The Cellular Hypoxic Response upon Giardia Duodenalis Infection
Date
2024-08-08
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Abstract
Oxygen tension plays an integral role in gastrointestinal homeostasis. When oxygen concentrations become suboptimal (hypoxia), mammalian cells rely on the hypoxia-inducible factor (HIF) to combat cellular stress and augment glycolytic flux. In the gastrointestinal epithelium, this cellular response is paramount as the luminal facing epithelial cells exist in a state of physiologic hypoxia that can be further altered by pathogens. Although growing evidence suggests tissue and blood protozoan parasites can activate HIF in a mammalian host, much remains to be understood in the context of enteric protozoan infections. This study uncovered the role of HIF-1α and associated epithelial hypoxic signature upon Giardia duodenalis infection, a leading cause of diarrheal disease worldwide. Coculture experiments were carried out using Caco-2 colonic epithelial cells infected with a human isolate of G. duodenalis (GSM) in normoxic (21% O2) or hypoxic (1% O2) conditions. Under normoxic conditions, infected cells displayed a time-dependent increase in HIF-1α protein expression, the oxygen-dependent subunit of HIF. This observation was concomitant with increased expression of HIF-target genes, including those responsible for combatting cellular stress (i.e., VEGFA, GADD45A, ANKRD37), and augmenting glycolytic flux (i.e., HK2, LDHA). Intracellular metabolomic analysis of normoxic infected cells revealed simultaneous increases in glucose-6-phosphate and lactate, the metabolic outputs of HK2 and LDHA, respectively. Under hypoxic conditions, HIF-1α stabilization was not significantly different compared to uninfected hypoxic control cells. However, HIF-target genes were still upregulated, albeit to a lesser degree compared to normoxic infected cells. Importantly, the metabolome of infected epithelial cells differed greatly between normoxic and hypoxic conditions, highlighting the influential role of oxygen during G. duodenalis infection. After 24 hours, HIF-1α stabilization and alterations to HIF-target gene expression were no longer detected. These findings indicate G. duodenalis induces a hypoxic response driven by HIF-1α stabilization in normoxic intestinal epithelial cells, while simply exacerbating this cellular response in hypoxic conditions. The stabilization of HIF-1α in the absence of oxygenic stress highlights a novel metabolic cell rescue mechanism in response to enteropathogens.
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Keywords
Giardia, Hypoxia, Gastrointestinal, Oxygen, Glycolysis
Citation
DeMichele, E. (2024). The cellular hypoxic response upon Giardia duodenalis infection (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.