Early-life stress elicits peripheral and brain immune activation differently in wild type and 5xFAD mice in a sex-specific manner.

BACKGROUND: The risk of developing Alzheimer's disease (AD) is modulated by genetic and environmental factors. Early-life stress (ELS) exposure during critical periods of brain development can impact later brain function and health, including increasing the risk of developing AD. Microglial dysfunction and neuroinflammation have been implicated as playing a role in AD pathology and may be modulated by ELS. To complicate matters further, sex-specific effects have been noted in response to ELS and in the incidence and progression of AD. METHODS: Here, we subjected male and female mice with either a wild type or 5xFAD familial AD-model background to maternal separation (MS) from postnatal day 2 to 14 to induce ELS. RESULTS: We detected hippocampal neuroinflammatory alterations already at postnatal day 15. By 4 months of age, MS mice presented increased immobility time in the forced swim test and a lower discrimination index in the novel object recognition memory test compared to controls. We found altered Bdnf and Arc expression in the hippocampus and increased microglial activation in the prefrontal cortex due to MS in a sex-dependent manner. In 5xFAD mice specifically, MS exacerbated amyloid-beta deposition, particularly in females. In the periphery, the immune cell population was altered by MS exposure. CONCLUSION: Overall, our results demonstrate that MS has both short- and long-term effects on brain regions related to memory and on the inflammatory system, both in the brain and periphery. These ELS-related effects that are detectable even in adulthood may exacerbate pathology and increase the risk of developing AD via sex-specific mechanisms.

Maternal separation differentially modulates early pathology by sex in 5xFAD Alzheimer's disease-transgenic mice.

Alzheimer's disease (AD) is the most common neurodegenerative disease. Most cases of AD are considered idiopathic and likely due to a combination of genetic, environmental, and lifestyle-related risk factors. Despite occurring decades before the typical age of an AD diagnosis, early-life stress (ELS) has been suggested to have long-lasting effects that may contribute to AD risk and pathogenesis. Still, the mechanisms that underlie the role of ELS on AD risk remain largely unknown. Here, we used 5xFAD transgenic mice to study relatively short-term alterations related to ELS in an AD-like susceptible mouse model at 6 weeks of age. To model ELS, we separated pups from their dams for 3 h per day from postnatal day 2-14. Around 6 weeks of age, we found that maternally separated (MS) 5xFAD mice, particularly female mice, displayed increased amyloid-ß-immunoreactivity in the anterior cingulate cortex (ACC) and basolateral amygdala (BLA). In anterior cingulate cortex, we also noted significantly increased intraneuronal amyloid-ß-immunoreactivity associated with MS but only in female mice. Moreover, IBA1-positive DAPI density was significantly increased in relation to MS in ACC and BLA, and microglia in BLA of MS mice had significantly different morphology compared to microglia in non-MS 5xFAD mice. Cytokine analysis showed that male MS mice, specifically, had increased levels of neuroinflammatory markers CXCL1 and IL-10 in hippocampal extracts compared to non-MS counterparts. Additionally, hippocampal extracts from both male and female MS 5xFAD mice had decreased levels of synapse- and activity-related markers Bdnf, 5htr6, Cox2, and Syp in hippocampus. Lastly, we performed behavioral tests to evaluate anxiety- and depressive-like behavior and working memory but could not detect any significant differences between groups. Overall, we detected several sex-specific molecular and cellular alterations in 6-week-old adolescent 5xFAD mice associated with MS that may help explain the connection between ELS and AD risk.

Estrogen reduces neuronal generation of Alzheimer beta-amyloid peptides.

Alzheimer's disease (AD) is characterized by the accumulation of cerebral plaques composed of 40- and 42-amino acid beta-amyloid (Abeta) peptides, and autosomal dominant forms of AD appear to cause disease by promoting brain Abeta accumulation. Recent studies indicate that postmenopausal estrogen replacement therapy may prevent or delay the onset of AD. Here we present evidence that physiological levels of 17beta-estradiol reduce the generation of Abeta by neuroblastoma cells and by primary cultures of rat, mouse and human embryonic cerebrocortical neurons. These results suggest a mechanism by which estrogen replacement therapy can delay or prevent AD.

