Plasma noradrenalin as marker of neuroinvasion in prion diseases

The Role of the Mammalian Prion Protein in the Control of Sleep

Sleep disruption is a prevalent clinical feature in many neurodegenerative disorders, including human prion diseases where it can be the defining dysfunction, as in the case of the "eponymous" fatal familial insomnia, or an early-stage symptom as in certain types of Creutzfeldt-Jakob disease. It is important to establish the role of the cellular prion protein (PrP^C), the key molecule involved in prion pathogenesis, within the sleep-wake system in order to understand fully the mechanisms underlying its contribution to both healthy circadian rhythmicity and sleep dysfunction during disease. Although severe disruption to the circadian rhythm and melatonin release is evident during the pathogenic phases of some prion diseases, untangling whether PrP^C plays a role in circadian rhythmicity, as suggested in mice deficient for PrP^C expression, is challenging given the lack of basic experimental research. We provide a short review of the small amount of direct literature focused on the role of PrP^C in melatonin and circadian rhythm regulation, as well as suggesting mechanisms by which PrP^C might exert influence upon noradrenergic and dopaminergic signaling and melatonin synthesis. Future research in this area should focus upon isolating the points of dysfunction within the retino-pineal pathway and further investigate PrP^C mediation of pinealocyte GPCR activity.

Transmission of chronic wasting disease identifies a prion strain causing cachexia and heart infection in hamsters

Chronic wasting disease (CWD) is an emerging prion disease of free-ranging and captive cervids in North America. In this study we established a rodent model for CWD in Syrian golden hamsters that resemble key features of the disease in cervids including cachexia and infection of cardiac muscle. Following one to three serial passages of CWD from white-tailed deer into transgenic mice expressing the hamster prion protein gene, CWD was subsequently passaged into Syrian golden hamsters. In one passage line there were preclinical changes in locomotor activity and a loss of body mass prior to onset of subtle neurological symptoms around 340 days. The clinical symptoms included a prominent wasting disease, similar to cachexia, with a prolonged duration. Other features of CWD in hamsters that were similar to cervid CWD included the brain distribution of the disease-specific isoform of the prion protein, PrP^Sc, prion infection of the central and peripheral neuroendocrine system, and PrP^Sc deposition in cardiac muscle. There was also prominent PrP^Sc deposition in the nasal mucosa on the edge of the olfactory sensory epithelium with the lumen of the nasal airway that could have implications for CWD shedding into nasal secretions and disease transmission. Since the mechanism of wasting disease in prion diseases is unknown this hamster CWD model could provide a means to investigate the physiological basis of cachexia, which we propose is due to a prion-induced endocrinopathy. This prion disease phenotype has not been described in hamsters and we designate it as the ‘wasting’ or WST strain of hamster CWD.

Changes in sympathetic activity in prion neuroinvasion

Prion diseases are neurodegenerative diseases affecting humans and animals in which the infectious agent or prion is PrP(res), a protease-resistant conformer of the cell protein PrP. The natural transmission route of prion diseases is peripheral infection, with the lymphoreticular system (LRS) and peripheral nerves being involved in animal models of scrapie neuroinvasion and human prion diseases. To study the effects of PrP neuroinvasion on sympathetic nerve function, we measured plasma catecholamine levels, blood pressure, heart rate, and PrP tissue levels in intraperitoneally or intracerebrally infected mice. The results indicate a specific alteration in sympathetic nerve function because the levels of noradrenaline (but not adrenaline) were increased in the animals infected peripherally (but not in those infected intracerebrally) and correlated with increased blood pressure. These findings confirm that prion neuroinvasion uses the sympathetic nervous system to spread from the periphery to the central nervous system after invading the LRS.