Virus infections in infant mice causing persistent impairment of turnover of brain catecholamines

Dengue Virus Replication Is Associated with Catecholamine Biosynthesis and Metabolism in Hepatocytes

Previously, the association between the catecholamine biosynthetic enzyme L-Dopa decarboxylase (DDC) and Dengue virus (DV) replication was demonstrated in liver cells and was found to be mediated at least by the interaction between DDC and phosphoinositide 3-kinase (PI3K). Here, we show that biogenic amines production and uptake impede DV replication in hepatocytes and monocytes, while the virus reduces catecholamine biosynthesis, metabolism, and transport. To examine how catecholamine biosynthesis/metabolism influences DV, first, we verified the role of DDC by altering DDC expression. DDC silencing enhanced virus replication, but not translation, attenuated the negative effect of DDC substrates on the virus and reduced the infection related cell death. Then, the role of the downstream steps of the catecholamine biosynthesis/metabolism was analyzed by chemical inhibition of the respective enzymes, application of their substrates and/or their products; moreover, reserpine, the inhibitor of the vesicular monoamine transporter 2 (VMAT2), was used to examine the role of uptake/storage of catecholamines on DV. Apart from the role of each enzyme/transporter, these studies revealed that the dopamine uptake, and not the dopamine-signaling, is responsible for the negative effect on DV. Accordingly, all treatments expected to enhance the accumulation of catecholamines in the cell cytosol suppressed DV replication. This was verified by the use of chemical inducers of catecholamine biosynthesis. Last, the cellular redox alterations due to catecholamine oxidation were not related with the inhibition of DV replication. In turn, DV apart from its negative impact on DDC, inhibits tyrosine hydroxylase, dopamine beta-hydroxylase, monoamine oxidase, and VMAT2 expression.

Association of Hepatitis C Virus Replication with the Catecholamine Biosynthetic Pathway

A bidirectional negative relationship between Hepatitis C virus (HCV) replication and gene expression of the catecholamine biosynthetic enzyme L-Dopa decarboxylase (DDC) was previously shown in the liver and attributed at least to an association of DDC with phosphatidylinositol 3-kinase (PI3K). Here, we report that the biosynthesis and uptake of catecholamines restrict HCV replication in hepatocytes, while HCV has developed ways to reduce catecholamine production. By employing gene silencing, chemical inhibition or induction of the catecholamine biosynthetic and metabolic enzymes and transporters, and by applying the substrates or the products of the respective enzymes, we unravel the role of the different steps of the pathway in viral infection. We also provide evidence that the effect of catecholamines on HCV is strongly related with oxidative stress that is generated by their autoxidation in the cytosol, while antioxidants or treatments that lower cytosolic catecholamine levels positively affect the virus. To counteract the effect of catecholamines, HCV, apart from the already reported effects on DDC, causes the down-regulation of tyrosine hydroxylase that encodes the rate-limiting enzyme of catecholamine biosynthesis and suppresses dopamine beta-hydroxylase mRNA and protein amounts, while increasing the catecholamine degradation enzyme monoamine oxidase. Moreover, the NS4B viral protein is implicated in the effect of HCV on the ratio of the ~50 kDa DDC monomer and a ~120 kDa DDC complex, while the NS5A protein has a negative effect on total DDC protein levels.

Alteration of L-Dopa decarboxylase expression in SARS-CoV-2 infection and its association with the interferon-inducible ACE2 isoform

L-Dopa decarboxylase (DDC) is the most significantly co-expressed gene with ACE2, which encodes for the SARS-CoV-2 receptor angiotensin-converting enzyme 2 and the interferon-inducible truncated isoform dACE2. Our group previously showed the importance of DDC in viral infections. We hereby aimed to investigate DDC expression in COVID-19 patients and cultured SARS-CoV-2-infected cells, also in association with ACE2 and dACE2. We concurrently evaluated the expression of the viral infection- and interferon-stimulated gene ISG56 and the immune-modulatory, hypoxia-regulated gene EPO. Viral load and mRNA levels of DDC, ACE2, dACE2, ISG56 and EPO were quantified by RT-qPCR in nasopharyngeal swab samples from COVID-19 patients, showing no or mild symptoms, and from non-infected individuals. Samples from influenza-infected patients were analyzed in comparison. SARS-CoV-2-mediated effects in host gene expression were validated in cultured virus-permissive epithelial cells. We found substantially higher gene expression of DDC in COVID-19 patients (7.6-fold; p = 1.2e-13) but not in influenza-infected ones, compared to non-infected subjects. dACE2 was more elevated (2.9-fold; p = 1.02e-16) than ACE2 (1.7-fold; p = 0.0005) in SARS-CoV-2-infected individuals. ISG56 (2.5-fold; p = 3.01e-6) and EPO (2.6-fold; p = 2.1e-13) were also increased. Detected differences were not attributed to enrichment of specific cell populations in nasopharyngeal tissue. While SARS-CoV-2 virus load was positively associated with ACE2 expression (r≥0.8, p<0.001), it negatively correlated with DDC, dACE2 (r≤-0.7, p<0.001) and EPO (r≤-0.5, p<0.05). Moreover, a statistically significant correlation between DDC and dACE2 expression was observed in nasopharyngeal swab and whole blood samples of both COVID-19 and non-infected individuals (r≥0.7). In VeroE6 cells, SARS-CoV-2 negatively affected DDC, ACE2, dACE2 and EPO mRNA levels, and induced cell death, while ISG56 was enhanced at early hours post-infection. Thus, the regulation of DDC, dACE2 and EPO expression in the SARS-CoV-2-infected nasopharyngeal tissue is possibly related with an orchestrated antiviral response of the infected host as the virus suppresses these genes to favor its propagation.

