The Role of Malfunctioning DNA Damage Response (DDR) in Brain Degeneration

Maintenance of genome stability in the face of DNA damage is essential for cellular homeostasis and prevention of cancer and brain degeneration. The DNA damage response (DDR) is a complex response that is rapidly activated when a DNA lesion occurs in chromosomal DNA. Mutations affecting the proteins involved in the DDR can lead to genomic instability syndromes that involve tissue degeneration, cancer predisposition, premature aging, and brain mal-development and degeneration. Mutation of the kinase ATM leads to a prototype genomic instability syndrome, ataxia-telangiectasia (A-T). A-T is characterized by progressive cerebellar degeneration, immunodeficiency, genome instability, premature aging, gonadal dysgenesis, extreme radiosensitivity, and high incidence of lymphoreticular malignancies. One of the most devastating symptoms of A-T — cerebellar ataxia — develops progressively into general motor dysfunction. Based on our previous studies we hypothesized that the neurological deficits in genomic instability disorders stem (at least in part) from significant reduction in functionality of glial cells. We further hypothesized that impaired vascularization affects the environment in which the neurons and glial cells function, thereby reducing neuronal cell functionality. We found that ATM deficiency led to aberrant astrocytic morphology and alterations of vasculature both in cerebellum and the visual system. Moreover, we found reduced myelin basic protein immunoreactivity and signs of inflammation in ATM-deficient cerebella and optic nerve. Interestingly, similar findings have been reported in patients with other genomic instability disorders. These observations bolster the notion that astrocyte-specific pathologies and hampered vascularization and astrocyte-neuron interactions in the CNS play crucial roles in the etiology of genome instability brain disorders and underlie brain degeneration at specific sites.