Abrogation of the Circadian Nuclear Receptor REV-ERBα Exacerbates 6-Hydroxydopamine-Induced Dopaminergic Neurodegeneration.

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive degeneration of dopaminergic (DAergic) neurons, particularly in the substantia nigra (SN). Although circadian dysfunction has been suggested as one of the pathophysiological risk factors for PD, the exact molecular link between the circadian clock and PD remains largely unclear. We have recently demonstrated that REV-ERBα, a circadian nuclear receptor, serves as a key molecular link between the circadian and DAergic systems. It competitively cooperates with NURR1, another nuclear receptor required for the optimal development and function of DA neurons, to control DAergic gene transcription. Considering our previous findings, we hypothesize that REV-ERBα may have a role in the onset and/or progression of PD. In the present study, we therefore aimed to elucidate whether genetic abrogation of REV-ERBα affects PD-related phenotypes in a mouse model of PD produced by a unilateral injection of 6-hydroxydopamine (6-OHDA) into the dorsal striatum. REV-ERBα deficiency significantly exacerbated 6-OHDA-induced motor deficits as well as DAergic neuronal loss in the vertebral midbrain including the SN and the ventral tegmental area. The exacerbated DAergic degeneration likely involves neuroinflammation-mediated neurotoxicity. The knockout mice showed prolonged microglial activation in the SN along with the overproduction of interleukin 1β, a pro-inflammatory cytokine, in response to 6-OHDA. In conclusion, the present study demonstrates for the first time that genetic abrogation of REV-ERBα can increase vulnerability of DAergic neurons to neurotoxic insults, such as 6-OHDA, thereby implying that its normal function may be beneficial for maintaining DAergic neuron populations during PD progression.