Adult Prg4+ progenitors repair long-term articular cartilage wounds in vivo
Mei Massengale, … , Henry M. Kronenberg, David T. Scadden
Mei Massengale, … , Henry M. Kronenberg, David T. Scadden
Published September 8, 2023
Citation Information: JCI Insight. 2023;8(17):e167858. https://doi.org/10.1172/jci.insight.167858.
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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 Barywano, 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 1

Adult aggrecan-lineage cells in homeostasis and articular cartilage wounds.

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Adult aggrecan-lineage cells in homeostasis and articular cartilage woun...
(A–C) Homeostasis: Fluorescence images of Aggrecan CreERt;tdTomato mouse knee articular cartilage. (A) Overview. (B) Marrow. (C) Maximum intensity projection (projection of brightest signals only). AC, articular cartilage; GP, growth plate; BM, marrow; SYN, synovium; P, periosteum; LIG, ligaments; PAT-C, patellar cartilage; PAT-T, patellar tendon; JC, joint capsule. Dotted lines: tidemark (boundary between noncalcified and calcified cartilage). Arrowheads: superficial zone (SFZ) chondrocytes. (D–G) Injury: Alcian blue and fluorescence images (low and high magnification) of adjacent sections of cartilage wounds of Aggrecan CreERt;tdTomato at 7, 10, and 21 dpi (D–G), with 4 mg tamoxifen, 1.5-week washout allowing tamoxifen metabolism, and then injury using needle (D–F). (G) Tamoxifen (8 mg), 6-week washout allowing aggrecan-expressing marrow stromal cells to proliferate, and then injury using 0.3-mm-diameter biopsy punch. Dashed contours: soft tissue superficial to the wound. Dotted contours: wound boundary determined by histology, brightfield, or fluorescence images. Red, tdTomato. Blue, DAPI. Scale bar: 500 μm (A) and 50 μm (B–G). (H) Quantification: aggrecan-lineage cells in homeostasis vs. wounds. 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 3-zonal structure typical of articular cartilage (e.g., the periphery of articular cartilage or soft tissue attachment points). Wound excluded surrounding soft tissues. Also see Methods. Sample size: homeostasis, n = 5 (8 mg tamoxifen, n = 3; 10 mg, n = 2); 7 dpi, n = 3 (all using needle); 10 dpi, n = 3 (all needle, with 1 receiving 8 mg tamoxifen); 21 dpi, n = 5 (needle, n = 2; punch, n = 3), with 1 in punch group receiving 8 mg tamoxifen; 60 dpi, n = 5 (all punch; 2 were aged mice in Supplemental Figure 3F). One-way ANOVA, F = 11737 (degrees of freedom between groups = 4 and within groups = 16). ****P < 0.0001.