Arne Herring

Environmental enrichment enhances cellular plasticity in transgenic mice with Alzheimer-like pathology

Alzheimers disease (AD) is accompanied by hippocampal neuronal loss and abnormal neurogenesis, both of which probably contributing to AD-related cognitive deficits. Mounting evidence indicates that cognitive and physical stimulation provided by environmental enrichment improves neurogenesis in healthy animals and counteracts beta-amyloid pathology in mouse models of AD. Here, we hypothesized that environmental enrichment has also an impact on hippocampal neurogenesis in mice with AD-like pathology. Therefore, TgCRND8 mice and wild type littermates were either housed under standard conditions or in an enriched environment for 4 months. Standard housed TgCRND8 mice revealed diminished hippocampal cell proliferation and reduced number of mature newborn neurons compared to wild type littermates under the same housing condition. However, environmental enrichment reversed this genotype effect. Here, we show that cognitive and physical stimulation is capable of increasing the number of newborn mature hippocampal neurons in transgenic mice to wild type levels. Moreover, the expression of various plasticity associated molecules was enhanced in transgenic mice due to enriched housing. This study identifies that environmental enrichment improves diminished cellular plasticity in AD brain, probably enhancing the brain capacity to better compensate for neurodegeneration.

Wheel-running in a transgenic mouse model of Alzheimer's disease: Protection or symptom?

Several studies on both humans and animals reveal benefits of physical exercise on brain function and health. A previous study on TgCRND8 mice, a transgenic model of Alzheimers disease, reported beneficial effects of premorbid onset of long-term access to a running wheel on spatial learning and plaque deposition. Our study investigated the effects of access to a running wheel after the onset of Abeta pathology on behavioural, endocrinological, and neuropathological parameters. From day 80 of age, the time when Abeta deposition becomes apparent, TgCRND8 and wildtype mice were kept with or without running wheel. Home cage behaviour was analysed and cognitive abilities regarding object recognition memory and spatial learning in the Barnes maze were assessed. Our results show that, in comparison to Wt mice, Tg mice were characterised by impaired object recognition memory and spatial learning, increased glucocorticoid levels, hyperactivity in the home cage and high levels of stereotypic behaviour. Access to a running wheel had no effects on cognitive or neuropathological parameters, but reduced the amount of stereotypic behaviour in transgenics significantly. Furthermore, wheel-running was inversely correlated with stereotypic behaviour, suggesting that wheel-running may have stereotypic qualities. In addition, wheel-running positively correlated with plaque burden. Thus, in a phase when plaques are already present in the brain, it may be symptomatic of brain pathology, rather than protective. Whether or not access to a running wheel has beneficial effects on Alzheimer-like pathology and symptoms may therefore strongly depend on the exact time when the wheel is provided during development of the disease.

Environmental Enrichment Counteracts Alzheimer’s Neurovascular Dysfunction in TgCRND8 Mice

We and others have recently demonstrated that cognitive and physical stimulation in form of environmental enrichment reduces cerebral β‐amyloid (Aβ) deposition in transgenic mouse models of Alzheimer’s disease. This effect was independent from amyloid precursor protein (APP) expression or processing and rather a consequence of enhanced clearance of Aβ. However, the detailed mechanisms remain unclear. In the present study, we show that environmental enrichment in TgCRND8 mice (carrying human APPSwedish+Indiana) affect the neurovascular unit by increased angiogenesis and differential regulation of Aβ receptor/transporter molecules, namely up‐regulation of LRP1, ApoE and A2M as well as down‐regulation of RAGE so that brain to blood Aβ clearance is facilitated. These results suggest a hitherto unknown effect of environmental enrichment counteracting the vascular dysfunction in Alzheimer diseased brain.

Exercise during pregnancy mitigates Alzheimer-like pathology in mouse offspring

Physical activity protects brain function in healthy individuals and those with Alzheimers disease (AD). Evidence for beneficial effects of parental exercise on the health status of their progeny is sparse and limited to nondiseased individuals. Here, we questioned whether maternal running interferes with offsprings AD‐like pathology and sought to decipher the underlying mechanisms in TgCRND8 mice. Maternal stimulation was provided by voluntary wheel running vs. standard housing during pregnancy. Following 5 mo of standard housing of transgenic and wild‐type offspring, their brains were examined for AD‐related pathology and/or plasticity changes. Running during pregnancy reduced β‐amyloid (Aβ) plaque burden (–35%, P= 0.017) and amyloidogenic APP processing in transgenic offspring and further improved the neurovascular function by orchestrating different Aβ transporters and increasing angiogenesis (+29%, P=0.022). This effect was accompanied by diminished inflammation, as indicated by reduced microgliosis (–20%, P=0.002) and down‐regulation of other proinflammatory mediators, and resulted in less oxidative stress, as nitrotyrosine levels declined (–28%, P=0.029). Moreover, plasticity changes (in terms of up‐regulation of reelin, synaptophysin, and ARC) were found not only in transgenic but also in wild‐type offspring. We conclude that exercise during pregnancy provides long‐lasting protection from neurodegeneration and improves brain plasticity in the otherwise unstimulated progeny.—Herring, A., Donath, A., Yarmolenko, M., Uslar, E., Conzen, C., Kanakis, D., Bosma, C., Worm, K., Paulus, W., Keyvani, K. Exercise during pregnancy mitigates Alzheimer‐like pathology in mouse offspring. FASEB J. 26, 117–128 (2012). www.fasebj.org

