Carlos A. Pardo

Knockout of Glutamate Transporters Reveals a Major Role for Astroglial Transport in Excitotoxicity and Clearance of Glutamate

Three glutamate transporters have been identified in rat, including astroglial transporters GLAST and GLT-1 and a neuronal transporter EAAC1. Here we demonstrate that inhibition of the synthesis of each glutamate transporter subtype using chronic antisense oligonucleotide administration, in vitro and in vivo, selectively and specifically reduced the protein expression and function of glutamate transporters. The loss of glial glutamate transporters GLAST or GLT-1 produced elevated extracellular glutamate levels, neurodegeneration characteristic of excitotoxicity, and a progressive paralysis. The loss of the neuronal glutamate transporter EAAC1 did not elevate extracellular glutamate in the striatum but did produce mild neurotoxicity and resulted in epilepsy. These studies suggest that glial glutamate transporters provide the majority of functional glutamate transport and are essential for maintaining low extracellular glutamate and for preventing chronic glutamate neurotoxicity.

An adverse property of a familial ALS-linked SOD1 mutation causes motor neuron disease characterized by vacuolar degeneration of mitochondria

Mutations in Cu/Zn superoxide dismutase (SOD1) cause a subset of cases of familial amyotrophic lateral sclerosis. Four lines of mice accumulating one of these mutant proteins (G37R) develop severe, progressive motor neuron disease. At lower levels of mutant accumulation, pathology is restricted to lower motor neurons, whereas higher levels cause more severe abnormalities and affect a variety of other neuronal populations. The most obvious cellular abnormality is the presence in axons and dendrites of membrane-bounded vacuoles, which appear to be derived from degenerating mitochondria. Since multiple lines of mice expressing wild-type human SOD1 at similar and higher levels do not show disease, the disease in mice expressing the G37R mutant SOD1 must arise from the acquisition of an adverse property by the mutant enzyme, rather than elevation or loss of SOD1 activity.

Neuroglial activation and neuroinflammation in the brain of patients with autism.

Autism is a neurodevelopmental disorder characterized by impaired communication and social interaction and may be accompanied by mental retardation and epilepsy. Its cause remains unknown, despite evidence that genetic, environmental, and immunological factors may play a role in its pathogenesis. To investigate whether immune‐mediated mechanisms are involved in the pathogenesis of autism, we used immunocytochemistry, cytokine protein arrays, and enzyme‐linked immunosorbent assays to study brain tissues and cerebrospinal fluid (CSF) from autistic patients and determined the magnitude of neuroglial and inflammatory reactions and their cytokine expression profiles. Brain tissues from cerebellum, midfrontal, and cingulate gyrus obtained at autopsy from 11 patients with autism were used for morphological studies. Fresh‐frozen tissues available from seven patients and CSF from six living autistic patients were used for cytokine protein profiling. We demonstrate an active neuroinflammatory process in the cerebral cortex, white matter, and notably in cerebellum of autistic patients. Immunocytochemical studies showed marked activation of microglia and astroglia, and cytokine profiling indicated that macrophage chemoattractant protein (MCP)–1 and tumor growth factor–β1, derived from neuroglia, were the most prevalent cytokines in brain tissues. CSF showed a unique proinflammatory profile of cytokines, including a marked increase in MCP‐1. Our findings indicate that innate neuroimmune reactions play a pathogenic role in an undefined proportion of autistic patients, suggesting that future therapies might involve modifying neuroglial responses in the brain. Ann Neurol 2005

The Neurobiology of Autism

Improving clinical tests are allowing us to more precisely classify autism spectrum disorders and diagnose them at earlier ages. This raises the possibility of earlier and potentially more effective therapeutic interventions. To fully capitalize on this opportunity, however, will require better understanding of the neurobiological changes underlying this devastating group of developmental disorders. It is becoming clear that the normal trajectory of neurodevelopment is altered in autism, with aberrations in brain growth, neuronal patterning and cortical connectivity. Changes to the structure and function of synapses and dendrites have also been strongly implicated in the pathology of autism by morphological, genetic and animal modeling studies. Finally, environmental factors are likely to interact with the underlying genetic profile, and foster the clinical heterogeneity seen in autism spectrum disorders. In this review we attempt to link the molecular pathways altered in autism to the neurodevelopmental and clinical changes that characterize the disease. We focus on signaling molecules such as neurotrophin, Reelin, PTEN and hepatocyte growth factor, neurotransmitters such as serotonin and glutamate, and synaptic proteins such as neurexin, SHANK and neuroligin. We also discuss evidence implicating oxidative stress, neuroglial activation and neuroimmunity in autism.

Human immunodeficiency virus-associated dementia: An evolving disease

This article reviews the changing epidemiology of HIV-associated dementia, current concepts of the different patterns of dementia under the influence of highly active antiretroviral therapy, and reviews therapeutic aspects.

