Mitovesicles secreted into the extracellular space of brains with mitochondrial dysfunction impair synaptic plasticity.

BACKGROUND: Hypometabolism tied to mitochondrial dysfunction occurs in the aging brain and in neurodegenerative disorders, including in Alzheimer's disease, in Down syndrome, and in mouse models of these conditions. We have previously shown that mitovesicles, small extracellular vesicles (EVs) of mitochondrial origin, are altered in content and abundance in multiple brain conditions characterized by mitochondrial dysfunction. However, given their recent discovery, it is yet to be explored what mitovesicles regulate and modify, both under physiological conditions and in the diseased brain. In this study, we investigated the effects of mitovesicles on synaptic function, and the molecular players involved. METHODS: Hippocampal slices from wild-type mice were perfused with the three known types of EVs, mitovesicles, microvesicles, or exosomes, isolated from the brain of a mouse model of Down syndrome or of a diploid control and long-term potentiation (LTP) recorded. The role of the monoamine oxidases type B (MAO-B) and type A (MAO-A) in mitovesicle-driven LTP impairments was addressed by treatment of mitovesicles with the irreversible MAO inhibitors pargyline and clorgiline prior to perfusion of the hippocampal slices. RESULTS: Mitovesicles from the brain of the Down syndrome model reduced LTP within minutes of mitovesicle addition. Mitovesicles isolated from control brains did not trigger electrophysiological effects, nor did other types of brain EVs (microvesicles and exosomes) from any genotype tested. Depleting mitovesicles of their MAO-B, but not MAO-A, activity eliminated their ability to alter LTP. CONCLUSIONS: Mitovesicle impairment of LTP is a previously undescribed paracrine-like mechanism by which EVs modulate synaptic activity, demonstrating that mitovesicles are active participants in the propagation of cellular and functional homeostatic changes in the context of neurodegenerative disorders.

Cocaine perturbs mitovesicle biology in the brain.

Cocaine, an addictive psychostimulant, has a broad mechanism of action, including the induction of a wide range of alterations in brain metabolism and mitochondrial homeostasis. Our group recently identified a subpopulation of non-microvesicular, non-exosomal extracellular vesicles of mitochondrial origin (mitovesicles) and developed a method to isolate mitovesicles from brain parenchyma. We hypothesised that the generation and secretion of mitovesicles is affected by mitochondrial abnormalities induced by chronic cocaine exposure. Mitovesicles from the brain extracellular space of cocaine-administered mice were enlarged and more numerous when compared to controls, supporting a model in which mitovesicle biogenesis is enhanced in the presence of mitochondrial alterations. This interrelationship was confirmed in vitro. Moreover, cocaine affected mitovesicle protein composition, causing a functional alteration in mitovesicle ATP production capacity. These data suggest that mitovesicles are previously unidentified players in the biology of cocaine addiction and that target therapies to fine-tune brain mitovesicle functionality may be beneficial to mitigate the effects of chronic cocaine exposure.

The role of tau oligomers in the onset of Alzheimer's disease neuropathology.

Most neurodegenerative diseases are characterized by the presence of protein aggregates. Alzheimer's disease (AD) is the most common cause of dementia in people over age 60. One of the histopathological hallmarks of AD is the presence of tau protein aggregates. Historically, it has been thought that paired helical filaments (PHFs) were the toxic form of tau that assembled to form neurofibrillary tangles (NFTs), but recently there has been evidence that tau oligomers, which form before PHFs and NFTs, could be the structures mediating neurodegeneration even before the fibrillary tau is deposited. Here, we discuss the recent advances in tau oligomer research, their implications on AD and other tauopathies, the mechanisms of tau turnover by the principal protein clearance systems (the proteasome and autophagy), and the potential use of tau oligomers as drug targets for the development of new therapeutic approaches.

Decreased pre-existing Ad5 capsid and Ad35 neutralizing antibodies increase HIV-1 infection risk in the Step trial independent of vaccination.

