Showing papers by "Jacob Raber published in 2022"

Brain integrity is altered by hepatic APOE ε4 in humanized-liver mice

Abstract: Abstract Liver-generated plasma apolipoprotein E (apoE) does not enter the brain but nonetheless correlates with Alzheimer’s disease (AD) risk and AD biomarker levels. Carriers of APOE ε4, the strongest genetic AD risk factor, exhibit lower plasma apoE and altered brain integrity already at mid-life versus non- APOE ε4 carriers. Whether altered plasma liver-derived apoE or specifically an APOE ε4 liver phenotype promotes neurodegeneration is unknown. Here we investigated the brains of Fah−/− , Rag2−/−, Il2rg−/− mice on the Non-Obese Diabetic (NOD) background (FRGN) with humanized-livers of an AD risk-associated APOE ε4/ε4 versus an APOE ε2/ε3 genotype. Reduced endogenous mouse apoE levels in the brains of APOE ε4/ε4 liver mice were accompanied by various changes in markers of synaptic integrity, neuroinflammation and insulin signaling. Plasma apoE4 levels were associated with unfavorable changes in several of the assessed markers. These results propose a previously unexplored role of the liver in the APOE ε4-associated risk of neurodegenerative disease.

Serum Levels of α-Klotho Are Correlated with Cerebrospinal Fluid Levels and Predict Measures of Cognitive Function

Abstract: Background: α-klotho might play a role in neurodegenerative diseases. Objective: To determine levels of α-klotho and apoE in serum and cerebrospinal fluid (CSF) samples and their relationship with the Mini-Mental State Examination (MMSE) and Clinical Dementia Rating (CDR). Methods: All subjects were between age 39 to 83+ (n = 94). CDR and MMSE were administered to all participants. CSF was collected in the early afternoon by lumbar puncture. Results: Serum and CSF levels of α-klotho are positively correlated and both predict scores on the MMSE and CDR, regardless of sex or apoE4 status. Conclusion: Our results demonstrate that α-klotho may be an important biomarker of cognitive health and neurodegeneration, and that relatively non-invasive sampling of α-klotho from serum is likely highly reflective of CSF levels.

Insulin Resistance in Peripheral Tissues and the Brain: A Tale of Two Sites

Abstract: The concept of insulin resistance has been around since a few decades after the discovery of insulin itself. To allude to the classic Charles Dicken’s novel published 62 years before the discovery of insulin, in some ways, this is the best of times, as the concept of insulin resistance has expanded to include the brain, with the realization that insulin has a life beyond the regulation of glucose. In other ways, it is the worst of times as insulin resistance is implicated in devastating diseases, including diabetes mellitus, obesity, and Alzheimer’s disease (AD) that affect the brain. Peripheral insulin resistance affects nearly a quarter of the United States population in adults over age 20. More recently, it has been implicated in AD, with the degree of brain insulin resistance correlating with cognitive decline. This has led to the investigation of brain or central nervous system (CNS) insulin resistance and the question of the relation between CNS and peripheral insulin resistance. While both may involve dysregulated insulin signaling, the two conditions are not identical and not always interlinked. In this review, we compare and contrast the similarities and differences between peripheral and CNS insulin resistance. We also discuss how an apolipoprotein involved in insulin signaling and related to AD, apolipoprotein E (apoE), has distinct pools in the periphery and CNS and can indirectly affect each system. As these systems are both separated but also linked via the blood–brain barrier (BBB), we discuss the role of the BBB in mediating some of the connections between insulin resistance in the brain and in the peripheral tissues.

Fecal Implants From AppNL–G–F and AppNL–G–F/E4 Donor Mice Sufficient to Induce Behavioral Phenotypes in Germ-Free Mice

