Parasite-Mediated Remodeling of the Host Microfilament Cytoskeleton Enables Rapid Egress of Trypanosoma cruzi following Membrane Rupture

Trypanosoma cruzi infection induces DNA double-strand breaks and activates DNA damage response pathway in host epithelial cells

Trypanosoma cruzi, the etiological agent of Chagas disease, invades many cell types affecting numerous host-signalling pathways. During the T. cruzi infection, we demonstrated modulations in the host RNA polymerase II activity with the downregulation of ribonucleoproteins affecting host transcription and splicing machinery. These alterations could be a result of the initial damage to the host DNA caused by the presence of the parasite, however, the mechanisms are not well understood. Herein, we examined whether infection by T. cruzi coincided with enhanced DNA damage in the host cell. We studied the engagement of the DNA damage response (DDR) pathways at the different time points (0-24 h post-infection, hpi) by T. cruzi in LLC-MK2 cells. In response to double-strand breaks (DSB), maximum phosphorylation of the histone variant H2AX is observed at 2hpi and promotes recruitment of the DDR p53-binding protein (53BP1). During T. cruzi infection, Ataxia-telangiectasia mutated protein (ATM) and DNA-PK protein kinases remained active in a time-dependent manner and played roles in regulating the host response to DSB. The host DNA lesions caused by the infection are likely orchestrated by the non-homologous end joining (NHEJ) pathway to maintain the host genome integrity.

Differentiating Trypanosoma cruzi in a Host Mammalian Cell Imaged in Aqueous Liquid by Atmospheric Scanning Electron Microscopy

Atmospheric Scanning Electron Microscopy (ASEM) is a powerful tool to observe a wet specimen at high resolution under atmospheric pressure. Here, we visualized a protozoan parasite Trypanosoma cruzi over the course of its infection cycle in the host mammalian cell. This is the first observation of intracellular parasite using a liquid-phase EM. Unlike regular SEM, aldehyde-fixed cell body of T. cruzi appears translucent, allowing the visualization of internal structures such as kinetoplast of trypomastigote and nucleus of amastigote. Plasma membrane of the host mammalian cell also appears translucent, which enabled direct observation of differentiating intracellular parasites and dynamic change of host cellular structures in their near-natural states. Various water-rich structures including micro- and macro- vesicles were visualized around T. cruzi. In addition, Correlative Light and Electron Microscopy exploiting open sample dish of ASEM allowed identification of parasite nucleus and transfected fluorescence-labeled parasites soon after internalization, while location of this morphological intermediate was otherwise obscure. Successful visualization of the differentiation of T. cruzi within the host cell demonstrated here opens up the possibility of using ASEM for observation of variety of intracellular parasites. IMPORTANCE Using Atmospheric Scanning Electron Microscopy (ASEM), we visualized interaction between infectious stage of Trypanosoma cruzi and completely intact host mammalian cell. Plasma membrane appears translucent under ASEM, which not only enables direct observation of T. cruzi within its host cell, but also reveals internal structures of the parasite itself. Sample deformation is minimal, since the specimen remains hydrated under atmospheric pressure at all times. This nature of ASEM, along with the open structure of ASEM sample dish, is suited for correlative light-electron microscopy, which can further be exploited in identification of fluorescent protein in the intracellular parasites.