Vilmantas Giedraitis

η-Secretase processing of APP inhibits neuronal activity in the hippocampus

Alzheimer disease (AD) is characterized by the accumulation of amyloid plaques, which are predominantly composed of amyloid-β peptide. Two principal physiological pathways either prevent or promote amyloid-β generation from its precursor, β-amyloid precursor protein (APP), in a competitive manner. Although APP processing has been studied in great detail, unknown proteolytic events seem to hinder stoichiometric analyses of APP metabolism in vivo. Here we describe a new physiological APP processing pathway, which generates proteolytic fragments capable of inhibiting neuronal activity within the hippocampus. We identify higher molecular mass carboxy-terminal fragments (CTFs) of APP, termed CTF-η, in addition to the long-known CTF-α and CTF-β fragments generated by the α- and β-secretases ADAM10 (a disintegrin and metalloproteinase 10) and BACE1 (β-site APP cleaving enzyme 1), respectively. CTF-η generation is mediated in part by membrane-bound matrix metalloproteinases such as MT5-MMP, referred to as η-secretase activity. η-Secretase cleavage occurs primarily at amino acids 504–505 of APP695, releasing a truncated ectodomain. After shedding of this ectodomain, CTF-η is further processed by ADAM10 and BACE1 to release long and short Aη peptides (termed Aη-α and Aη-β). CTFs produced by η-secretase are enriched in dystrophic neurites in an AD mouse model and in human AD brains. Genetic and pharmacological inhibition of BACE1 activity results in robust accumulation of CTF-η and Aη-α. In mice treated with a potent BACE1 inhibitor, hippocampal long-term potentiation was reduced. Notably, when recombinant or synthetic Aη-α was applied on hippocampal slices ex vivo, long-term potentiation was lowered. Furthermore, in vivo single-cell two-photon calcium imaging showed that hippocampal neuronal activity was attenuated by Aη-α. These findings not only demonstrate a major functionally relevant APP processing pathway, but may also indicate potential translational relevance for therapeutic strategies targeting APP processing.

Mosaic loss of chromosome Y in peripheral blood is associated with shorter survival and higher risk of cancer

Incidence and mortality for sex-unspecific cancers are higher among men, a fact that is largely unexplained. Furthermore, age-related loss of chromosome Y (LOY) is frequent in normal hematopoietic cells, but the phenotypic consequences of LOY have been elusive. From analysis of 1,153 elderly men, we report that LOY in peripheral blood was associated with risks of all-cause mortality (hazards ratio (HR) = 1.91, 95% confidence interval (CI) = 1.17–3.13; 637 events) and non-hematological cancer mortality (HR = 3.62, 95% CI = 1.56–8.41; 132 events). LOY affected at least 8.2% of the subjects in this cohort, and median survival times among men with LOY were 5.5 years shorter. Association of LOY with risk of all-cause mortality was validated in an independent cohort (HR = 3.66) in which 20.5% of subjects showed LOY. These results illustrate the impact of post-zygotic mosaicism on disease risk, could explain why males are more frequently affected by cancer and suggest that chromosome Y is important in processes beyond sex determination. LOY in blood could become a predictive biomarker of male carcinogenesis.

Plasma β Amyloid and the Risk of Alzheimer Disease and Dementia in Elderly Men : A Prospective, Population-Based Cohort Study

