Altered palmitoylation and neuropathological deficits in mice lacking HIP14

Huntingtin interacting protein 14 (HIP14, ZDHHC17) is a huntingtin (HTT) interacting protein with palmitoyl transferase activity. In order to interrogate the function of Hip14, we generated mice with disruption in their Hip14 gene. Hip14-/- mice displayed behavioral, biochemical and neuropathological defects that are reminiscent of Huntington disease (HD). Palmitoylation of other HIP14 substrates, but not Htt, was reduced in the Hip14-/- mice. Hip14 is dysfunctional in the presence of mutant htt in the YAC128 mouse model of HD, suggesting that altered palmitoylation mediated by HIP14 may contribute to HD.     

Intracellular Abeta and cognitive deficits precede beta-amyloid deposition in transgenic arcAbeta mice

The brain pathology of Alzheimer's disease is characterized by abnormally aggregated Abeta in extracellular beta-amyloid plaques and along blood vessel walls, but the relation to intracellular Abeta remains unclear. To address the role of intracellular Abeta deposition in vivo, we expressed human APP with the combined Swedish and Arctic mutations in mice (arcAbeta mice). Intracellular punctate deposits of Abeta occurred concomitantly with robust cognitive impairments at the age of 6 months before the onset of beta-amyloid plaque formation and cerebral beta-amyloid angiopathy. beta-Amyloid plaques from arcAbeta mice had distinct dense-core morphologies with blood vessels appearing as seeding origins, suggesting reduced clearance of Abeta across blood vessels in arcAbeta mice. The co-incidence of intracellular Abeta deposits with behavioral deficits support an early role of intracellular Abeta in the pathophysiological cascade leading to beta-amyloid formation and functional impairment.     

Reversal of presynaptic deficits of apolipoprotein E-deficient mice in human apolipoprotein E transgenic mice

Apolipoprotein E genotype is an important risk factor of Alzheimer's disease, which is associated with the degeneration of distinct brain neuronal systems. In the present study we employed apolipoprotein E-deficient mice and human apolipoprotein E3 and apolipoprotein E4 transgenic mice on a null mouse apolipoprotein E background, to examine the extent to which distinct brain neuronal systems are affected by apolipoprotein E and the isoform specificity of this effect. This was pursued by histological and autoradiographic measurements utilizing neuron specific presynaptic markers. The results thus obtained revealed significant reductions in the levels of brain cholinergic and noradrenergic nerve terminals in young apolipoprotein E-deficient mice and no changes in brain dopaminergic nerve terminals. These cholinergic and noradrenergic presynaptic derangements were ameliorated similarly in human apolipoprotein E3 and apolipoprotein E4 transgenic mice. In the case of the cholinergic system, this resulted in complete reversal of the presynaptic deficits, whereas in the case of the noradrenergic neurons the amelioration was partial.These findings suggest that brain cholinergic and noradrenergic neurons are markedly more dependent on brain apolipoprotein E than brain dopaminergic neurons and that the isoform specificity of these effects is not apparent at a young age under non-challenged conditions.     

Heterogeneity of semantic and visuospatial deficits in early Alzheimer's disease

Staging of visuospatial and semantic deficits in patients with dementia of the Alzheimer type (DAT) was examined. The authors hypothesized that semantic ability would be more impaired in these patients, reflecting predominant temporal pathology early in the disease. However, in the 1st study (n = 26), 3 patients (11.5%) had marked visual but no semantic impairment. This finding was extended in a 2nd study with a 2nd patient sample (n = 21) and more specific tasks. Two patients (9.5%) again had visual but no semantic impairment. These studies confirm that, in patients with DAT presenting with relatively focal deficits, visual deficits sometimes occur before semantic problems. The findings are discussed with regard to the cognitive demands and neuroanatomical underpinning of the tests used and point to the necessity of using cognitively specific tests to enable accurate analysis of deficits in the context of the neuroanatomical basis of impairment.     

