Major hypercorticism is an endocrine feature of ewes with naturally occurring scrapie

Membrane toxicity of abnormal prion protein in adrenal chromaffin cells of scrapie infected sheep

Transmissible spongiform encephalopathies (TSEs) or prion diseases are associated with accumulations of disease specific PrP (PrP(d)) in the central nervous system (CNS) and often the lymphoreticular system (LRS). Accumulations have additionally been recorded in other tissues including the peripheral nervous system and adrenal gland. Here we investigate the effect of sheep scrapie on the morphology and the accumulation of PrP(d) in the adrenal medulla of scrapie affected sheep using light and electron microscopy. Using immunogold electron microscopy, non-fibrillar forms of PrP(d) were shown to accumulate mainly in association with chromaffin cells, occasional nerve endings and macrophages. PrP(d) accumulation was associated with distinctive membrane changes of chromaffin cells including increased electron density, abnormal linearity and invaginations. Internalisation of PrP(d) from the chromaffin cell plasma membrane occurred in association with granule recycling following hormone exocytosis. PrP(d) accumulation and internalisation from membranes is similarly associated with perturbations of membrane structure and trafficking in CNS neurons and tingible body macrophages of the LRS. These data suggest that a major toxic effect of PrP(d) is at the level of plasma membranes. However, the precise nature of PrP(d)-membrane toxicity is tissue and cell specific suggesting that the normal protein may act as a multi-functional scaffolding molecule. We further suggest that the co-localisation of PrP(d) with exocytic granules of the hormone trafficking system may provide an additional source of infectivity in blood.

Presence of an acute phase response in sheep with clinical classical scrapie

Background

Work with experimental scrapie in sheep has been performed on-site for many years including studies on PrP^Sc dissemination and histopathology of organs and tissues both at preclinical and clinical stages. In this work serum was sampled at regular intervals from lambs which were infected immediately after birth and from parallel healthy controls, and examined for acute phase proteins. In contrast to earlier experiments, which extensively studied PrP^Sc dissemination and histopathology in peripheral tissues and brain, this experiment is focusing on examination of serum for non-PrP^Sc markers that discriminates the two groups, and give insight into other on-going processes detectable in serum samples.

Results

There was clear evidence of an acute phase response in sheep with clinical scrapie, both experimental and natural. All the three proteins, ceruloplasmin, haptoglobin and serum amyloid A, were increased at the clinical stage of scrapie.

Conclusion

There was evidence of a systemic measurable acute phase response at the clinical terminal end-stage of classical scrapie.

Sensory circumventricular organs in health and disease

Circumventricular organs (CVOs) are specialized brain structures located around the third and fourth ventricles. They differ from the rest of the brain parenchyma in that they are highly vascularised areas that lack a blood-brain barrier. These neurohaemal organs are classified as "sensory", when they contain neurons that can receive chemical inputs from the bloodstream. This review focuses on the sensory CVOs to describe their unique structure, and their functional roles in the maintenance of body fluid homeostasis and cardiovascular regulation, and in the generation of central acute immune and febrile responses. In doing so, the main neural connections to visceral regulatory centres such as the hypothalamus, the medulla oblongata and the endocrine hypothalamic-pituitary axis, as well as some of the relevant chemical substances involved, are described. The CVOs are vulnerable to circulating pathogens and can be portals for their entry in the brain. This review highlights recent investigations that show that the CVOs and related structures are involved in pathological conditions such as sepsis, stress, trypanosomiasis, autoimmune encephalitis, systemic amyloidosis and prion infections, while detailed information on their role in other neurodegenerative diseases such as Alzheimer's disease or multiple sclerosis is lacking. It is concluded that studies of the CVOs and related structures may help in the early diagnosis and treatment of such disorders.

Brain transcriptional stability upon prion protein-encoding gene invalidation in zygotic or adult mouse

BACKGROUND

The physiological function of the prion protein remains largely elusive while its key role in prion infection has been expansively documented. To potentially assess this conundrum, we performed a comparative transcriptomic analysis of the brain of wild-type mice with that of transgenic mice invalidated at this locus either at the zygotic or at the adult stages.

