Ancestral origin of ApoE ε4 Alzheimer disease risk in Puerto Rican and African American populations

The ApoE ε4 allele is the most significant genetic risk factor for late-onset Alzheimer disease. The risk conferred by ε4, however, differs across populations, with populations of African ancestry showing lower ε4 risk compared to those of European or Asian ancestry. The cause of this heterogeneity in risk effect is currently unknown; it may be due to environmental or cultural factors correlated with ancestry, or it may be due to genetic variation local to the ApoE region that differs among populations. Exploring these hypotheses may lead to novel, population-specific therapeutics and risk predictions. To test these hypotheses, we analyzed ApoE genotypes and genome-wide array data in individuals from African American and Puerto Rican populations. A total of 1,766 African American and 220 Puerto Rican individuals with late-onset Alzheimer disease, and 3,730 African American and 169 Puerto Rican cognitively healthy individuals (> 65 years) participated in the study. We first assessed average ancestry across the genome (“global” ancestry) and then tested it for interaction with ApoE genotypes. Next, we assessed the ancestral background of ApoE alleles (“local” ancestry) and tested if ancestry local to ApoE influenced Alzheimer disease risk while controlling for global ancestry. Measures of global ancestry showed no interaction with ApoE risk (Puerto Rican: p-value = 0.49; African American: p-value = 0.65). Conversely, ancestry local to the ApoE region showed an interaction with the ApoE ε4 allele in both populations (Puerto Rican: p-value = 0.019; African American: p-value = 0.005). ApoE ε4 alleles on an African background conferred a lower risk than those with a European ancestral background, regardless of population (Puerto Rican: OR = 1.26 on African background, OR = 4.49 on European; African American: OR = 2.34 on African background, OR = 3.05 on European background). Factors contributing to the lower risk effect in the ApoE gene ε4 allele are likely due to ancestry-specific genetic factors near ApoE rather than non-genetic ethnic, cultural, and environmental factors

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Using the Lens of Local Ancestry to Focus Risk in Alzheimer Disease (5420)

Objective: Our objective is to assess the effect of Southern European (SE) genetic ancestry on APOE gene using Caribbean Hispanic Puerto Rican (CHIPR) population Background: Alzheimer disease (AD) is a progressive neurodegenerative disease and occurs in all ethnic and racial groups. The APOE ɛ4 allele is a major risk factor for AD whose effect shows strong racial/ethnic differences. Among the non-Hispanic White populations APOE shows the strongest effect in North Europeans and has a relatively lower effect in SE populations. Hispanic/Latino populations with a large proportion of SE ancestry provides a unique opportunity to assess the role of SE ancestry in AD. Thus, our goal to assess the relevance of the SE genetic ancestry to the differential effect of the APOE using CHIPR population. Design/Methods: APOE and genome-wide genotyping were performed in 412 CHPR (231 cases, 181 controls). Local ancestry was calculated using SHAPEIT and RFMix. Global ancestry was assessed using GENESIS. Association between affection status and APOE genotype was analyzed using logistic regression models by adjusting for age, gender, and population substructure. Results: The admixture analysis showed that the origin of European ancestry in CHIPR is from SE. The distribution of the parental ancestries local to the APOE gene was 68% SE, 20% AF, and 12% AI. Logistic regression model showed significant association of the APOE ɛ4 risk allele with AD (CHIPR: OR = 1.9 CI:1.3–2.8, p-value = 4.4e-4). Conclusions: Our results showed that the effect of the ɛ4 risk allele in CHIPR with the dominantly (~67%) SE ancestral background is less than it was observed in overall NHW population and close to APOE effect observed in the population from the Iberian Peninsula. Our data support the findings that suggests an interaction between the genetic risk allele ɛ4 and ancestral backgrounds located around the genomic region of APOE gene. Disclosure: Dr. Rajabli has nothing to disclose. Dr. Feliciano-Astacio has nothing to disclose. Dr. Celis has nothing to disclose. Dr. Vance has received royalty, license fees, or contractual rights payments from Athena Diagnostics. Dr. Beecham has nothing to disclose. Dr. Pericak-Vance has nothing to disclose