Animal models of virus-induced neurobehavioral sequelae: recent advances, methodological issues, and future prospects

Converging lines of clinical and epidemiological evidence suggest that viral infections in early developmental stages may be a causal factor in neuropsychiatric disorders such as schizophrenia, bipolar disorder, and autism-spectrum disorders. This etiological link, however, remains controversial in view of the lack of consistent and reproducible associations between viruses and mental illness. Animal models of virus-induced neurobehavioral disturbances afford powerful tools to test etiological hypotheses and explore pathophysiological mechanisms. Prenatal or neonatal inoculations of neurotropic agents (such as herpes-, influenza-, and retroviruses) in rodents result in a broad spectrum of long-term alterations reminiscent of psychiatric abnormalities. Nevertheless, the complexity of these sequelae often poses methodological and interpretational challenges and thwarts their characterization. The recent conceptual advancements in psychiatric nosology and behavioral science may help determine new heuristic criteria to enhance the translational value of these models. A particularly critical issue is the identification of intermediate phenotypes, defined as quantifiable factors representing single neurochemical, neuropsychological, or neuroanatomical aspects of a diagnostic category. In this paper, we examine how the employment of these novel concepts may lead to new methodological refinements in the study of virus-induced neurobehavioral sequelae through animal models.

COX-2 inhibitors as adjunctive therapy in schizophrenia

Cyclooxygenase-2 (COX-2) is constitutively expressed in the central nervous system, and is thought to have an important functional role therein. COX-2 interacts with neurotransmitters such as acetylcholine, 5-hydroxytryptamine and glutamate but is also involved in the regulation of the central nervous system immune system and in inflammation via the effects of prostaglandins, in particular prostaglandin E2. A general therapeutic effect of the COX-2 inhibitor celecoxib on symptoms of schizophrenia was observed during a prospective, randomised, double-blind study of celecoxib add-on treatment to the atypical antipsychotic risperidone. The results from this trial of adjunctive therapy with a COX-2 inhibitor in schizophrenia are encouraging, and the findings support the view that an immunological/inflammatory process is involved in the pathogenesis of the disease. The add-on to an antipsychotic design of the study was chosen due to ethical reasons; in less acute schizophrenic states a monotherapy with COX-2 inhibitors would be interesting. From a theoretical point of view, other psychiatric indications for selective COX-2 inhibitors are discussed. COX-2 inhibitors have failed to show therapeutic effects in Alzheimer's disease but studies from basic research and a clinical perspective suggest it has an effect on disturbed cognition. In depression, however, signs of inflammation have been described for many years. Although results of clinical studies with COX-2 inhibitors in depression are still lacking, clinical improvement of a depressive syndrome has been observed in patients who have been treated with the COX-2 inhibitor rofecoxib due to other indications. These preliminary clinical data are encouraging for clinical therapeutic effects of the selective COX-2 inhibitors in psychiatric disorders, although these effects have to be confirmed in larger clinical studies.

Schizophrenia and viral infection during neurodevelopment: a focus on mechanisms

The task of defining schizophrenia pathogenesis has fascinated and frustrated researchers for nearly a century. In recent years, unprecedented advances from diverse fields of study have given credence to both viral and developmental theories. This review considers possible mechanisms by which viral and developmental processes may interact to engender schizophrenia. Many of the current controversies in schizophrenia pathogenesis are reviewed in light of the viral hypothesis, including: epidemiological findings and the role of a genetic diathesis, phenotype heterogeneity, abnormalities in excitatory and inhibitory neurotransmitter systems, anomalous cerebral latereralization, and static vs progressive disease. The importance of animal models in elucidating the impact of viral infections on developing neurons is illustrated by recent studies in which neonatal rats are infected with lymphocytic choriomeningitis virus in order to examine alterations in hippocampal circuitry. Finally, consideration is given to a new hypothesis that some cases of schizophrenia could be instigated by a viral infection that disrupts developing inhibitory circuits, consequently unleashing glutamatergic neurotransmission leading to selective excitotoxicity, and a degenerative disease course.