BACKGROUND: The Step trial raised the possibility that uncircumcised men with pre-existing Ad5 neutralizing antibodies carried an increased risk of HIV infection after vaccination. Thus, understanding Ad seropositivity in humans is important to the development of an AIDS vaccine. Here, we analyze the impact of different Ad5-specific neutralizing antibodies on immune function and clinical outcome. METHODS AND FINDINGS: Ad seropositivity in the Step trial volunteers was analyzed using chimeric rAd5/35 vectors to characterize their specificity for Ad5 fiber and non-fiber external (capsid) proteins. Immune responses and HIV seropositivity were correlated with the specificity of Ad5-neutralizing antibodies. Neutralizing antibodies induced by the vaccine in Ad5 seronegative subjects were directed preferentially to Ad5 capsid proteins, although some fiber-neutralizing antibodies could be detected. Pre-vaccination Ad5 serostatus did not affect the capsid-directed response after three vaccinations. In contrast, anti-fiber antibody titers were significantly higher in volunteers who were Ad5 seropositive prior to vaccination. Those Ad5 seropositive subjects who generated anti-capsid responses showed a marked reduction in vaccine-induced CD8 responses. Unexpectedly, anti-vector immunity differed qualitatively in Ad5 seropositive participants who became HIV-1 infected compared to uninfected case controls; Ad5 seropositive participants who later acquired HIV had lower neutralizing antibodies to capsid. Moreover, Ad35 seropositivity was decreased in HIV-infected subjects compared with uninfected case controls, while seroprevalence for other serotypes including Ad14, Ad28 and Ad41 was similar in both groups. CONCLUSIONS: Together, these findings suggest that the case subjects were less immunologically responsive prior to infection. Subjects infected during the Step trial had qualitative differences in immunity that increased their risk of HIV-1 infection independent of vaccination.

Cystatin C rescues degenerating neurons in a cystatin B-knockout mouse model of progressive myoclonus epilepsy.

In vitro studies have shown that cystatin C (CysC) is neuroprotective. Here we demonstrate that CysC is neuroprotective in vivo, in a mouse model of the inherited neurodegenerative disorder, progressive myoclonic epilepsy type 1 (EPM1). Loss-of-function mutations in the cystatin B (CysB) gene, an intracellular cysteine protease inhibitor, lead to this human disease. A CysB-knockout (CysBKO) mouse model develops symptoms that mimic EPM1. CysB deficiency in these mice results in enhanced cathepsin B and D activities, indicating lysosomal dysfunction. We show that expression of CysC is enhanced in the brains of CysBKO mice. Crossbreeding of CysBKO mice with either CysC-overexpressing transgenic mice or CysC-knockout mice demonstrates that clinical symptoms and neuropathologies, including motor coordination disorder, cerebellar atrophy, neuronal loss in the cerebellum and cerebral cortex, and gliosis caused by CysB deficiency, are rescued by CysC overexpression and exacerbated by CysC deficiency. Thus, CysC effectively rescues the CysB loss-of-function mutations, facilitating the reversal of pathophysiological changes and suggesting a novel therapeutic intervention for patients with EPM1 and other neurodegenerative disorders.

Hyperhomocysteinemic Alzheimer's mouse model of amyloidosis shows increased brain amyloid beta peptide levels.

