Mehrdad Shamloo

Uncoupling protein-2 prevents neuronal death and diminishes brain dysfunction after stroke and brain trauma.

Whereas uncoupling protein 1 (UCP-1) is clearly involved in thermogenesis, the role of UCP-2 is less clear. Using hybridization, cloning techniques and cDNA array analysis to identify inducible neuroprotective genes, we found that neuronal survival correlates with increased expression of Ucp2. In mice overexpressing human UCP-2, brain damage was diminished after experimental stroke and traumatic brain injury, and neurological recovery was enhanced. In cultured cortical neurons, UCP-2 reduced cell death and inhibited caspase-3 activation induced by oxygen and glucose deprivation. Mild mitochondrial uncoupling by 2,4-dinitrophenol (DNP) reduced neuronal death, and UCP-2 activity was enhanced by palmitic acid in isolated mitochondria. Also in isolated mitochondria, UCP-2 shifted the release of reactive oxygen species from the mitochondrial matrix to the extramitochondrial space. We propose that UCP-2 is an inducible protein that is neuroprotective by activating cellular redox signaling or by inducing mild mitochondrial uncoupling that prevents the release of apoptogenic proteins.

Autism-linked neuroligin-3 R451C mutation differentially alters hippocampal and cortical synaptic function

Multiple independent mutations in neuroligin genes were identified in patients with familial autism, including the R451C substitution in neuroligin-3 (NL3). Previous studies showed that NL3R451C knock-in mice exhibited modestly impaired social behaviors, enhanced water maze learning abilities, and increased synaptic inhibition in the somatosensory cortex, and they suggested that the behavioral changes in these mice may be caused by a general shift of synaptic transmission to inhibition. Here, we confirm that NL3R451C mutant mice behaviorally exhibit social interaction deficits and electrophysiologically display increased synaptic inhibition in the somatosensory cortex. Unexpectedly, however, we find that the NL3R451C mutation produced a strikingly different phenotype in the hippocampus. Specifically, in the hippocampal CA1 region, the NL3R451C mutation caused an ∼1.5-fold increase in AMPA receptor-mediated excitatory synaptic transmission, dramatically altered the kinetics of NMDA receptor-mediated synaptic responses, induced an approximately twofold up-regulation of NMDA receptors containing NR2B subunits, and enhanced long-term potentiation almost twofold. NL3 KO mice did not exhibit any of these changes. Quantitative light microscopy and EM revealed that the NL3R451C mutation increased dendritic branching and altered the structure of synapses in the stratum radiatum of the hippocampus. Thus, in NL3R451C mutant mice, a single point mutation in a synaptic cell adhesion molecule causes context-dependent changes in synaptic transmission; these changes are consistent with the broad impact of this mutation on murine and human behaviors, suggesting that NL3 controls excitatory and inhibitory synapse properties in a region- and circuit-specific manner.

Transplanted Stem Cell‐Secreted Vascular Endothelial Growth Factor Effects Poststroke Recovery, Inflammation, and Vascular Repair

Cell transplantation offers a novel therapeutic strategy for stroke; however, how transplanted cells function in vivo is poorly understood. We show for the first time that after subacute transplantation into the ischemic brain of human central nervous system stem cells grown as neurospheres (hCNS‐SCns), the stem cell‐secreted factor, human vascular endothelial growth factor (hVEGF), is necessary for cell‐induced functional recovery. We correlate this functional recovery to hVEGF‐induced effects on the host brain including multiple facets of vascular repair and its unexpected suppression of the inflammatory response. We found that transplanted hCNS‐SCns affected multiple parameters in the brain with different kinetics: early improvement in blood‐brain barrier integrity and suppression of inflammation was followed by a delayed spatiotemporal regulated increase in neovascularization. These events coincided with a bimodal pattern of functional recovery, with, an early recovery independent of neovascularization, and a delayed hVEGF‐dependent recovery coincident with neovascularization. Therefore, cell transplantation therapy offers an exciting multimodal strategy for brain repair in stroke and potentially other disorders with a vascular or inflammatory component. STEM CELLS 2011;29:274–285

