Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Cell Biology, Neurobiology and Anatomy

Abstract

Every year there are nearly 500,000 reported burn injuries in the United States; half of which occur under the influence of alcohol. Clinical studies have shown that burn patients who are intoxicated at the time of injury have a worse prognosis; including increased risk of multiple organ dysfunction syndrome (MODS) and sepsis. The etiology behind these pathological consequences of ethanol and burn injury remains to be elucidated. The Gut-lymph hypothesis of MODS theorizes that trauma (e.g. ethanol and burn injury) results in a redistribution of blood flow to protect more vital organs which leads to ischemia/hypoxia (diminished oxygen delivery) in the intestines. Hypoxia has been demonstrated to negatively affect microRNA (miR) biogenesis. As microRNAs are central to many cellular functions; disruption of these molecules due to hypoxic insult could influence tissue damage, tight junction protein expression and inflammation. However, the role of hypoxia in mediating intestinal barrier disruption following ethanol and burn injury remains largely unknown.

The overall objective of this dissertation is to examine how hypoxia following ethanol and burn injury modulates expression of microRNA biogenesis components and microRNAs resulting intestinal barrier disruption. The central hypothesis is that, hypoxic insult following acute ethanol intoxication and burn injury disrupts microRNA biogenesis, resulting in decreased miR-150 expression in isolated small intestinal epithelial cells and increased intestinal permeability in vivo.

Our results show that ethanol and burn injury diminishes expression of tight junction proteins, microRNA biogenesis components: (drosha and argonaute-2) and select microRNAs. Furthermore, these changes accompany elevated inflammation, hypoxia (HIF-1α) and bacterial overgrowth. Treatment of mice at the time of injury with PX-478, a HIF-1α inhibitor, restored expression of microRNA biogenesis components, and normalizes the expression of miRs (-7a and -150). These changes coincided with reduced microbial overgrowth, increased tight junction protein expression and decreased intestinal permeability. Together, this work has illuminated the relationship of hypoxia and microRNAs and their role in regulation of the intestinal barrier following ethanol and burn injury.

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