Exosomes are small membrane bound extracellular vesicles able to transfer from one cell to another active molecules potentially regulating tissue homeostasis. Among bioactive molecules, small non coding microRNAs (miRNAs) are loaded into exosomal cargo, ultimately affecting gene expression by targeting specific mRNAs and inhibiting their translation into protein. Notably, exosomal miRNAs have been found involved in novel mechanisms shaping the epigenetic landscape of a distant cell. Moreover, metabolic alterations associated with dysmetabolism massively alter the cell epigenome, establishing the so-called epi-metabolic memory. Nevertheless, the contribution of exosome transfer and the role of delivered exosomal miRNAs have not been specifically addressed in the context of epi-metabolic memory.
The brain is emerging as an organ particularly sensitive to metabolic alterations including insulin resistance. Indeed, astrocytes, mature neurons, and neural stem cells exposed to dysmetabolic conditions show molecular hallmarks of insulin resistance. In vivo development of brain insulin resistance (BIR)-related cognitive decline is associated with the impairment of both adult neurogenesis and synaptic plasticity as well as the development of neuroinflammation. However, the role of extracellular vesicle-mediated cell-cell communication and brain exosome-dependent paracrine miRNA delivery in BIR-related cognitive decline has not been investigated so far. Here, exosomal miRNAs will be isolated and characterized from both primary neurons and astrocytes upon stimulation with a cocktail of palmitic acid and insulin (IPA), able to mimic BIR-related molecular alterations observed in the brain of high-fat diet fed mice. Exosome miRNAome will be evaluated and subsequently analyzed by bioinformatics tools to point out dysmetabolism-dependent affected targets mainly involved in synaptic plasticity/brain homeostasis. Furthermore, isolated exosomes will be intranasally administered in mice in order to deliver the insulin resistant cell-derived vesicles into the hippocampus. Mice will be then assessed for cognitive functions by specific behavioural tests. Lastly, the ability of IPA-treated cell-derived exosomes to transfer dysmetabolic signals and to induce brain insulin resistance molecular hallmarks will be tested in both primary isolated astrocytes/neurons and mice (see Graphical abstract).
Our findings will shed light on dysmetabolism-associated exosomal miRNA fluctuations and the role of different brain cell-derived exosomes in the insulin resistance-alteration of brain homeostasis. Moreover, the expected results will reveal novel epi-metabolic mechanisms underlying the spreading of brain insulin resistance-related cognitive impairment.