BNIP3 mediates the different adaptive responses of fibroblast-like synovial cells to hypoxia in patients with osteoarthritis and rheumatoid arthritis

Abstract

Background Hypoxia is one of the important characteristics of synovial microenvironment in rheumatoid arthritis (RA), and plays an important role in synovial hyperplasia. In terms of cell survival, fibroblast-like synovial cells (FLSs) are relatively affected by hypoxia. In contrast, fibroblast-like synovial cells from patients with RA (RA-FLSs) are particularly resistant to hypoxia-induced cell death. The purpose of this study was to evaluate whether fibroblast-like synovial cells in patients with osteoarthritis (OA-FLSs) and RA-FLSs have the same adaptation to hypoxia. Methods CCK-8, flow cytometry and BrdU were used to detect the proliferation of OA-FLSs and RA-FLSs under different oxygen concentrations. Apoptosis was detected by AV/PI, TUNEL and Western blot, mitophagy was observed by electron microscope, laser confocal microscope and Western blot, the state of mitochondria was detected by ROS and mitochondrial membrane potential by flow cytometry, BNIP3 and HIF-1α were detected by Western blot and RT-qPCR. The silencing of BNIP3 was achieved by stealth RNA system technology. Results After hypoxia, the survival rate of OA-FLSs decreased, while the proliferation activity of RA-FLSs further increased. Hypoxia induced an increase in apoptosis and inhibition of mitophagy in OA-FLSs, but not in RA-FLSs. Hypoxia led to a more lasting adaptive response. RA-FLSs displayed a more significant increase in the expression of genes transcriptionally regulated by HIF-1α. Interestingly, they showed higher BNIP3 expression than OA-FLSs, and showed stronger mitophagy and proliferation activities. BNIP3 siRNA experiment confirmed the potential role of BNIP3 in the survival of RA-FLSs. Inhibition of BNIP3 resulted in the decrease of cell proliferation, mitophagy and the increase of apoptosis. Conclusion In summary, RA-FLSs maintained intracellular redox balance through mitophagy to promote cell survival under hypoxia. The mitophagy of OA-FLSs was too little to maintain the redox balance of mitochondria, resulting in apoptosis. The difference of mitophagy between OA-FLSs and RA-FLSs under hypoxia is mediated by the level of BNIP3 expression.

The HIF-1/ BNIP3 pathway mediates mitophagy to inhibit the pyroptosis of fibroblast-like synoviocytes in rheumatoid arthritis

“…The well known, the receptor-mediated mitophagy can be activated by hypoxia, such as BNIP3-mediated mitophagy [31][32]. FLS maintained intracellular redox balance through BNIP3-mediated mitophagy to promote cell survival under hypoxia in RA [17]. Our results also showed that the expressions of mitophagy related proteins BNIP3 and LC3B in RA synovium were significantly increased (Fig.…”

“…However, one of the major pathological features of RA is the abnormal proliferation of FLS, manifesting as hyperplasia of synovial tissue [16]. Recent research has found that FLS of RA maintained intracellular redox balance through BCL2/adenovirus e1B 19 kDa protein interacting protein 3 (BNIP3)-mediated mitochondrial autophagy (mitophagy) to promote cell survival under hypoxia [17].…”

“…The difference of BNIP3 expression in FLS is one of the important reasons for the different pathological manifestations of osteoarthritis and RA [17]. Mitophagy is a mitochondrial quality control mechanism that selectively removes damaged mitochondria via autophagic degradation [18].…”

Identification of a novel, MSC-induced macrophage subtype via single-cell sequencing: implications for intervertebral disc degeneration therapy

“…To generate conditioned medium, we cultured STRO3 + enriched MSCs for 24 h at either atmospheric oxygen tension, or 2% O 2 to simulate the hypoxic environment of the intervertebral disc. MSCs cultured in hypoxia exhibited reduced survival time, as evidenced by reduced numbers of CD90 + cells ( Figure 4C ) and enhanced expression of BNIP3, a marker of cell death induced by hypoxia ( Zhang and Ney, 2009 ; Deng et al, 2022 ), after 48 h ( Figure 4D ). To limit the confounding effects of cell death in hypoxia, MSCs were cultured for 24 h in either normoxic or hypoxic conditions and CM were collected for subsequent experiments.…”

Metabolic changes in fibroblast-like synoviocytes in rheumatoid arthritis: state of the art review

“…In hypoxic environments, RA-FLS cells exhibited a more pronounced increase in the expression of HIF-1α transcriptional regulatory genes, higher BNIP3 expression, and stronger mitochondrial autophagy and proliferative activity ( 63 ).…”