Prp-c and Prp-Sc at the fetal-maternal interface

Detection of prions in oocytes and ovaries of ewes naturally infected with classical scrapie

Classical scrapie is a prion disease that affects goats and sheep and is transmitted mainly horizontally. However, infection can also occur vertically, from mother to offspring, but the exact mechanism is unclear. The possibilities include transmission during pregnancy, birth, or after birth. Some studies have reported that prions are present in various reproductive tissues and fluids, suggesting that vertical transmission could occur through the germ line. However, the presence of prions in female reproductive tissues and oocytes has not been extensively studied, so their role in vertical transmission is unknown. Oocytes and ovarian tissues from 25 naturally infected ewes (ARQ/ARQ and VRQ/VRQ genotypes) and healthy controls were analysed. The samples were subjected to PMCA for prion detection. Histopathological and immunohistochemical evaluations of ovarian tissues were also performed. We demonstrated that PrPSc can accumulate in the oocytes and ovaries of scrapie-infected ewes, indicating a potential germline route of transmission. Prion accumulation appears to be influenced by the host genotype and prion strain, emphasizing the need for ultrasensitive detection techniques. Further research under controlled conditions is necessary to elucidate the mechanisms and implications for disease control and breeding programs.

Vertical transmission of chronic wasting disease in free-ranging white-tailed deer populations

Chronic wasting disease (CWD) is a fatal neurodegenerative disease affecting cervids across North America, Northern Europe, and Asia. Disease transmission among cervids has historically been attributed to direct animal-to-animal contact with 'secreta' (saliva, blood, urine, and feces) containing the infectious agent, and indirect contact with the agent shed to the environment in these bodily components. Mounting evidence provides another mechanism of CWD transmission, that from mother-to-offspring, including during pregnancy (vertical transmission). Here we describe the detection of the infectious CWD agent and prion seeding in fetal and reproductive tissues collected from healthy-appearing free-ranging white-tailed deer (Odocoileus virginianus) from multiple U.S. states by mouse bioassay and in vitro prion amplification assays. This is the first report of the infectious agent in several in utero derived fetal and maternal-fetal reproductive tissues, providing evidence that CWD infections are propagated within gestational fetal tissues of white-tailed deer populations. This work confirms previous experimental and field findings in several cervid species supporting vertical transmission as a mechanism of CWD transmission and helps to further explain the facile dissemination of this disease among captive and free-ranging cervid populations.

Physiology of Cellular Prion Proteins in Reproduction

Cellular prion protein (PrPC) encoded at Prnp gene is well-known to form a misfolded isoform, termed scrapie PrP (PrPSC) that cause transmissible degenerative diseases in central nervous system. The physiological role of PrPC has been proposed by many studies, showing that PrPC interacts with various intracellular, membrane, and extracellular molecules including mitochondrial inner membrane as a scaffold. PrPC is expressed in most cell types including reproductive organs. Numerous studies using PrPC knockout rodent models found no obvious phenotypic changes, in particular the clear phenotypes in development and reproduction have not demonstrated in these knockout models. However, various roles of PrPC have been evaluated at the cellular levels. In this review, we summarized the known roles of PrPC in various cell types and tissues with a special emphasis on those involved in reproduction.

Uterine secretome: What do the proteins say about maternal-fetal communication in buffaloes?

