TWIST1 controls cellular senescence and energy metabolism in mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are promising cells for regenerative medicine therapies because they can differentiate towards multiple cell lineages. However, the occurrence of cellular senescence and the acquiring of the senescence-associated secretory phenotype (SASP) limit their clinical use. Since the transcription factor TWIST1 influences expansion of MSCs, its role in regulating cellular senescence was investigated. The present study demonstrated that silencing of TWIST1 in MSCs increased the occurrence of senescence, characterised by a SASP profile different from irradiation-induced senescent MSCs. Knowing that senescence alters cellular metabolism, cellular bioenergetics was monitored by using the Seahorse XF apparatus. Both TWIST1-silencing-induced and irradiation-induced senescent MSCs had a higher oxygen consumption rate compared to control MSCs, while TWIST1-silencing-induced senescent MSCs had a low extracellular acidification rate compared to irradiation-induced senescent MSCs. Overall, data indicated how TWIST1 regulation influenced senescence in MSCs and that TWIST1 silencing-induced senescence was characterised by a specific SASP profile and metabolic state.

Cell-surface markers identify tissue resident multipotential stem/stromal cell subsets in synovial intimal and sub-intimal compartments with distinct chondrogenic properties.

OBJECTIVE: Synovium contains multipotent progenitor/stromal cells (MPCs) with potential to participate in cartilage repair. Understanding the identity of these MPCs will allow their therapeutic potential to be fully exploited. Hence this study aimed to identify primary synovial MPCs and characterize them in the context of cartilage regeneration. METHODS: Primary MPC/MPC-subset specific markers in synovium were identified by FACS analysis of uncultured cells. MPC-subsets from human synovium obtained from patients undergoing total knee arthroplasty were FACS sorted, cultured, immunophenotyped and chondrogenically differentiated. The anatomical localization of MPCs in synovium was examined using immunohistochemistry. Finally, the presence of these MPC subsets in healthy synovium obtained from human organ donors was examined. RESULTS: A combination of CD45, CD31, CD73 and CD90 can isolate two distinct MPC-subsets in synovium. These MPC-subsets, freshly isolated from synovium, did not express CD45 or CD31, but expressed CD73. Additionally, a sub-population of CD73+ cells also expressed CD90. CD45-CD31-CD73+CD90- cells were significantly more chondrogenic than CD45-CD31-CD73+CD90+ cells in the presence of TGFß1. Interestingly, reduced chondrogenic ability of CD73+CD90+ cells could be reversed by the addition of BMP2, showing discrete chondrogenic factor requirements by distinct cell-subsets. In addition, these MPCs had distinct anatomical localization; CD73 was expressed both in intimal and sub-intimal region while CD90 was enriched in the sub-intimal region. We further demonstrated that these subsets are also present in healthy synovium. CONCLUSIONS: We provide indications that primary MPCs in synovial intima and sub-intima are phenotypically and functionally distinct with different chondrogenic properties.

Recellularization of auricular cartilage via elastase-generated channels.

Decellularized tissue matrices are promising substrates for tissue generation by stem cells to replace poorly regenerating tissues such as cartilage. However, the dense matrix of decellularized cartilage impedes colonisation by stem cells. Here, we show that digestion of elastin fibre bundles traversing auricular cartilage creates channels through which cells can migrate into the matrix. Human chondrocytes and bone marrow-derived mesenchymal stromal cells efficiently colonise elastin-treated scaffolds through these channels, restoring a glycosaminoglycan-rich matrix and improving mechanical properties while maintaining size and shape of the restored tissue. The scaffolds are also rapidly colonised by endogenous cartilage-forming cells in a subcutaneously implanted osteochondral biopsy model. Creating channels for cells in tissue matrices may be a broadly applicable strategy for recellularization and restoration of tissue function.

Encapsulation of allogeneic mesenchymal stem cells in alginate extends local presence and therapeutic function.

