Traumatic Brain Injury Induces Genome-Wide Transcriptomic, Methylomic, and Network Perturbations in Brain and Blood Predicting Neurological Disorders.

The complexity of the traumatic brain injury (TBI) pathology, particularly concussive injury, is a serious obstacle for diagnosis, treatment, and long-term prognosis. Here we utilize modern systems biology in a rodent model of concussive injury to gain a thorough view of the impact of TBI on fundamental aspects of gene regulation, which have the potential to drive or alter the course of the TBI pathology. TBI perturbed epigenomic programming, transcriptional activities (expression level and alternative splicing), and the organization of genes in networks centered around genes such as Anax2, Ogn, and Fmod. Transcriptomic signatures in the hippocampus are involved in neuronal signaling, metabolism, inflammation, and blood function, and they overlap with those in leukocytes from peripheral blood. The homology between genomic signatures from blood and brain elicited by TBI provides proof of concept information for development of biomarkers of TBI based on composite genomic patterns. By intersecting with human genome-wide association studies, many TBI signature genes and network regulators identified in our rodent model were causally associated with brain disorders with relevant link to TBI. The overall results show that concussive brain injury reprograms genes which could lead to predisposition to neurological and psychiatric disorders, and that genomic information from peripheral leukocytes has the potential to predict TBI pathogenesis in the brain

Pathogenesis of proximal autosomal recessive spinal muscular atrophy

Although it is known that deletions or mutations of the SMN1 gene on chromosome 5 cause decreased levels of the SMN protein in subjects with proximal autosomal recessive spinal muscular atrophy (SMA), the exact sequence of pathological events leading to selective motoneuron cell death is not fully understood yet. In this review, new findings regarding the dual cellular role of the SMN protein (translocation of β-actin to axonal growth cones and snRNP biogenesis/pre-mRNA splicing) were integrated with recent data obtained by detailed neuropathological examination of SMA and control subjects. A presumptive series of 10 pathogenetic events for SMA is proposed as follows: (1) deletions or mutations of the SMN1 gene, (2) increased SMN mRNA decay and reduction in full-length functional SMN protein, (3) impaired motoneuron axonoand dendrogenesis, (4) failure of motoneurons to form synapses with corticospinal fibers from upper motoneurons, (5) abnormal motoneuron migration towards ventral spinal roots, (6) inappropriate persistence of motoneuron apoptosis due to impaired differentiation and motoneuron displacement, (7) substantial numbers of motoneurons continuing to migrate abnormally (“heterotopic motoneurons”) and entering into the ventral roots, (8) attracted glial cells following these heterotopic motoneurons, which form the glial bundles of ventral roots, (9) impaired axonal transport of actin, causing remaining motoneurons to become chromatolytic, and (10) eventual death of all apoptotic, heterotopic and chromatolytic neurons, with apoptosis being more rapid and predominating in the earlier stages, with death of heterotopic and chromatolytic neurons occurring more slowly by necrosis during the later stages of SMA. According to this model, the motoneuron axonopathy is more important for pathogenesis than the ubiquitous nuclear splicing deficit. It is also supposed that individually variable levels of SMN protein, together with influences of other phenotype modifier genes and their products, cause the clinical SMA spectrum through differential degree of motoneuron functional loss

Epilepsy Caused by an Abnormal Alternative Splicing with Dosage Effect of the SV2A Gene in a Chicken Model

Photosensitive reflex epilepsy is caused by the combination of an individual's enhanced sensitivity with relevant light stimuli, such as stroboscopic lights or video games. This is the most common reflex epilepsy in humans; it is characterized by the photoparoxysmal response, which is an abnormal electroencephalographic reaction, and seizures triggered by intermittent light stimulation. Here, by using genetic mapping, sequencing and functional analyses, we report that a mutation in the acceptor site of the second intron of SV2A (the gene encoding synaptic vesicle glycoprotein 2A) is causing photosensitive reflex epilepsy in a unique vertebrate model, the Fepi chicken strain, a spontaneous model where the neurological disorder is inherited as an autosomal recessive mutation. This mutation causes an aberrant splicing event and significantly reduces the level of SV2A mRNA in homozygous carriers. Levetiracetam, a second generation antiepileptic drug, is known to bind SV2A, and SV2A knock-out mice develop seizures soon after birth and usually die within three weeks. The Fepi chicken survives to adulthood and responds to levetiracetam, suggesting that the low-level expression of SV2A in these animals is sufficient to allow survival, but does not protect against seizures. Thus, the Fepi chicken model shows that the role of the SV2A pathway in the brain is conserved between birds and mammals, in spite of a large phylogenetic distance. The Fepi model appears particularly useful for further studies of physiopathology of reflex epilepsy, in comparison with induced models of epilepsy in rodents. Consequently, SV2A is a very attractive candidate gene for analysis in the context of both mono- and polygenic generalized epilepsies in humans