Reduction of Cerebral Oxidative Stress Following Environmental Enrichment in Mice with Alzheimer-Like Pathology

Oxidative stress is a key feature during progression of chronic neurodegenerative conditions such as Alzheimers disease. In aging humans and animals, voluntary exercise lowers oxidative stress reactions. Additionally, recent work in our lab demonstrated that cognitive and physical stimulation (termed environmental enrichment) counteracts amyloid beta pathology, neurovascular dysfunction and behavioral symptoms in mice with Alzheimer‐like disease. Based on these facts, we hypothesized that cognitive and physical activity can also protect against oxidative stress in Alzheimer‐diseased brain. We, therefore, kept female TgCRND8 mice under standard and enriched housing from day 30 until 5 months of age. Environmental stimulation attenuated pro‐oxidative processes and triggered anti‐oxidative defense mechanisms as indicated by diminished biomarkers for reactive oxygen and nitrogen species, downregulation of pro‐inflammatory and pro‐oxidative mediators, decreased expression of pro‐apoptotic caspases, and upregulation of SOD1 and SOD2. This study identifies a thus far undescribed antagonizing effect of environmental stimulation on Alzheimers disease‐related oxidative damage.

Levodopa ameliorates learning and memory deficits in a murine model of Alzheimer's disease

Dopamine plays an important role in learning and memory processes. A deficit of this neurotransmitter as it is apparent in Alzheimers disease (AD) may contribute to cognitive decline, a major symptom of AD patients. The aim of this study was to elucidate whether or not stimulation of the dopaminergic system leads to an improvement of cognitive function and reduction of non-cognitive behavioral alterations in a murine model of AD. Transgenic and wild type male mice of the TgCRND8 line were treated either with the dopamine precursor levodopa or vehicle and tested in two learning tasks, the object-recognition task and the Barnes maze test. Additionally 24 h spontaneous behavior in the home cage was analyzed. In both memory tasks wild type mice performed significantly better than transgenics. However, transgenics treated with levodopa showed a significant object recognition memory and improved acquisition of spatial memory in the Barnes maze compared to vehicle treated transgenics. Concerning spontaneous behavior transgenic mice performed much more stereotypies than wild types. However, there was a trend for reduced stereotypies in the levodopa group in the time the drug was active. Neurochemical analysis revealed elevated levels of dopamine in the neostriata and frontal cortices and reduced levels in the hippocampi of transgenic mice compared to wild types. Thus cognitive deficits and stereotypies may be due to changes in the dopaminergic system as they could be ameliorated by levodopa treatment, that might also have a therapeutic significance for AD.

Reelin Depletion is an Early Phenomenon of Alzheimer's Pathology

Alterations in the expression of Reelin (RELN) have been implicated in the pathology of Alzheimers disease (AD). However, whether these changes are cause or consequence of AD remains to be resolved. To better understand the role of RELN pathway in the development of AD, we examined the expression profile of RELN and its downstream signaling members APOER2, VLDLR, and DAB1 in AD-vulnerable regions of transgenic and wildtype mice as well as in AD patients and controls across disease stages and/or aging. We show that both AD pathology and aging are associated with perturbation of the RELN pathway in a species-, region-, and molecule-specific manner. Further, we show that depletion of RELN, but not its downstream signaling molecules, is detectable long before the onset of amyloid-β pathology in the murine hippocampus and in a pre-clinical AD stage in the human frontal cortex. This early event hints at a possible causative role of RELN decline in the precipitation of AD pathology and supports RELNs potential as a pre-clinical marker for AD.

