Claudia Laperchia

Trypanosoma brucei invasion and T-cell infiltration of the brain parenchyma in experimental sleeping sickness: timing and correlation with functional changes

Background The timing of Trypanosoma brucei entry into the brain parenchyma to initiate the second, meningoencephalitic stage of human African trypanosomiasis or sleeping sickness is currently debated and even parasite invasion of the neuropil has been recently questioned. Furthermore, the relationship between neurological features and disease stage are unclear, despite the important diagnostic and therapeutic implications. Methodology Using a rat model of chronic Trypanosoma brucei brucei infection we determined the timing of parasite and T-cell neuropil infiltration and its correlation with functional changes. Parasite DNA was detected using trypanosome-specific PCR. Body weight and sleep structure alterations represented by sleep-onset rapid eye movement (SOREM) periods, reported in human and experimental African trypanosomiasis, were monitored. The presence of parasites, as well as CD4+ and CD8+ T-cells in the neuropil was assessed over time in the brain of the same animals by immunocytochemistry and quantitative analyses. Principal findings Trypanosome DNA was present in the brain at day 6 post-infection and increased more than 15-fold by day 21. Parasites and T-cells were observed in the parenchyma from day 9 onwards. Parasites traversing blood vessel walls were observed in the hypothalamus and other brain regions. Body weight gain was reduced from day 7 onwards. SOREM episodes started in most cases early after infection, with an increase in number and duration after parasite neuroinvasion. Conclusion These findings demonstrate invasion of the neuropil over time, after an initial interval, by parasites and lymphocytes crossing the blood-brain barrier, and show that neurological features can precede this event. The data thus challenge the current clinical and cerebrospinal fluid criteria of disease staging.

Two-Photon Microscopy Imaging of thy1GFP-M Transgenic Mice: A Novel Animal Model to Investigate Brain Dendritic Cell Subsets In Vivo

Transgenic mice expressing fluorescent proteins in specific cell populations are widely used for in vivo brain studies with two-photon fluorescence (TPF) microscopy. Mice of the thy1GFP-M line have been engineered for selective expression of green fluorescent protein (GFP) in neuronal populations. Here, we report that TPF microscopy reveals, at the brain surface of these mice, also motile non-neuronal GFP+ cells. We have analyzed the behavior of these cells in vivo and characterized in brain sections their immunophenotype. With TPF imaging, motile GFP+ cells were found in the meninges, subarachnoid space and upper cortical layers. The striking feature of these cells was their ability to move across the brain parenchyma, exhibiting evident shape changes during their scanning-like motion. In brain sections, GFP+ cells were immunonegative to antigens recognizing motile cells such as migratory neuroblasts, neuronal and glial precursors, mast cells, and fibroblasts. GFP+ non-neuronal cells exhibited instead the characteristic features and immunophenotype (CD11c and major histocompatibility complex molecule class II immunopositivity) of dendritic cells (DCs), and were immunonegative to the microglial marker Iba-1. GFP+ cells were also identified in lymph nodes and blood of thy1GFP-M mice, supporting their identity as DCs. Thus, TPF microscopy has here allowed the visualization for the first time of the motile behavior of brain DCs in situ. The results indicate that the thy1GFP-M mouse line provides a novel animal model for the study of subsets of these professional antigen-presenting cells in the brain. Information on brain DCs is still very limited and imaging in thy1GFP-M mice has a great potential for analyses of DC-neuron interaction in normal and pathological conditions.