RESULTS

Only subtle transcriptomic differences resulting from the Prnp knockout could be evidenced, beside Prnp itself, in the analyzed adult brains following microarray analysis of 24 109 mouse genes and QPCR assessment of some of the putatively marginally modulated loci. When performed at the adult stage, neuronal Prnp disruption appeared to sequentially induce a response to an oxidative stress and a remodeling of the nervous system. However, these events involved only a limited number of genes, expression levels of which were only slightly modified and not always confirmed by RT-qPCR. If not, the qPCR obtained data suggested even less pronounced differences.

CONCLUSIONS

These results suggest that the physiological function of PrP is redundant at the adult stage or important for only a small subset of the brain cell population under classical breeding conditions. Following its early reported embryonic developmental regulation, this lack of response could also imply that PrP has a more detrimental role during mouse embryogenesis and that potential transient compensatory mechanisms have to be searched for at the time this locus becomes transcriptionally activated.

Neurodevelopmental expression and localization of the cellular prion protein in the central nervous system of the mouse

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative disorders caused by PrP(Sc), or prion, an abnormally folded form of the cellular prion protein (PrP(C)). The abundant expression of PrP(C) in the central nervous system (CNS) is a requirement for prion replication, yet despite years of intensive research the physiological function of PrP(C) still remains unclear. Several routes of investigation point out a potential role for PrP(C) in axon growth and neuronal development. Thus, we undertook a detailed analysis of the spatial and temporal expression of PrP(C) during mouse CNS development. Our findings show regional differences of the expression of PrP, with some specific white matter structures showing the earliest and highest expression of PrP(C). Indeed, all these regions are part of the thalamolimbic neurocircuitry, suggesting a potential role of PrP(C) in the development and functioning of this specific brain system.

Hypothalamic-pituitary-adrenal axis disregulation in PrPC-null mice

As manifestations of prion diseases include disturbances of hypothalamic and pituitary functions, we tested the hypothesis that the cellular prion protein (PrPC) has a role as modulator of the hypothalamic-pituitary-adrenal axis. The level of corticosterone and adrenocorticotropic hormone were compared in PrPC null (PrP 0/0) and wild-type (PrP+/+) mice. PrP 0/0 showed hypercorticism during the dark part of day. After acute stress, corticosterone and adrenocorticotropic hormone increased similarly in PrP+/+ and PrP 0/0 mice. Adrenocorticotropic hormone, however, remained elevated in PrP+/+ 0/0 mice at corticosterone levels that are inhibitory in PrP mice. Pretreatment with corticosterone or dexamethasone inhibited stress-induced elevation of adrenocorticotropic hormone in PrP+/+ but not in PrP 0/0 mice. Thus, PrPC may play a role in the negative feedback regulation of axis.

Prion disease induced alterations in gene expression in spleen and brain prior to clinical symptoms

Prion diseases are fatal neurodegenerative disorders that affect animals and humans. There is a need to gain understanding of prion disease pathogenesis and to develop diagnostic assays to detect prion diseases prior to the onset of clinical symptoms. The goal of this study was to identify genes that show altered expression early in the disease process in the spleen and brain of prion disease-infected mice. Using Affymetrix microarrays, we identified 67 genes that showed increased expression in the brains of prion disease-infected mice prior to the onset of clinical symptoms. These genes function in many cellular processes including immunity, the endosome/lysosome system, hormone activity, and the cytoskeleton. We confirmed a subset of these gene expression alterations using other methods and determined the time course in which these changes occur. We also identified 14 genes showing altered expression prior to the onset of clinical symptoms in spleens of prion disease infected mice. Interestingly, four genes, Atp1b1, Gh, Anp32a, and Grn, were altered at the very early time of 46 days post-infection. These gene expression alterations provide insights into the molecular mechanisms underlying prion disease pathogenesis and may serve as surrogate markers for the early detection and diagnosis of prion disease.

