Faculty Bibliography

Background: The regulation of CSF Abeta42 is poorly understood. Recent studies show Abeta42 levels affected by sleep, stress, diet, depression, ApoE genotype, white matter lesions (WML), and Abeta plaques. The purpose of this study was to examine the heterogeneity of Abeta42 as related to ApoE genotype when interacting with known AD risk factors in healthy, cognitively normal subjects. Methods: In cross-section, we examined the Abeta42, T-Tau and P-tau levels as predicted by ApoE4 status in its interaction with depressive symptoms (HAM-D), MRI white-matter hyperintensity volume (WMH V), and memory (Wechsler Logical-Memory). We studied 41 ApoE4+ and 71 ApoE4- subjects (mean age 62.0 6 11.9). All participants were non-depressed (HAM-D-10), cognitively normal (CDR = 0) and free of MRI brain pathology. Results: ApoE4+ subjects compared to the ApoE4- had lower levels of Abeta42 (442 6 27 vs. 603 6 22 ng/L; P <0.01), higher levels of T-Tau (289617 vs. 229613 ng/L; P <0.01), higher p-Tau (2861.6 vs. 17 6 21.9ng/L; P <0.01) and higher WMHv (3.77 6 0.41 vs. 2.67 6 0.32 cm 3, P<0.05). Predicting CSF Abeta42 levels, controlling for age, we observed three significant 2-way interactions: ApoE genotype X mood, ApoE genotype X memory, ApoE genotype X WMH V (F-values range = 4.03-12.35, P<0.05). No interactions were seen for T-tau or P-Tau. Among ApoE4-, mood symptoms, and to a lesser extent worse memory, had a negative correlation with Abeta42 (r = .-44, n = 71, P <0.01 and r = -.22, n = 71, P = 0.07). Among ApoE4+ there was a negative correlation between Abeta42 and WMH V (r = -0.45, n = 26, P<0.05). Conclusions: This is the first study to report the effect of multiple risk factor interactions on CSFAbeta42 levels in cognitively normal subjects with different ApoE4 alleles. Our results indicate that the relationship between risk factors and CSF Abeta42 is dependent on the presence/absence of ApoE4. E4 carriers show reduced CSF Abeta42, and lower Abeta42 was associated with more MRI-WML whereas a more typical clinical AD-type phenotype (poor memory, minor depressive symptoms), was associated with decreased CSF Abeta42 levels in the ApoE4-non-carriers. These data suggest that Apoe4 carriers and noncarriers may offer divergent trajectories of brain and symptom changes. A better knowledge of the presymptomatic early stages of AD and the interactions with the ApoE4 allele may help us understand the variability of our CSF biomarker measures

OBJECTIVE: Major depressive disorder is common in the elderly, and symptoms are often not responsive to conventional antidepressant treatment, especially in the long term. Soluble oligomeric and aggregated forms of amyloid beta peptides, especially amyloid beta 42, impair neuronal and synaptic function. Amyloid beta 42 is the main component of plaques and is implicated in Alzheimer's disease. Amyloid beta peptides also induce a depressive state in rodents and disrupt major neurotransmitter systems linked to depression. The authors assessed whether major depression was associated with CSF levels of amyloid beta, tau protein, and F2-isoprostanes in elderly individuals with major depressive disorder and age-matched nondepressed comparison subjects. METHOD: CSF was obtained from 47 cognitively intact volunteers (major depression group, N=28; comparison group, N=19) and analyzed for levels of soluble amyloid beta, total and phosphorylated tau proteins, and isoprostanes. RESULTS: Amyloid beta 42 levels were significantly lower in the major depression group relative to the comparison group, and amyloid beta 40 levels were lower but only approaching statistical significance. In contrast, isoprostane levels were higher in the major depression group. No differences were observed in total and phosphorylated tau proteins across conditions. Antidepressant use was not associated with differences in amyloid beta 42 levels. CONCLUSIONS: Reduction in CSF levels of amyloid beta 42 may be related to increased brain amyloid beta plaques or decreased soluble amyloid beta production in elderly individuals with major depression relative to nondepressed comparison subjects. These results may have implications for our understanding of the pathophysiology of major depression and for the development of treatment strategies.

