The APOE-R136S mutation protects against APOE4-driven Tau pathology, neurodegeneration and neuroinflammation

Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for late-onset Alzheimer's disease (LOAD), leading to earlier age of clinical onset and exacerbating pathologies. There is a critical need to identify protective targets. Recently, a rare APOE variant, APOE3-R136S (Christchurch), was found to protect against early-onset AD in a PSEN1-E280A carrier. In this study, we sought to determine if the R136S mutation also protects against APOE4-driven effects in LOAD. We generated tauopathy mouse and human iPSC-derived neuron models carrying human APOE4 with the homozygous or heterozygous R136S mutation. We found that the homozygous R136S mutation rescued APOE4-driven Tau pathology, neurodegeneration and neuroinflammation. The heterozygous R136S mutation partially protected against APOE4-driven neurodegeneration and neuroinflammation but not Tau pathology. Single-nucleus RNA sequencing revealed that the APOE4-R136S mutation increased disease-protective and diminished disease-associated cell populations in a gene dose-dependent manner. Thus, the APOE-R136S mutation protects against APOE4-driven AD pathologies, providing a target for therapeutic development against AD.

Quantitative proteomic analysis reveals apoE4-dependent phosphorylation of the actin-regulating protein VASP

Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer's Disease (AD). While neurons generally produce a minority of the apoE in the central nervous system, neuronal expression of apoE increases dramatically in response to stress and is sufficient to drive pathology. Currently, the molecular mechanisms of how apoE4 expression may regulate pathology are not fully understood. Here we expand upon our previous studies measuring the impact of apoE4 on protein abundance to include the analysis of protein phosphorylation and ubiquitylation signaling in isogenic Neuro-2a cells expressing apoE3 or apoE4. ApoE4 expression resulted in a dramatic increase in VASP S235 phosphorylation in a PKA-dependent manner. This phosphorylation disrupted VASP interactions with numerous actin cytoskeletal and microtubular proteins. Reduction of VASP S235 phosphorylation via PKA inhibition resulted in a significant increase in filopodia formation and neurite outgrowth in apoE4-expressing cells, exceeding levels observed in apoE3-expressing cells. Our results highlight the pronounced and diverse impact of apoE4 on multiple modes of protein regulation and identify protein targets to restore apoE4-related cytoskeletal defects.

Apolipoprotein E4 targets mitochondria and the mitochondria-associated membrane complex in neuropathology, including Alzheimer's disease

Apolipoprotein (apo) E4 sets the stage for neuropathology in Alzheimer's disease (AD) by causing mitochondrial dysfunction and altering mitochondria-associated membranes. Contact and apposition of mitochondrial-endoplasmic reticulum membranes are enhanced in brain cells in AD and associated with increases in tethering and spacing proteins that modulate many cellular processes. Contact site protein levels are higher in apoE4 cells. In apoE4 neurons, the NAD⁺/NADH ratio is lowered, reactive oxygen species are increased, and NAD/NADH pathway components and redox proteins are decreased. Oxidative phosphorylation is impaired and reserve ATP generation capacity is lacking. ApoE4 neurons have ∼50% fewer respiratory complex subunits (e.g., ATP synthase) and may increase translocase levels of the outer and inner mitochondrial membranes to facilitate delivery of nucleus-encoded complex subunits. Respiratory complex assembly relies on mitochondrial cristae organizing system subunits that are altered in apoE4 cells, and apoE4 increases mitochondrial proteases that control respiratory subunit composition for complex assembly.

A common transcriptional mechanism involving R-loop and RNA abasic site regulates an enhancer RNA of APOE

RNA is modified by hundreds of chemical reactions and folds into innumerable shapes. However, the regulatory role of RNA sequence and structure and how dysregulation leads to diseases remain largely unknown. Here, we uncovered a mechanism where RNA abasic sites in R-loops regulate transcription by pausing RNA polymerase II. We found an enhancer RNA, AANCR, that regulates the transcription and expression of apolipoprotein E (APOE). In some human cells such as fibroblasts, AANCR is folded into an R-loop and modified by N-glycosidic cleavage; in this form, AANCR is a partially transcribed nonfunctional enhancer and APOE is not expressed. In contrast, in other cell types including hepatocytes and under stress, AANCR does not form a stable R-loop as its sequence is not modified, so it is transcribed into a full-length enhancer that promotes APOE expression. DNA sequence variants in AANCR are associated significantly with APOE expression and Alzheimer's Disease, thus AANCR is a modifier of Alzheimer's Disease. Besides AANCR, thousands of noncoding RNAs are regulated by abasic sites in R-loops. Together our data reveal the essentiality of the folding and modification of RNA in cellular regulation and demonstrate that dysregulation underlies common complex diseases such as Alzheimer's disease.

Neuronal Apolipoprotein E4 Expression Results in Proteome-Wide Alterations and Compromises Bioenergetic Capacity by Disrupting Mitochondrial Function

Apolipoprotein (apo) E4, the major genetic risk factor for Alzheimer's disease (AD), alters mitochondrial function and metabolism early in AD pathogenesis. When injured or stressed, neurons increase apoE synthesis. Because of its structural difference from apoE3, apoE4 undergoes neuron-specific proteolysis, generating fragments that enter the cytosol, interact with mitochondria, and cause neurotoxicity. However, apoE4's effect on mitochondrial respiration and metabolism is not understood in detail. Here we used biochemical assays and proteomic profiling to more completely characterize the effects of apoE4 on mitochondrial function and cellular metabolism in Neuro-2a neuronal cells stably expressing apoE4 or apoE3. Under basal conditions, apoE4 impaired respiration and increased glycolysis, but when challenged or stressed, apoE4-expressing neurons had 50% less reserve capacity to generate ATP to meet energy requirements than apoE3-expressing neurons. ApoE4 expression also decreased the NAD+/NADH ratio and increased the levels of reactive oxygen species and mitochondrial calcium. Global proteomic profiling revealed widespread changes in mitochondrial processes in apoE4 cells, including reduced levels of numerous respiratory complex subunits and major disruptions to all detected subunits in complex V (ATP synthase). Also altered in apoE4 cells were levels of proteins related to mitochondrial endoplasmic reticulum-associated membranes, mitochondrial fusion/fission, mitochondrial protein translocation, proteases, and mitochondrial ribosomal proteins. ApoE4-induced bioenergetic deficits led to extensive metabolic rewiring, but despite numerous cellular adaptations, apoE4-expressing neurons remained vulnerable to metabolic stress. Our results provide insights into potential molecular targets of therapies to correct apoE4-associated mitochondrial dysfunction and altered cellular metabolism.

