Adult Prg4+ progenitors repair long-term articular cartilage wounds in vivo
Mei Massengale, Justin L. Massengale, Catherine R. Benson, Ninib Baryawno, Toshihiko Oki, Matthew L. Steinhauser, Alissa Wang, Deepak Balani, Luke S. Oh, Mark A. Randolph, Thomas J. Gill III, Henry M. Kronenberg, David T. Scadden
Mei Massengale, Justin L. Massengale, Catherine R. Benson, Ninib Baryawno, Toshihiko Oki, Matthew L. Steinhauser, Alissa Wang, Deepak Balani, Luke S. Oh, Mark A. Randolph, Thomas J. Gill III, Henry M. Kronenberg, David T. Scadden
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Research Article Cell biology

Adult Prg4+ progenitors repair long-term articular cartilage wounds in vivo

Abstract

The identity and origin of the stem/progenitor cells for adult joint cartilage repair remain unknown, impeding therapeutic development. Simulating the common therapeutic modality for cartilage repair in humans, i.e., full-thickness microfracture joint surgery, we combined the mouse full-thickness injury model with lineage tracing and identified a distinct skeletal progenitor cell type enabling long-term (beyond 7 days after injury) articular cartilage repair in vivo. Deriving from a population with active Prg4 expression in adulthood while lacking aggrecan expression, these progenitors proliferate, differentiate to express aggrecan and type II collagen, and predominate in long-term articular cartilage wounds, where they represent the principal repair progenitors in situ under native repair conditions without cellular transplantation. They originate outside the adult bone marrow or superficial zone articular cartilage. These findings have implications for skeletal biology and regenerative medicine for joint injury repair.

Authors

Mei Massengale, Justin L. Massengale, Catherine R. Benson, Ninib Baryawno, Toshihiko Oki, Matthew L. Steinhauser, Alissa Wang, Deepak Balani, Luke S. Oh, Mark A. Randolph, Thomas J. Gill III, Henry M. Kronenberg, David T. Scadden

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Figure 6

mRNA FISH analysis of Prg4+ articular chondrocytes.

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mRNA FISH analysis of Prg4+ articular chondrocytes. (A) Confocal fluores...
(A) Confocal fluorescence images of aggrecan mRNA FISH assay in Prg4 CreERt2;tdTomato knee articular chondrocytes with mice following the protocol used in Figure 2A, with aggrecan mRNA probe showing articular chondrocytes: single Z section and maximum intensity projection (projection of maximum intensity signals only). The z-axis thickness within 16 μm was selected to be smaller than 20 μm, the typical diameter of a chondrocyte, to avoid positional artifacts in the maximum intensity projection. Blue: DAPI. Red: tdTomato. Red was pseudocolored based on the staining signals of anti-tdTomato secondary antibody. Green: aggrecan mRNA transcripts. Green was pseudocolored based on FISH staining using far-red fluorophores to eliminate the background associated with cartilage matrix autofluorescence. Scale bars: 50 μm. (B) Quantification: Percentage Prg4+ (tdTomato+) cells in synovium, articular cartilage, and SFZ that express aggrecan mRNA (n = 4); SFZ chondrocytes were defined as flat cells in the top 2 layers of articular chondrocytes, superficial to the underlying middle and deep zones, excluding free cells outside the cartilage matrix or tissue without zonal architecture typical of articular cartilage, e.g., the periphery of articular cartilage or soft tissue attachment points. One-way ANOVA: F = 1336 (degrees of freedom between groups = 3 and within groups = 12). *P < 0.05; ****P < 0.0001.