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Abstract Background Mesenchymal stem cells (MSCs) are adult stem cells with self-renewal and multi-directional differentiation potential and possess the functions of immunomodulation, regulation of cell growth, and repair of damage. Over recent years, MSCs have been found to regulate the secretion of inflammatory factors and to exert regulatory effects on various lymphocytes in inflammatory states, and on the subsequent repair of tissue damage caused by inflammation. In the present study, we analyzed the effects of tissue inflammation on the characteristics of MSCs. Methods Human fat derived from the infrapatellar fat pad (IPFP) of knees with differing degrees of inflammation was extracted from specimens derived from total knee arthroplasties. HE and immunohistochemical staining was performed to directly observe the evidence and degree of inflammation in human infrapatellar fat pad tissue in order to classify MSCs cells, by their origin, into highly inflamed and lowly inflamed groups, and to study the effect of tissue inflammation on cell acquisition rates via cellular counting data. Flow cytometry assays were performed to investigate the effect of tissue inflammation on MSC surface marker expression. Trilineage differentiation, including osteogenesis, adipogenesis, and chondrogenesis, was performed to assess the effect of tissue inflammation on the ability of MSCs to undergo directed differentiation. The effect of tissue inflammation on the ability of MSCs to proliferate was investigated via clone formation studies. RNA-sequencing was performed to evaluate the transcriptomes of MSCs derived from different areas of inflammation. The effect of tissue inflammation on tissue repair capacity and safety of MSCs was investigated via a murine model of acute liver injury. Results The results of cell count data indicate that a high degree of tissue inflammation significantly decreases the acquisition rate of MSCs, and the proportion of CD34+ and CD146+ cells. The results of our trilineage differentiation assay show that a higher degree of inflammation decreases osteogenic differentiation and enhances adipogenic and chondrogenic differentiation of MSCs. However, these differences were not statistically significant. Clone formation assays indicate that the degree of tissue inflammation at the MSC source does not significantly affect the proliferative capacity of MSCs. The transcriptomes of MSCs remain relatively stable in fat pad tissues derived from both highly and lowly inflamed samples. The results of acute liver injury investigations in mice indicate that MSCs of high and low inflammatory tissue origin have no significant difference in their tissue repair capability. Conclusions High tissue inflammation at the source of MSCs reduces the acquisition rate of MSCs and the percentage of CD34+ and CD146+ cells acquisition. However, source tissue inflammation may not significantly affect trilineage differentiation potential and proliferative capacity of MSCs. Also, MSCs obtained from differing source degrees of inflammation retain stable and similar transcriptomic profile and are both safe and efficacious for tissue repair/regeneration without detectable differences. Graphical Abstract

Background: Cell source plays a key role in cell-based cartilage repair and regeneration. Recent efforts in cell coculture have attempted to combine the advantages and negate the drawbacks of the constituent cell types. The aim of this study was to evaluate the chondrogenic outcome of articular chondrocytes (ACs) and infrapatellar fat pad (IPFP)- derived mesenchymal stem cells (MSCs) in direct coculture. Methods: ACs and IPFP MSCs from the same patients with knee osteoarthritis (OA) were cocultured in monolayer and in pellets. The monocultures of each cell type were also used as controls. Morphological and histologic analysis, immunofluorescence staining, reverse transcription-polymerase chain reaction, and enzyme-linked immunosorbent assay were performed to characterize the chondrogenic differentiation of cocultures. Furthermore, the effects of chitosan/hyaluronic acid (CS/HA) nanoparticle exposure on the chondrogenesis of cocultures were examined. Results: In both monolayer and pellet coculture, the hypertrophy of MSCs and the inflammatory activities of ACs were inhibited, although the chondrogenic production in coculture was not promoted compared with that in monoculture. In addition, the exposure of CS/HA nanoparticles to pellet coculture improved the production of type II collagen and aggrecan. Conclusions: We demonstrate for the first time that pellet coculture of ACs and IPFP MSCs with CS/HA nanoparticles could promote chondrogenic outcome while preventing the inflammatory status of ACs and the hypertrophic differentiation of MSCs. These findings suggest that the combination of ACs, IPFP MSCs, and CS/HA might be useful in cartilage repair in knee OA. [ABSTRACT FROM AUTHOR]