Astrocytic Neurexin-1 Orchestrates Functional Synapse Assembly

ABSTRACTAt tripartite synapses, astrocytes surround synaptic contacts, but how astrocytes contribute to the assembly and function of synapses remains unclear. Here we show that neurexin-1α, a presynaptic adhesion molecule that controls synapse properties, is also abundantly expressed by astrocytes. Strikingly, astrocytic neurexin-1α, but not neuronal neurexin-1α, is highly modified by heparan sulfate. Moreover, astrocytic neurexin-1α is uniquely alternatively spliced and invariably contains an insert in splice-site #4, thereby restricting the range of ligands to which it binds. Deletion of neurexin-1 from astrocytes or neurons does not alter synapse numbers or synapse ultrastructure, but differentially impairs synapse function. At hippocampal Schaffer-collateral synapses, neuronal neurexin-1 is essential for normal NMDA-receptor-mediated synaptic responses, whereas astrocytic neurexin-1 is required for normal AMPA-receptor-mediated synaptic responses and for long-term potentiation of these responses. Thus, astrocytes directly shape synapse properties via a neurexin-1-dependent mechanism that involves a specific molecular program distinct from that of neuronal neurexin-1.

The ApoE-dependent Neuroprotective Effects of Sesamol on Diet-induced Obese Mice: The Role of Gut Microbiota and SCFAs (P06-049-19)

Objectives Sesamol, an antioxidant lignan from sesame oil, possesses lipid lowering and neuroprotective bioactivities. Considering the distribution of sesamol in gut is much higher than brain after administration, the present work was aimed to elucidate the systemic protective effects of sesamol on dietary-induced cognitive deficits, and to determine the possible link between gut and brain. Methods Both wildtype and ApoE-/- mice were fed with high-fat diet (HFD) and treated with sesamol (0.05%, w/v) in drinking water for 10 weeks. The cognitive and anxiety behavioral assessment were evaluated by Morris-water maze, Y-maze, and elevated plus maze tests. The synapse ultrastructure was also detected by transmission electron microscope. Moreover, the alteration of gut microbiome and microbial metabolites short chain fatty acids (SCFAs) were also determined by 16S rDNA sequencing and GC, respectively. Results Sesamol prevented HFD-induced bodyweight gain, insulin resistance, and hyperlipidemia. However, the behavioral tests including Morris-water maze, Y-maze, and elevated plus maze tests indicated that sesamol could only improve cognitive deficits and anxiety behaviors in wildtype but not ApoE deficient mice. Consistently, sesamol improved synapse ultrastructure and inhibited brain Aβ accumulation in brain in an ApoE-dependent manner. Moreover, sesamol prevented HFD-induced gut barrier damages and systemic inflammation. Sesamol also re-shaped gut microbiome and consequently improved the generation of microbial metabolites short chain fatty acids including acetate, propionate, and butyrate. Conclusions To summarized, this study revealed that the possible mechanism of neuroprotective effects of sesamol might be ApoE-dependent, and the beneficial effects of sesamol on gut microbiota/metabolites could be translated into metabolic and neurodegenerative diseases treatment. Funding Sources This work was financially supported by the National Key Research and Development Program of China, National Natural Science Foundation of China. Supporting Tables, Images and/or Graphs