Short-term treatment of mice with GHK peptide enhances resilience to age-related cognitive decline

Abstract

Age-related cognitive decline (ARCD) is a neurodegenerative process accompanied with memory loss, neuronal dysfunction, and more such as chronic inflammation and increased cellular senescence. It impacts a large percentage of the aging population, increases in prevalence with age, and is a known risk factor for more severe neurodegenerative diseases such as Alzheimer’s Disease. Currently, there are no known treatments to stop or reverse the process of ARCD which presents a clear knowledge gap and opportunity to investigate potential gerotherapeutics. Glycyl-L-histidyl-L-lysine (GHK) is a naturally occurring peptide that forms complexes with copper (II) to improve wound healing and improve several age-related skin changes. Several studies have connected treatment of GHK-Cu to improvement of several hallmarks of aging via the inhibition of TGF-β and provides reasoning for exploring GHK-Cu as a potential gerotherapeutic. To test this potential, a short-term five-day treatment of GHK-Cu in middle-aged mice was performed. C57BL/6 mice, 20 to 22-months of age, were administered an intraperitoneal (IP) injection of GHK-Cu daily for five days. Cognitive function was assessed on the fifth day of treatment via a spatial navigation learning task. Several markers in the brain were assessed via immunohistochemistry (IHC) of the hippocampus and cerebellum. These markers include TGF-β1, GFAP, and phosphorylated-SMAD2 to assess the TGF-β pathway, synaptophysin and PSD95 to assess pre- and post-synaptic function, and p21 and MCP-1 to investigate cellular senescence and inflammation respectively. Aging pathways and gene regulation of GHK-Cu was investigated by RNA sequencing of the hippocampus. Results suggest improvement of cognitive function in male mice treated with GHK-Cu across several aspects including learning and memory shown via a behavioral assay, and decreased inflammation and cellular senescence. Results also revealed strong sex-dependent phenotypes within this treatment pathway as female mice treated with GHK-Cu showed less cognitive rescue when compared to male mice. This study provides support that a short-term treatment of GHK-Cu can positively impact cognitive function in middle-aged mice in a sex-dependent manner and provides potential pathways of interest for further investigation into the sex-dependent phenotypes observed. This provides support for GHK-Cu’s potential as a gerotherapeutic and progress in alleviating the negative effects of ARCD.