Human mesenchymal stem cells (hMSCs) are considered a highly promising candidate cell type for cell-based tissue engineering and regeneration because of their self-renewal and multi-lineage differentiation characteristics. Increased levels of reactive oxygen/nitrogen species (ROS/RNS) are associated with tissue injury and inflammation, impact a number of cellular processes, including cell adhesion, migration, and proliferation, and have been linked to cellular senescence in MSCs, potentially compromising their activities. Naturally occurring polyphenolic compounds (polyphenols), epigallocatechin-3-gallate (EGCG), and curcumin, block ROS/RNS and are potent inflammation-modulating agents. However, their potential protective effects against oxidative stress in hMSCs have not been examined. In this study, we carried out a systematic analysis of the effects of polyphenols on hMSCs in their response to oxidative stress in the form of treatment with H(2)O(2) and S-nitroso-N-acetylpenicillamine (SNAP), respectively. Parameters measured included colony forming activity, apoptosis, and the levels of antioxidant enzymes and free reactive species. We found that polyphenols reversed H(2)O(2) -induced loss of colony forming activity in hMSCs. In a dose-dependent manner, polyphenols inhibited increased levels of ROS and NO, produced by H(2)O(2) or SNAP, respectively, in MSCs. Notably, polyphenols rapidly and almost completely blocked H(2)O(2) -induced ROS in the absence of significant direct effect on H(2)O(2) itself. Polyphenols also protected the antioxidant enzymes and reduced apoptotic cell death caused by H(2)O(2) exposure. Taken together, these findings demonstrate that EGCG and curcumin are capable of suppressing inducible oxidative stress in hMSCs, and suggest a possible new approach to maintain MSC viability and potency for clinical application.

Introduction: There have been limited advances in the treatment of bone and joint infections, which currently involves a combination of surgery and antibiotic administration. There is a timely need in orthopedics to develop more effective and less invasive forms of antimicrobial prophylaxis and treatment. The antibacterial effect of adult tissue-derived mesenchymal stem cells (MSCs) has recently been investigated against Escherichia coli and Staphylococcus aureus. The main mechanism of action is postulated to be via MSC production of the cationic antimicrobial peptide, LL-37. Methods: This study examines the antimicrobial activity of adipose-derived human MSCs (ASCs) on S. aureus, specifically examining the role of LL-37 and regulation of its expression. Bacteria colony-forming unit (CFU) assay was used to assess antimicrobial activity. Results: Our results showed that the ASC-conditioned medium significantly inhibited the growth of S. aureus under standard culture conditions with or without the continued presence of ASCs. Also, the treatment of ASCs with 1,25dihydroxy vitamin D 3 elevated LL-37 expression and enhanced their antimicrobial activity. In support, treatment with the vitamin D receptor inhibitor, GW0742, blocked the antimicrobial activity of ASCs. Conclusion: Our findings clearly demonstrate the antimicrobial activity of adult ASCs against S. aureus and implicate a key regulatory role for vitamin D. Further testing in in vivo models is being pursued to assess the potential application of ASCs as a biocompatible, adjunct treatment for musculoskeletal infections.

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Diseases of the knee joint such as osteoarthritis (OA) affect all joint elements. An in vitro human cell-derived microphysiological system capable of simulating intraarticular tissue crosstalk is desirable for studying etiologies/pathogenesis of joint diseases and testing potential therapeutics. Herein, a human mesenchymal stem cell-derived miniature joint system (miniJoint) is generated, in which engineered osteochondral complex, synovial-like fibrous tissue, and adipose tissue are integrated into a microfluidics-enabled bioreactor. This novel design facilitates different tissues communicating while still maintaining their respective phenotypes. The miniJoint exhibits physiologically relevant changes when exposed to interleukin-1𝜷 mediated inflammation, which are similar to observations in joint diseases in humans. The potential of the miniJoint in predicting in vivo efficacy of drug treatment is confirmed by testing the "therapeutic effect" of the nonsteroidal anti-inflammatory drug, naproxen, as well as four other potential disease-modifying OA drugs. The data demonstrate that the miniJoint recapitulates complex tissue interactions, thus providing a robust organ chip model for the study of joint pathology and the development of novel therapeutic interventions.

Organoids offer a promising strategy for articular tissue regeneration, joint disease modeling, and development of precision medicine. In this study, two types of human stem cells—primary mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs)—were employed to engineer organoids that mimicked bone, cartilage and adipose tissue, three key tissue components in articular joints. Prior to organoidogenesis, the iPSCs were first induced into mesenchymal progenitor cells (iMPCs). After characterizing the MSCs and iMPCs, they were used to generate cell-embedded extracellular matrix (ECM) constructs, which then underwent self-aggregation and lineage-specific differentiation in different induction media. Hydroxyapatite nanorods, an osteoinductive bioceramic, were leveraged to generate bone and osteochondral organoids, which effectively enhanced mineralization. The phenotypes of the generated organoids were confirmed on the basis of gene expression profiling and histology. Our findings demonstrate the feasibility and potential of generating articular tissue-recapitulating organoids from MSCs and iPSCs.