Striatal neuronal death mediated by astrocytes from the Gcdh-/- mouse model of glutaric acidemia type I.

Glutaric acidemia type I (GA-I) is an inherited neurometabolic childhood disorder caused by defective activity of glutaryl CoA dehydrogenase (GCDH) which disturb lysine (Lys) and tryptophan catabolism leading to neurotoxic accumulation of glutaric acid (GA) and related metabolites. However, it remains unknown whether GA toxicity is due to direct effects on vulnerable neurons or mediated by GA-intoxicated astrocytes that fail to support neuron function and survival. As damaged astrocytes can also contribute to sustain high GA levels, we explored the ability of Gcdh-/- mouse astrocytes to produce GA and induce neuronal death when challenged with Lys. Upon Lys treatment, Gcdh-/- astrocytes synthetized and released GA and 3-hydroxyglutaric acid (3HGA). Lys and GA treatments also increased oxidative stress and proliferation in Gcdh-/- astrocytes, both prevented by antioxidants. Pretreatment with Lys also caused Gcdh-/- astrocytes to induce extensive death of striatal and cortical neurons when compared with milder effect in WT astrocytes. Antioxidants abrogated the neuronal death induced by astrocytes exposed to Lys or GA. In contrast, Lys or GA direct exposure on Gcdh-/- or WT striatal neurons cultured in the absence of astrocytes was not toxic, indicating that neuronal death is mediated by astrocytes. In summary, GCDH-defective astrocytes actively contribute to produce and accumulate GA and 3HGA when Lys catabolism is stressed. In turn, astrocytic GA production induces a neurotoxic phenotype that kills striatal and cortical neurons by an oxidative stress-dependent mechanism. Targeting astrocytes in GA-I may prompt the development of new antioxidant-based therapeutical approaches.

Ultrastructural features of aberrant glial cells isolated from the spinal cord of paralytic rats expressing the amyotrophic lateral sclerosis-linked SOD1G93A mutation.

In the rat model of amyotrophic lateral sclerosis expressing the G93A superoxide dismutase-1 mutation, motor neuron death and rapid paralysis progression are associated with the emergence of a population of aberrant glial cells (AbAs) that proliferate in the degenerating spinal cord. Targeting of AbAs with anti-neoplasic drugs reduced paralysis progression, suggesting a pathogenic potential contribution of these cells accelerating paralysis progression. In the present study, analyze the cellular and ultrastructural features of AbAs following their isolation and establishment in culture during several passages. We found that AbAs exhibit permanent loss of contact inhibition, absence of intermediate filaments and abundance of microtubules, together with an important production of extracellular matrix components. Remarkably, AbAs also exhibited exacerbated ER stress together with a significant abundance of lipid droplets, as well as autophagic and secretory vesicles, all characteristic features of cellular stress and inflammatory activation. Taken together, the present data show AbA cells as a unique aberrant phenotype for a glial cell that might explain their pathogenic and neurotoxic effects.

Astrocyte Dysfunction in Developmental Neurometabolic Diseases.

Astrocytes play crucial roles in maintaining brain homeostasis and in orchestrating neural development, all through tightly coordinated steps that cooperate to maintain the balance needed for normal development. Here, we review the alterations in astrocyte functions that contribute to a variety of developmental neurometabolic disorders and provide additional data on the predominant role of astrocyte dysfunction in the neurometabolic neurodegenerative disease glutaric acidemia type I. Finally, we describe some of the therapeutical approaches directed to neurometabolic diseases and discuss if astrocytes can be possible therapeutic targets for treating these disorders.

Phenotypically aberrant astrocytes that promote motoneuron damage in a model of inherited amyotrophic lateral sclerosis.

