Characterization of cellular prion protein (PrPC) in Caenorhabditis elegans

Abstract

Cellular prion protein (PrPC) is a conserved glycoprotein predominantly expressed in neurons, glial and lymphatic cells. It is associated with the broad group of prion diseases in which PrPC becomes misfolded. However, the purpose of PrPC in living cells is still enigmatic. To elucidate its debated function in oxidative stress resistance, human PrPC was extrachromosomally expressed in the nematode Caenorhabditis elegans (C. elegans). It was co-expressed with GFP and the thermoselective worm gene pha-1 for verification of correct expression. C. elegans strains expressing PrPC were compared with controls in a variety of lifespan experiments. Under non stressful conditions, nematodes expressing PrPC had a positive effect after population size shrank to about 50%. For further investigation, strains were exposed to Paraquat causing the creation of superoxide anions. PrPC expressing nematodes showed a significant advantage compared to controls. Interaction with DAF-16/FoxO and SKN1 were excluded by knock-out or iRNA inhibited strains. Expression of PrPC showed no effect in handling other stressors like hydrogen peroxide, heat and copper ions intoxication. Further testing showed Paraquat resistance being SOD-1 dependent. However, advantageous resistance of PrPC strains is only achieved via SOD-4 and SOD-5 expression. It can be inferred that additional resistance of prion protein strains is caused by SOD-1 overexpression regulated by SOD-4 and SOD-5 which is coherent to the SOD Enzyme Assay results. False positive results by changes in chemosensory neurons were excluded by dye fill procedure. Hence, it can be concluded that C. elegans was established as a new model system in prion research. It was further proven that human cellular PrPC is capable of improving resistance of C. elegans against superoxide anions, while it is shown that PrPC modifies the expression or activity level of SOD-1 by interacting with SOD-4 and SOD-5, which, in turn, act as regulator enzymes.