Microarray profiling predicts early neurological and immune phenotypic traits in advance of CNS disease during disease progression in Trypanosoma. b. brucei infected CD1 mouse brains.

Paul Montague,Jean Rodgers,Peter G E Kennedy,Barbara Bradley,Margaret A Phillips

doi:10.1371/journal.pntd.0009892

Paul Montague, Jean Rodgers + Show 3 more

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https://doi.org/10.1371/journal.pntd.0009892

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Abstract

Human African trypanosomiasis (HAT), also known as sleeping sickness, is a major cause of mortality and morbidity in sub-Saharan Africa. We hypothesised that recent findings of neurological features and parasite brain infiltration occurring at much earlier stages in HAT than previously thought could be explained by early activation of host genetic programmes controlling CNS disease. Accordingly, a transcriptomal analysis was performed on brain tissue at 0, 7, 14, 21 and 28dpi from the HAT CD1/GVR35 mouse model. Up to 21dpi, most parasites are restricted to the blood and lymphatic system. Thereafter the trypanosomes enter the brain initiating the encephalitic stage. Analysis of ten different time point Comparison pairings, revealed a dynamic transcriptome comprising four message populations. All 7dpi Comparisons had by far more differentially expressed genes compared to all others. Prior to invasion of the parenchyma, by 7dpi, ~2,000 genes were up-regulated, denoted [7dpi↑] in contrast to a down regulated population [7dpi↓] also numbering ~2,000. However, by 14dpi both patterns had returned to around the pre-infected levels. The third, [28dpi↑] featured over three hundred transcripts which had increased modestly up to14dpi, thereafter were significantly up-regulated and peaked at 28dpi. The fourth, a minor population, [7dpi↑-28dpi↑], had similar elevated levels at 7dpi and 28dpi. KEGG and GO enrichment analysis predicted a diverse phenotype by 7dpi with changes to innate and adaptive immunity, a Type I interferon response, neurotransmission, synaptic plasticity, pleiotropic signalling, circadian activity and vascular permeability without disruption of the blood brain barrier. This key observation is consistent with recent rodent model neuroinvasion studies and clinical reports of Stage 1 HAT patients exhibiting CNS symptoms. Together, these findings challenge the strict Stage1/Stage2 phenotypic demarcation in HAT and show that that significant neurological, and immune changes can be detected prior to the onset of CNS disease.

Highlights

At least 70 million people in 36 countries throughout sub-Saharan Africa are at risk from the neglected tropical disease human African trypanosomiasis (HAT) commonly termed sleeping sickness. [1]
By day 7, the activity of over 4,000 genes were altered and genetic programmes, responsible for the development of the Stage 2 encephalitic symptoms were activated prior to any significant breakdown of the blood brain barrier. These findings challenge this traditional Stage1/ Stage 2 phenotypic demarcation and accords with reports of Stage 1 patients presenting with Stage 2 encephalitic symptoms and the diagnosis of asymptomatic patients reflects the complex interaction between host and parasite genetics that impact on disease progression
The condition results from infection of the morphologically indistinguishable extracellular haemoflagellate protozoan parasites, the West African form Trypanosoma brucei gambiense and the East Africa type T. brucei rhodesiense transmitted by the bite of the teste fly (Glossina sp)

Summary

Introduction

At least 70 million people in 36 countries throughout sub-Saharan Africa are at risk from the neglected tropical disease human African trypanosomiasis (HAT) commonly termed sleeping sickness. [1]. After a variable period, which is more prolonged in the gambiense form, trypanosomes invade the CNS initiating the encephalitic Stage 2 of the disease characterised clinically by protean neurological features and pathologically by the presence in the brain of trypanosomes, macrophages, lymphocytes, cytokines and chemokines in the CSF [3] and activation of microglia and astrocytes [4] This exacerbates the cytokine mediated blood brain barrier (BBB) breakdown thereby amplifying the inflammatory response with a worsening debilitating neuropsychiatric impairment and the disruption of circadian rhythm control giving rise to major alterations of sleep structure, the hallmark CNS presentation [5]. Brucei GVR35 stabilate, has been widely used for over 30 years in molecular pathogenesis studies and provides the focus of the current investigation [8, 9] In these various studies, the consensus has been that up to 21dpi, most parasites are essentially restricted to the haemolymphatic system, beyond which, the infection can no longer be effectively treated with Stage-1 drugs. If not treated with Stage-2 drugs, the mice succumb to a combination of neurological and immunosuppressive complications resulting in death

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