Abstract: The gut microbiome and the gut brain axis are potential determinants of Alzheimer’s disease (AD) etiology or severity and gut microbiota might coordinate with the gut-brain axis to regulate behavioral phenotypes in AD mouse models. Using 6-month-old human amyloid precursor protein (hAPP) knock-in (KI) mice, which contain the Swedish and Iberian mutations [APP NL-F (AppNL–F)] or the Arctic mutation as third mutation [APP NL-G-F (AppNL–G–F)], behavioral and cognitive performance is associated with the gut microbiome and APP genotype modulates this association. In this study, we determined the feasibility of behavioral testing of mice in a biosafety cabinet and whether stool from 6-month-old AppNL–G–F mice or AppNL–G–F crossed with human apoE4 targeted replacement mice is sufficient to induce behavioral phenotypes in 4-5 month-old germ-free C57BL/6J mice 4 weeks following inoculation. We also compared the behavioral phenotypes of the recipient mice with that of the donor mice. Finally, we assessed cortical Aβ levels and analyzed the gut microbiome in the recipient mice. These results show that it is feasible to behaviorally test germ-free mice inside a biosafety cabinet. However, the host genotype was critical in modulating the pattern of induced behavioral phenotypes as compared to those seen in the genotype- and sex-match donor mice. Male mice that received stool from AppNL–G–F and AppNL–G–F/E4 donor genotypes tended to have lower body weight as compared to wild type, an effect not observed among donor mice. Additionally, AppNL–G–F/E4 recipient males, but not females, showed impaired object recognition. Insoluble Aβ40 levels were detected in AppNL–G–F and AppNL–G–F/E4 recipient mice. Recipients of AppNL–G–F, but not AppNL–G–F/E4, donor mice carried cortical insoluble Aβ40 levels that positively correlated with activity levels on the first and second day of open field testing. For recipient mice, the interaction between donor genotype and several behavioral scores predicted gut microbiome alpha-diversity. Similarly, two behavioral performance scores predicted microbiome composition in recipient mice, but this association was dependent on the donor genotype. These data suggest that genotypes of the donor and recipient might need to be considered for developing novel therapeutic strategies targeting the gut microbiome in AD and other neurodegenerative disorders.

A Review of Oxylipins in Alzheimer’s Disease and Related Dementias (ADRD): Potential Therapeutic Targets for the Modulation of Vascular Tone and Inflammation

Abstract: There is now a convincing body of evidence from observational studies that the majority of modifiable Alzheimer’s disease and related dementia (ADRD) risk factors are vascular in nature. In addition, the co-existence of cerebrovascular disease with AD is more common than AD alone, and conditions resulting in brain ischemia likely promote detrimental effects of AD pathology. Oxylipins are a class of bioactive lipid mediators derived from the oxidation of long-chain polyunsaturated fatty acids (PUFAs) which act as modulators of both vascular tone and inflammation. In vascular cognitive impairment (VCI), there is emerging evidence that oxylipins may have both protective and detrimental effects on brain structure, cognitive performance, and disease progression. In this review, we focus on oxylipin relationships with vascular and inflammatory risk factors in human studies and animal models pertinent to ADRD. In addition, we discuss future research directions with the potential to impact the trajectory of ADRD risk and disease progression.

Apolipoprotein E Isoform-specific changes related to stress and trauma exposure

Abstract: Post-Traumatic Stress Disorder (PTSD) is a highly prevalent mental health disorder. Due to the high level of variability in susceptibility and severity, PTSD therapies are still insufficient. In addition to environmental exposures, genetic risks play a prominent role and one such factor is apolipoprotein E. The protein (apoE) is functionally involved in cholesterol transport and metabolism and exists as 3 major isoforms in humans: E2, E3, and E4. To model the role of apolipoprotein E isoform in stress-related changes in behavior and cognition, female and male mice (3-5 months of age) expressing E2, E3, or E4 were used. Mice were either placed into control groups or exposed to chronic variable stress (CVS), which has been shown to induce PTSD-like behavioral and neuroendocrine changes. E2 mice showed a unique response to CVS compared to E3 and E4 mice that included impaired spatial learning and memory, increased adrenal gland weight, and no increase in glucocorticoid receptor protein levels (normalized to apoE levels). In addition, the cholesterol metabolite 7-ketocholesterol was elevated in the cortex after CVS in E3 and E4, but not E2 female mice. E2 confers unique changes in behavioral, cognitive, and biomarker profiles after stress exposure and identify 7-ketocholesterol as a possible novel biomarker of the traumatic stress response. We further explored the relationship between E2 and PTSD in an understudied population by genotyping 102 patients of Cambodian and Vietnamese ethnicity. E2 carriers demonstrated a higher odds ratio of having a PTSD diagnosis compared to E3/E3 carriers, supporting that the E2 genotype is associated with PTSD diagnosis after trauma exposure in this population.