Abnormalities of the hypothalamic-pituitary-adrenal (HPA) axis have been reported in subjects with Alzheimer's disease (AD) and may include increased cerebrospinal fluid (CSF) cortisol concentrations. Moreover, presence of the APOE varepsilon4 allele, which is an established risk factor for the development of AD, has been shown to associate with higher CSF cortisol levels, especially in AD sufferers. In this study, we examined whether TOMM40 variants, which have been reported to influence age of onset of AD, also had an effect on CSF cortisol levels, in healthy, cognitively intact individuals with or without APOE varepsilon4. In our results, the increase in CSF cortisol associated with the presence of the APOE varepsilon4 allele was only detected when a short TOMM40 poly-T variant, shown to associate with later age of onset of AD in varepsilon4 carriers, was not present. These results are consistent with previous reports (e.g., Roses et al., 2009) suggesting that TOMM40 poly-T variants influence the effects of APOE alleles

Neurofilament light (NFL) proteins in cerebrospinal fluid (CSF) are a marker of neuronal damage, especially subcortical axonal injury and white matter disease. Subjects with Alzheimer's disease (AD) have shown elevated levels of CSF NFL as compared to controls. However, the presence of the APOE epsilon4 allele, an established risk factor for AD, was not found to associate with higher CSF NFL concentrations. We examined whether TOMM40 variants, which have been reported to influence age of onset of AD and are in linkage disequilibrium with APOE, have an effect on CSF NFL levels, in 47 healthy, cognitively intact individuals with or without APOE epsilon4. Our results show that the presence of APOE epsilon4 alone does not affect CSF NFL levels significantly; however APOE and TOMM40 appear to interact. Subjects with APOE epsilon4 have higher CSF NFL levels than non-epsilon4 carriers, only when they do not carry a short poly-T variant of TOMM40, which is associated with later age of onset of AD, and may act as protective against the dose effect of epsilon4

Background: Reductions in brain-derived neurotrophic factor (BDNF) have been implicated in the pathophysiology of depression. Nevertheless, the factors influencing central and peripheral BDNF levels are still poorly understood. Cerebral microvascular endothelial cells are known to be a major source of BDNF within the brain. Exposure of these cells to amyloid beta (Abeta), which may play a role in the pathophysiology of late-life depression, results in cell death or injury with significant reductions in BDNF secretion. Moreover, in rodents, infusion of Abeta40 into the carotid artery resulted in a disruption of endothelial cells, which was not observed with Abeta42 infusion. Therefore, we hypothesized that concentrations of plasma Abeta40, but not Abeta42, would have a negative effect on plasma BDNF levels. Methods: We examined BDNF and Abeta levels in plasma via immunoblotting and ELISA assays, respectively, from 88 subjects with intact cognition (no dementia and a Mini-Mental State Exam score of at least 28) and no gross MRI abnormalities other than white matter hyperintensities. As these subjects were originally recruited for a study on major depressive disorder (MDD), 45 had MDD and 43 were age-matched controls. Results: Consistent with our prediction, Abeta40 levels were inversely correlated with BDNF concentrations (p<.001), whereas Abeta42 levels were independent of BDNF expression (p=.231). This pattern was similar when MDD and control subjects were analyzed separately. Discussion: Our results are consistent with the hypothesis that cerebral endothelial cells are a contributing source of peripheral BDNF and that their disruption by circulating Abeta40 results in reduction in BDNF. However, these preliminary findings need confirmation, and the mechanisms for our observation, including Abeta40-induced cerebral endothelial cell dysfunction, will have to be clarified

A variable poly-T polymorphism in the TOMM40 gene, which is in linkage disequilibrium with APOE, was recently implicated with increased risk and earlier onset age for late-onset Alzheimer's disease in APOE epsilon3 carriers. To elucidate potential neurobiological mechanisms underlying this association, we compared the effect of TOMM40 poly-T variants to the effect of APOE, an established LOAD-risk modulator, on cerebrospinal fluid (CSF) amyloid beta (Abeta) and tau levels, in cognitively intact elderly subjects. APOE epsilon4 carriers showed significant reductions in Abeta 1-42 levels compared to non-epsilon4 carriers, but no differences were detected across TOMM40 variants. Neither Abeta 1-40 nor tau levels were affected by APOE or TOMM40

Introduction: An important goal of ongoing Alzheimer's disease (AD) research is to identify markers that allow one to predict risk for the development of this type of dementia in cognitively intact elderly. Known cognitive changes associated with AD, possibly reflecting hippocampal pathology, include a worse recall of primacy items and better immediate recall of items learned at the end of a list compared to the middle (recency effect). Aims: The aim of our study was to examine whether learning and recall of primacy and recency words predicted future decline in intact elderly subjects. Methods: Individuals with MMSE of 28 or over at baseline were included in the study. Of these, 211 had at least two successive cognitive evaluations; mean age at baseline was 69.5 (SD=8.0). We regressed MMSE decline on baseline Auditory-Verbal Learning Test (AVLT) memory measures, focusing especially on learning and recall of primacy and recency words, and controlling for baseline age, time since baseline and other variables. Results: Worse learning/delayed recall of primacy words on AVLT trials consistently predicted greater subsequent cognitive decline. Additionally, this effect was stronger among older subjects than among younger ones. APOE e4, a well established genetic risk factor for late-onset AD, was not a significant predictor of MMSE decline in this sample. Conclusions: Decreased learning and poorer recall of primacy words in the AVLT is a predictor of decline in healthy elderly individuals, and future studies should examine if decreased learning and recall can predict conversion to AD