Classical MHCI Molecules Regulate Retinogeniculate Refinement and Limit Ocular Dominance Plasticity

Major histocompatibility complex class I (MHCI) genes were discovered unexpectedly in healthy CNS neurons in a screen for genes regulated by neural activity. In mice lacking just 2 of the 50+ MHCI genes H2-K(b) and H2-D(b), ocular dominance (OD) plasticity is enhanced. Mice lacking PirB, an MHCI receptor, have a similar phenotype. H2-K(b) and H2-D(b) are expressed not only in visual cortex, but also in lateral geniculate nucleus (LGN), where protein localization correlates strongly with synaptic markers and complement protein C1q. In K(b)D(b-/-) mice, developmental refinement of retinogeniculate projections is impaired, similar to C1q(-/-) mice. These phenotypes in K(b)D(b-/-) mice are strikingly similar to those in beta2 m(-/-)TAP1(-/-) mice, which lack cell surface expression of all MHCIs, implying that H2-K(b) and H2-D(b) can account for observed changes in synapse plasticity. H2-K(b) and H2-D(b) ligands, signaling via neuronal MHCI receptors, may enable activity-dependent remodeling of brain circuits during developmental critical periods.

Activation of the extracellular signal-regulated protein kinase cascade in the hippocampal CA1 region in a rat model of global cerebral ischemic preconditioning

A short period of sublethal preconditioning ischemia (3 min) followed by two days of reperfusion provides almost complete protection against ischemic cell death induced by a second (9 min) lethal ischemic episode. Here, we have investigated the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase, two kinases known to activate gene transcription and to be of importance for cell survival, after sublethal preconditioning ischemia in the rat hippocampal CA1 region. The activation levels of these two kinases were also studied after a second ischemic episode both in preconditioned and nonconditioned brains. An increased phosphorylation of the extracellular signal-regulated protein kinase kinase was found in neuronal cell bodies, particularly in the nucleus, 30 min, 4 h and two days of reperfusion after preconditioning ischemia. Two days after preconditioning ischemia both extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase were markedly phosphorylated. During the early reperfusion period (30 min) after the second ischemic insult the phosphorylation levels of these two kinases were increased in both nonconditioned and preconditioned brains. In the late reperfusion time (one day), the phosphorylation levels of the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase were decreased in preconditioned brains, but remained elevated in nonconditioned brains. We conclude that phosphorylation of the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase after sublethal ischemia correlates with the neuroprotection induced by preconditioning, possibly by transcriptional activation of neuroprotective genes. Also, preconditioning enhances normalization of the disturbed cell signaling through the extracellular signal-regulated protein kinase cascade induced by lethal ischemia.

A Dramatic Increase of C1q Protein in the CNS during Normal Aging

The decline of cognitive function has emerged as one of the greatest health threats of old age. Age-related cognitive decline is caused by an impacted neuronal circuitry, yet the molecular mechanisms responsible are unknown. C1q, the initiating protein of the classical complement cascade and powerful effector of the peripheral immune response, mediates synapse elimination in the developing CNS. Here we show that C1q protein levels dramatically increase in the normal aging mouse and human brain, by as much as 300-fold. This increase was predominantly localized in close proximity to synapses and occurred earliest and most dramatically in certain regions of the brain, including some but not all regions known to be selectively vulnerable in neurodegenerative diseases, i.e., the hippocampus, substantia nigra, and piriform cortex. C1q-deficient mice exhibited enhanced synaptic plasticity in the adult and reorganization of the circuitry in the aging hippocampal dentate gyrus. Moreover, aged C1q-deficient mice exhibited significantly less cognitive and memory decline in certain hippocampus-dependent behavior tests compared with their wild-type littermates. Unlike in the developing CNS, the complement cascade effector C3 was only present at very low levels in the adult and aging brain. In addition, the aging-dependent effect of C1q on the hippocampal circuitry was independent of C3 and unaccompanied by detectable synapse loss, providing evidence for a novel, complement- and synapse elimination-independent role for C1q in CNS aging.

