Microvesicles: neuroglial unconventional signaling to cortical brain cells

Extracellular vesicles (EVs) represent an alternative and recently discovered way by which diverse cell phenotype can deliver complex messages through released vesicles and their cargoes to neighbor or distant targets. EVs mediate fundamental physiological and pathological processes in biological systems. In particular, we focused on neuron-glia communication mediated by microvesicles (MVs), a subpopulation of EVs that directly originate by outward budding of cellular plasma membrane, which are mostly released under specific stimuli. Given the nanosized dimension and origin of MVs, we tested the ability of carbon-based nanomaterial (small graphene oxide nanoflakes, s-GO), which are demonstrated to interface cells and interact with their physiology at the level of their plasma membrane, to affect the mechanisms governing vesicles release. We first investigated whether s-GO affected the ability of astrocytes to release synaptic-like MVs in pure glial cultures. Our results describe the potential of GO nanosheets to alter different modes of interneuronal communication systems in the central nervous system (CNS). We further tested the reactivity of microglia, a sub-population of neuroglia that acts as the first active immune response, when challenged by chronic s-GO delivery at high doses. We investigated the tissue reactivity in 3D tissue models by using organotypic spinal cord cultures, ideally suited for studying long-term interference with cues delivered at controlled times and concentrations and in isolated neuroglia cultures. In the latter condition, we further tested the role of microglial micro-vesicle release in mediating cell responses to s-GO. Finally, starting from the observation that small graphene oxide flakes (s-GO) are able to boost MVs basal release in cortical glial cells of rodents after a sub-chronic treatment of 6-8 days, we compared through the use of highly sensitive and resolutive nanotechnological tools, MVs obtained under s-GO exposure with MVs obtained by stimulation with the purinergic agonist bzATP, known to induce such release in glial cells. The structural and macromolecular similarities found, suggested a comparable nature of s-GO-derived MVs with the bzATP-derived ones, despite the unusual induction of release. We finally investigated the acute effects of those populations of vesicles exerted on single cortical neurons by focusing on their synaptic activity. We found that both the MVs types 4 induced an increase in spontaneous post synaptic currents (PSCs) on neurons, after 15 minutes from MVs administration.