Motoneuron loss and reactive astrocytosis are pathological hallmarks of amyotrophic lateral sclerosis (ALS), a paralytic neurodegenerative disease that can be triggered by mutations in Cu-Zn superoxide dismutase (SOD1). Dysfunctional astrocytes contribute to ALS pathogenesis, inducing motoneuron damage and accelerating disease progression. However, it is unknown whether ALS progression is associated with the appearance of a specific astrocytic phenotype with neurotoxic potential. Here, we report the isolation of astrocytes with aberrant phenotype (referred as "AbA cells") from primary spinal cord cultures of symptomatic rats expressing the SOD1(G93A) mutation. Isolation was based on AbA cells' marked proliferative capacity and lack of replicative senescence, which allowed oligoclonal cell expansion for 1 y. AbA cells displayed astrocytic markers including glial fibrillary acidic protein, S100ß protein, glutamine synthase, and connexin 43 but lacked glutamate transporter 1 and the glial progenitor marker NG2 glycoprotein. Notably, AbA cells secreted soluble factors that induced motoneuron death with a 10-fold higher potency than neonatal SOD1(G93A) astrocytes. AbA-like aberrant astrocytes expressing S100ß and connexin 43 but lacking NG2 were identified in nearby motoneurons, and their number increased sharply after disease onset. Thus, AbA cells appear to be an as-yet unknown astrocyte population arising during ALS progression with unprecedented proliferative and neurotoxic capacity and may be potential cellular targets for slowing ALS progression.

Cerebral White Matter Alterations Associated With Oligodendrocyte Vulnerability in Organic Acidurias: Insights in Glutaric Aciduria Type I.

The white matter is an important constituent of the central nervous system, containing axons, oligodendrocytes, and its progenitor cells, astrocytes, and microglial cells. Oligodendrocytes are central for myelin synthesis, the insulating envelope that protects axons and allows normal neural conduction. Both, oligodendrocytes and myelin, are highly vulnerable to toxic factors in many neurodevelopmental and neurodegenerative disorders associated with disturbances of myelination. Here we review the main alterations in oligodendrocytes and myelin observed in some organic acidurias/acidemias, which correspond to inherited neurometabolic disorders biochemically characterized by accumulation of potentially neurotoxic organic acids and their derivatives. The yet incompletely understood mechanisms underlying the high vulnerability of OLs and/or myelin in glutaric acidemia type I, the most prototypical cerebral organic aciduria, are particularly discussed.

Acute Genetic Damage Induced by Ethanol and Corticosterone Seems to Modulate Hippocampal Astrocyte Signaling.

Astrocytes maintain CNS homeostasis but also critically contribute to neurological and psychiatric disorders. Such functional diversity implies an extensive signaling repertoire including extracellular vesicles (EVs) and nanotubes (NTs) that could be involved in protection or damage, as widely shown in various experimental paradigms. However, there is no information associating primary damage to the astrocyte genome, the DNA damage response (DDR), and the EV and NT repertoire. Furthermore, similar studies were not performed on hippocampal astrocytes despite their involvement in memory and learning processes, as well as in the development and maintenance of alcohol addiction. By exposing murine hippocampal astrocytes to 400 mM ethanol (EtOH) and/or 1 µM corticosterone (CTS) for 1 h, we tested whether the induced DNA damage and DDR could elicit significant changes in NTs and surface-attached EVs. Genetic damage and initial DDR were assessed by immunolabeling against the phosphorylated histone variant H2AX (γH2AX), DDR-dependent apoptosis by BAX immunoreactivity, and astrocyte activation by the glial acidic fibrillary protein (GFAP) and phalloidin staining. Surface-attached EVs and NTs were examined via scanning electron microscopy, and labeled proteins were analyzed via confocal microscopy. Relative to controls, astrocytes exposed to EtOH, CTS, or EtOH+CTS showed significant increases in nuclear γlH2AX foci, nuclear and cytoplasmic BAX signals, and EV frequency at the expense of the NT amount, mainly upon EtOH, without detectable signs of morphological reactivity. Furthermore, the largest and most complex EVs originated only in DNA-damaged astrocytes. Obtained results revealed that astrocytes exposed to acute EtOH and/or CTS preserved their typical morphology but presented severe DNA damage, triggered canonical DDR pathways, and early changes in the cell signaling mediated by EVs and NTs. Further deepening of this initial morphological and quantitative analysis is necessary to identify the mechanistic links between genetic damage, DDR, cell-cell communication, and their possible impact on hippocampal neural cells.

