The Role of Sensory Receptors in Angelman Syndrome

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Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability and atypical behavior. AS results from a loss of expression of the E3 ubiquitin-protein ligase (UBE3A) from the maternal allele. The UBE3A gene is paternally imprinted (i.e., repressed) in most neurons of humans and mice. Deletion, mutation, or loss of expression of the maternal allele results in AS. Individuals with AS display impaired motor coordination (e.g., inability to reach objects), gait deficits (i.e., instability while walking), and seizures. There are no interventions for ameliorating gait deficits. A critical barrier for treating this condition is that the molecular mechanisms that give rise to gait deficits in AS are unknown. Proprioception confers the ability to sense movement, balance, and limb position. The mechanosensitive ion channel PIEZO2 is expressed in sensory neurons innervating muscle spindles and Golgi tendon organs, where it mediates proprioception, gait, and balance. Mice and humans lacking PIEZO2 expression have an unsteady gait, increased stride-to-stride variability in step length, and postural deficits. The rationale for these studies relies on the evidence from human genetics and mouse models suggesting that individuals with AS or PIEZO2 loss-of-function mutations may share mechanosensation deficits. Our hypothesis is that AS-associated gait deficits originate from reduced PIEZO2 function in sensory neurons. Our preliminary data support our hypothesis because it shows that PIEZO2 currents are reduced in Ube3a-deficient mouse neurons, human cells with UBE3A knock-down, and stem cell-derived neurons from individuals with AS. There are no available agonists to increase PIEZO2 activity. Molecules that enhance PIEZO2 function could bypass the mechanical deficits associated with the loss of UBE3A expression. We determined that a safflower oil diet, enriched in linoleic acid (LA), increases PIEZO2 currents and mechanical excitability, as well as improves gait in AS mice. Likewise, LA supplementation enhances PIEZO2 function in stem cell-derived neurons from individuals with AS. Our overall objective is to determine the mechanisms by which loss of UBE3A expression decreases PIEZO2 currents (and/or expression) and LA recovers channel function. To this end, we will carry out electrophysiological, biochemical, biophysical, and behavioral analyses to provide a detailed understanding of the contribution of UBE3A and PIEZO2 to AS. We will pursue three Specific Aims: 1) Determine the mechanism whereby loss of UBE3A expression decreases PIEZO2 currents, 2) Determine the mechanism by which LA increases PIEZO2 activity, and 3) Test the hypothesis that LA ameliorates gait deficits in AS through PIEZO2. The proposed research is significant because it is expected to provide a detailed understanding of the molecular mechanisms that accounts for diminished PIEZO2 currents in AS and the role of LA-enriched membranes in increasing PIEZO2 function.