Metal chelator decreases Alzheimer beta-amyloid plaques.

Transgenic mice developing beta-amyloid (Abeta) plaques are advancing experimental treatment strategies for Alzheimer's disease. The metal chelator, clioquinol, is reported by Cherny et al. (2001) to reduce Abeta plaques, presumably by chelation of Abeta-associated zinc and copper. This and other recent Abeta-modulating treatment approaches are discussed.

Pre-plaque conformational changes in Alzheimer's disease-linked Aß and APP.

Reducing levels of the aggregation-prone Aß peptide that accumulates in the brain with Alzheimer's disease (AD) has been a major target of experimental therapies. An alternative approach may be to stabilize the physiological conformation of Aß. To date, the physiological state of Aß in brain remains unclear, since the available methods used to process brain tissue for determination of Aß aggregate conformation can in themselves alter the structure and/or composition of the aggregates. Here, using synchrotron-based Fourier transform infrared micro-spectroscopy, non-denaturing gel electrophoresis and conformational specific antibodies we show that the physiological conformations of Aß and amyloid precursor protein (APP) in brain of transgenic mouse models of AD are altered before formation of amyloid plaques. Furthermore, focal Aß aggregates in brain that precede amyloid plaque formation localize to synaptic terminals. These changes in the states of Aß and APP that occur prior to plaque formation may provide novel targets for AD therapy.

Stimulation of beta-amyloid precursor protein trafficking by insulin reduces intraneuronal beta-amyloid and requires mitogen-activated protein kinase signaling.

Alzheimer's Disease (AD) is characterized by cerebral accumulation of beta-amyloid peptides (Abeta), which are proteolytically derived from beta-amyloid precursor protein (betaAPP). betaAPP metabolism is highly regulated via various signal transduction systems, e.g., several serine/threonine kinases and phosphatases. Several growth factors known to act via receptor tyrosine kinases also have been demonstrated to regulate sbetaAPP secretion. Among these receptors, insulin and insulin-like growth factor-1 receptors are highly expressed in brain, especially in hippocampus and cortex. Emerging evidence indicates that insulin has important functions in brain regions involved in learning and memory. Here we present evidence that insulin significantly reduces intracellular accumulation of Abeta and that it does so by accelerating betaAPP/Abeta trafficking from the trans-Golgi network, a major cellular site for Abeta generation, to the plasma membrane. Furthermore, insulin increases the extracellular level of Abeta both by promoting its secretion and by inhibiting its degradation via insulin-degrading enzyme. The action of insulin on betaAPP metabolism is mediated via a receptor tyrosine kinase/mitogen-activated protein (MAP) kinase kinase pathway. The results suggest cell biological and signal transduction mechanisms by which insulin modulates betaAPP and Abeta trafficking in neuronal cultures.

Highly selective effects of nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 on intact and injured basal forebrain magnocellular neurons.

