monocyte chemotactic and potentially increased leukocyte tissue infiltration in APS-2 patients.