[Show abstract][Hide abstract] ABSTRACT: The perineuronal net (PN) is a subtype of extracellular matrix appearing as a net-like structure around distinct neurons throughout the whole CNS. PNs surround the soma, proximal dendrites, and the axonal initial segment embedding synaptic terminals on the neuronal surface. Different functions of the PNs are suggested which include support of synaptic stabilization, inhibition of axonal sprouting, and control of neuronal plasticity. A number of studies provide evidence that removing PNs or PN-components results in renewed neurite growth and synaptogenesis. In a mouse model for Purkinje cell degeneration, we examined the effect of deafferentation on synaptic remodeling and modulation of PNs in the deep cerebellar nuclei. We found reduced GABAergic, enhanced glutamatergic innervations at PN-associated neurons, and altered expression of the PN-components brevican and hapln4. These data refer to a direct interaction between ECM and synapses. The altered brevican expression induced by activated astrocytes could be required for an adequate regeneration by promoting neurite growth and synaptogenesis.
[Show abstract][Hide abstract] ABSTRACT: The transcriptome of a cell is made up of a varied array of RNA species, including protein-coding RNAs, long non-coding RNAs, short non-coding RNAs, and circular RNAs. The cellular transcriptome is dynamic and can change depending on environmental factors, disease state and cellular context. The human brain has perhaps the most diverse transcriptome profile that is enriched for many species of RNA, including antisense transcripts. Antisense transcripts are produced when both the plus and minus strand of the DNA helix are transcribed at a particular locus. This results in an RNA transcript that has a partial or complete overlap with an intronic or exonic region of the sense transcript. While antisense transcription is known to occur at some level in most organisms, this review focuses specifically on antisense transcription in the brain and how regulation of genes by antisense transcripts can contribute to functional aspects of the healthy and diseased brain. First, we discuss different techniques that can be used in the identification and quantification of antisense transcripts. This is followed by examples of antisense transcription and modes of regulatory function that have been identified in the brain.
No preview · Article · Dec 2015 · Journal of Molecular Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Perineuronal nets (PNs) are a specialized form of brain extracellular matrix, consisting of negatively charged glycosaminoglycans, glycoproteins and proteoglycans in the direct microenvironment of neurons. Still, locally immobilized charges in the tissue have not been accessible so far to direct observations and quantifications. Here, we present a new approach to visualize and quantify fixed charge-densities on brain slices using a focused proton-beam microprobe in combination with ionic metallic probes. For the first time, we can provide quantitative data on the distribution and net amount of pericellularly fixed charge-densities, which, determined at 0.4–0.5 M, is much higher than previously assumed. PNs, thus, represent an immobilized ion exchanger with ion sorting properties high enough to partition mobile ions in accord with Donnan-equilibrium. We propose that fixed charge-densities in the brain are involved in regulating ion mobility, the volume fraction of extracellular space and the viscosity of matrix components.
Full-text · Article · Dec 2015 · Scientific Reports
[Show abstract][Hide abstract] ABSTRACT: Alzheimer's disease (AD) is a degenerative disorder where the distribution of pathology throughout the brain is not random but follows a predictive pattern used for pathological staging. While the involvement of defined functional systems is fairly well established for more advanced stages, the initial sites of degeneration are still ill defined. The prevailing concept suggests an origin within the transentorhinal and entorhinal cortex (EC) from where pathology spreads to other areas. Still, this concept has been challenged recently suggesting a potential origin of degeneration in nonthalamic subcortical nuclei giving rise to cortical innervation such as locus coeruleus (LC) and nucleus basalis of Meynert (NbM). To contribute to the identification of the early site of degeneration, here, we address the question whether cortical or subcortical degeneration occurs more early and develops more quickly during progression of AD. To this end, we stereologically assessed neurone counts in the NbM, LC and EC layer-II in the same AD patients ranging from preclinical stages to severe dementia. In all three areas, neurone loss becomes detectable already at preclinical stages and is clearly manifest at prodromal AD/MCI. At more advanced AD, cell loss is most pronounced in the NbM > LC > layer-II EC. During early AD, however, the extent of cell loss is fairly balanced between all three areas without clear indications for a preference of one area. We can thus not rule out that there is more than one way of spreading from its site of origin or that degeneration even occurs independently at several sites in parallel.
