In utero ethanol exposure causes Fetal Alcohol Spectrum Disorders, associated with reduced brain plasticity; the mechanisms of these effects are not well understood, particularly with respect to glial involvement.
Astrocytes release factors that modulate neurite outgrowth. We explored the hypothesis that ethanol inhibits neurite outgrowth by increasing the release of inhibitory chondroitin sulfate proteoglycans (CSPGs) from astrocytes.
Astrocyte treatment with ethanol inhibited the activity of arylsulfatase B (ARSB), the enzyme that removes sulfate groups from chondroitin-4-sulfate (C4S) and triggers the degradation of C4S, increased total sulfated glycosaminoglycans (GAGs), C4S, and neurocan core-protein content and inhibited neurite outgrowth in neurons co-cultured with ethanol-treated astrocytes in vitro, effects reversed by treatment with recombinant ARSB.
Ethanol also inhibited ARSB activity and increased sulfate GAG and neurocan levels in the developing hippocampus after in vivo ethanol exposure.
ARSB silencing increased the levels of sulfated GAGs, C4S, and neurocan in astrocytes and inhibited neurite outgrowth in co-cultured neurons, indicating that ARSB activity directly regulates C4S and affects neurocan expression.
In summary, this study reports two major findings: ARSB modulates sulfated GAG and neurocan levels in astrocytes and astrocyte-mediated neurite outgrowth in co-cultured neurons; and ethanol inhibits the activity of ARSB, increases sulfated GAG, C4S, and neurocan levels, and thereby inhibits astrocyte-mediated neurite outgrowth.
An unscheduled increase in CSPGs in the developing brain may lead to altered brain connectivity and to premature decrease in neuronal plasticity and therefore represents a novel mechanism by which ethanol can exert its neurodevelopmental effects.