Microglial activation and increased microglial density observed in the dorsolateral prefrontal cortex in autism

BACKGROUND In the neurodevelopmental disorder autism, several neuroimmune abnormalities have been reported. However, it is unknown whether microglial somal volume or density are altered in the cortex and whether any alteration is associated with age or other potential covariates. METHODS Microglia in sections from the dorsolateral prefrontal cortex of nonmacrencephalic male cases with autism (n = 13) and control cases (n = 9) were visualized via ionized calcium binding adapter molecule 1 immunohistochemistry. In addition to a neuropathological assessment, microglial cell density was stereologically estimated via optical fractionator and average somal volume was quantified via isotropic nucleator. RESULTS Microglia appeared markedly activated in 5 of 13 cases with autism, including 2 of 3 under age 6, and marginally activated in an additional 4 of 13 cases. Morphological alterations included somal enlargement, process retraction and thickening, and extension of filopodia from processes. Average microglial somal volume was significantly increased in white matter (p = .013), with a trend in gray matter (p = .098). Microglial cell density was increased in gray matter (p = .002). Seizure history did not influence any activation measure. CONCLUSIONS The activation profile described represents a neuropathological alteration in a sizeable fraction of cases with autism. Given its early presence, microglial activation may play a central role in the pathogenesis of autism in a substantial proportion of patients. Alternatively, activation may represent a response of the innate neuroimmune system to synaptic, neuronal, or neuronal network disturbances, or reflect genetic and/or environmental abnormalities impacting multiple cellular populations.

Immunity, neuroglia and neuroinflammation in autism

Autism is a complex neurodevelopmental disorder of early onset that is highly variable in its clinical presentation. Although the causes of autism in most patients remain unknown, several lines of research support the view that both genetic and environmental factors influence the development of abnormal cortical circuitry that underlies autistic cognitive processes and behaviors. The role of the immune system in the development of autism is controversial. Several studies showing peripheral immune abnormalities support immune hypotheses, however until recently there have been no immune findings in the CNS. We recently demonstrated the presence of neuroglial and innate neuroimmune system activation in brain tissue and cerebrospinal fluid of patients with autism, findings that support the view that neuroimmune abnormalities occur in the brain of autistic patients and may contribute to the diversity of the autistic phenotypes. The role of neuroglial activation and neuroinflammation are still uncertain but could be critical in maintaining, if not also in initiating, some of the CNS abnormalities present in autism. A better understanding of the role of neuroinflammation in the pathogenesis of autism may have important clinical and therapeutic implications.

Extensive astrocyte infection is prominent in human immunodeficiency virus-associated dementia.

Astrocyte infection with human immunodeficiency virus (HIV) is considered rare, so astrocytes are thought to play a secondary role in HIV neuropathogenesis. By combining double immunohistochemistry, laser capture microdissection, and highly sensitive multiplexed polymerase chain reaction to detect HIV DNA in single astrocytes in vivo, we showed that astrocyte infection is extensive in subjects with HIV‐associated dementia, occurring in up to 19% of GFAP+ cells. In addition, astrocyte infection frequency correlated with the severity of neuropathological changes and proximity to perivascular macrophages. Our data indicate that astrocytes can be extensively infected with HIV, and suggest an important role for HIV‐infected astrocytes in HIV neuropathogenesis. Ann Neurol 2009;66:253–258

Detection of MHC class II-antigens on macrophages and microglia, but not on astrocytes and endothelia in active multiple sclerosis lesions

Tissue sections of brains from patients with multiple sclerosis (MS) and from control individuals were immunostained with MHC class II and glial or vascular endothelial cell antibodies and analyzed by confocal microscopy. MHC class II was abundant in and around actively demyelinating MS lesions and was detected on microglia, phagocytic macrophages, and perivascular macrophages. Astrocytes and vascular endothelial cells were MHC class II-negative. Changes in the size and shape of MHC class II-positive cells associated with MS lesions suggest that microglia transform into phagocytic macrophages, and that they are actively involved in demyelination. Many MHC class II-positive perivascular macrophages within MS lesions contained abundant intracellular MHC class II immunoreactivity; these cells may be involved in antigen presentation and in T cell activation.

Perturbation of sphingolipid metabolism and ceramide production in HIV-dementia

Infection by the human immunodeficiency virus type 1 (HIV‐1) often results in neurological dysfunction including HIV dementia (HIVD). Alterations in cytokine and redox balance are thought to play important roles in the pathogenesis of HIVD, but the specific mechanisms underlying neuronal dysfunction and death are unknown. Activation of cytokine receptors and oxidative stress can induce the production of ceramide from membrane sphingomyelin, and recent findings suggest that ceramide is an important mediator of a form of programmed cell death called apoptosis. We now report that levels of ceramide, sphingomyelin, and hydroxynonenal (HNE) are significantly increased in brain tissues and cerebrospinal fluid of HIVD patients. Exposure of cultured neurons to the neurotoxic HIV proteins gp120 and Tat resulted in increased cellular levels of sphingomyelin, ceramide, and HNE. The ceramide precursor palmitoyl‐CoA sensitized neurons to Tat and gp120 toxicity, whereas an inhibitor of ceramide production reduced Tat and gp120‐induced increases of ceramide and HNE and protected the neurons from Tat and gp120‐induced death. These results suggest that HIV‐1 infection may promote a lipid imbalance in neural cells, resulting in an overproduction of ceramide and consequent cellular dysfunction and death.