DOK3 Modulates Bone Remodeling by Negatively Regulating Osteoclastogenesis and Positively Regulating...

Area of Science:

• Cell Biology
• Bone Biology
• Immunology

Background:

• Osteoclastogenesis, driven by Receptor Activator of NF-κB ligand (RANKL), requires co-stimulation via immunoreceptor tyrosine-based activation motif (ITAM)-coupled receptors.
• Triggering receptor expressed on myeloid cells-2 (TREM2) coupled to DNAX activation protein 12kDa (DAP12) provides this co-stimulation.
• Downstream of kinase-3 (DOK3) was previously shown to inhibit toll-like receptor (TLR)-induced inflammatory signaling in macrophages by associating with DAP12.

Purpose of the Study:

• To investigate the role of DOK3 in DAP12-dependent osteoclastogenesis.
• To elucidate the mechanisms by which DOK3 modulates bone remodeling.
• To determine if DOK3 influences osteoblast function.

Main Methods:

• Comparative analysis of bone microarchitecture and histology in wild-type (WT) and DOK3-deficient (DOK3-/-) mice.
• In vitro studies using bone marrow-derived macrophages (BMMs) and osteoclasts from WT, DOK3-/-, and DOK3/DAP12 double-deficient (DKO) mice.
• Assessment of osteoblastogenesis and osteoclastogenesis in vitro and in co-culture systems.

Main Results:

• DOK3-/- mice exhibited significantly reduced trabecular bone mass, increased TRAP+ osteoclasts, larger osteoclasts with more nuclei, and enhanced resorptive capacity.
• DOK3 deficiency led to increased M-CSF-induced proliferation and heightened sensitivity to RANKL in osteoclast differentiation.
• DOK3 limits osteoclastogenesis by inhibiting Syk and ERK activation and also positively regulates osteoblastogenesis, as evidenced by reduced osteoblast parameters and impaired osteoblastogenesis in DOK3-/- mice.

Conclusions:

• DOK3 is a critical negative regulator of osteoclastogenesis and a positive regulator of osteoblastogenesis, thereby controlling bone remodeling.
• DOK3's function in osteoclastogenesis is partly DAP12-dependent but also involves DAP12-independent pathways.
• Dysregulation of DOK3 impacts skeletal homeostasis, highlighting its potential as a therapeutic target for bone diseases.