Specific infection and destruction of dopaminergic neurons in the substantia nigra by Theiler's virus

Theiler's murine encephalomyelitis virus was stereotaxically inoculated unilaterally into the substantia nigra of the mouse brain. Virus specifically infected tyrosine hydroxylase-positive neurons and spread rostrocaudally throughout this subpopulation of neurons, resulting in impaired function and degeneration of the substantia nigra. The spread of the virus to other areas of the brain was minimal and rare.

Monoamine metabolites in 'leftover' newborn human cerebrospinal fluid--a potential resource for biobehavioral research

Although variations in monoamine neurotransmission have been implicated in a variety of psychopathologic outcomes in man, little is known about how monoamines influence or are affected by developmental processes early in childhood. In this study, assays for 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were obtained from leftover cerebrospinal fluid (CSF) of 119 human newborns. The levels of these monoamine metabolites were in keeping with pre-existing 'normative' data from two small previously published studies. The levels were largely unaffected by variations in the infants' physiologic condition at the time of lumbar puncture, and exhibited evidence for circadian rhythms. Among 32 infants (8 neurologically normal, 24 neurologically compromised) for whom more than one CSF sample was obtained during the first year of life, the correlations between baseline and follow-up measurements for 5-HIAA and HVA were on the order of 0.75. Correlations between twins (four sets) were significantly higher than those between unrelated individuals for 5-HIAA and HVA. At 9-month follow-up, neurologically normal infants in the lower extreme 15% of the distribution for 5-HIAA exhibited a trend toward lower scores for sociability on the Colorado Childhood Temperament Inventory (maternal report) than their counterparts at the upper extreme of the 5-HIAA distribution. Leftover CSF is a readily available resource for measurements of monoamine metabolites (and possibly other CSF constituents) in population-based samples of human newborns.

Dopaminergic neurotransmission in chronic herpes simplex virus brain infection in rabbits

In this study we have examined brain concentrations of monoamine neurotransmitters and striatal and mesencephalic D-2 receptors in a chronic model of herpes simplex virus (HSV) encephalitis. The HSV-inoculated rabbits were killed two months after inoculation. Dopamine (DA), noradrenaline, serotonin and their metabolites were determined in the substantia nigra, caudate nucleus, putamen, nucleus accumbens, and olfactory tubercles using HPLC with electrochemical detection. The Bmax and Kd values of D-2 receptors were studied in the striatum and in the mesencephalon using 3H-spiroperidol as ligand. The animals showed rotational behaviour, consisting of posture tilting to the inoculated side and circling in the same direction during the first week, then slowly subsiding. Compared with controls, the concentration of homovanillic acid (HVA) was reduced in the ascending DA system on both sides. Neither in the number nor affinity of D-2 receptors were there any differences between the HSV-inoculated and control rabbits. The decreased HVA concentrations suggest that dopaminergic hypofunction can develop as a consequence of previously experienced acute HSV brain infection.

Behavioral effects of neonatal herpes simplex type 1 infection of mice

Neonatal infection with a mutant herpes simplex type 1 virus produced hyperactivity in mice. Activity was measured throughout a 24 hour period during adulthood, and the elevation of activity occurred during the period of the day when mice are normally inactive. In a second experiment, infected mice showed deficits in learning to inhibit behavior in a passive avoidance task, but no deficit in learning a complex spatial task. Virus was detected in the brain by 5 days of age. The peak percentage of mice infected was reached at 10 days of age and declined thereafter. Mortality due to the virus declined with age at which the mouse was infected, but rates of hyperactivity were not different when injection occurred within the first 4 days of life. The viral infection produced no deficit in body weight in suckling mice. Thus we have shown that a mild neonatal virus infection can produce specific behavioral deficits.

Hemophilus influenzae meningitis in the rat: behavioral, electrophysiological, and biochemical consequences

Hemophilus influenzae is the most common cause of bacterial meningitis in children, and a high percentage of survivors are at risk for long-term sequelae. To explore the mechanisms responsible for these sequelae, a neonatal rat model was used to define the behavioral, electrophysiological, and biochemical changes following meningitis. Three days after inoculation of 6-day-old rats with a minimum of 1 X 10(7) colony-forming units of a virulent Hemophilus influenzae, type b, cerebrospinal fluid and blood were cultured to confirm the presence of meningitis and bacteremia, respectively. At this time, forebrain norepinephrine and dopamine levels were significantly elevated in meningitic rats when standardized on a wet-weight basis. No changes in brain serotonin or heart norepinephrine levels could be found in the 9-day-old rats. No residual changes were found in steady-state concentrations of norepinephrine or dopamine in surviving adult rats. However, survivors that had had meningitis as neonates showed significant impairment in active and passive avoidance learning tasks and demonstrated a significantly higher level of activity during a habituation period in circular photocell activity cages. No change in the flinch-jump threshold was detected. Brainstem auditory evoked potentials showed delays of various waves in 3 of 10 Hemophilus influenzae type b-treated adult rats tested. These rats also exhibited markedly augmented locomotory responses to d-amphetamine (1 mg/kg), suggesting a long-lasting perturbation of central monoamine neuronal transmission.

