Decoding the impact of exercise and αCGRP signaling on murine post-traumatic osteoarthritis progression

Abstract

Background: Osteoarthritis (OA) is a chronic degenerative joint disease characterized by cartilage breakdown, subchondral bone remodeling, and inflammation. Mechanical stress, such as exercise, can influence OA progression, acting as either a therapeutic intervention or a risk factor depending on intensity. The sensory neuropeptide αCGRP plays a role in modulating cartilage, bone, and inflammatory responses, making it a potential mediator of exercise effects on OA. This study investigated the impact of αCGRP deficiency and exercise intensity on OA progression in a post-traumatic murine model.

Methods: OA was induced in male αCGRP knockout (KO) and wild type (C57Bl/6J) mice via destabilization of the medial meniscus (DMM). Mice underwent moderate or intense treadmill exercise for up to 6 weeks (8 weeks post-surgery). Histological analyses were performed to assess cartilage degradation. Subchondral and metaphyseal bone morphology as well as cartilage stiffness were evaluated by nanoCT and atomic force microscopy (AFM), respectively. Serum inflammatory markers were analyzed using multiplex immunoassays.

Results: Serum levels of proinflammatory markers were elevated in αCGRP-deficient mice, particularly after intense exercise, independent of OA progression. DMM surgery induced significant cartilage degradation. Gross cartilage morphology was not influenced by exercise intensity or αCGRP deficiency, but αCGRP deficiency prevented articular cartilage extracellular matrix stiffening after DMM and intense exercise. Subchondral bone sclerosis was induced by αCGRP deficiency and DMM but mitigated by intense exercise. In metaphyseal bone, intense exercise induced trabecular loss in αCGRP-deficient mice.

Conclusions: This study highlights αCGRP as an intrinsic regulator of joint and bone responses to mechanical loading during OA. While cartilage degradation after DMM and treadmill exercise was unaffected by lack of αCGRP, its deficiency altered ECM stiffness, bone remodeling, and inflammatory responses. These findings position αCGRP as a critical regulator of joint homeostasis, particularly for bone health during running exercise and OA progression.

Keywords: Alpha-calcitonin gene-related peptide; Bone; Cartilage; Destabilization of the medial meniscus; Exercise; Osteoarthritis.

Fig. 1

Impact of αCGRP deficiency and exercise intensity on medial cartilage degradation after OA induction Cartilage was evaluated for grades of destruction according to the OARSI guidelines for murine OA. Cartilage of the right knee joints of WT and KO mice exposed to moderate or intense exercise were graded 4 weeks (A) and 8 weeks (B) after Sham or DMM surgery. Means of the maximal OARSI scores of the medial tibial and femoral cartilage together were compared. Statistical analysis is using Kruskal-Wallis and Dunn’s test for multiple comparisons. * p < 0.05, ** p < 0.01. N = 6–10

Fig. 2

Atomic force microscopy-based analysis of cartilage matrix stiffness in αCGRP deficient mice after OA-induction and forced exercise Analysis of articular cartilage of the right knee joint of WT and KO mice exposed to moderate and intense exercise at 8 weeks after DMM or Sham surgery A) Histograms of Young’s modulus (stiffness) distribution of the deep zone cartilage matrix (histograms of superficial and middle zone are in the supplementary material). The black line in each histogram represents a fit to the data using a linear combination of two Gaussian distributions. The dashed black lines show the individual Gaussian distributions representing the proteoglycan (E1, σ1) and the collagen (E2, σ2) Young’s moduli, respectively, as described in detail in the methods section. N = 3 B-C) Mean Young’s modulus (stiffness) of the proteoglycan (B) and collagen (C) peaks of superficial zone, middle zone, and deep zone cartilage. Bars show mean ± standard deviation. Statistical analysis using Two-Way ANOVA and Tukey’s multiple comparisons test. * p < 0.05, ** p < 0.01. N = 3

Fig. 3

Effect of αCGRP deficiency and forced exercise on meniscal ossification after OA-induction Ultra-high resolution nanoCT analysis of medial and lateral meniscal ossicle formation in WT and KO mice exposed to moderate or intense exercise at 8 weeks after DMM or Sham surgery. Analysis of (A) bone mineral density (BMD), (B) bone surface (BS), and (C) bone volume (BV). Statistical analysis using Two-Way ANOVA and Tukey’s multiple comparisons test. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. N = 3

Fig. 4

Effect of αCGRP deficiency and forced exercise on osteophyte formation after OA-induction Ultra-high resolution nanoCT analysis of the medial (A) and lateral (B) tibia plateau diameter in WT and KO mice exposed to moderate or intense exercise at 8 weeks after DMM or Sham surgery. Statistical analysis using Two-Way ANOVA and Tukey’s multiple comparisons test. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. N = 3

Fig. 5

Effect of αCGRP deficiency and forced exercise on subchondral bone morphology after OA-induction Ultra-high resolution nanoCT analysis of the subchondral bone of the medial tibia in WT and KO mice exposed to moderate or intense exercise at 8 weeks after DMM or Sham surgery. Analysis of (A) bone volume to total volume ratio (BV/TV), (B) trabecular thickness (Tb. Th.), (C) trabecular separation (Tb. Sp.). Statistical analysis using Two-Way ANOVA and Tukey’s multiple comparisons test. * p < 0.05, ** p < 0.01, *** p < 0.001. N = 3

Fig. 6

Effect of αCGRP deficiency and forced exercise on metaphyseal bone morphology after OA-induction Ultra-high resolution nanoCT analysis of the metaphyseal bone of the medial tibia in WT and KO mice exposed to moderate or intense exercise at 8 weeks after DMM or Sham surgery. Analysis of (A) bone mineral density (BMD), (B) bone volume to total volume ratio (BV/TV), (C) trabecular number (Tb. N.), (D) Connectivity Density (Conn. D.), and (E) trabecular thickness (Tb. Th.). (F) Representative images highlighting morphological differences in WT and KO mice after DMM and moderate or intense exercise. Statistical analysis using Two-Way ANOVA and Tukey’s multiple comparisons test. * p < 0.05, ** p < 0.01. N = 3

Fig. 7

OA-associated serum factors in αCGRP deficient mice after OA-induction and forced exercise Serum marker concentration of WT and KO mice exposed to moderate or intense exercise at 8 weeks after Sham or DMM surgery. Statistical analysis using Two-Way ANOVA and Tukey’s multiple comparisons test. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. N = 6