BACKGROUND Beta amyloid (Abeta) protein accumulates in the brains of individuals with Alzheimer disease (AD) and is detectable in cerebrospinal fluid and plasma. OBJECTIVE To examine plasma levels of Abeta peptides Abeta(40) and Abeta(42) as predictors of incident AD and other types of dementia. DESIGN Prospective, population-based cohort study. SETTING The Uppsala Longitudinal Study of Adult Men. PARTICIPANTS Plasma Abeta(40) and Abeta(42) levels were analyzed as predictors of incident AD in 1045 men at age 70 years and 680 men at age 77 years using Cox proportional hazards analyses. Alzheimer disease and other types of dementia were diagnosed by standardized screening, clinical evaluation, and medical record review. MAIN OUTCOME MEASURES Hazard ratios of AD (primary outcome) and vascular dementia or other dementia (secondary outcomes) according to baseline levels of plasma Abeta(40) and Abeta(42). RESULTS From the age of 77 years at baseline, 46 individuals developed AD at follow-up (median, 5.3 years). A low plasma Abeta(40) level at age 77 years was associated with higher incidence of AD. The multivariate-adjusted hazard ratio was 4.87 (95% confidence interval, 1.63-14.6) for the lowest Abeta(40) tertile compared with the highest tertile. On follow-up from age 70 years at baseline (median, 11.2 years), 82 individuals developed AD. Plasma Abeta(40) and Abeta(42) levels measured at age 70 years were not significantly associated with incident AD. CONCLUSIONS Low plasma Abeta(40) levels predicted incident AD in elderly men independently of potential confounders. Plasma Abeta(42) levels were not significantly associated with AD incidence. The clinical value of Abeta measurement in plasma remains to be established in future studies.

Age-Related Somatic Structural Changes in the Nuclear Genome of Human Blood Cells

Structural variations are among the most frequent interindividual genetic differences in the human genome. The frequency and distribution of de novo somatic structural variants in normal cells is, however, poorly explored. Using age-stratified cohorts of 318 monozygotic (MZ) twins and 296 single-born subjects, we describe age-related accumulation of copy-number variation in the nuclear genomes in vivo and frequency changes for both megabase- and kilobase-range variants. Megabase-range aberrations were found in 3.4% (9 of 264) of subjects ≥60 years old; these subjects included 78 MZ twin pairs and 108 single-born individuals. No such findings were observed in 81 MZ pairs or 180 single-born subjects who were ≤55 years old. Recurrent region- and gene-specific mutations, mostly deletions, were observed. Longitudinal analyses of 43 subjects whose data were collected 7-19 years apart suggest considerable variation in the rate of accumulation of clones carrying structural changes. Furthermore, the longitudinal analysis of individuals with structural aberrations suggests that there is a natural self-removal of aberrant cell clones from peripheral blood. In three healthy subjects, we detected somatic aberrations characteristic of patients with myelodysplastic syndrome. The recurrent rearrangements uncovered here are candidates for common age-related defects in human blood cells. We anticipate that extension of these results will allow determination of the genetic age of different somatic-cell lineages and estimation of possible individual differences between genetic and chronological age. Our work might also help to explain the cause of an age-related reduction in the number of cell clones in the blood; such a reduction is one of the hallmarks of immunosenescence.

Rapid Progression from Mild Cognitive Impairment to Alzheimer’s Disease in Subjects with Elevated Levels of Tau in Cerebrospinal Fluid and the APOE ε4/ε4 Genotype

Background/Aims: Increased cerebrospinal fluid (CSF) tau, decreased CSF amyloid-β42 (Aβ42) and the apolipoprotein E gene (APOE) ε4 allele predict progression from mild cognitive impairment (MCI) to Alzheimer’s disease (AD). Here, we investigated these markers to assess their predictive value and influence on the rate of disease progression. Methods: Using ELISA, we measured the CSF biomarkers in 47 AD patients, 58 patients with MCI and 35 healthy control subjects. Twenty-eight MCI patients revisited the clinic and half of them progressed to AD during a period of 3–12 years. Results: The expected changes in CSF total (T)-tau, phosphorylated (P)-tau and Aβ42 levels were found in AD, confirming the diagnostic value of these biomarkers. We were also able to corroborate an increased risk for progression from MCI to AD with elevated CSF T-tau and P-tau and with the presence of the APOE ε4/ε4 genotype, but not with decreased Aβ42. Finally, for the first time we demonstrated that MCI subjects with high CSF T-tau or P-tau and APOE ε4 homozygosity progressed faster from MCI to AD. Conclusions: CSF T-tau and P-tau as well as the APOE ε4/ε4 genotype are robust predictors of AD and are also associated with a more rapid progression from MCI to AD.

