Biology subjects

Bergersen, K. V.

Publications and source records attributed to Bergersen, K. V..

3 recordsLinked to original sources

bioRxiv2024

Toxoplasma gondii infection of neurons alters the production and content of extracellular vesicles altering astrocyte phenotype and contributing to the loss of GLT-1 in the infected brain

Toxoplasma gondii (T. gondii) cyst formation in the central nervous system only occurs in neurons allowing the parasite to remain latent for the lifetime of the host. Astrocytes are fundamental to neuronal health by providing nutrients and structural support and help regulate neurotransmitters by continuous communication with neurons. It is not yet known how infection and the presence of intracellular cysts, disrupts the crucial relationship between these cells. Extracellular vesicles (EVs) function in intracellular communication and can contain proteins, lipids, DNA, miRNA, and other RNA subtypes. EVs are produced by all cells including neurons and play an important role in neuronal-astrocyte interactions including the regulation of glutamate receptors on astrocytes. Previous work has demonstrated Toxoplasma infection reduces astrocytic expression of the primary glutamate transporter, GLT-1. Here we tested if cyst infection of neurons alters the production and content of EVs. EVs were isolated from uninfected and infected primary murine cortical neurons and their size, concentration, and characterization were confirmed with nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), CD63 ELISA, liquid chromatography (LC)-mass spectrometry (MS)/MS, and microRNA Sequencing. Analysis reveals that infection of neurons reduced neuronal production of EVs and altered their protein and miRNA content. EVs from infected neurons contained secreted Toxoplasma proteins GRA1, GRA2, GRA7, MAG1 and MAG2 associated with cyst formation. Following incubation of neuronal EVs with primary astrocytes, a proportion of EVs colocalize to the nucleus. EVs from infected neurons altered gene expression of astrocytes leading to a downregulation of GLT-1 protein expression and an increase in pro-inflammatory transcriptional signatures. These results demonstrate the ability of a parasitic infection in the brain to alter EV production and the fundamental communication between neurons and astrocytes.

microbiology↗

bioRxiv2022

Neutrophils in the brain are sources of neuroprotective molecules and demonstrate functional heterogeneity during chronic Toxoplasma gondii infection

Infection with the protozoan parasite Toxoplasma gondii leads to the formation of lifelong cysts in neurons of the brain that can have devastating consequences in the immunocompromised. However, despite the establishment of a chronic inflammatory state and infection-induced neurological changes, there are limited signs of clinical neuropathology resulting in an asymptomatic infection in the immunocompetent. This suggests the work of neuroprotective mechanisms to prevent clinical manifestations of disease. However, such sources of neuroprotection during infection remain largely unknown. This study identifies a population of neutrophils chronically present in the brain during Toxoplasma infection that express the neuroprotective molecules NRG-1, ErbB4, and MSR1. Further phenotyping of this population via flow cytometry and singe-cell RNA sequencing reveals two distinct subsets of neutrophils based on age that display functional heterogeneity. This includes cells transcriptionally prepared to function both as anti-parasitic effector cells and in a more alternative protective manner. Chronic depletion of neutrophils results in increased parasite burden and infection-induced vascular pathology. Lack of neutrophils during chronic infection also deleteriously affects neuronal regeneration and repair mechanisms. In conclusion, this work identifies and demonstrates a functionally diverse chronic neutrophil population that plays a dynamic role in controlling infection outcome in the CNS by balancing classical responses with neuroprotective functions. Author SummaryThe predominantly asymptomatic nature of chronic Toxoplasma gondii infection despite the life-long infection of neurons suggests that there are neuroprotective mechanisms at work in the brain to maintain homeostasis and integrity. This study identifies neutrophils, normally considered a first-responding innate immune cell, as a prominent source of neuroprotective molecules during Toxoplasma infection. Aged neutrophils in the brain exhibit an ability to be functionally flexible expressing signatures of classical proinflammatory responses; and neuroprotective, pro-angiogenic indicators. Lack of neutrophils during chronic infection leads to increased parasite burden, increased vascular damage, and decreased neuronal regeneration. We conclude that chronic brain neutrophils are a functionally dynamic population and a source of neuroprotection during infection and suggest that this is a potentially novel target to promote brain tissue repair without compromising anti-microbial activity.

immunology↗

bioRxiv2020

An ex vivo model of Toxoplasma recrudescence

Toxoplasma has been a useful parasite model for decades because it is relatively easy to genetically modify and culture, however, attempts to generate and study the recrudescence of tissue cysts have come up short with lab-adapted strains generating low numbers of tissue cysts in vivo. Here we have established a new model of Toxoplasma recrudescence using bradyzoites from an unadapted Type II ME49 strain (ME49EW) isolated from murine brain tissue. Ex vivo bradyzoite infection of fibroblasts and astrocytes produced sequential tachyzoite growth stages; a fast-growing stage was followed by formation of a slower-growing stage. In astrocytes, but not in fibroblasts, bradyzoites also initiated a second recrudescent pathway involving bradyzoite to bradyzoite replication. Intraperitoneal infections of mice with either bradyzoites or the fast-growing tachyzoite stage efficiently disseminated to brain tissue leading to high numbers of tissue cysts, while infections with the slow-growing tachyzoite stage were largely retained in the peritoneum. Poor infection and cyst formation of slow-growing tachyzoites was reversible by serial tissue cyst passage, while the poor tissue cyst formation of lab-adapted tachyzoites was not reversible by these approaches. To distinguish strain developmental competency, we identified Toxoplasma genes highly expressed in ME49EW in vivo tissue cysts and developed a qPCR approach that differentiates immature from mature bradyzoites. In summary, the results presented describe a new ex vivo bradyzoite recrudescence model that fully captures the growth and developmental processes during toxoplasmosis reactivation in vivo opening the door to the further study of these important features of the Toxoplasma intermediate life cycle.

microbiology↗