Sharpin is a key regulator of skeletal homeostasis in a TNF-dependent manner.

OBJECTIVES: SHARPIN is a subunit of LUBAC and regulates activation of NF-κB, a pivotal transcription factor in skeletal homeostasis. Mutated SHARPIN gene (cpdm) mice develop chronic proliferative dermatitis and systemic inflammation. Cpdm mice have an osteopaenic phenotype characterised by decreased cortical and trabecular bone volume, but whether this is a consequence of the hyper-inflammatory phenotype is unknown. The inflammatory phenotype of cpdm mice is prevented by Tnf deficiency so we examined cpdm.Tnf (-/-) mice to examine the role of SHARPIN in skeletal development. METHODS: This research determined the extent to which SHARPIN and TNF interact within the skeleton through analyses of gene expression, µCT and biomechanical properties of bones of control (CTRL), cpdm, Tnf (-/-) (TNF KO) and cpdm.Tnf (-/-) (cpdm/TNF KO) mice. RESULTS: Gene expression of IL-1ß, TNF and caspase-3 increased in cpdm mice but was comparable to control values in cpdm/TNF KO mice. Decreased cortical and trabecular bone in cpdm mice translated to a loss in bone strength (ultimate stress and peak force). Cpdm/TNF KO mice developed bones similar to, or stronger than, control bones. CONCLUSIONS: Our results suggest that SHARPIN plays a significant role in skeletal homeostasis and that this role is strongly regulated through TNF pathways.

Galnon, a galanin receptor agonist, improves intrinsic cortical bone tissue properties but exacerbates bone loss in an ovariectomised rat model.

OBJECTIVES: Previous studies have shown galanin (GAL) injections onto mouse calvaria increased bone thickness and osteoblast number. This study investigated the effects of the GAL receptor agonist galnon on bone loss using the ovariectomised (OVX) rat model. METHODS: OVX rats were treated with either vehicle or galnon for 6 weeks via mini-osmotic pumps. Plasma osteocalcin concentrations, osseous cell gene expression, morphological and biomechanical properties of the skeleton were compared between the two groups. RESULTS: Treatment with galnon increased RANKL:OPG gene ratio (p<0.001) plus expression of TNF-α (p<0.05) and cathepsin K (p<0.05). µCT analyses revealed galnon-treated OVX animals had reduced trabecular and cortical morphology compared to control animals. Biomechanically, galnon OVX animals required similar peak force to failure to that of control OVX animals although galnon treatment did enhance the mechanical properties of Young's modulus and ultimate tensile stress. CONCLUSIONS: Our research suggests that galnon, a GAL receptor agonist, may enhance osteoclastic bone resorption in OVX rats. Although galnon reduced bone volume, biomechanical testing revealed that bone of galnon-treated animals was mechanically superior per unit area. Taken together, galnon simultaneously improves the intrinsic quality of cortical bone whilst stimulating osteoclastic activity in the OVX rat model.