Proteomic Analysis of Adult Human Hippocampal Subfields Demonstrates Regional Heterogeneity in the Protein Expression

Mapping the hippocampal spatial proteomic signature in male and female mice of an early Alzheimer's disease model

BACKGROUND

Hippocampal dysfunction induced by soluble amyloid-β oligomers (oAβ) is an early neuropathological hallmark of Alzheimer's disease (AD). oAβ shifts hippocampal synaptic-plasticity induction threshold facilitating long-term depression (LTD) instead of long-term potentiation (LTP, the functional basis of memory), thereby leading to memory deficits in early AD-like amyloidosis mouse models. In this regard, the spatial distribution of the underlying synaptic-plasticity/memory proteome changes in the hippocampus, and potential sex differences, remain unknown. Here we postulated that some protein changes related to synaptic-plasticity and memory may be unique to sex and/or specific to the dorsal or ventral hippocampus -as both regions have distinct functionality and connectivity-, potentially providing sex- and spatial-specific proteomic phenotypes for early AD-amyloidosis interventions.

METHODS

An innovative spatial-resolution proteomics study was performed to map whole hippocampal proteome distribution using matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry. For this purpose, sixteen adult male and female mouse brains intracerebroventricularly injected with oAβ1-42/vehicle were analyzed. MALDI-imaging RapifleXTM-MALDI-TissuetyperTM TOF/TOF mass spectrometer was used, followed by traditional tandem mass spectrometry (MS/MS) for precise protein identification on tissue.

RESULTS

34 proteins showed significant differences in expression levels due to treatment, sex, or hippocampal location among 234 peptides initially detected; and displayed significant protein-protein interaction (PPI), indicating main functional relationship to LTP/LTD pathways and memory. Thus, 14 proteins related to synaptic-plasticity and/or AD were further studied, showing that most modulated glycogen synthase kinase-3β (GSK-3β), a protein widely involved in synaptic-plasticity induction threshold regulation towards LTD. Accordingly, hippocampal GSK-3β was found to be overactivated in AD-like amyloidosis mice.

CONCLUSIONS

We show for the first-time specific sex-dependent synaptic-plasticity proteome changes in dorsal/ventral hippocampi that modulate GSK-3β activity. These findings provide new insight into the early amyloidosis pathogenesis in AD and offer valuable, unique proteomic phenotypes as potential biomarkers and targets for early diagnosis and therapy in both sexes.

Regional Microglial Response in Entorhino-Hippocampal Slice Cultures to Schaffer Collateral Lesion and Metalloproteinases Modulation

Microglia and astrocytes are essential in sustaining physiological networks in the central nervous system, with their ability to remodel the extracellular matrix, being pivotal for synapse plasticity. Recent findings have challenged the traditional view of homogenous glial populations in the brain, uncovering morphological, functional, and molecular heterogeneity among glial cells. This diversity has significant implications for both physiological and pathological brain states. In the present study, we mechanically induced a Schaffer collateral lesion (SCL) in mouse entorhino-hippocampal slice cultures to investigate glial behavior, i.e., microglia and astrocytes, under metalloproteinases (MMPs) modulation in the lesioned area, CA3, and the denervated region, CA1. We observed distinct response patterns in the microglia and astrocytes 3 days after the lesion. Notably, GFAP-expressing astrocytes showed no immediate changes post-SCL. Microglia responses varied depending on their anatomical location, underscoring the complexity of the hippocampal neuroglial network post-injury. The MMPs inhibitor GM6001 did not affect microglial reactions in CA3, while increasing the number of Iba1-expressing cells in CA1, leading to a withdrawal of their primary branches. These findings highlight the importance of understanding glial regionalization following neural injury and MMPs modulation and pave the way for further research into glia-targeted therapeutic strategies for neurodegenerative disorders.