ALTERATIONS OF OREXINERGIC AND MELANIN-CONCENTRATING HORMONE NEURONS IN EXPERIMENTAL SLEEPING SICKNESS

Human African trypanosomiasis or sleeping sickness is a severe, neglected tropical disease caused by the extracellular parasite Trypanosoma brucei. The disease, which leads to chronic neuroinflammation, is characterized by sleep and wake disturbances, documented also in rodent models. In rats and mice infected with Trypanosoma brucei brucei, we here tested the hypothesis that the disease could target neurons of the lateral hypothalamus (LH) containing orexin (OX)-A or melanin-concentrating hormone (MCH), implicated in sleep/wake regulation. In the cerebrospinal fluid of infected rats, the OX-A level was significantly decreased early after parasite neuroinvasion, and returned to the control level at an advanced disease stage. The number of immunohistochemically characterized OX-A and MCH neurons decreased significantly in infected rats during disease progression and in infected mice at an advanced disease stage. A marked reduction of the complexity of dendritic arborizations of OX-A neurons was documented in infected mice. The evaluation of NeuN-immunoreactive neurons did not reveal significant neuronal loss in the LH of infected mice, thus suggesting a potential selective vulnerability of OX-A and MCH neurons. Immunophenotyping and quantitative analysis showed in infected mice marked activation of microglial cells surrounding OX-A neurons. Day/night oscillation of c-Fos baseline expression was used as marker of OX-A neuron activity in mice. In control animals Fos was expressed in a higher proportion of OX-A neurons in the night (activity) phase than in the day (rest) phase. Interestingly, in infected mice the diurnal spontaneous Fos oscillation was reversed, with a proportion of OX-A/Fos neurons significantly higher at daytime than at nighttime. Altogether the findings reveal a progressive decrease of OX-A and MCH neurons and dysregulation of OX-A neuron diurnal activity in rodent models of sleeping sickness. The data point to the involvement of these peptidergic neurons in the pathogenesis of sleep/wake alterations in the disease and to their vulnerability to inflammatory signaling.

Regional Myelin and Axon Damage and Neuroinflammation in the Adult Mouse Brain After Long-Term Postnatal Vanadium Exposure

Environmental exposure to vanadium occurs in areas of persistent burning of fossil fuels; this metal is known to induce oxidative stress and oligodendrocyte damage. Here, we determined whether vanadium exposure (3 mg/kg) in mice during the first 3 postnatal months leads to a sustained neuroinflammatory response. Body weight monitoring, and muscle strength and open field tests showed reduction of body weight gain and locomotor impairment in vanadium-exposed mice. Myelin histochemistry and immunohistochemistry for astrocytes, microglia, and nonphosphorylated neurofilaments revealed striking regional heterogeneity. Myelin damage involved the midline corpus callosum and fibers in cortical gray matter, hippocampus, and diencephalon that were associated with axonal damage. Astrocyte and microglial activation was identified in the same regions and in the internal capsule; however, no overt myelin and axon damage was observed in the latter. Double immunofluorescence revealed induction of high tumor necrosis factor (TNF) immunoreactivity in reactive astrocytes. Western blotting analysis showed significant induction of TNF and interleukin-1&bgr; expression. Together these findings show that chronic postnatal vanadium exposure leads to functional deficit and region-dependent myelin damage that does not spare axons. This injury is associated with glial cell activation and proinflammatory cytokine induction, which may reflect both neurotoxic and neuroprotective responses.

Expression of interferon-inducible chemokines and sleep/wake changes during early encephalitis in experimental African trypanosomiasis

Background Human African trypanosomiasis or sleeping sickness, caused by the parasite Trypanosoma brucei, leads to neuroinflammation and characteristic sleep/wake alterations. The relationship between the onset of these alterations and the development of neuroinflammation is of high translational relevance, but remains unclear. This study investigates the expression of interferon (IFN)-γ and IFN-inducible chemokine genes in the brain, and the levels of CXCL10 in the serum and cerebrospinal fluid prior to and during the encephalitic stage of trypanosome infection, and correlates these with sleep/wake changes in a rat model of the disease. Methodology/Principal findings The expression of genes encoding IFN-γ, CXCL9, CXCL10, and CXCL11 was assessed in the brain of rats infected with Trypanosoma brucei brucei and matched controls using semi-quantitative end-point RT-PCR. Levels of CXCL10 in the serum and cerebrospinal fluid were determined using ELISA. Sleep/wake states were monitored by telemetric recording. Using immunohistochemistry, parasites were found in the brain parenchyma at 14 days post-infection (dpi), but not at 6 dpi. Ifn-γ, Cxcl9, Cxcl10 and Cxcl11 mRNA levels showed moderate upregulation by 14 dpi followed by further increase between 14 and 21 dpi. CXCL10 concentration in the cerebrospinal fluid increased between 14 and 21 dpi, preceded by a rise in the serum CXCL10 level between 6 and 14 dpi. Sleep/wake pattern fragmentation was evident at 14 dpi, especially in the phase of wake predominance, with intrusion of sleep episodes into wakefulness. Conclusions/Significance The results show a modest increase in Cxcl9 and Cxcl11 transcripts in the brain and the emergence of sleep/wake cycle fragmentation in the initial encephalitic stage, followed by increases in Ifn-γ and IFN-dependent chemokine transcripts in the brain and of CXCL10 in the cerebrospinal fluid. The latter parameter and sleep/wake alterations could provide combined humoral and functional biomarkers of the early encephalitic stage in African trypanosomiasis.