Altered atrial neurotransmitter release in transgenic p75 and gp130 KO mice

Heart rate is controlled by stimulatory sympathetic and inhibitory parasympathetic nerves innervating the sino-atrial node and cardiac conduction system. Sympathetic release of norepinephrine (NE) and parasympathetic release of acetylcholine (ACh) are controlled by the central nervous system, and by pre-synaptic inhibition of transmitter release within the atria. An increase in cardiac sympathetic transmission relative to parasympathetic transmission is pathological as it can lead to disturbances in heart rhythm, catecholaminergic toxicity and development of arrhythmias or fibrillation. Mice lacking the p75 neurotrophin receptor (p75^−/−) have elevated atrial NE but a low heart rate suggesting autonomic dysregulation. Similarly, mice whose sympathetic neurons lack the gp130 cytokine receptor (gp130 KO) have a normal heart rate but enhanced bradycardia after vagal nerve stimulation. What is unclear is whether cardiac autonomic disturbances in these animals reflect systemic alterations in nerve activity or whether localized defects in neurotransmitter stores or release are involved. To examine local stimulus-evoked release of neurotransmitters, we have developed a novel method for simultaneous quantification of both NE and ACh after ex vivo atrial field stimulation. Using HPLC with electrochemical detection for NE, and HPLC with mass spectrometry for ACh, we found that following field stimulation NE release was impaired in p75^−/− atria while ACh content and release was elevated in gp130 KO atria. Thus, alterations in localized transmitter release from atrial explants are consistent with in vivo deficits in heart rate control, suggesting peripheral alterations in autonomic transmission in these mice.     

Altered course of visceral leishmaniasis in mice expressing transgenic I-E molecules.

Previous studies had shown that the outcome of infection with Leishmania donovani was exquisitely sensitive to the influence of the major histocompatibility complex. In this study, we have examined the course of infection in non-obese diabetic (NOD) and NOD-E-3 mice, the latter expressing an I-E molecule as a result of transgenic introduction of the wild-type Ed alpha gene. Introduction of this transgene significantly altered the course of infection allowing for enhanced parasite multiplication in the viscera from day 14 to day 28. This was associated with both a delayed and reduced tissue granulomatous response in NOD-E-3 mice. In vitro, spleen cells from these mice produced equivalent levels of interferon (IFN)-gamma during the early phase of infection but this originated from populations having a different balance of T cells subsets. In NOD mice CD8+ T cells contribute substantially to the total levels of IFN-gamma produced, but in transgenic mice the contribution from this subset is significantly decreased. This is reflected in a reduction in the proportion of Leishmania-specific CD8+ T cells, which could only partially be accounted for by deletion of V beta 5- and V beta 3-expressing CD8+ T cells in NOD-E-3 mice. This study highlights the impact of the introduction of a class II gene product on disease outcome and unexpectedly on the functional potential of CD8+ T cells.     

Correlation between cognitive deficits and Abeta deposits in transgenic APP+PS1 mice

Doubly transgenic mAPP+mPS1 mice (15-16 months) had impaired cognitive function in a spatial learning and memory task that combined features of a water maze and a radial arm maze. Nontransgenic mice learned a new platform location each day during 4 consecutive acquisition trials, and exhibited memory for this location in a retention trial administered 30 min later. In contrast, transgenic mice were, on average, unable to improve their performance in finding the hidden platform over trials. The cognitive performance of individual mice within the transgenic group were inversely related to the amount of Abeta deposited in the frontal cortex and hippocampus. These findings imply that mAPP+mPS1 transgenic mice develop deficits in cognitive ability as Abeta deposits increase. These data argue that radial arm water maze testing of doubly transgenic mice may be a useful behavioral endpoint in evaluating the functional consequences of potential AD therapies, especially those designed to reduce Abeta load.     

Lack of LDL receptor aggravates learning deficits and amyloid deposits in Alzheimer transgenic mice

Emerging evidence indicates that cholesterol metabolism affects the pathogenesis of Alzheimer's disease (AD). The LDL receptor (LDLR) is obligatory in maintaining cholesterol homeostasis in the periphery. To investigate the role of LDLR in the development of AD-like behavior and pathology, Tg2576 mice, a well-characterized transgenic mouse model of AD, with different genotypes of LDLR were generated. Here we show that LDLR-deficient Tg2576 mice developed hypercholesterolemia and age-dependent cerebral beta-amyloidosis. Before the manifestation of amyloid-beta (Abeta) deposition, these mice displayed hyperactivity, reduced anxiety, and impaired spatial learning regardless of LDLR genotypes. After the manifestation of Abeta deposition, LDLR-deficient Tg2576 mice showed more spatial learning deficits than LDLR-intact Tg2576 mice. Although LDLR genotypes did not affect the expression level of the amyloid-beta precursor protein transgene, there was a significant increase in Abeta deposition accompanied with an increase of apoE expression in LDLR-deficient Tg2576 mice. Our results suggest that the LDLR plays a role in the development of Alzheimer-type learning impairment and amyloidosis and can be a novel therapeutic target for AD.     

