Therapeutic RNAi Targeting CKIP-1 for Promoting Bone Formation in Postmenopausal Osteoporosis: A Translational Study of CKIP-1

We raised the hypothesis that therapeutic RNAi targeting of CKIP-1 might promote bone formation for reversing postmenopausal bone loss. To test the hypothesis, we performed several studies to achieve the following specific aims: (1) To explore the relationship between CKIP-1 expression and bone formation in aged postmenopausal osteoporosis; (2) To Identify a cross-species CKIP-1 siRNA sequence with high knockdown efficiency; (3) To validate of the identified CKIP-1 siRNA in healthy rodents in vivo; (4) To examine the anabolic effect of the identified CKIP-1 siRNA on bone in osteoporotic animal models.;The relationship between CKIP-1 gene expression and bone formation in bone specimens from aged postmenopausal women: To explore the association between CKIP-1 gene expression and bone formation in bone specimens from aged postmenopausal women, the gene expression of CKIP-1 and ALP in the bone specimens from aged female patients were examined. We found the protein expression of CKIP-1 increased during aging and negatively correlate to bone formation as indicated by the mRNA expression of ALP (Guo, Zhang. et al. 2011). Further, we also found the decreased bone formation during aging was partly rescued in Ckip-1 KO mice during aging.;A cross-species CKIP-1 siRNA sequence: Recently, we identified a specific CKIP-1 siRNA sequence (CKIP-1 siRNA si-3) with high knockdown efficiency across rat, mouse, rhesus, and human osteoblast-like cells that does not induce immunostimulatory activity and promotes osteoblast differentiation across the species in vitro and bone formation in rats in vivo (Guo, Zheng et al. 2012).;Validation of the CKIP-1 siRNA si-3 capsulated by bone-targeted siRNA delivery system in healthy rodents in vivo: We developed a bone-targeting siRNA delivery system (tripeptide aspartate-serine-serine linked with liposome, i.e. (Asp-Ser-Ser)6-liposome) that can remarkably reduce the exposure of non-bone tissue to CKIP-1 siRNA (Zhang, Guo et al. 2012). To validate the identified CKIP-1 siRNA in healthy rodents in vivo, the established continuous CKIP-1 gene silencing protocol is optimized in adult rats and mice in vivo by hydrodynamic tail vein injection of 3.75mg/kg for rats and 7.5 mg/kg for mice every 2 weeks (Guo, Zhang et al. 2010). The osteogenic effects of CKIP-1 siRNA in both rats and mice were further validated in vivo..;Anabolic effect of CKIP-1 siRNA si-3 on bone in aged postmenopausal osteoporosis: For evaluation of the anabolic effect of CKIP-1 siRNA si-3 on reversing bone loss due to osteoporosis in an animal model, we intravenously injected ovariectomized (OVX) rats and mice with CKIP-1 siRNA delivered by the (Asp-Ser-Ser)6-liposome, a liposome linked with six repeated aspartate-serine-serine moiety, every 2 weeks for 6 weeks. In vivo and ex vivo microCT analysis demonstrated a change over time in the variables examined and different change patterns over time among the groups examined after administration. We found that the siRNA group had experienced a significant increase in bone mineral density (BMD), relative bone volume (BV/TV), and trabecular thickness (Tb.Th) between weeks 0 and 6; had a higher BMD, BV/TV, and Tb.Th compared to the OVX group at week 6; and had a similar Tb.Th to that of the SHAM group at week 6. Registration analysis between week 0 and other time points revealed that the siRNA had a greater number of newly formed bone than the OVX and SHAM groups. Histomorphometric analysis showed that the siRNA group had a significantly higher mineralization rate (MAR), a significantly higher bone-formation rate (BFR), a significantly larger osteoblast surface (Ob.S/BS) at both the distal and mid-shaft femur compared to the OVX group after 6 weeks of treatment but not a significantly different Oc.S/BS. (Abstract shortened by UMI.).