New craniofacial bone engineering through miR-23-27-24 cluster mediated osteogenic-angiogenic coupling

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Blood vessels affect all aspects of bone physiology, including mineral growth during new bone formation. To engineer bone as a vascularized tissue we have now focused on microRNAs as molecular engineering tools because of their ability to reversibly target multiple regulatory networks. Recent studies from our and other laboratories have demonstrated that miRNAs promote bone lineage differentiation and new bone formation through WNT, BMP, and Notch signaling pathways and also control bone resorption. In our quest for novel therapeutics that promote coupled bone remodeling and angiogenesis for the treatment of large bone defects we have here identified the miR-27~23~24 microRNA cluster as a highly promising miRNA candidate reagent. Our preliminary analysis revealed multiple miR-23 and miR-27 binding sites on the untranslated region (UTR) of the Wnt antagonist Sfrp1 and Nlk 3’, which in conjunction with miR-24 binding sites on the UTR of the angiogenesis inhibitors BIM and SEMA4A demonstrate the potential of the miR-27-23-24 microRNA cluster for coupled osteogenic and angiogenic molecular engineering strategies. In preliminary studies, we have demonstrated that miR-23-27-24 cluster member expression was greatly reduced in inflammatory tissues. Conversely, miR-27 mimic treatment of diseased periodontal tissues with severe vertical bone defects resulted in unexpectedly extensive new bone formation as evidenced by 80% complete restoration of vertical bone height and new deposition of mineralized tissue in large calvarial bone defects after 8 weeks of miR-27 application. Implants containing PEG-PLGA-PLL-miR- 27 nanoparticles promoted matrix remodeling, new blood vessel formation, and substantial amounts of calvarial bone regeneration in critical size defects. On a cellular level, miR-27 overexpression increased alkaline phosphatase activity and bone marker gene expression, while inhibition of miR-27 resulted in a dramatic increase in the expression of osteoclastogenesis related genes and bone resorption. Both miR-24 and miR-27 promoted endothelial cell proliferation and blood vessel tube formation. Together, these exciting preliminary data prompted us to propose a novel molecular engineering strategy that will harness the osteogenic and pro-angiogenic qualities of miR-23/27/24 cluster members in conjunction with suitable scaffolds and re-balance alveolar and calvarial bone homeostasis for new craniofacial bone formation.