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. 2025 Mar 18;26(1):274.
doi: 10.1186/s12891-025-08509-y.

Osteopontin inhibits autophagy via CD44 and avβ3 integrin and promotes cell proliferation in osteoarthritic fibroblast-like synoviocytes

Min Li  1 , Chang-Bao Wei  1 , Hai-Feng Li  1 , Ke He  2 , Rui-Jun Bai  3 , Fang-Jie Zhang  4   5
Affiliations

Osteopontin inhibits autophagy via CD44 and avβ3 integrin and promotes cell proliferation in osteoarthritic fibroblast-like synoviocytes

Min Li et al. BMC Musculoskelet Disord. .

Abstract

Objective: Osteoarthritis (OA) is closely related to aging, and autophagy is implicated in the retardation of aging. Activated synoviocytes play important roles in OA; the synoviocytes could produce osteopontin (OPN) and its main receptors CD44 and integrin, which are all involved in OA. The purpose of this study is to investigate whether OPN has an effect on autophagy in osteoarthritic synoviocytes.

Methods: We cultured human OA fibroblast-like synoviocytes (FLS) and treated them with rhOPN and antibodies against CD44 and CD51/61 (αvβ3 integrin) or isotype IgG to block the interaction between receptors and ligands. Infection with lentivirus mRFP-GFP-LC3, laser confocal imaging and Western blotting were used to determine changes in the expression of autophagy markers, and cell proliferation of FLS was assessed with a CCK-8 assay.

Results: Our results showed the expression level of autophagy marker protein LC3 II and the mRFP-GFP-LC3 puncta were significantly decreased after treatment with rhOPN when compared with the control group, when the FLS were incubated with antibodies against CD44 or CD51/61 (αvβ3 integrin) or with control isotype IgG for 1 h, followed by rhOPN treatment for 48 h, rhOPN could suppress the relative expression of LC3 II and Beclin1 via integrin and CD44 in the FLS, CCK-8 assay also showed that rhOPN significantly increased the cell proliferation and viability of FLS.

Conclusions: OPN could inhibit autophagy via CD44 and αvβ3 integrin and promote the proliferation of FLS, playing an important role in OA synovitis.

Keywords: Autophagy; CD44; Integrin; Osteoarthritis; Osteopontin; Synoviocyte.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate and publication: The studies that involved human participants were meticulously reviewed and granted approval by the Institutional Review Board of Xiangya Hospital, Central South University. All patients/participants provided their written informed consent prior to their involvement in this study. Data Sharing Statement: All data generated or analyzed during this study are included in the manuscript. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Phenotypic features of the FLS passages 4 through 6. (A) Light microscopy showed that FLS were homogeneous and spindle-shaped in morphology. (B) Immunocytochemical staining revealed that the majority of FLS stained positive with anti-vimentin antibody
Fig. 2
Fig. 2
rhOPN inhibits autophagy activity via suppressing the expression of LC3. (A) The LC3 II of FLS was significantly decreased in rhOPN group compared to the control group. (B) The expression of LC3 II between the two groups were statistically significant. (C) The mRFP-GFP-LC3 puncta confirmed the inhibitory effects of LC3 II in rhOPN group compared to the control group. (D) The expression of the mRFP-GFP-LC3 puncta between these two groups were statistically significant; * means P < 0.05 when compared between the two groups, ** means P < 0.01 when compared between the two groups
Fig. 3
Fig. 3
rhOPN inhibits autophagy activity through the intervene of Integrin in FLS. (A) The expression of LC3 II and Beclin1 in FLS treated by rhOPN, CD44 Ab + rhOPN, Ig G2 + rhOPN, CD51 Ab + rhOPN, Ig G1 + rhOPN compared to the control group. (B) The analysis showed that expression of LC3 II was statistically significant in groups Control vs. rhOPN, control vs. Ig G2 + rhOPN and Control vs. Ig G1 + rhOPN; (C) The analysis showed that expression of Beclin1 was statistically significant in groups Control vs. rhOPN, Control vs. Ig G2 + rhOPN and Control vs. Ig G1 + rhOPN. * means P < 0.05 when compared between the two groups
Fig. 4
Fig. 4
rhOPN could promote the cell proliferation of FLS in vitro and that even CD44 and CD51 Ab or their isotype Ig G could not block this effect. The CCK8 results showed the FLS proliferation were statistically significant in groups Control vs. rhOPN, Control vs. rhOPN + CD44 Ab, Control vs. Ig G2 + rhOPN, Control vs. rhOPN + CD51 Ab, and Control vs. Ig G1 + rhOPN. * means P < 0.05 when compared between the two groups, ** means P < 0.01 when compared between the two groups
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