Abstract
Recent studies have suggested that cortical astroglia play an important role in depressive-like behaviors. Potential astroglial contributions have been proposed based on their known neuroplastic functions, such as glutamate recycling and synaptic plasticity. However, the specific mechanisms by which astroglial cells may contribute or protect against a depressive phenotype remain unknown. To delineate astroglial changes that accompany depressive-like behavior, we used astroglial-specific bacTRAP mice exposed to chronic variable stress (CVS) and profiled the astroglial translatome using translating ribosome affinity purification (TRAP) in conjunction with RNAseq. As expected, CVS significantly increased anxiety- and depressive-like behaviors and corticosterone levels and decreased GFAP expression in astroglia, although this did not reflect a change in the total number of astroglial cells. TRAPseq results showed that CVS decreased genes associated with astroglial plasticity: RhoGTPases, growth factor signaling, and transcription regulation, and increased genes associated with the formation of extracellular matrices such as perineuronal nets (PNNs). PNNs inhibit neuroplasticity and astroglia contribute to the formation, organization, and maintenance of PNNs. To validate our TRAPseq findings, we showed an increase in PNNs following CVS. Degradation of PNNs in the prefrontal cortex of mice exposed to CVS reversed the CVS-induced behavioral phenotype in the forced swim test. These data lend further support to the neuroplasticity hypothesis of depressive behaviors and, in particular, extend this hypothesis beyond neuronal plasticity to include an overall decrease in genes associated with cortical astroglial plasticity following CVS. Further studies will be needed to assess the antidepressant potential of directly targeting astroglial cell function in models of depression.
Highlights
Depression is among the leading causes of disability worldwide [1], with an estimated 350 million people affected
We used unbiased stereology to count the total number of astroglia in the cortex of ALDH-L1-L10-GFP+ mice, which constitutively express GFP in all astroglial cells, and found that the total number of GFP+ astrocytes did not change with chronic variable stress (CVS) (p = 0.8) (Fig. 2a, d, e)
The use of the CVS paradigm employed in this study induced a reliable behavioral phenotype and allowed us to examine astroglial plasticity that may result from stress of a more chronic nature
Summary
Depression is among the leading causes of disability worldwide [1], with an estimated 350 million people affected. Treatments for depression include psychotherapy, antidepressant medications, and in some extreme cases, electroconvulsive therapy; an estimated 30–40% of individuals are treatment resistant [2]. Several theories, such as the monoaminergic hypothesis, have been used to explain the neurobiological basis of mood disorders; these fail to resolve key findings, including considerable lags between monoamine level changes and symptom relief. Like neurons, astroglial cells include several subtypes that differ in function and show distinct protein expression patterns. Throughout the lifespan, astroglia play pivotal roles in metabolizing neurotransmitters, modifying cell connectivity, and providing trophic support to neurons; as neural stem cells, astroglia give rise to astrocytes, oligodendrocytes, and neurons both under basal conditions and in response to injury [5, 6]
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