Cell origin, volume and arrangement are drivers of articular cartilage formation, morphogenesis and response to injury in mouse limbs

Abstract

Limb synovial joints are composed of distinct tissues, but it is unclear which progenitors produce those tissues and how articular cartilage acquires its functional postnatal organization characterized by chondrocyte columns, zone-specific cell volumes and anisotropic matrix. Using novel Gdf5CreERT2 (Gdf5-CE), Prg4-CE and Dkk3-CE mice mated to R26-Confetti or single-color reporters, we found that knee joint progenitors produced small non-migratory progenies and distinct local tissues over prenatal and postnatal time. Stereological imaging and quantification indicated that the columns present in juvenile-adult tibial articular cartilage consisted of non-daughter, partially overlapping lineage cells, likely reflecting cell rearrangement and stacking. Zone-specific increases in cell volume were major drivers of tissue thickening, while cell proliferation or death played minor roles. Second harmonic generation with 2-photon microscopy showed that the collagen matrix went from being isotropic and scattered at young stages to being anisotropic and aligned along the cell stacks in adults. Progenitor tracing at prenatal or juvenile stages showed that joint injury provoked a massive and rapid increase in synovial Prg4+ and CD44+/P75+ cells some of which filling the injury site, while neighboring chondrocytes appeared unresponsive. Our data indicate that local cell populations produce distinct joint tissues and that articular cartilage growth and zonal organization are mainly brought about by cell volume expansion and topographical cell rearrangement. Synovial Prg4+ lineage progenitors are exquisitely responsive to acute injury and may represent pioneers in joint tissue repair.

Expression of p16INK4a is a biomarker of chondrocyte aging but does not cause osteoarthritis

“…For example, synovial fibroblasts and progenitor cells in the superficial zone of cartilage could be targeted for p16 INK4a loss with the Prg4 tm1(GFP/cre/ERT2)Abl allele (Kozhemyakina et al., 2015). Lineage tracing studies have suggested that subpopulations of synovial cells harbor regenerative potential (Decker et al., 2017) and a proliferative block in these cells through senescence may limit this capacity with aging. Our findings may have also been influenced by the development of medullary neoplasia with associated bone production in the Acan tm1(cre/ERT2)Crm p16 L/L mice.…”

“…These cells exhibit an interesting replicative biology, showing extremely low proliferation rates in adult humans and mice during homeostasis (Aigner et al., 2001; Decker et al., 2017). Chondrocyte proliferation can occur during the development of osteoarthritis (OA) in the form of cell clusters, but it is not known if this replicative response is regenerative, pathologic, or epiphenomenal (Lotz et al., 2010).…”

Articular cartilage and joint development from embryogenesis to adulthood

“…(Fig. 1 B, Decker et al, 2016). These positively labeled cells and/or their progeny remained in the articular cartilage through at least 6 months of age (Fig.…”

“…1 A, C, E, Koyama et al, 2008). We recently developed a novel inducible BAC transgenic Gdf5 CreERT2 mouse line, and when the mice were crossed with R26R zsGreen mice, we were able to more selectively, although less abundantly, label specific cell populations (Decker et al, 2016). For example, when tamoxifen was administered at late embryonic time points, Gdf5 CreERT2 + cell labeling was more restricted to cells within the eventual articular cartilage.…”

Next generation tissue engineering of orthopedic soft tissue-to-bone interfaces

“…[112] GDFs, specifically GDF-5, interact closely with BMPs and act as signaling molecules in the growth and differentiation of cartilage, tendon, and ligament. [113–117] TGF-βs are prevalent in all of these tissues and are known to play a role in proliferation and stem cell differentiation. [118] In particular, TGF-β is heavily implicated for its role in chondrogenic differentiation and development.…”