Bone marrow derived mesenchymal stem cells (MSCs) have immunomodulatory and trophic capacities. For therapeutic application in local chronic inflammatory diseases, MSCs, preferably of allogeneic origin, have to retain immunomodulatory properties. This might be achieved by encapsulation of MSCs in a biomaterial that protects them from the host immune system. Most studies investigating the properties of MSCs for therapeutic application use short term cultures of cells in monolayer. Since the physical environment of MSCs can influence their functionality, we evaluated the feasibility of preserving the immunomodulatory properties of MSCs encapsulated in a three-dimensional alginate construct. After 5 weeks of implantation in immunocompetent rats, active allogeneic MSCs encapsulated in alginate were still detectable by Bio Luminescence Imaging and Magnetic Resonance Imaging of luciferase transduced and superparamagnetic iron oxide labelled MSCs. MSCs injected in saline were only detectable up to 1 week after injection. Moreover, the MSCs encapsulated in alginate responded to inflammatory stimuli similarly to MSCs in monolayer culture. In addition, MSC-alginate beads secreted immunomodulatory and trophic factors and inhibited T-cell proliferation after 30 d of in vitro culture. Our data indicate that allogeneic MSCs encapsulated in alginate persist locally and could act as an interactive immunomodulatory or trophic factor release system for several weeks, making this an interesting system to investigate for application in inflammatory disease conditions.

Chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells in a simulated osteochondral environment is hydrogel dependent.

Hydrogels pose interesting features for cartilage regeneration strategies, such as the option for injectability and in situ gelation resulting in optimal filling of defects. We aimed to study different hydrogels for their capability to support chondrogenesis of human bone marrow-derived mesenchymal stem cells (hBMSCs). hBMSCs were encapsulated in alginate, alginate with hyaluronic acid (alginate/HA), fibrin or thermoresponsive HA grafted with poly(N-isopropyl acrylamide) side-chains (HA-pNIPAM). Glycosaminoglycan production and cartilage-related gene expression were significantly higher in hBMSC-alginate and hBMSC-fibrin constructs than in the other constructs. Supplementation of alginate with HA was not beneficial. hBMSC-alginate, hBMSC-fibrin and hBMSC-HA-pNIPAM constructs were placed in simulated defects in osteochondral biopsies and cultured in vitro for 28 d. Biopsies containing hBMSC-alginate and hBMSC-fibrin were implanted subcutaneously in nude mice for 12 weeks. hBMSC-alginate constructs had significantly higher cartilage-related gene expression after 28 d of culture as well as significantly more safranin-O positive repair tissue after 12 weeks in vivo than hBMSC-fibrin constructs. Although initial experiments with hBMSC-hydrogel constructs suggested comparable results of hBMSC-alginate, hBMSC-fibrin and hBMSC-HA-pNIPAM constructs, culture in the osteochondral biopsy model in vitro as well as in vivo revealed differences, suggests that chondrogenesis of hBMSCs in an osteochondral environment is hydrogel-dependent.

Stromal cells from murine embryonic aorta-gonad-mesonephros region, liver and gut mesentery expand human umbilical cord blood-derived CAFC(week6) in extended long-term cultures.

The first definitive long-term repopulating hematopoietic stem cells (HSCs) emerge from and undergo rapid expansion in the embryonic aorta-gonad-mesonephros (AGM) region. To investigate the presumptive unique characteristics of the embryonic hematopoietic microenvironment and its surrounding tissues, we have generated stromal clones from subdissected day 10 and day 11 AGMs, embryonic livers (ELs) and gut mesentery. We here examine the ability of 19 of these clones to sustain extended long-term cultures (LTCs) of human CD34(+) umbilical cord blood (UCB) cells in vitro. The presence of in vitro repopulating cells was assessed by sustained production of progenitor cells (extended LTC-CFC) and cobblestone area-forming cells (CAFC). The embryonic stromal clones differed greatly in their support for human HSCs. Out of eight clones tested in the absence of exogenous cytokines, only one (EL-derived) clone was able to provide maintenance of HSCs. Addition of either Tpo or Flt3-L + Tpo improved the long-term support of about 50% of the tested clones. Cultures on four out of 19 clones, ie the EL-derived clone mentioned, two urogenital-ridge (UG)-derived clones and one gastrointestinal (GI)-derived clone, allowed a continuous expansion of primitive CAFC and CFU-GM with over several hundred-fold more CAFC(week6) produced in the 12th week of culture. This expansion was considerably higher than that found with the FBMD-1 cell line, which is appreciated by many investigators for its support of human HSCs, under comparable conditions. This stromal cell panel derived from the embryonic regions may be a powerful tool in dissecting the factors mediating stromal support for maintenance and expansion of HSCs.