[Show abstract][Hide abstract] ABSTRACT: Alzheimeŕs disease (AD) is a chronic degenerative disorder characterized by fibrillary aggregates of Aß and Tau-protein. Formation and progressionof these pathological hallmarks throughout the brain follow a specific spatio-temporal pattern which provides the basis for neuropathological staging. Previously, we could demonstrate that cortical and subcortical neurons are less frequently affected by neurofibrillary degeneration if they are enwrapped by a specialized form of the hyaluronan-based extracellular matrix (ECM), the so called 'perineuronal net' (PN). PNs are composed of large aggregating chondroitin sulphate proteoglycans connected to a hyaluronan backbone, stabilized by link proteins and cross-linked via tenascin-R. Recently, PN-associated neurons were shown to be better protected against iron-induced neurodegeneration compared to neurons without PN, indicating a neuroprotective function. Here, we investigated a role of the PNs in distribution and internalization of exogenous Tau-protein by using organotypic slice cultures of wildtype mice as well as mice lacking the ECM-components aggrecan, HAPLN1 or tenascin-R. We could demonstrate that PNs restrict both distribution and internalization of Tau. Accordingly, PN-ensheathed neurons were less frequently affected by Tau-internalization, than neurons without PN. Finally, the PNs as well as their three investigated components were shown to modulate the processes of distribution as well as internalization of Tau.
[Show abstract][Hide abstract] ABSTRACT: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by fibrillary aggregates of Aβ peptide and tau protein. The distribution of these pathological hallmarks throughout the brain is not random; it follows a predictive pattern that is used for pathological staging. However, most etiopathogenetic concepts, irrespective of whether they focus on Aβ or tau pathology, leave a key question unanswered: what is the explanation for the different vulnerabilities of brain regions in AD? The pattern of regional progression of neurofibrillary degeneration in AD to some extent inversely recapitulates ontogenetic and phylogenetic brain development. Accordingly, degeneration preferentially affects brain areas that have recently been acquired or restructured during anthropoid evolution, which means that the involvement of a neurodevelopmental mechanism is highly likely. Since evolutionary expansion of the neocortex is based on a substantial extension of the mitotic activity of progenitor cells, we propose a conceptual link between neurogenesis in anthropoid primates and a higher risk of accumulating mitotic errors that give rise to genomic aberrations commonly referred to as DNA content variation (DCV). If increased rates of DCV make neurons more vulnerable to AD-related pathology, one might expect there to be a higher rate of DCV in areas that are affected very early during the course of AD, as compared to areas which are hardly affected or are affected only during the most advanced stages. Therefore, in the present study, we comparatively analyzed the DCV in five different cortical areas that are affected during the early stage (entorhinal cortex), the intermediate stage (temporal, frontal, and parietal association cortex), and the late stage (primary sensory occipital cortex) of AD in both normal elderly subjects and AD patients. On average, we observed about 10 % neuronal mosaic DCV in the normal elderly and a two- to threefold increase in DCV in AD patients. We were able to demonstrate, moreover, that the neuronal DCV in the cerebral cortex of the normal elderly as well as the increased neuronal DCV in AD patients are not randomly distributed but instead show systematic regional differences which correspond to differences in vulnerability. These findings provide additional evidence that mosaic genomic heterogeneity may play a key role in AD pathology.
