I-cultured mixed populations resemble more closely cocultured BMSCs. Also, stimulation of mixed monocultures with IL-1 and IL-6 resulted in changes 3-Bromo-5-chloro-2-fluoroaniline in gene expression of collagens which were similar to the changes for BMSC monocultures. This PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/14960617 observation is in contrast to other studies which report anabolic effects of cocultured chondrocytes on BMSCs with respect to biomechanical properties, collagen, and GAG production [15,16]. On the other hand, Giovanni and colleagues [17] report that influence of cocultured chondrocytes was restricted to early signs of neochondrogenesis and did not prevent hypertrophy of BMSCs. We thus suggest that chondrocytes in the mixed cultures do not seriously alter BMSC metabolism in tri-cultures with cartilage explants and that response of mixed cultures to cartilage explants resembles that of cocultured BMSCs rather than that of cocultured chondrocytes.differentiation of undifferentiated BMSCs and formation of a stable and mechanical stress-resistant ECM. This observation will have an impact on future therapeutic strategies to halt or even reverse OA progression. In consequence, microenvironmental factors from surrounding cartilage tissue need to be taken into serious consideration when trying to implement novel OA treatment strategies (that is, implanting cells into lesions and fissures prevalent in late stages of OA cartilage).Additional filesAdditional file 1: Figure S1. Vitality and percentage of proliferating cell nuclear antigen (PCNA)-positive cells of fibrin gel-embedded monocultures and coculture setups. Vitality of (A) bone marrow-derived stem cell (BMSCs), (B) mixed cultures (BMSCs and chondrocytes in a ratio of 1:1), and (C) chondrocytes was determined in monocultures (F) and cocultures with articular PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/10572343 osteoarthritis (OA) cartilage (FC) kept in chondrogenic medium. Content of lactate dehydrogenase (LDH) was quantified in the supernatant of days 7, 14, 21, and 28 and compared with controls (high control = all cells in a fibrin gel were lysed; low control = spontaneous cell death of an equivalent cell amount in monolayer). Owing to high inter-experimental variability, we have calculated the raw data as percentage of control per individual experiment. (D) Mitotic activity of BMSCs (white bars), mixed cultures (light grey bars), and chondrocytes (dark grey bars) was determined in monocultures (F) and cocultures with articular OA cartilage (FC) kept in chondrogenic medium. PCNA-positive stained cell nuclei were counted at days 7 and 28, and percentage of positive cells to total cell number was calculated. Results are presented as mean with standard deviation. *P ijms17122034 three-dimensional; BMSC: bone marrow-derived stem cell; COL10A1: collagen X A1 (gene); Ethyl 5-bromo-6-chloropicolinate COL1A1: collagen I A1 (gene); COL2A1: collagen II A1 (gene); COL3A1: collagen III A1 (gene); DMMB: dimethylmethylene blue; E.