DJ-1 protects cell death from a mitochondrial oxidative stress due to GBA1 deficiency

GBA1 mutations are the most common genetic risk factor for development of Parkinson's disease (PD). The loss of catalytic activity in GBA1, as well as the reduction of the GBA1 protein in certain cellular compartment, may increase disease progression. However, the mechanisms underlying cellular dysfunction caused by GBA1 deficiency are still mostly unknown.

In this study, we focus on the genetic interaction between GBA1 deficiency and PD-causing genes, such as DJ-1, in mitochondrial dysfunction.

GBA1 knockout (KO) SH-SY5Y cells were used to assess DJ-1 functions against oxidative stress in vitro. The levels of cellular reactive oxygen species were monitored with MitoSOX reagent. The expression of the PARK7 gene was analyzed using the quantitative real-time PCR (qRT-PCR). To understand the mechanism underlying DJ-1 upregulation in GBA1 KO cells, we assess ROS levels, antioxidant protein, and cell viability in GBA1 KO cells with treatment of ROS inhibitor N-acetyl-cysteine or miglustat, which is an inhibitor of glucosylceramide synthase. Dopaminergic degeneration was assessed from Gba1 L444P heterozygous mice mated with Park7 knockout mice.

We find that DJ-1 is significantly upregulated in GBA1 KO cells. Elevated levels of DJ-1 are attributed to the transcriptional expression of PARK7 mRNA, but not the inhibition of DJ-1 protein degradation. Because DJ-1 expression is highly linked to oxidative stress, we observe cellular reactive oxygen species (ROS) in GBA1 KO cells. Moreover, several antioxidant gene expressions and protein levels are increased in GBA1 KO cells. To this end, GBA1 KO cells are more susceptible to H₂O₂-induced cell death. Importantly, there is a significant reduction in dopaminergic neurons in the midbrain from Gba1 L444P heterozygous mice mated with Park7 knockout mice, followed by mild motor dysfunction.

Taken together, our results suggest that DJ-1 upregulation due to GBA1 deficiency has a protective role against oxidative stress. It may be supposed that mutations or malfunctions in the DJ-1 protein may have disadvantages in the survival of dopaminergic neurons in the brains of patients harboring GBA1 mutations.