Differentiation of stem cells from human infrapatellar fat pad: characterization of cells undergoing chondrogenesis.

Hyaline cartilage repair is a significant challenge in orthopedics and current techniques result in formation of fibrocartilage. Human infrapatellar fat pad (hIPFP)-derived mesenchymal stem cells (MSCs) are capable of differentiation into multiple tissue lineages, including cartilage and bone. Chondrogenesis is a crucial part of normal skeletal development but the molecular mechanisms are yet to be completely defined. In this study we sourced hIPFP-derived MSCs utilizing chondrogenic growth factors, transforming growth factor beta-3, and bone morphogenetic protein-6, to form hyaline-like cartilage in micromass cultures and we studied chondrogenic development of 7, 14, and 28 days. The purpose of this study was (1) to characterize chondrogenesis from MSCs derived from hIPFP tissue by conventional techniques and (2) to characterize temporal changes of key molecular components during chondrogenesis using microarray gene expression. Endpoints included histology, immunohistochemistry (IHC), gene expression profiles using a microarray technique, and changes in expression of specific genes using quantitative real-time polymerase chain reaction. Over 14-28 days, clusters of encapsulated chondrocytes formed surrounded by collagen type II and aggrecan in the extracellular matrix (ECM). Collagen type II and aggrecan production was confirmed using IHC and chondrogenic lineage markers were studied; SRY-related transcription factor (SOX9), collagen type II alpha 1 (COL2A1), and aggrecan gene expression increased significantly over the time course. Normalized microarray highlighted 608 differentially expressed genes; 10 chondrogenic genes were upregulated (2- to 87-fold), including COL2A1, COL10A1, COL9A1, COL11A1, COL9A2, COL11A2, COL1A1, COMP, SOX9, and COL3A1. We found that the upregulated genes (twofold or greater) represent significant level of expression (enrichment score) for the ECM structural constituent of the molecular functional at days 7, 14, and 28 during chondrogenesis. Therefore, we have successfully demonstrated in vitro production of hyaline-like cartilage from IPFP-derived MSCs in micromass culture. Microarray has provided information concerning genes involved in chondrogenesis of hIPFP-derived MSCs and our approach offers a viable strategy for generating clinically relevant cartilage for therapeutic use.