Composition and Evolution of the Vertebrate and Mammalian Selenoproteomes

Background: Selenium is an essential trace element in mammals due to its presence in proteins in the form of selenocysteine (Sec). Human genome codes for 25 Sec-containing protein genes, and mouse and rat genomes for 24. Methodology/Principal Findings: We characterized the selenoproteomes of 44 sequenced vertebrates by applying gene prediction and phylogenetic reconstruction methods, supplemented with the analyses of gene structures, alternative splicing isoforms, untranslated regions, SECIS elements, and pseudogenes. In total, we detected 45 selenoprotein subfamilies. 28 of them were found in mammals, and 41 in bony fishes. We define the ancestral vertebrate (28 proteins) and mammalian (25 proteins) selenoproteomes, and describe how they evolved along lineages through gene duplication (20 events), gene loss (10 events) and replacement of Sec with cysteine (12 events). We show that an intronless selenophosphate synthetase 2 gene evolved in early mammals and replaced functionally the original multiexon gene in placental mammals, whereas both genes remain in marsupials. Mammalian thioredoxin reductase 1 and thioredoxinglutathione reductase evolved from an ancestral glutaredoxin-domain containing enzyme, still present in fish. Selenoprotein V and GPx6 evolved specifically in placental mammals from duplications of SelW and GPx3, respectively, and GPx6 lost Sec several times independently. Bony fishes were characterized by duplications of several selenoprotein families (GPx1, GPx3, GPx4, Dio3, MsrB1, SelJ, SelO, SelT, SelU1, and SelW2). Finally, we report identification of new isoforms for several selenoproteins and describe unusually conserved selenoprotein pseudogenes. Conclusions/Significance: This analysis represents the first comprehensive survey of the vertebrate and mammal selenoproteomes, and depicts their evolution along lineages. It also provides a wealth of information on these selenoproteins and their forms

Exploration of TRPV1 Splice Variant Expression in Rat Dorsal Root Ganglia Following Sciatic Nerve Injury

Transient Receptor Potential Vanilloid 1 (TRPV1) is ligand-gated ion channel that plays an important role in the pain signaling pathway. It is predominantly expressed by sensory neurons located in trigeminal ganglia or dorsal root ganglia (DRG). TRPV1 has been shown to play a crucial role in the generation and maintenance of inflammatory and neuropathic pain. The involvement of splice variants of TRPV1 in pain pathways is not well known. In this study, the mRNA expression of TRPV1 and 3 splice variants (TRPV1.b, TRPV1.β, and TRPV1.var) in DRG was measured following chronic constriction injury of the sciatic nerve in rats. This is the first study to isolate TRPV1.β in rat DRG. The expression of TRPV1 mRNA was elevated following peripheral nerve damage, but not TRPV1.b, TRPV1.var or TRPV1.β. These novel findings suggest that the expression of TRPV1 splice variants is not regulated by sciatic nerve injury

ANALYSIS OF DIFFERENTIAL GENE EXPRESSION AND ALTERNATIVE SPLICING IN THE LIVER AND GASTROINTESTINAL TRACT IN THE LACTATING RAT

Rat exon microarrays were utilized to detect changes in mRNA expression and alternative splicing in the liver, duodenum, jejunum, and ileum of the lactating rat when compared to age-matched virgin controls. Analysis of data at the level of gene expression revealed differential expression of genes involved in cholesterol biosynthesis in each tissue examined, suggesting increased Sterol Response Element Binding Protein activity. We also detected decreased mRNA from components of the T-cell signaling pathway in the jejunum and ileum. We characterized expression of solute carrier and adenosine triphosphate binding cassette proteins. In addition to characterizing genes by pathway, we have also grouped genes based on their pattern of expression to identify important genes. Amongst genes upregulated in all tissues was Slc39a4, which is a critical transporter in the absorption of zinc in enterocytes. Alternative splicing analysis detected a substantial amount of alternative splicing in the ileum compared to other tissues. In addition, in the liver Abcg8, a protein that functions as a heterodimer to export cholesterol in the bile, shows differential splicing in the liver, but not in other tissues. We also detected differential expression of Ugt1a6 in the liver based on usage of an alternative first exon, which is consistent with altered protein levels observed previously. Differential splicing also appears to occur in Ace2 in the ileum, which could have consequences on the renin-angiotensin pathway

Alternative pre-mRNA splicing of the mu opioid receptor gene, OPRM1: Insight into complex mu opioid actions

Most opioid analgesics used clinically, including morphine and fentanyl, as well as the recreational drug heroin, act primarily through the mu opioid receptor, a class A Rhodopsin-like G protein-coupled receptor (GPCR). The single-copy mu opioid receptor gene

Mutagenesis in rodents using the L1 retrotransposon

LINE1 (L1) retrotransposons are genetic elements that are present in all mammalian genomes. L1s are active in both humans and mice, and are capable of copying themselves and inserting the copy into a new genomic location. These de novo insertions occasionally result in disease. Endogenous L1 retrotransposons can be modified to increase their activity and mutagenic power in a variety of ways. Here we outline the advantages of using modified L1 retrotransposons for performing random mutagenesis in rodents and discuss several potential applications