The Human Affectome

Abstract: We present here a unifying framework for affective phenomena: the Human Affectome. By synthesizing a large body of literature, we have converged on definitions that disambiguate the commonly used terms—affect, feeling, emotion, and mood. Based on this definitional foundation, and under the premise that affective states reflect allostatic concerns, we take a goal-directed, enactive perspective. The human affectome is comprised of allostatic features (valence, motivation, and arousal) and allostatic concerns, which differ in the amount of action required to alleviate allostatic load. Allostatic concerns often fall into three ranges: physiological (the most immediate), operational (intermediate to distal), and global. Global concerns involve summations of overall trajectory, general wellbeing, and self-identity. Within this organizational scheme, the human affectome allows vastly different scientific interests to reside within the same theoretical framework and relate to each other. We hope this framework serves as a common focal point for affective research.

GPR39 Deficiency Impairs Memory and Alters Oxylipins and Inflammatory Cytokines Without Affecting Cerebral Blood Flow in a High-Fat Diet Mouse Model of Cognitive Impairment

Abstract: Vascular cognitive impairment (VCI) is the second most common cause of dementia. There is no treatment for VCI, in part due to a lack of understanding of the underlying mechanisms. The G-protein coupled receptor 39 (GPR39) is regulated by arachidonic acid (AA)-derived oxylipins that have been implicated in VCI. Furthermore, GPR39 is increased in microglia of post mortem human brains with VCI. Carriers of homozygous GPR39 SNPs have a higher burden of white matter hyperintensity, an MRI marker of VCI. We tested the hypothesis that GPR39 plays a protective role against high-fat diet (HFD)-induced cognitive impairment, in part mediated via oxylipins actions on cerebral blood flow (CBF) and neuroinflammation. Homozygous (KO) and heterozygous (Het) GPR39 knockout mice and wild-type (WT) littermates with and without HFD for 8 months were tested for cognitive performance using the novel object recognition (NOR) and the Morris water maze (MWM) tests, followed by CBF measurements using MRI. Brain tissue and plasma oxylipins were quantified with high-performance liquid chromatography coupled to mass spectrometry. Cytokines and chemokines were measured using a multiplex assay. KO mice, regardless of diet, swam further away from platform location in the MWM compared to WT and Het mice. In the NOR test, there were no effects of genotype or diet. Brain and plasma AA-derived oxylipins formed by 11- and 15-lipoxygenase (LOX), cyclooxygenase (COX) and non-enzymatically were increased by HFD and GPR39 deletion. Interleukin-10 (IL-10) was lower in KO mice on HFD than standard diet (STD), whereas IL-4, interferon γ-induced protein-10 (IP-10) and monocyte chemotactic protein-3 (MCP-3) were altered by diet in both WT and KO, but were not affected by genotype. Resting CBF was reduced in WT and KO mice on HFD, with no change in vasoreactivity. The deletion of GPR39 did not change CBF compared to WT mice on either STD or HFD. We conclude that GPR39 plays a role in spatial memory retention and protects against HFD-induced cognitive impairment in part by modulating inflammation and AA-derived oxylipins. The results indicate that GPR39 and oxylipin pathways play a role and may serve as therapeutic targets in VCI.

Age-dependent cognitive impairment, hydrocephalus and leukocyte infiltration in transgenic mice with endothelial expression of human EPHX2

Abstract: Soluble epoxide hydrolase (sEH) is upregulated in microvascular endothelium of human brain with vascular cognitive impairment (VCI). Transgenic endothelial expression of human sEH in mice (Tie2hsEH) induces endothelial dysfunction (ED), a pathogenetic mechanism of VCI. We sought to determine if endothelial upregulation of sEH is sufficient to cause cognitive impairment, and if cognitive impairment due to chronic hypoperfusion induced by unilateral common carotid artery occlusion (CCAO) is exacerbated in Tie2hsEH mice. Behavioral performance was assessed by the open field, rotarod, novel object, Morris water maze and fear conditioning tests. Cerebral blood flow and brain morphology were evaluated by MRI, and inflammatory changes investigated using immunohistochemistry and flow cytometry. We demonstrate that transgenic endothelial expression of sEH is sufficient to induce cognitive impairment, associated with leukocyte infiltration, brain atrophy and accelerated, age-dependent ventriculomegaly, identifying ED and sEH upregulation as potential underlying mechanisms and therapeutic targets for VCI.