No preview · Article · Aug 2015 · Acta Neuropathologica
[Show abstract][Hide abstract] ABSTRACT: The extracellular matrix is an integral part of the neural tissue. Its most conspicuous manifestation in the brain are the perineuronal nets (PNs) which surround somata and proximal dendrites of distinct neuron types. The chondroitin sulfate proteoglycan brevican is a major component of PNs. In contrast to other PN-comprising proteoglycans (e.g. aggrecan and neurocan), brevican is mainly expressed in the perisynaptic space closely associated with both the pre- and postsynaptic membrane. This specific localization prompted the hypothesis that brevican might play a role in synaptic transmission. In the present study we specifically investigated the role of brevican in synaptic transmission at a central synapse, the calyx of Held in the medial nucleus of the trapezoid body by the use of in vivo electrophysiology, immunohistochemistry, biochemistry and electron microscopy. In vivo extracellular single-unit recordings were acquired in brevican-deficient mice and the dynamics and reliability of synaptic transmission were compared to wildtype littermates. In knockout mice, the speed of pre-to-postsynaptic action potential (AP) transmission was reduced and the duration of the respective pre- and postsynaptic APs increased. The reliability of signal transmission, however, was not affected by the lack of brevican. The changes in dynamics of signal transmission were accompanied by the reduction of (i) presynaptic vGlut1 and (ii) the size of subsynaptic cavities. The present results suggest an essential role of brevican for the functionality of high-speed synaptic transmission at the calyx of Held. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Full-text · Article · Jul 2015 · The Journal of Physiology
[Show abstract][Hide abstract] ABSTRACT: Electroporation is a useful technique to study gene function during development but its broad application is hampered due to the expensive equipment needed. We describe the construction of a transportable, simple and inexpensive electroporator delivering square pulses with varying length and amplitude. The device was successfully used for in utero electroporation in mouse with a performance comparable to that of commercial products. Electroporation is a useful technique to study gene function during development but its broad application is hampered due to the expensive equipment needed. We describe the construction of a transportable, simple and inexpensive electroporator delivering square pulses with varying length and amplitude. The device was successfully used for in utero electroporation in mouse with a performance comparable to that of commercial products.
No preview · Article · May 2015 · Development Growth and Regeneration
[Show abstract][Hide abstract] ABSTRACT: Defects in intracellular transport are implicated in the pathogenesis of Alzheimer's disease (AD). Hook proteins are a family of cytoplasmic linker proteins that participate in endosomal transport. In this study we show that Hook1 and Hook3 are expressed in neurons while Hook2 is predominantly expressed in astrocytes. Furthermore, Hook proteins are associated with pathological hallmarks in AD; Hook1 and Hook3 are localized to tau aggregates and Hook2 to glial components within amyloid plaques. Additionally, the expression of Hook3 is reduced in AD. Modelling of Hook3 deficiency in cultured cells leads to slowing of endosomal transport and increases β-amyloid production. We propose that Hook3 plays a role in pathogenic events exacerbating AD.
[Show abstract][Hide abstract] ABSTRACT: Aging is the main risk factor for Alzheimer's disease (AD). With aging, inflammation has been recognized as potential trigger for starting the neurodegenerative cascade leading to neuronal death. Before Aβ and tau accumulation, evidence has put alterations of the cell cycle at the core of these processes. Still, a number of features of the cell cycle re-entry phenotype have remained elusive to the role of ectopic protein expression in the process of neuroinflammation and consequently neuronal cell death. Recently, a novel cyclin dependent kinase CDK11 has been found to be involved in astrocyte mediated inflammatory response and Alzheimer's disease. In this review, we aim to establish the missing part of the puzzle between neuroinflammation and APP / Aβ deregulation in AD by evaluating the role of a cyclin, CDK11. CDK11 may play a vital role in cell cycle re-entry in AD neurons in an APP-dependent manner, thus presenting an intriguing novel function of the APP signaling pathway in AD.