Early temporal short-term memory deficits in double transgenic APP/PS1 mice

We tested single APP (Tg2576) transgenic, PS1 (PS1dE9) transgenic, and double APP/PS1 transgenic mice at 3 and 6 months of age on the acquisition of a hippocampal-dependent operant “differential reinforcement of low rate schedule” (DRL) paradigm. In this task mice are required to wait for at least 10 seconds (DRL-10s) between 2 consecutive nose poke responses. Our data showed that while single APP and PS1 transgene expression did not affect DRL learning and performance, mice expressing double APP/PS1 transgenes were impaired in the acquisition of DRL-10s at 6 months, but not at 3 months of age. The same impaired double transgenic mice, however, were perfectly capable of normal acquisition of signaled DRL-10s (SDRL-10s) task, a hippocampal-independent task, wherein mice were required to emit responses when the end of the 10-second delay was signaled by a lighting of the chamber. The age-dependent and early deficits of APP/PS1 mice suggest that the appetitive DRL paradigm is sensitive to the amyloid pathology present in double APP/PS1 mice, and that this mouse line represents a good model with which to study the efficacy of therapeutic strategies against Alzheimer's disease.     

Locus coeruleus degeneration exacerbates olfactory deficits in APP/PS1 transgenic mice

Neuronal loss in the locus coeruleus (LC) is 1 of the early pathological events in Alzheimer's disease (AD). Projections of noradrenergic neurons of the LC innervate the olfactory bulb (OB). Because olfactory deficits have been reported in early AD, we investigated the effect of induced LC degeneration on olfactory memory and discrimination in an AD mouse model. LC degeneration was induced by treating APP/PS1 mice with N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (DSP4) repeatedly between 3 and 12 months of age. Short term odor retention, ability for spontaneous habituation to an odor, and spontaneous odor discrimination were assessed by behavioral tests. DSP4 treatment in APP/PS1 mice resulted in an exacerbation of short term olfactory memory deficits and more discrete weakening of olfactory discrimination abilities, suggesting that LC degeneration contributes to olfactory deficits observed in AD. Importantly, DSP4 treatment also increased amyloid β (Aβ) deposition in the olfactory bulb of APP/PS1 mice, which correlated with olfactory memory, not with discrimination deficits.     

Early-onset cognitive deficits and axonal transport dysfunction in P301S mutant tau transgenic mice

Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) are neurodegenerative “tauopathies” characterized by hyperphosphorylated tau accumulation and neurofibrillary tangles. The P301S mutation of tau, a causal mutation of a familial type of FTLD, is believed to be involved in neurodegenerative progression. We developed a transgenic mouse, named TPR50, harboring human P301S tau. Tau phosphorylation in the hippocampus of TPR50 mice increased with age, particularly at S202/T205. Insolubilization and intracellular accumulation of tau were detected in the hippocampus by 9 months of age. Expression of calbindin was significantly reduced in 6- and 9-month-old TPR50 mice but not in 3-month-old mice. TPR50 mice demonstrated cognitive dysfunction at 5 months. At this age or earlier, although no intracellular tau accumulation was observed in the hippocampus, abnormally increased microtubule (MT)-related proteins and MT hyperdynamics in the hippocampus, and impaired axonal transport in the septo-hippocampal pathway were already observed. Therefore, cognitive dysfunction in TPR50 mice may result from early MT dysfunction and impaired axonal transport rather than accumulation of insoluble tau and neurodegeneration. TPR50 mice are a valuable new model to study progression of tauopathies at both the behavioral and neurocellular levels and may also prove useful for testing new therapies for neurodegenerative diseases.     

Lamotrigine attenuates deficits in synaptic plasticity and accumulation of amyloid plaques in APP/PS1 transgenic mice

Hyperactivity and its compensatory mechanisms may causally contribute to synaptic and cognitive deficits in Alzheimer's disease (AD). Blocking the overexcitation of the neural network, with levetiracetam (LEV), a sodium channel blocker applied in the treatment of epilepsy, prevented synaptic and cognitive deficits in human amyloid precursor protein (APP) transgenic mice. This study has brought the potential use of antiepileptic drugs (AEDs) in AD therapy. We showed that the chronic treatment with lamotrigine (LTG), a broad-spectrum AED, suppressed abnormal spike activity, prevented the loss of spines, synaptophysin immunoreactivity, and neurons, and thus attenuated the deficits in synaptic plasticity and learning and memory in APP and presenilin 1 (PS1) mice, which express human mutant APP and PS1. In contrast with LEV, which failed to reduce the generation of amyloid β, the chronic LTG treatment reduced the cleavage of APP by β-secretase and thus the numbers and the size of amyloid plaques in the brains of APP and PS1 mice. Moreover, the levels of brain-derived neurotrophic growth factor (BDNF) and nerve growth factor (NGF) were enhanced in the brains of APP and PS1 mice by the chronic LTG treatment. Therefore, these observations demonstrate that LTG attenuates AD pathology through multiple mechanisms, including modulation of abnormal network activity, reduction of the generation of amyloid beta and upregulation of BDNF and NGF.     