Apolipoprotein E: from cardiovascular disease to neurodegenerative disorders

Apolipoprotein (apo) E was initially described as a lipid transport protein and major ligand for low density lipoprotein (LDL) receptors with a role in cholesterol metabolism and cardiovascular disease. It has since emerged as a major risk factor (causative gene) for Alzheimer's disease and other neurodegenerative disorders. Detailed understanding of the structural features of the three isoforms (apoE2, apoE3, and apoE4), which differ by only a single amino acid interchange, has elucidated their unique functions. ApoE2 and apoE4 increase the risk for heart disease: apoE2 increases atherogenic lipoprotein levels (it binds poorly to LDL receptors), and apoE4 increases LDL levels (it binds preferentially to triglyceride-rich, very low density lipoproteins, leading to downregulation of LDL receptors). ApoE4 also increases the risk for neurodegenerative diseases, decreases their age of onset, or alters their progression. ApoE4 likely causes neurodegeneration secondary to its abnormal structure, caused by an interaction between its carboxyl- and amino-terminal domains, called domain interaction. When neurons are stressed or injured, they synthesize apoE to redistribute cholesterol for neuronal repair or remodeling. However, because of its altered structure, neuronal apoE4 undergoes neuron-specific proteolysis, generating neurotoxic fragments (12-29 kDa) that escape the secretory pathway and cause mitochondrial dysfunction and cytoskeletal alterations, including tau phosphorylation. ApoE4-associated pathology can be prevented by small-molecule structure correctors that block domain interaction by converting apoE4 to a molecule that resembles apoE3 both structurally and functionally. Structure correctors are a potential therapeutic approach to reduce apoE4 pathology in both cardiovascular and neurological disorders.

Central Nervous System Lipoproteins: ApoE and Regulation of Cholesterol Metabolism

ApoE on high-density lipoproteins is primarily responsible for lipid transport and cholesterol homeostasis in the central nervous system (CNS). Normally produced mostly by astrocytes, apoE is also produced under neuropathologic conditions by neurons. ApoE on high-density lipoproteins is critical in redistributing cholesterol and phospholipids for membrane repair and remodeling. The 3 main structural isoforms differ in their effectiveness. Unlike apoE2 and apoE3, apoE4 has markedly altered CNS metabolism, is associated with Alzheimer disease and other neurodegenerative disorders, and is expressed at lower levels in brain and cerebrospinal fluid. ApoE4-expressing cultured astrocytes and neurons have reduced cholesterol and phospholipid secretion, decreased lipid-binding capacity, and increased intracellular degradation. Two structural features are responsible for apoE4 dysfunction: domain interaction, in which arginine-61 interacts ionically with glutamic acid-255, and a less stable conformation than apoE3 and apoE2. Blocking domain interaction by gene targeting (replacing arginine-61 with threonine) or by small-molecule structure correctors increases CNS apoE4 levels and lipid-binding capacity and decreases intracellular degradation. Small molecules (drugs) that disrupt domain interaction, so-called structure correctors, could prevent the apoE4-associated neuropathology by blocking the formation of neurotoxic fragments. Understanding how to modulate CNS cholesterol transport and metabolism is providing important insights into CNS health and disease.

Apolipoprotein E: structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases

Apolipoprotein (apo) E is a multifunctional protein with central roles in lipid metabolism, neurobiology, and neurodegenerative diseases. It has three major isoforms (apoE2, apoE3, and apoE4) with different effects on lipid and neuronal homeostasis. A major function of apoE is to mediate the binding of lipoproteins or lipid complexes in the plasma or interstitial fluids to specific cell-surface receptors. These receptors internalize apoE-containing lipoprotein particles; thus, apoE participates in the distribution/redistribution of lipids among various tissues and cells of the body. In addition, intracellular apoE may modulate various cellular processes physiologically or pathophysiologically, including cytoskeletal assembly and stability, mitochondrial integrity and function, and dendritic morphology and function. Elucidation of the functional domains within this protein and of the three-dimensional structure of the major isoforms of apoE has contributed significantly to our understanding of its physiological and pathophysiological roles at a molecular level. It is likely that apoE, with its multiple cellular origins and multiple structural and biophysical properties, is involved widely in processes of lipid metabolism and neurobiology, possibly encompassing a variety of disorders of neuronal repair, remodeling, and degeneration by interacting with different factors through various pathways.

Ancient human genomes suggest three ancestral populations for present-day Europeans

We sequenced the genomes of a ~7,000 year old farmer from Germany and eight ~8,000 year old hunter-gatherers from Luxembourg and Sweden. We analyzed these and other ancient genomes^1–4 with 2,345 contemporary humans to show that most present Europeans derive from at least three highly differentiated populations: West European Hunter-Gatherers (WHG), who contributed ancestry to all Europeans but not to Near Easterners; Ancient North Eurasians (ANE) related to Upper Paleolithic Siberians³, who contributed to both Europeans and Near Easterners; and Early European Farmers (EEF), who were mainly of Near Eastern origin but also harbored WHG-related ancestry. We model these populations’ deep relationships and show that EEF had ~44% ancestry from a “Basal Eurasian” population that split prior to the diversification of other non-African lineages.

Advancing Alzheimer's disease diagnosis, treatment, and care: recommendations from the Ware Invitational Summit

To address the pending public health crisis due to Alzheimer's disease (AD) and related neurodegenerative disorders, the Marian S. Ware Alzheimer Program at the University of Pennsylvania held a meeting entitled "State of the Science Conference on the Advancement of Alzheimer's Diagnosis, Treatment and Care," on June 21-22, 2012. The meeting comprised four workgroups focusing on Biomarkers; Clinical Care and Health Services Research; Drug Development; and Health Economics, Policy, and Ethics. The workgroups shared, discussed, and compiled an integrated set of priorities, recommendations, and action plans, which are presented in this article.

Small-molecule structure correctors target abnormal protein structure and function: structure corrector rescue of apolipoprotein E4-associated neuropathology

An attractive strategy to treat proteinopathies (diseases caused by malformed or misfolded proteins) is to restore protein function by inducing proper three-dimensional structure. We hypothesized that this approach would be effective in reversing the detrimental effects of apolipoprotein (apo) E4, the major allele that significantly increases the risk of developing Alzheimer's disease and other neurodegenerative disorders. ApoE4's detrimental effects result from its altered protein conformation ("domain interaction"), making it highly susceptible to proteolytic cleavage and the generation of neurotoxic fragments. Here, we review apoE structure and function and how apoE4 causes neurotoxicity, and describe the identification of potent small-molecule-based "structure correctors" that induce proper apoE4 folding. SAR studies identified a series of small molecules that significantly reduced apoE4's neurotoxic effects in cultured neurons and a series that reduced apoE4 fragment levels in vivo, providing proof-of-concept for our approach. Structure-corrector-based therapies could prove to be highly effective for the treatment of many protein-misfolding diseases.

Turkish population structure and genetic ancestry reveal relatedness among Eurasian populations

Turkey has experienced major population movements. Population structure and genetic relatedness of samples from three regions of Turkey, using over 500,000 SNP genotypes, were compared together with Human Genome Diversity Panel (HGDP) data. To obtain a more representative sampling from Central Asia, Kyrgyz samples (Bishkek, Kyrgyzstan) were genotyped and analysed. Principal component (PC) analysis reveals a significant overlap between Turks and Middle Easterners and a relationship with Europeans and South and Central Asians; however, the Turkish genetic structure is unique. FRAPPE, STRUCTURE, and phylogenetic analyses support the PC analysis depending upon the number of parental ancestry components chosen. For example, supervised STRUCTURE (K=3) illustrates a genetic ancestry for the Turks of 45% Middle Eastern (95% CI, 42-49), 40% European (95% CI, 36-44) and 15% Central Asian (95% CI, 13-16), whereas at K=4 the genetic ancestry of the Turks was 38% European (95% CI, 35-42), 35% Middle Eastern (95% CI, 33-38), 18% South Asian (95% CI, 16-19) and 9% Central Asian (95% CI, 7-11). PC analysis and FRAPPE/STRUCTURE results from three regions in Turkey (Aydin, Istanbul and Kayseri) were superimposed, without clear subpopulation structure, suggesting sample homogeneity. Thus, this study demonstrates admixture of Turkish people reflecting the population migration patterns.

