Cerebellar protein expression in three different mouse strains and their relevance for motor performance

Western diet-induced fear memory impairment is attenuated by 6-shogaol in C57BL/6N mice

Dementia is a progressive cognitive diminution impeding with normal daily activities that is constantly on the increase. Currently, the estimated prevalence is 50 million affected people worldwide, a figure expected to triple within the next 30 years. While the pathophysiology of the different types of dementia is complex, likely involving the interplay between multiple genetic and environmental factors, strong evidence points towards an important link between diet and cognitive health. Here we examined the consequences of high-fat, high-sugar Western diet (HFSD)-induced obesity on cognitive performance in the fear conditioning task in mice and explored a possible beneficial effect of 6-shogaol (6S), an active constituent of ginger, in this model. Chronic exposure to HFSD significantly enhanced body weight gain in C57BL/6N mice and this effect was prevented by treatment with 6S. HFSD + vehicle-treated mice presented with a selective deficit in cued fear memory, which was not observed in HFSD + 6S-treated animals. The findings of this study provide first evidence for a beneficial effect of 6S on HFSD-induced obesity and emotional memory deficit in mice.

Impaired neural stem cell expansion and hypersensitivity to epileptic seizures in mice lacking the EGFR in the brain

Mice lacking the epidermal growth factor receptor (EGFR) develop an early postnatal degeneration of the frontal cortex and olfactory bulbs and show increased cortical astrocyte apoptosis. The poor health and early lethality of EGFR^−/− mice prevented the analysis of mechanisms responsible for the neurodegeneration and function of the EGFR in the adult brain. Here, we show that postnatal EGFR‐deficient neural stem cells are impaired in their self‐renewal potential and lack clonal expansion capacity in vitro. Mice lacking the EGFR in the brain (EGFR^Δbrain) show low penetrance of cortical degeneration compared to EGFR^−/− mice despite genetic recombination of the conditional allele. Adult EGFR^Δ mice establish a proper blood–brain barrier and perform reactive astrogliosis in response to mechanical and infectious brain injury, but are more sensitive to Kainic acid‐induced epileptic seizures. EGFR‐deficient cortical astrocytes, but not midbrain astrocytes, have reduced expression of glutamate transporters Glt1 and Glast, and show reduced glutamate uptake in vitro, illustrating an excitotoxic mechanism to explain the hypersensitivity to Kainic acid and region‐specific neurodegeneration observed in EGFR‐deficient brains.

The brain-tumor related protein podoplanin regulates synaptic plasticity and hippocampus-dependent learning and memory

INTRODUCTION

Podoplanin is a cell-surface glycoprotein constitutively expressed in the brain and implicated in human brain tumorigenesis. The intrinsic function of podoplanin in brain neurons remains however uncharacterized.

MATERIALS AND METHODS

Using an established podoplanin-knockout mouse model and electrophysiological, biochemical, and behavioral approaches, we investigated the brain neuronal role of podoplanin.

RESULTS

Ex-vivo electrophysiology showed that podoplanin deletion impairs dentate gyrus synaptic strengthening. In vivo, podoplanin deletion selectively impaired hippocampus-dependent spatial learning and memory without affecting amygdala-dependent cued fear conditioning. In vitro, neuronal overexpression of podoplanin promoted synaptic activity and neuritic outgrowth whereas podoplanin-deficient neurons exhibited stunted outgrowth and lower levels of p-Ezrin, TrkA, and CREB in response to nerve growth factor (NGF). Surface Plasmon Resonance data further indicated a physical interaction between podoplanin and NGF.

DISCUSSION

This work proposes podoplanin as a novel component of the neuronal machinery underlying neuritogenesis, synaptic plasticity, and hippocampus-dependent memory functions. The existence of a relevant cross-talk between podoplanin and the NGF/TrkA signaling pathway is also for the first time proposed here, thus providing a novel molecular complex as a target for future multidisciplinary studies of the brain function in the physiology and the pathology. Key messages Podoplanin, a protein linked to the promotion of human brain tumors, is required in vivo for proper hippocampus-dependent learning and memory functions. Deletion of podoplanin selectively impairs activity-dependent synaptic strengthening at the neurogenic dentate-gyrus and hampers neuritogenesis and phospho Ezrin, TrkA and CREB protein levels upon NGF stimulation. Surface plasmon resonance data indicates a physical interaction between podoplanin and NGF. On these grounds, a relevant cross-talk between podoplanin and NGF as well as a role for podoplanin in plasticity-related brain neuronal functions is here proposed.