Contributions of neuronal prion protein on sleep recovery and stress response following sleep deprivation

In order to gain insights on the function of the cellular prion protein (PrP(C)) sleep and the levels of the stress hormones corticosterone (CORT) and the adrenocorticotropic hormone (ACTH) before and after sleep deprivation (SD) were compared in two wild type (WT) mice strains and the following three PrP(C) transgenic lines: mice null for PrP(C) (mPrP(0/0)) and mice with specific and central expression of PrP in neurons (NSE-HPrP/mPrP(0/0)) or in glia cells (GFAP-HPrP/mPrP(0/0)). After SD mPrP(0/0) mice showed a larger degree of sleep fragmentation and of latency to enter rapid eye movement (REM) and non-REM sleep (NREM) than WT. During sleep recovery, the amount of NREM sleep and the slow-wave activity (SWA) were reduced in mPrP(0/0) mice. After SD, CORT and ACTH levels have distinct patterns in WT and mPrP(0/0). The NREM and SWA deficit was restored in NSE-HPrP/mPrP(0/0) mice but not in GFAP-HPrP/mPrP(0/0). Hormonal profile was only partially restored in NSE-HPrP/mPrP(0/0) mice and was similar to that of mPrP(0/0) and GFAP-HPrP/mPrP(0/0) mice. These findings demonstrate that neuronal, but not non-neuronal, PrP(C) is involved in sleep homeostasis and sleep continuity. They also suggest that neuronal PrP(c)-dependent hormonal regulation of HPA axis may contribute to the sleep homeostasis.

Abnormal prion protein in the pituitary in sporadic and variant Creutzfeldt-Jakob disease

By using high-sensitivity Western blotting and immunohistochemistry, pituitary glands from patients with sporadic and variant Creutzfeldt-Jakob disease (sCJD and vCJD, respectively) were analysed for the presence of the protease-resistant form of the prion protein (PrPres). PrPres was detected in a greater proportion of vCJD pituitaries than sCJD pituitaries and was localized predominantly in the neurohypophysis. PrPres was also detected in a recurrent pituitary adenoma from an sCJD patient. Immunohistochemical analysis showed sparse positive labelling, predominantly in folliculostellate cells, in vCJD and sCJD adenohypophyses. The PrPres glycosylation pattern in the vCJD neurohypophyses showed a predominance of the unglycosylated band, which differed markedly from patterns found in all other vCJD tissues. The presence of PrPres in the pituitary of CJD patients at autopsy suggests that human growth hormone-related iatrogenic CJD may have indeed resulted from infectivity in collected pituitaries rather than necessarily from contamination of pituitary pools by adjacent brain tissue.

Prominent corticosteroid disturbance in experimental prion disease

Prion diseases comprise a group of neurodegenerative disorders that invariably lead to death in affected individuals. The most prominent event in these diseases is a rapid and pronounced neuronal loss, although the cause and the precise mechanisms of neuronal cell death have not been identified so far. Recently, it has been suggested that corticosteroids might play a role in the pathogenesis of neurodegenerative disorders in general, as the regulation of these hormones was found to be disturbed in Alzheimer's and Parkinson's disease, as well as in a transgenic mouse model of Alzheimer's disease. To evaluate the possible corticosteroid disturbances in prion diseases, we determined the concentration of corticosterone metabolites in the faeces of scrapie-inoculated mice during the course of the clinical disease. We observed markedly elevated concentrations of the metabolites during the last 5 weeks of the disease, as well as a severe disturbance of circadian periodicity of corticosterone excretion as much as 2 weeks before this elevation. A simultaneous downregulation of cerebral neuronal glucocorticoid receptors was not detectable by immunohistochemistry, indicating that increased corticosteroids can elicit their effects in mouse scrapie freely. The dysregulation of corticosteroid excretion might act as a further cofactor in the pathogenesis of scrapie, for example by preconditioning nerve cells to disease-immanent neurotoxic stimuli, such as oxidative stress, and to apoptosis.

