Evaluating the Role of Bacterial Lipopolysaccharide on Etiology and Pathogenesis of Transmissible Spongiform Encephalopathies

  • Author / Creator
    Goldansaz, Seyed Ali
  • Transmissible spongiform encephalopathies (TSEs) or otherwise known as prion diseases are a class of fatal neurodegenerative diseases related to irreversible brain damage. Presently, there is no effective treatment or preventive strategy for this disease because the etiology and biological behavior of the causative agent, prion protein, is not yet understood very well. Although the disease is related to misfolding of a normal cellular prion protein (PrPC) into an abnormal one, known as scrapie (PrPSc), there is increasing evidence for a potential role of endogenous/exogenous cofactors in the pathogenesis of the disease. Furthermore, it has been reported that in presence of cofactors prion disease tends to aggravate. Of note, none of the cofactors identified so far have been able to independently induce prion disease in various animal models. In this study, we hypothesized that bacterial lipopolysaccharide (LPS), derived from Gram-negative bacteria, and recombinant PrP converted in vitro into a beta-rich isoform resistant to proteinase K digestion (moPrPres) through incubation with bacterial LPS, can cause prion-like disease in a murine model. LPS is a cell wall component of all Gram-negative bacteria commonly found in the environment, and highly abundant in the digestive tract. Lipopolysaccharide has been extensively used to mimic bacterial infection in various studies. In neurodegenerative diseases, LPS has shown to contribute to exacerbating existing neurodegenerative disease conditions. Recently our team reported that incubation of LPS with PrPC under normal in vitro conditions and without presence of other cofactors can convert PrPC to an isoform rich in beta sheets and resistant to proteinase K digestion, which we are defining as resistant mouse recombinant prion protrein (moPrPres). To test this hypothesis and to investigate the degree of moPrPres pathogenicity and infectivity, one experiment was conducted in which FVB/N female mice were inoculated subcutaneously with the infectious agents. To do so, 90 FVB/N female mice at the age of 6 week (wk) were randomly assigned into 6 treatment groups (n=15 per group) including: 1) saline (negative control), 2) LPS, 3) moPrPres, 4) moPrPres+LPS, 5) RML (Rocky mountain laboratory scrapie prions) +LPS, and 6) RML (positive control). Lipopolysaccharide and saline were administered subcutaneously for a period of 6 wk, whereas moPrPres and RML were injected one time subcutaneously at the start of the experiment. Mice inoculated with LPS or moPrPres exhibited prion-like disease signs with weight loss accompanied with 50% and 60% mortality rates, respectively, over long incubation days in comparison to the positive controls. Immunohistochemical (IHC) staining of brain sections from the mice treated with LPS or moPrPres showed extensive vacuolation patterns comparable to the positive control although with larger size and some degree of PrPSc accumulation in the brain. In addition presence of astrogliosis and deposition of amyloid plaques were detected in some brain regions. However, when chronic subcutaneous administration of LPS was accompanied with RML, IHC stainings revealed aggravation in vacuolation, accumulation of PrPSc, and astrogliosis in comparison to the RML-only treated mice. Furthermore, gene expression profiling of all treatment groups in comparison to the negative control indicated various alterations most importantly down-regulation in expression level of genes encoding the prion protein (Prnp) and shadow of prion protein (Sprn), with the exception of the LPS-only treated group that had no effect on Prnp. Down-regulation of Prnp and Sprn are considered gene expression signatures specific to prion diseases. In addition, using non-targeted metabolomics approach multiple metabolite alterations were detected in the serum and urine of RML- and RML+LPS-infected mice, which might serve as predictive biomarkers of disease at early stages of pathogenesis.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.