The Ca2+ sensor S100A1 modulates neuroinflammation, histopathology and Akt activity in the PSAPP Alzheimer's disease mouse model.

The contribution of the Ca(2+) sensor S100A1 to in vivo Alzheimer's disease (AD) pathobiology has not been elucidated although S100A1 regulates numerous cellular processes linked to AD. This study uses genetic ablation to ascertain the effects of S100A1 on neuroinflammation, beta-amyloid (Aß) plaque deposition and Akt activity in the PSAPP AD mouse model. PSAPP/S100A1(-/-) mice exhibited decreases in astrocytosis (GFAP burden), microgliosis (Iba1 burden) and plaque load/number when compared to PSAPP/S100A1(+/+) mice at six and twelve months of age. The presence of detectable S100A1 staining in human AD specimens is consistent with a detrimental gain of S100A1 function in AD. S100A1 ablation also reduced plaque associated and increased non-plaque associated PO4-Akt and PO4-GSK3ß staining. S100A1·Akt complexes were undetectable in PC12 cells and AD brain tissue suggesting that S100A1 indirectly modulates Akt activity. In contrast, S100A1·RyR (ryanodine receptor) complexes were present in human/mouse AD brain and exhibited Ca(2+)-dependent formation in neuronal cells. This is the first direct demonstration of an S100A1· target protein complex in tissue/cells and identifies the RyR as a primary S100A1 target protein in the brain. Collectively, these data suggest that S100A1 inhibition may be a novel strategy for normalizing aberrant Ca(2+) signaling in AD.

PSAPP mice exhibit regionally selective reductions in gliosis and plaque deposition in response to S100B ablation.

BACKGROUND: Numerous studies have reported that increased expression of S100B, an intracellular Ca2+ receptor protein and secreted neuropeptide, exacerbates Alzheimer's disease (AD) pathology. However, the ability of S100B inhibitors to prevent/reverse AD histopathology remains controversial. This study examines the effect of S100B ablation on in vivo plaque load, gliosis and dystrophic neurons. METHODS: Because S100B-specific inhibitors are not available, genetic ablation was used to inhibit S100B function in the PSAPP AD mouse model. The PSAPP/S100B-/- line was generated by crossing PSAPP double transgenic males with S100B-/- females and maintained as PSAPP/S100B+/- crosses. Congo red staining was used to quantify plaque load, plaque number and plaque size in 6 month old PSAPP and PSAPP/S100B-/- littermates. The microglial marker Iba1 and astrocytic marker glial fibrillary acidic protein (GFAP) were used to quantify gliosis. Dystrophic neurons were detected with the phospho-tau antibody AT8. S100B immunohistochemistry was used to assess the spatial distribution of S100B in the PSAPP line. RESULTS: PSAPP/S100B-/- mice exhibited a regionally selective decrease in cortical but not hippocampal plaque load when compared to PSAPP littermates. This regionally selective reduction in plaque load was accompanied by decreases in plaque number, GFAP-positive astrocytes, Iba1-positive microglia and phospho-tau positive dystrophic neurons. These effects were not attributable to regional variability in the distribution of S100B. Hippocampal and cortical S100B immunoreactivity in PSAPP mice was associated with plaques and co-localized with astrocytes and microglia. CONCLUSIONS: Collectively, these data support S100B inhibition as a novel strategy for reducing cortical plaque load, gliosis and neuronal dysfunction in AD and suggest that both extracellular as well as intracellular S100B contribute to AD histopathology.

Lipid oxidation and modification of amyloid-ß (Aß) in vitro and in vivo.