Altered aging-related thymic involution in T cell receptor transgenic, MHC-deficient, and CD4-deficient mice

During aging in mice and humans, a gradual decline in thymus integrity and function occurs (thymic involution). To determine whether T cell reactivity or development affects thymic involution, we compared the thymic phenotype in old (12 months) and young (2 months) mice transgenic for rearranged alphabeta or beta 2B4 T cell receptor (TCR) genes, mice made deficient for CD4 by gene targetting (CD4(-/-)), mice made deficient for major histocompatibility complex (MHC) class I (beta2M-/-) or class II genes (A(beta)(b-/-) on C57Bl/6 background) or both. The expected aging-related reductions in thymic weights were observed for all strains except those bearing disruption of both class I and class II MHC genes. Therefore, disruption of MHC class I and class II appeared to reverse or delay aging-related thymic atrophy at 12 months. Immunohistochemical analysis of aging-associated alterations in thymic morphology revealed that TCR alphabeta transgenes, CD4 disruption, and MHC class II disruption all reduced or eliminated these changes. All strains examined at 12 months showed alterations in the distribution of immature thymocyte populations relative to young controls. These results show that aging-associated thymic structural alterations, size reductions, and thymocyte developmental delays can be separated and are therefore causally unrelated. Furthermore, these results suggest that the T cell repertoire and/or its development play a role in aging-related thymic involution.     

Altered metabolism of familial Alzheimer's disease-linked amyloid precursor protein variants in yeast artificial chromosome transgenic mice

Missense mutations in the beta-amyloid precursor protein gene (APP) co- segregate with a small subset of autosomal dominant familial Alzheimer's disease (FAD) cases wherein deposition of the 39-43 amino acid beta-amyloid (A beta) peptide and neurodegeneration are principal neuropathological hallmarks. To accurately examine the effect of missense mutations on APP metabolism and A beta production in vivo, we have introduced yeast artificial chromosomes (YACs) containing the entire approximately 400 kbp human APP gene encoding APP harboring either the asparagine for lysine and leucine for methionine FAD substitution at codons 670 and 671 (APP(K670N/M671L)), the isoleucine for valine FAD substitution at codon 717 (APP(V7171)) or a combination of both substitutions into transgenic mice. We demonstrate that, relative to YAC transgenic mice expressing wild-type APP, high levels of A beta peptides are detected in the brains of YAC transgenic mice expressing human APP(K670N/M671L) that is associated with a concomitant diminution in the levels of apha-secretase-generated soluble APP derivatives. Moreover, the levels of longer A beta peptides (species terminating at amino acids 42/43) are elevated in YAC transgenic mice expressing human APP(V7171). These mice should prove valuable for detailed analysis of the in vivo effects of the APP FAD mutations in a variety of tissues and throughout aging and for testing therapeutic agents that specifically alter APP metabolism and A beta production.      

Early-onset subicular microvascular amyloid and neuroinflammation correlate with behavioral deficits in vasculotropic mutant amyloid beta-protein precursor transgenic mice

Cerebral microvascular amyloid beta protein (Abeta) deposition and associated neuroinflammation are increasingly recognized as an important component leading to cognitive impairment in Alzheimer's disease and related cerebral amyloid angiopathy (CAA) disorders. Transgenic mice expressing the vasculotropic Dutch/Iowa (E693Q/D694N) mutant human Abeta precursor protein in brain (Tg-SwDI) accumulate abundant cerebral microvascular fibrillar amyloid deposits exhibiting robust neuroinflammation. In the present study, we sought to determine if the unique amyloid pathology of Tg-SwDI mice was associated with deficits in behavioral performance. Behavioral performance tests that assessed a variety of psychological functions, including overall activity, motor ability, balance and strength, anxiety, impulsivity, and learning were conducted on homozygous Tg-SwDI mice and similarly aged wild-type C57Bl/6 mice. Our results indicate that Tg-SwDI mice were impaired in the performance of the Barnes maze learning and memory task at 3, 9, and 12 months of age. While more widespread cerebral microvascular Abeta pathology was evident in older animals, the evaluation of the Abeta pathology in the 3 months old transgenic animals revealed specific accumulation of microvascular amyloid and markedly elevated numbers of reactive astrocytes and activated microglia restricted to the subiculum. These findings indicate that early-onset accumulation of subicular microvascular amyloid and accompanying neuroinflammation correlates with impaired performance in the learning and memory task in Tg-SwDI mice.     