The normal equilibrium between CSF and plasma amyloid beta levels is disrupted in Alzheimer's disease

Amyloid-beta (Abeta) with 40 (Abeta40) and 42 (Abeta42) amino acids, the main components of amyloid plaques in the Alzheimers disease (AD) brain, can be measured in human cerebrospinal fluid (CSF) and plasma. Whereas CSF Abeta42 is decreased in AD, some studies have reported changed plasma Abeta levels in AD and in subjects with mild cognitive impairment (MCI). To this date it is unclear if and how CSF and plasma levels of Abeta correlate with each other in healthy individuals, albeit earlier studies on AD patients found no correlation between CSF and plasma Abeta. We have measured Abeta40 and Abeta42 in paired CSF and plasma samples from patients with AD (n=39), MCI (n=29) and healthy control subjects (n=18). We observed a clear correlation between CSF and plasma levels for both Abeta40 and Abeta42 in healthy individuals, whereas no such correlation could be seen for AD or MCI cases. Similarly to other studies we also found low levels of Abeta42 in AD CSF, whereas there were no significant differences in plasma Abeta levels between the diagnostic groups. Our findings suggest that the normal equilibrium between CSF and plasma Abeta may be disrupted with the initiation of amyloid deposition in the brain.

Common Genetic Variants Highlight the Role of Insulin Resistance and Body Fat Distribution in Type 2 Diabetes, Independent of Obesity

We aimed to validate genetic variants as instruments for insulin resistance and secretion, to characterize their association with intermediate phenotypes, and to investigate their role in type 2 diabetes (T2D) risk among normal-weight, overweight, and obese individuals. We investigated the association of genetic scores with euglycemic-hyperinsulinemic clamp– and oral glucose tolerance test–based measures of insulin resistance and secretion and a range of metabolic measures in up to 18,565 individuals. We also studied their association with T2D risk among normal-weight, overweight, and obese individuals in up to 8,124 incident T2D cases. The insulin resistance score was associated with lower insulin sensitivity measured by M/I value (β in SDs per allele [95% CI], −0.03 [−0.04, −0.01]; P = 0.004). This score was associated with lower BMI (−0.01 [−0.01, −0.0]; P = 0.02) and gluteofemoral fat mass (−0.03 [−0.05, −0.02; P = 1.4 × 10−6) and with higher alanine transaminase (0.02 [0.01, 0.03]; P = 0.002) and γ-glutamyl transferase (0.02 [0.01, 0.03]; P = 0.001). While the secretion score had a stronger association with T2D in leaner individuals (Pinteraction = 0.001), we saw no difference in the association of the insulin resistance score with T2D among BMI or waist strata (Pinteraction > 0.31). While insulin resistance is often considered secondary to obesity, the association of the insulin resistance score with lower BMI and adiposity and with incident T2D even among individuals of normal weight highlights the role of insulin resistance and ectopic fat distribution in T2D, independently of body size.

Genetic Analysis of Alzheimer's Disease in the Uppsala Longitudinal Study of Adult Men

Background/Aims: Genetic factors influencing common complex conditions have proven difficult to identify, and data from numerous investigations have provided incomplete conclusions as to the identity of these genes. Here we aimed to identify susceptibility genes for late-onset Alzheimer’s disease (AD). Methods: The case-control analysis included samples from 86 AD patients and 404 cognitively healthy controls selected from the Uppsala Longitudinal Study of Adult Men (ULSAM). In the incidence analysis, all 1,088 genotyped ULSAM participants were included. DNA samples from ULSAM participants were analyzed for 2,578 single nucleotide polymorphisms (SNP) within 368 genes. The selection of genes tested for association to AD within this cohort was based on genes previously implicated in conditions with relevance to ULSAM, such as dementia, cardiovascular disease, diabetes and metabolic syndrome, osteoporosis, and cancer. Results/Conclusion: Association analysis revealed 82 genes containing at least 1 significant SNP at p < 0.05 with association to AD. Only 20 genes remained significant after a permutation test to correct for multiple comparisons within individual genes. Using publicly available data from 2 genome-wide association (GWA) studies and linkage disequilibrium data from HapMap, we attempted to replicate the AD association identified in ULSAM. In addition to apolipoprotein E, we were able to replicate 5 other genes in both GWA studies at p < 0.05.

