Intracellular transport is critical for the function and viability of neurons throughout life. Splicing factor proline- glutamine rich (SFPQ) is an RNA-binding protein that packages trophic-regulated transcripts, such as Bclw, into RNA granules (RNAGs). Local translation of these transcripts is critical for protecting axons from degeneration. The objective of this grant is to understand the mechanism by which SFPQ RNAGs are localized to axons and translated there. This investigation builds on my key findings that: 1) SFPQ specifically binds to only one of three members of the kinesin-1 family of motors, KIF5A, and to only one of the associated kinesin light chains (KLC), KLC1; 2) a newly defined consensus EDxYxE motif within the coiled coil (CC) region of SFPQ is required for binding to KIF5A/KLC1; and 3) the variable carboxy-terminal tail (CTT) region of KIF5A is required for binding to SFPQ. These data demonstrating selectivity of the kinesins is highly relevant to human disease as KIF5A is the only kinesin-1 motor that is mutated in Charcot-Marie-Tooth disease (CMT), hereditary spastic paraplegia (HSP) and in amyotrophic lateral sclerosis (ALS). Moreover, ALS mutations in SFPQ lie within the CC region adjacent to EDxYxE motif. Together, I propose a CENTRAL HYPOTHESIS that SFPQ RNAGs are localized to axons through a highly specific KIF5A/KLC1-dependent transport and that disruption of this pathway results in KIF5A and SFPQ-related neurological diseases. In this proposal I will test the following predictions of this Hypothesis: 1) anterograde transport of SFPQ depends on interactions mediated by the CTT of KIF5A and by KLC1; 2) axonal survival requires KIF5A-mediated transport of SFPQ RNAGs to axons; and 3) Bclw mimetics can prevent axonal degeneration caused by interruption of KIF5A-mediated transport of SFPQ. These 3 Aims will reveal mechanistic understanding of how defect in specific kinesin-driven transport characteristically leads to axon degeneration in neurological disease and will assess the therapeutic potential of a highly innovative Bclw peptide. I have designed an effective training plan to execute this proposal and to advance in 4 specialized training areas: 1) compartmented neuronal culture system to study spatial regulation of protein expression; 2) advanced quantitative live cell imaging techniques in axons; 3) transcriptomics and proteomics to profile and determine regulatory mechanism of specialized motor adaptor complex formation by alternative splicing and post-translational modifications; and 4) use of in vivo disease models for therapeutic intervention. My career development plan is designed to be highly collaborative; several advisors are readily available within the multi-disciplinary environment of the greater Harvard Medical School campus. Upon conclusion I will initiate the first step towards my overarching goal in understanding how defects in microtubule- based transport in neurons lead to neurological diseases; why mutations in a specific motor component cause degeneration in neurons; and to bridge basic neuroscience discovery into new therapeutics against neurological diseases of sensory and motor neurons including CMT, HSP and ALS.
The proposed research is highly relevant to public health as Charcot-Marie-Tooth disease (CMT), hereditary spastic paraplegia (HSP), and amyotrophic lateral sclerosis (ALS) can all be caused by mutations in motor proteins or cargoes that we are investigating. When completed, these studies will reveal mechanistic understanding of the interactions between axonal cargo and motors; and how disruptions of these interactions or in transport of RNA granules cause degenerative disease. Importantly, this study provides the possibility for a new therapeutic intervention leveraging peptide mimetics in preventing axonal degeneration in CMT and ALS.!