Foot Fat Pad: Characterization by Mesenchymal Stromal Cells in Rats.

Foot fat pad (FFP) is a highly functionalized fat depot in the foot, of great significance in weight-bearing. Mesenchymal stromal cells (MSCs) in subcutaneous adipose tissues are widely studied for regenerative potentials. MSCs in FFP, which may contribute to the physiological and pathological conditions of the foot, have not been characterized. In this study, MSCs were isolated from FFP (designated as MSCs-ffp) and subcutaneous adipose tissue (designated as MSCs-sub) from rats. The cell surface markers, proliferation and efficiency of colony formation were compared between MSCs-ffp and MSCs-sub. In addition, MSCs-ffp were induced for osteogenic, chondrogenic and adipogenic differentiation. The tri-lineage differentiation potentials were compared between MSCs-ffp and MSCs-sub by the expression of Runx2, Sox9 and PPAR-γ, respectively, using quantitative polymerized chain reaction (qPCR). The expression of elastin and associated genes by MSCs-ffp were also evaluated. MSCs-ffp, like MSCs-sub, expressed CD44, CD73 and CD90. MSCs-ffp and MSCs-sub proliferated at similar rates but MSCs-ffp formed more colonies than MSCs-sub. MSCs-ffp were capable of differentiating into osteogenic, chondrogenic and adipogenic lineages. Under the conditions of osteogenic and adipogenic differentiation, MSCs-sub expressed more Runx2 and PPAR-γ, respectively, than MSCs-ffp. The undifferentiated MSCs-ffp up-regulated the expression of fibulin-5. In conclusion, MSCs-ffp shared common biology with MSCs-sub but were more efficient in colony formation, less adipogenic and osteogenic, and participated in elastogenesis. The unique features of MSCs-ffp may relate to their roles in the physiological functions of FFP.