Casein kinase 2 activity is a host restriction factor for AAV transduction

Despite rapid progress in the development of new therapies based on adeno-associated viral vectors (AAVs) in recent years, successful transduction of the human heart remains challenging. So far, the mechanisms that impede AAV transduction, especially in humans are poorly understood, hampering the introduction of new, effective gene therapy strategies. Therefore, the aim of this study was to identify and overcome the main cellular barriers to successful transduction in the heart, using iPSC-derived cardiomyocytes (iPSC-CMs), cardiac fibroblasts (iPSC-CFs), and primary endothelial cells (HAECs) to model vector-host interactions. Through phosphoproteome analysis of AAV9-transduced iPSC-CFs we established that casein kinase 2 (CK2) signalling is one of the most significantly affected pathways upon AAV exposure. Importantly, transient inhibition of CK2 activity with silmitasertib substantially enhanced the transduction rate of AAV2, AAV6 and AAV9 in all tested cell types (iPSC-CMs, iPSC-CFs and HAECs), demonstrating the versatility of this approach. CK2 inhibition improved the trafficking of AAVs through the cytoplasm and impaired DNA-damage response through destabilisation of Mre11, sensor of dsDNA breaks, that directly binds the ITRs of the vector genome. Silmitasertib treatment also allowed for improvement of transgene expression in already transduced iPSC-CFs, which retain AAV genomes in a functional, but probably silent form. Furthermore, our analysis revealed that AAV transduction may interfere with RNA processing pathways, identifying matrin-3 as a necessary factor for efficient transgene delivery. In summary, presented study provides new insights into the current understanding of the host-AAV vector interaction, identifying CK2 activity as a key barrier to efficient transduction and transgene expression, therefore offering a promising strategy to improve the outcome of AAV-based therapies in the future.