CD11b Signaling Prevents Chondrocyte Mineralization and Attenuates the Severity of Osteoarthritis

Abstract

Osteoarthritis (OA) is a progressive joint disease that is strongly associated with calcium-containing crystal formation (mineralization) by chondrocytes leading ultimately to cartilage calcification. However, this calcification process is poorly understood and treatments targeting the underlying disease mechanisms are lacking. The CD11b/CD18 integrin (Mac-1 or αMβ2), a member of the beta 2 integrin family of adhesion receptors, is critically involved in the development of several inflammatory diseases, including rheumatoid arthritis and systemic lupus erythematosus. We found that in a collagen-induced arthritis, CD11b-deficient mice exhibited increased cartilage degradation compared to WT control animals. However, the functional significance of CD11b integrin signaling in the pathophysiology of chondrocytes remains unknown. CD11b expression was found in the extracellular matrix and in chondrocytes in both healthy and damaged human and murine articular cartilage. Primary murine CD11b KO chondrocytes showed increased mineralization when induced in vitro by secondary calciprotein particles (CPP) and quantified by Alizarin Red staining. This increased propensity to mineralize was associated with an increased alkaline phosphatase (Alp) expression (measured by qRT-PCR and activity assay) and an enhanced secretion of the pro-mineralizing IL-6 cytokine compared to control wild-type cells (measured by ELISA). Accordingly, addition of an anti-IL-6 receptor antibody to CD11b KO chondrocytes reduced significantly the calcification and identified IL-6 as a pro-mineralizing factor in these cells. In the same conditions, the ratio of qRT-PCR expression of collagen X over collagen II, and that of Runx2 over Sox9 (both ratio being indexes of chondrocyte hypertrophy) were increased in CD11b-deficient cells. Conversely, the CD11b activator LA1 reduced chondrocyte mineralization, Alp expression, IL-6 production and collagen X expression. In the meniscectomy (MNX) model of murine knee osteoarthritis, deficiency of CD11b led to more severe OA (OARSI scoring of medial cartilage damage in CD11b: 5.6 ± 1.8, in WT: 1.2 ± 0.5, p < 0.05, inflammation in CD11b: 2.8 ± 0.2, in WT: 1.4 ± 0.5). In conclusion, these data demonstrate that CD11b signaling prevents chondrocyte hypertrophy and chondrocyte mineralization in vitro and has a protective role in models of OA in vivo.

Design and Pharmacological Characterization of α4β1 Integrin Cyclopeptide Agonists: Computational Investigation of Ligand Determinants for Agonism versus Antagonism

“…Accordingly, α M allosteric agonists promoting the anti-inflammatory functions of α M integrin, could be useful in the treatment of lupus nephritis, a debilitating and severe complication of systemic lupus erythematosus characterized by infiltration of immune cells to the kidneys . Moreover, α M β 2 integrin agonists have also been suggested for the therapy of osteoarthritis; given that this integrin is involved in preventing chondrocyte hypertrophy and chondrocyte mineralization, activation of α M β 2 with agonists could lead to reduced inflammatory response …”

Strontium Regulates the Proliferation and Differentiation of Isolated Primary Bovine Chondrocytes via the TGFβ/SMAD Pathway

“…The TGFβ co-receptor Cripto promoted COL10A1 by inducing SMAD1/5/9 signaling in ATDC5 cells and immortalized C28/12 human chondrocytes ( Garcia de Vinuesa et al, 2021 ). A role for ALPL in the maturation and mineralization as well as the inhibitory effect of Sr on SPP1, COL10A1, and ALPL was reported in murine chondrocytes ( Ehirchiou et al, 2020 ). Thus, together, available data suggest a mechanistic function for the systemic supply of Sr on fundamental aspects of chondrocyte development ( Figure 7 ).…”

Caspase-1 Inhibition Impacts the Formation of Chondrogenic Nodules, and the Expression of Markers Related to Osteogenic Differentiation and Lipid Metabolism

“…Moreover, both molecules can play a role in lipid metabolism [33,34]. Itgam, another downregulated factor after caspase-1 inhibition, participates in signaling causing reduced chondrocyte mineralization [35]. This could contribute to alterations in the phenotype of the inhibited micromasses.…”

“…Vdr polymorphisms were associated with susceptibility for primary osteoarthritis [38]. Itgam affects the severity of osteoarthritis [35]. The effect of caspase-1 inhibition on cartilage maintenance involves also the most upregulated genes, Bmp7 and Gdf10.…”