Osteoclastogenesis and Immune Regulation Mechanisms

Osteoclastogenesis, the process by which specialised bone-resorbing cells differentiate from monocyte–macrophage precursors, lies at the heart of skeletal remodelling and systemic calcium homeostasis. Central to this process is the ligand–receptor axis comprising RANKL (receptor activator of nuclear factor κB ligand), its cognate receptor RANK on osteoclast progenitors, and the decoy receptor osteoprotegerin (OPG). When RANKL binds RANK, it activates downstream signalling cascades—most notably NF-κB and MAPK pathways—culminating in the expression of osteoclast-specific genes such as cathepsin K and tartrate-resistant acid phosphatase. Immune cells contribute directly to this regulatory network: T cells and B cells can both produce RANKL, while dendritic cells modulate local cytokine milieus that influence osteoclast differentiation. Conversely, osteoclasts and their precursors release cytokines and chemokines that shape immune responses, establishing a bidirectional communication channel termed “osteoimmunology.” Dysregulation of this interplay underlies a spectrum of pathologies, from postmenopausal osteoporosis and inflammatory arthritis to tumour-induced osteolysis. Recent advances have elucidated how co-repressor complexes, non-coding RNAs and local microenvironmental cues fine-tune osteoclast formation, and how immune checkpoints modulate bone resorption under both physiological and pathological conditions.

Research from Nature Portfolio

Studies employing genetically modified mice resistant to shedding of membrane-bound RANKL have clarified the distinct contributions of soluble versus membrane-anchored forms. In adult animals, absence of soluble RANKL diminishes osteoclast number and increases cancellous bone mass, demonstrating that shed RANKL augments homeostatic bone remodelling beyond its membrane-bound activity. Remarkably, this loss of soluble ligand does not impede the bone loss triggered by oestrogen deficiency, nor does it compromise lymphoid organ development or mammary gland morphogenesis. These findings reveal that, while membrane-bound RANKL suffices for most developmental and immune functions, the soluble cytokine modulates osteoclastogenesis in specific adult contexts and may represent a selective target for interventions aimed at reducing pathological bone turnover without broad immunological consequences.

Osteoclastogenesis and Immune Regulation Mechanisms publication trend

The graph below shows the total number of articles in osteoclastogenesis and immune regulation mechanisms across all publications each year (not limited to Nature Index journals).

Technical terms

RANKL (Receptor Activator of Nuclear Factor κB Ligand): A member of the tumour necrosis factor superfamily produced by osteoblasts and immune cells that binds RANK to drive osteoclast differentiation.

RANK (Receptor Activator of Nuclear Factor κB): A cell-surface receptor on osteoclast precursors; engagement by RANKL initiates signalling cascades essential for osteoclastogenesis.

Osteoprotegerin (OPG): A soluble decoy receptor for RANKL that inhibits osteoclast formation by preventing RANKL–RANK interaction.

NF-κB (Nuclear Factor κB): A transcription factor activated downstream of RANK that promotes expression of osteoclast-specific and pro-inflammatory genes.

Osteoimmunology: The interdisciplinary field examining the interplay between the skeletal system and immune regulation, particularly the mutual regulation of bone cells and immune cells.

Pyroptosis: A form of pro-inflammatory programmed cell death mediated by inflammasome activation and caspase-1, leading to cytokine release and membrane pore formation.

References

1. RANK ligand converts the NCoR/HDAC3 co-repressor to a PGC1β- and RNA-dependent co-activator of osteoclast gene expression. Molecular Cell (2023).
2. Reduced OPG expression by osteocytes may contribute to rebound resorption after denosumab discontinuation. JCI Insight (2023).
3. The Mechanism of Osteoprotegerin-Induced Osteoclast Pyroptosis In Vitro. International Journal of Molecular Sciences (2023).
4. RANKL biology: bone metabolism, the immune system, and beyond. Inflammation and Regeneration (2020).
5. Soluble RANKL contributes to osteoclast formation in adult mice but not ovariectomy-induced bone loss. Nature Communications (2018).