Cholinergic neurons of the basal nucleus complex (BNC) respond to nerve growth factor (NGF), the first member of a polypeptide gene family that also includes brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5). NGF, BDNF, and NT-3 are enriched in hippocampus. In addition, NGF and, more recently, BDNF have been shown to stimulate the cholinergic differentiation and enhance the survival of BNC cells in vitro. The present investigation was designed to test, in a comparative fashion, the in vivo effects of human recombinant NGF, BDNF, and NT-3 with confirmed activities in vitro on cholinergic and gamma-aminobutyric acid (GABA)-ergic BNC neurons. The specific questions asked were whether and, to what extent, biologically active recombinant neurotrophins stimulate the transmitter phenotypes of intact cholinergic and GABAergic neurons of the BNC, and whether, and to what extent, recombinant neurotrophins protect the transmitter phenotypes of axotomized cholinergic and GABAergic neurons of the BNC following complete transections of the fimbria-fornix (measured by ChAT enzyme activity and ChAT immunoreactivity and ChAT, p75NGFR, and GAD mRNA hybridization). Our results confirm the profound stimulatory and protective effects of recombinant NGF on the transmitter phenotype of cholinergic BNC neurons at the mRNA and protein levels. The effect of NGF on injured cholinergic neurons of the BNC is very specific and saturated at a dose of 20 micrograms/2 weeks. BDNF appeared to increase moderately p75NGFR expression in both intact and axotomized cholinergic neurons and to exert minor effects on some cholinergic markers (e.g., ChAT immunoreactivity). NT-3 had no effects on cholinergic neurons or the BNC. Moreover, NGF, BDNF, and NT-3 had no influence on GABAergic BNC neurons. Taken together, these results indicate that, despite their significant sequence homologies and their shared abundance in target fields of BNC neurons, NGF, BDNF, and NT-3 show striking differences in their efficacies as cholinergic trophic factors. GABAergic neurons of the BNC are resistant to neurotrophins. The results of the present investigation establish that NGF excels among neurotrophins as a trophic factor for intact and injured basal forebrain cholinergic neurons.

Cellular and molecular basis of beta-amyloid precursor protein metabolism.

In molecular neurobiology, perhaps no molecule has been as thoroughly examined as Alzheimer's beta-amyloid precursor protein (betaAPP). In the ten years since the cDNA encoding betaAPP was cloned, the protein has been the subject of unparalleled scrutiny on all levels. From molecular genetics and cellular biology to neuroanatomy and epidemiology, no scientific discipline has been left unexplored - and with good reason. beta-amyloid (Abeta) is the main constituent of the amyloidogenic plaques which are a primary pathological hallmark of Alzheimer's disease, and betaAPP is the protein from which Abeta is cleaved and released. Unraveling the molecular events underlying Abeta generation has been, and remains, of paramount importance to scientists in our field. In this review we will trace the progress that has been made in understanding the molecular and cellular basis of betaAPP trafficking and processing, or alternatively stated, the molecular basis for Abeta generation. Imperative to a complete understanding of Abeta generation is the delineation of its subcellular localization and the identification of proteins which play either direct or accessory roles in Abeta generation. We will focus on the regulation of betaAPP cleavage through diverse signal transduction mechanisms and discuss possible points of therapeutic intercession in what has been postulated to be a seminal molecular step in the cascade of events terminating in the onset of dementia, a loss of neurons, and tragically, eventual death from Alzheimer's disease.

Cellular and molecular basis of beta-amyloid precursor protein metabolism.

In molecular neurobiology, perhaps no molecule has been as thoroughly examined as Alzheimer's beta-amyloid precursor protein (beta-APP). In the years since the cDNA encoding beta-APP was cloned, the protein has been the subject of unparalleled scrutiny on all levels. From molecular genetics and cellular biology to neuroanatomy and epidemiology, no scientific discipline has been left unexplored - and with good reason. beta-amyloid (Abeta) is the main constituent of the amyloidogenic plaques which are a primary pathological hallmark of Alzheimer's disease, and bta-APP is the protein from which Abeta is cleaved and released. Unraveling the molecular events underlying Abeta generation has been, and remains, of paramount importance to scientists in our field. In this review we will trace the progress that has been made in understanding the molecular and cellular basis of beta-APP trafficking and processing, or alternatively stated, the molecular basis for Abeta generation. Imperative to a complete understanding of Abeta generation is the delineation of its subcellular localization and the identification of proteins that play either direct or accessory roles in Abeta generation. We will focus on the regulation of beta-APP cleavage through diverse signal transduction mechanisms and discuss possible points of therapeutic intercession in what has been postulated to be a seminal molecular step in the cascade of events terminating in the onset of dementia, loss of neurons, and eventual death from Alzheimer's disease.

Mesencephalic clefts with associated eye movement disorders.

