The clinical diagnosis of Parkinson’s disease (PD) relies on the presence of specific motor symptoms, although non-motor symptoms such as hyposmia, depression, anxiety, dementia, autonomic and cognitive dysfunction or REM sleep behavior disorder can be present up to 20 years prior to initial PD diagnosis1,2. PD has an increasing incidence in the population above the age of 653, while prevalence and incidence of PD are higher in males than in females4,5. One of the most characteristic neuropathological hallmarks of PD is the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc of the midbrain) leading to striatal dopamine deficiency6. One of the main drivers of this loss is oxidative stress and subsequent mitochondrial dysfunction, resulting in increased levels of reactive oxygen species (ROS)7,8,9. Neurons depend on glial cells such as microglia, oligodendrocytes, and astrocytes for their protection against oxidative stress. The accumulation of ROS in all these cell types is sensed by NRF2 pathway through oxidation of Kelch-like ECH-associated protein 1 (KEAP1) that leads to release and stabilization of Nuclear factor erythroid 2-related factor 2 (NFE2L2, also known as NRF2), and its nuclear translocation, thereby inducing the expression of antioxidant response genes. A failure in antioxidant response can lead to oxidative stress10. Interestingly, the antioxidant response can be modulated by developmental signaling pathways and sexual hormones such as retinoic acid and estrogen, respectively, leading to differences in response depending on the cell state or sex11. In particular estrogen is associated with neuroprotection, possibly due to improved antioxidant response, and could contribute to sexual dimorphism of disease-risk in many disorders, including PD12,13.
DJ-1 (encoded by Parkinsonism associated deglycase or PARK7) has been characterized as a causative gene for autosomal recessive, early onset PD14 and the PD-associated mutations in the gene are typically leading to loss or reduction of the functional DJ-1 protein15. To date, various functions have been reported for DJ-1, mostly associated with mitochondrial biology and oxidative stress16. In both mouse and human cell lines, DJ-1 was shown to stabilize NRF2 through inhibition of its interaction with KEAP117. Different primary mouse cell and animal models have been utilized to investigate the consequences of Park7 gene disruption. However, the literature shows inconsistent results with respect to Park7-/- mouse models for studying PD. Most of the studies show no dopaminergic neurodegeneration in the SNpc18,19,20,21,22. In addition, Pham and colleagues show that these mice have less dopaminergic neurons in the VTA and exhibit non-motor symptoms associated with early phases of PD, such as impairment in motivated behavior and cognition22. Goldberg et al. reported abnormal nigral dopaminergic physiology in Park7-/- mice, including altered excitability and firing of dopamine neurons projecting to the striatum, together with defects in locomotor activity18. In contrast to these studies, Rousseaux and colleagues report that their Park7-/- mouse model show early onset progressive dopaminergic cell loss, advancing from unilateral to bilateral with aging23. The authors also see degeneration at the locus coeruleus and mild motor behavior deficits at later time points23. Taken together, controversy still exists regarding the dopaminergic system phenotype exhibited by Park7-/- mice, with notable variations across studies. It is worth noting that some previous studies did not specify the sex of the used animals, which is a critical variable that could influence the observed phenotypes in this mouse model.
Here, we investigated the early gene expression changes in the midbrain of both male and female Park7-/- mice to obtain insights into the early events triggered by absence of DJ-1 in vivo and to investigate the possible sex-specific differences. Moreover, we performed cell type-specific investigation of Park7-depletion in cultured primary astrocytes through RNAi experiments, and confirmed the disease-relevance of our findings using human iPSC-derived astrocytes carrying a PARK7 mutation. Together our results identify many changes specifically in the male midbrain with processes such as EMT and focal adhesion becoming altered in astrocytes in an NRF2-dependent manner. These findings could have implications on understanding of the mechanisms of DJ-1-associated PD and the higher PD-risk of males, and help to reconcile discrepant results regarding different Park7-/--mouse models.