Investigating the functional consequences of SynGAP1 SUMOylation at mammalian synapses

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ntellectual disability (ID) affects millions of individuals worldwide and represents a major health and economic burden. ID results from mutations altering the function of different brain proteins. One of these proteins is SynGAP1. In humans, truncated or missense variants in the SYNGAP1 gene are associated with ID, epilepsy and autism spectrum disorders. SynGAP1 is critical for synapse formation and morphology and is a negative regulator of excitatory neurotransmission. Furthermore, the post-translational modification process of SUMOylation is emerging as a key regulator of synapse development and function. I have key pilot data showing that SynGAP1 is a SUMO target at synapses. This raises the hypothesis that SUMOylation regulates SynGAP1 activity and function, to play a pivotal role in synapse formation, morphology and function. To unveil the physiological consequences of SynGAP1 SUMOylation on its molecular function, I will determine which signaling cascades mediate its SUMOylation, and how this impacts its enzyme activity, molecular interactions and subcellular localisation. To determine effects on synapse morphology and neurotransmission (which are controlled by SynGAP1 and usually altered in ID), I will exploit live-cell imaging and electrophysiological approaches with sophisticated biochemical assays in Syngap1-/- neurons that express a form of SynGAP that cannot bind to SUMO (SynGAP1-K149R). Therefore, the proposed project will exploit state of the art technologies to directly address the molecular mechanisms regulating SynGAP1 function in neurons and the synaptic events it controls. Furthermore, it will reveal essential insights regarding the role of SUMO in the development of ID. This is an emerging issue of critical importance, since several proteins essential for correct brain development and function are SUMO targets. Therefore, this project will also facilitate future strategies to restore disrupted synaptic function by targeting SUMO.ntellectual disability (ID) affects millions of individuals worldwide and represents a major health and economic burden. ID results from mutations altering the function of different brain proteins. One of these proteins is SynGAP1. In humans, truncated or missense variants in the SYNGAP1 gene are associated with ID, epilepsy and autism spectrum disorders. SynGAP1 is critical for synapse formation and morphology and is a negative regulator of excitatory neurotransmission. Furthermore, the post-translational modification process of SUMOylation is emerging as a key regulator of synapse development and function. I have key pilot data showing that SynGAP1 is a SUMO target at synapses. This raises the hypothesis that SUMOylation regulates SynGAP1 activity and function, to play a pivotal role in synapse formation, morphology and function. To unveil the physiological consequences of SynGAP1 SUMOylation on its molecular function, I will determine which signaling cascades mediate its SUMOylation, and how this impacts its enzyme activity, molecular interactions and subcellular localisation. To determine effects on synapse morphology and neurotransmission (which are controlled by SynGAP1 and usually altered in ID), I will exploit live-cell imaging and electrophysiological approaches with sophisticated biochemical assays in Syngap1-/- neurons that express a form of SynGAP that cannot bind to SUMO (SynGAP1-K149R). Therefore, the proposed project will exploit state of the art technologies to directly address the molecular mechanisms regulating SynGAP1 function in neurons and the synaptic events it controls. Furthermore, it will reveal essential insights regarding the role of SUMO in the development of ID. This is an emerging issue of critical importance, since several proteins essential for correct brain development and function are SUMO targets. Therefore, this project will also facilitate future strategies to restore disrupted synaptic synaptic function by targeting SUMO.