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Articular cartilage regeneration by activated skeletal stem cells

Abstract

Osteoarthritis (OA) is a degenerative disease resulting in irreversible, progressive destruction of articular cartilage1. The etiology of OA is complex and involves a variety of factors, including genetic predisposition, acute injury and chronic inflammation2,3,4. Here we investigate the ability of resident skeletal stem-cell (SSC) populations to regenerate cartilage in relation to age, a possible contributor to the development of osteoarthritis5,6,7. We demonstrate that aging is associated with progressive loss of SSCs and diminished chondrogenesis in the joints of both mice and humans. However, a local expansion of SSCs could still be triggered in the chondral surface of adult limb joints in mice by stimulating a regenerative response using microfracture (MF) surgery. Although MF-activated SSCs tended to form fibrous tissues, localized co-delivery of BMP2 and soluble VEGFR1 (sVEGFR1), a VEGF receptor antagonist, in a hydrogel skewed differentiation of MF-activated SSCs toward articular cartilage. These data indicate that following MF, a resident stem-cell population can be induced to generate cartilage for treatment of localized chondral disease in OA.

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Fig. 1: Age-related changes in articular mSSC activity.
Fig. 2: The effect of focal MF on mSSCs at the articular surface.
Fig. 3: Manipulating the adult articular microenvironment to facilitate mSSC-derived chondrogenesis.
Fig. 4: Regeneration of human articular cartilage in a preclinical xenograft model.

Data availability

Microarray data described in this study was deposited with the gene expression omnibus with the accession number GSE151303. There are no restrictions on sharing the data. All data are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors thank N. Williams, C. Queen, C. Crumpton, E. Kang, M. Butcher, L. Quinn, P. Perira and R. Mann for advice and assistance, and A. McCarty, M. Alvarez, and VSC Staff for animal model support. The authors also thank M. Ekhart, and the PAN facility at Stanford for help in gene-expression analysis. In addition, the authors thank S. Goodman and the Orthopedic Department of Stanford for donation of human adult specimens. The study was supported by NIH (R01 DE027323, R56 DE025597, R01 DE026730, R01 DE021683, R21 DE024230, U01HL099776, U24DE026914 and R21 DE019274), CIRMTR1-01249, Oak Foundation, Hagey Laboratory, Pitch Johnson Fund and Gunn/Olivier Research Fund to M.T. Longaker; Siebel Fellowship, PCF YI Award, Stinehart/Reed, and NIHNIAK99AG049958-01A1, American Federation of Aging Research and Arthritis National Research Foundation to C.K.F.C.; HHMI Fellowship to G.S.G.; the German Research Foundation (DFG) Fellowship 399915929 to T.H.A.; NIH, NIGMS R01GM123069, NIH1R01AR071379, ACS Clowes Award, Department of Defense CDMRP W81XWH-18-1-0653, OR170174 to B.L; PSRF National Endowment and Stanford TTE fellowship to M.P.M.; NIHS10 RR02933801 to Stanford Stem Cell FACS core. The project was supported, in part, by Award Number 1S10OD021514-01 from the National Center for Research Resources (NCRR). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NCRR or the National Institutes of Health.

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Contributions

Conception and design was done by M.P.M., I.L.W., M.T. Longaker and C.K.F.C. Experiments, data analysis and data interpretation were carried out by M.P.M., L.S.K., M.T. Lopez, T.H.A., G.S.G., O.M., Y.W., R.C.R., M.Y.H., H.S., and L.Z. Synthesis of hydrogels was carried out by X.T. and F.Y. Atomic Force Microscopy training and assistance was provided by M.P.W. Drafting and revision of the manuscript was carried out by M.P.M., L.S.K., N.Q., B.L., D.C.W., S.B.G., M.T. Longaker and C.F.K.C. All authors received and approved the final document.

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Correspondence to Michael T. Longaker or Charles K. F. Chan.

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Peer review information Michael Basson and Brett Benedetti were the primary editors on this article and managed its editorial process and peer review in collaboration with the rest of the editorial team.

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Extended data

Extended Data Fig. 1 Mouse microarray data analysis.

a, Pathways significantly enriched in Ad/MF and P3 mSSC populations. Top, (from left-right) Protein secretion, MYC targets, E2F targets. Bottom, (from left-right) G2M checkpoint, oxidative phosphorylation and TGFb signaling. b-c, mSSC expression (b) and bulk tissue expression (c) of key genes involved in cartilage development, cell cycle and inflammation. d, mSSC gene expression levels after in vitro treatment of PBS, BMP2, or sVEGFR1.

