Culture Conditions that Support Expansion and Chondrogenesis of Middle-Aged Rat Mesenchymal Stem Cells.

Objective: Rats are an early preclinical model for cartilage tissue engineering, and a practical species for investigating the effects of aging. However, rats may be a poor aging model for mesenchymal stem cells (MSCs) based on laboratory reports of a severe decline in chondrogenesis beyond young adulthood. Such testing has not been conducted with MSCs seeded in a scaffold, which can improve the propensity of MSCs to undergo chondrogenesis. Therefore, the objective of this study was to evaluate chondrogenesis of middle-aged rat MSCs encapsulated in agarose.

Design: MSCs from 14- to 15-month-old rats were expanded, seeded into agarose, and cultured in chondrogenic medium with or without 5% serum for 15 days. Samples were evaluated for cell viability and cartilaginous extracellular matrix (ECM) accumulation. Experiments were repeated using MSCs from 6-week-old rats.

Results: During expansion, middle-aged rat MSCs demonstrated a diminishing proliferation rate that was improved ~2-fold in part by transient exposure to chondrogenic medium. In agarose culture in defined medium, middle-aged rat MSCs accumulated ECM to a much greater extent than negative controls. Serum supplementation improved cell survival ~2-fold, and increased ECM accumulation ~3-fold. Histological analysis indicated that defined medium supported chondrogenesis in a subset of cells, while serum-supplementation increased the frequency of chondrogenic cells. In contrast, young rat MSCs experienced robust chondrogenesis in defined medium that was not improved with serum-supplementation.

Conclusions: These data demonstrate a previously-unreported propensity of middle-aged rat MSCs to undergo chondrogenesis, and the potential of serum to enhance chondrogenesis of aging MSCs.