Novel Variants in LRRK2 and GBA Identified in Latino Parkinson Disease Cohort Enriched for Caribbean Origin

Background: The Latino population is greatly understudied in biomedical research, including genetics. Very little information is available on presence of known variants originally identified in non-Hispanic white patients or novel variants in the Latino population. The Latino population is admixed, with contributions of European, African, and Amerindian ancestries. Therefore, the ancestry surrounding a gene (local ancestry, LA) can be any of the three contributing ancestries and thus can determine the presence or risk effect of variants detected. Methods: We sequenced the major exons and exons of reported Latino-specific variants in GBA and LRRK2 and performed genome-wide genotyping for LA assessments in 79 Latino Parkinson disease (PD) patients, of which ~80% identified as Caribbean Latino. Results: We observed five carriers of LRRK2 p.G2019S, one GBA p.T408M, and three GBA p.N409S on European as well as three GBA p.L13R on African LA backgrounds. Previous Latino variant GBA p.K237E was not observed in this dataset. A novel highly conserved and predicted damaging variant LRRK2 p.D734N was identified in two unrelated individuals with African LA. Additionally, we identified rare, functional variants LRRK2 p.P1480L and GBA p.S310G in one individual each heterozygous for European/Amerindian LA. Discussion: Additional functional analysis will be needed to determine the pathogenicity of the novel variants in PD. However, the identification of novel disease variants in the Latino cohort potentially contributing to PD supports to importance of inclusion of Latinos in genetics research to provide insight in PD genetics in Latinos specifically as well as other populations with the same ancestral contributions

Identification of differential regulation of European versus African local ancestry haplotypes surrounding ApoEε4

Background The risk for late‐onset Alzheimer disease (AD) in ApoEε4 carriers differs between ancestral groups. ApoEε4 Non‐Hispanic White (NHW) homozygotes have an odds ratio of 14.9 while the risk is much lower in Africans (AF) (OR 2.2‐5.7). Local ancestry (LA) analyses in ApoEε4 carrier populations have shown the protective effect in Africans relative to NHW is due to factors lying in the LA surrounding ApoEε4. No coding differences between genes in the LA have been observed between AF and NHW ancestries. Thus regulatory differences in LA non‐coding regions are most likely involved in the protective factor(s) lowering the risk for AF carriers of ApoEε4. Enhancers are the most common regulatory element, and thus we sought to identify if any of these variants had functional enhancer effects between the two ancestries. Little functional characterization of genetic regulation in AF ancestries has been investigated. Method We identified 56 significant sequence differences among AF and ApoEε4 haplotypes from the 1000 genomes in a topologically associated area (56kb) surrounding ApoE. None of these differences were identified to be protein coding. We applied Massively Parallel Reporter Assay (MPRA) supplemented with single variant reporter assays using Promega Dual Glo‐Luciferase System in AD relevant cell lines to identify the regulatory potential of these variants and their surrounding regions and to assess the differential effect sizes of the variant alleles on enhancer activity. Result For MPRA and complementary single variants reporter assays, we generated ∼900bp PCR fragments surrounding these variants to ensure full representation of potential regulatory elements. MPRA vector library or single reporter vectors were transfected in three cell lines (SHY‐SY5Y neuronal cells, U‐118 astrocytes and HMC3 microglia). We identified evidence for differential regulation between AF and EU variant haplotypes in intron 5 of PVRL2, TOMM40 intronic regions and a large region located 3’ of APOC1. The latter encompasses a putative enhancer identified through ENCODE analyses in brains with NHW ancestry. Conclusion Our results indicate several areas of differential regulation in this LA region on ApoEε4 haplotypes. Follow‐up of the identified regulatory regions is currently ongoing using publicly available data and in‐house iPSC derived cell lines

African and European local ancestry surrounding Apolipoprotein E has a differential biological effect upon acute amyloid beta exposure in iPSC‐differentiated astrocytes

