Neurodegenerative disorders affect many millions of people around the world, particularly in the aging population. The vast majority of these diseases are not familial and the mutations that have been associated with rare familial forms of these disorders underscore the complexity of this group of diseases. To begin to understand this complexity, we have used forward genetic approaches to pinpoint the molecular pathways that maintain neuronal homeostasis in the aging mammalian brain. Using this approach we recently demonstrated that unresolved ribosome stalling is a novel mechanism for neurodegeneration. Despite the fundamental importance of translation, the cellular consequences of ribosome stalling in mammalian cells had been unknown until our discovery that a mutation in a novel mammalian ribosome rescue factor Gtpbp2 causes ataxia and degeneration of cerebellar granule cells, cortical and hippocampal neurons, and multiple retinal neurons. Importantly we demonstrated that loss of Gtpbp2 epistatically interacts with a mutation in a CNS- specific, cytoplasmic tRNAArgUCU in the widely used C57BL6/J (B6J) mouse strain to cause neurodegeneration. Our ribosome footprinting experiments revealed that loss of this tRNA led to low levels of ribosome stalling at Arginine AGA codons that was not associated with neurodegeneration. However, stalling was dramatically increased in the absence of Gtpbp2, demonstrating that this protein normally resolves ribosomal stalls. In this application we propose to determine the function of these and other ribosome rescue factors in neuron survival, the impact of increasing age on ribosome stalling in the brain, and additional molecular mechanisms which cause ribosome stalling in mammalian neurons.
In Aim 1 we will determine the effects of loss of the ribosome rescue factors Gtpbp1, Hbs1l, and Pelo with- and without- tRNA deficiency. These studies will be complemented by novel computational methods to infer ribosomal locations at increased precision and ascertain mechanisms that distinguish strains using parameter-dependent simulations of the translation process.
In Aim 2 we will determine the effects of aging on ribosome stalling and neurodegeneration in the brains of aged wild type and ribosome rescue mutant mice without the tRNA mutation and generate and analyze ribosome footprinting and RNA-Seq data from cerebella of aged mice.
In Aim 3 we will investigate pathways that lead to cell death and determine their uniqueness for neurons. We will determine if deficiency of ubiquitously expressed tRNAs induces ribosome stalling and pathology in other organs, analyze the effects of the GCN2/ATF4 and P53 pathways on neurodegeneration, and identify additional modifier genes of neurodegeneration in Gtpbp2-/- mice. Together, we expect these studies to reveal the mechanisms by which dysregulation of translation elongation leads to cellular death and their specificity for neurodegenerative disease.
Neurodegenerative disease affects millions of people in the United States, with an estimated economic burden of many billions of dollars per year, illustrating the need for deeper research into the mechanisms that underlie neurodegeneration. Using mice, we have identified mutations that distort mRNA translation and lead to progressive neuron death. Here we propose to study the mechanisms by which these, and novel, mutations interact with the translational machinery to induce neurodegeneration to inform the development of new models and treatments for these disorders.
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|Kapur, Mridu; Ackerman, Susan L (2018) mRNA Translation Gone Awry: Translation Fidelity and Neurological Disease. Trends Genet 34:218-231|
|Kapur, Mridu; Monaghan, Caitlin E; Ackerman, Susan L (2017) Regulation of mRNA Translation in Neurons-A Matter of Life and Death. Neuron 96:616-637|
|Ishimura, Ryuta; Nagy, Gabor; Dotu, Ivan et al. (2016) Activation of GCN2 kinase by ribosome stalling links translation elongation with translation initiation. Elife 5:|