Glutamatergic neurons induce expression of functional glutamatergic synapses in primary myotubes

Background The functioning of the nervous system depends upon the specificity of its synaptic contacts. The mechanisms triggering the expression of the appropriate receptors on postsynaptic membrane and the role of the presynaptic partner in the differentiation of postsynaptic structures are little known. Methods and Findings To address these questions we cocultured murine primary muscle cells with several glutamatergic neurons, either cortical, cerebellar or hippocampal. Immunofluorescence and electrophysiology analyses revealed that functional excitatory synaptic contacts were formed between glutamatergic neurons and muscle cells. Moreover, immunoprecipitation and immunofluorescence experiments showed that typical anchoring proteins of central excitatory synapses coimmunoprecipitate and colocalize with rapsyn, the acetylcholine receptor anchoring protein at the neuromuscular junction. Conclusions These results support an important role of the presynaptic partner in the induction and differentiation of the postsynaptic structures.

Neural Damage in Experimental Trypanosoma brucei gambiense: Infection: Hypothalamic Peptidergic Sleep and Wake-Regulatory Neurons.

Neuron populations of the lateral hypothalamus which synthesize the orexin (OX)/hypocretin or melanin-concentrating hormone (MCH) peptides play crucial, reciprocal roles in regulating wake stability and sleep. The disease human African trypanosomiasis (HAT), also called sleeping sickness, caused by extracellular Trypanosoma brucei (T. b.) parasites, leads to characteristic sleep-wake cycle disruption and narcoleptic-like alterations of the sleep structure. Previous studies have revealed damage of OX and MCH neurons during systemic infection of laboratory rodents with the non-human pathogenic T. b. brucei subspecies. No information is available, however, on these peptidergic neurons after systemic infection with T. b. gambiense, the etiological agent of 97% of HAT cases. The present study was aimed at the investigation of immunohistochemically characterized OX and MCH neurons after T. b. gambiense or T. b. brucei infection of a susceptible rodent, the multimammate mouse, Mastomys natalensis. Cell counts and evaluation of OX fiber density were performed at 4 and 8 weeks post-infection, when parasites had entered the brain parenchyma from the periphery. A significant decrease of OX neurons (about 44% reduction) and MCH neurons (about 54% reduction) was found in the lateral hypothalamus and perifornical area at 8 weeks in T. b. gambiense-infected M. natalensis. A moderate decrease (21% and 24% reduction, respectively), which did not reach statistical significance, was found after T. b. brucei infection. In two key targets of diencephalic orexinergic innervation, the peri-suprachiasmatic nucleus (SCN) region and the thalamic paraventricular nucleus (PVT), densitometric analyses showed a significant progressive decrease in the density of orexinergic fibers in both infection paradigms, and especially during T. b. gambiense infection. Altogether the findings provide novel information showing that OX and MCH neurons are highly vulnerable to chronic neuroinflammatory signaling caused by the infection of human-pathogenic African trypanosomes.

Brain dendritic cells

Dendritic cells (DCs) are a subset of leukocytes highly specialized in antigen-presentation to T cells, thus promoting the immune response. DCs occur in the meninges and choroid plexus. Brain DCs and brain-derived antigens are drained by cerebrospinal fluid in the afferent lymphatic vessels of cervical lymph nodes (cLNs) for antigen presentation. Information on the role of DCs in intracerebral immune response is still limited. We recently demonstrated (Laperchia et al., 2013) that in thy1GFP-M transgenic mice, engineered for the expression of green fluorescent protein (GFP) in a proportion of neurons, also myeloid DCs are GFP-tagged. Our in vivo analysis by two-photon microscopy on young (3-6 months) thy1GFP-M mice showed DCs floating in the cerebrospinal fluid or static at the pia mater/parenchyma interface. We are using this animal model to study brain DCs trafficking by two-photon microscopy in two different inflammatory conditions. The first concerns chronic encephalitis caused by the extracellular parasite Trypanosoma brucei. During the first, hemolymphatic stage of this infection, direct interactions between DCs and parasites were seen within meningeal and cortical microvessels. In the second stage, determined by parasite neuroinvasion, DCs invaded the brain parenchyma, exhibiting a random motion for target antigen recognition. With disease progression, intraparenchymal brain DCs were instead mainly arranged in static clusters which incorporated parasites for efficient antigen capture, and extravasated cytotoxic CD8+ T cells established contact with parasites. Ex vivo analysis on cLNs shown that the subcapsular zone was invaded by migratory DCs, and both migratory and resident DCs preferentially contacted CD8+ T cells. The second condition concerns normal aging (18-20 month old mice), which is known to be associated with low-grade chronic inflammation level and with functional impairments of the immune system, also known as immunosenescence. In these mice we observed that DCs infiltrate the brain parenchyma by transmigration from blood vessels and exhibit a motile behavior suggesting a scanning motion. Moreover, some DCs showed a progressive reduction of their motility until convergence, in about 30 minutes, into clusters whose functional significant has yet to be elucidated. Taken together, our studies enlightens key events of the intracerebral immune response both in presence of pathogens and in physiological aging.

