PROJECT SUMMARY Spinal muscular atrophies (SMAs) are monogenetic motor neuron (MN) diseases that cause debilitating muscle weakness and often early mortality. My research program focuses on advancing therapeutics for two forms of SMA: proximal SMA caused by recessive, loss-of-function mutations of the survival motor neuron 1 gene (SMN1) and distal SMA (dSMA) caused by dominant mutations of the transient receptor potential vanilloid 4 gene (TRPV4). Our overarching approach is to integrate findings from human patients with experimentation in animal and iPSC-derived models to elucidate pathomechanistic pathways relevant to human disease and identify promising therapeutic opportunities. Here, we will leverage unique resources and state-of-the-art technologies to define factors limiting efficacy of current SMA therapeutics, characterize cellular and molecular mechanisms driving SMA pathology, and identify and validate novel therapeutic strategies. Proximal SMA is at the forefront of rapidly evolving gene-targeting therapeutics, with two recently approved SMN-inducing treatments and a third under FDA review. While a transformative success, the clinical efficacy of these treatments is highly variable, ranging from normal attainment of early motor milestones to no improvement in motor function. In the last 5 years, our studies have revealed that proximal SMA pathology begins in utero, before treatments are currently initiated in patients. In both humans and mice, SMA MNs exhibit impaired maturation during gestation and precipitous neonatal degeneration, paralleled by a marked decline in SMN expression. Here, we will build on these observations to 1) dissect the specific mechanisms regulating SMN expression during development and treatment, 2) identify the molecular mechanisms causing impaired maturation and degeneration of SMA MNs, and 3) use these insights to develop novel and in utero SMA therapeutic strategies. In parallel studies on dSMA, we have recently demonstrated that neuropathogenic mutations in TRPV4, a cell surface cation channel, disrupt regulatory protein-protein interactions and cause a gain of channel function. Existing TRPV4 antagonists have good tolerability in humans, making the channel a promising therapeutic target. Strikingly, mutant TRPV4 knock-in mouse models develop severe neurological phenotypes due to focal breakdown of blood-neural barriers (BNBs), which are rescued by selective genetic deletion of TRPV4 from endothelial cells (ECs) or treatment of symptomatic mice with TRPV4 antagonists. These studies suggest that TRPV4 activation can drive neuropathology in a non-cell autonomous manner by regulating BNBs. Here, we will 1) characterize protein interactions regulating TRPV4 channel activity, 2) evaluate the role of TRPV4 in modulating EC barrier function, and 3) assess TRPV4 antagonists as a therapeutic strategy in dSMA mice and ultimately other disorders characterized by BNB disruption. Together, our studies will further our ...