Biological potential alterations of migratory chondrogenic progenitor cells during knee osteoarthritic progression

Although increasing studies have demonstrated that chondrogenic progenitor cells (CPCs) remain present in human osteoarthritic cartilage, the biological alterations of the CPCs from the less diseased lateral tibial condyle and the more diseased medial condyle of same patient remain to be investigated.

CPCs were isolated from paired grade 1-2 and grade 3-4 osteoarthritic cartilage by virtue of cell migratory capacities. The cell morphology, immunophenotype, self-renewal, multi-differentiation, and cell migration of these CPCs were evaluated. Additionally, the distributions of CD105⁺/CD271⁺ cells in OA osteochondral specimen were determined. Furthermore, a high-throughput mRNA sequencing was performed.

Migratory CPCs (mCPCs) robustly outgrew from mildly collagenases-digested osteoarthritic cartilages. The mCPCs from grade 3-4 cartilages (mCPCs, grades 3-4) harbored morphological characteristics, cell proliferation, and colony formation capacity that were similar to those of the mCPCs from the grade 1-2 OA cartilages (mCPCs, grades 1-2). However, the mCPCs (grades 3-4) highly expressed CD271. In addition, the mCPCs (grades 3-4) showed enhanced osteo-adipogenic activities and decreased chondrogenic capacity. Furthermore, the mCPCs (grades 3-4) exhibited stronger cell migration in response to osteoarthritis synovial fluids. More CD105⁺/CD271⁺ cells resided in grade 3-4 articular cartilages. Moreover, the results of mRNA sequencing showed that mCPCs (grades 3-4) expressed higher migratory molecules.

Our data suggest that more mCPCs (grades 3-4) migrate to injured articular cartilages but with enhanced osteo-adipogenic and decreased chondrogenic capacity, which might explain the pathological changes of mCPCs during the progression of OA from early to late stages. Thus, these dysfunctional mCPCs might be optional cell targets for OA therapies.