Mechanisms of DNA Single-Strand Break-Induced Genetic Disease and Opportunities for Therapeutic Intervention

My laboratory is focused on understanding how breaks in the genetic material (DNA) can lead to disease. The proposed work will address exciting new hypotheses that have arisen during my current research programme concerning the mechanism/s by which unrepaired DNA single-strand breaks (SSBs), which are breaks in one strand of the DNA double helix, trigger neurodegeneration. To date, six human genetic diseases have been identified in which there is a defect in SSB repair; the latest one being identified under the auspices of my current MRC research programme (spinocerebellar ataxia autosomal recessive 26; SCAR26, which is mutated in the protein, XRCC1). Excitingly, we have discovered how unprepared SSBs trigger this disease, providing not only the first molecular explanation for how SSBs cause disease but also opening up possible new avenues for therapeutic intervention. We plan to pursue these novel discoveries in the new research programme proposed here. We will employ a combination of molecular, cellular, and physiological experimental models to build on our recent discoveries and define at the mechanistic level how SSBs cause defects in neuronal function in vitro and in vivo, and how such defects lead to neurological disease. Importantly, we will also continue to develop our work in a clinical direction, by testing the ability of existing and novel drugs/drug-like molecules for their ability to restore normal neuron function and prevent neurological diseases that arise from SSBs. Whilst we are focusing on experimental models of rare genetic diseases to address our scientific questions, the relevance of this work may extend to more common degenerative diseases and even to the normal ageing population. This is because SSBs are the commonest form of DNA damage arising in cells and are induced not only by oxidative stress (which is elevated in brain and is believed to contribute to human ageing) but as discovered in our recent work also by the normal processes by which human neurons regulate the expression of their genes.

My laboratory is focused on understanding how DNA single-strand breaks (SSBs) lead to human disease, and how this understanding can be exploited for therapeutic benefit. To date, at least six hereditary neurodegenerative diseases exist that are associated with genetic defects in SSB repair (SSBR), the most recently identified of which was discovered under the auspices of my current research programme (spinocerebellar ataxia autosomal recessive 26, in which the central SSBR scaffold protein XRCC1 is mutated). Notably, all six SSBR-defective diseases identified to date are caused by mutations in either XRCC1 itself or in protein partners of XRCC1. During the current research programme, excitingly, we have established that pathological activation of the SSB sensor protein PARP1 is responsible for much of the neuropathology in XRCC1-defective disease, and we have uncovered a molecular mechanism by which this activation disrupts transcriptional regulation and normal synaptic function in affected neurons (see case for support). As a result of these and other novel discoveries in my current MRC research programme, the hypotheses that we wish to address and explore in the new programme are (i), that XRCC1-mutated disease results from pathogenic activity of PARP1 at SSBs arising specifically during DNA base excision repair and that a major source of which is the regulation of neuronal gene expression by epigenetic (re)programming and (ii), that PARP1-induced pathogenicity extends beyond XRCC1-mutated disease and contributes to or causes other SSBR-defective diseases in which DNA base excision repair is affected. Finally, and importantly, we will exploit our discoveries to identify new avenues for therapeutic intervention in SSBR-defective disease, with a particular focus on PARP1 as a pharmacological and therapeutic target.