Glial Activation in Aged Memory Impaired Rats

Sugaya, Kiminobu

Abstract

This application is focused on the topic #23) non-neuronal cells in the nervous system listed in PAR-98-021. The PI is a new investigator who is trying to establish his career in the aging study field. This proposal is to study the glial activation which may cause oxidative stress during the aging process and to seek the relationship of mitochondrial DNA (mtDNA) damage to cognitive impairment and other biological markers in aged rodent models. This proposal is related to my previous study , the levels of gene expression for b-amyloid protein precursor (APP), manganese super oxide dismutase (Mn-SOD) and glial fibrillary acidic protein (GFAP) in aged Long-Evans rats. All of the above markers were correlated with the degree of memory impairment in this model animal. These results indicate the presence of oxidative stress and glial activation during the aging process. Our preliminary experiment also revealed mtDNA damaged in aged memory impaired rats. MtDNA is a naked circular double-stranded DNA and due to the lack of proofreading during the replication and a less organized DNA repair system, it is extremely vulnerable to oxidative stress. Considering the production of oxidative stress during aging, accumulation of mtDNA damage may play an important pathophysiological role in the neurodegenerative process of aging and diseases. The activated glial cells are known to produce oxidative stress, while they support neuronal activity by the production of the nerve factors. In fact, we observed a much higher level of an indelible type nitric oxide gene expression in some of the aged memory impaired rats. Thus, we hypothesized that glial activation causes memory impairment by oxidative damaged during the aging process. To investigate this hypothesis, we propose the following studies. We will measure the GFAP, Mn-SOD and APP genes expression in young and aged rats with/without glial activation. We will inject lipopoly saccharide (LPS) into the cerebro-ventricle to activate the glia. The spatial memory will be tested by the Morris water maze before and after the injection. We will also measure mtDNA damage in these animals using quantitative PCR. This quantitative PCR assay to detect DNA damage is based on the evidence that several DNA lesions are able to block the progression of Taq DNA polymerase which results in a decreased PCR amplification. We will analyze these biological and behavioral data by linear regression analysis and ANOVA. We would expect that the candidate genes expression and the mtDNA damage are increased by the aging and glial activation and that the level of biological markers may be correlated with the memory impairment. This proposal allows us to prepare the preliminary data to expand the study to regulate the glial activity during the aging process. Subsequently, if we establish a relationship between memory impairment and glial activation in this animal model, it will be a good tool to develop noel therapeutics based on regulation of glial activity.