Oxidative damage and amyloid-ß (Aß) protein misfolding are prominent features of Alzheimer's disease (AD). In vitro studies indicated a direct linkage between these two features, where lipid oxidation products augmented Aß misfolding. We tested this linkage further, mimicking specific conditions present in amyloid plaques. In vitro lipid oxidation and lipid modification of Aß were thus performed with elevated levels of copper or physiological levels of calcium. These in vitro experiments were then confirmed by in vivo immunohistochemical and chemical tagging of oxidative damage in brains from the PSAPP mouse model of AD. Our in vitro findings indicate that: 1) high levels of copper prevent lipid oxidation; 2) physiological concentrations of calcium reduce 4 hydroxy-2-nonenal (HNE) modification of Aß; and 3) anti-Aß and HNE antibody epitopes are differentially masked. In vivo we demonstrated increased lipid oxidation around plaques but 4) a lack of immunological colocalization of HNE-adducts with Aß. Thus, the lack of colocalization of Aß and HNE-adduct immunostaining is most likely due to a combination of metals inhibiting HNE modification of Aß, quenching lipid oxidation and a masking of HNE-Aß histopathology. However, other forms of oxidative damage colocalize with Aß in plaques, as demonstrated using a chemical method for identifying oxidative damage. Additionally, these findings suggest that HNE modification of Aß may affect therapeutic antibodies targeting the amino terminal of Aß and that metals effect on lipid oxidation and lipid modification of Aß could raise concerns on emerging anti-AD treatments with metal chelators.

Centella asiatica extract selectively decreases amyloid beta levels in hippocampus of Alzheimer's disease animal model.

PSAPP mice expressing the 'Swedish' amyloid precursor protein and the M146L presenilin 1 mutations are a well-characterized model for spontaneous amyloid beta plaque formation. Centella asiatica has a long history of use in India as a memory enhancing drug in Ayurvedic literature. The study investigated whether Centella asiatica extract (CaE) can alter the amyloid pathology in PSAPP mice by administering CaE (2.5 or 5.0 g/kg/day) starting at 2 months of age prior to the onset of detectable amyloid deposition and continued for either 2 months or 8 months. A significant decrease in amyloid beta 1-40 and 1-42 was detectable by ELISA following an 8 month treatment with 2.5 mg/kg of CaE. A reduction in Congo Red stained fibrillar amyloid plaques was detected with the 5.0 mg/kg CaE dose and long-term treatment regimen. It was also confirmed that CaE functions as an antioxidant in vitro, scavenging free radicals, reducing lipid peroxidation and protecting against DNA damage. The data indicate that CaE can impact the amyloid cascade altering amyloid beta pathology in the brains of PSAPP mice and modulating components of the oxidative stress response that has been implicated in the neurodegenerative changes that occur with Alzheimer's disease.

Major depression, 5HTTLPR genotype, suicide and antidepressant influences on thalamic volume.

BACKGROUND: The 5HTTLPR genetic variant of the serotonin transporter gene (SERT or 5-HTT), which is comprised of a short (SERT-s) and a long (SERT-l) allele, is associated with major depressive disorder and post-traumatic brain disorder. AIMS: The present study sought to determine whether the total thalamus and major subregions are altered in size in major depressive disorder and in relation to the 5HTTLPR genotype. METHOD: We investigated the influence of 5HTTLPR genotype, psychiatric diagnosis, suicide and other clinical factors on the volume of the entire post-mortem thalamus. RESULTS: Major depressive disorder, SERT-ss genotype and suicide emerged as independent factors contributing to an enlargement of the total thalamus. The majority of the volume enlargement associated with the SERT-ss genotype occurred in the pulvinar, whereas enlargement associated with major depressive disorder occurred in the limbic nuclei and in other regions of the thalamus. A history of antidepressant treatment was associated with reduced thalamic volume. CONCLUSIONS: The 5HTTLPR genetic variation may affect behaviour and psychiatric conditions, in part, by altering the anatomy of the thalamus.

Neuroprotective mechanisms of ayurvedic antidementia botanical Bacopa monniera.

