Recombinant sclerostin inhibits bone formation in vitro and in a mouse model of sclerosteosis

摘要

BackgroundSclerosteosis, a severe autosomal recessive sclerosing skeletal dysplasia characterised by excessive bone formation, is caused by absence of sclerostin, a negative regulator of bone formation that binds LRP5/6 Wnt co-receptors. Current treatment is limited to surgical management of symptoms arising from bone overgrowth. This study investigated the effectiveness of sclerostin replacement therapy in a mouse model of sclerosteosis.MethodsRecombinant wild type mouse sclerostin (mScl) and novel mScl fusion proteins containing a C-terminal human Fc (mScl hFc), or C-terminal human Fc with a poly-aspartate motif (mScl hFc PD), were produced and purified using mammalian expression and standard chromatography methods.In vitrofunctionality and efficacy of the recombinant proteins were evaluated using three independent biophysical techniques and anin vitrobone nodule formation assay. Pharmacokinetic properties of the proteins were investigatedin vivofollowing a single administration to young female wild type (WT) or SOST knock out (SOST-/-) mice. In a six week proof-of-conceptin vivostudy, young female WT or SOST-/-mice were treated with 10?mg/kg mScl hFc or mScl hFc PD (weekly), or 4.4?mg/kg mScl (daily). The effect of recombinant sclerostin on femoral cortical and trabecular bone parameters were assessed by micro computed tomography (μCT).ResultsRecombinant mScl proteins bound to the extracellular domain of the Wnt co-receptor LRP6 with high affinity (nM range) and completely inhibited matrix mineralisationin vitro. Pharmacokinetic assessment following a single dose administered to WT or SOST-/-mice indicated the presence of hFc increased protein half-life from less than 5?min to at least 1.5 days. Treatment with mScl hFc PD over a six week period resulted in modest but significant reductions in trabecular volumetric bone mineral density (vBMD) and bone volume fraction (BV/TV), of 20% and 15%, respectively.ConclusionAdministration of recombinant mScl hFc PD partially corrected the high bone mass phenotype in SOST-/-mice, suggesting that bone-targeting of sclerostin engineered to improve half-life was able to negatively regulate bone formation in the SOST-/-mouse model of sclerosteosis.The translational potential of this articleThese findings support the concept that exogenous sclerostin can reduce bone mass, however the modest efficacy suggests that sclerostin replacement may not be an optimal strategy to mitigate excessive bone formation in sclerosteosis, hence alternative approaches should be explored.