Background: Paraoxonase 2 (PON2) and neuronal uncoupling proteins (UCP4 and UCP5) possess antioxidant, anti-apoptotic activities and minimize accumulation of reactive oxygen species in mitochondria. While age and sex are risk factors for several disorders that are linked with oxidative stress, no study has explored the age- and sex-dependent expression of PON2 isoforms, UCP4 and UCP5 in primate brain or identified a drug to activate UCP4 and UCP5 in vivo. Preclinical studies suggest that the peroxisome proliferator-activated receptor gamma agonist, pioglitazone (PIO), can be neuroprotective, although the mechanism responsible is unclear. Our previous studies demonstrated that pioglitazone activates PON2 in primate brain and we hypothesized that pioglitazone also induces UCP4/5. This study was designed to elucidate the age- and sex-dependent expression of PON2 isoforms, UCP4 and UCP5, in addition to examining the impact of systemic PIO treatment on UCP4 and UCP5 expression in primate brain.
Methods: Western blot technique was used to determine the age- and sex-dependent expression of UCP4 and UCP5 in substantia nigra and striatum of African green monkeys. In addition, we tested the impact of daily oral pioglitazone (5 mg/kg/day) or vehicle for 1 or 3 weeks on expression of UCP4 and UCP5 in substantia nigra and striatum in adult male monkeys. PIO levels in plasma and cerebrospinal fluid (CSF) were determined using LC-MS.
Results: We found no sex-based difference in the expression of PON2 isoforms, UCP4 and UCP5 in striatum and substantia nigra of young monkeys. However, we discovered that adult female monkeys exhibit greater expression of PON2 isoforms than males in substantia nigra and striatum. Our data also revealed that adult male monkeys exhibit greater expression of UCP4 and UCP5 than females in substantia nigra but not in striatum. PIO increased UCP4 and UCP5 expression in substantia nigra and striatum at 1 week, but after 3 weeks of treatment this activation had subsided.
Conclusions: Our findings demonstrate a sex-, age- and region-dependent profile to the expression of PON2, UCP4 and UCP5. These data establish a biochemical link between PPARγ, PON2, UCP4 and UCP5 in primate brain and demonstrate that PON2, UCP4 and UCP5 can be pharmacologically stimulated in vivo, revealing a novel mechanism for observed pioglitazone-induced neuroprotection. We anticipate that these outcomes will contribute to the development of novel neuroprotective treatments for Parkinson's disease and other CNS disorders.
Keywords: Nonhuman primate; Oxidative stress; Pioglitazone; Striatum; Substantia nigra; Uncoupling protein.
Parkinson’s disease (PD) is less common in women than men, which may be related to the protective effect of high levels of estrogens in women that maintain the activity of neuroprotective proteins in brain mitochondria. Our previous work suggests that paraoxonase-2 (PON2), uncoupling protein-4 (UCP4) and uncoupling protein-5 (UCP5) play vital roles in maintaining the health of brain dopamine neurons that are lost in PD. This work tested the hypothesis that female primate brains expresses higher levels of these proteins than males. In addition, this research investigated whether estrogen regulates the expression these factors and whether they can be pharmacologically activated later in life to protect dopamine neurons at a time when symptoms of PD typically emerge. The results indicate that before puberty when estrogen levels in females are relatively low, there is no difference in PON2, UCP4, UCP5 brain levels between males and females, but in adults PON2 is up to 3 × higher in females compared with males in regions relevant to PD, consistent with estrogen activation of PON2. Earlier studies have shown that pioglitazone can be neuroprotective in several adverse brain conditions, although the mechanism is not clear. The current research demonstrates that pioglitazone transiently activates by about twofold the expression of PON2, UCP4, UCP5 in vivo in primate brain, suggesting their involvement in the neuroprotective properties of the drug. Overall, the current data provides impetus for further work on activating protective factors that alter mitochondrial dynamics and function, leading to improved understanding and treatment of multiple diseases.
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