Progressive Loss of Astrocytic AIBP Expression during Alzheimer's Disease Pathology

Astrocytes and microglia play crucial roles in mediating neuroinflammation during Alzheimer's disease (AD) progression. ApoA-I binding protein (APOA1BP, also known as AIBP/NAXE) attenuates neuroinflammation by blocking amyloid β-induced TLR4 inflammaraft formation and oxidative stress. Apoa1bp knockout in APP/PS1 mice exacerbates microgliosis, increases amyloid plaque burden, neuronal cell loss, and reduces survival at 6 months. Although APOA1BP mRNA is ubiquitously expressed in humans, its cell-type-specific distribution in the brain remains unclear. To examine AIBP protein expression in the human brain, we performed immunohistochemistry on hippocampal sections from postmortem brain specimens from subjects aged 75-96 of both sexes. Using GFAP and IBA1 to label astrocytes and microglia, respectively, we found that AIBP protein was highly expressed in astrocytes, but not in microglia. Stratification of subjects by Braak stage (I-II, III-IV, V-VI) revealed a progressive decline in astrocytic AIBP expression with advancing AD pathology. Meta-analysis of RNA-seq profiling indicated enriched Apoa1bp expression in adult mouse astrocytes. Systemic Apoa1bp knockout in the APP/PS1 mouse exacerbated astrogliosis. These findings demonstrate that AIBP is predominantly expressed in astrocytes and its expression declines with AD progression, suggesting a potential role for AIBP in astrocyte-mediated neuroprotection and AD pathogenesis.