Accumulation of murine amyloid-ß mimics early Alzheimer's disease.

Amyloidosis mouse models of Alzheimer's disease are generally established by transgenic approaches leading to an overexpression of mutated human genes that are known to be involved in the generation of amyloid-ß in Alzheimer's families. Although these models made substantial contributions to the current knowledge about the 'amyloid hypothesis' of Alzheimer's disease, the overproduction of amyloid-ß peptides mimics only inherited (familiar) Alzheimer's disease, which accounts for <1% of all patients with Alzheimer's disease. The inherited form is even regarded a 'rare' disease according to the regulations for funding of the European Union (www.erare.eu). Here, we show that mice that are double-deficient for neprilysin (encoded by Mme), one major amyloid-ß-degrading enzyme, and the ABC transporter ABCC1, a major contributor to amyloid-ß clearance from the brain, develop various aspects of sporadic Alzheimer's disease mimicking the clinical stage of mild cognitive impairment. Using behavioural tests, electrophysiology and morphological analyses, we compared different ABC transporter-deficient animals and found that alterations are most prominent in neprilysin × ABCC1 double-deficient mice. We show that these mice have a reduced probability to survive, show increased anxiety in new environments, and have a reduced working memory performance. Furthermore, we detected morphological changes in the hippocampus and amygdala, e.g. astrogliosis and reduced numbers of synapses, leading to defective long-term potentiation in functional measurements. Compared to human, murine amyloid-ß is poorly aggregating, due to changes in three amino acids at N-terminal positions 5, 10, and 13. Interestingly, our findings account for the action of early occurring amyloid-ß species/aggregates, i.e. monomers and small amyloid-ß oligomers. Thus, neprilysin × ABCC1 double-deficient mice present a new model for early effects of amyloid-ß-related mild cognitive impairment that allows investigations without artificial overexpression of inherited Alzheimer's disease genes.

Sideritis spp. Extracts Enhance Memory and Learning in Alzheimer's ß-Amyloidosis Mouse Models and Aged C57Bl/6 Mice.

Nowadays, Alzheimer's disease is the most prevalent epiphenomenon of the aging population. Although soluble amyloid-ß (Aß) species (monomers, oligomers) are recognized triggers of the disease, no therapeutic approach is able to stop it. Herbal medicines are used to treat different diseases in many regions of the world. On the Balkan Peninsula, at the eastern Mediterranean Sea, and adjacent regions, Sideritis species are used as traditional medicine to prevent age-related problems in elderly. To evaluate this traditional knowledge in controlled experiments, we tested extracts of two commonly used Sideritis species, Sideritis euboea and Sideritis scardica, with regard to their effects on cognition in APP-transgenic and aged, non-transgenic C57Bl/6 mice. Additionally, histomorphological and biochemical changes associated with Aß deposition and treatment were assessed. We found that daily oral treatment with Sideritis spp. extracts highly enhanced cognition in aged, non-transgenic as well as in APP-transgenic mice, an effect that was even more pronounced when extracts of both species were applied in combination. The treatment strongly reduced Aß42 load in APP-transgenic mice, accompanied by increased phagocytic activity of microglia, and increased expression of the α-secretase ADAM10. Moreover, the treatment was able to fully rescue neuronal loss of APP-transgenic mice to normal levels as seen in non-transgenic controls. Having the traditional knowledge in mind, our results imply that treatment with Sideritis spp. extracts might be a potent, well-tolerated option for treating symptoms of cognitive impairment in elderly and with regard to Alzheimer's disease by affecting its most prominent hallmarks: Aß pathology and cognitive decline.

Reduced Alzheimer's disease pathology by St. John's Wort treatment is independent of hyperforin and facilitated by ABCC1 and microglia activation in mice.

Soluble ß-amyloid peptides (Aß) and small Aß oligomers represent the most toxic peptide moieties recognized in brains affected by Alzheimer's disease (AD). Here we provide the first evidence that specific St. John's wort (SJW) extracts both attenuate Aß-induced histopathology and alleviate memory impairments in APP-transgenic mice. Importantly, these effects are attained independently of hyperforin. Specifically, two extracts characterized by low hyperforin content (i) significantly decrease intracerebral Aß42 levels, (ii) decrease the number and size of amyloid plaques, (iii) rescue neocortical neurons, (iv) restore cognition to normal levels, and (iv) activate microglia in vitro and in vivo. Mechanistically, we reveal that the reduction of soluble Aß42 species is the consequence of a highly increased export activity in the bloodbrain barrier ABCC1transporter, which was found to play a fundamental role in Aß excretion into the bloodstream. These data (i) support the significant beneficial potential of SJW extracts on AD proteopathy, and (ii) demonstrate for the first time that hyperforin concentration does not necessarily correlate with their therapeutic effects. Hence, by activating ABC transporters, specific extracts of SJW may be used to treat AD and other diseases involving peptide accumulation and cognition impairment. We propose that the anti-depressant and anti-dementia effects of these hyperforin-reduced phytoextracts could be combined for treatment of the elderly, with a concomitant reduction in deleterious hyperforin-related side effects.

