ApoE4 Exacerbates Hippocampal Pathology Following Acute Brain Penetration Injury in Female Mice

Chemotherapy promotes astrocytic response to Aβ deposition, but not Aβ levels, in a mouse model of amyloid and APOE

Many cancer survivors experience cancer-related cognitive impairment (CRCI), which is characterized by problems of attention, working memory, and executive function following chemotherapy and/or hormonal treatment. APOE4, the strongest genetic risk factor for Alzheimer's Disease (AD), is also a risk factor for CRCI, especially among survivors exposed to chemotherapy. We explored whether the effects of APOE genotype to chemotherapy were associated with an increase in AD pathological processes, using a mouse model of amyloid (5XFAD) along with the E3 or E4 alleles of human APOE (E3FAD and E4FAD). Six-month-old female E3FAD mice (control n = 5, treated n = 5) and E4FAD (control n = 6, treated n = 6) were treated with two doses of doxorubicin (total 10 mg/kg) or DMSO vehicle. After six weeks, mice were euthanized and brains were analyzed by immunohistochemistry and biochemical assays. Doxorubicin-treated mice had the same level of Aβ in the brain as control mice, as measured by 6E10 immunohistochemistry, Aβ40 and Aβ42 ELISAs, and plaque morphologies. Doxorubicin significantly increased the level of the astrocytic response to Aβ deposits, which was independent of APOE genotype; no effects of doxorubicin were observed on the microglial responses. These data are consistent with a model in which the effects of doxorubicin on risk of CRCI are unrelated amyloid accumulation, but possibly related to glial responses to damage.

Somatic Mutations and Alzheimer’s Disease

Alzheimer’s disease (AD) represents a global health challenge, with an estimated 55 million people suffering from the non-curable disease across the world. While amyloid-β plaques and tau neurofibrillary tangles in the brain define AD proteinopathy, it has become evident that diverse coding and non-coding regions of the genome may significantly contribute to AD neurodegeneration. The diversity of factors associated with AD pathogenesis, coupled with age-associated damage, suggests that a series of triggering events may be required to initiate AD. Since somatic mutations accumulate with aging, and aging is a major risk factor for AD, there is a great potential for somatic mutational events to drive disease. Indeed, recent data from the Gozes team/laboratories as well as other leading laboratories correlated the accumulation of somatic brain mutations with the progression of tauopathy. In this review, we lay the current perspectives on the principal genetic factors associated with AD and the potential causes, highlighting the contribution of somatic mutations to the pathogenesis of late onset Alzheimer’s disease. The roles that artificial intelligence and big data can play in accelerating the progress of causal somatic mutation markers/biomarkers identification, and the associated drug discovery/repurposing, have been highlighted for future AD and other neurodegenerative studies, with the aim to bring hope for the vulnerable aging population.

A diet rich in docosahexaenoic acid enhances reactive astrogliosis and ramified microglia morphology in apolipoprotein E epsilon 4-targeted replacement mice

Docosahexaenoic acid (DHA) consumption reduces spatial memory impairment in mice carrying the human apolipoprotein E ε4 (APOE4) allele. The current study evaluated whether astrocyte and microglia morphology contribute to the mechanism of this result. APOE3 and APOE4 mice were fed either a DHA-enriched diet or a control diet from 4 to 12 months of age. Coronal brain sections were immunostained for GFAP, Iba1, and NeuN. Astrocytes from APOE4 mice exhibited signs of reactive astrogliosis compared to APOE3 mice. Consumption of DHA exacerbated reactive astrocyte morphology in APOE4 carriers. Microglia from APOE4-control mice exhibited characteristics of amoeboid morphology and other characteristics of ramified morphology (more processes, greater process complexity, and greater distance between neighboring microglia). DHA enhanced ramified microglia morphology in APOE4 mice. In addition, APOE4 mice fed the DHA diet had lower hippocampal concentrations of interleukin-7, lipopolysaccharide-induced CXC chemokine and monocyte chemoattractant protein 1, and higher concentration of interferon-gamma compared to APOE4-control mice. Our results indicate that a diet rich in DHA enhances reactive astrogliosis and ramified microglia morphology in APOE4 mice.

Apolipoprotein e (APOE) ε4 genotype influences memory performance following remote traumatic brain injury in U.S. military service members and veterans

The purpose of this study was to examine the association between the apolipoprotein E (APOE) ε4 allele and neurocognitive functioning following traumatic brain injury (TBI) in military service members and veterans (SMVs). Participants included 176 SMVs with a history of remote TBI (≥1 year post-injury), categorized into mild (n = 100), moderate (n = 40), and severe (n = 36) TBI groups. Participants completed a neuropsychological assessment and APOE genotyping (n = 46 ε4+, n = 130 ε4-). Neurocognitive composite scores representing memory, executive functioning, and visual processing speed were computed. ANCOVAs adjusting for race, education, combat exposure, and PTSD symptom severity showed a significant main effect of ε4 on the memory composite, such that ε4+ SMVs exhibited poorer memory performance than ε4- SMVs. When ε2 allele carriers were removed from the analyses, associations with memory were strengthened, demonstrating a possible protective effect of the ε2 allele. No main effect of TBI group was identified on any cognitive composite, nor were there any significant TBI group × ε4 status interactions for any cognitive composite. Future studies with larger samples are needed to verify these findings, but our results suggest an important relationship between ε4 status and memory functioning following remote TBI of all severities.

