286 OSTEOGENIC DIFFERENTIATION IN VITRO OF PORCINE ADULT MESENCHYMAL STEM CELLS

Abstract

The quantity and accessibility of subcutaneous adipose tissue in humans make it an attractive alternative to bone marrow as a source of adult stem cells for therapeutic purposes. However, before such a cell source substitution can be proposed, the properties of stem cells derived from adipose (ADSCs) and bone marrow (MSCs) and their differentiated progeny must be compared in an animal model that adequately simulates the structure and physiology of humans. The objective of this work was to induce adult porcine stem cells isolated from subcutaneous adipose tissue and bone marrow to differentiate in vitro along the osteoblastic lineage and to compare their morphological, phenotypic, and genotypic properties. MSCs and ADSCs were isolated respectively from femurs and subcutaneous adipose tissue of adult pigs and cultured in vitro using DMEM supplemented with 10% fetal bovine serum (FBS), 1% penicillin G-streptomycin, and 5.6 mg L^–1 amphotericin B. After 3 passages, cells were differentiated along the osteogenic lineage using lineage-specific inducing medium. Osteogenic medium contained 100 nm dexamethasone, 10 mm β-glycerophosphate, and 0.005 mm ascorbic acid-2-phosphate. Osteogenic cultures were incubated for 4 weeks in 95% air and 5% CO₂ at 39°C. Spent medium was replaced with fresh medium every 3 days. Histological staining with alkaline phosphatase, Von Kossa, and alizarin red S were performed at 0, 2, 4, 7, 14, 21, and 28 days of differentiation (dd). At the same time points, RNA was extracted. qPCR was performed on COL1A1, BGLAP, SPARC, and SPP1. As internal control, the geometrical mean of GTF2H, NUBP, and PPP2C was used. Relative mRNA abundance between cell types was calculated using 1/efficiency^dCT. The osteogenic differentiation of both MSCs and ADScs was confirmed by the organization of the cells in nodules and by alkaline phosphatase-, Von Kossa-, and alizarin red S-positive staining. The percent relative abundance of the 4 genes in both cell types was COL1A1 (ca. 50) > SPARC (ca. 45) > SPP1 (ca. 5) > BGLAP ( < 0.1). Cell types showed similar mRNA abundance for COL1A1 and SPARC while SPP1 and BGLAP were, respectively, 10- and 19-fold higher in MSCs than in ADSCs. All of the genes had the same pattern among tissues during differentiation except for SPP1, which showed a >10-fold increase at 14 v. 0 dd only for MSCs. Adipose-derived stem cells demonstrated a clear osteogenic differentiation and similar expression and pattern of the two osteogenic genes most abundant in MSCs (COL1A1 and SPARC). However, the higher abundance of SPP1 and BGLAP and the different behavior of SPP1 in MSCs suggest a different transcription profile between the two cell types. From these preliminary results, adipose tissue can be a practical alternative source for stem cells in future human clinical applications.