MEF2D and type 2 diabetes mellitus: Bacteroides fragilis EVs, while promoting M2 polarization via Sting-Sgpl1-Sema7a signaling under certain conditions, paradoxically exacerbate vascular calcification in type 2 diabetes through stimulator of interferon response cGAMP interactor 1 (Sting)-mediated phosphorylation of myocyte enhancer factor 2D (Mef2d) and subsequent upregulation of serpin family E member 1 (Serpine1).190