Strain-dependent role of copper in prion disease through binding to histidine residues in the N-terminal domain of prion protein.

The cellular prion protein, PrP , is a copper-binding protein abundantly expressed in the brain, particularly by neurons, and its conformational conversion into the amyloidogenic isoform, PrP , plays a key pathogenic role in prion diseases. However, the role of copper binding to PrP in prion diseases remains unclear. Here, we fed mice with a low-copper or regular diet and intracerebrally inoculated them with two different mouse-adapted RML scrapie and BSE prions. Mice with a low-copper diet developed disease significantly but only slightly later than those with a regular diet after inoculation with BSE prions, but not with RML prions, suggesting that copper could play a minor role in BSE prion pathogenesis, but not in RML prion pathogenesis. We then generated two lines of transgenic mice expressing mouse PrP with copper-binding histidine (His) residues in the N-terminal domain replaced with alanine residues, termed TgPrP(5H > A)-7342/Prnp and TgPrP(5H > A)-7524/Prnp mice, and similarly inoculated RML and BSE prions into them. Due to 2-fold higher expression of PrP(5H > A) than PrP in wild-type (WT) mice, TgPrP(5H > A)-7524/Prnp mice were highly susceptible to these prions, compared to WT mice. However, TgPrP(5H > A)-7342/Prnp mice, which express PrP(5H > A) 1.2-fold as high as PrP in WT mice, succumbed to disease slightly, but not significantly, later than WT mice after inoculation with RML prions, but significantly so after inoculation with BSE prions. Subsequent secondary inoculation experiments revealed that amino acid sequence differences between PrP(5H > A) and WT PrP created no prion transmission barrier to BSE prions. These results suggest that copper-binding His residues in PrP are dispensable for RML prion pathogenesis but have a minor effect on BSE prion pathogenesis. Taken together, our current results suggest that copper could have a minor effect on prion pathogenesis in a strain-dependent manner through binding to His residues in the N-terminal domain of PrP .