Small molecule structure correctors abolish detrimental effects of apolipoprotein E4 in cultured neurons

Apolipoprotein E4 (apoE4), the major genetic risk factor for late onset Alzheimer disease, assumes a pathological conformation, intramolecular domain interaction. ApoE4 domain interaction mediates the detrimental effects of apoE4, including decreased mitochondrial cytochrome c oxidase subunit 1 levels, reduced mitochondrial motility, and reduced neurite outgrowth in vitro. Mutant apoE4 (apoE4-R61T) lacks domain interaction, behaves like apoE3, and does not cause detrimental effects. To identify small molecules that inhibit domain interaction (i.e. structure correctors) and reverse the apoE4 detrimental effects, we established a high throughput cell-based FRET primary assay that determines apoE4 domain interaction and secondary cell- and function-based assays. Screening a ChemBridge library with the FRET assay identified CB9032258 (a phthalazinone derivative), which inhibits domain interaction in neuronal cells. In secondary functional assays, CB9032258 restored mitochondrial cytochrome c oxidase subunit 1 levels and rescued impairments of mitochondrial motility and neurite outgrowth in apoE4-expressing neuronal cells. These benefits were apoE4-specific and dose-dependent. Modifying CB9032258 yielded well defined structure-activity relationships and more active compounds with enhanced potencies in the FRET assay (IC(50) of 23 and 116 nm, respectively). These compounds efficiently restored functional activities of apoE4-expressing cells in secondary assays. An EPR binding assay showed that the apoE4 structure correction resulted from direct interaction of a phthalazinone. With these data, a six-feature pharmacophore model was constructed for future drug design. Our results serve as a proof of concept that pharmacological intervention with apoE4 structure correctors negates apoE4 detrimental effects in neuronal cells and could be further developed as an Alzheimer disease therapeutic.

Glucuronic acid epimerase is associated with plasma triglyceride and high-density lipoprotein cholesterol levels in Turks

We narrowed chromosome 15q21-23 linkage to plasma high-density lipoprotein cholesterol (HDL-C) levels in Turkish families by fine mapping, then focused on glucuronic acid epimerase (GLCE), a heparan sulfate proteoglycan (HSPG) biosynthesis enzyme. HSPGs participate in lipid metabolism along with apolipoprotein (apo) E. Of 31 SNPs in the GLCE locus, nine analyzed by haplotype were associated with HDL-C and triglyceride levels (permuted p = 0.006 and 0.013, respectively) in families. Of five tagging GLCE SNPs in two cohorts of unrelated subjects, three (rs16952868, rs11631403, and rs3865014) were associated with triglyceride and HDL-C levels in males (nonpermuted p < 0.05). The association was stronger in APOE 2/3 subjects (apoE2 has reduced binding to HSPGs) and reached multiple-testing significance (p < 0.05) in both males and females (n= 2612). Similar results were obtained in the second cohort (n= 1164). Interestingly, at the GLCE locus, bounded by recombination hotspots, Turks had a minor allele frequency of SNPs resembling Chinese more than European ancestry; adjoining regions resembled the European pattern. Studies of glce(+/-) apoe(-/-) mice fed a chow or high-fat diet supported a role for GLCE in lipid metabolism. Thus, SNPs in GLCE are associated with triglyceride and HDL-C levels in Turks, and mouse studies support a role for glce in lipid metabolism.

Structure-dependent impairment of intracellular apolipoprotein E4 trafficking and its detrimental effects are rescued by small-molecule structure correctors

Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer disease (AD) and likely contributes to neuropathology through various pathways. Here we report that the intracellular trafficking of apoE4 is impaired in Neuro-2a cells and primary neurons, as shown by measuring fluorescence recovery after photobleaching. In Neuro-2a cells, more apoE4 than apoE3 molecules remained immobilized in the endoplasmic reticulum (ER) and the Golgi apparatus, and the lateral motility of apoE4 was significantly lower in the Golgi apparatus (but not in the ER) than that of apoE3. Likewise, the immobile fraction was larger, and the lateral motility was lower for apoE4 than apoE3 in mouse primary hippocampal neurons. ApoE4 with the R61T mutation, which abolishes apoE4 domain interaction, was less immobilized, and its lateral motility was comparable with that of apoE3. The trafficking impairment of apoE4 was also rescued by disrupting domain interaction with the small-molecule structure correctors GIND25 and PH002. PH002 also rescued apoE4-induced impairments of neurite outgrowth in Neuro-2a cells and dendritic spine development in primary neurons. ApoE4 did not affect trafficking of amyloid precursor protein, another AD-related protein, through the secretory pathway. Thus, domain interaction renders more newly synthesized apoE4 molecules immobile and slows their trafficking along the secretory pathway. Correcting the pathological structure of apoE4 by disrupting domain interaction is a potential therapeutic approach to treat or prevent AD related to apoE4.

Apolipoprotein E4 domain interaction mediates detrimental effects on mitochondria and is a potential therapeutic target for Alzheimer disease

Apolipoprotein (apo) E4 is the major genetic risk factor for late-onset Alzheimer disease (AD). ApoE4 assumes a pathological conformation through an intramolecular interaction mediated by Arg-61 in the amino-terminal domain and Glu-255 in the carboxyl-terminal domain, referred to as apoE4 domain interaction. Because AD is associated with mitochondrial dysfunction, we examined the effect of apoE4 domain interaction on mitochondrial respiratory function. Steady-state amounts of mitochondrial respiratory complexes were examined in neurons cultured from brain cortices of neuron-specific enolase promoter-driven apoE3 (NSE-apoE3) or apoE4 (NSE-apoE4) transgenic mice. All subunits of mitochondrial respiratory complexes assessed were significantly lower in NSE-apoE4 neurons compared with NSE-apoE3 neurons. However, no significant differences in levels of mitochondrial complexes were detected between astrocytes expressing different apoE isoforms driven by the glial fibrillary acidic protein promoter, leading to our conclusion that the effect of apoE4 is neuron specific. In neuroblastoma Neuro-2A (N2A) cells, apoE4 expression reduced the levels of mitochondrial respiratory complexes I, IV, and V. Complex IV enzymatic activity was also decreased, lowering mitochondrial respiratory capacity. Mutant apoE4 (apoE4-Thr-61) lacking domain interaction did not induce mitochondrial dysfunction in N2A cells, indicating that the effect is specific to apoE4-expressing cells and dependent on domain interaction. Consistent with this finding, treatment of apoE4-expressing N2A cells with a small molecule that disrupts apoE4 domain interaction restored mitochondrial respiratory complex IV levels. These results suggest that pharmacological intervention with small molecules that disrupt apoE4 domain interaction is a potential therapeutic approach for apoE4-carrying AD subjects.

