Fonctions de la protéine prion PrPc

Sleep disturbance in clinical and preclinical scrapie-infected sheep measured by polysomnography

Neurodegenerative diseases are characterised by neuronal loss and abnormal deposition of pathological proteins in the nervous system. Among the most common neurodegenerative diseases are Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease and transmissible spongiform encephalopathies (TSEs). Sleep and circadian rhythm disturbances are one of the most common symptoms in patients with neurodegenerative diseases. Currently, one of the main objectives in the study of TSEs is to try to establish an early diagnosis, as clinical signs do not appear until the damage to the central nervous system is very advanced, which prevents any therapeutic approach. In this paper, we provide the first description of sleep disturbance caused by classical scrapie in clinical and preclinical sheep using polysomnography compared to healthy controls. Fifteen sheep classified into three groups, clinical, preclinical and negative control, were analysed. The results show a decrease in total sleep time as the disease progresses, with significant changes between control, clinical and pre-clinical animals. The results also show an increase in sleep fragmentation in clinical animals compared to preclinical and control animals. In addition, sheep with clinical scrapie show a total loss of Rapid Eye Movement sleep (REM) and alterations in Non Rapid Eyes Movement sleep (NREM) compared to control sheep, demonstrating more shallow sleep. Although further research is needed, these results suggest that prion diseases also produce sleep disturbances in animals and that polysomnography could be a diagnostic tool of interest in clinical and preclinical cases of prion diseases.

An Update on Peripheral Blood Extracellular Vesicles as Biomarkers for Parkinson's Disease Diagnosis

Parkinson's disease (PD) is the world's second primary neurodegenerative disease, and the diagnosis and treatment of PD have become mainstream research. Over the past decades, several studies have identified potential biomarkers for diagnosing PD. Among them, extracellular vesicles (EVs) can carry specific biomarkers reflecting the physiological and pathological state of the body. Due to the blood-brain barrier (BBB) limitation, peripheral blood is limited in diagnosing neurodegenerative diseases. With the increasing research on EVs, their ability to pass through BBB indicated that peripheral blood could depict disease status like cerebrospinal fluid (CSF). Peripheral blood is a clinically available sample and has recently been widely used by researchers in various studies. In this review, we summarized previous studies on PD diagnosis biomarkers in peripheral blood EVs and evaluated their diagnostic value. Some EV surface markers were also described, which can extract EVs from specific cell origins. In addition, the combination of several biomarkers demonstrated good diagnostic performance in PD diagnosis compared with a single biomarker, suggesting the focus of future research.

Impact of the Renin-Angiotensin System on the Pathogeny and Pharmacotherapeutics of Neurodegenerative Diseases

Brain neurodegenerative diseases (BND) are debilitating conditions that are especially characteristic of a certain period of life and considered major threats to human health. Current treatments are limited, meaning that there is a challenge in developing new options that can efficiently tackle the different components and pathophysiological processes of these conditions. The renin-angiotensin-aldosterone system (RAS) is an endocrine axis with important peripheral physiological functions such as blood pressure and cardiovascular homeostasis, as well as water and sodium balance and systemic vascular resistance-functions which are well-documented. However, recent work has highlighted the paracrine and autocrine functions of RAS in different tissues, including the central nervous system (CNS). It is known that RAS hyperactivation has pro-inflammatory and pro-oxidant effects, thus suggesting that its pharmacological modulation could be used in the management of these conditions. The present paper underlines the involvement of RAS and its components in the pathophysiology of BNDs such as Parkinson's disease (PD), Alzheimer's disease (AD), multiple sclerosis (MS), Huntington's disease (HD), motor neuron disease (MND), and prion disease (PRD), as well as the identification of drugs and pharmacologically active substances that act upon RAS, which could alleviate their symptomatology or evolution, and thus, contribute to novel therapeutic approaches.

Role of Prion protein in premature senescence of human fibroblasts

Prion protein (PrP) is essentially known for its capacity to induce neurodegenerative prion diseases in mammals caused by a conformational change in its normal cellular isoform (PrP^C) into an infectious and disease-associated misfolded form, called scrapie isoform (PrP^Sc). Although its sequence is highly conserved, less information is available on its physiological role under normal conditions. However, increasing evidence supports a role for PrP^C in the cellular response to oxidative stress. In the present study, a new link between PrP and senescence is highlighted. The role of PrP in premature senescence induced by copper was investigated. WI-38 human fibroblasts were incubated with copper sulfate (CuSO₄) to trigger premature senescence. This induced an increase of PrP mRNA level, an increase of protein abundance of the normal form of PrP and a nuclear localization of the protein. Knockdown of PrP expression using specific small interfering RNA (siRNA) gave rise to appearance of several biomarkers of senescence as a senescent morphology, an increase of senescence associated β-galactosidase activity and a decrease of the cellular proliferative potential. Overall these data suggest that PrP protects cells against premature senescence induced by copper.