Brain atlas of the annual Garcialebias charrua fish.

Annual fish have become attractive study models for a wide range of disciplines, including neurobiology. These fish have developed different survival strategies. As a result, their nervous system is under considerable selective pressure when facing extreme environmental situations. Fish from the Austrolebias group exhibit rapid neurogenesis in different brain regions, possibly as a result of the demanding conditions of a changing habitat. Knowledge of cerebral histology is essential for detecting ontogenic, anatomical, or cytoarchitectonic changes in the brain during the short lifespan of these fish, such as those reflecting functional adaptive plasticity in different systems, including sensory structures. The generation of an atlas of Garcialebias charrua (previously known as Austrolebias charrua) establishes its anatomical basis as a representative of a large group of fish that share similarities in their way of life. In this work, we present a detailed study of both gross anatomy and microscopic anatomy obtained through serial sections stained with the Nissl technique in three orientations: transverse, horizontal, and parasagittal planes. This atlas includes accurate drawings of the entire adult brain of the male fish Garcialebias charrua, showing dorsal, ventral, and lateral views, including where emergence and origin of cranial nerves. This brain atlas allows us to understand histoarchitecture as well as the location of neural structures that change during adult neurogenesis, enabling comparisons within the genus. Simultaneously, this atlas constitutes a valuable tool for comparing the brains of other fish species with different behaviors and neuroecologies.

Adult aberrant astrocytes submitted to late passage cultivation lost differentiation markers and decreased their pro-inflammatory profile.

In amyotrophic lateral sclerosis (ALS), astrocytes are considered key players in some non-cell non-neuronal autonomous mechanisms that underlie motor neuron death. However, it is unknown how much of these deleterious features were permanently acquired. To assess this point, we evaluated if the most remarkable features of neurotoxic aberrant glial phenotypes (AbAs) isolated from paralytic rats of the ALS model G93A Cu/Zn superoxide dismutase 1 (SOD1) could remain upon long lasting cultivation. Real time PCR, immunolabelling and zymography analysis showed that upon many passages, AbAs preserved the cell proliferation capacity, mitochondrial function and response to different compounds that inhibit some key astrocyte functions but decreased the expression of parameters associated to cell lineage, homeostasis and inflammation. As these results are contrary to the sustained inflammatory status observed along disease progression in SOD1G93A rats, we propose that the most AbAs remarkable features related to homeostasis and neurotoxicity were not permanently acquired and might depend on the signaling coming from the injuring microenvironment present in the degenerating spinal cord of terminal rats.

Dual Effect of Carnosine on ROS Formation in Rat Cultured Cortical Astrocytes.

Carnosine is composed of ß-alanine and L-histidine and is considered to be an important neuroprotective agent with antioxidant, metal chelating, and antisenescence properties. However, children with serum carnosinase deficiency present increased circulating carnosine and severe neurological symptoms. We here investigated the in vitro effects of carnosine on redox and mitochondrial parameters in cultured cortical astrocytes from neonatal rats. Carnosine did not alter mitochondrial content or mitochondrial membrane potential. On the other hand, carnosine increased mitochondrial superoxide anion formation, levels of thiobarbituric acid reactive substances and oxidation of 2',7'-dichlorofluorescin diacetate (DCF-DA), indicating that carnosine per se acts as a pro-oxidant agent. Nonetheless, carnosine prevented DCF-DA oxidation induced by H2O2 in cultured cortical astrocytes. Since alterations on mitochondrial membrane potential are not likely to be involved in these effects of carnosine, the involvement of N-Methyl-D-aspartate (NMDA) receptors in the pro-oxidant actions of carnosine was investigated. MK-801, an antagonist of NMDA receptors, prevented DCF-DA oxidation induced by carnosine in cultured cortical astrocytes. Astrocyte reactivity induced by carnosine was also prevented by the coincubation with MK-801. The present study shows for the very first time the pro-oxidant effects of carnosine per se in astrocytes. The data raise awareness on the importance of a better understanding of the biological actions of carnosine, a nutraceutical otherwise widely reported as devoid of side effects.