Alteration of tyrosine hydroxylase activity in PC12 cells infected with herpes simplex virus type 1

During infection with herpes simplex virus type 1 (HSV-1) the activity of tyrosine hydroxylase (TH) in PC12 pheochromocytoma cells was initially depressed reaching a nadir at 6 hours post-inoculation, but recovered rapidly with a return to baseline activity by 8 to 9 hours post-inoculation. Subsequently, TH activity again fell with a second more variable rise in activity occurring at 24 hours post-inoculation. Studies with metabolic inhibitors and 2 temperature-sensitive viral mutants indicated that these alterations of TH activity were dissociated from morphological cytopathology and likely required expression of "late" viral gene products. Immunotitration using anti-TH antibody suggested that early depression of TH activity resulted principally from loss of enzyme protein rather than simple enzyme inactivation, and that reconstitution of activity at 9 hours was related to augmented enzyme synthesis. These observations illustrate the complexity of perturbed cellular metabolism during HSV-1 infection and suggest involvement of two unexpected processes: alteration of a specialized cell function as a result of viral genes expressed late in the replicative cycle, and augmented synthesis of a cell-coded gene product during the course of infection.

Tyrosine hydroxylase activity in the superior cervical ganglion during herpes simplex virus infection: correlation with viral titers and viral antigen

The activity of tyrosine hydroxylase (TH) was measured in the superior cervical ganglion (SCG) of the mouse during herpes simplex virus (HSV) infection. TH activity remained at control levels or actually increased during acute infection at a time when viral titers of SCG homogenates were at their peak and viral antigen was detected in from one-third to one-half of ganglionic neurons. A rapid decline in TH activity followed and coincided with falling viral titers, disappearance of viral antigen and replacement of neurons by inflammatory cells. Immunization partially prevented this reduction of TH activity. In addition, when mice were immunosuppressed by cyclophosphamide, TH activity was relatively preserved early in the course of infection despite high viral titers in the ganglion and the presence of viral antigen and histopathological alterations in nearly 100% of neurons. These results suggest that a cellular 'luxury function', in this case TH activity, can be preserved and perhaps even augmented during neuronal HSV infection. Indeed, activity of this enzyme may persist until late into the acute phase of infection, perhaps up to the point of cell death induced either by immune-mediated or direct virus-induced cell lysis.

Tyrosine hydroxylase activity in Venezuelan equine encephalomyelitis virus infection

In rats inoculated with the Venezuelan equine encephalomyelitis (VEE) virus, a significant decrease was found in the tyrosine hydroxylase activity of neostriatum, midbrain, and hypothalamus during the acute phase of the infection. In animals that survived the acute infection, we observed no changes in the enzymatic activity in the same regions studied. Our findings suggest a vulnerability of the dopaminergic and noradrenergic pathways to the infection produced by VEE virus.

Locomotor effects of catecholaminergic drugs on herpes-infected mice

Changes in spontaneous, amphetamine (AMP) and apomorphine (APO) induced locomotor activity were used to assess the effects of central nervous system (CNS) infection with herpes type 1 virus. A dual herpesvirus inoculation procedure was used in which the animals received an immunizing footpad inoculation followed at 2 weeks by an identical intracerebral challenge. Four weeks later the animals were tested with intraperitoneal injections of saline or d-l-amphatmine (0.5 and 2.0 mg/kg). When footpad herpes-virus was given via one or two injections, it had no effect on spontaneous or AMP induced activity. When food-pad-intracerebral herpes mice were tested 28-33 days post intracerebral inoculation, they demonstrated depressed AMP-induced but not spontaneous activity. AMP at a dosage of 5.0 mg/kg overcame the herpesvirus blockage of 0.5 and 2.0 mg/kg AMP induced activity. Intraperitoneal injection of APO in day 3 post-IC animals produced less suppression of activity in the virus group than in the controls. These results suggest that non-fatal CNS herpes infection produces hypoactivity, in contrast to thehyperactivity during acute fatal CNS herpes encephalitis (Lycke & Roos, 1975), and that the effect may be due to alterations in postsynaptic receptor sensitivity.