The Role of Forebrain Cholinergic Signalling In Regulating Hippocampal Function And Neuropathology

Cholinergic dysfunction has been associated with cognitive abnormalities in a variety of neurodegenerative and neuropsychiatric disorders, including Alzheimer’s Disease (AD). Cumulative use of drugs with anticholinergic activity is associated with increased risk for dementia and AD. Also, cholinergic function has been implicated in predicting the development of key neuropathological hallmarks seen in AD. However, the relationship between cholinergic dysfunction and conservation of cognitive ability as well as neuronal cell maintenance is not fully understood. Here, we tested how information processing and distinct molecular mechanisms associated with AD are regulated by cholinergic tone in genetically-modified mice in which cholinergic transmission was altered by targeting the vesicular acetylcholine transporter (VAChT), a protein required for acetylcholine storage and release. We assessed the long-term consequences of loss of central cholinergic signalling for hippocampal vulnerability to age-induced stress. We show that deletion of forebrain-specific ACh release leads to age-related increases in neuronal vulnerability, protein aggregation, tau Thr-231 phosphorylation and misfolding, and neuroinflammation. Moreover, inhibition of forebrain cholinergic neurotransmission led to a disturbance in adult hippocampal neurogenesis, highlighted by decreased proliferation and cell survival in neural precursor cells. Additionally, we measured long-term potentiation of Schaffer collateral-CA1 synapses in vivo and assessed information processing by using a mouse touchscreen version of Paired Associates Learning task (PAL). Acquisition in the mouse PAL task was impaired in forebrain-specific VAChT-deficient mice, suggesting a critical role for cholinergic tone. Accordingly, synaptic plasticity in the hippocampus in vivo was disturbed, but not completely abolished, by decreased hippocampal cholinergic signalling. In contrast, spatial memory was relatively preserved. Moreover, we assessed the functional consequence of impaired neurogenesis by testing pattern separation using a Location Discrimination task. Mice with compromised cholinergic signalling were impaired when stimuli were presented with small separation, but not when stimuli were presented with high separation, suggesting that deficient cholinergic tone has major consequences on pattern separation. The pathological changes in the hippocampus we observed in VAChT-deficient mice have important consequences as they presented age-related deterioration in spatial navigation. Our findings provide a refined understanding of the importance of acetylcholine in modulating molecular mechanisms and key cognitive behaviours involved in AD

Positional identification and functional analysis of genes regulating autoimmune arthritis

The major histocompatibility complex (MHC) is the most gene-dense and polymorphic region in the human genome with strong associations to many autoimmune disorders, including rheumatoid arthritis (RA). However, even the genetic association between MHC and RA was known more than 40 years ago, we still have not fully explained the functional roles of the MHC genes and identified the underlying specific polymorphisms. This thesis describes some of our research aimed for a better understanding of this topic, which can largely be divided into three parts as follows. First, we made use of a panel of MHC class II (MHC-II) congenic strains to evaluate the functional roles of MHC-II polymorphisms in arthritis. By performing an extensive genetic and functional analysis, we showed that MHC-II RT1-B (the rat orthologs of HLA-DQ) determines the onset and severity of experimental arthritis, possibly due to the amino acid variations in the P1 pocket of RT1-B. In addition, we showed that natural allelic variants in Tap2, another gene in the MHC-II region, regulates the thymic selection of CD8+ T cells. Second, in order to investigate whether other MHC genes also contribute to arthritis susceptibility, we assessed arthritis development in congenic strains mapped to other parts of the MHC region. We identified a second arthritis-regulatory QTL in the MHC class III region, that regulates not only the onset and severity, but also chronicity of arthritis. We subsequently mapped this effect to a conserved, 33-kb large haplotype Ltab-Ncr3 comprising five polymorphic genes. Interestingly, unlike other positionally-identified arthritis genes in rats, Ltab-Ncr3 regulates only adjuvant arthritis models but not autoimmunity triggered by specific tissue antigens, such as type II collagen. Furthermore, we found that gene expression and alternative splicing of the Ltab-Ncr3 genes correlate remarkably with arthritis severity and some of the gene expression differences were reproduced in a cohort of RA patients and healthy controls. Third, the MHC-II gene expression is regulated by class II transactivator (CIITA or C2TA), and in humans, genetic variation in CIITA has been associated with differential expression of MHC-II and susceptibility to autoimmune diseases. Using a congenic mouse strain with an allelic variant in the type I promoter of C2ta, we demonstrate that whereas genetic polymorphisms in C2ta promoter result in differential MHC-II expression and antigen presentation, these do not necessarily have a strong impact on autoimmune diseases such as arthritis. In summary, these studies demonstrate how the congenic approach remains powerful to conclusively identify and characterise genes regulating a complex disease like arthriti