Transcriptomic analysis of probable asymptomatic and symptomatic Alzheimer Brains

Objectives: Individuals with intact cognition and neuropathology consistent with Alzheimer’s disease (AD) are referred to as asymptomatic AD (AsymAD). These individuals are highly likely to develop AD, yet transcriptomic changes in the brain which might reveal mechanisms for their AD vulnerability are currently unknown. Methods: Differential and co-expression analysis was performed on microarray profiled human brains of 27 control , 33 AsymAD and 52 AD subjects. Tissues known to be affected by AD neuropathology (entorhinal cortex, temporal cortex, frontal cortex) and tissue partially spared by the disease (cerebellum). Results: The AsymAD subjects exhibited significant changes in transcriptomic activity in the frontal cortex when compared to AD and control subjects. Fourteen genes (GPM6B, ANKEF1, NPC2, ALDH2, FBLN2, METTL7A, FLCN, ASPHD1, ARL5A, GPR162, HBA2, PCID2, BEND3 and RAP1Gap) were highly associated with AD neuropathology with overall disturbances in the “glutamate-glutamine cycle”, “oxidative phosphorylation”, “innate immune system”, “TYROBP network”, “neutrophil degranulation” and “amino acid metabolism” in both the AsymAD and AD subjects. Conclusions: Transcriptomic activity in AsymAD subjects suggests fundamental changes in AD brains may begin within the frontal cortex region. In addition, we provide new insight into the earliest biological changes occurring in the brain prior to clinical AD diagnosis which offers new avenues for therapeutic interventions for preventing AD. We provide access of gene-level results to the broader research community through a publicly available R SHINY web-application accessible at: https://phidatalab-shiny.rosalind.kcl.ac.uk/ADbrainDE Total RNA obtained from entorhinal cortex, temporal cortex, frontal cortex and cerebellum brain region from controls, asymptomatic AD and AD subjects.