Alteration of glutamatergic synaptic plasticity in the Nucleus Accumbens (NAc) has been implicated in cocaine-seeking behaviors. Astroglial mechanisms for maintaining extracellular glutamate homeostasis through cysteine/glutamate exchanger (xCT) and glutamate transporter GLT1 are dysregulated following cocaine exposure and contribute to altered glutamatergic synaptic plasticity. However, how these astroglial proteins become dysregulated in cocaine addiction remains unknown. We recently showed that neuron to astroglial exosome signaling is essential to maintain GLT1 protein expression by transferring neuronal miR-124-3p into astrocytes to suppress GLT1-inhibiting microRNAs (miRs) in astrocytes. In the current study, by selectively labeling neuronal exosomes using CD63-GFP f/+ exosome reporter mice, we examined how the self-administration and extinction stages of the mouse cocaine self-administration model alter neuronal exosome signaling to astrocytes and microglia in the NAc. We found that cocaine (but not food) self-administration strongly reduces the internalization of neuronal exosomes, particularly in astrocytes in the NAc (but not in motor cortex), which can be effectively reversed by extinction training. In parallel, cocaine self-administration alone specifically and differentially affects activation of glial cells by decreasing GFAP expression in astrocytes but increasing Iba1 expression in microglia. However, extinction training fully reverses the increased Iba1 expression in microglia but only partially reverses the reduction of GFAP in astrocytes. Taken together, our study reveals altered in vivo dynamics of NAc neuronal exosomes in the cocaine addiction model, providing new insights about how altered neuron to glial exosome signaling may contribute to astroglial dysfunction in cocaine addiction.

The loss of fragile X mental retardation protein (FMRP) causes fragile X syndrome (FXS), the most common inherited intellectual disability. How the loss of FMRP alters protein expression and astroglial functions remains essentially unknown. Here we showed that selective loss of astroglial FMRP in vivo up-regulates a brain-enriched miRNA, miR-128-3p, in mouse and human FMRP-deficient astroglia, which suppresses developmental expression of astroglial metabotropic glutamate receptor 5 (mGluR5), a major receptor in mediating developmental astroglia to neuron communication. Selective in vivo inhibition of miR-128-3p in FMRP-deficient astroglia sufficiently rescues decreased mGluR5 function, while astroglial overexpression of miR-128-3p strongly and selectively diminishes developmental astroglial mGluR5 signaling. Subsequent transcriptome and proteome profiling further suggests that FMRP commonly and preferentially regulates protein expression through posttranscriptional, but not transcriptional, mechanisms in astroglia. Overall, our study defines an FMRP-dependent cell-autonomous miR pathway that selectively alters developmental astroglial mGluR5 signaling, unveiling astroglial molecular mechanisms involved in FXS pathogenesis.

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Developing astroglia play important roles in regulating synaptogenesis through secreted and contact signals. Whether they regulate postnatal axon growth is unknown. By selectively isolating exosomes using size-exclusion chromatography (SEC) and employing cell-type specific exosome reporter mice, our current results define a secreted astroglial exosome pathway that can spread long-range in vivo and stimulate axon growth of cortical pyramidal neurons. Subsequent biochemical and genetic studies found that surface expression of glial HepaCAM protein essentially and sufficiently mediates the axon-stimulating effect of astroglial exosomes. Interestingly, apolipoprotein E (ApoE), a major astroglia-secreted cholesterol carrier to promote synaptogenesis, strongly inhibits the stimulatory effect of astroglial exosomes on axon growth. Developmental ApoE deficiency also significantly reduces spine density of cortical pyramidal neurons. Together, our study suggests a surface contact mechanism of astroglial exosomes in regulating axon growth and its antagonization by ApoE, which collectively coordinates early postnatal pyramidal neuronal axon growth and dendritic spine formation.