OBJECTIVE: To describe two patients with mesencephalic midline clefts and associated eye movement disorders. DESIGN: Case reports. RESULTS: The first patient developed bilateral internuclear ophthalmoplegia with exotropia, reduced convergence, right ptosis, right fourth-nerve palsy, and right elevator palsy several years after meningitis with hydrocephalus. The second patient had bilateral internuclear ophthalmoplegia with exotropia, reduced convergence, bilateral ptosis, limited upward gaze, and right hypertropia since childhood. In both patients, magnetic resonance imaging showed a midline cleft extending from the cerebral aqueduct into the midbrain. CONCLUSION: It is likely that the clefts affected the oculomotor nuclei and medial longitudinal fasciculi, accounting for the eye movement disorders.

Alzheimer beta-amyloid peptides: normal and abnormal localization.

Alzheimer's disease (AD) neuropathology is characterized by accumulation of "senile" plaques (SPs) and neurofibrillary tangles (NFTs) in vulnerable brain regions. SPs are principally composed of aggregates of up to 42/43 amino acid beta-amyloid (A beta) peptides. The discovery of familial AD (FAD) mutations in the genes for the amyloid precursor protein (APP) and presenilins (PSs), all of which increase A beta42 production, support the view that A beta is centrally involved in the pathogenesis of AD. A beta42 aggregates readily, and is thought to seed the formation of fibrils, which then act as templates for plaque formation. A beta is generated by the sequential intracellular cleavage of APP by beta-secretase to generate the N-terminal end of A beta, and intramembranous cleavage by gamma-secretase to generate the C-terminal end. Cell biological studies have demonstrated that A beta is generated in the ER, Golgi, and endosomal/lysosomal system. A central question involving the role of A beta in AD concerns how A beta causes disease and whether it is extracellular A beta deposition and/or intracellular A beta accumulation that initiates the disease process. The most prevalent view is that SPs are composed of extracellular deposits of secreted A beta and that A beta causes toxicity to surrounding neurons as extracellular SP. The recent emphasis on the intracellular biology of APP and A beta has led some investigators to consider the possibility that intraneuronal A beta may directly cause toxicity. In this review we will outline current knowledge of the localization of both intracellular and extracellular A beta.

Tyrosine-hydroxylase-containing neurons in the primate basal forebrain magnocellular complex.

Immunocytochemistry and in situ hybridization for tyrosine hydroxylase (TH) were used to study the distribution of putative catecholaminergic neurons in the basal forebrain magnocellular complex (BFMC) of monkeys and humans. Magnocellular TH-expressing neurons in the primate BFMC are distributed along a rostrocaudal gradient, with the largest proportion of these cells located in the medial septal nucleus and nucleus of the diagonal band of Broca; smaller TH-containing neurons generally follow the same distribution. These findings suggest that, within rostromedial segments of the BFMC, there is a distinct subpopulation of neurons that express catecholamine-synthesizing enzymes. Further research is necessary to establish whether these neurons utilize one or more catecholamines as neurotransmitters.

Decreased senile plaque density in Alzheimer neocortex adjacent to an omental transposition.

Post-mortem studies of the brain of an Alzheimer patient indicate fewer senile plaques in the crests of cortical gyri underneath an omental transposition than in neighboring cortical areas.

Increased apolipoprotein E epsilon 4 in epilepsy with senile plaques.

Inheritance of the apolipoprotein E (ApoE) epsilon 4 allele is a risk factor for Alzheimer's disease (AD) and is associated with increased deposition of beta-amyloid (A beta) in AD, Down's syndrome, and normal aging. A beta deposition in the form of senile plaques (SPs) has recently been described in patients with temporal lobe epilepsy (TLE). We studied the relationship between ApoE epsilon 4 genotype and the deposition of A beta in temporal lobe tissue from patients who underwent temporal lobectomy for intractable epilepsy. TLE patients with SPs had a 70% ApoE epsilon 4 carrier frequency compared with a 27% carrier frequency among age-matched TLE controls without SPs. Our data suggest that the association between ApoE epsilon 4 and intracerebral A beta accumulation is not unique to the elderly or to those with dementia, and may be a feature of conditions in which there is both an ApoE epsilon 4 allele and over-production of A beta precursor protein, and, presumably, A beta.

