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Articular cartilage is coating the layers of freely movable joints, enabling a smooth surface\nand acts resisting to forces. The tissue is aneural and avascular, and has a poor ability to selfrenew\nin cases of tissue damage. Therefore, cartilage lesions often lead to degenerative\ndisorders such as osteoarthritis (OA). OA is considered the most common form of arthritis\naffecting people worldwide, causing pain and physical disability. Approaches in cartilage\nregeneration, especially the use of mesenchymal stem cells (MSCs), have been promising, yet\nlimited. Finding a the most suitable cell type for transplantation strategies is still matter of\ndebate. The recent discovery of a pluripotent stem cell type that represent a minor fraction of\nthe stromal cells present in tissues (MUSE-cells) offer an attractive alternative that deserve to\nbe investigated.\nThe main objective of this study was to establish protocols for the isolation and\ncharacterization of MUSE-cells from Hoffa’s fat pad (HFP) and umbilical cords (MC), and to\ncompare the chondrogenic differentiation potential between the MUSE- and non-MUSE-cell\npopulations. MUSE-cells were isolated from the total pull of mesenchymal stem cells by cell\nsorting, using the embryonic marker SSEA-3 as specific cell surface antigen. Scaffold-free 3D\ncultures maintained in chondrogenic conditions were used to induce cartilage differentiation.\nSingle cell cluster formation assays were used for functional characterization of MUSE.\nPluripotent NTERA-2 cells were used as positive control.\nMesenchymal cells displaying phenotypic characteristics of stem cells (MSCs) were\nsuccessfully isolated from fresh tissues. Scaffold-free spheroids of HFP-MSCs showed a more\nintense Alcian blue (matrix) staining and had better cartilage-like morphology than those\nformed from mixed cord MSCs (MC-MSCs). SSEA-3+ MUSE-cells could be identified and\nisolated from HFP (8% of total MSCs) but were nearly undetectable in MC (0.8% of total\nMSCs). Phenotypic characterization of sorted cells after cell expansion, and functional\ncharacterization by single cell cluster formation abilities confirmed the pluripotent nature of\nthe cells.\nIV\nWe have demonstrated that the adipose tissue of the infrapatellar pocket (HFP) is a good\nsource of MSCs, with the ability to produce cartilage-like spheroids, and contain a fraction of\nSSEA-3+ cells (MUSE-cells) with the ability to self-renew. This cell subtype was also highly\npositive for the pluripotency marker SSEA-4. MC-MSCs on the other hand, did not manage to\nproduce spheroids with properties similar to those of native cartilage, and had not SSEA-3+\nMUSE-cells. The chondrogenic abilities of MUSE- and non-MUSE-cells from HFP is under\ninvestigation at the time of writing this thesis.\n\nKeywords: Articular cartilage, Articular cartilage disorders, Multilineage-differentiating\nstress enduring (MUSE) cells, Regenerative medicine, Hoffa’s fat pad, Umbilical cord,\nChondrogenesis, Mesenchymal stem cells, SSEA-3, SSEA-4, Cell sorting.