Preventive and therapeutic types of environmental enrichment counteract beta amyloid pathology by different molecular mechanisms

Combined preventive and therapeutic physical/cognitive stimulation starting before disease onset and continuing over its progression reduce Alzheimer-related pathology in transgenic mice. We now report that exposure of TgCRND8 mice to an enriched environment as either a preventive or therapeutic approach is also capable to reduce Aβ burden, though with different plaque and cerebral amyloid angiopathy (CAA) morphology. Preventive treatment resulted in fewer and smaller plaques without affecting CAA, whereas in therapeutically treated mice beside reduction of CAA extent, numerous plaques of strongly diminished size were found, so that total plaque loads declined as well. These effects seemed to be mediated by distinct molecular pathways. In preventive but not therapeutic group a shift of Aβ(42/40) ratio towards Aβ(40) and up-regulation of Aβ clearing and degrading molecules were found. Contrariwise anti-oxidative defense mechanisms were induced only in therapy but not preventive group. We hypothesize that preventive enrichment lowers the amounts of plaque seeds and decelerates plaque growth by degradation and clearance of Aβ, while therapeutic enrichment mitigates growth and fusion of plaque seeds to large plaques by inhibiting further Aβ aggregation. This study provides an experimental basis for application of physical/cognitive training in both prophylaxis and therapy of Alzheimers disease.

Acute systemic rapamycin induces neurobehavioral alterations in rats

Rapamycin is a drug with antiproliferative and immunosuppressive properties, widely used for prevention of acute graft rejection and cancer therapy. It specifically inhibits the activity of the mammalian target of rapamycin (mTOR), a protein kinase known to play an important role in cell growth, proliferation and antibody production. Clinical observations show that patients undergoing therapy with immunosuppressive drugs frequently suffer from affective disorders such as anxiety or depression. However, whether these symptoms are attributed to the action of the distinct compounds remains rather elusive. The present study investigated in rats neurobehavioral consequences of acute rapamycin treatment. Systemic administration of a single low dose rapamycin (3mg/kg) led to enhanced neuronal activity in the amygdala analyzed by intracerebral electroencephalography and FOS protein expression 90min after drug injection. Moreover, behavioral investigations revealed a rapamycin-induced increase in anxiety-related behaviors in the elevated plus-maze and in the open-field. The behavioral alterations correlated to enhanced amygdaloid expression of KLK8 and FKBP51, proteins that have been implicated in the development of anxiety and depression. Together, these results demonstrate that acute blockade of mTOR signaling by acute rapamycin administration not only causes changes in neuronal activity, but also leads to elevated protein expression in protein kinase pathways others than mTOR, contributing to the development of anxiety-like behavior. Given the pivotal role of the amygdala in mood regulation, associative learning, and modulation of cognitive functions, our findings raise the question whether therapy with rapamycin may induce alterations in patients neuropsychological functioning.

Amyloid-β dimers in the absence of plaque pathology impair learning and synaptic plasticity.

Despite amyloid plaques, consisting of insoluble, aggregated amyloid-β peptides, being a defining feature of Alzheimers disease, their significance has been challenged due to controversial findings regarding the correlation of cognitive impairment in Alzheimers disease with plaque load. The amyloid cascade hypothesis defines soluble amyloid-β oligomers, consisting of multiple amyloid-β monomers, as precursors of insoluble amyloid-β plaques. Dissecting the biological effects of single amyloid-β oligomers, for example of amyloid-β dimers, an abundant amyloid-β oligomer associated with clinical progression of Alzheimers disease, has been difficult due to the inability to control the kinetics of amyloid-β multimerization. For investigating the biological effects of amyloid-β dimers, we stabilized amyloid-β dimers by an intermolecular disulphide bridge via a cysteine mutation in the amyloid-β peptide (Aβ-S8C) of the amyloid precursor protein. This construct was expressed as a recombinant protein in cells and in a novel transgenic mouse, termed tgDimer mouse. This mouse formed constant levels of highly synaptotoxic soluble amyloid-β dimers, but not monomers, amyloid-β plaques or insoluble amyloid-β during its lifespan. Accordingly, neither signs of neuroinflammation, tau hyperphosphorylation or cell death were observed. Nevertheless, these tgDimer mice did exhibit deficits in hippocampal long-term potentiation and age-related impairments in learning and memory, similar to what was observed in classical Alzheimers disease mouse models. Although the amyloid-β dimers were unable to initiate the formation of insoluble amyloid-β aggregates in tgDimer mice, after crossbreeding tgDimer mice with the CRND8 mouse, an amyloid-β plaque generating mouse model, Aβ-S8C dimers were sequestered into amyloid-β plaques, suggesting that amyloid-β plaques incorporate neurotoxic amyloid-β dimers that by themselves are unable to self-assemble. Our results suggest that within the fine interplay between different amyloid-β species, amyloid-β dimer neurotoxic signalling, in the absence of amyloid-β plaque pathology, may be involved in causing early deficits in synaptic plasticity, learning and memory that accompany Alzheimers disease.