Investigating mechanisms of pathogenesis in TBK1-associated amyotrophic lateral sclerosis

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The purpose of this mentored career development award is to propel an early stage PI towards independence as a physician-scientist with a research program on mechanisms of amyotrophic lateral sclerosis (ALS) and clinical focus on neuromuscular medicine. ALS is a rapidly progressive neurologic disorder characterized by motor neuron degeneration that leads to death in 3-5 years and for which there are no effective treatments. TANK binding kinase 1 (TBK1) was recently uncovered as a novel causative gene in sporadic and familial ALS and frontotemporal dementia (FTD). However, the mechanisms by which variants in TBK1 because disease remain unclear. Under the guidance of Dr. Timothy Miller, I propose to investigate how disruptions in TBK1, a ubiquitously expressed kinase that functions at the intersection of two processes implicated in ALS pathogenesis, autophagy and innate immunity, lead to disease pathogenesis. Although a subset of TBK1 mutations cause truncation and reduced expression of the protein, the significance and pathogenicity of many missense variants remain uncharacterized. Notably, haploinsufficiency of microglial- derived genes such as progranulin (PGRN) and triggering receptor expressed on myeloid cells 2 (TREM2) has been shown to cause or increase risk for Alzheimer's disease, frontotemporal dementia, and ALS [10] by altering inflammatory signaling and phagocytic function. Given the contribution of non-cell-autonomous mechanisms in motor neuron cell death in ALS and known expression of TBK1 in neuronal and non-neuronal cell types, I will also examine the impact of TBK1 loss of function (LoF) in astrocytes and microglia, the primary immune cells of the central nervous system. In order to understand how TBK1 LoF influences manifestation of disease, an animal model of disease would be an incredibly valuable tool. Unfortunately, previously described TBK1 knock out mice are embryonic lethal which precluded an analysis of neurological phenotypes. Based on these considerations, I propose the a research program incorporating the following aims: 1) Determine the functional consequences of TBK1 missense and LoF variants on autophagy using biochemical and histopathological methods 2) Determine the effect of TBK1 LoF on phagocytosis, autophagy, and inflammatory signaling in astrocytes and microglia 3) Determine whether TBK1 causes ALS via cell autonomous or non-cell autonomous mechanisms by examining phenotypes of mice with selective loss of TBK1 in motor neurons, astrocytes, and microglia The experiments proposed above are expected to clarify the role of TBK1 in ALS pathogenesis and reveal novel therapeutic targets. The research training supported by the award will fortify my skill set and knowledge base for translating basic science discoveries to novel bedside treatment and diagnostic markers for ALS and potentially other neurodegenerative diseases.