In the era of Antiretroviral Therapy (ART), reductions in neuronal connectivity, synaptic simplification and reductions in dendritic complexity are correlated with the severity of cognitive impairments in HIV-infected individuals. There is also considerable evidence that synaptic damage, and cognitive impairments are worse in HIV-infected people who use opiate drugs. Although a number of studies have shown that morphine interacts with HIV and components of HIV to dysregulate astrocyte and neuronal biology, the mechanisms for these interactions are not understood. Bi-directional communication between astrocytes and neurons regulates synaptic formation, synaptic strength, and participates in the regulation of neural circuitry by coordinating activity among groups of neurons. Recent advancements in the biology of extracellular vesicles have begun to implicate glial released microparticles as mediators of glia to neuron communication. In preliminary experiments we found that astrocyte exosomes (released in response to a endogenous stimuli) regulated a neurotrophic response when applied onto neurons. We determined that the molecular cargo of exosomes is complex and contains ~280 distinct proteins, 114 miRNA, and hundreds of lipid species. Moreover, the molecular composition of astrocyte exosomes was modified by the stimulus used to induce release. Based on these preliminary findings we reasoned that a scientific focus on any one protein, lipid or miRNA would be unlikely to produce a true representation of function for these important signaling complexes. Therefore, we used bioinformatics approaches to understand how the entire composition of exosomes interacts with neuronal signaling pathways, and focused our efforts on a small number of the identified pathways. In particular we concentrated on neural pathways associated with synapse formation, spine formation, and neurite outgrowth, as these pathways were consistent with the neurotrophic response to astrocyte exosomes released in response to an endogenous stimuli. The goals of this application are to understand how HIV and morphine modulate the cargo of astrocyte exosomes and how these differences in cargo regulate dendritic and synaptic functions in neurons.
Comorbidities such as opiate use/abuse contribute to the occurrence and progression of HAND, although the mechanisms for these interactions are not entirely clear. Our preliminary findings suggest that exosomes released from stimulated astrocytes regulate the molecular aspects of learning and memory in adjacent neurons. A greater understanding of how morphine modified exosomes impact neuronal structure and function will open new areas of investigation in drug addiction and neurodegenerative research.