Converging orexinergic and reticular thalamic inputs on thalamic paraventricular neurons in normal conditions and experimental sleeping sickness

A subset of excitatory neurons in the lateral hypothalamus, known to express the peptide orexin/hypocretin (Ox), play a key role in maintaining wakefulness. Projections from Ox neurons are widely distributed in the neuraxis but terminations are heavily concentrated in the thalamus along the midline, especially the paraventricular thalamic nucleus (PVT). The same areas receive afferents from inhibitory, GABAergic neurons expressing parvalbumin (Pv) in the thalamic reticular nucleus (Rt), which has long been considered essential for sleep regulation. While the two circuitries have been regarded as distinct, we tested the hypothesis that PVT neurons represent a common target for both afferent systems by means of confocal microscopy of multiple immunofluorescence labeling in the mouse brain. Calretinin (Cr) was used as marker of PVT neurons. Almost 90% of PVT perikarya were contacted by Pv+ terminals, confirming the prominent role of Rt in modulating PVT activity. Interestingly, about a third of these neurons were also reached by Ox+ terminals, suggesting a key role of the thalamic midline in integrating information pertaining vigilance state control. PVT cells receiving Ox+ but not Pv+ contacts were observed only rarely. In mice infected with the parasite Trypanosoma brucei brucei, the causal agent of the neuroinflammatory disease “sleeping sickness”, Pv+ afferents into PVT were largely preserved, while orexinergic fibers appeared fragmented and reduced in density. Importantly, the fraction of PVT perikarya receiving both Pv+ and Ox+ terminals was reduced by about 50%. The substantially decreased convergence of the two regulatory systems, in association with infection-induced disrupted sleep and sleep/wake cycles, further supports the hypothesis that PVT contributes to vigilance and arousal in physiological conditions.

Peptidergic innervation of the olfactory bulb: a sleep/wake-regulatory route through the nose

Olfactory epithelium receptor neurons in the nasal cavity, which are exposed to the external environment, reach the olfactory bulb (OB), representing a direct port of entry to the brain. Through retrograde axonal transport, pathogens, toxins and misfolded proteins can reach brain cell groups which innervate the OB and result in functional alterations. Indeed, influenza virus nasal instillation was found to target brainstem and hypothalamic cell groups and result in narcoleptic-like sleep/wake changes [1]. These cell groups included the wake-promoting orexin (OX)-containing neurons, and the sleep-promoting melanin-concentrating hormone (MCH)-containing neurons [1]. Orexinergic innervation of the OB has been reported, but OX and MCH neurons innervating the OB have never been visualized. OX immunoreactivity in the mouse olfactory receptor neurons has been ascribed to the olfactory mucosa. Sources of input to the OB have been studied [2] before the discovery of OX in 1998. Orexinergic innervation of the prefrontal cortex is instead well established. Aim of this study was to reveal OX- and MCH-containing neurons projecting to the OB. Unilateral injections of the retrograde fluorescent tracer Fluoro-Gold (FG) confined to the OB of adult mice were combined with immunophenotyping and quantitative analysis of retrogradely labeled neurons. The findings were compared with those obtained after FG injections in the prefrontal cortex. Following FG injections in the OB, labeled neurons were found in the ipsilateral lateral hypothalamus, and included intermingled OX-A- or MCH-immunoreactive cells. About 8% of orexinergic neurons were labeled when the tracer was confined to the OB. This proportion increased (13±2.49 %) in cases in which a faint halo of tracer diffusion to the lateral portion of the prefrontal cortex was observed. Preliminary data indicate retrograde labeling from the OB of almost 15% of MCH-containing neurons. The findings demonstrate that OX and MCH neurons reach the OB directly, thus providing to environmental agents a route to sleep/wake-regulatory nodes via the nasal cavity.