Disruption of brain redox homeostasis in glutaryl-CoA dehydrogenase deficient mice treated with high dietary lysine supplementation.

Deficiency of glutaryl-CoA dehydrogenase (GCDH) activity or glutaric aciduria type I (GA I) is an inherited neurometabolic disorder biochemically characterized by predominant accumulation of glutaric acid and 3-hydroxyglutaric acid in the brain and other tissues. Affected patients usually present acute striatum necrosis during encephalopathic crises triggered by metabolic stress situations, as well as chronic leukodystrophy and delayed myelination. Considering that the mechanisms underlying the brain injury in this disease are not yet fully established, in the present study we investigated important parameters of oxidative stress in the brain (cerebral cortex, striatum and hippocampus), liver and heart of 30-day-old GCDH deficient knockout (Gcdh(-/-)) and wild type (WT) mice submitted to a normal lysine (Lys) (0.9% Lys), or high Lys diets (2.8% or 4.7% Lys) for 60 h. It was observed that the dietary supplementation of 2.8% and 4.7% Lys elicited noticeable oxidative stress, as verified by an increase of malondialdehyde concentrations (lipid oxidative damage) and 2-7-dihydrodichlorofluorescein (DCFH) oxidation (free radical production), as well as a decrease of reduced glutathione levels and alteration of various antioxidant enzyme activities (antioxidant defenses) in the cerebral cortex and the striatum, but not in the hippocampus, the liver and the heart of Gcdh(-/-) mice, as compared to WT mice receiving the same diets. Furthermore, alterations of oxidative stress parameters in the cerebral cortex and striatum were more accentuated in symptomatic, as compared to asymptomatic Gcdh(-/-) mice exposed to 4.7% Lys overload. Histopathological studies performed in the cerebral cortex and striatum of these animals exposed to high dietary Lys revealed increased expression of oxidative stress markers despite the absence of significant structural damage. The results indicate that a disruption of redox homeostasis in the cerebral cortex and striatum of young Gcdh(-/-) mice exposed to increased Lys diet may possibly represent an important pathomechanism of brain injury in GA I patients under metabolic stress.

Astrocyte DNA damage and response upon acute exposure to ethanol and corticosterone.

Introduction: Astrocytes are the glial cells responsible for brain homeostasis, but if injured, they could damage neural cells even deadly. Genetic damage, DNA damage response (DDR), and its downstream cascades are dramatic events poorly studied in astrocytes. Hypothesis and methods: We propose that 1 h of 400 mmol/L ethanol and/or 1 µmol/L corticosterone exposure of cultured hippocampal astrocytes damages DNA, activating the DDR and eliciting functional changes. Immunolabeling against γH2AX (chromatin DNA damage sites), cyclin D1 (cell cycle control), nuclear (base excision repair, BER), and cytoplasmic (anti-inflammatory functions) APE1, ribosomal nucleolus proteins together with GFAP and S100ß plus scanning electron microscopy studies of the astrocyte surface were carried out. Results: Data obtained indicate significant DNA damage, immediate cell cycle arrest, and BER activation. Changes in the cytoplasmic signals of cyclin D1 and APE1, nucleolus number, and membrane-attached vesicles strongly suggest a reactivity like astrocyte response without significant morphological changes. Discussion: Obtained results uncover astrocyte genome immediate vulnerability and DDR activation, plus a functional response that might in part, be signaled through extracellular vesicles, evidencing the complex influence that astrocytes may have on the CNS even upon short-term aggressions.

Morphological evidence of the protective effects of a synthetic chalcone against the striatal myelin damage induced by glutaric acid.

