For functional tissue engineering, it is key to effectively control the lineage-specific differentiation of mesenchymal stromal cells (MSCs). Epigenetic approaches such as the inhibition of histone deacetylase (HDAC) enzymes have been shown to control MSCs fate, with HDAC3 isoform closely linked to osteogenic differentiation. Therefore, the research presented in this thesis aims to investigate the effects of the novel selective HDAC2 and 3 inhibitor - MI192 on the behaviour and osteogenic capacity of clinically relevant MSCs (hDPSCs and hBMSCs), to enhance their efficacy for bone augmentation strategies. In monolayer culture, a time-dose dependent decrease in MSCs
viability was observed following MI192 treatment. MI192 halted cell cycle progression of MSCs in the G2/M phase. MSCs HDAC activity was inhibited upon MI192 treatment, resulting in an increase in H3K9 histone acetylation. Alkaline Phosphatase Specific Activity (ALPSA) was significantly increased in hDPSCs and hBMSCs following a pre-treatment strategy of 2 and 50 μM MI192 for 48 hours,
respectively. Using these conditions, it was demonstrated that MI192 pre-treatment increased MSCs osteoblast-related gene/protein expression throughout osteogenic culture (Runx2, ALP, BMP2, Col1a and OCN) and enhanced calcium deposition/extracellular matrix mineralisation. MI192 pre-treatment enhanced hDPSCs ALPSA, osteoblast-related gene expression (RUNX2, ALP, BMP2, COL1A and OCN), extracellular matrix protein deposition (ALP, Col1a, OCN) and calcium
deposition/mineralisation within the lyophilised Bombyx Mori silk scaffold and the bioassembled microtissue (BMT) construct (microtissues and 3D printed PEGT/PBT scaffold). However, substantially increased bone-like tissue formation induced by MI192 was observed within the BMT model. Similarly, MI192 pre-treatment enhanced hBMSCs osteogenic capacity (ALPSA, extracellular matrix protein expression and calcium deposition/mineralisation) within the GelMA hydrogel (GelMA alone and GelMA-PEGT/PBT construct) and BMT model. However, the bone-like tissue formation induced by MI192 pre-treatment was substantially enhanced within the BMT construct. After intraperitoneal implantation within CD1 nude mice using diffusion chambers, the MI192 pre-treated MSCs within the BMT construct exhibited increased extracellular matrix protein expression and calcium deposition/mineralisation, while inhibited the expression of chondrogenic proteins. Together, the findings presented in this thesis demonstrated that the selective HDAC2 & 3 inhibitor - MI192 promotes the in vitro and in vivo osteogenic capacity of MSCs acquired from human bone marrow and dental pulp tissues, indicating the potential of using epigenetic approaches to enhance MSCs efficacy for bone augmentation strategies.