Genetic variants influencing circulating lipid levels and risk of coronary artery disease

OBJECTIVE

Genetic studies might provide new insights into the biological mechanisms underlying lipid metabolism and risk of CAD. We therefore conducted a genome-wide association study to identify novel genetic determinants of low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides.

METHODS AND RESULTS

We combined genome-wide association data from 8 studies, comprising up to 17 723 participants with information on circulating lipid concentrations. We did independent replication studies in up to 37 774 participants from 8 populations and also in a population of Indian Asian descent. We also assessed the association between single-nucleotide polymorphisms (SNPs) at lipid loci and risk of CAD in up to 9 633 cases and 38 684 controls. We identified 4 novel genetic loci that showed reproducible associations with lipids (probability values, 1.6×10(-8) to 3.1×10(-10)). These include a potentially functional SNP in the SLC39A8 gene for HDL-C, an SNP near the MYLIP/GMPR and PPP1R3B genes for LDL-C, and at the AFF1 gene for triglycerides. SNPs showing strong statistical association with 1 or more lipid traits at the CELSR2, APOB, APOE-C1-C4-C2 cluster, LPL, ZNF259-APOA5-A4-C3-A1 cluster and TRIB1 loci were also associated with CAD risk (probability values, 1.1×10(-3) to 1.2×10(-9)).

CONCLUSIONS

We have identified 4 novel loci associated with circulating lipids. We also show that in addition to those that are largely associated with LDL-C, genetic loci mainly associated with circulating triglycerides and HDL-C are also associated with risk of CAD. These findings potentially provide new insights into the biological mechanisms underlying lipid metabolism and CAD risk.

GABAergic interneuron dysfunction impairs hippocampal neurogenesis in adult apolipoprotein E4 knockin mice

Apolipoprotein (apo) E, a polymorphic protein with three isoforms (apoE2, apoE3, and apoE4), is essential for lipid homeostasis. Carriers of apoE4 are at higher risk for developing Alzheimer's disease. We have investigated adult neurogenesis in mice with knockout (KO) for apoE or with knockin (KI) alleles for human apoE3 or apoE4, and we report that neurogenesis is reduced in both apoE-KO and apoE4-KI mice. In apoE-KO mice, increased BMP signaling promoted glial differentiation at the expense of neurogenesis. In contrast, in apoE4-KI mice, presynaptic GABAergic input-mediated maturation of newborn neurons was diminished. Tau phosphorylation, an Alzheimer's disease characteristic, and levels of neurotoxic apoE fragments were both elevated in apoE4-KI hippocampal neurons concomitant with decreased GABAergic interneuron survival. Potentiating GABAergic signaling restored neuronal maturation and neurogenesis in apoE4-KI mice to normal levels. These findings suggest that GABAergic signaling can be targeted to mitigate the deleterious effects of apoE4 on neurogenesis.

Polymorphisms in the hepatic lipase gene affect plasma HDL-cholesterol levels in a Turkish population

We investigated the effects of single nucleotide polymorphisms (SNPs) of the hepatic lipase gene (LIPC) on plasma HDL-cholesterol (HDL-C) levels in Turks, a population with low levels of HDL-C. All exons and six evolutionarily conserved regions from 28 Turkish subjects were sequenced. We found 51 SNPs, nine of which were novel. Those 51 SNPs and SNPs from the National Center for Biotechnology Information dbSNP were evaluated by bioinformatics approaches. The population frequencies and linkage disequilibrium among SNPs from HapMap were combined with results from transcriptional factor prediction tools and the literature to select SNPs for genotyping. We found that five tagging LIPC SNPs, two reported here for the first time, were significantly associated with plasma HDL-C levels in both men and women (n = 2,612). These results were replicated in a separate Turkish cohort (n = 1,164). Plasma HDL-C levels were higher in subjects homozygous for the minor alleles of rs4775041, rs1800588 (-514C>T), and rs11858164 and lower in subjects homozygous for the minor alleles of rs11856322 and rs2242061. These SNPs seemed to have independent and additive effects on plasma HDL-C levels (1.5-5.2 mg/dl). Hepatic lipase activity in a subset (n = 260) of the main cohort was also significantly associated with all five SNPs. Thus, five LIPC SNPs, two novel, are associated with plasma HDL-C levels and hepatic lipase activity in two cohorts of Turkish subjects.

Genome-wide linkage and association analyses to identify genes influencing adiponectin levels: the GEMS Study

Adiponectin has a variety of metabolic effects on obesity, insulin sensitivity, and atherosclerosis. To identify genes influencing variation in plasma adiponectin levels, we performed genome-wide linkage and association scans of adiponectin in two cohorts of subjects recruited in the Genetic Epidemiology of Metabolic Syndrome Study. The genome-wide linkage scan was conducted in families of Turkish and southern European (TSE, n = 789) and Northern and Western European (NWE, N = 2,280) origin. A whole genome association (WGA) analysis (500K Affymetrix platform) was carried out in a set of unrelated NWE subjects consisting of approximately 1,000 subjects with dyslipidemia and 1,000 overweight subjects with normal lipids. Peak evidence for linkage occurred at chromosome 8p23 in NWE subjects (lod = 3.10) and at chromosome 3q28 near ADIPOQ, the adiponectin structural gene, in TSE subjects (lod = 1.70). In the WGA analysis, the single-nucleotide polymorphisms (SNPs) most strongly associated with adiponectin were rs3774261 and rs6773957 (P < 10(-7)). These two SNPs were in high linkage disequilibrium (r(2) = 0.98) and located within ADIPOQ. Interestingly, our fourth strongest region of association (P < 2 x 10(-5)) was to an SNP within CDH13, whose protein product is a newly identified receptor for high-molecular-weight species of adiponectin. Through WGA analysis, we confirmed previous studies showing SNPs within ADIPOQ to be strongly associated with variation in adiponectin levels and further observed these to have the strongest effects on adiponectin levels throughout the genome. We additionally identified a second gene (CDH13) possibly influencing variation in adiponectin levels. The impact of these SNPs on health and disease has yet to be determined.

Apolipoprotein E: structure determines function, from atherosclerosis to Alzheimer's disease to AIDS

Apolipoprotein (apo) E has roles beyond lipoprotein metabolism. The detrimental effects of apoE4 in cardiovascular, neurological, and infectious diseases correlate with its structural features (e.g., domain interaction) that distinguish it from apoE3 and apoE2. Structure/function studies revealed that apoE2 is severely defective in LDL receptor binding because of a structural difference that alters the receptor binding region and helped unravel the mechanism of type III hyperlipoproteinemia. ApoE4 is the major genetic risk factor for Alzheimer's disease and sets the stage for neuropathological disorders precipitated by genetic, metabolic, and environmental stressors. ApoE also influences susceptibility to parasitic, bacterial, and viral infections. In HIV-positive patients, apoE4 homozygosity hastens progression to AIDS and death and increases susceptibility to opportunistic infections. The next phase in our understanding of apoE will be characterized by clinical intervention to prevent or reverse the detrimental effects of apoE4 by modulating its structure or blocking the pathological processes it mediates.