Ultrastructural features of striatal white matter and cells in an in vivo model of glutaric acidemia type I created by intracerebral injection of glutaric acid (GA) were analyzed by transmission electron microscopy and immunohistochemistry. To test if the white matter damage observed in this model could be prevented, we administered the synthetic chemopreventive molecule CH38 ((E)-3-(4-methylthiophenyl)-1-phenyl-2-propen-1-one) to newborn rats, previous to an intracerebroventricular injection of GA. The study was done when striatal myelination was incipient and when it was already established (at 12 and 45 days post-injection [DPI], respectively). Results obtained indicate that that the ultrastructure of astrocytes and neurons did not appear significantly affected by the GA bolus. Instead, in oligodendrocytes, the most prominent GA-dependent injury defects included endoplasmic reticulum (ER) stress and nuclear envelope swelling at 12 DPI. Altered and reduced immunoreactivities against heavy neurofilament (NF), proteolipid protein (PLP), and myelin-associated glycoprotein (MAG) together with axonal bundle fragmentation and decreased myelin were also found at both ages analyzed. CH38 by itself did not affect striatal cells or axonal packages. However, the group of rats that received CH38 before GA did not show evidence neither of ER stress nor nuclear envelope dilation in oligodendrocytes, and axonal bundles appeared less fragmented. In this group, labeling of NF and PLP was similar to the controls. These results suggest that the CH38 molecule is a candidate drug to prevent or decrease the neural damage elicited by a pathological increase of GA in the brain. Optimization of the treatments and identification of the mechanisms underlying CH38 protective effects will open new therapeutic windows to protect myelin, which is a vulnerable target of numerous nervous system diseases.

A Focus on Astrocyte Contribution to Parkinson's Disease Etiology.

Parkinson's disease (PD) is an incurable neurodegenerative disease of high prevalence, characterized by the prominent death of dopaminergic neurons in the substantia nigra pars compacta, which produces dopamine deficiency, leading to classic motor symptoms. Although PD has traditionally been considered as a neuronal cell autonomous pathology, in which the damage of vulnerable neurons is responsible for the disease, growing evidence strongly suggests that astrocytes might have an active role in the neurodegeneration observed. In the present review, we discuss several studies evidencing astrocyte implications in PD, highlighting the consequences of both the loss of normal homeostatic functions and the gain in toxic functions for the wellbeing of dopaminergic neurons. The revised information provides significant evidence that allows astrocytes to be positioned as crucial players in PD etiology, a factor that needs to be taken into account when considering therapeutic targets for the treatment of the disease.

Gestational and Lactational Iron Deficiency Anemia Impairs Myelination and the Neurovascular Unit in Infant Rats.

Iron deficiency anemia is a prevalent health problem among pregnant women and infants, particularly in the developing countries that causes brain development deficits and poor cognitive outcomes. Since tissue iron depletion may impair myelination and trigger cellular hypoxic signaling affecting blood vessels, we studied myelination and the neurovascular unit (NVU) in infant rats born to mothers fed with an iron deficient (ID) or control diet from embryonic day 5 till weaning. Blood samples and brains of rat pups at postnatal day (PND) 14 and 30 were analyzed. PND 14 ID rats had severe microcytic hypochromic anemia that was almost reversed at PND 30 although hypomyelination and astrocyte immature phenotype in the corpus callosum were significant at that age. In CA1 hippocampal region, PND 14 and PND 30 ID rats showed significant reduced expression of the receptor ß of the platelet-derived growth factor localized in pericytes and associated to aquaporin 4 (AQP4) immunopositive capillaries. Shorter AQP4 + capillaries and reduced AQP4 expression were also evidenced in PND 14 and PND 30 ID rats. In addition, pericyte membrane permeability through large-pore channels was transiently increased in ID rats at PND 14 but not at PND 30, while the blood-brain barrier permeability was not affected. Remarkably, transient increased pericyte permeability found in PND 14 ID rats was not directly related to iron depletion, suggesting the involvement of other iron deficiency anemia-induced mechanisms. In summary, severe ID during gestation and lactation produces persistent hypomyelination and significantly affects hippocampal pericytes and astrocytes in the NVU which may trigger impaired neurovascular function.

Patched-Related Is Required for Proper Development of Embryonic Drosophila Nervous System.

