Friday, April 4, 2025
4/4/2025
Defining cerebellar pathophysiology in Ataxia Telangiectasia - PROJECT SUMMARY Ataxia Telangiectasia (A-T) is a rare (~1 in every 100,000 live births) but catastrophic disease that causes premature death between the ages of 10 and 30 years. There is no cure or disease altering therapy available. It is characterized by a progressive and severe loss of motor coordination (ataxia) and cerebellar neurodegeneration. Immune deficiency and cancer are also prevalent symptoms. In 1995, deficiency in the A-T mutated (ATM) protein was identified as the underlying cause of A-T. However, researchers have yet to determine how a DNA repair pathway protein like ATM preferentially induces cerebellar pathology and ataxia. This knowledge gap arises from the lack of a suitable animal research model that recapitulates the clinical ataxia and cerebellar pathology—more than six different ATM deficient mouse variants have been generated but all fail to develop a clinical phenotype. We recently overcame this roadblock by enhancing the rate of genotoxic stress in the mouse using a genetic double-hit strategy. Our novel double knockout (dKO) mouse lacks expression of both Atm and aprataxin (Aptx), a related DNA repair gene. We find the dKO mice develop a clinical phenotype, including progressive and severe ataxia along with cerebellar neurodegeneration that is not present in either the Atm or Aptx single knockouts. In ataxic dKO mice, we find that a subset of genes controlling Purkinje neuron function are preferentially downregulated (e.g., Itpr1 and Car8) due a distinct chromatin architecture that leaves them preferentially open to DNA damage. Consistent with this, our initial examination shows that Purkinje neurons in dKO mice display significant signs of physiological and morphological abnormalities. We therefore hypothesize that progressive ataxia in A-T results from DNA damage induced downregulation of genes that control PN physiology leading to increased PN dysfunction and abnormal cerebellar circuit activity and output to motor centers. In three AIMs, we propose experiments to establish a temporal link between ataxia severity and the magnitude of protein downregulation, PN pathophysiology, and abnormal cerebellar circuit activity at the molecular, cellular, circuit, and system levels. In Aim 1, we will correlate the temporal progression (early to late) of increasing ataxia to a specific set of Purkinje neuron pathologies using in vitro electrophysiological, Ca2+ imaging, histology, and measurements of gene expression. In Aim 2, we will establish the pathogenic neural circuit activity changes that arise in A-T both within the cerebellum and its downstream projections (e.g., motor thalamus) using a cutting-edge, in vivo multielectrode array recording technique in awake behaving mice. Finally, in Aim 3, we will assess the pivotal role Purkinje neurons play in A-T etiology by testing whether loss of ATM expression alone in these cells is sufficient to generate ataxia and cerebellar defects. Moreover, in Aim 3, we will test if selective chemogenetic and pharmacological modulation of pathological Purkinje neurons can alleviate ataxia. Results will provide new therapeutic targets and a broad understanding of how ATM deficiency can alter cerebellar structure/function and circuit to cause a relentless ataxia.
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