Tipping the balance between erythroid cell differentiation and induction of anemia in response to the inflammatory pathology associated with chronic trypanosome infections

Abstract

Infection caused by extracellular single-celled trypanosomes triggers a lethal chronic wasting disease in livestock and game animals. Through screening of 10 Trypanosoma evansi field isolates, exhibiting different levels of virulence in mice, the current study identifies an experimental disease model in which infection can last well over 100 days, mimicking the major features of chronic animal trypanosomosis. In this model, despite the well-controlled parasitemia, infection is hallmarked by severe trypanosomosis-associated pathology. An in-depth scRNA-seq analysis of the latter revealed the complexity of the spleen macrophage activation status, highlighting the crucial role of tissue resident macrophages (TRMs) in regulating splenic extramedullary erythropoiesis. These new data show that in the field of experimental trypanosomosis, macrophage activation profiles have so far been oversimplified into a bi-polar paradigm (M1 vs M2). Interestingly, TRMs exert a double-sided effect on erythroid cells. On one hand, these cells express an erythrophagocytosis associated signature. On another hand, TRMs show high levels of Vcam1 expression, known to support their interaction with hematopoietic stem and progenitor cells (HSPCs). During chronic infection, the latter exhibit upregulated expression of Klf1, E2f8, and Gfi1b genes, involved in erythroid differentiation and extramedullary erythropoiesis. This process gives rise to differentiation of stem cells to BFU-e/CFU-e, Pro E, and Baso E subpopulations. However, infection truncates progressing differentiation at the orthochromatic erythrocytes level, as demonstrated by scRNAseq and flow cytometry. As such, these cells are unable to pass to the reticulocyte stage, resulting in reduced number of mature circulating RBCs and the occurrence of chronic anemia. The physiological consequence of these events is the prolonged poor delivery of oxygen to various tissues, triggering lactic acid acidosis and the catabolic breakdown of muscle tissue, reminiscent of the wasting syndrome that is characteristic for the lethal stage of animal trypanosomosis.

From helping to regulating – A transcriptomic profile of Ifng+ Il10+ Il21+ Cd4+ Th1 cells indicates their role in regulating inflammation during experimental trypanosomosis

“…In the field of trypanosomosis research in particular, the use of scRNA-seq has recently revealed significant new findings on immune cell heterogeneity and response mechanisms to infection. These help to better understanding intercellular communications during infection, within various tissue microenvironments (3,10,12,13). Taking advantage of the technique, our present study provides a comprehensive customized pipeline for the handling of infection-derived scRNA-seq datasets, capturing (i) the transcriptomic landscape of immune cells, and (ii) the heterogeneity and alteration of CD4 + T cells in particular, along with their potential interactions with other cell populations.…”

“…It is known that in order to counterbalance INF-g-associated inflammation, the trypanosome infected host must be able to mount an anti-inflammatory IL-10 response. An imbalance between these two leads to the early death of the host (3,26,62). Interestingly, our analysis demonstrates that the accumulation of Th1 cells throughout infection goes along with the induction of double-positive Il10 + Ifng + CD4 + T cells.…”

“…Trypanosoma evansi (T. evansi), also referred to as Trypanosoma brucei evansi, is a unicellular salivarian protozoan parasite that causes animal trypanosomosis (Surra) and, in rare cases, atypical Human Trypanosomosis (1,2). In livestock as well as murine models, T. evansi infections often trigger a chronic wasting disease hallmarked by anemia, muscle breakdown and weight loss (1,3). Even though T. evansi is genetically related to T. brucei, it lacks the capacity to be cyclically transmitted by tsetse flies due to the partial or complete lack of its kinetoplast DNA.…”

“…However, to investigate these events at a cellular resolution, most conventional technologies such as flow cytometry and in vitro culturing techniques are inadequate. The introduction of transcriptome approaches, including scRNA-seq analysis, has more recently allowed acquiring new in-depth knowledge of the pathological events that are associated to trypanosome infections at the level of the brain, the liver, the adipose tissue, and the spleen (3,(9)(10)(11)(12)(13). The latter has been of particular importance for the understanding of mechanisms that drive the induction of infection associated anemia, as well as general immunopathology.…”

Advances in the Immunology of the Host–Parasite Interactions in African Trypanosomosis, including Single-Cell Transcriptomics

“…(b.) evansi , T. congolense and T. vivax -infected mice [ 10 , 11 , 132 , 133 ]. In mice, splenomegaly becomes evident after the first week of infection, reaching excessive proportions towards the 3rd week, where a 20-fold increase in spleen volume has been reported.…”