Alzheimer's disease risk factor lymphocyte-specific protein tyrosine kinase regulates long-term synaptic strengthening, spatial learning and memory

The lymphocyte-specific protein tyrosine kinase (Lck), which belongs to the Src kinase-family, is expressed in neurons of the hippocampus, a structure critical for learning and memory. Recent evidence demonstrated a significant downregulation of Lck in Alzheimer's disease. Lck has additionally been proposed to be a risk factor for Alzheimer's disease, thus suggesting the involvement of Lck in memory function. The neuronal role of Lck, however, and its involvement in learning and memory remain largely unexplored. Here, in vitro electrophysiology, confocal microscopy, and molecular, pharmacological, genetic and biochemical techniques were combined with in vivo behavioral approaches to examine the role of Lck in the mouse hippocampus. Specific pharmacological inhibition and genetic silencing indicated the involvement of Lck in the regulation of neuritic outgrowth. In the functional pre-established synaptic networks that were examined electrophysiologically, specific Lck-inhibition also selectively impaired the long-term hippocampal synaptic plasticity without affecting spontaneous excitatory synaptic transmission or short-term synaptic potentiation. The selective inhibition of Lck also significantly altered hippocampus-dependent spatial learning and memory in vivo. These data provide the basis for the functional characterization of brain Lck, describing the importance of Lck as a critical regulator of both neuronal morphology and in vivo long-term memory.

Altered sensitivity to excitotoxic cell death and glutamate receptor expression between two commonly studied mouse strains

Alterations in glutamatergic synapse function have been implicated in the pathogenesis of many different neurological disorders, including ischemia, epilepsy, Parkinson's disease, Alzheimer's disease, and Huntington's disease. While studying glutamate receptor function in juvenile Batten disease on the C57BL/6J and 129S6/S(v)E(v) mouse backgrounds, we noticed differences unlikely to be due to mutation difference alone. We report here that primary cerebellar granule cell cultures from C57BL/6J mice are more sensitive to N-methyl-D-aspartate (NMDA)-mediated cell death. Moreover, sensitivity to AMPA-mediated excitotoxicity is more variable and is dependent on the treatment conditions and age of the cultures. Glutamate receptor surface expression levels examined in vitro by in situ ELISA and in vivo by Western blot in surface cross-linked cerebellar samples indicated that these differences in sensitivity likely are due to strain-dependent differences in cell surface receptor expression levels. We propose that differences in glutamate receptor expression and in excitotoxic vulnerability should be taken into consideration in the context of characterizing disease models on the C57BL/6J and 129S6/S(v)E(v) mouse backgrounds.

Proteome analysis of brain in murine experimental autoimmune encephalomyelitis

Multiple sclerosis is considered a prototype inflammatory autoimmune disorder of the CNS. Experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein is one of the best-characterized animal models of multiple sclerosis. Comprehensive understanding of gene expression in EAE can help identify genes that are important in drug response and pathogenesis. We applied a 2-DE-based proteomics approach to analyze the protein expression pattern of the brain in healthy and EAE samples. Of more than 1000 protein spots we analyzed, 70 showed reproducible and significant changes in EAE compared to controls. Of these, 42 protein spots could be identified using MALDI TOF-TOF-MS. They included mitochondrial and structural proteins as well as proteins involved in ionic and neurotransmitter release, blood barriers, apoptosis, and signal transduction. The possible role of these proteins in the responses of mice to animal models of multiple sclerosis is discussed.

A mouse model of anxiety molecularly characterized by altered protein networks in the brain proteome

Recently, several attempts have been made to describe changes related to certain anxiety states in the proteome of experimental animal models. However, these studies are restricted by limitations regarding the number and correct identification of separated proteins. Moreover, the application of a systems biology approach to discover the molecular mechanisms of anxiety requires genetically homogenous inbred animal models. Therefore, we developed a novel mouse model of anxiety using a combination of crossbreeding (inbred for 35 generations) and behavioral selection. We found significant changes in 82 proteins in the total brain proteome compared to the control proteome. Thirty-four of these proteins had been previously identified in other anxiety, depression or repeated psychosocial stress studies. The identified proteins are associated with different cellular functions, including synaptic transmission, metabolism, proteolysis, protein biosynthesis and folding, cytoskeletal proteins, brain development and neurogenesis, oxidative stress, signal transduction. Our proteomics data suggest that alterations in serotonin receptor-associated proteins, in the carbohydrate metabolism, in the cellular redox system and in synaptic docking are all involved in anxiety.

Novel subtractive transcription-based amplification of mRNA (STAR) method and its application in search of rare and differentially expressed genes in AD brains

Background

Alzheimer's disease (AD) is a complex disorder that involves multiple biological processes. Many genes implicated in these processes may be present in low abundance in the human brain. DNA microarray analysis identifies changed genes that are expressed at high or moderate levels. Complementary to this approach, we described here a novel technology designed specifically to isolate rare and novel genes previously undetectable by other methods. We have used this method to identify differentially expressed genes in brains affected by AD. Our method, termed Subtractive Transcription-based Amplification of mRNA (STAR), is a combination of subtractive RNA/DNA hybridization and RNA amplification, which allows the removal of non-differentially expressed transcripts and the linear amplification of the differentially expressed genes.