Inhibition of mitochondrial fragmentation diminishes Huntington's disease-associated neurodegeneration.

Huntingtons disease (HD) is the result of expression of a mutated Huntingtin protein (mtHtt), and is associated with a variety of cellular dysfunctions including excessive mitochondrial fission. Here, we tested whether inhibition of excessive mitochondrial fission prevents mtHtt-induced pathology. We developed a selective inhibitor (P110-TAT) of the mitochondrial fission protein dynamin-related protein 1 (DRP1). We found that P110-TAT inhibited mtHtt-induced excessive mitochondrial fragmentation, improved mitochondrial function, and increased cell viability in HD cell culture models. P110-TAT treatment of fibroblasts from patients with HD and patients with HD with iPS cell-derived neurons reduced mitochondrial fragmentation and corrected mitochondrial dysfunction. P110-TAT treatment also reduced the extent of neurite shortening and cell death in iPS cell-derived neurons in patients with HD. Moreover, treatment of HD transgenic mice with P110-TAT reduced mitochondrial dysfunction, motor deficits, neuropathology, and mortality. We found that p53, a stress gene involved in HD pathogenesis, binds to DRP1 and mediates DRP1-induced mitochondrial and neuronal damage. Furthermore, P110-TAT treatment suppressed mtHtt-induced association of p53 with mitochondria in multiple HD models. These data indicate that inhibition of DRP1-dependent excessive mitochondrial fission with a P110-TAT-like inhibitor may prevent or slow the progression of HD.

Critical role of acetylation in tau-mediated neurodegeneration and cognitive deficits

Tauopathies, including frontotemporal dementia (FTD) and Alzheimers disease (AD), are neurodegenerative diseases in which tau fibrils accumulate. Recent evidence supports soluble tau species as the major toxic species. How soluble tau accumulates and causes neurodegeneration remains unclear. Here we identify tau acetylation at Lys174 (K174) as an early change in AD brains and a critical determinant in tau homeostasis and toxicity in mice. The acetyl-mimicking mutant K174Q slows tau turnover and induces cognitive deficits in vivo. Acetyltransferase p300-induced tau acetylation is inhibited by salsalate and salicylate, which enhance tau turnover and reduce tau levels. In the PS19 transgenic mouse model of FTD, administration of salsalate after disease onset inhibited p300 activity, lowered levels of total tau and tau acetylated at K174, rescued tau-induced memory deficits and prevented hippocampal atrophy. The tau-lowering and protective effects of salsalate were diminished in neurons expressing K174Q tau. Targeting tau acetylation could be a new therapeutic strategy against human tauopathies.

Restoration of Norepinephrine-Modulated Contextual Memory in a Mouse Model of Down Syndrome

