Proteomic profiling of human brain coupled to functional assays for the identification of neurotoxic proteins

Abstract

AbstractBackgroundAlzheimer’s Disease (AD) affects millions globally, but therapy development is lagging. The dearth of new therapies requires a reconsideration of pre‐clinical models of AD to facilitate the discovery of efficacious treatments. Ideally, such models would allow for monitoring the functional behavior of neurons in conditions approximating the AD brain.MethodsTowards the goal of developing more representative, pre‐clinical AD models, we employ multiple‐electrode arrays (MEAs) and live‐cell imaging for assessing neuronal firing and neurite integrity (NI), respectively. We use this system to examine changes in neuronal activity and neurite integrity following treatment with TBS‐soluble human brain extract from a panel of 43 individuals comprised of AD patients, unaffected persons not exhibiting AD pathology nor cognitively impaired, and individuals not cognitively impaired but exhibited AD‐related postmortem pathology. To determine the molecular etiology of these functional changes in an unbiased manner, we perform label‐free proteomic analyses on the panel of 43 brain extracts.ResultsAmyloid‐β (Aβ) and tau accumulate in the AD brain, and specific forms of each of these proteins have shown neurotoxic properties. We observe associations between spontaneous activity and Aβ42:40 levels, and between neurite integrity and oligomeric Aβ or tau containing N inserts. Additionally, the proteomic analyses reveal several candidates whose expression correlated with changes in neuronal structure and activity. Proteins associated with neurotoxic activities in MEA and NI assays are enriched in proteins implicated in lysosomal storage disorders, while proteins associated with neuroprotective properties are enriched in proteins of the WAVE regulatory complex that are involved in the regulation of actin polymerization. We further show that elevated GM2A in the AD brain and AD CSF is associated with reductions in both neurite integrity and MEA activity. Applying cell derived GM2A in the absence of brain extract is sufficient to induce a subtle but significant loss of neurite integrity.ConclusionThe techniques and data herein introduce a system for modeling neuronal vulnerability in response to factors present in the aged human brain and provide insights into proteins potentially contributing to AD pathogenesis.