Charcot-Marie-Tooth (CMT) comprises a heterogeneous group of peripheral neuropathies caused by mutations in over 90 genes. Mutation of ATP1A1, which encodes for the Na+,K+-ATPase (NKA) ?1 subunit, has been recently associated with CMT2, a CMT form characterized by axonal degeneration. NKA is a heterodimeric (??) protein that hydrolyzes ATP to build and maintain the Na+ and K+ gradients across the plasma membrane of all human cells. Different tissues present distinct NKA isozymes. ATP1A1 is ubiquitously expressed and the mutations linked to CMT2 cause NKA loss of function. Loss of NKA function is also observed in ATP1A1 mutants associated with other diseases, including primary hyperaldosteronism and a form of hypomagnesemia accompanied by seizures and cognitive delay. However, the lack of appropriate model systems has prevented a detailed understanding of the pathophysiology of these ATP1A1 mutation linked disorders. The long-term goal of our laboratory is to understand the mechanisms of NKA function and their roles in physiological and disease states. The objective of this proposal is to develop and evaluate animal models to study ATP1A1-linked disease, with an emphasis on CMT2.
Aim 1. Comprehensive neuropathic evaluation of heterozygous ATP1A1 knockout mice to test our central hypothesis, that the severe effect of loss-of-function mutations seen in CMT2 patients, including the highly variables symptom intensity and age of onset, should be recapitulated in ATP1A1+/- mice.
Aim 2. Develop and evaluate novel ATP1A1 loss-of-function-mutation models using CRE-LoxP technology to test the hypotheses that deletion of one ATP1A1 allele in adulthood accelerates the onset of CMT2 symptoms and that neuronal haploinsufficiency is sufficient to induce CMT2. Through the generation of tissue- and time-dependent conditional knockout mice using tamoxifen inducible CreER lines, we will be able to determine age-dependent compensatory mechanisms, and necessity of local or systemic haploinsufficiency for CMT2 induction. Successful completion of these studies will lead to viable NKA-linked pathophysiological model to gain insight into CMT2 mechanisms. The results from this project will provide a tool for future testing of specific treatments for NKA-linked CMT2. Additionally, the experiments outlined here are likely to provide models for the other ATP1A1 mutation-linked diseases. Scientifically, our results will uncover the functional roles of NKA ?1 in neuron physiology elucidating its importance in both the peripheral and central nervous systems. These mouse models will be made available to the scientific community through standard multi-institutional MTAs.
Charcot-Marie-Tooth type 2, hyperaldosteronism with secondary hypertension and a form of hypomagnesemia accompanied by seizures and cognitive delay, are diseases due to mutation in a gene that encodes a form of the sodium/potassium pump, an omnipresent protein in the human body. The lack of appropriate model systems to study dysfunction of this essential protein has prevented a detailed understanding of the pathophysiology of these disorders. Here we propose to generate and to validate the first animal models of CMT2 caused by sodium/potassium pump mutation, to uncover the mechanisms of disease induction and for the future use in development of mutation-specific therapies.
