Study on the relationship between vitamin D level and macrophage typing in patients with type 2 diabetes mellitus

Objective Population studies have shown that vitamin D (VitD) deficiency is associated with an increased incidence of type 2 diabetes mellitus (T2DM), VitD deficiency is a potential risk factor for T2DM, and the proportion of M1-type macrophages and M2-type macrophages in T2DM patients is imbalanced. Another study reported that VitD can affect the differentiation of macrophages into M1 and M2 types. However, there is no definitive result about the correlation between plasma VitD levels and macrophage typing in patients with T2DM. Whether VitD affects the progression of T2DM by regulating the polarization type of macrophages and the specific regulatory mechanism is not very clear. Therefore, we carried out the following research. Methods We first used flow cytometry to detect the proportions of M1 and M2 macrophages in peripheral blood of T2DM patients with different VitD levels. Furthermore, we used ELISA to detect the inflammatory factors affecting macrophage differentiation in patients' plasma, including IL-6 secreted by M1-type macrophages and TGF-beta secreted by M2-type macrophages. Mononuclear cells were separated from human peripheral blood with immunomagnetic beads, cultured in vitro, and treated with different concentrations of VitD, and the ratio of differentiation into M1 and M2 macrophages was detected by flow cytometry. Results With the increase of serum 25(OH)D levels in patients with T2DM, the proportion of M1 and M2 macrophages in peripheral blood decreased, that is, the polarized phenotype of macrophages was more inclined to M2 type, while plasma IL-6 gradually decreased, and TGF-beta gradually increased. In addition, VitD can promote the differentiation of CD14-positive monocytes cultured in vitro into M2 macrophages. Conclusions When the level of VitD in T2DM patients is low, there are more M1-type macrophages in peripheral blood, and when the level of VitD is increased, M2-type macrophages are increased. Changes in related inflammatory factors were also consistent. In vitro culture of monocytes further confirmed that VitD can promote the differentiation of macrophages to M2 type in T2DM patients.