Smoking is associated with mosaic loss of chromosome Y

Men beware, when smoke gets in your Ys The relationship between tobacco smoking and elevated cancer risk has been recognized for 60 years. Yet what smoking does to our genetic material is still not fully understood. New work suggests that men should be particularly concerned. In a study of over 6000 men, Dumanski et al. find that men who smoke are more than three times as likely as nonsmokers to show loss of the Y chromosome in their blood cells. Whether this is a causal factor in cancer development or simply a marker of more consequential damage on other chromosomes could not be deduced from the study. Science, this issue p. 81 Men who smoke are over three times more likely than nonsmokers to show loss of the Y chromosome in their blood cells. Tobacco smoking is a risk factor for numerous disorders, including cancers affecting organs outside the respiratory tract. Epidemiological data suggest that smoking is a greater risk factor for these cancers in males compared with females. This observation, together with the fact that males have a higher incidence of and mortality from most non–sex-specific cancers, remains unexplained. Loss of chromosome Y (LOY) in blood cells is associated with increased risk of nonhematological tumors. We demonstrate here that smoking is associated with LOY in blood cells in three independent cohorts [TwinGene: odds ratio (OR) = 4.3, 95% confidence interval (CI) = 2.8 to 6.7; Uppsala Longitudinal Study of Adult Men: OR = 2.4, 95% CI = 1.6 to 3.6; and Prospective Investigation of the Vasculature in Uppsala Seniors: OR = 3.5, 95% CI = 1.4 to 8.4] encompassing a total of 6014 men. The data also suggest that smoking has a transient and dose-dependent mutagenic effect on LOY status. The finding that smoking induces LOY thus links a preventable risk factor with the most common acquired human mutation.

Serum cystatin C and the risk of Alzheimer disease in elderly men.

Background: Multiple lines of research suggest that increased cystatin C activity in the brain protects against the development of Alzheimer disease (AD). Methods: Serum cystatin C levels were analyzed at two examinations of the Uppsala Longitudinal Study of Adult Men, a longitudinal, community-based study of elderly men (age 70 years, n = 1,153 and age 77 years, n = 761, a subset of the age 70 examination). Cox regressions were used to examine associations between serum cystatin C and incident AD. AD cases were identified by cognitive screening and comprehensive medical chart review in all subjects. Results: On follow-up (median 11.3 years), 82 subjects developed AD. At age 70 years, lower cystatin C was associated with higher risk of AD independently of age, APOE4 genotype, glomerular filtration rate, diabetes, hypertension, stroke, cholesterol, body mass index, smoking, education level, and plasma amyloid-β protein 40 and 42 levels (hazard ratio [HR] for lowest [<1.12 μmol/L] vs highest [>1.30 μmol/L] tertile = 2.67, 95% CI 1.22–5.83, p < 0.02). The results were similar at age 77 years (43 participants developed AD during follow-up). Furthermore, a 0.1-μmol/L decrease of cystatin C between ages 70 and 77 years was associated with a 29% higher risk of incident AD (HR 1.29, 95% CI 1.03–1.63, p < 0.03). Conclusions: Low levels of serum cystatin C precede clinically manifest Alzheimer disease (AD) in elderly men free of dementia at baseline and may be a marker of future risk of AD. These findings strengthen the evidence for a role for cystatin C in the development of clinical AD. GLOSSARY: Aβ40 = amyloid-β protein 40; Aβ42 = amyloid-β protein 42; AD = Alzheimer disease; BMI = body mass index; GFR = glomerular filtration rate; HR = hazard ratio; ICD = International Classification of Diseases; ULSAM = Uppsala Longitudinal Study of Adult Men.