REV-ERB-alpha and -beta coordinately regulate astrocyte reactivity and proteostatic function

The molecular circadian clock is a ubiquitous transcriptional-translational feedback loop that regulates CNS function, glial responses, and neurodegenerative pathology. The druggable nuclear receptors REV-ERB-ɑ (gene: Nr1d1) and REV-ERB-.Beta. (gene: Nr1d2) are components of the core circadian clock. REV-ERB proteins regulate neuroinflammatory responses, synaptic pruning, and protein aggregation, though the cell type-specific effects and relative compensatory effects of REV-ERB-ɑ AND -.Beta. in the brain are unknown. To study the CNS functions of REV-ERBs, we developed mouse lines with global or astrocyte-specific, conditional knockout of both REV-ERB-ɑ and -.Beta.. We demonstrate that inducible post-natal global deletion of REV-ERB-ɑ and -.Beta. in vivo results in robust spontaneous astrocyte activation and increases gene expression of disease-relevant pathways such as protein catabolism, complement, and oxidative stress. Furthermore, in vivo astrocyte-specific deletion of REV-ERB-ɑ/-.Beta. recapitulates the spontaneous astrocyte activation phenotype seen in global REV-ERB-ɑ/-.Beta. KO mice, as well as in mice with deletion of key core clock gene Bmal1, indicating that REV-ERBs regulate astrocyte activation in a cell-autonomous manner downstream of the core circadian clock. REV-ERB-ɑ/-.Beta. repress transcription of Stat3 in the brain, and deletion of REV-ERBs in astrocytes induces increased astrocytic STAT3 expression and downstream STAT3-mediated gene changes, a mechanistic link to the astrocyte reactivity shift. This astrocyte activation phenotype decreases alpha-synuclein pathology in an in vivo model of Parkinson’s Disease-related alpha-synucleinopathy and increases astrocytic protein uptake and degradation in vitro. This study therefore provides insight into astrocyte function and could elucidate novel regulatory mechanisms that are candidates for therapeutic manipulation through modulating REV-ERB activity.