ABC transporters B1, C1 and G2 differentially regulate neuroregeneration in mice.

BACKGROUND: ATP-binding cassette (ABC) transporters are essential regulators of organismic homeostasis, and are particularly important in protecting the body from potentially harmful exogenous substances. Recently, an increasing number of in vitro observations have indicated a functional role of ABC transporters in the differentiation and maintenance of stem cells. Therefore, we sought to determine brain-related phenotypic changes in animals lacking the expression of distinct ABC transporters (ABCB1, ABCG2 or ABCC1). METHODOLOGY AND PRINCIPAL FINDINGS: Analyzing adult neurogenesis in ABC transporter-deficient animals in vivo and neuronal stem/progenitor cells in vitro resulted in complex findings. In vivo, the differentiation of neuronal progenitors was hindered in ABC transporter-deficient mice (ABCB1(0/0)) as evidenced by lowered numbers of doublecortin(+) (-36%) and calretinin(+) (-37%) cells. In vitro, we confirmed that this finding is not connected to the functional loss of single neural stem/progenitor cells (NSPCs). Furthermore, assessment of activity, exploratory behavior, and anxiety levels revealed behavioral alterations in ABCB1(0/0) and ABCC1(0/0) mice, whereas ABCG2(0/0) mice were mostly unaffected. CONCLUSION AND SIGNIFICANCE: Our data show that single ABC transporter-deficiency does not necessarily impair neuronal progenitor homeostasis on the single NSPC level, as suggested by previous studies. However, loss of distinct ABC transporters impacts global brain homeostasis with far ranging consequences, leading to impaired neurogenic functions in vivo and even to distinct behavioral phenotypes. In addition to the known role of ABC transporters in proteopathies such as Parkinson's disease and Alzheimer's disease, our data highlight the importance of understanding the general function of ABC transporters for the brain's homeostasis and the regeneration potential.

Determination of spatial and temporal distribution of microglia by 230nm-high-resolution, high-throughput automated analysis reveals different amyloid plaque populations in an APP/PS1 mouse model of Alzheimer's disease.

One early and prominent pathologic feature of Alzheimer's disease (AD) is the appearance of activated microglia in the vicinity of developing ß-amyloid deposits. However, the precise role of microglia during the course of AD is still under discussion. Microglia have been reported to degrade and clear ß-amyloid, but they also can exert deleterious effects due to overwhelming inflammatory reactions. Here, we demonstrate the occurrence of developing plaque populations with distinct amounts of associated microglia using time-dependent analyses of plaque morphology and the spatial distribution of microglia in an APP/PS1 mouse model. In addition to a population of larger plaques (>700µm(2)) that are occupied by a moderate contingent of microglial cells across the course of aging, a second type of small ß-amyloid deposits develops (≤400µm(2)) in which the plaque core is enveloped by a relatively large number of microglia. Our analyses indicate that microglia are strongly activated early in the emergence of senile plaques, but that activation is diminished in the later stages of plaque evolution (>150 days). These findings support the view that microglia serve to restrict the growth of senile plaques, and do so in a way that minimizes local inflammatory damage to other components of the brain.

Cerebral amyloid-ß proteostasis is regulated by the membrane transport protein ABCC1 in mice.

In Alzheimer disease (AD), the intracerebral accumulation of amyloid-ß (Aß) peptides is a critical yet poorly understood process. Aß clearance via the blood-brain barrier is reduced by approximately 30% in AD patients, but the underlying mechanisms remain elusive. ABC transporters have been implicated in the regulation of Aß levels in the brain. Using a mouse model of AD in which the animals were further genetically modified to lack specific ABC transporters, here we have shown that the transporter ABCC1 has an important role in cerebral Aß clearance and accumulation. Deficiency of ABCC1 substantially increased cerebral Aß levels without altering the expression of most enzymes that would favor the production of Aß from the Aß precursor protein. In contrast, activation of ABCC1 using thiethylperazine (a drug approved by the FDA to relieve nausea and vomiting) markedly reduced Aß load in a mouse model of AD expressing ABCC1 but not in such mice lacking ABCC1. Thus, by altering the temporal aggregation profile of Aß, pharmacological activation of ABC transporters could impede the neurodegenerative cascade that culminates in the dementia of AD.