THE EFFECTS OF ANDROGENS ON CASPASE-1 MEDIATED SIGNALING IN OXIDATIVE STRESSED DOPAMINE NEURONS

Parkinson’s disease (PD), a neurodegenerative disorder characterized by oxidative stress and the loss of dopamine neurons in the midbrain, affects the aging population. In fact, males have a higher risk for PD than females. While the mechanisms remain elusive, one possibility may be that androgens, such as testosterone, play a potential role. Our studies suggest that androgens can increase the expression of Caspase-1, an enzyme whose activity increases with oxidative stress and can result in mitochondrial collapse, ubiquitination, alpha-synuclein–positive lewy body accumulation, inflammation and apoptosis. Therefore, we hypothesize that in oxidative stress conditions, androgens suppress KLF4, a negative regulator of caspase-1, resulting in the increase of Caspase-1 to promote toxic protein accumulation, inflammation, and apoptotic neuronal cell death. This study is related to the role of testosterone in high levels of oxidative stress associated with aging. Purpose (a): Oxidative stress and an extensive loss of dopamine neurons in the nigrostriatal pathway are hallmarks of Parkinson’s disease (PD), a neurodegenerative disorder affecting millions of people. Males have a higher risk for PD than females. While the mechanisms remain elusive, one possibility may be that androgens, such as testosterone, play a potential role. Our studies suggest that androgens can increase the expression of Caspase-1, an enzyme whose activity increases with oxidative stress and can result in mitochondrial collapse, ubiquitination, alpha-synuclein–positive lewy body accumulation, inflammation and apoptosis. We hypothesize that in oxidative stress conditions, androgens suppress KLF4, a negative regulator of caspase-1, resulting in overexpression of Caspase-1 leading to toxic protein accumulation, inflammation, and apoptosis. Methods (b): We exposed a dopaminergic cell line (N27 cells) to a sublethal concentration of the pro-oxidant, tert-butyl hydrogen peroxide (H2O2) for 24 hrs and assessed cell viability in the presence or absence of testosterone. Results (c): Physiologically relevant concentrations of testosterone (0, 1, 10, 100 nM) failed to compromise cell viability in non-oxidatively stressed cells1. In contrast, testosterone did promote cell death in the H2O2 pre-treated cells. In H202 treated cells, testosterone increased caspase-1 expression and activation, as evidenced by an increase in cleaved caspase-1. In addition, KLF4 expression was decreased by testosterone in H2O2 treated cells. The role of KLF4 as a negative regulator of caspase-1 was confirmed in experiments showing that siRNA-mediated knockdown of KLF4 increased caspase-1 levels in H2O2 treated cells. Testosterone increased H202 mediated expression of COX2 signaling, a protein associated with inflammation. Also, testosterone decreased H2O2-induced ubiquitin expression resulting in the accumulation of toxic proteins. Further, testosterone increased H202 induced in apoptosis. Conclusions (d): Overall, these results indicate that androgens such as testosterone exert negative effects under oxidative stress conditions through the suppression of KLF4 and activation of caspase-1 signaling pathways leading to cell death. Thus, supporting a role for androgens for the gender bias observed in PD.