Testosterone reduces neuronal secretion of Alzheimer's beta-amyloid peptides.

Alzheimer's disease (AD) is characterized by the age-related deposition of beta-amyloid (Abeta) 40/42 peptide aggregates in vulnerable brain regions. Multiple levels of evidence implicate a central role for Abeta in the pathophysiology of AD. Abeta peptides are generated by the regulated cleavage of an approximately 700-aa Abeta precursor protein (betaAPP). Full-length betaAPP can undergo proteolytic cleavage either within the Abeta domain to generate secreted sbetaAPPalpha or at the N- and C-terminal domain(s) of Abeta to generate amyloidogenic Abeta peptides. Several epidemiological studies have reported that estrogen replacement therapy protects against the development of AD in postmenopausal women. We previously reported that treating cultured neurons with 17beta-estradiol reduced the secretion of Abeta40/42 peptides, suggesting that estrogen replacement therapy may protect women against the development of AD by regulating betaAPP metabolism. Increasing evidence indicates that testosterone, especially bioavailable testosterone, decreases with age in older men and in postmenopausal women. We report here that treatment with testosterone increases the secretion of the nonamyloidogenic APP fragment, sbetaAPPalpha, and decreases the secretion of Abeta peptides from N2a cells and rat primary cerebrocortical neurons. These results raise the possibility that testosterone supplementation in elderly men may be protective in the treatment of AD.

Myotonia in colchicine myoneuropathy.

Colchicine may induce a myoneuropathy in patients with renal insufficiency. To date, myotonia has not been described in this disorder. We recently studied 4 patients treated with routine doses of colchicine who, in the setting of renal insufficiency, developed a severe myoneuropathy characterized by prominent myotonic discharges on electromyography. In addition, 1 of the 4 patients had profound clinical myotonia. In the 3 patients in whom biopsies were performed, marked myopathic change with intracytoplasmic vacuolization was identified. All 4 patients improved rapidly with discontinuation of the medication. The patient in whom electrophysiologic studies were repeated had a complete resolution of the myotonic discharges. Colchicine myoneuropathy can present with prominent clinical and electrophysiologic myotonia that resolves completely with discontinuation of the medication.

Generation and regulation of beta-amyloid peptide variants by neurons.

Studies of processing of the Alzheimer beta-amyloid precursor protein (betaAPP) have been performed to date mostly in continuous cell lines and indicate the existence of two principal metabolic pathways: the "beta-secretase" pathway, which generates beta-amyloid (A beta(1-40/42); approximately 4 kDa), and the "alpha-secretase" pathway, which generates a smaller fragment, the "p3" peptide (A beta(17-40/42); approximately 3 kDa). To determine whether similar processing events underlie betaAPP metabolism in neurons, media were examined following conditioning by primary neuronal cultures derived from embryonic day 17 rats. Immunoprecipitates of conditioned media derived from [35S]methionine pulse-labeled primary neuronal cultures contained 4- and 3-kDa A beta-related species. Radiosequencing analysis revealed that the 4-kDa band corresponded to conventional A beta beginning at position A beta(Asp1), whereas both radiosequencing and immunoprecipitation-mass spectrometry analyses indicated that the 3-kDa species in these conditioned media began with A beta(Glu11) at the N terminus, rather than A beta(Leu17) as does the conventional p3 peptide. Either activation of protein kinase C or inhibition of protein phosphatase 1/2A increased soluble betaAPP(alpha) release and decreased generation of both the 4-kDa A beta and the 3-kDa N-truncated A beta. Unlike results obtained with continuously cultured cells, protein phosphatase 1/2A inhibitors were more potent at reducing A beta secretion by neurons than were protein kinase C activators. These data indicate that rodent neurons generate abundant A beta variant peptides and emphasize the role of protein phosphatases in modulating neuronal A beta generation.