Vit D effect on αVβ3 clustering is enhanced on FN-coated surfaces. Confocal images showing the expression of integrin αVβ3 (green) after 7 days of osteogenic differentiation. (a-b) show the integrin distribution in cells cultured on PLL coating (CTR); in the case of untreated cells (vehicle (VHC)), αVβ3 appeared to be present homogeneously in the whole cell, while Vit D treatment induced an accumulation of the receptor in the focal contacts (b–d). αVβ3 clustering was increased on FN coating (c-d), more evident in Vit D treatment (d) compared to the VHC (c). Blue for nuclei and green for αVβ3. The table shows the FA quantification performed with ImageJ software.