Region-Specific Differences in the Apoe4-dependent Response to Focal Brain Injury

Apolipoprotein E (apoE) plays a role in various physiological functions including lipid transport, synaptic plasticity, and immune modulation. Epidemiological studies suggest that the apoE4 allele increases the risk of post-traumatic sequelae. This study was performed to investigate regionspecific effects of the apoE4 isoform on post-traumatic neurodegeneration. Two focal brain injuries were introduced separately in the motor cortex and hippocampus of apoE4 knock-in, apoE3 knock-in, apoE knockout, and wild-type (WT) mice. Western blotting showed that the expression levels of pre-synaptic and post-synaptic markers at the recovery stage were lower in the hippocampal injury core in apoE4 mice, compared with apoE3 and WT mice. Fast glial activation (determined by immunohistochemistry with glial fibrillary acidic protein, ionized calcium binding adaptor molecule 1, and cluster of differentiation 45 antibodies) was characteristic of apoE4 mice with hippocampal injury penumbra. apoE4-specific changes were not observed after cortical injury. The intensity of microglial activation in the hippocampus was inversely correlated with the volume of injury reduction on sequential magnetic resonance imaging examinations, when validated using matched samples. These findings indicate that the effects of the interaction between apoE4 and focal brain damage are specific to the hippocampus. Manipulation of inflammatory cell responses could be beneficial for reducing post-traumatic hippocampal neurodegeneration in apoE4 carriers.

Dynamic changes in Beclin-1, LC3B and p62 at various time points in mice with temporary middle cerebral artery occlusion and reperfusion (tMCAO)

Ischaemic stroke is attributable to cerebrovascular disease and is associated with high morbidity, disability, mortality and recurrence. Autophagy is a critical mediator and plays dual roles in ischaemic stroke. Autophagy can protect against ischaemic brain injury during the early stage of ischaemic stroke, while excessive autophagy can induce apoptosis and exacerbate brain injury. However, the time-dependent variations in autophagy in ischaemic stroke are unknown. C57BL/6 mice were used to establish a model of temporary middle cerebral artery occlusion and reperfusion (tMCAO). The neurological functional scores and infarct volumes were determined at 1 d, 3 d, 5 d, and 7 d after modelling. The levels of Beclin-1, LC3B, p62, GFAP, TNF-α, IL-6, IL-10, ROS, 4-HNE and 8-OHDG were measured by ELISA, RT-PCR, immunofluorescence analysis and western blotting. The morphology of autophagosomes of ischaemic penumbra was observed by transmission electron microscopy (TEM). Beclin-1, LC3B, ROS, 4-HNE, 8-OHDG, GFAP, TNF-α and IL-6 levels increased (P < 0.01), while p62 and IL-10 levels decreased (P < 0.01) after tMCAO compared to those in the sham group. Beclin-1, LC3B, ROS, 4-HNE, 8-OHDG, GFAP, TNF-α and IL-6 levels were reduced in tMCAO mice at 3 d, 5 d and 7 d (P<0.05), and p62 and IL-10 levels were enhanced (P < 0.05) compared to those at 1 d. In addition, Beclin-1 positively correlated with LC3B, GFAP, TNF-α, IL-6, ROS, 4-HNE and 8-OHDG (P < 0.05), and Beclin-1 negatively correlated with p62 and IL-10 (P < 0.05). The number of autophagosomes was consistent with the expression of autophagy marker proteins, both showing a steady decrease. In summary, autophagy was activated within 7 d of tMCAO induction, and it strengthened at 1 d and then weakened steadily from 3 to 7 d. In addition, this study verified that autophagy positively correlated with the inflammatory response and oxidative stress at 7 d after tMCAO.

Cancer Chemotherapy Related Cognitive Impairment and the Impact of the Alzheimer's Disease Risk Factor APOE

Cancer related cognitive impairment (CRCI) is a serious impairment to maintaining quality of life in cancer survivors. Cancer chemotherapy contributes to this condition through several potential mechanisms, including damage to the blood brain barrier, increases in oxidative stress and inflammation in the brain, and impaired neurogenesis, each of which lead to neuronal dysfunction. A genetic predisposition to CRCI is the E4 allele of the Apolipoprotein E gene (APOE), which is also the strongest genetic risk factor for Alzheimer's disease. In normal brains, APOE performs essential lipid transport functions. The APOE4 isoform has been linked to altered lipid binding, increased oxidative stress and inflammation, reduced turnover of neural progenitor cells, and impairment of the blood brain barrier. As chemotherapy also affects these processes, the influence of APOE4 on CRCI takes on great significance. This review outlines the main areas where APOE genotype could play a role in CRCI. Potential therapeutics based on APOE biology could mitigate these detrimental cognitive effects for those receiving chemotherapy, emphasizing that the APOE genotype could help in developing personalized cancer treatment regimens.