Patched-related (Ptr), classified primarily as a neuroectodermal gene, encodes a protein with predicted topology and domain organization closely related to those of Patched (Ptc), the canonical receptor of the Hedgehog (Hh) pathway. To investigate the physiological function of Ptr in the developing nervous system, Ptr null mutant embryos were immunolabeled and imaged under confocal microscopy. These embryos displayed severe alterations in the morphology of the primary axonal tracts, reduced number, and altered distribution of the Repo-positive glia as well as peripheral nervous system defects. Most of these alterations were recapitulated by downregulating Ptr expression, specifically in embryonic nerve cells. Because similar nervous system phenotypes have been observed in hh and ptc mutant embryos, we evaluated the Ptr participation in the Hh pathway by performing cell-based reporter assays. Clone-8 cells were transfected with Ptr-specific dsRNA or a Ptr DNA construct and assayed for changes in Hh-mediated induction of a luciferase reporter. The results obtained suggest that Ptr could act as a negative regulator of Hh signaling. Furthermore, co-immunoprecipitation assays from cell culture extracts premixed with a conditioned medium revealed a direct interaction between Ptr and Hh. Moreover, in vivo Ptr overexpression in the domain of the imaginal wing disc where Engrailed and Ptc coexist produced wing phenotypes at the A/P border. Thus, these results strongly suggest that Ptr plays a crucial role in nervous system development and appears to be a negative regulator of the Hh pathway.

Plasticity of cell proliferation in the retina of Austrolebias charrua fish under light and darkness conditions.

Austrolebias annual fishes exhibit cell proliferation and neurogenesis throughout life. They withstand extreme environmental changes as their habitat dries out, pressuring nervous system to adapt. Their visual system is challenged to adjust as the water becomes turbid. Therefore, this study focused on how change in photic environment can lead to an increased cell proliferation in the retina. We administered 5-chloro-2'- deoxyuridine (CldU) and 5-iodo-2'-deoxyuridine (IdU) at different temporal windows to detect cell proliferation in natural light and permanent darkness. Stem/progenitor cells were recognized as IdU+/CldU + nuclei co-labeled with Sox2, Pax6 or BLBP found in the ciliary marginal zone (CMZ). The expression pattern of BLBP + glial cells and ultrastructural analysis indicates that CMZ has different cell progenitors. In darkness, the number of dividing cells significantly increased, compared to light conditions. Surprisingly, CMZ IdU+/CldU + cell number was similar under light and darkness, suggesting a stable pool of stem/progenitor cells possibly responsible for retinal growth. Therefore, darkness stimulated cell progenitors outside the CMZ, where Müller glia play a crucial role to generate rod precursors and other cell types that might integrate rod-dependent circuits to allow darkness adaptation. Thus, the Austrolebias fish retina shows great plasticity, with cell proliferation rates significantly higher than that of brain visual areas.

Neuroprotective effects of violacein in a model of inherited amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive death of motor neurons and muscle atrophy, with defective neuron-glia interplay and emergence of aberrant glial phenotypes having a role in disease pathology. Here, we have studied if the pigment violacein with several reported protective/antiproliferative properties may control highly neurotoxic astrocytes (AbAs) obtained from spinal cord cultures of symptomatic hSOD1G93A rats, and if it could be neuroprotective in this ALS experimental model. At concentrations lower than those reported as protective, violacein selectively killed aberrant astrocytes. Treatment of hSOD1G93A rats with doses equivalent to the concentrations that killed AbAs caused a marginally significant delay in survival, partially preserved the body weight and soleus muscle mass and improved the integrity of the neuromuscular junction. Reduced motor neuron death and glial reactivity was also found and likely related to decreased inflammation and matrix metalloproteinase-2 and -9. Thus, in spite that new experimental designs aimed at extending the lifespan of hSOD1G93A rats are needed, improvements observed upon violacein treatment suggest a significant therapeutic potential that deserves further studies.

Dissection of Single Skeletal Muscle Fibers for Immunofluorescent and Morphometric Analyses of Whole-Mount Neuromuscular Junctions.