A functional genomic study on NCI's anticancer drug screen

Pharmacogenomics requires massive computer exploration on heterogeneous databases. COMPARE, the gateway to the NCI's anticancer drug screen database, allows users to correlate drug-sensitivity profiles with a functional genomic database. However, most drugs of known molecular mechanism turn out to be uncorrelated with their molecular-target gene expression. Based on a novel statistical concept, liquid association, we develop an on-line system to identify candidate genes that intervene, confound and weaken the drug-gene correlation. The system takes queries and returns button-clickable tables of functionally associated genes for rerouting to knowledgebases such as Locus Link, OMIM and PubMed. We report results that link methotrexate resistance to DNA component biosynthesis, and taxol sensitivity to genes associated with human immunodeficiency virus infection. The drug-sensitivity database can be synergistically coanalyzed with gene expression data to study proteins of poorly understood physiological roles. When applied to the human prion, a cellular context embroidered with the gene expression network of Alzheimer disease is revealed.

First case of feline spongiform encephalopathy in a captive cheetah born in France: PrP(sc) analysis in various tissues revealed unexpected targeting of kidney and adrenal gland

Feline spongiform encephalopathy (FSE), affecting domestic and captive feline species, is a prion disease considered to be related to bovine spongiform encephalopathy. Here we report an immunohistological analysis of the first FSE-affected cheetah born in France. The duration of clinical signs, of which ataxia was the main one, was about 8 weeks. The distribution of abnormal prion protein (PrP(sc)) was studied by immunohistochemistry within 27 different tissues. Different antibodies were used to visualise abnormal PrP deposits in situ. PrP(sc )accumulation was detected in the central nervous system (cerebral cortex, cerebellum, brain stem, spinal cord, retina), in peripheral nerves and in lymphoid organs. PrP(sc) deposits were not observed within the enteric nervous system nor in several other organs, such as pancreas, ovary, liver and muscle. More interestingly, unusual PrP(sc )deposits were observed within the zona fasciculata/reticularis of the adrenal gland and within some glomeruli of the kidney raising the question of possible PrP(sc) excretion. The sympathetic innervation of these two organs was visualised and compared to the distribution of PrP(sc) deposits. Our results suggest the possibility that the infectious agent is spread by both haematogenous and nervous pathways.

Discriminant value of blood and urinary corticoids for the diagnosis of scrapie in live sheep

The mean (sd) concentration of plasma 20beta-dihydrocortisol in 126 scrapie-affected sheep was 5-5 (7.0) ng/ml compared with 1.1 (0.7) ng/ml in 52 healthy sheep. The mean (sd) concentration of creatinine in the urine of 93 scrapie-affected sheep was 2.43 (1.56) microg/ml compared with 0.94 (0.86) pg/ml in 49 healthy sheep and 1.10 (0-95) pg/ml in 25 sheep with other diseases. These discriminant analyses carried out on healthy and scrapie-affected sheep showed that plasma 20beta-dihydrocortisol and urinary creatinine were the best predictors of the disease, and classified correctly 98 per cent of healthy sheep and 82 per cent of scrapie-affected sheep.

A nonlabeled method to evaluate cortisol production rate by modeling plasma CBG-free cortisol disposition

This study aimed to develop a nonlabeled method for the measurement of cortisol production rate to evaluate adrenal function. The cortisol production rate determination requires that of cortisol clearance, which is not a parameter but a variable resulting from the saturable binding of cortisol to corticosteroid-binding globulin (CBG). Our method is based on evaluation of the plasma clearance of the CBG-free cortisol fraction. This parameter was evaluated from a pharmacokinetic model of total plasma cortisol disposition that takes into account specific binding of the corticoid to CBG in the plasma. We have shown that the CBG-free cortisol kinetics and CBG-binding parameters thus evaluated are not statistically different from those obtained by the radioisotopic method and equilibrium dialysis, suggesting that the plasma CBG-free cortisol clearance is independent of the total plasma cortisol concentrations and represents the actual parameter of cortisol elimination. We validated this modeling approach by using it to calculate the in vivo entry rate of cortisol mimicked by the perfusion of cortisol at a known rate.