Amyotrophic Lateral Sclerosis (ALS) is a fatal disease characterized by the dysfunction and death of motor neurons. Some ALS patients develop widespread neuronal damage leading to Frontotemporal Dementia (FTD), which is characterized by progressive behavioral change and language decline. Significant overlap exists between ALS and FTD regarding the genetic causes, suggesting that they may share common pathogenic mechanisms. Recently, mutations in motor protein, KIF5A, were identified in patients with ALS, ALS/FTD, and FTD alone. These concentrate in the splicing regulatory sites flanking exon 27 leading to its exclusion and abnormal KIF5A C-terminal domain structure. Our preliminary findings suggest that KIF5A ALS/FTD mutations result in the production of a constitutively active protein that causes disease through toxic gain of function. This proposal will test the hypothesis that KIF5A ALS/FTD is caused by gain of function of KIF5A activity in axonal transport and cytoskeletal regulation. To ensure that our work will be highly disease relevant we will utilize human iPSC derived motor neurons and mouse models harboring KIF5A ALS/FTD mutation. In Aim 1: we will define the effects of KIF5A ALS mutations on the assembly and motility of motor/cargo complexes. Specifically, we will utilize live-cell imaging of cargo motility, assessment of cargo distribution by IHC and transmission electron microscopy (TEM), candidate-based biochemical assessment of interactions with cargo adaptors, and unbiased assessment of interactions with potentially novel cargo adaptors and regulatory proteins using proximity labelling. In Aim 2: we will characterize the effects of KIF5A ALS/FTD mutation on cytoskeletal structure using IHC and TEM, live-imaging of MT dynamics and sliding, and analysis of MT post-translational modifications. In Aim 3: we will develop a mouse model of KIF5A ALS/FTD and perform analysis of longevity, behavior, and pathology. The mouse model will be an invaluable resource to validate findings from our in vitro studies and to advance knowledge regarding key features of neurodegeneration in KIF5A ALS/FTD. My ultimate goal is to become a successful physician-scientist with an independent research program investigating the mechanisms of neurodegeneration in motor neuron disease with a specific focus on axonal transport and cytoskeletal dynamics. Northwestern University has unique strengths in the study of ALS, FTD, and cytoskeletal biology and an outstanding commitment to the development of physician-scientists. The mentorship team includes renowned scientists with strong records in mentorship including Han-Xiang Deng M.D., Ph.D. (Primary Mentor) and Robert Kalb M.D (co-mentor). The career development plan focuses on broadening the awardee’s portfolio of research publications and presentations, which will be necessary for successful competition for RO1 funding. Career development activities will bolster grantsmanship and manuscript preparation skills and...