Gender differences in the relationship of ENPP1/PC-1 variants to obesity in a Turkish population

The ectoenzyme ENPP1 (also termed membrane glycoprotein PC-1 or ENPP1/PC-1) is an inhibitor of insulin-induced activation of the insulin receptor. There is evidence from previous studies that coding variants of ENPP1/PC-1 (K121Q) are associated with type 2 diabetes (T2D) and obesity. Studies in the general Turkish population have demonstrated: unique plasma lipid characteristics, a high prevalence of cardiovascular risk factors, and an increased prevalence of obesity and T2D. We investigated, therefore, the association of ENPP1/PC-1 variants with obesity and T2D in Turkish individuals. The TaqMan allelic discrimination assay was used for genotyping the relationship of ENPP1/PC-1 variants to obesity and T2D in a genetic association study of 1,553 genotyped, randomly selected subjects from the Turkish Heart Study. The K121Q (rs1044498) variant and other previously reported variants (rs997509, rs1799774, rs1044548, rs11964389, rs7754561) were analyzed. In this cohort, the minor allele frequency (MAF) of the K121Q variant was associated with obesity in male, but not in female subjects (male, odds ratio 1.64, 95% confidence interval 1.004-2.698, P = 0.048; female, odds ratio 1.003, 95% confidence interval 0.684-1.471, P = ns). In addition, the previously reported ENPP1/PC-1 "risk haplotype" (Q (rs1044498), delT (rs1799774), and G (rs7754561) alleles) was found to be associated with obesity in male, but not in female, subjects (P = 0.035). In contrast, there was no association of either the K121Q variant or the ENPP1/PC-1 haplotype with T2D. We find evidence that variants of ENPP1/PC-1 are associated with obesity in the male Turkish population; thus, these variants may contribute to the development of the obesity in these individuals.

Genes contributing to prion pathogenesis

Prion diseases are caused by conversion of a normally folded, non-pathogenic isoform of the prion protein (PrP(C)) to a misfolded, pathogenic isoform (PrP(Sc)). Prion inoculation experiments in mice expressing homologous PrP(C) molecules on different genetic backgrounds displayed different incubation times, indicating that the conversion reaction may be influenced by other gene products. To identify genes that contribute to prion pathogenesis, we analysed incubation times of prions in mice in which the gene product was inactivated, knocked out or overexpressed. We tested 20 candidate genes, because their products either colocalize with PrP, are associated with Alzheimer's disease, are elevated during prion disease, or function in PrP-mediated signalling, PrP glycosylation, or protein maintenance. Whereas some of the candidates tested may have a role in the normal function of PrP(C), our data show that many genes previously implicated in prion replication have no discernible effect on the pathogenesis of prion disease. While most genes tested did not significantly affect survival times, ablation of the amyloid beta (A4) precursor protein (App) or interleukin-1 receptor, type I (Il1r1), and transgenic overexpression of human superoxide dismutase 1 (SOD1) prolonged incubation times by 13, 16 and 19 %, respectively.

LDL-cholesterol concentrations: a genome-wide association study

BACKGROUND

LDL cholesterol has a causal role in the development of cardiovascular disease. Improved understanding of the biological mechanisms that underlie the metabolism and regulation of LDL cholesterol might help to identify novel therapeutic targets. We therefore did a genome-wide association study of LDL-cholesterol concentrations.

METHODS

We used genome-wide association data from up to 11,685 participants with measures of circulating LDL-cholesterol concentrations across five studies, including data for 293 461 autosomal single nucleotide polymorphisms (SNPs) with a minor allele frequency of 5% or more that passed our quality control criteria. We also used data from a second genome-wide array in up to 4337 participants from three of these five studies, with data for 290,140 SNPs. We did replication studies in two independent populations consisting of up to 4979 participants. Statistical approaches, including meta-analysis and linkage disequilibrium plots, were used to refine association signals; we analysed pooled data from all seven populations to determine the effect of each SNP on variations in circulating LDL-cholesterol concentrations.

FINDINGS

In our initial scan, we found two SNPs (rs599839 [p=1.7x10(-15)] and rs4970834 [p=3.0x10(-11)]) that showed genome-wide statistical association with LDL cholesterol at chromosomal locus 1p13.3. The second genome screen found a third statistically associated SNP at the same locus (rs646776 [p=4.3x10(-9)]). Meta-analysis of data from all studies showed an association of SNPs rs599839 (combined p=1.2x10(-33)) and rs646776 (p=4.8x10(-20)) with LDL-cholesterol concentrations. SNPs rs599839 and rs646776 both explained around 1% of the variation in circulating LDL-cholesterol concentrations and were associated with about 15% of an SD change in LDL cholesterol per allele, assuming an SD of 1 mmol/L.

INTERPRETATION

We found evidence for a novel locus for LDL cholesterol on chromosome 1p13.3. These results potentially provide insight into the biological mechanisms that underlie the regulation of LDL cholesterol and might help in the discovery of novel therapeutic targets for cardiovascular disease.

Rosiglitazone increases dendritic spine density and rescues spine loss caused by apolipoprotein E4 in primary cortical neurons

Convergent evidence has revealed an association between insulin resistance and Alzheimer's disease (AD), and the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, rosiglitazone, an insulin sensitizer and mitochondrial activator, improves cognition in patients with early or mild-to-moderate AD. Apolipoprotein (apo) E4, a major genetic risk factor for AD, exerts neuropathological effects through multiple pathways, including impairment of dendritic spine structure and mitochondrial function. Here we show that rosiglitazone significantly increased dendritic spine density in a dose-dependent manner in cultured primary cortical rat neurons. This effect was abolished by the PPAR-gamma-specific antagonist, GW9662, suggesting that rosiglitazone exerts this effect by activating the PPAR-gamma pathway. Furthermore, the C-terminal-truncated fragment of apoE4 significantly decreased dendritic spine density. Rosiglitazone rescued this detrimental effect. Thus, rosiglitazone might improve cognition in AD patients by increasing dendritic spine density.

Atherogenic remnant lipoproteins: role for proteoglycans in trapping, transferring, and internalizing

Unraveling the mechanisms controlling remnant lipoprotein clearance is important, as these lipoproteins are highly atherogenic. The most critical molecule in this process is apoE, which mediates high-affinity binding of remnant lipoproteins to members of the LDL receptor (LDLR) family and cell-surface heparan sulfate proteoglycans (HSPGs), which have been shown to play major independent as well as cooperative roles in remnant lipoprotein clearance. While all the players may have been identified, our understanding of how they interact and function together continues to evolve. In this issue of the JCI, MacArthur et al. (see the related article beginning on page 153) demonstrated that HSPGs under normal physiological conditions are critically important in the clearance of remnant lipoproteins, independent of LDLR family members. The complexity of VLDL and chylomicron remnant clearance was exemplified by the studies of Jones et al., also in this issue (see the related article beginning on page 165). Despite defective clearance of LDL in mice with a deficiency in the adaptor protein controlling internalization of the LDLR, called autosomal recessive hypercholesterolemia (ARH), remnant lipoprotein clearance was not grossly abnormal. A likely explanation is that the abnormal LDLRs bind the remnants and then transfer them to another acceptor for internalization. While the studies clearly demonstrate that the LDLR-related protein 1 is not involved and suggest a role for an additional unidentified receptor, it remains a possibility that HSPGs are responsible for remnant uptake by hepatocytes in the presence of defective LDLR internalization.