Common cancer treatments targeting DNA double strand breaks affect long-term memory and relate to immediate early gene expression in a sex-dependent manner

Abstract: DNA double strand breaks (DSBs) have been highly studied in the context of cancers, as DSBs can lead to apoptosis or tumorigenesis. Several pharmaceuticals are widely used to target DSBs during cancer therapy. Amifostine (WR-2721) and etoposide are two commonly used drugs: amifostine reduces DSBs, whereas etoposide increases DSBs. Recently, a novel role for DSBs in immediate early gene expression, learning, and memory has been suggested. Neither amifostine nor etoposide have been assessed for their effects on learning and memory without confounding factors. Moreover, sex-dependent effects of these drugs have not been reported. We administered amifostine or etoposide to 3–4-month-old male and female C57Bl/6J mice before or after training in fear conditioning and assessed learning, memory, and immediate early genes. We observed sex-dependent baseline and drug-induced differences, with females expressing higher cFos and FosB levels than males. These were affected by both amifostine and etoposide. Post-training injections of amifostine affected long-term contextual fear memory; etoposide affected contextual and cued fear memory. These data support the hypothesis that DSBs contribute to learning and memory, and that these could play a part in cognitive side effects during common treatment regimens. The sex-dependent effects also highlight an important factor when considering treatment plans.

Apolipoprotein E Isoform-Dependent Effects on Human Amyloid Precursor Protein/Aβ-Induced Behavioral Alterations and Cognitive Impairments and Insoluble Cortical Aβ42 Levels

Abstract: Mice expressing human amyloid precursor protein (APP) containing the dominant Swedish and Iberian mutations (AppNL–F) or also Arctic mutation (AppNL–G–F) show neuropathology and hippocampus-dependent cognitive impairments pertinent to Alzheimer’s disease (AD) in mouse models at 18 and 6 months of age, respectively. Apolipoprotein E, involved in cholesterol metabolism, plays an important role in maintaining the brain. There are three human apolipoprotein E isoforms: E2, E3, and E4. Compared to E3, E4 increases while E2 protects against AD risk. At 6 months of age, prior to the onset of plaque pathology, E3, but not E4, protected against hAPP/Aβ-induced impairments in spatial memory retention in the Morris water maze. However, these earlier studies were limited as hapoE was not expressed outside the brain and E3 or E4 was not expressed under control of an apoE promotor, E2 was often not included, hAPP was transgenically overexpressed and both mouse and hAPP were present. Therefore, to determine whether apoE has isoform-dependent effects on hAPP/Aβ-induced behavioral alterations and cognitive impairments in adult female and male mice at 6 and 18 months of age, we crossed AppNL–G–F and AppNL–F mice with E2, E3, and E4 mice. To distinguish whether genotype differences seen at either time point were due to main effects of hAPP, hapoE, or hAPP × hapoE genetic interactions, we also behavioral and cognitively tested E2, E3, and E4 female and male mice at 6 and 18 months of age. We also compared behavioral and cognitive performance of 18-month-old AppNL–G–F and AppNL–F female and male mice on a murine apoE background along with that of age—and sex-matched C57BL/6J wild-type mice. For many behavioral measures at both time points there were APP × APOE interactions, supporting that apoE has isoform-dependent effects on hAPP/Aβ-induced behavioral and cognitive performance. NL-G-F/E3, but not NL-G-F/E2, mice had lower cortical insoluble Aβ42 levels than NL-G-F/E4 mice. NL-F/E3 and NL-F/E2 mice had lower cortical insoluble Aβ42 levels than NL-F/E4 mice. These results demonstrate that there are apoE isoform-dependent effects on hAPP/Aβ-induced behavioral alterations and cognitive impairments and cortical insoluble Aβ42 levels in mouse models containing only human APP and apoE.

