Human astrovirus interactions with the intestinal epithelial barrier

About This Grant

Summary The gastrointestinal (GI) tract is the largest mucosal surface in the body. A single cell layer thick intestinal epi- thelium separates the host interior from luminal pathogens while at the same time a series of intercellular junc- tions, including tight junctions, allow for selective movement of nutrients, ions, and water. Maintenance of this barrier is critical for a healthy intestine and its disruption leads to diseases such as diarrhea, a common outcome of enteric viral infections. Notably, the GI tract is not uniform; it exhibits distinct anatomical and functional prop- erties between the small and large intestine, including variations in tight junction protein expression. Enteric pathogens evolved to overcome the intestinal barrier to infect the host. However, how intestinal regionalization impacts pathogenesis of human enteric viruses is largely unknown. Human astroviruses (HAstV) are a good model to address this fundamental question in viral pathogenesis. We have demonstrated that epithelium-only human intestinal organoids (HIO), which are “miniguts” derived from stem cells isolated from human intestinal biopsy tissues or surgical resections, support HAstV infections from all clades and in all segments of the intestine. HAstVs are highly prevalent viruses that infect the entire lengths of the GI tract causing mostly pediatric diarrhea but can also cause disseminated disease in the immunocompromised. They are genetically diverse and classi- fied into classical human astroviruses, serotypes 1 – 8 (HAstV 1- 8), and two non-classical clades, VA and MLB. In vitro work from polarized model colonic epithelial Caco-2 cells suggests that the pathogenic mechanism of classical HAstV-1, but not VA1, occurs when the enterotoxin function of the HAstV-1 capsid disrupts tight junc- tions by downregulating occludin. Our new findings demonstrate that VA1 alters electrical conductance of T84, another model human colonic epithelial cell line, (but not Caco-2) by modulating a different group of tight junction transmembrane proteins, the claudins. Some members of the claudin family but not occludin exhibit intestinal segment specific expression patterns. This raises the fundamental question whether HAstVs may interact with the intestinal epithelial barrier in a segment-specific manner and positions HIO as an ideal non-transformed and physiologically relevant model of the human intestinal epithelium for detailed mechanistic studies of HAstV inter- action with the small and large intestine. The goal of our research is to advance our understanding of HAstV pathogenesis by determining the interaction of HAstVs with the intestinal epithelial barrier. Towards that end, we will use a combination of virological, molecular, genetic, and imaging approaches to pursue the following aims: 1) Investigate barrier properties of the small and large intestinal epithelium infected with HAstVs, and 2) Deter- mine whether the VA1 spike changes claudins and paracellular permeability. These aims are in direct response to NIH Notice of Special Interest (NOSI) AI-23-048, as they will “improve understanding of basic virology of understudied viruses such as HAstV”. This research has high potential for transformative impacts on our under- standing of the pathogenesis of viral gastroenteritis and intestinal epithelial biology.