Background: Lubricin, a proteoglycan encoded by the PRG4 gene, is synthesised by superficial zone (SFZ) chondrocytes and synovial cells. It reduces friction between joints and allows the smooth sliding of tendons. Although lubricin has been shown to be effective against osteoarthritis and synovitis in animals, its clinical application remains untested. In this study, we aimed to induce lubricin-expressing cells from pluripotent stem cells (iPSCs) and applied them locally via cell transplantation.

Methods: To generate iPSCs, OCT3/4, SOX2, KLF4, and L-MYC were transduced into fibroblasts derived from Prg4-mRFP1 transgenic mice. We established a protocol for the differentiation of iPSC-derived Prg4-mRFP1-positive cells and characterised their mRNA expression profile. Finally, we injected Prg4-mRFP1-positive cells into the paratenon surrounding the Achilles tendons and knee joints of severe combined immunodeficiency mice and assessed lubricin expression.

Results: Wnt3a, activin A, TGF-β1, and bFGF were applied to induce the differentiation of iPSC-derived Prg4-mRFP1-positive cells. Markers related to SFZ chondrocytes and fibroblast-like synovial cells (FLSs) were expressed during differentiation. RNA-sequencing indicated that iPSC-derived Prg4-mRFP1-positive cells manifested expression profiles typical of SFZ chondrocytes and FLSs. Transplanted iPSC-derived Prg4-mRFP1-positive cells survived around the Achilles tendons and in knee joints.

Conclusions: The present study describes a protocol for the differentiation of iPSC-derived Prg4-positive cells with characteristics of SFZ chondrocytes and FLSs. Transplantation of lubricin-expressing cells offers promise as a therapy against arthritis and synovitis.

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