[Show abstract][Hide abstract] ABSTRACT: The brains of Alzheimer’s disease (AD) patients are characterized by deposits of Abeta peptides and by accompanying chronic inflammation. Here, we provide evidence that the enzyme isoglutaminyl cyclase (isoQC) is a novel factor contributing to both aspects of AD pathology. Two putative substrates of isoQC, N-truncated Abeta peptides and the monocyte chemoattractant chemokine CCL2, undergo isoQC-catalyzed pyroglutamate (pGlu) modification. This triggers Abeta aggregation and facilitates the biological activity of CCL2, which collectively results in the formation of high molecular weight Abeta aggregates, glial cell activation, neuroinflammation and neuronal cell death. In mouse brain, we found isoQC to be neuron-specifically expressed in neocortical, hippocampal and subcortical structures, localized to the endoplasmic reticulum and Golgi apparatus as well as co-expressed with its substrate CCL2. In aged APP transgenic Tg2576 mice, both isoQC and CCL2 mRNA levels are up-regulated and isoQC and CCL2 proteins were found to be co-induced in Abeta plaque-associated reactive astrocytes. Also, in mouse primary astrocyte culture, a simultaneous up-regulation of isoQC and CCL2 expression was revealed upon Abeta and pGlu-Abeta stimulation. In brains of AD patients, the expression of isoQC and CCL2 mRNA and protein is up-regulated compared to controls and correlates with pGlu-Abeta load and with the decline in mini-mental state examination. Our observations provide evidence for a dual involvement of isoQC in AD pathogenesis by catalysis of pGlu-Abeta and pGlu-CCL2 formation which mutually stimulate inflammatory events and affect cognition. We conclude that isoQC inhibition may target both major pathological events in the development of AD.
Electronic supplementary material
The online version of this article (doi:10.1007/s00401-015-1395-2) contains supplementary material, which is available to authorized users.
Full-text · Article · Feb 2015 · Acta Neuropathologica
[Show abstract][Hide abstract] ABSTRACT: Oxidative stress is thought to be one of the main mediators of neuronal damage in human neurodegenerative disease. Still, the dissection of causal relationships has turned out to be remarkably difficult. Here, we have analyzed global protein oxidation in terms of carbonylation of membrane proteins and cytoplasmic proteins in three different mammalian species: aged human cortex and cerebellum from patients with or without Alzheimer’s disease, mouse cortex and cerebellum from young and old animals, and adult rat hippocampus and cortex subjected or not subjected to cerebral ischemia. Most tissues showed relatively similar levels of protein oxidation. However, human cortex was affected by severe membrane protein oxidation, while exhibiting lower than average cytoplasmic protein oxidation. In contrast, ex vivo autooxidation of murine cortical tissue primarily induced aqueous protein oxidation, while in vivo biological aging or cerebral ischemia had no major effect on brain protein oxidation. The unusually high levels of membrane protein oxidation in the human cortex were also not predicted by lipid peroxidation, as the levels of isoprostane immunoreactivity in human samples were considerably lower than in rodent tissues. Our results indicate that the aged human cortex is under steady pressure from specific and potentially detrimental membrane protein oxidation. The pronounced difference between humans, mice and rats regarding the primary site of cortical oxidation might have contributed to the unresolved difficulties in translating into therapies the wealth of data describing successful antioxidant neuroprotection in rodents.
[Show abstract][Hide abstract] ABSTRACT: Sporadic Alzheimer’s disease (AD) is a chronic progressive neurodegenerative disorder of unknown cause characterized by fibrillar accumulation of the Aß-peptide and aggregates of the microtubule-associated protein tau in a hyperphosphorylated form. Already at preclinical stages, AD is characterized by hypometabolic states which are a good predictor of cognitive decline. Here, we summarize recent evidence derived from the study of hibernating animals that brain hypometabolism can trigger PHF-like hyperphosphorylation of tau. We put forward the concept that particular types of neurons respond to a hypometabolic state with an elevated phosphorylation of tau protein which represents a physiological mechanism involved in regulating synaptic gain. If, in contrast to hibernation, the hypometabolic state is not terminated after a definite time but rather persists and progresses, the elevated phosphorylation of tau protein endures and the protective reaction associated with it might turn into a pathological cascade leading to neurodegeneration.
No preview · Article · Dec 2014 · Journal of Neural Transmission