Results

Using the STAR technology we have identified over 800 differentially expressed sequences in AD brains, both up- and down- regulated, compared to age-matched controls. Over 55% of the sequences represent genes of unknown function and roughly half of them were novel and rare discoveries in the human brain. The expression changes of nearly 80 unique genes were further confirmed by qRT-PCR and the association of additional genes with AD and/or neurodegeneration was established using an in-house literature mining tool (LitMiner).

Conclusion

The STAR process significantly amplifies unique and rare sequences relative to abundant housekeeping genes and, as a consequence, identifies genes not previously linked to AD. This method also offers new opportunities to study the subtle changes in gene expression that potentially contribute to the development and/or progression of AD.

Optimized proteomic analysis of a mouse model of cerebellar dysfunction using amine-specific isobaric tags

Recent proteomic applications have demonstrated their potential for revealing the molecular mechanisms underlying neurodegeneration. The present study quantifies cerebellar protein changes in mice that are deficient in plasma membrane calcium ATPase 2 (PMCA2), an essential neuronal pump that extrudes calcium from cells and is abundantly expressed in Purkinje neurons. PMCA2-null mice display motor dyscoordination and unsteady gait deficits observed in neurological diseases such as multiple sclerosis and ataxia. We optimized an amine-specific isobaric tags (iTRAQ)-based shotgun proteomics workflow for this study. This workflow took consideration of analytical variance as a function of ion signal intensity and employed biological repeats to aid noise reduction. Even with stringent protein identification criteria, we could reliably quantify nearly 1000 proteins, including many neuronal proteins that are important for synaptic function. We identified 21 proteins that were differentially expressed in PMCA2-null mice. These proteins are involved in calcium homeostasis, cell structure and chromosome organization. Our findings shed light on the molecular changes that underlie the neurological deficits observed in PMCA2-null mice. The optimized workflow presented here will be valuable for others who plan to implement the iTRAQ method.

Biomarker discovery in breast cancer serum using 2-D differential gel electrophoresis/ MALDI-TOF/TOF and data validation by routine clinical assays

In the present study, we used 2-D differential gel electrophoresis (2-D DIGE) and MS to screen biomarker candidates in serum samples obtained from 39 patients with breast cancer and 35 controls. First, we pooled the serum samples matched with age and menopausal status. Then, we depleted the two most abundant proteins albumin and IgG by immunoaffinity chromatography under partly denaturing conditions in order to enrich low-abundance proteins and proteins with low molecular weight. Concentrated and desalted samples were labeled with three different CyDyes including one internal standard, pooled from all the samples, and separated with 2-D DIGE in triplicate experiments. Biological variations of the protein expression level were analyzed with DeCyder software and evaluated for reproducibility and statistical significance. The profile of differentially expressed protein spots between patients and controls revealed proapolipoprotein A-I, transferrin, and hemoglobin as up-regulated and three spots, apolipoprotein A-I, apolipoprotein C-III, and haptoglobin alpha2 as down-regulated in patients. Finally, routine clinical immunochemical reactions were used to validate selected candidate biomarkers by quantitative determination of specific proteins in all individual serum samples. The serum level of transferrin correlated well with the 2-D-DIGE results. However, the serum levels of apolipoprotein A-I and haptoglobin could not be detected with the clinical routine diagnostic tests. This demonstrated an advantage 2-D DIGE still has over other techniques. 2-D DIGE can distinguish between isoforms of proteins, where the overall immunochemical quantification does fail due to a lack of isoform-special antibodies.

Enrichment of low-abundant serum proteins by albumin/immunoglobulin G immunoaffinity depletion under partly denaturing conditions

We present a simple protocol for affinity depletion to remove the two most abundant serum proteins, albumin and immunoglobulin G (IgG). Under native conditions, albumin/IgG were efficiently removed and several proteins were enriched as shown by two-dimensional electrophoresis (2-DE). Besides that, partly denaturing conditions were established by adding 5 or 20% acetonitrile (ACN) in order to disrupt the binding of low-molecular-weight (LMW) proteins to the carrier proteins albumin/IgG. 2-DE results showed that the total number of detected LMW proteins increased under denaturing conditions when compared to native conditions. Interestingly, the presence of 5% ACN in serum revealed better enrichment of LMW proteins when compared to 20% ACN condition. Seven randomly distributed spots in albumin/IgG depleted serum samples under 5% ACN condition were picked from the 2-DE gels and identified by mass spectrometry (MS). The intensity of five LMW protein spots increased under denaturing conditions when compared to native conditions. Three of the seven identified spots (serum amyloid P, vitamin D-binding protein, and transthyretin) belong to a group of relatively low-abundant proteins, which make up only 1% of all serum proteins. The method presented here improves the resolution of the serum proteome by increasing the number of visualized spots on 2-D gels and allowing the detection and MS identification of LMW proteins and proteins of lower abundance.