Altered structural networks and executive deficits in traumatic brain injury patients

Recent research on traumatic brain injury (TBI) has shown that impairments in cognitive and executive control functions are accompanied by a disrupted neural connectivity characterized by white matter damage. We constructed binary and weighted brain structural networks in 21 patients with chronic TBI and 17 healthy young adults utilizing diffusion tensor tractography and calculated topological properties of the networks using a graph theoretical method. Executive function was assessed with the local global task and the trail making task, requiring inhibition, updating, and switching. The results revealed that TBI patients were less successful than controls on the executive tasks, as shown by the higher reaction times, higher switch costs, and lower accuracy rates. Moreover, both TBI patients and controls exhibited a small world topology in their white matter networks. More importantly, the TBI patients demonstrated increased shortest path length and decreased global efficiency of the structural network. These findings suggest that TBI patients have a weaker globally integrated structural brain network, resulting in a limited capacity to integrate information across brain regions. Furthermore, we showed that the white matter networks of both groups contained highly connected hub regions that were predominately located in the parietal cortex, frontal cortex, and basal ganglia. Finally, we showed significant correlations between switching performance and network property metrics within the TBI group. Specifically, lower scores on the switching tasks corresponded to a lower global efficiency. We conclude that analyzing the structural brain network connectivity provides new insights into understanding cognitive control changes following brain injury.     

Genetically augmenting Abeta42 levels in skeletal muscle exacerbates inclusion body myositis-like pathology and motor deficits in transgenic mice

The pathogenic basis of inclusion body myositis (IBM), the leading muscle degenerative disease afflicting the elderly, is unknown, although the histopathological features are remarkably similar to those observed in Alzheimer's disease. One leading hypothesis is that the buildup of amyloid-beta (Abeta) peptide within selective skeletal muscle fibers contributes to the degenerative phenotype. Abeta is a small peptide derived via endoproteolysis of the amyloid precursor protein (APP). To determine the pathogenic effect of augmenting Abeta42 levels in skeletal muscle, we used a genetic approach to replace the endogenous wild-type presenilin-1 (PS1) allele with the PS1(M146V) allele in MCK-APP mice. Although APP transgene expression was unaltered, Abeta levels, particularly Abeta42, were elevated in skeletal muscle of the double transgenic (MCK-APP/PS1) mice compared to the parental MCK-APP line. Elevated phospho-tau accumulation was found in the MCK-APP/PS1 mice, and the greater activation of GSK-3beta and cdk5 were observed. Other IBM-like pathological features, such as inclusion bodies and inflammatory infiltrates, were more severe and prominent in the MCK-APP/PS1 mice. Motor coordination and balance were more adversely affected and manifested at an earlier age in the MCK-APP/PS1 mice. The data presented here provide experimental evidence that Abeta42 plays a proximal and critical role in the muscle degenerative process.     

Altered medial temporal lobe responses during visuospatial encoding in healthy APOE*4 carriers

The apolipoprotein varepsilon4 allele (APOE*4) is a major genetic risk factor for Alzheimer's disease (AD) and has been associated with altered cortical activation as assessed by functional neuroimaging in cognitively normal younger and older carriers. We chose to evaluate medial temporal lobe (MTL) activation during encoding and recognition using a perspective-dependent (route or survey) visuospatial memory task by monitoring the blood-oxygen-level-dependent (BOLD) fMRI response in older, non-demented APOE*4 carriers (APOE*4+) and non-carriers (APOE*4-). During encoding, the APOE*4- group had greater average task-associated BOLD responses in ventral visual pathways, including the MTLs, as compared to the APOE*4+ group. Furthermore, MTL activation was greater during route encoding than survey encoding on average in APOE*4-, but not APOE*4+, subjects. During recognition, both groups performed similarly and no BOLD signal differences were found. Finally, within-group analysis revealed MTL activation during encoding was correlated with recognition performance in APOE*4-, but not APOE*4+ subjects. Reduced task-associated MTL activation that does not correlate with either visuospatial perspective or task performance suggests that MTL dysregulation occurs prior to clinical symptoms of dementia in APOE*4 carriers.