The neuromuscular junction (NMJ) is a specialized point of contact between the motor nerve and the skeletal muscle. This peripheral synapse exhibits high morphological and functional plasticity. In numerous nervous system disorders, NMJ is an early pathological target resulting in neurotransmission failure, weakness, atrophy, and even in muscle fiber death. Due to its relevance, the possibility to quantitatively assess certain aspects of the relationship between NMJ components can help to understand the processes associated with its assembly/disassembly. The first obstacle when working with muscles is to gain the technical expertise to quickly identify and dissect without damaging their fibers. The second challenge is to utilize high-quality detection methods to obtain NMJ images that can be used to perform quantitative analysis. This article presents a step-by-step protocol for dissecting extensor digitorum longus and soleus muscles from rats. It also explains the use of immunofluorescence to visualize pre and postsynaptic elements of whole-mount NMJs. Results obtained demonstrate that this technique can be used to establish the microscopic anatomy of the synapsis and identify subtle changes in the status of some of its components under physiological or pathological conditions.

Glutaric Acid Affects Pericyte Contractility and Migration: Possible Implications for GA-I Pathogenesis.

Glutaric acidemia I (GA-I) is an inherited neurometabolic childhood disease characterized by bilateral striatal neurodegeneration upon brain accumulation of millimolar concentrations of glutaric acid (GA) and related metabolites. Vascular dysfunction, including abnormal cerebral blood flow and blood-brain barrier damage, is an early pathological feature in GA-I, although the affected cellular targets and underlying mechanisms remain unknown. In the present study, we have assessed the effects of GA on capillary pericyte contractility in cerebral cortical slices and pericyte cultures, as well as on the survival, proliferation, and migration of cultured pericytes. GA induced a significant reduction in capillary diameter at distances up to ~ 10 µm from the center of pericyte somata. However, GA did not affect the contractility of cultured pericytes, suggesting that the response elicited in slices may involve GA evoking pericyte contraction by acting on other cellular components of the neurovascular unit. Moreover, GA indirectly inhibited migration of cultured pericytes, an effect that was dependent on soluble glial factors since it was observed upon application of conditioned media from GA-treated astrocytes (CM-GA), but not upon direct GA addition to the medium. Remarkably, CM-GA showed increased expression of cytokines and growth factors that might mediate the effects of increased GA levels not only on pericyte migration but also on vascular permeability and angiogenesis. These data suggest that some effects elicited by GA might be produced by altering astrocyte-pericyte communication, rather than directly acting on pericytes. Importantly, GA-evoked alteration of capillary pericyte contractility may account for the reduced cerebral blood flow observed in GA-I patients.

Long Lasting High Lysine Diet Aggravates White Matter Injury in Glutaryl-CoA Dehydrogenase Deficient (Gcdh-/-) Mice.

Glutaric acidemia type I (GA-I) is a neurometabolic disease caused by deficient activity of glutaryl-CoA dehydrogenase (GCDH) that results in accumulation of metabolites derived from lysine (Lys), hydroxylysine, and tryptophan catabolism. GA-I patients typically develop encephalopatic crises with striatal degeneration and progressive white matter defects. However, late onset patients as well as Gcdh-/- mice only suffer diffuse myelinopathy, suggesting that neuronal death and white matter defects are different pathophysiological events. To test this hypothesis, striatal myelin was studied in Gcdh-/- mice fed from 30 days of age during up to 60 days with a diet containing normal or moderately increased amounts of Lys (2.8%), which ensure sustained elevated levels of GA-I metabolites. Gcdh-/- mice fed with 2.8% Lys diet showed a significant decrease in striatal-myelinated areas and progressive vacuolation of white matter tracts, as compared with animals fed with normal diet. Myelin pathology increased with the time of exposure to high Lys diet and was also detected in 90-day old Gcdh-/- mice fed with normal diet, suggesting that dietary Lys accelerated the undergoing white matter damage. Gcdh-/- mice fed with 2.8% Lys diet also showed increased GRP78/BiP immunoreactivity in oligodendrocytes and neurons, denoting ER stress. However, the striatal and cortical neuronal density was unchanged with respect to normal diet. Thus, myelin damage seen in Gcdh-/- mice fed with 2.8% Lys seems to be mediated by a long-term increased levels of GA-I metabolites having deleterious effects in myelinating oligodendrocytes over neurons.