The endothelial cell receptor GRP78 is required for mucormycosis pathogenesis in diabetic mice
Mingfu Liu, Brad Spellberg, Quynh T. Phan, Yue Fu, Yong Fu, Amy S. Lee, John E. Edwards Jr., Scott G. Filler, Ashraf S. Ibrahim
Mingfu Liu, Brad Spellberg, Quynh T. Phan, Yue Fu, Yong Fu, Amy S. Lee, John E. Edwards Jr., Scott G. Filler, Ashraf S. Ibrahim
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Research Article Infectious disease

The endothelial cell receptor GRP78 is required for mucormycosis pathogenesis in diabetic mice

Abstract

Mucormycosis is a fungal infection of the sinuses, brain, or lungs that causes a mortality rate of at least 50% despite first-line therapy. Because angioinvasion is a hallmark of mucormycosis infections, we sought to define the endothelial cell receptor(s) for fungi of the order Mucorales (the fungi that cause mucormycosis). Furthermore, since patients with elevated available serum iron, including those with diabetic ketoacidosis (DKA), are uniquely susceptible to mucormycosis, we sought to define the role of iron and glucose in regulating the expression of such a receptor. Here, we have identified glucose-regulated protein 78 (GRP78) as what we believe to be a novel host receptor that mediates invasion and damage of human endothelial cells by Rhizopus oryzae, the most common etiologic species of Mucorales, but not Candida albicans or Aspergillus fumigatus. Elevated concentrations of glucose and iron, consistent with those seen during DKA, enhanced GRP78 expression and the resulting R. oryzae invasion and damage of endothelial cells in a receptor-dependent manner. Mice with DKA, which have enhanced susceptibility to mucormycosis, exhibited increased expression of GRP78 in sinus, lungs, and brain compared with normal mice. Finally, GRP78-specific immune serum protected mice with DKA from mucormycosis. These results suggest a unique susceptibility of patients with DKA to mucormycosis and provide a foundation for the development of new therapeutic interventions for these deadly infections.

Authors

Mingfu Liu, Brad Spellberg, Quynh T. Phan, Yue Fu, Yong Fu, Amy S. Lee, John E. Edwards Jr., Scott G. Filler, Ashraf S. Ibrahim

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Figure 3

Anti-GRP78 Ab blocks endothelial cell endocytosis of and damage by R. oryzae but not damage caused by C. albicans or A. fumigatus.

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Anti-GRP78 Ab blocks endothelial cell endocytosis of and damage by R. or...
Adherence and endocytosis (determined by differential fluorescence) assays were carried out using endothelial cells split on 12-mm glass coverslips, while damage was carried out using the 96-well plate 51Cr release method. Endothelial cells were incubated with 50 μg/ml anti-GRP78 or anti-p53 Ab (control) (Santa Cruz Biotechnology Inc.) for 1 hour prior to addition of R. oryzae germlings. Blocking of GRP78 with Ab abrogates endocytosis of R. oryzae by endothelial cells (data derived from >700 fungal cells interacting with approximately 200 endothelial cells/each group/experiment, with an average of 59% cells being endocytosed in the control) (A) and reduces the ability of the fungus to cause endothelial cell damage (B). However, anti-GRP78 Ab did not block damage caused by C. albicans (C) or A. fumigatus (D). *P < 0.01 compared with anti-p53 Ab by Wilcoxon rank-sum test. n = 6 slides per group from 3 independent experiments for endocytosis, and n = 6 wells per group from 2 independent experiments for damage assay. Data are expressed as median ± interquartile range.