CELLULAR PRION PROTEIN MODULATES BRAIN MITOCHONDRIA CALCIUM DYNAMICS

The cellular prion protein (PrP^C) is primarily expressed in cells of the central nervous system and participates in several signaling pathways, modulating functions such as cell death and immunoregulation, although it lacks a known exclusive physiological function. The conformational conversion of PrP^C into its pathogenic form, prion scrapie (PrP^Sc), is associated with the loss of its function and the formation of amyloid aggregates in the brain, which are central to prion diseases. Although PrP^C is classically considered a plasma membrane protein, in 2017 its presence was demonstrated in the inner mitochondrial membrane of brain mitochondria (mPrP^C). The role of mPrP^C in the physiology of these mitochondria, however, remains unclear, making it relevant to investigate the functional nature of this interaction. To this end, we performed experiments using mitochondria isolated from the brains of wild-type C57BL/6 (WT) mice and PrP^C knockout (PrP-KO) mice. To investigate mitochondrial calcium uptake, we evaluated the fluorescence of the calcium-binding probe Calcium Green 5N using a Cary Eclipse fluorimeter. Our results demonstrate an alteration in the calcium dynamics of PrP-KO brain mitochondria, which uptake a significantly higher concentration of calcium than WT mitochondria. Through Western Blotting, we demonstrated that this modulation does not involve alterations in the level of the mitochondrial calcium uniporter (MCU) or mitochondrial hexokinase (mt−HK), an important modulator of calcium uptake by brain mitochondria. The enzymatic activity of mt-HK was determined by spectrophotometry and was also similar between the WT and PrP-KO samples. Preliminary experiments suggest that the increase in calcium uptake by PrP-KO mitochondria may occur through mitochondrial NMDA-type receptors, due to the loss of their functional interaction with mPrP^C. Interestingly, our results demonstrate that PrP-KO mitochondria exhibit increased activity of the matrix enzymes α-ketoglutarate dehydrogenase and pyruvate dehydrogenase, which utilize calcium as a cofactor, potentially correlating with higher intramitochondrial calcium content. Our results suggest PrP^C as a physiological regulator of mitochondrial calcium dynamics, and further investigation is important for a more complete and precise understanding of this intricate relationship.