Rebecca L Cunningham - US grants

[unreadable] DESCRIPTION (provided by applicant): PROBLEM: Parkinson's disease (PD) has a higher prevalence in the human male population. PD is characterized by motor dysfunction, rigidity, and bradykinesia. Current research suggests that gender plays a role in this condition, since males have a greater incidence of PD. It is believed that the underlying mechanism of PD involves oxidative stress leading to cellular apoptosis. In many peripheral cells and some neuronal cells, androgens have been shown to increase apoptosis. PURPOSE: The goal of these studies is to determine androgen's effects on dopaminergic cells following oxidative stress by using both in vitro and in vivo methods. The central hypothesis of this proposal is that androgens increase cellular vulnerability to oxidative stress-induced neurotoxicity in dopaminergic neurons. RESEARCH QUESTIONS: The first specific aim of this proposal is to determine the apoptotic signaling pathways activated by androgens in dopaminergic N27 cells following oxidative stress (hydrogen peroxide). The second specific aim is designed to evaluate the effects of androgens on estrogen-mediated neuroprotection in dopaminergic N27 neurons following oxidative stress. These aims will be accomplished through in vitro molecular studies with and without the presence of astroglia cells and the androgen receptor antagonist, hydroxyflutamide. Lastly, the third specific aim will characterize the in vivo effects of androgens on tyrosine hydroxylase expression, neuronal death, and motor behavior in aged male rats exposed to 6-OHDA, which induces oxidative stress and apoptosis in the substantia nigra and striatum. In vivo hormone treatment groups will consist of gonadectomized aged males, gonadally intact aged males, and gonadectomized aged males plus replacement androgen (testosterone or dihydrotestosterone) for either a chronic (3 months) or acute (1 week) treatment time length prior to 6-OHDA lesion. Immunocytochemical and behavioral techniques will be used to accomplish this aim. OUTCOMES: This study will provide basic knowledge on how androgens modulate dopaminergic cellular vulnerability to oxidative stress. Ultimately, this knowledge can be used to provide a foundation to understanding the mechanisms underlying sex differences in neurodegenerative disorders. [unreadable] [unreadable]

? DESCRIPTION (provided by applicant): Two common risk factors for the development of Parkinson's disease (PD) are oxidative stress and male gender. It is unclear how these conditions increase the risk for PD in men. Our data suggests that the major male sex hormone, testosterone (T), is involved in mediating this gender difference. This is of concern as T therapy use has increased 3-fold in aging men just this past decade, yet we know little about how T impacts brain vulnerability to age-related disorders. In this proposal, we will investigate the rol of T on oxidative stress generation in substantia nigral dopamine neurons, which are lost during PD progression. T and oxidative stress are hypothesized to cooperatively increase PD progression. Both T and oxidative stress affect key features of PD pathology, including NADPH oxidases and ?-synuclein accumulation. We postulate that an interaction between T and oxidative stress increases PD pathogenesis through cell signaling pathways that regulate these aspects of PD pathology. To investigate these hypotheses, we propose three aims. In Aim 1, we will determine whether a G-protein coupled receptor mediates T induced oxidative stress generation in a dopaminergic cell line and an early stage PD animal model. In Aim 2, we will investigate if T increases oxidative stress by activating NADPH oxidases, key enzymes involved in oxidative stress generation, in a dopaminergic cell line and early stage PD animal model. Finally, in Aim 3 we will characterize the effects of T on oxidative stress generation in an advanced stage PD animal model. These three aims will allow us to examine the effects of T and oxidative stress on dopaminergic neuronal function from early stage to advanced stage PD. Completion of our studies will mechanistically define interactions between T and oxidative stress and how they promote PD progression in men. Further, our studies will address the NIH Institute of Medicine's recommendation for more research on T therapy in aging men.

? DESCRIPTION (provided by applicant): Current estimates of the US population suggest greater than 20% of men over 45 years of age may be hypogonadal (total Testosterone <300 pg/dL), and more than 30% of US men over 70 are considered hypogonadal. Over the last decade prescriptions for testosterone replacement therapy (TRT) have increased 3-fold. However, recent studies suggest that TRT can increase cardiovascular and cerebrovascular morbidity and mortality. The reasons underlying these risks are unknown. An understanding of the mechanism of action of T's effects on the cerebrovasculature and brain could lead to optimized therapies with respect not just to timing, but also dose, route, and formulation for TRT. Recent evidence indicates that there is a critical window for hormone therapy in postmenopausal women, beyond which estrogens lose their beneficial effects, and may even have detrimental effects on cognition and brain aging. Because many of T's effects in the brain involve conversion to estrogen and antioxidant effects similar to estrogen, we hypothesize that the beneficial effects of T in the brain may also have a critical window of efficacy in males. Further, oxidative stress levels may mediate this critical window. We have recently found that T levels are inversely related to cognitive function only under conditions of high oxidative stress in men. This PILOT grant seeks to investigate the concept of a critical window for TRT on cognition, brain aging, and response to oxidative injury. Morphological and behavioral studies will be used to define the role of dose and time-dependent steroid replacement regimens in a rat model. The overall goal is to establish a model of successful and refractory TRT that can then be used to generate mechanistic hypotheses for subsequent extramural grant submissions using natural aging and comorbid conditions in the context of TRT. Aim 1 will test the hypothesis that the beneficial effects of TRT on cognition and oxidative stress are diminished following long-term testosterone deprivation (LTTD). Castrate middle-aged rats will undergo short (1d) or long-term (10 wk) testosterone deprivation before replacement to physiological levels. Cognitive function and peripheral and central oxidative stress will be compared to intact and castrate rats treated with vehicle. Aim 2 will test the hypothesis that long-term testosterone deprivation (LTTD) inhibits the neuroprotective effects of TRT in experimental stroke. Castrate male middle-aged rats will undergo short (1d) or long-term (10 wk) testosterone deprivation before replacement to physiological levels. Rats will undergo experimental stroke using intraparenchymal injection of endothelin-1 adjacent to the middle cerebral artery. Sensory-motor function, cognitive function and peripheral and central oxidative stress will be compared to intact and castrate rats treated with vehicle. Results of these PILOT studies not only will provide critical preliminary data for additional mechanistic extramural grant proposals, but also will provide important information for those men considering TRT.