16 - The human ApoE4 allele is a key regulator governing persistent astrocytic reactivity and dysfunction to adulthood and a possible therapeutic target following neonatal hypoxia-ischemia.

Monday, May 1, 2023

9:30 AM – 11:30 AM ET

Poster Number: 16
Publication Number: 16.434

Raul Chavez-Valdez, Johns Hopkins University School of Medicine, CATONSVILLE, MD, United States; Mark St. Pierre, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Michael Nugent, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Katherine M. Carlin, United States Air Force, FPO, Armed Forces - AP, United States; Sarah Ann W. Duck, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Michelle M. Nazareth, Johns Hopkins University, Baltimore, MD, United States; Salma Nassar, Johns Hopkins University, Brookfield, CT, United States; Charles Pinto, The Johns Hopkins Hospital, Cary, NC, United States; Frances J.. Northington, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Lee J. Martin, Johns Hopkins University School of Medicine Department of Pathology, Baltimore, MD, United States

Presenting Author(s)

Raul Chavez-Valdez, MD (he/him/his)

Associate Professor
Johns Hopkins University School of Medicine
Baltimore, Maryland, United States

Background:

The human apolipoprotein E allele ε4 (ApoE4), a major risk factor for neurodegenerative disorders (i.e. AD) and a synaptic regulator produced by astrocytes in the brain, is associated with reduced temporal cortex thickness and hippocampal volume predicting lower working memory in healthy children. Astrocytes have key roles in the pathobiology of neonatal hypoxia-ischemia (HI) brain injury, but the effects of ApoE4 on these responses and subsequent maturation to adulthood are unknown

Objective: To test if ApoE4 predisposes the injured neonatal brain to sustained astrocytic reactivity and dysfunction persisting to adulthood as neuroinflammation, synaptic glutamate transport defects, and lasting neurodegeneration

Design/Methods:

Cerebral HI injury (Vannucci) was produced on postnatal day (P)10 ApoE ^-/- mice genetically humanized by global ApoE ε3 or ε4 allele knock-in. Controls were HI and sham wildtype (wt) C57BL6 mice and sham ApoE mice. Hippocampus of survivors was interrogated at 6 mo of age for RNAseq and a combination of immunoblotting and IF-IHC with Imaris processing for GFAP, EAAT2(GLT1), HK1, TNF-α, and Ser396 phosphorylated Tau⁺ cells

Results: RNA levels for astrocyte reactivity markers were upregulated in 6 mo HI-ApoE4 hippocampus vs. sham (A, RNAseq), including the C1q-C3 cascade linked to chronic astrocytic activation (A’). Increased GFAP protein levels (B) in HI-ApoE4 hippocampus (vs. controls) correlated with rise in ApoE4 levels. GFAP⁺ astrocyte number and complexity were also increased in HI-ApoE4 hippocampus vs. controls (C1-2). GFAP⁺ astrocytes had more Sholl branching (C3) mainly in the CA3 of HI (blue) ApoE4 mice (but not ApoE3) vs. sham (maroon) or hypoxia-alone (contralateral to HI, green). GFAP⁺ astrocyte complexity directly correlated with the number of dying pTau⁺ cells (C4-5). Inflammatory molecules known to be produced by glial cells were upregulated in RNAseq (D). Decreased astroglial glutamate transporter EAAT2 (GLT1) gene expression (in A, RNASeq) and protein levels (E) came along with decrease in hexokinase 1 (HK1) (F), an enzyme essential for EAAT function

Conclusion(s): The human ApoE4 allele in mice primes the injured neonatal brain for astrocyte pathology and dysfunction in later life. The disease- and injury-related ApoE4 effects found in the adult brain after neonatal HI included neuroinflammation and decreased glutamate transporter mechanisms, both of which are related to excitotoxic neurodegeneration. We propose chronic astroglia pathobiology as a central mechanism involved in suspected late-life consequences of perinatally acquired brain injury in ApoE4 carriers