SIRT5-JIP4 Interaction Promotes Osteoclastogenesis by Modulating RANKL-Induced Signaling Transduction

Research Background

Osteoporosis is a common bone disease characterized by reduced bone density and disrupted bone microstructure, leading to an increased risk of fractures. Osteoclasts, the primary cells responsible for bone resorption, play a critical role in osteoporosis and other bone-related diseases. The differentiation and function of osteoclasts are regulated by multiple signaling pathways, among which the RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand) signaling pathway is particularly important. RANKL binds to the RANK receptor, activating downstream signaling pathways such as TRAF6, NF-κB, and MAPK, thereby regulating osteoclast differentiation and function. However, the specific molecular mechanisms underlying RANKL signaling remain incompletely understood.

Recent studies have shown that SIRT5, an NAD+-dependent lysine deacetylase, plays an important role in various cellular differentiation processes. SIRT5 is primarily localized in the mitochondrial matrix and regulates cellular energy metabolism by modulating the function of mitochondrial metabolic enzymes. Given that osteoclast differentiation is a highly energy-consuming process, SIRT5 may play a significant role in osteoclastogenesis. However, the specific functions and molecular mechanisms of SIRT5 in osteoclast differentiation have not been thoroughly investigated.

Source of the Paper

This paper was co-authored by Kecheng Zhu, Chunxiang Sheng, and others, with the research team affiliated with the Institute of Endocrine and Metabolic Diseases, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine. The paper was published in 2025 in the journal Cell Communication and Signaling, titled “The SIRT5-JIP4 interaction promotes osteoclastogenesis by modulating RANKL-induced signaling transduction”.

Research Process and Results

1. Role of SIRT5 in Osteoclast Differentiation

The study first investigated the effects of SIRT5 on bone mass and strength using a SIRT5 knockout mouse model (SIRT5−/−). Micro-CT analysis revealed that SIRT5 knockout mice exhibited significantly increased bone mass and strength, particularly in trabecular bone volume density (vBMD) and cortical thickness (Ct.Th). Further biomechanical testing showed that the bone fracture resistance of SIRT5 knockout mice was enhanced.

To determine the impact of SIRT5 knockout on bone metabolism, the research team measured serum bone metabolism markers. The results showed that the bone resorption marker CTX-I (C-terminal telopeptide of type I collagen) levels were significantly reduced in SIRT5 knockout mice, while the bone formation markers PINP (N-terminal propeptide of type I procollagen) and OCN (osteocalcin) levels remained unchanged. This suggests that SIRT5 knockout primarily increases bone mass by inhibiting bone resorption rather than promoting bone formation.

2. Molecular Mechanisms of SIRT5 in Regulating Osteoclast Differentiation

To further investigate the role of SIRT5 in osteoclast differentiation, the research team isolated bone marrow-derived macrophages (BMDMs) from mice and induced their differentiation into osteoclasts using RANKL. The study found that SIRT5 expression was significantly upregulated during osteoclast differentiation. Knockdown of SIRT5 using RNA interference significantly reduced the expression of osteoclast differentiation-related genes (such as NFATc1, MITF, DC-STAMP, OC-STAMP, TRAP, and CTSK) and decreased the number of TRAP-positive multinucleated osteoclasts. Conversely, overexpression of SIRT5 significantly promoted osteoclast differentiation.

3. Interaction Between SIRT5 and JIP4

To elucidate the molecular mechanisms by which SIRT5 regulates osteoclast differentiation, the research team identified SIRT5-interacting proteins using co-immunoprecipitation (co-IP) and mass spectrometry (MS). The results showed that SIRT5 interacts with JIP4 (JNK-interacting protein 4) in the cytoplasm. JIP4 is a scaffold protein that regulates the activation of the MAPK signaling pathway. The study found that SIRT5 promotes RANKL-induced phosphorylation of p38 and JNK through its interaction with JIP4, thereby regulating osteoclast differentiation.

4. Potential Therapeutic Applications of SIRT5 in Osteoporosis

To validate the potential therapeutic value of SIRT5 in osteoporosis, the research team treated ovariectomized (OVX) mice with the SIRT5 inhibitor NRD167. The results showed that NRD167 significantly improved bone loss in OVX mice and reduced serum CTX-I levels. This suggests that inhibiting SIRT5 activity may be an effective strategy for treating osteoporosis.

Conclusions and Significance

This study is the first to reveal the critical role of SIRT5 in osteoclast differentiation and to elucidate the molecular mechanism by which SIRT5 regulates the RANKL signaling pathway through its interaction with JIP4. The findings indicate that the SIRT5-JIP4 axis is a novel positive regulator of osteoclast differentiation, and targeting this axis may provide a new strategy for the treatment of osteoporosis.

Research Highlights

1. Key Role of SIRT5 in Osteoclast Differentiation: The study is the first to reveal the important role of SIRT5 in osteoclast differentiation, filling a gap in this field of research.
2. Interaction Between SIRT5 and JIP4: The study found that SIRT5 regulates the MAPK signaling pathway through its interaction with JIP4, providing new insights into the molecular mechanisms of osteoclast differentiation.
3. Therapeutic Potential of SIRT5 Inhibitors: The study confirmed the potential therapeutic value of the SIRT5 inhibitor NRD167 in osteoporosis, providing a theoretical basis for the development of new therapeutic drugs.

Additional Valuable Information

The study also found that SIRT5 primarily regulates osteoclast differentiation by modulating mitochondrial energy metabolism. Knockdown of SIRT5 led to decreased mitochondrial basal metabolism and ATP production, while overexpression of SIRT5 significantly enhanced mitochondrial energy metabolism. This suggests that SIRT5 not only regulates signaling pathways but also influences cellular function by modulating energy metabolism during osteoclast differentiation.

This study provides new perspectives on understanding the molecular mechanisms of osteoclast differentiation and offers potential new targets for the treatment of osteoporosis.