Delivery of miRNAs Using Porous Silicon Nanoparticles Incorporated into 3D Hydrogels Enhances MSC Osteogenesis by Modulation of Fatty Acid Signalling and Silicon Degradation.

Bone tissue engineering strategies incorporating mesenchymal stromal cells (MSC), hydrogels and osteoinductive signals offer great promise for bone repair and regeneration. Commonly used osteoinductive signals such as growth factors face challenges in clinical translation due to their high cost, low stability and potential immunogenicity. Therefore, interest is growing in the delivery of microRNAs as a simple, inexpensive and powerful alternative to modulate MSC osteogenesis. Nevertheless, challenges associated with the selection of appropriate miRNA candidates and their efficient delivery must be overcome to make this a reality. This study performed a systematic evaluation to identify pro-osteogenic miRNAs and developed a system using porous silicon nanoparticles (pSiNP) modified with polyamidoamine (PAMAM) dendrimers (PAMAM-pSiNP) to deliver these directly to MSC encapsulated within a photo-crosslinkable gelatin-polytheylene glycol (PEG) hydrogel. Here, we have identified miR-29b-3p, miR-101-3p and miR-125b-5p as strong pro-osteogenic miRNAs which were shown to collectively act upon fatty acid synthase (FASN) and ELOVL Fatty Acid Elongase 4 (ELOVL4) in the fatty acid biosynthesis pathway to modulate MSC osteogenesis. This work also demonstrated delivery of miRNA:PAMAM-pSiNP complexes to MSC encapsulated within a 3D hydrogel, showing enhanced transfection when compared to standard 2D transfection. A complete system for bone tissue engineering was developed in which the osteogenic potential of hBMSC in gelatin-PEG hydrogels loaded with miR-125b:PAMAM-pSiNP complexes was evaluated. Importantly, a dual-effect on osteogenesis was observed, whereby the miRNAs increased expression of the osteogenic genes alkaline phosphatase (ALP) and Runt-related transcription factor 2 (RUNX2) whilst the pSiNP themselves substantially enhanced mineralisation, likely via their degradation into silicic acid. Overall, this work presents insights into to the role of miR-29b-3p, miR-101-3p and miR-125b-5p and fatty acid signalling in the regulation of osteogenesis, which may provide future targets to improve bone formation, as well as a promising system to enhance osteogenesis for MSC-based bone tissue engineering. This article is protected by copyright. All rights reserved.