Extended Data Fig. 2 In vitro assays for groups (N, MF).

a, Alizarin red staining of uninjured/normal adult (N) and adult MF mSSCs (left) and mBCSPs (right), and quantification of the alizarin red stain after extraction and photometric measurement at OD450. (n = 3 mice per group). * 0.032; ** 0.0014. b, Alcian blue staining of N and MF mSSCs (left) and mBCSPs (right), and quantification of the Alcian blue stain after extraction and photometric measurement at OD595. (n = 3 mice per group). ** 0.0010; *** 0.0004. c, Oil red O staining of Ad and Ad/MF mSSCs (Left) and mBCSPs (Right). Scale bar 100μm. (n = 3 mice per group). Graphs show mean + /- s.e.m. Two-tailed Student’s t-test. Exact P values to 2 significant figures.

Extended Data Fig. 3 Microdissection before and after MF surgery.

a, Schematic depicting the distal femur of a mouse and its major tissue layers before and after MF surgery. b, Representative flow cytometry analysis of the articular surface (top), the periosteum (middle), and bone (bottom) with relative populations of mOP, mCP, mBCSP, and mSSC. c, Quantification of mSSC/million events in bone, cartilage, and periosteum. Graph shows mean + /- s.e.m. Ordinary one-way ANOVA test with post-hoc analysis using Šídák method to compare between specific means. Exact P values to 2 significant figures. (n = 5 mice per group). d, Quantification of mSSC/million events comparing MF joints and joints with articular cartilage and periosteum removed prior to MF surgery (mMF). (n = 5 mice per group). e, Alcian blue staining of mSSC following chondrogenic differentiation with treatment of PBS or BMP2 + sVEGFR1. Scale bars 100μm. Representative of three independent experiments. f, Quantification of the Alcian blue stain after extraction and photometric measurement at OD595. Unless otherwise stated, graphs show mean + /- s.e.m. Two-tailed Student’s t-test. Exact P values to 2 significant figures.

Extended Data Fig. 4 OA progression.

a, Schematic of the experimental outline. Destabilization of the medial meniscus (DMM) was performed on adult mice, and the distal femurs were harvested after 8 weeks. Analysis was performed by IF, pentachrome, and Safranin-O Fast Green staining. b, Left, representative IF of indicated markers in sham and DMM joints. Scale bars 100μm. Right, Safranin-O Fast Green and pentachrome stains of sham and joints 8 weeks after DMM. Scale bars 500μm. (n = 3 per group). c, Quantification of IF stains in sham versus DMM. Graphs show mean + /- s.e.m. Two-tailed Student’s t-test. Exact P values to 2 significant figures. (n = 3 per group).

Extended Data Fig. 5 IHC and quantification of OA/MF with factors at 4 weeks.

a, Representative IF of (from left-right) ACAN, COL 1, COL 2, COL 10 and MMP 13 in 3 treatment conditions (top: PBS, middle: BMP2, bottom: BMP2 + sVEGFR1) at 4 weeks after MF. Scale bars 250μm. (n = 8 per group). b, Quantification of IF stains for indicated markers of MF + factors at 4 weeks. Graphs show mean + /- s.e.m. Ordinary one-way ANOVA test with post-hoc analysis using Šídák method to compare between specific means. Exact P values to 2 significant figures. c, Representative IF isotype and positive controls. (n = 3 per group). d, Repeat examples of pentachrome staining of BMP2 + sVEGFR1 sections at low (scale bars 500μm) and high (scale bars 100μm) magnification. Representatives of eight independent experiments.

Extended Data Figure 6 Histology of OA/MF at 2 weeks and 8 weeks.

a, Representative pentachrome stains and respective IF of (from left-right) ACAN, COL 1, COL 2, COL 10 and MMP 13 in 3 treatment conditions (top: PBS; middle: BMP2; bottom: BMP2 + sVEGFR1) at 2 weeks after MF. Scale bars 500μm. (n = 4 per group). b, Representative pentachrome stains and respective IF stains for the indicated markers in 3 treatment conditions (top row: PBS; middle: BMP2; bottom: BMP2 + sVEGFR1) at 8 weeks after MF. Scale bars 500μm. (n = 4 per group). c, Quantification of IF stains for the indicated markers at 2 weeks (top) and 8 weeks (bottom) after MF. (n = 3 per group per timepoint). Graphs show mean + /- s.e.m. Ordinary one-way ANOVA test with post-hoc analysis using Šídák method to compare between specific means. Exact P values to 2 significant figures.

