Brd4 Inactivation Increases Adenoviral Delivery of BMP2 for Paracrine Stimulation of Osteogenic Differentiation as a Gene Therapeutic Concept to Enhance Bone Healing

Bromodomain (BRD) proteins are histone code interpreters that recognize acetylated lysines and link the dynamic state of chromatin with the transcriptional machinery. Here, we demonstrate that ablation of the Brd4 gene in primary mouse bone marrow–derived mesenchymal stem cells via a conditional Brd4^fl/fl allele suppresses osteogenic lineage commitment. Remarkably, loss of Brd4 function also enhances expression of genes in engineered adenoviral vectors, including Cre recombinase and green fluorescent protein (GFP). Similarly, vector-based expression of BMP2 mRNA and protein levels are enhanced upon Brd4 depletion in cells transduced with an adenoviral vector that expresses BMP2 (Ad-BMP2). Importantly, Brd4 depletion in MC3T3-E1 and human adipose-derived mesenchymal stem cells (AMSCs) transduced with Ad-BMP2 enhances osteogenic differentiation of naïve MC3T3-E1 cells via paracrine mechanisms based on transwell and conditioned medium studies. Our studies indicate that Brd4 depletion enhances adenoviral transgene expression in mammalian cells, which can be leveraged as a therapeutic strategy to improve viral vector-based gene therapies.