The expression levels of cellular prion protein affect copper isotopic shifts in the organs of mice

Abstract

The metabolic processes involving copper, such as cellular assimilation, electron transfer and protein formation, can partition copper isotopes in the body amongst different organs and bodily fluids. Systematic changes in copper isotopic composition in the body may assist in identifying regions where copper metabolism has been altered. The cellular prion protein (PrP^C) is a copper-binding protein that is highly expressed in the brain. Its misfolded isoform PrP^Sc is required for the development of prion diseases, fatal neurological diseases including Scrapie and Creutzfeldt-Jacob's disease. As this protein is implicated in copper metabolism, we investigated how expression levels of PrP^C could affect the distribution of copper isotopes in the body. We used a novel ion exchange method to isolate copper for stable copper isotope analysis of the liver, kidney, red blood cells, serum, and different regions of the brain of wild type, PrP^C knockout (Prnp^−/−) and mice in which the copper-binding sites of the octarepeat region were mutated (His → Ala, Cu-del). We found the liver, kidney and brain tissue samples to be enriched in ⁶⁵Cu compared to the food, but only in the liver were differences observed associated with genotype when considering the absolute δ⁶⁵Cu values. Characteristic isotopic shifts were identified between the serum and the liver (all genotypes, p = 0.022), and between the serum and the hippocampus, cerebral cortex, and brainstem (Prnp^−/− and Cu-del only, p values were 0.002, 0.053, and 0.017 respectively). We have demonstrated that altering the gene expression of a single protein, in this case PrP^C, can produce systematic changes in copper isotopic distribution in transgenic mice.