Extended Data Fig. 7 Week 16 timepoint.

a, Representative pentachrome and respective IF of (from left-right) ACAN, COL 1, COL 2, COL 10 and MMP 13 in 3 treatment conditions (top: PBS, middle: BMP2, bottom: BMP2 + sVEGFR1). Scale bars 500μm. (n = 4 per group). b, Quantification of IF stains for indicated markers of MF + factors. Graphs show Mean + /- SEM. Ordinary one-way ANOVA test with post-hoc analysis using Šídák method to compare between specific means. Exact P values to 2 significant figures. (n = 3 per group). c, From left-right, gross images of distal femur (scale bars 1 mm); respective pentachrome (scale bars 500μm); 3D Peak Force Error; 3D Deformation; Force Volume in 4 conditions (PBS, BMP2, BMP2 + sVEGFR1, Uninjured). (n = 4 per group).

Extended Data Fig. 8 Effects of aged and irradiated niches.

a, Quantification of mSSC/million events in normal and MF joints of adult (9wks) and aged (1 yr) mice. Graph shows mean + /- s.e.m. Two-tailed Student’s t-test. Exact P values to 2 significant figures. (n = 10 mice per group). b, Representative pentachrome stains of 2-weeks post MF surgery in aged joints with (from left-right) PBS, BMP2, and BMP2 + sVEGFR1. Scale bar 500μm. (n = 3 per group). c, Schematic of the experimental outline. Microfracture surgery is performed on the joints of GFP + adult mice (Ad/MF). GFP + mSSCs are sorted by flow cytometry and cotransplanted with BMP2 + sVEGFR1 into MF defects of irradiated mice. Analysis is performed by brightfield microscopy (BF), immunofluorescence (IF), and pentachrome staining. d, Top, Representative BF (left) and fluorescence microscopy (right) of GFP + Ad/MF mSSC 4 weeks after they were transplanted into the MF defect of an irradiated joint. Scale bars 500μm. (n = 5 mice). Middle, Representative pentachrome stain (scale bar 500μm) shown with higher magnification (scale bar 100μm) and respective IF of GFP + Ad/MF mSSC 4 weeks after they were transplanted into the MF defect of an irradiated joint. Positive staining marked by white arrows. Representatives of three separate experiments. Bottom right, a negative control IF stain was performed for each experiment. Scale bars 500μm.

Extended Data Fig. 9 Atomic Force Microscopy at 8 weeks post MF.

a, Left and middle, schematic of Rheology experimental outline. Right, Quantification for the modulus of the regenerate (PBS, BMP2, BMP2 + sVEGFR1.) Graph shows mean + /- s.e.m. Ordinary one-way ANOVA test (p = <0.0001) with post-hoc analysis using Šídák method to compare between specific means. Exact P values to 2 significant figures. (n = 10 mice per group). b, From left-right, gross images of distal femur (scale bars 1 mm); respective pentachrome (scale bars 500μm); 3D Peak Force Error; 3D Deformation; Force Volume in 4 conditions (PBS, BMP2, BMP2 + sVEGFR1, Uninjured) (n = 4 per group). Scale bar 500μm. c, Force graphs for PBS, BMP2, BMP2 + sVEGFR1, and uninjured. (n = 4 per group).

Extended Data Fig. 10 Functional assessment.

a, Schematic of the gait analysis performed on Ad/MF mice. b, Grimace assessment scores for adult mice following MF surgery of the distal femur with 3 treatment conditions (PBS, BMP2, BMP2 + sVEGFR1). Graphs show mean + /- s.e.m. Ordinary one-way ANOVA test (p = <0.0001) with post-hoc analysis using Šídák method to compare between specific means. Exact P values to 2 significant figures. (n = 5 mice per group). c, Gait assessment scores for maximum contact mean intensity with 4 conditions (PBS, BMP2, BMP2 + sVEGFR1, and Uninjured) at 4, 8, and 16 weeks after surgery. (n = 3 mice per group per timepoint).

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Murphy, M.P., Koepke, L.S., Lopez, M.T. et al. Articular cartilage regeneration by activated skeletal stem cells. Nat Med 26, 1583–1592 (2020). https://doi.org/10.1038/s41591-020-1013-2

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