Gradual cognitive decline does develop with senescence. However, it has frequently been noted that cognitive declines in older individuals often occur precipitously, & that these drops are typically preceded by events (surgery, viral or bacterial infection, injury) that involve peripheral inflammation/innate immune cell activation. Importantly, even when there is recovery from such declines, their occurrence is a predisposing factor to the development of long-term dementia. The cause(s) of this type of aging-related cognitive decline are unknown, & the long-term goal is to understand the mechanisms involved & develop appropriate therapies. During the past grant period we validated an animal model of this process, developed a mechanistic set of hypotheses to account for this phenomenon, & provided preliminary evidence in support. Work conducted during the past grant period & the further work here proposed is directed at understanding this phenomenon & its causes, as well as the discovery of therapeutic interventions. The hypothesis that has been developed involves several steps: 1) Peripheral inflammatory events signal the brain. 2) Microglia in specific brain regions become activated as part of the cascade of events in the brain induced by the I am sick/injured signal from the periphery, & the microglia produce inflammatory mediators, such as interleukin-1 (IL-1). Thus, peripheral inflammation leads to neuroinflammation. 3) Inflammatory mediators, particularly IL-1, can interfere with neural plasticity (e.g., long-term potentiation, LP) in regions such as the hippocampus, & therefore disrupt processes such as hippocampal long-term memory formation. IL-1 can do so directly & by interfering with other processes known to be critical for neural plasticity & memory formation. We have, & continue to test the hypothesis that large & prolonged elevations of IL-1 interfere with brain derived neurotrophic factor (BDNF) transcription & post-translational processing, & BDNF is well accepted as a critical mediator of synaptic plasticity & memory. 4) Aging primes or sensitizes microglia. This is the key assertion with regard to aging. During neurodegenerative disease microglia are overtly inflammatory in that their phenotype has shifted to ongoing production of inflammatory molecules. During pre-senescent aging, microglia show upregulated markers of activation, but they do not typically produce increased ongoing levels of inflammatory products such as IL-1. However, if stimulated they produce exaggerated quantities of inflammatory products, & do so for prolonged periods. 5) Thus, peripheral inflammation should lead to an exaggerated neuroinflammatory response in aging individuals, & we have demonstrated that this is the case. 6) The exaggerated amount & duration of the brain IL-1 increase in aging subjects during peripheral inflammation should interfere with cognitive processes such as memory for a prolonged period of time. Here these will all be tested. Here we explore the nature of microglia sensitization with age, its causes, and its cures. We also determine whether these cures prevent IL-1, BDNF, and memory deterioration.

R01AG028271

2006-04-01

2018-02-28