Megalin mediates 25-hydroxyvitamin D₃ actions in human mesenchymal stem cells

Area of Science:

• Biochemistry
• Cell Biology
• Endocrinology

Background:

• Human mesenchymal stem cells (hMSCs) differentiate into osteoblasts, a process influenced by vitamin D metabolites.
• 1α,25-dihydroxycholecalciferol [1α,25(OH)2D3] and 25-hydroxycholecalciferol [25(OH)D3] stimulate osteoblast differentiation.
• Megalin, a receptor for the 25(OH)D3-DBP complex, is known in kidney cells but its role in hMSCs is unclear.

Purpose of the Study:

• To investigate the role of megalin in mediating vitamin D actions in hMSCs.
• To determine if megalin is required for 25(OH)D3 and 1α,25(OH)2D3 stimulated osteoblastogenesis.
• To assess megalin's involvement in 1α,25(OH)2D3 biosynthesis within hMSCs.

Main Methods:

• RT-PCR analysis of megalin expression in hMSCs.
• Treatment of hMSCs with 25(OH)D3 and 1α,25(OH)2D3.
• Utilizing small interfering RNA (si-Meg) to knockdown megalin expression.
• Measuring osteoblastogenesis and 1α,25(OH)2D3 biosynthesis.
• Investigating the effect of leptin on megalin expression.

Main Results:

• hMSCs express megalin, which is essential for 25(OH)D3 to stimulate osteoblastogenesis.
• Megalin deficiency (low expression or si-Meg) reduced 1α,25(OH)2D3 biosynthesis.
• 1α,25(OH)2D3 stimulated osteoblastogenesis more effectively than 25(OH)D3 in megalin-deficient cells.
• Leptin significantly increased megalin expression in hMSCs with low megalin.

Conclusions:

• Megalin is expressed in hMSCs and plays a critical role in mediating vitamin D actions.
• Megalin is required for the uptake of the 25(OH)D3-DBP complex and subsequent stimulation of vitamin D receptor targets.
• Megalin is essential for efficient 1α,25(OH)2D3 biosynthesis and osteoblastogenesis in hMSCs.