Biology subjects

Harty, J. T.

Publications and source records attributed to Harty, J. T..

3 recordsLinked to original sources

bioRxiv2022

ISG15-modification of the Arp2/3 complex restricts pathogen spread

The ubiquitin-like protein, ISG15, can act as a cytokine or can covalently modify host and pathogen-derived proteins. The consequences of ISG15 modification on substrate fate remain unknown. Here we reveal that ISGylation of the Arp2/3 complex slows actin filament formation and stabilizes Arp2/3 dependent structures including cortical actin and lamella. When properly controlled, this serves as an antibacterial and antiviral host defense strategy to directly restrict actin-mediated pathogen spread. However, Listeria monocytogenes takes advantage in models of dysregulated ISGylation, leading to increased mortality due to augmented spread. The underlying molecular mechanism responsible for the ISG15-dependent impact on actin-based motility is due to failed bacterial separation after division. This promotes spread by enabling the formation of multi-headed bacterial "bazookas" with stabilized comet tails that can disseminate deeper into tissues. A bacterial mutant that cannot recruit Arp2/3 or a non-ISGylatable mutant of Arp3 is sufficient to rescue slowed comet tail speed and restrict spread. Importantly, ISG15-deficient neonatal mice have aberrant epidermal epithelia characterized by keratinocytes with diffuse cortical actin, which could underlie observed defects in wound healing in human patients who lack ISG15. Ultimately, our discovery links host innate immune responses to cytoskeletal dynamics with therapeutic implications for viral infection and metastasis.

cell biology↗

bioRxiv2022

Antigen presentation by discrete class I molecules on brain endothelium dynamically regulates T-cell mediated neuropathology in experimental cerebral malaria

CD8 T cell engagement of brain vasculature is a putative mechanism of neuropathology in human cerebral malaria. To define contributions of brain endothelial cell MHC class I antigen-presentation to CD8 T cells in establishing this pathology, we developed novel H-2Kb LoxP and H-2Db LoxP mice crossed with Cdh5-Cre mice to achieve targeted deletion of discrete class I molecules on brain endothelium. Using the Plasmodium berghei ANKA model of experimental cerebral malaria (ECM), we observe that H-2Kb and H-2Db regulate distinct patterns of disease onset, CD8 T cell infiltration, targeted cell death, and regional blood-brain barrier (BBB) disruption. Strikingly, ablation of H-2Kb or H-2Db from brain endothelial cells resulted in reduced CD8 T cell activation, attenuated T cell interaction with brain vasculature, lessened targeted cell death, preserved BBB integrity, and prevented ECM and the death of the animal. These data demonstrate that interactions of CD8 T cells with discrete MHC class I molecules on brain endothelium regulate development of ECM neuropathology. Therefore, targeting MHC class I interactions therapeutically may hold potential for treatment of cases of severe malaria.

neuroscience↗

bioRxiv2021

Altered cleavage of Caspase-1 in hepatocytes limits control of malaria in the liver

Malaria, caused by Plasmodium parasites, is a devastating disease that kills over half a million people each year1. Plasmodium sporozoites inoculated by mosquitoes into mammalian hosts undergo a clinically silent phase of obligatory development and replication in hepatocytes before initiating the life-threatening blood-stage of malaria2. Thus, understanding the immune responses elicited by Plasmodium infection in the liver is key to controlling clinical malaria and transmission3,4. Here, we show that Plasmodium DNA can be detected by AIM2 (absent in melanoma 2) sensors in the infected hepatocytes, resulting in Caspase-1 activation and pyroptotic cell-death. However, Caspase-1 was observed to undergo only partial cleavage in hepatocytes, limiting pyroptosis, and the maturation of pro-inflammatory cytokines classically associated with Caspase-1 activation. We discovered that the extent of Caspase-1 cleavage in cells is determined by the expression of ASC (apoptosis-associated speck-like protein containing a CARD). ASC expression is inherently low in hepatocytes, and transgenically enhancing it in the hepatocytes induced complete processing of Caspase-1, efficient secretion of pro-inflammatory cytokines, enhanced pyroptotic cell-death, and markedly improved control of malaria infection in the liver. In addition to describing a novel pathway of natural immunity to malaria, our findings uncover a key aspect of liver biology that may have been exploited during evolution by successful hepatotropic pathogens.

immunology↗