Behavioral Phenotypes of Foxg1 Heterozygous Mice

Abstract: FOXG1 syndrome (FS, aka a congenital variant of Rett syndrome) is a recently defined rare and devastating neurodevelopmental disorder characterized by various symptoms, including severe intellectual disability, autistic features, involuntary, and continuous jerky movements, feeding problems, sleep disturbances, seizures, irritability, and excessive crying. FS results from mutations in a single allele of the FOXG1 gene, leading to impaired FOXG1 function. Therefore, in establishing mouse models for FS, it is important to test if heterozygous (HET) mutation in the Foxg1 gene, mimicking genotypes of the human FS individuals, also manifests phenotypes similar to their symptoms. We analyzed HET mice with a null mutation allele in a single copy of Foxg1, and found that they show various phenotypes resembling the symptoms of the human FS individuals. These include increased anxiety in the open field as well as impairment in object recognition, motor coordination, and fear learning and contextual and cued fear memory. Our results suggest that Foxg1 HET mice recapitulate at least some symptoms of the human FS individuals.

ApoE isoform-dependent effects of xanthohumol on high fat diet-induced cognitive impairments and hippocampal metabolic pathways

Abstract: Consumption of a high fat diet (HFD) is linked to metabolic syndrome and cognitive impairments. This is exacerbated in age-related cognitive decline (ACD) and in individuals with a genetic risk for Alzheimer’s disease (AD). Apolipoprotein E (apoE) is involved in cholesterol metabolism. In humans, there are three major isoforms, E2, E3, and E4. Compared to E3, E4 increases ACD and AD risk and vulnerability to the deleterious cognitive effects of a HFD. The plant compound Xanthohumol (XN) had beneficial effects on cognition and metabolism in C57BL/6J wild-type (WT) male mice put on a HFD at 9 weeks of age for 13 weeks. As the effects of XN in the context of a HFD in older WT, E3, and E4 female and male mice are not known, in the current study male and female WT, E3, and E4 mice were fed a HFD alone or a HFD containing 0.07% XN for 10 or 19 weeks, starting at 6 months of age, prior to the beginning of behavioral and cognitive testing. XN showed sex- and ApoE isoform-dependent effects on cognitive performance. XN-treated E4 and WT, but not E3, mice had higher glucose transporter protein levels in the hippocampus and cortex than HFD-treated mice. E3 and E4 mice had higher glucose transporter protein levels in the hippocampus and lower glucose transporter protein levels in the cortex than WT mice. In the standard experiment, regardless of XN treatment, E4 mice had nearly double as high ceramide and sphingomyelin levels than E3 mice and male mice had higher level of glycosylated ceramide than female mice. When the differential effects of HFD in E3 and E4 males were assessed, the arginine and proline metabolism pathway was affected. In the extended exposure experiment, in E3 males XN treatment affected the arginine and proline metabolism and the glycine, serine, and threonine metabolism. Myristic acid levels were decreased in XN-treated E3 males but not E3 females. These data support the therapeutic potential for XN to ameliorate HFD-induced cognitive impairments and highlight the importance of considering sex and ApoE isoform in determining who might most benefit from this dietary supplement.

Association of fall rate and functional status by APOE genotype in cancer survivors after exercise intervention.

Abstract: PURPOSE/OBJECTIVES Cancer treatment survivors often report impaired functioning and increased falls. Not all survivors experience the same symptom burden, suggesting individual susceptibilities. APOE genotype is a potential genetic risk factor for cancer treatment related side effects. Lifestyle factors such as physical activity can mitigate the effect of APOE genotype on measures of clinical interest in individuals without a history of cancer. We tested the hypothesis that APOE genotype influences cancer treatment related side effects and symptoms as well as response to exercise intervention. MATERIALS AND METHODS Data from a subsample of a study of fall prevention exercise in post-treatment female cancer survivors aged 50-75 years old (https://clinicaltrials.gov NCT01635413) were used to conduct a secondary data analysis. ApoE genotype was determined by serum sampling. Physical functioning, frequency of falls, and symptom burden were assessed using survey instruments. RESULTS Data from 126 female cancer survivors a median of 49 months out from cancer diagnosis were analyzed. ApoE4 carriers trended toward a higher fall rate at baseline (p = 0.059), but after exercise intervention had a fall rate lower than E4 non-carriers both immediately after structured intervention (p = 0.013) and after 6 months of follow up (p = 0.002). E2 carriers did not show improved measures of depressive symptoms and self-report disability after exercise intervention. E3 homozygotes showed increased self report physical activity after the 6 month exercise intervention, but E4 and E2 carriers did not. CONCLUSIONS APOE genotype may modulate cancer treatment related side effects and symptoms and response to exercise intervention.

