Project description:Carrying premature termination codons in one allele of the ABCA7 gene is associated with an increased risk for Alzheimer’s disease (AD). While the primary function of ABCA7 is to regulate the transport of phospholipids and cholesterol, ABCA7 is also involved in maintaining homeostasis of the immune system. Since inflammatory pathways causatively or consequently participate in AD pathogenesis, we studied the effects of Abca7 haplodeficiency in mice on brain immune responses under acute or chronic conditions. When the acute inflammation was induced through peripheral lipopolysaccharide (LPS) injection in control or heterozygous Abca7 knockout mice, partial ABCA7 deficiency diminished pro-inflammatory responses by impairing CD14 expression in the brain.
Project description:ABCA7 loss-of-function variants are associated with increased risk of Alzheimer’s disease (AD). Using ABCA7 knockout human iPSC models generated with CRISPR/Cas9, we investigated the impacts of ABCA7 deficiency on neuronal metabolism and function. Lipidomics revealed that mitochondria-related phospholipids, such as phosphatidylglycerol and cardiolipin were reduced in the ABCA7-deficient iPSC-derived cortical organoids. Consistently, ABCA7 deficiency induced alterations of mitochondrial morphology accompanied by reduced ATP synthase activity and exacerbated oxidative damage in the organoids.
Project description:The adenosine triphosphate–binding cassette transporter A7 (ABCA7) gene is ranked as one of the top susceptibility loci for Alzheimer’s disease (AD). While ABCA7 mediates lipid transport across cellular membranes, ABCA7 loss of function has been shown to exacerbate amyloid-β (Aβ) pathology and compromise microglial function. Our family-based study uncovered an extremely rare ABCA7 p.A696S variant that was substantially segregated with the development of AD in 3 African American families. Using the knockin mouse model, we investigated the effects of ABCA7-A696S substitution on amyloid pathology and brain immune response in 5xFAD transgenic mice. Importantly, our study demonstrated that ABCA7-A696S substitution reduces amyloid plaque–associated microgliosis and increases dystrophic neurites around amyloid deposits compared to control mice. We also found increased X-34–positive amyloid plaque burden in 5xFAD mice with ABCA7-A696S substitution, while there was no evident difference in insoluble Aβ levels between mouse groups. Thus, ABCA7-A696S substitution may disrupt amyloid compaction resulting in aggravated neuritic dystrophy due to insufficient microglia barrier function. In addition, we observed that ABCA7-A696S substitution disturbs the induction of proinflammatory cytokines interleukin 1β and interferon γ in the brains of 5xFAD mice, although some disease-associated microglia gene expression, including Trem2 and Tyrobp, are upregulated. Lipidomics also detected higher total lysophosphatidylethanolamine levels in the brains of 5xFAD mice with ABCA7-A696S substitution than controls. These results suggest that ABCA7-A696S substitution might compromise the adequate innate immune response to amyloid pathology in AD by modulating brain lipid metabolism, providing novel insight into the pathogenic mechanisms mediated by ABCA7.
Project description:Genetic variants in ABCA7, an Alzheimer's disease (AD)-associated gene, elevate AD risk, yet its functional relevance to the etiology is unclear. We generated a CRISPR-Cas9-mediated abca7 knockout zebrafish to explore ABCA7's role in AD. Single-cell transcriptomics in heterozygous abca7+/- knockout combined with Aβ42 toxicity revealed that ABCA7 is crucial for neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), and nerve growth factor receptor (NGFR) expressions, which are crucial for synaptic integrity, astroglial proliferation, and microglial prevalence. Impaired NPY induction decreased BDNF and synaptic density, which are rescuable with ectopic NPY. In induced pluripotent stem cell-derived human neurons exposed to Aβ42, ABCA7-/- suppresses NPY. Clinical data showed reduced NPY in AD correlated with elevated Braak stages, genetic variants in NPY associated with AD, and epigenetic changes in NPY, NGFR, and BDNF promoters linked to ABCA7 variants. Therefore, ABCA7-dependent NPY signaling via BDNF-NGFR maintains synaptic integrity, implicating its impairment in increased AD risk through reduced brain resilience.
Project description:Loss-of-function variants of the ABCA7 gene are associated with the increased risk of Alzheimer's disease (AD). How neuronal ABCA7 contributes to AD pathogenesis is unknown. Using neuron-specific Abca7 knockout mice (nAbca7−/−) with or without 5×FAD amyloid model background and postmortem AD brains, we investigated AD-related phenotypes through comprehensive approaches including transcriptomics and lipidomics. Lipidomics analysis detected altered lipid profiles in the brains and synaptosomes of 5×FAD; nAbca7−/− mice compared to controls. Transcriptomics profiling revealed that neuronal ABCA7 deficiency altered the expression of genes and pathways related to mitochondrial homeostasis and apoptosis, particularly in excitatory neurons. Consistently, synaptosomes isolated from 5×FAD; nAbca7−/− mice showed diminished mitochondria respiration and reduced synaptic protein levels, which are further supported by results from human AD brains. Our findings reveal that neuronal ABCA7 plays a critical role in mitochondrial homeostasis important for neuronal function and survival in the presence of AD pathology.
Project description:Loss-of-function variants of the ABCA7 gene are associated with the increased risk of Alzheimer's disease (AD). How neuronal ABCA7 contributes to AD pathogenesis is unknown. Using neuron-specific Abca7 knockout mice (nAbca7−/−) with or without 5×FAD amyloid model background and postmortem AD brains, we investigated AD-related phenotypes through comprehensive approaches including transcriptomics and lipidomics. Lipidomics analysis detected altered lipid profiles in the brains and synaptosomes of 5×FAD; nAbca7−/− mice compared to controls. Transcriptomics profiling revealed that neuronal ABCA7 deficiency altered the expression of genes and pathways related to mitochondrial homeostasis and apoptosis, particularly in excitatory neurons. Consistently, synaptosomes isolated from 5×FAD; nAbca7−/− mice showed diminished mitochondria respiration and reduced synaptic protein levels, which are further supported by results from human AD brains. Our findings reveal that neuronal ABCA7 plays a critical role in mitochondrial homeostasis important for neuronal function and survival in the presence of AD pathology.
Project description:Loss-of-function variants of the ABCA7 gene are associated with the increased risk of Alzheimer's disease (AD). How neuronal ABCA7 contributes to AD pathogenesis is unknown. Using neuron-specific Abca7 knockout mice (nAbca7−/−) with or without 5×FAD amyloid model background and postmortem AD brains, we investigated AD-related phenotypes through comprehensive approaches including transcriptomics and lipidomics. Lipidomics analysis detected altered lipid profiles in the brains and synaptosomes of 5×FAD; nAbca7−/− mice compared to controls. Transcriptomics profiling revealed that neuronal ABCA7 deficiency altered the expression of genes and pathways related to mitochondrial homeostasis and apoptosis, particularly in excitatory neurons. Consistently, synaptosomes isolated from 5×FAD; nAbca7−/− mice showed diminished mitochondria respiration and reduced synaptic protein levels, which are further supported by results from human AD brains. Our findings reveal that neuronal ABCA7 plays a critical role in mitochondrial homeostasis important for neuronal function and survival in the presence of AD pathology.