Age-related dysregulation of proteasome-independent K63 polyubiquitination in the hippocampus and amygdala

Abstract

Cognitive decline with aging is a complex process involving multiple brain regions and molecular mechanisms. While the role of the canonical protein degradation function of the ubiquitin–proteasome system (UPS) has been well studied in the context of aging and age-associated memory loss, the non-proteolytic functions of ubiquitin activity remain poorly understood. Here, we investigated the role of lysine-63 (K63) polyubiquitination, the most abundant form of proteasome-independent ubiquitination, in aged rats, focusing on the hippocampus and amygdala, two brain regions reported to have cellular and molecular alterations with age that are associated with age-related memory loss. Using an unbiased proteomic approach, we observed a significant increase of K63 polyubiquitination in the hippocampus across the lifespan. Reducing K63 polyubiquitination in the hippocampus of aged male rats using the CRISPR-dCas13 RNA editing system enhanced contextual fear memory, while similar manipulations in middle-aged rats, which typically have normal memory, had no effect, emphasizing the age-dependent role of K63 polyubiquitination in memory formation. Conversely, the amygdala showed a consistent reduction of K63 polyubiquitination protein targets across the lifespan, and further reductions of K63 polyubiquitination improved memory retention in aged, but not middle-aged, male rats. Together, our findings reveal the dynamic and region-specific functions of K63 polyubiquitination in the brain aging process, providing novel insights into its contribution to age-associated memory decline.