Xanthohumol improves cognition in farnesoid X receptor-deficient mice on a high-fat diet

Abstract: ABSTRACT Xanthohumol (XN) improves cognition of wild-type rodents on a high-fat diet (HFD). Bile acids and ceramide levels in the liver and hippocampus might be linked to these effects. XN modulates activity of the nuclear farnesoid X receptor (FXR; also known as NR1H4), the primary receptor for bile acids. To determine the role of FXR in the liver and intestine in mediating the effects of XN on cognitive performance, mice with intestine- and liver-specific FXR ablation (FXRIntestine−/− and FXRLiver−/−, respectively) on an HFD or an HFD containing XN were cognitively tested. XN improved cognitive performance in a genotype- and sex-dependent manner, with improved task learning in females (specifically wild-type), reversal learning in males (specifically wild-type and FXRIntestine−/− mutant) and spatial learning (both sexes). XN increased hippocampal diacylglycerol and sphingomyelin levels in females but decreased them in males. XN increased the ratio of shorter-chain to longer-chain ceramides and hexaceramides. Higher diacylglycerol and lower longer-chain ceramide and hexaceramide levels were linked to improved cognitive performance. Thus, the beneficial sex-dependent cognitive effects of XN are linked to changes in hippocampal diacylglycerol and ceramide levels. This article has an associated First Person interview with the first author of the paper.

Recording large-scale, cellular-resolution neuronal activity from freely-moving mice

Abstract: To date, recording of cellular-resolution activity from awake mice has required either head fixation under a microscope or attaching a miniaturized device to the skull, both of which inevitably affect mouse behavior. We demonstrate a new approach for recording thousands of neurons in freely-moving, non-restricted mice during several behavioral tasks using the calcium integrator CaMPARI and a simple optical setup without any optical device attached to the mouse during testing.

Cognitive effects of Xanthohumol in wild-type and mutant mice lacking FXR in the intestine or liver on a high-fat diet.

Abstract: Xanthohumol (XN) improves cognition of wild-type rodents on a high fat diet. Bile acids and ceramide levels in the liver and hippocampus might be linked to these effects. XN modulates activity of the nuclear farsenoid X receptor (FXR), the primary receptor family for bile acids. To determine the role of FXR in the liver and intestine in mediating the effects of XN on cognitive performance, mice with intestine- and liver-specific FXR-ablation (FXRIntestine-/- and FXRLiver-/-) on a HFD or a HFD containing XN were cognitively tested. XN improved cognitive performance in a genotype- and sex- dependent manner with improved task learning in females (specifically wild-types), in reversal learning in males (specifically wild-type and FXRIntestine-/- mutants), and in spatial learning (both sexes). XN increased hippocampal diacylglycerol and sphingomyelin levels in females but decreased them in males. XN increased the ratio of shorter-chain to longer chain ceramides and hexaceramides. Higher diacylglycerol and lower of longer chain ceramides and hexaceramides levels were linked to improved cognitive performance. Thus, beneficial sex-dependent cognitive effects of XN are linked to changes in hippocampal diacylglycerol and ceramide levels.

Infusion of etoposide in the CA1 disrupts hippocampal immediate early gene expression and hippocampus-dependent learning

Abstract: Abstract Tight regulation of immediate early gene (IEG) expression is important for synaptic plasticity, learning, and memory. Recent work has suggested that DNA double strand breaks (DSBs) may have an adaptive role in post-mitotic cells to induce IEG expression. Physiological activity in cultured neurons as well as behavioral training leads to increased DSBs and subsequent IEG expression. Additionally, infusion of etoposide—a common cancer treatment that induces DSBs—impairs trace fear memory. Here, we assessed the effects of hippocampal infusion of 60 ng of etoposide on IEG expression, learning, and memory in 3–4 month-old C57Bl/6J mice. Etoposide altered expression of the immediate early genes cFos and Arc in the hippocampus and impaired hippocampus-dependent contextual fear memory. These data add to the growing evidence that DSBs play an important role in IEG expression, learning, and memory, opening avenues for developing novel treatment strategies for memory-related disorders.