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The Mechanism of Osteoprotegerin-Induced Osteoclast Pyroptosis In Vitro
Jiaqiao Zhu1,2,3, Yonggang Ma1,2,3, Jie Wang1,2,3
1College of Veterinary Medicine, Yangzhou University, Yangzhou 225009, China.
Abstract:
Osteoprotegerin (OPG) is a new member of the tumor necrosis factor (TNF) receptor superfamily, which can inhibit the differentiation and activity of osteoclasts by binding to nuclear factor kappa B receptor activator (RANK) competitively with nuclear factor kappa B receptor activator ligand (RANKL). The previous experiments found that OPG can induce apoptosis of mature osteoclasts in vitro, which can inhibit the activity of mature osteoclasts, thereby exerting its role in protecting bone tissue. In addition, pyroptosis is a new type of cell death that is different from apoptosis. It is unclear whether OPG can induce mature osteoclast pyroptosis and thereby play its role in protecting bone tissue. In this study, the results showed that compared with the control group, the survival rate of osteoclasts in the OPG group was significantly reduced, and the contents of IL-1β, IL-18, and LDH in the supernatant both increased. Many osteoclast plasma membranes were observed to rupture in bright fields, and OPG induced loss of their morphology. Flow cytometry was used to analyze the pyroptosis rate; OPG significantly increased the osteoclast pyroptosis rate. To further reveal the mechanism of OPG-induced osteoclast pyroptosis, we examined the expression level of pyroptosis-related genes and proteins, and the results found that OPG increased the expression of NLRP3, ASC, caspase-1, and GSDMD-N compared with the control group. In summary, OPG can induce osteoclast pyroptosis, and its mechanism is related to the expression levels of ASC, NLRP3, caspase 1 and GSDMD, which were included in the classical pathway of pyroptosis.
Insights
Osteoprotegerin (OPG) induces pyroptosis, a form of programmed cell death, in mature osteoclasts. This mechanism, involving NLRP3 and caspase-1, contributes to OPG's bone-protective effects.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Osteoprotegerin (OPG) is a TNF receptor superfamily member inhibiting osteoclast activity via RANK/RANKL.
- OPG induces osteoclast apoptosis, protecting bone tissue.
- Pyroptosis, a distinct cell death pathway, is investigated for its role in OPG's function.
Purpose of the Study:
- To determine if OPG induces pyroptosis in mature osteoclasts.
- To elucidate the molecular mechanisms underlying OPG-induced osteoclast pyroptosis.
Main Methods:
- In vitro culture of osteoclasts treated with OPG.
- Measurement of IL-1β, IL-18, and LDH levels in supernatant.
- Morphological analysis of osteoclasts.
- Flow cytometry for pyroptosis rate assessment.
- Analysis of pyroptosis-related gene and protein expression (NLRP3, ASC, caspase-1, GSDMD-N).
Main Results:
- OPG significantly reduced osteoclast survival and increased IL-1β, IL-18, and LDH.
- Osteoclast plasma membrane rupture and morphological changes were observed.
- OPG treatment markedly elevated the pyroptosis rate in osteoclasts.
- Expression of NLRP3, ASC, caspase-1, and GSDMD-N was upregulated by OPG.
Conclusions:
- OPG effectively induces pyroptosis in mature osteoclasts.
- The mechanism involves the classical pyroptosis pathway, including NLRP3, ASC, caspase-1, and GSDMD.
- OPG-induced osteoclast pyroptosis is a novel pathway contributing to bone protection.
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