Alzheimer's disease is a neurodegenerative disorder characterized by progressive dementia. Bacopa monniera is described in the Ayurvedic Materia Medica, as a therapeutically useful herb for the treatment of cognitive impairment, thus supporting its possible anti-Alzheimer's properties. Our studies have shown that Bacopa monniera reduces beta-amyloid deposits in the brain of an Alzheimer's disease animal model. The objective of this study was to establish the presence of endogenous substances in Bacopa monniera extract (BmE) that will impact components of the oxidative stress cascade such as the reduction of divalent metals, scavenging of reactive oxygen species, alterations of lipoxygenase activity and hydrogen peroxide-induced lipid peroxidation. The extract contained polyphenols and sulfhydryl contents suggestive of endogenous antioxidant activity. The results demonstrated that BmE reduced divalent metals, dose-dependently scavenged reactive oxygen species, decreased the formation of lipid peroxides and inhibited lipoxygenase activity. These data combined with our previous studies that have shown that BmE treatment reduces beta-amyloid levels in the brain of an Alzheimer's disease doubly transgenic mouse model of rapid amyloid deposition (PSAPP mice) suggesting mechanisms of action relevant to the treatment of Alzheimer's disease.

5HTTLPR polymorphism and enlargement of the pulvinar: unlocking the backdoor to the limbic system.

BACKGROUND: The 5HTTLPR genetic variant of the serotonin transporter (SERT), which consists of a long (SERT-l) and short (SERT-s) allele, has emerged as a major factor influencing emotional behavior and brain anatomy. The pulvinar nucleus of the thalamus projects to important limbic nuclei including the amygdala and cingulate cortex, is involved in the processing of stimuli with emotional content, and contains an abundance of SERT. METHODS: Stereological methods were used to measure pulvinar neuron number in postmortem tissue from major depressive disorder (n = 11), bipolar disorder (n = 11), schizophrenia (n = 12), and control (n = 15) specimens from the Stanley Foundation Neuropathology Consortium. The effect of SERT genotype on pulvinar volume and neuron number was investigated by using analysis of covariance. RESULTS: Analysis of covariance with diagnosis, SERT genotype, age, hemisphere, postmortem interval, and time-in-formalin covariates identified a 20% increase in pulvinar neuron number and volume in SERT-ss subjects. CONCLUSIONS: The elevated number of pulvinar neurons in subjects with a SERT-ss genotype may serve to enhance subcortical input of emotionally relevant stimuli to the limbic system, providing a mechanism for the 5HTTLPR genetic variant to affect predisposition to conditions such as major depression.

Bacopa monniera extract reduces amyloid levels in PSAPP mice.

PSAPP mice expressing the "Swedish" amyloid precursor protein and M146L presenilin-1 mutations are a well-characterized model for spontaneous amyloid plaque formation. Bacopa monniera has a long history of use in India as an anti-aging and memory-enhancing ethnobotanical therapy. To evaluate the effect of Bacopa monniera extract (BME) on amyloid (Abeta) pathology in PSAPP mice, two doses of BME (40 or 160 mg/kg/day) were administered starting at 2 months of age for either 2 or 8 months. Our present data suggests that BME lowers Abeta 1-40 and 1-42 levels in cortex by as much as 60%, and reverses Y-maze performance and open field hyperlocomotion behavioral changes present in PSAPP mice. The areas encompassed by Congo Red-positive fibrillar amyloid deposits, however, were not altered by BME treatment. The data suggest that BME has potential application in Alzheimer's disease therapeutics.

Clozapine and the mitogen-activated protein kinase signal transduction pathway: implications for antipsychotic actions.