Apolipoprotein (apo) E4 and Alzheimer's disease: unique conformational and biophysical properties of apoE4 can modulate neuropathology

The unique structural and biophysical features of apolipoprotein (apo) E4 - domain interaction and molten globule formation - have been correlated with the detrimental effects of apoE4 in neuropathology. Two examples of how the structure of apoE4 determines the pathological outcome in neurons include apoE4 potentiation of amyloid beta-induced lysosomal leakage and apoptosis and the proteolytic cleavage of apoE synthesized by neurons. Thus, a new therapeutic target is to identify small molecules to modulate the inherent neuropathological structure of apoE4, i.e. to prevent domain interaction and to convert apoE4 to an apoE3-like molecule. A second therapeutic target is to inhibit the apoE-cleaving enzyme. This would prevent the generation of the reactive carboxyl-terminal fragments of apoE that enter the cytosol, disrupt the cytoskeleton, and cause neurodegeneration. ApoE4 is more susceptible than apoE3 to proteolytic cleavage and is thus more likely to cause detrimental effects in the central nervous system. It is predictable that apoE4 acts through various pathways to cause cognitive decline and neurodegeneration.

Human prions and plasma lipoproteins

Prions are composed solely of an alternatively folded isoform of the prion protein (PrP), designated PrP(Sc). The polyoxometalate phosphotungstic acid has been used to separate PrP(Sc) from its precursor PrP(C) by selective precipitation; notably, native PrP(Sc) has not been solubilized by using nondenaturing detergents. Because of the similarities between PrP(Sc) and lipoproteins with respect to hydrophobicity and formation of phosphotungstic acid complexes, we asked whether these molecules are bound to each other in blood. Here we report that prions from the brains of patients with sporadic Creutzfeldt-Jakob disease (CJD) bind to very low-density (VLDL) and low-density (LDL) lipoproteins but not to high-density lipoproteins (HDL) or other plasma components, as demonstrated both by affinity assay and electron microscopy. Immunoassays demonstrated that apolipoprotein B (apoB), which is the major protein component of VLDL and LDL, bound PrP(Sc) through a highly cooperative process. Approximately 50% of the PrP(Sc) bound to LDL particles was released after exposure to 4 M guanidine hydrochloride at 80 degrees C for 20 min. The apparent binding constants of native human (Hu) PrP(Sc) or denatured recombinant HuPrP(90-231) for apoB and LDL ranged from 28 to 212 pM. Whether detection of PrP(Sc) in VLDL and LDL particles can be adapted into an antemortem diagnostic test for prions in the blood of humans, livestock, and free-ranging cervids remains to be determined.

Putting cholesterol in its place: apoE and reverse cholesterol transport

To avoid toxic overload of cholesterol in peripheral cells, the reverse cholesterol transport pathway directs excess cholesterol through HDL acceptors to the liver for elimination. In this issue of the JCI, a study by Matsuura et al. reveals new features of this pathway, including the importance of the ATP-binding cassette transporter G1 in macrophages and apoE in cholesteryl efflux from cells to cholesterol ester-rich (CE-rich) HDL(2) acceptors (see the related article beginning on page 1435). One proposal for boosting reverse cholesterol transport has been to elevate plasma HDL levels by inhibiting CE transfer protein (CETP), which transfers CE from HDL to lower-density lipoproteins. However, there has been concern that large, CE-rich HDL(2) generated by CETP inhibition might impair reverse cholesterol transport. ApoE uniquely facilitates reverse cholesterol transport by allowing CE-rich core expansion in HDL. In lower species, these large HDLs are not atherogenic. Thus, CETP might not be essential for reverse cholesterol transport in humans, raising hope of using a CETP inhibitor to elevate HDL levels.

Complex disease-associated pharmacogenetics: drug efficacy, drug safety, and confirmation of a pathogenetic hypothesis (Alzheimer's disease)

Safety and efficacy pharmacogenetics can be applied successfully to the drug discovery and development pipeline at multiple phases. We review drug-target screening using high throughput SNP associations with complex diseases testing more than 1,800 candidate targets with approximately 7,000 SNPs. Alzheimer's disease data are provided as an example. The supplementation of target-selected screening with genome-wide SNP association, to also define susceptibility genes and relevant disease pathways for human diseases, is discussed. Applications for determining predictive genetic or genomic profiles, or derived biomarkers, for drug efficacy and safety during clinical development are exemplified by several successful experiments at different phases of development. A Phase I-IIA study of side effects using an oral drug for the treatment of breast cancer is used as an example of early pipeline pharmacogenetics to predict side effects and allow optimization of dosing. References are provided for several other recently published genetic association studies of adverse events during drug development. We illustrate the early identification of gene variant candidates related to efficacy in a Phase IIA obesity drug trial to generate hypotheses for testing in subsequent development. How these genetic data generated in Phase IIA are subsequently incorporated as hypotheses into later Phase clinical protocols is discussed. A Phase IIB clinical trial for Alzheimer's disease is described that exemplifies the major pipeline decision between program attrition and further clinical development. In this case, there was no significant improvement in 511 intention-to-treat patients but, applying a confirmed prognostic biomarker (APOE4) to segment the clinical trial population, all three doses of rosiglitazone demonstrated improvement in patients who did not carry the APOE4 allele. The data for the APOE4 carriers demonstrated no significant improvement but suggested that there may be a need for higher doses. Thus, a development program that would have been terminated progressed to Phase III registration trials based on the results of prospective efficacy pharmacogenetic analyses. The implications of using APOE genotype as a biomarker to predict efficacy and possibly dose, as well as supporting the basic neurobiology and pharmacology that provided the original target validation, is discussed. Citations are provided that support a slow neurotoxic effect over many years of a specific fragment of apoE protein (over-produced by apoE4 substrate compared to apoE3) on mitochondria and the use of rosiglitazone to increase mitochondrial biogenesis and improve glucose utilization. Pharmacogenetics is currently being used across the pipeline to prevent attrition and to create safer and more effective medicines.