Neuroimmune connections in ovine pharyngeal tonsil: potential site for prion neuroinvasion

Recent studies have established the involvement of nasal-associated lymphoid tissues, mainly the pharyngeal tonsil, in prion pathogenesis. However, the mechanisms of the associated neuroinvasion are still debated. To determine potential sites for prion neuroinvasion inside the ovine pharyngeal tonsil, the topography of heavy (200 kDa) and light (70 kDa) neurofilaments and of glial fibrillar acidic protein has been semi-quantitatively analysed inside the various compartments of the tonsil. The results show that the most innervated areas are the interfollicular area and the connective tissue located beneath the respiratory epithelium. The existence of rare synapses between follicular dendritic cells and nerve fibres inside the germinal centre indicates that this mechanism of neuroinvasion is possible but, since germinal centres of lymphoid follicles are poorly innervated, other routes of neuroinvasion are likely. The host PRNP genotype does not influence the pattern of innervation in these various tonsil compartments, unlike ageing during which an increase of nerve endings occurs in a zone of high trafficking cells beneath the respiratory epithelium. A minimal age-related increase of innervation inside the lymphoid follicles has also been observed. An increase in nerve fibre density around the lymphoid follicles, in an area rich in mobile cells such as macrophages and dendritic cells capable of capturing and conveying pathogen prion protein (PrPd), might ensure more efficient infectivity, not in the early phase but in the advanced phase of lymphoinvasion after the amplification of PrPd; alternatively, this area might even act as a direct site of entry during neuroinvasion.

Hypoxia protects neuronal cells from human prion protein fragment-induced apoptosis

Prion diseases are neurodegenerative disorders characterized by the accumulation of an abnormal isoform of the prion protein PrP(Sc). Human prion protein fragment, PrP (106-126) (prion protein peptide 106-126), may contain most of the pathological features associated with PrP(Sc). Hypoxic conditions elicit cellular responses adaptively designed to improve cell survival and have an important role in the process of cell survival. We investigate the effects of hypoxia on PrP (106-126)-induced apoptosis in the present study. Human neuroblastoma and glioblastoma cells were incubated with varied doses of PrP (106-126) under both normoxic or hypoxic conditions, in order to determine the regulatory effects of hypoxia on PrP (106-126)-induced apoptosis. The results indicate that hypoxia protects neuronal cells against PrP (106-126)-induced cell death by activating the Akt signal, which is inactivated by prion proteins, and inhibiting PrP (106-126)-induced caspase 3 activation. Low oxygen conditions increase the Bcl-2 protein, which is associated with anti-apoptotic signals, and recover the PrP (106-126)-induced reduction in mitochondrial transmembrane potential. This study demonstrates that hypoxia inhibits PrP (106-126)-induced neuron cell death by regulating Akt and Akt-related signaling, and it also suggests that prion-related neuronal damage and disease may be regulated by hypoxia or by hypoxic-inducing genes.

[Prions: where do we stand 20 years after the appearance of bovine spongiform encephalopathy?]

Bovine spongiform encephalopathy (BSE) is a transmissible spongiform encephalopathy (TSE) identified twenty years ago in the British cattle herds. Creutzfeldt-Jakob disease (CJD) is a TSE that occurs in humans. In 1996, scientists found a possible link between BSE and a new variant of CJD (vCJD). The fact that the non conventional infectious agent of TSE, named prions, could cross the species barrier from cattle to human through meat consumption, raised a tremendous concern for public safety in Europe. This led to the development in the following two decades of substantial and expensive measures to contain BSE and prevent its transmission to humans. In parallel, scientific programs have been funded to progress through the comprehension of the physiopathology of these fatal disorders. In Europe, the BSE epidemics is now ending and the number of cases is decreasing thanks to the strict control of animal foodstuff that was the main source of prion contamination. Only a small number of vCJD have been detected, however, additional concerns have been raised recently for public safety as secondary transmission of CJD through medical procedure and blood transfusion is possible. In addition, the possibility that the BSE was transmitted to other animals including small ruminants is also worrisome. Research efforts are now focussing on decontamination and ante mortem diagnosis of TSE to prevent animal and human transmission. However, needs for fundamental research are still important as many questions remain to be addressed to understand the mechanism of prion transmission, as well as its pathogenesis.