The Role of nitric oxide-mediated homeostatic synaptic plasticity in autism spectrum disorder

• Applicant: Professor Dr. Andreas Vlachos
• Subject Area: Experimental Models for the Understanding of Nervous System Diseases ; Molecular Biology and Physiology of Neurons and Glial Cells ; Nuclear Medicine, Radiotherapy, Radiobiology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 520268027

Nitric oxide (NO) is an important multifunctional signaling molecule in the brain. Pioneering works demonstrated the crucial role of NO in synaptic transmission and plasticity. Increased brain NO levels and the related posttranslational S-nitrosylation (SNO) of proteins have been linked to the pathogenesis of various neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s diseases. In work leading to this proposal, we demonstrated increased NO and protein SNO levels in a mouse model of ASD (i.e., Shank3 InsG3680 mutant mice). However, the biological significance of NO/SNO for synaptic plasticity under physiological and pathological conditions remained unknown. The overall goal of this project is to investigate the role of NO/SNO in homeostatic synaptic plasticity–a compensatory form of plasticity considered fundamental for the functioning of neuronal networks, working to maintain network activity within a functional dynamic range. We hypothesize that a prolonged (insufficient) attempt to compensate for a pathological synaptic phenotype (i.e., Shank3 InsG3680 mutation) leads to excessive levels of NO and protein SNO. In turn, increased NO levels and aberrant SNO of proteins leads to alterations in synaptic transmission and disruption of homeostatic synaptic plasticity; hence, resulting in a vicious cycle that contributes to the ASD pathology. At the subcellular and molecular level, we aim at better understanding the role of synaptopodin-associated intracellular Ca2+ stores (i.e., spine apparatus organelles), which mediate synaptic plasticity. Indeed, induction of homeostatic synaptic plasticity triggers NO-signaling pathways and synaptopodin is among the SNOed proteins in Shank3 InsG3680 mutant mice. We will use single-cell electrophysiology, structural (light- and electron-microscopy) and molecular analyses (SNO-proteome analysis) in organotypic tissue cultures prepared from wild type mice, synaptopodin-deficient mice, and Shank3 InsG3680 mutant mice as well as in vivo behavioral experiments to test whether the deleterious effects of pathologically increased NO-levels and protein SNO can be prevented by inhibiting NO-synthase activity. Moreover, we will use genetic modifications that yield synaptopodin resistant to NO-mediated protein SNO and test whether the expression of cys/ser mutated synaptopodin rescues the ability of neurons to express homeostatic synaptic plasticity and the behavioral deficits seen in Shank3 mutant mice. Thus, this project aims at demonstrating the role of NO and protein SNO in synaptopodin-dependent homeostatic synaptic plasticity under physiological conditions and ASD pathology, thereby suggesting novel therapeutic targets for the treatment of patients with ASD.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicant: Professor Dr. Haitham Amal