Recent epidemiological and clinical data suggest that elevated serum homocysteine levels may increase the risk of developing Alzheimer's disease (AD), but the underlying mechanisms are unknown. We tested the hypothesis that high serum homocysteine concentration may increase amyloid beta-peptide (Abeta) levels in the brain and could therefore accelerate AD neuropathology. For this purpose, we mated a hyperhomocysteinemic CBS(tm1Unc) mouse carrying a heterozygous dominant mutation in cystathionine-beta-synthase (CBS*) with the APP*/PS1* mouse model of brain amyloidosis. The APP*/PS1*/CBS* mice showed significant elevations of serum homocysteine levels compared to the double transgenic APP*/PS1* model of amyloidosis. Results showed that female (but not male) APP*/PS1*/CBS* mice exhibited significant elevations of Abeta40 and Abeta42 levels in the brain. Correlations between homocysteine levels in serum and brain Abeta levels were statistically significant. No increases in beta secretase activity or evidence of neuronal cell loss in the hyperhomocysteinemic mice were found. The causes of neuronal dysfunction and degeneration in AD are not fully understood, but increased production of Abeta seems to be of major importance. By unveiling a link between homocysteine and Abeta levels, these findings advance our understanding on the mechanisms involved in hyperhomocysteinemia as a risk factor for AD.

Changes in apolipoprotein E expression in response to dietary and pharmacological modulation of cholesterol.

Apolipoprotein E (ApoE) influences the risk of late onset Alzheimer's disease (AD) in an isoform-dependent manner, such that the presence of the apoE epsilon4 allele increases the risk of AD while the presence of the apoE epsilon2 allele appears to be protective. Although a number of ApoE functions are isoform dependent and may underlie the "risk factor" activity of AD, its ability to bind amyloid beta peptides and influence their clearance and/or deposition has gained strong experimental support. Evidence suggests that in addition to genotype, increased ApoE transcription can contribute to AD risk. There is growing evidence in support of the hypothesis that disrupted cholesterol metabolism is an early risk factor for AD. Studies in animal models have shown that chronic changes in cholesterol metabolism associate with changes in brain Abeta accumulation, a process instrumental for establishing AD pathology. ApoE mediates cholesterol homeostasis in the body and is a major lipid carrier in brain. As such, its expression in the periphery and in brain changes in response to changes in cholesterol metabolism. Here, we used a transgenic mouse model of Alzheimer's amyloidosis to examine whether the diet-induced or pharmacologically induced changes in plasma cholesterol that result in altered brain amyloidosis also affect ApoE content in liver and in brain. We found that chronic changes in total cholesterol in plasma lead to changes in ApoE mRNA levels in brain. We also found that cholesterol loading of primary glial cells increases cellular and secreted ApoE levels and that long-term treatment of astrocytes and microglia with statins leads to a decrease in the cellular and/or secreted ApoE. These observations suggest that disrupted cholesterol metabolism may increase the risk of developing AD in part due to the effect of cholesterol on brain ApoE expression.

Statin therapy for Alzheimer's disease: will it work?

Disease-modifying therapies are being developed for Alzheimer's disease (AD). These are expected to slow the clinical progression of the disease or delay its onset. Cerebral accumulation of amyloid beta (A beta) peptides is an early and perhaps necessary event for establishing AD pathology. Consequently therapies aimed at attenuating brain amyloidosis are expected to be disease modifying. Based on the epidemiological evidence pointing to a link between cholesterol metabolism and AD and the numerous laboratory studies implicating cholesterol in the process of A beta production and accumulation, it is now believed that cholesterol-lowering therapies will be of value as disease modifying agents. Several epidemiological studies revealed that statin use for the treatment of coronary arterial disease is associated with a decreased prevalence or a decreased risk of developing AD. These observations require both preclinical and clinical validation. The former involves testing statins in one or more animal models of AD in order to establish which disease features are affected by statin treatment, the relative efficacy with which different statins modify these features and the mechanism(s) by which statins affect AD phenotypes. The latter requires prospective, randomized, placebo controlled trials to evaluate the effect of statin treatment on cognitive and AD biomarker outcomes. We have initiated a study aimed at determining the effects of atorvastatin (Lipitor), a statin with the largest US market share, on brain A beta deposition in the PSAPP transgenic mouse model of Alzheimer's amyloidosis. Our results indicate that Lipitor treatment markedly attenuates A beta deposition in this animal model.