Pharmacological inhibition of Dock5 prevents osteolysis by affecting osteoclast podosome organization while preserving bone formation

Abstract

Osteoporosis is caused by excessive activity of bone-degrading osteoclasts over bone-forming osteoblast. Standard antiosteolytic treatments inhibit bone resorption by inducing osteoclast loss, with the adverse effect of hindering also bone formation. Formation of the osteoclast sealing zone requires Dock5, a guanine nucleotide exchange factor for the small GTPase Rac, and C21, a chemical inhibitor of Dock5, decreases bone resorption by cultured osteoclasts. Here we show that C21 directly inhibits the exchange activity of Dock5 and disrupts osteoclast podosome organization. Remarkably, C21 administration protects mice against bone degradation in models recapitulating major osteolytic diseases: menopause, rheumatoid arthritis and bone metastasis. Furthermore, C21 administration does not affect bone formation and is not toxic. Our results validate the pharmacological inhibition of Dock5 as a novel therapeutic route for fighting osteolytic diseases while preserving bone formation.

Tensin 3 is a new partner of Dock5 that controls osteoclast podosome organization and activity

“…We show here that tensin 3 can potentiate Dock5 exchange activity towards Rac. We also found that tensin 3 is necessary for the correct patterning of osteoclast podosomes, which is known to also require Dock5 (Vives et al, 2011), Rac (Razzouk et al, 1999;Wang et al, 2008;Croke et al, 2011) and the activation of Rac by Dock5 (Vives et al, 2015).…”

“…We reported previously that Dock5, an activator of the GTPase Rac, participates in osteoclast podosome organization and is essential for bone resorption (Vives et al, 2011). We also showed that systemic injection of a small chemical compound that targets Dock5 exchange activity can prevent pathological bone loss in the mouse, whereas bone formation is preserved (Vives et al, 2015). We performed proteomic analysis of Dock5 partners in osteoclasts to investigate further the molecular mechanisms controlling podosome patterning in osteoclasts and, hence, bone resorption.…”

“…Dock5 drives the assembly of osteoclast podosomes into a belt, thereby controlling bone resorption by osteoclasts and, hence, bone mass in vivo in the developing, growing and adult mouse (Vives et al, 2011;Touaitahuata et al, 2014b). Moreover, the systemic injection of a small chemical compound inhibitor of Rac activation by Dock5 prevents bone loss in mice subjected to ovariectomy, collageninduced arthritis or bone metastases, whereas bone formation by osteoblasts is preserved, thereby highlighting Dock5 as a novel target for the treatment of osteoporosis (Vives et al, 2015).…”

“…Tensin 3 participates in the organization of podosomes and can activate Dock5, an exchange factor for the GTPase Rac, which we identified previously as a regulator of osteoclast adhesion and activity (Vives et al, 2011(Vives et al, , 2015.…”

“…Active Rac1 and RhoA quantification GTP-bound Rac1 was pulled down from HEK293T and osteoclast cell extracts using GST-fused PAK1 CRIB domain, as described previously (Vives et al, 2011(Vives et al, , 2015, and revealed by western blotting with anti-Rac1 antibodies. Active Rac1 was normalized to total Rac1 and to Dock5 expression as determined by western blotting on the corresponding whole-cell extracts.…”