Profile and regulation of apolipoprotein E (ApoE) expression in the CNS in mice with targeting of green fluorescent protein gene to the ApoE locus

To study the profile and regulation of apolipoprotein E (apoE) expression in the CNS, we generated mice in which apoE expression can be detected in vivo with unprecedented sensitivity and resolution. cDNA encoding enhanced green fluorescent protein (EGFP) with a stop codon was inserted by gene targeting into the apoE gene locus (EGFPapoE) immediately after the translation initiation site. Insertion of EGFP into one apoE allele provides a real-time location marker of apoE expression in vivo; the remaining allele is sufficient to maintain normal cellular physiology. In heterozygous EGFPapoE mice, EGFP was highly expressed in hepatocytes and peritoneal macrophages. EGFP was also expressed in brain astrocytes; however some astrocytes (approximately 25%) expressed no EGFP, suggesting that a subset of these cells does not express apoE. EGFP was expressed in <10% of microglia after kainic acid treatment, suggesting that microglia are not a major source of brain apoE. Although hippocampal neurons did not express EGFP under normal conditions, kainic acid treatment induced intense expression of EGFP in injured neurons, demonstrating apoE expression in neurons in response to excitotoxic injury. The neuronal expression was confirmed by in situ hybridization of mouse apoE mRNA and by anti-apoE immunostaining. Smooth muscle cells of large blood vessels and cells surrounding small vessels in the CNS also strongly expressed EGFP, as did cells in the choroid plexus. EGFPapoE reporter mice will be useful for studying the regulation of apoE expression in the CNS and might provide insights into the diverse mechanisms of apoE4-related neurodegeneration.

Apolipoprotein E4: a causative factor and therapeutic target in neuropathology, including Alzheimer's disease

The premise of this review is that apolipoprotein (apo) E4 is much more than a contributing factor to neurodegeneration. ApoE has critical functions in redistributing lipids among CNS cells for normal lipid homeostasis, repairing injured neurons, maintaining synapto-dendritic connections, and scavenging toxins. In multiple pathways affecting neuropathology, including Alzheimer's disease, apoE acts directly or in concert with age, head injury, oxidative stress, ischemia, inflammation, and excess amyloid beta peptide production to cause neurological disorders, accelerating progression, altering prognosis, or lowering age of onset. We envision that unique structural features of apoE4 are responsible for apoE4-associated neuropathology. Although the structures of apoE2, apoE3, and apoE4 are in dynamic equilibrium, apoE4, which is detrimental in a variety of neurological disorders, is more likely to assume a pathological conformation. Importantly, apoE4 displays domain interaction (an interaction between the N- and C-terminal domains of the protein that results in a compact structure) and molten globule formation (the formation of stable, reactive intermediates with potentially pathological activities). In response to CNS stress or injury, neurons can synthesize apoE. ApoE4 uniquely undergoes neuron-specific proteolysis, resulting in bioactive toxic fragments that enter the cytosol, alter the cytoskeleton, disrupt mitochondrial energy balance, and cause cell death. Our findings suggest potential therapeutic strategies, including the use of "structure correctors" to convert apoE4 to an "apoE3-like" molecule, protease inhibitors to prevent the generation of toxic apoE4 fragments, and "mitochondrial protectors" to prevent cellular energy disruption.

Smoking and obesity make a bad problem worse: genetics and lifestyle affect high density lipoprotein levels in Turks

Low levels of high density lipoprotein cholesterol (HDL-C) are an independent risk factor for coronary heart disease. The Turkish Heart Study revealed very low levels of plasma HDL-C in the Turkish population, a fact confirmed by the Heart Disease and Risk Factors in Turkish Adults study. Low HDL-C levels have also been observed in Turks living in the United States, Germany, and the Netherlands. Dietary habits do not explain the low HDL-C levels, which were found in Turkish Heart Study participants from six regions of Turkey with significant differences in typical diets. Among newborns and pre-pubescent children, plasma HDL-C levels were similar in Turks and western Europeans. After puberty, however, HDL-C levels declined significantly in Turkish boys and girls. These results suggest a genetic basis for the low HDL-C levels. In fact, hepatic lipase activity modulated by sex hormones was 25-30% higher in the Turkish population than in other populations. Elevated hepatic lipase activity is clearly associated with low plasma HDL-C in many studies. Results of a recent genome-wide scan for plasma HDL-C in Turks revealed a linkage on chromosome 15q22 where the hepatic lipase gene is located and that low HDL-C was 80% heritable. In addition, evidence for an interaction between HDL-C levels and modifiable environmental factors, particularly smoking and obesity, came from the study of cholesterol ester transfer protein TaqIB polymorphism. This polymorphism was associated with plasma HDL-C levels in Turks. Subjects with the B2B2 genotype-both smokers and nonsmokers-had higher plasma HDL-C levels. Interestingly, B2B2 subjects were protected from the HDL-C-lowering effect of smoking, whereas B1B1 subjects who smoked had significantly lower HDL-C levels. A similar interaction was observed between TaqIB polymorphism and obesity. In conclusion, low HDL-C levels in Turks were modulated by genetic factors and their interaction with modifiable environmental factors, such as smoking and obesity.

Apolipoprotein A-V: a potential modulator of plasma triglyceride levels in Turks

The apolipoprotein A-V gene (APOA5) plays an important role in determining plasma triglyceride levels. We studied the effects of APOA5 polymorphisms on plasma triglyceride levels in Turks, a population with low levels of HDL cholesterol and a high prevalence of coronary artery disease. We found 15 polymorphisms, three of which were novel. Seven haplotype-tagging single nucleotide polymorphisms (SNPs) were chosen and genotyped in approximately 3,000 subjects. The rare alleles of the -1464T>C, -1131T>C, S19W, and 1259T>C SNPs were significantly associated with increased triglyceride levels (19-86 mg/dl; P < 0.05) and had clear gene-dose effects. Haplotype analysis of the nine common APOA5 haplotypes revealed significant effects on triglyceride levels (P < 0.001). Detailed analysis of haplotypes clearly showed that the -1464T>C polymorphism had no effect by itself but was a marker for the -1131T>C, S19W, and 1259T>C polymorphisms. The -1131T>C and 1259T>C polymorphisms were in a strong but incomplete linkage disequilibrium and appeared to have independent effects. Thus, the APOA5 -1131T>C, S19W, and 1259T>C rare alleles were associated with significant increases in plasma triglyceride levels. At least one of these alleles was present in approximately 40% of the Turks. Similar associations were observed for -1131T>C and S19W in white Americans living in San Francisco, California.

Apolipoprotein (apo) E4 enhances amyloid beta peptide production in cultured neuronal cells: apoE structure as a potential therapeutic target

Apolipoprotein (apo) E4 is a major risk factor for Alzheimer's disease, and many studies have suggested that apoE has isoform-specific effects on the deposition or clearance of amyloid beta (Abeta) peptides. We examined the effects of apoE isoforms on the processing of amyloid precursor protein (APP) and on Abeta production in rat neuroblastoma B103 cells stably transfected with human wild-type APP695 (B103-APP). Lipid-poor apoE4 increased Abeta production in B103-APP cells to a greater extent than lipid-poor apoE3 (60% vs. 30%) due to more pronounced stimulation of APP recycling by apoE4 than apoE3. The difference in Abeta production was abolished by preincubating the cells with the receptor-associated protein (25 nM), which blocks the low-density lipoprotein receptor-related protein (LRP) pathway, or by reducing LRP expression by small interference RNA. The differences were also attenuated by replacing Arg-61 with threonine in apoE4 or pretreating apoE4 with small molecules, both of which abolish apoE4 intramolecular domain interaction. Thus, apoE4 appears to modulate APP processing and Abeta production through both the LRP pathway and domain interaction. These findings provide insights into why apoE4 is associated with increased risk for Alzheimer's disease and may represent a potential target for drug development.

