Plasticity of clonal populations of dedifferentiated adult human articular chondrocytes

TLDR

The study aims to determine whether dedifferentiated adult human articular chondrocytes can differentiate into multiple mesenchymal lineages and how growth factors during monolayer expansion influence this plasticity, with the goal of identifying subpopulations that may enhance cartilage repair. Researchers expanded AHACs as multiclonal or clonal populations in control or TGF‑β1/FGF‑2/PDGF‑BB–supplemented medium, then induced chondrogenic, osteogenic, or adipogenic differentiation and evaluated the resulting phenotypes by histology, biochemistry, and RT‑PCR. Multiclonal AHACs differentiated into chondrogenic, osteogenic, and adipogenic lineages, while TGF‑β1/FGF‑2/PDGF‑BB treatment amplified chondrogenic and osteogenic potential and suppressed adipogenesis; clonal cultures expanded only with these factors, with most clones redifferentiating solely to chondrocytes, yet a minority displayed multipotency, demonstrating that dedifferentiated AHAC plasticity is growth‑factor‑dependent and highly heterogeneous among clones.

Abstract

Abstract Objective To investigate whether adult human articular chondrocytes (AHACs), dedifferentiated by monolayer expansion, can differentiate toward diverse mesenchymal lineages and, if so, whether this ability is regulated by growth factors during monolayer expansion. Methods AHACs were expanded as multiclonal or clonal populations in medium without (control) or with factors enhancing cell dedifferentiation (transforming growth factor β1, fibroblast growth factor 2, and platelet‐derived growth factor type BB [TFP]). Cells were then cultured under conditions promoting chondrogenic, osteogenic, or adipogenic differentiation, and the acquired phenotypes were assessed histologically, biochemically, and by real‐time reverse transcriptase–polymerase chain reaction. Results Multiclonal populations of both control‐ and TFP‐expanded AHACs differentiated toward the chondrogenic, osteogenic, and adipogenic lineages. Compared with control‐expanded AHACs, TFP‐expanded cells displayed enhanced chondrogenic differentiation capacity (2.4‐fold higher glycosaminoglycan/DNA content and 2,500‐fold higher up‐regulation of type II collagen) and osteogenic differentiation capacity (9.4‐fold higher increase in alkaline phosphatase activity and 12.4‐fold higher up‐regulation of bone sialoprotein), but reduced formation of adipocytes (5.2‐fold lower oil red O–positive cells/area). Clonal populations of AHACs could be efficiently expanded in TFP, but not in control medium. Most TFP‐expanded clones were able to redifferentiate only into chondrocytes (7 of 20) or were unable to differentiate (6 of 20). However, some clones (2 of 20) differentiated toward all of the lineages investigated, thus displaying characteristics of mesenchymal progenitor cells. Conclusion Dedifferentiated AHACs exhibit differentiation plasticity, which is modulated by growth factors used during monolayer expansion and is highly heterogeneous across different clones. Clonal culture of AHACs in the presence of regulatory molecules could lead to the identification of AHAC subpopulations with enhanced cartilage repair capacity.