Short regulatory DNA sequences to target brain endothelial cells for gene therapy

Gene vectors targeting CNS endothelial cells allow to manipulate the blood-brain barrier and to correct genetic defects in the CNS. Because vectors based on the adeno-associated virus (AAV) have a limited capacity, it is essential that the DNA sequence controlling gene expression is short. In addition, it must be specific for endothelial cells to avoid off-target effects. To develop improved regulatory sequences with selectivity for brain endothelial cells, we tested the transcriptional activity of truncated promoters of eleven (brain) endothelial-specific genes in combination with short regulatory elements, i.e., the woodchuck post-transcriptional regulatory element (W), the CMV enhancer element (C), and a fragment of the first intron of the Tie2 gene (S), by transfecting brain endothelial cells of three species. Four combinations of regulatory elements and short promoters (Cdh5, Ocln, Slc2a1, and Slco1c1) progressed through this in-vitro pipeline displaying suitable activity. When tested in mice, the regulatory sequences C-Ocln-W and C-Slc2a1-S-W enabled a stronger and more specific gene expression in brain endothelial cells than the frequently used CAG promoter. In summary, the new regulatory elements efficiently control gene expression in brain endothelial cells and may help to specifically target the blood-brain barrier with gene therapy vectors.