Cognitive deficits in mice with a Down syndrome–like genetic defect can be reversed with precursors to the neurotransmitter norepinephrine. Mutant Mice Take Stroll Down Memory Lane Just last month, the British Medical Journal published data from a study of pregnant women in England and Wales that revealed a startling statistic: The number of women in these countries who conceived babies with Down syndrome (DS) rose 70% over the past 20 years. Possible reasons include more sophisticated screening techniques and the fact that folks are starting families at older ages. People with DS suffer from myriad maladies, but the most life-altering likely is that which interferes with one’s ability to make independent decisions about one’s life—moderate to severe life-long learning deficits. Now, Salehi et al. describe a treatment that improves learning and memory in the Ts65Dn mouse, a model of DS. The most common cause of mental retardation in people, DS arises from a chromosomal abnormality called trisomy 21, in which a third copy of chromosome 21 is present in cells, yielding an extra dose of ~300 genes. Ts65Dn mice have an extra copy of a piece of mouse chromosome 16, which carries genes similar to about one-third of those on human chromosome 21. Like people with DS, Ts65Dn mice display defects in learning and memory, functions that require a brain region called the hippocampus and the norepinephrine (NE)–producing neurons that feed it, which begin in the locus coeruleus (LC), a nucleus in the brainstem. Salehi et al. found that although the LC in a Ts65Dn mouse suffers severe degeneration, the cells that are targets for LC-generated NE remain intact and respond to exogenously supplied neurotransmitter in vitro. When the Ts65Dn mice were treated with l-threo-3,4-dihydroxyphenylserine, a NE precursor that crosses the blood-brain barrier, two types of so-called contextual learning—fear conditioning and nest building—were restored. It remains unclear whether the LC functions in contextual learning in humans, but LC degeneration is evident in a variety of neurological disorders, including DS and Alzheimer’s disease (AD), and people with DS display hippocampal dysfunction as well as serious impairments in contextual learning. It is noteworthy that the App gene, which encodes the mouse homolog of the human amyloid β precursor protein, exists in triplicate in Ts65Dn mice. Fragments of this protein build up in the brains of early-onset AD patients, forming plaques that eventually kill neurons. Salehi et al. show that this extra measure of App is required for destruction of the LC neurons in Ts65Dn mice. Together, these new findings fill some of the knowledge gaps regarding the genesis of neurological defects in DS and point toward an already approved drug as a starting point for therapies that address these independence-robbing deficits. Down syndrome (trisomy 21) is the most common cause of mental retardation in children and leads to marked deficits in contextual learning and memory. In rodents, these tasks require the hippocampus and are mediated by several inputs, particularly those originating in the locus coeruleus. These afferents mainly use norepinephrine as a transmitter. To explore the basis for contextual learning defects in Down syndrome, we examined the Ts65Dn mouse model. These mice, which have three copies of a fragment of mouse chromosome 16, exhibited significant deficits in contextual learning together with dysfunction and degeneration of locus coeruleus neurons. However, the postsynaptic targets of innervation remained responsive to noradrenergic receptor agonists. Indeed, despite advanced locus coeruleus degeneration, we were able to reverse contextual learning failure by using a prodrug for norepinephrine called l-threo-3,4-dihydroxyphenylserine, or xamoterol, a β1-adrenergic receptor partial agonist. Moreover, an increased gene dosage of App, in the context of Down syndrome, was necessary for locus coeruleus degeneration. Our findings raise the possibility that restoring norepinephrine-mediated neurotransmission could reverse cognitive dysfunction in Down syndrome.

Mouse model of Timothy syndrome recapitulates triad of autistic traits

Autism and autism spectrum disorder (ASD) typically arise from a mixture of environmental influences and multiple genetic alterations. In some rare cases, such as Timothy syndrome (TS), a specific mutation in a single gene can be sufficient to generate autism or ASD in most patients, potentially offering insights into the etiology of autism in general. Both variants of TS (the milder TS1 and the more severe TS2) arise from missense mutations in alternatively spliced exons that cause the same G406R replacement in the CaV1.2 L-type calcium channel. We generated a TS2-like mouse but found that heterozygous (and homozygous) animals were not viable. However, heterozygous TS2 mice that were allowed to keep an inverted neomycin cassette (TS2-neo) survived through adulthood. We attribute the survival to lowering of expression of the G406R L-type channel via transcriptional interference, blunting deleterious effects of mutant L-type channel overactivity, and addressed potential effects of altered gene dosage by studying CaV1.2 knockout heterozygotes. Here we present a thorough behavioral phenotyping of the TS2-neo mouse, capitalizing on this unique opportunity to use the TS mutation to model ASD in mice. Along with normal general health, activity, and anxiety level, TS2-neo mice showed markedly restricted, repetitive, and perseverative behavior, altered social behavior, altered ultrasonic vocalization, and enhanced tone-cued and contextual memory following fear conditioning. Our results suggest that when TS mutant channels are expressed at levels low enough to avoid fatality, they are sufficient to cause multiple, distinct behavioral abnormalities, in line with the core aspects of ASD.