Background Studies have shown that the lower risk associated with the ε4 allele for African ancestry is associated with the local ancestry (LA) surrounding the ApoE gene. Previous studies have shown differences between ApoE3 and ApoE4 alleles in isogenic induced pluripotent stem cell (iPSC) models when exposed to Aβ. We hypothesized that ApoE4 individuals with African LA would respond differently to Aβ compared to European ApoE3 and European ApoE4 LA lines. However, as we cannot produce isogenic lines to test LA, we used RNA expression changes to Aβ exposure to increase our sensitivity to potential differences. Method We differentiated European LA ε4/ε4 and African LA ε4/ε4 allele astrocytes from iPSC lines. Astrocytes were exposed to exogenous Aβ and RNA was obtained at 0 and 24 hours. We performed bioinformatic analyses with the STAR algorithm and differential expression calculation using linear models implemented in edgeR. Pathway enrichment analysis for Gene Ontology Biological Processes, KEGG and Reactome pathways was performed using Metascape. Result Twenty‐four hours following Aβ exposure, 524 and 671 genes were deferentially expressed from baseline in African and European LA lines respectively. Analysis of the unregulated genes in the two different ancestries revealed markedly different pathways. The unregulated genes in African LA astrocytes were enriched for Ribosome Biogenesis and RNA modification processes while the upregulated genes in the European LA astrocytes were enriched for Cell Cycle and DNA modification processes. In the European LA astrocytes, downregulated genes were enriched for Synaptic Assembly and Kainate Receptor Activity while in the African LA astrocytes downregulated genes enriched for Extracellular Matrix‐related processes. Conclusion Our initial results suggest that the two ancestries respond differently to Aβ exposure. Whether this is due to global or local ancestry differences is unclear. Further studies including astrocytes bearing African LA ε3/ε3 are needed to clarify that question. Both ribosomal dysfunction and astrocyte‐neuronal and astrocyte‐microglia synaptic assembly have been implicated in Aβ clearance and/or AD. A potential link between LA and the regulation of these processes due to Aβ exposure could pave the path to a better understanding of LOAD pathology

Chromatin accessibility differences between African and European Alzheimer Disease brains. (P2-3.002)

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ATAC-seq on iPSC derived astrocytes to assess chromatin accessibility differences between African and European local ancestry

Local ancestry (LA) surrounding the APOE4 allele is associated with an increased risk for Alzheimer Disease (AD) in European (EU) LA compared to African (AF) LA. We recently demonstrated that APOE4 has significantly higher expression in astrocytes in brain from EU compared to AF APOE4 LA carriers, but the specific molecular mechanism leading to this difference is not known. We investigated whether evaluating chromatin accessibility and gene expression profiles of inducible pluripotent stem cell (iPSC) derived astrocytes in the LA region in both AF and EU LA could lead us to identify potential regulatory factors affecting chromatin remodeling and expression of APOE. We assayed for Transposase Accessible Chromatin (ATAC-seq), and RNA-seq in three iPSC derived astrocytes from two AF LA and one EU LA individuals with AD. We processed the ATAC-seq data with the ENCODE ATAC-seq pipeline and called peaks using MACS2. An average of 692 peaks were detected in the LA region with no statistical difference between EU and AF LA. Interestingly, an African APOE4 homozygote LA astrocyte line with high APOE expression had an exclusive ATAC peak at the APOE promoter. Amongst the transcription factors (TFs) suggested to bind this differentially accessible peak in APOE are HNF4A and TEAD4. Both TFs had significantly increased expression in this astrocyte line compared to the other lines. Additionally, differential accessibility in this line include peaks in an intragenic enhancer of PVRL2 and the promoter of CBLC, both shown to be bound by HNF4A and both overexpressed in this cell line and one in the promoter of CYP2S1 with TEAD4 binding, which was also overexpressed. This study is one of the first studies to compare chromatin accessibility in AF and EU ancestries. It also represents initial efforts to investigate potential mechanisms and factors, using iPSC-derived cell lines, that could contribute to the differential expression we have previously reported in APOE4 between AF and EU LA brains. Our data suggest that elevated astrocytic expression of APOE4 is associated with rs