Evaluating GII.4 human norovirus infection in enteroendocrine cells using human intestinal enteroids

Hephzibah Nwanosike, Baylor College of Medicine

Hephzibah Nwanosike, Mary K. Estes, Robert L. Atmar, Sasirekha Ramani. Baylor College of Medicine, Houston, Tx, USA

Structure & Pathogenesis

Human noroviruses (HuNoVs) cause acute, self-limiting illness in immunocompetent individuals and chronic illness in some immunocompromised patients. The mechanisms by which HuNoVs cause diarrhea and/or vomiting are poorly defined. Our previous work using patient biopsies and human intestinal enteroids (HIEs) showed that HuNoVs primarily infect enterocytes in the small intestine. However, two recent studies using intestinal biopsies from a 9-month-old patient and from a rhesus macaque model showed the presence of HuNoV RNA and capsid protein VP1 colocalized in enteroendocrine cells (EECs). Upon stimulation, these gut neurohormonal cells can signal to the enteric nervous system and activate brain centers involved in nausea and vomiting. We hypothesized that secretion of neuroactive hormones such as serotonin from infected EECs is a potential mechanism of HuNoV-associated vomiting. We used two models to test our hypothesis: a genetically modified NGN3 HIE line that can be induced to overexpress EECs, and two infant HIEs that naturally express higher numbers of EECs than adult HIEs. GII.4 HuNoV replication measured using RT-qPCR and immunofluorescence staining for VP1 was significantly lower in the induced NGN3 HIEs compared to the parental and uninduced lines. This could possibly be due to the low numbers of enterocytes in the induced HIE line. We also did not observe co-localization of VP1 with Chromogranin A, a marker of EECs in the NGN3 HIE line. GII.4 infection was not associated with increased secretion of serotonin in adult and infant HIEs. In on-going studies, we are examining whether other neuroactive hormones are produced following infection.