Lipid- and receptor-binding regions of apolipoprotein E4 fragments act in concert to cause mitochondrial dysfunction and neurotoxicity

Apolipoprotein (apo) E4, a 299-aa protein and a major risk factor for Alzheimer's disease, can be cleaved to generate C-terminal-truncated fragments that cause neurotoxicity in vitro and neurodegeneration and behavioral deficits in transgenic mice. To investigate this neurotoxicity, we expressed apoE4 with C- or N-terminal truncations or mutations in transfected Neuro-2a cells. ApoE4 (1-272) was neurotoxic, but full-length apoE4(1-299) and apoE4(1-240) were not, suggesting that the lipid-binding region (amino acids 241-272) mediates the neurotoxicity and that amino acids 273-299 are protective. A quadruple mutation in the lipid-binding region (I250A, F257A, W264R, and V269A) abolished the neurotoxicity of apoE4(1-272), and single mutations in the region of amino acids 273-299 (L279Q, K282A, or Q284A) made full-length apoE4 neurotoxic. Immunofluorescence staining showed that apoE4(1-272) formed filamentous inclusions containing phosphorylated tau in some cells and interacted with mitochondria in others, leading to mitochondrial dysfunction as determined by MitoTracker staining and flow cytometry. ApoE4(241-272) did not cause mitochondrial dysfunction or neurotoxicity, suggesting that the lipid-binding region alone is insufficient for neurotoxicity. Truncation of N-terminal sequences (amino acids 1-170) containing the receptor-binding region (amino acids 135-150) and triple mutations within that region (R142A, K146A, and R147A) abolished the mitochondrial interaction and neurotoxicity of apoE4(1-272). Further analysis showed that the receptor-binding region is required for escape from the secretory pathway and that the lipid-binding region mediates mitochondrial interaction. Thus, the lipid- and receptor-binding regions in apoE4 fragments act together to cause mitochondrial dysfunction and neurotoxicity, which may be important in Alzheimer's disease pathogenesis.

Reactivity of apolipoprotein E4 and amyloid beta peptide: lysosomal stability and neurodegeneration

We previously demonstrated that apolipoprotein E4 (apoE4) potentiates lysosomal leakage and apoptosis induced by amyloid beta (Abeta) peptide in cultured Neuro-2a cells and hypothesized that the low pH of lysosomes accentuates the conversion of apoE4 to a molten globule, inducing reactive intermediates capable of destabilizing cellular membranes. Here we report that neutralizing lysosomal pH with bafilomycin or NH4Cl abolished the apoE4 potentiation of Abeta-induced lysosomal leakage and apoptosis in Neuro-2a cells. Consistent with these results, apoE4 at acidic pH bound more avidly to phospholipid vesicles and disrupted them to a greater extent than at pH 7.4. Comparison of "Arctic" mutant Abeta, which forms multimers, and GM6 mutant Abeta, which remains primarily monomeric, showed that aggregation is essential for apoE4 to potentiate Abeta-induced lysosomal leakage and apoptosis. Both apoE4 and Abeta1-42 had to be internalized to exert these effects. Blocking the low density lipoprotein receptor-related protein with small interfering RNA abolished the enhanced effects of apoE4 and Abeta on lysosomes and apoptosis. In cultured Neuro-2a cells, Abeta1-42 increased lysosome formation to a greater extent in apoE3- or apoE4-transfected cells than in Neo-transfected cells, as shown by immunostaining for lysosome-associated membrane protein 1. Similarly, in transgenic mice expressing apoE and amyloid precursor protein, hippocampal neurons displayed increased numbers of lysosomes. Thus, apoE4 and Abeta1-42 may work in concert in neurons to increase lysosome formation while increasing the susceptibility of lysosomal membranes to disruption, release of lysosomal enzymes into the cytosol, and neuronal degeneration.

Multiple QTLs influencing triglyceride and HDL and total cholesterol levels identified in families with atherogenic dyslipidemia

We conducted a genome-wide scan using variance components linkage analysis to localize quantitative-trait loci (QTLs) influencing triglyceride (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol, and total cholesterol (TC) levels in 3,071 subjects from 459 families with atherogenic dyslipidemia. The most significant evidence for linkage to TG levels was found in a subset of Turkish families at 11q22 [logarithm of the odds ratio (LOD)=3.34] and at 17q12 (LOD=3.44). We performed sequential oligogenic linkage analysis to examine whether multiple QTLs jointly influence TG levels in the Turkish families. These analyses revealed loci at 20q13 that showed strong epistatic effects with 11q22 (conditional LOD=3.15) and at 7q36 that showed strong epistatic effects with 17q12 (conditional LOD=3.21). We also found linkage on the 8p21 region for TG in the entire group of families (LOD=3.08). For HDL-C levels, evidence of linkage was identified on chromosome 15 in the Turkish families (LOD=3.05) and on chromosome 5 in the entire group of families (LOD=2.83). Linkage to QTLs for TC was found at 8p23 in the entire group of families (LOD=4.05) and at 5q13 in a subset of Turkish and Mediterranean families (LOD=3.72). These QTLs provide important clues for the further investigation of genes responsible for these complex lipid phenotypes. These data also indicate that a large proportion of the variance of TG levels in the Turkish population is explained by the interaction of multiple genetic loci.

An interaction between the TaqIB polymorphism of cholesterol ester transfer protein and smoking is associated with changes in plasma high-density lipoprotein cholesterol levels in Turks

Low levels of high-density lipoprotein cholesterol (HDL-C) are an independent risk factor for atherosclerosis. We investigated the effects of the TaqIB polymorphism of cholesterol ester transfer protein (CETP) on CETP activity and plasma HDL-C levels in random nondiabetic and self-reported diabetic subjects in a population with very low HDL-C levels. The rare B2B2 genotype was associated with significantly higher HDL-C levels and lower CETP activity in random subjects and with higher HDL-C in diabetic subjects. After stratification of random subjects by smoking status, the common B1B1 genotype was associated with lower HDL-C levels than the B2B2 genotype. Although smoking was associated with lower HDL-C, especially in men, HDL-C levels between smokers and nonsmokers were not different in subjects with the B1B2 or B2B2 genotypes. However, smoking (20+ cigarettes/day) was associated with a marked reduction in HDL-C in the B1B1 subjects. The B1B1/smoking interaction was not reflected in a difference in CETP activity. High triglycerides and elevated body mass index (BMI) lower HDL-C. The B2B2 genotype was associated with the highest HDL-C levels, and these levels were significantly lower in the hypertriglyceridemic subjects (>or=50th percentile). The lowest HDL-C levels were seen in hypertriglyceridemic subjects with the B1B1 genotype. Although BMI (>or=50th vs<50th percentile) did not affect HDL-C in B2B2 subjects, a high BMI was associated with markedly lower HDL-C in B1B1 subjects. Thus, HDL-C levels in Turks may be modulated by an interaction between the CETP TaqIB polymorphism and smoking, as well as an interaction with hypertriglyceridemia and BMI.