BACKGROUND: Mitogen-activated protein kinase (MAPK) signaling pathways respond to dopaminergic and serotonergic agents and mediate short- and long-term effects of intracellular signaling in neurons. Here we show that the antipsychotic agent, clozapine, selectively activates the MEK/ERK MAPK pathway, and inhibition of this pathway reverses clozapine's actions in the conditioned avoidance response (CAR) paradigm, a rodent behavioral assay of antipsychotic activity. METHODS: Phosphorylation patterns of MAPK pathway enzymes were determined by quantitative immunoblot analysis and immunohistochemistry of rat prefrontal cortex. Kinase inhibitors were used to assess the role of MAPK signaling pathways in mediating clozapine-induced suppression of CAR. RESULTS: Clozapine administration selectively increased phosphorylation of MEK1/2 but had no effect on p38 or JNK phosphorylation. Pretreatment with the 5-HT2A agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride blocked the clozapine-induced increase in MEK1/2 phosphorylation. Immunohistochemistry revealed that clozapine treatment elevated the number of cells in the prefrontal cortex positive for phosphoERK, the downstream substrate of MEK1/2. Prior administration of MEK1/2 inhibitors U0126 or Sl327, or ERK inhibitor 5-iodotubercidin, reversed suppression of CAR induced by clozapine, whereas administration of vehicle, JNK or p38 inhibitors (L-JNK-1 and SB203580, respectively) had no effect. Inhibition of kinases upstream to MEK1/2 (PI-3K, PKC, and CaMKII) by administration of LY294002, bisindolylmaleimide, or KN-62, respectively, also reversed clozapine-induced suppression of CAR. CONCLUSIONS: These data support the hypothesis that the MEK/ERK signal transduction cascade participates in clozapine's antipsychotic actions.

Elevated neuron number in the limbic thalamus in major depression.

OBJECTIVE: The mediodorsal and anteroventral/anteromedial nuclei of the thalamus are brain regions of interest in the study of mood disorders because they connect subcortical limbic system structures such as the amygdala with the prefrontal, cingulate, and temporal cortices. Anatomical abnormalities have been observed both in the amygdala and in the aforementioned cortical regions in affective disorder patients. Neuroanatomical studies of the thalamus have rarely been conducted in patients with mood disorders. METHOD: Postmortem tissue from the Stanley Foundation Brain Bank was obtained from subjects diagnosed with major depressive disorder, bipolar disorder, and schizophrenia as well as a nonpsychiatric comparison group (N=10-13 per group). The optical disector stereological procedure was used to count neurons in the mediodorsal and anteroventral/anteromedial nuclei of the thalamus in each brain. RESULTS: There were significantly more neurons in the mediodorsal (37%) and anteroventral/anteromedial (26%) nuclei in subjects with major depressive disorder relative to the nonpsychiatric comparison subjects. Neuron numbers and volumes in these limbic thalamic nuclei were normal in the schizophrenia and bipolar subjects. CONCLUSIONS: The data indicate that there is an elevation in total neuron number in the limbic thalamus that is specific for major depressive disorder. This represents the first report of a neuropsychiatric disorder being associated with an increase in total regional neuron number. The present findings, along with recent data, indicate that significant anatomical and functional abnormalities are present in limbic circuits in major depressive disorder.

Time course of the development of Alzheimer-like pathology in the doubly transgenic PS1+APP mouse.

Doubly transgenic mice expressing both a mutated amyloid precursor protein and a mutated presenilin-1 protein accumulate A(beta) deposits as they age. The early A(beta) deposits were found to be primarily composed of fibrillar A(beta) and resembled compact amyloid plaques. As the mice aged, nonfibrillar A(beta) deposits increased in number and spread to regions not typically associated with amyloid plaques in Alzheimer's disease. The fibrillar, amyloid-containing deposits remained restricted to cortical and hippocampal structures and did not increase substantially beyond the 12-month time point. Even at early time points, the fibrillar deposits were associated with dystrophic neurites and activated astrocytes expressing elevated levels of glial fibrillary acidic protein. Microglia similarly demonstrated increased staining for complement receptor-3 in the vicinity of A(beta) deposits at early time points. However, when MHC-II staining was used to assess the degree of microglial activation, full activation was not detected until mice were 12 months or older. Overall, the regional pattern of A(beta) staining resembles that found in Alzheimer disease; however, a progression from diffuse A(beta) to more compact amyloid deposits is not observed in the mouse model. It is noted that the activation of microglia at 12 months is coincident with the apparent stabilization of fibrillar A(beta) deposits, raising the possibility that activated microglia might clear fibrillar A(beta) deposits at a rate similar to their rate of formation, thereby establishing a relatively steady-state level of amyloid-containing deposits.