Vitamin D Attenuates Hepatic Sinusoidal Capillarization in Type 2 Diabetes Mellitus– Metabolic Dysfunction-Associated Fatty Liver Disease via Dual Autophagy Activation and Pyroptosis Suppression in Liver Sinusoidal Endothelial Cells

<b>Background/Objectives:</b> Metabolic dysfunction-associated fatty liver disease (MAFLD) is closely associated with type 2 diabetes mellitus (T2DM), where T2DM serves as a crucial driving factor for MAFLD progression. While vitamin D (VD) demonstrates protective effects against MAFLD, the underlying mechanisms through which it influences MAFLD-related liver sinusoidal endothelial cell (LSEC) capillarization remain to be elucidated. This study aimed to explore how vitamin D ameliorates LSEC capillarization in T2DM-associated MAFLD. <b>Methods:</b> Culture human liver sinusoidal endothelial cells (HLSECs) according to the established protocol. After 1,25(OH)₂D₃ intervention in high glucose (HG)-induced HLSECs, determine the changes in liver sinusoidal capillarization-related proteins (LN, PLVAP), autophagy and pyroptosis levels. Observe the changes in cell lipid accumulation and fenestration structures. After adding Bafilomycin A1, MCC950, compound C and rapamycin to HLSECs, explore the therapeutic mechanism of 1,25(OH)₂D₃. After supplementing VD to MAFLD model mice, further verify the therapeutic mechanism of VD on MAFLD. <b>Results:</b> HG can induce the capillarization and lipid accumulation of HLSEC, increase the level of pyroptosis, and simultaneously reduce the autophagy level. Vitamin D alleviated high-glucose-induced pyroptosis (by suppressing GSDMD/NLRP3) and autophagic inhibition by activating the AMPK-mTOR axis (upregulating p-AMPK and downregulating mTOR), and improved lipid accumulation and hepatic sinusoidal capillarization. In the mouse model of MAFLD, VD supplementation can induce autophagy, inhibit pyroptosis and capillarization, and improve MAFLD. <b>Conclusions:</b> These results demonstrate, for the first time, that VD mitigates LSEC dysfunction through dual mechanisms: activating AMPK-dependent autophagy and inhibiting pyroptosis, providing a therapeutic rationale for VD in treating MAFLD-related sinusoidal pathology.