The aim was to compare the UF proteomics of pregnant and non-pregnant buffalo during early pregnancy. Forty-four females were submitted to hormonal estrus synchronization and randomly divided into two groups: pregnant (n = 30) and non-pregnant (n = 14). The pregnant group was artificially inseminated and divided into a further two groups: P12 (n = 15) and P18 (n = 15). Conceptus and uterine fluid samples were collected during slaughter at, respectively, 12 and 18 days after insemination. Of all the inseminated females, only eight animals in each group were pregnant, which reduced the sample of the groups to P12 (n = 8) and P18 (n = 8). The non-pregnant group was also re-divided into two groups at the end of synchronization: NP12 (n = 7) and NP18 (n = 7). The UF samples were processed for proteomic analysis. The results were submitted to multivariate and univariate analysis. A total of 1068 proteins were found in the uterine fluid in both groups. Our results describe proteins involved in the conceptus elongation and maternal recognition of pregnancy, and their action was associated with cell growth, endometrial remodeling, and modulation of immune and antioxidant protection, mechanisms necessary for embryonic maintenance in the uterine environment. SIGNIFICANCE: Uterine fluid is a substance synthesized and secreted by the endometrium that plays essential roles during pregnancy in ruminants, contributing significantly to embryonic development. Understanding the functions that the proteins present in the UF perform during early pregnancy, a period marked by embryonic implantation, and maternal recognition of pregnancy is of fundamental importance to understanding the mechanisms necessary for the maintenance of pregnancy. The present study characterized and compared the UF proteome at the beginning of pregnancy in pregnant and non-pregnant buffaloes to correlate the functions of the proteins and the stage of development of the conceptus and unravel their processes in maternal recognition of pregnancy. The proteins found were involved in cell growth and endometrial remodeling, in addition to acting in the immunological protection of the conceptus and performing antioxidant actions necessary for establishing a pregnancy.

PrPres in placental tissue following experimental transmission of atypical scrapie in ARR/ARR sheep is not infectious by Tg338 mouse bioassay

Nor98-like atypical scrapie is a sporadic disease that affects the central nervous system of sheep and goats that, in contrast to classical scrapie, is not generally regarded as naturally transmissible. However, infectivity has been demonstrated via bioassay not only of brain tissue but also of certain peripheral nerves, lymphoid tissues, and muscle. This study examines placental tissue, a well characterized route of natural transmission for classical scrapie. Further, this study was conducted in sheep homozygous for the classical scrapie resistant ARR genotype and is the first to characterize the transmission of Nor98-like scrapie between homozygous-ARR sheep. Nor98-like scrapie isolated from a United States ARR/ARR sheep was transmitted to four ARR/ARR ewes via intracerebral inoculation of brain homogenate. These ewes were followed and observed to 8 years of age, remained non-clinical but exhibited progression of infection that was consistent with Nor98-like scrapie, including characteristic patterns of PrPSc accumulation in the brain and a lack of accumulation in peripheral lymphoid tissues as detected by conventional methods. Immunoblots of placental tissues from the infected ewes revealed accumulation of a distinct conformation of PrPres, particularly as the animals aged; however, the placenta showed no infectivity when analyzed via ovinized mouse bioassay. Taken together, these results support a low risk for natural transmission of Nor98-like scrapie in ARR/ARR sheep.

Detection of Chronic Wasting Disease Prions in Fetal Tissues of Free-Ranging White-Tailed Deer

The transmission of chronic wasting disease (CWD) has largely been attributed to contact with infectious prions shed in excretions (saliva, urine, feces, blood) by direct animal-to-animal exposure or indirect contact with the environment. Less-well studied has been the role that mother-to-offspring transmission may play in the facile transmission of CWD, and whether mother-to-offspring transmission before birth may contribute to the extensive spread of CWD. We thereby focused on a population of free-ranging white-tailed deer from West Virginia, USA, in which CWD has been detected. Fetal tissues, ranging from 113 to 158 days of gestation, were harvested from the uteri of CWD+ dams in the asymptomatic phase of infection. Using serial protein misfolding amplification (sPMCA), we detected evidence of prion seeds in 7 of 14 fetuses (50%) from 7 of 9 pregnancies (78%), with the earliest detection at 113 gestational days. This is the first report of CWD detection in free ranging white-tailed deer fetal tissues. Further investigation within cervid populations across North America will help define the role and impact of mother-to-offspring vertical transmission of CWD.

Pathogenesis, detection, and control of scrapie in sheep

In sheep, scrapie is a fatal neurologic disease that is caused by a misfolded protein called a prion (designated PrP^Sc). The normal cellular prion protein (PrP^C) is encoded by an endogenous gene, PRNP, that is present in high concentrations within the CNS. Although a broad range of functions has been described for PrP^C, its entire range of functions has yet to be fully elucidated. Accumulation of PrP^Sc results in neurodegeneration. The PRNP gene has several naturally occurring polymorphisms, and there is a strong correlation between scrapie susceptibility and PRNP genotype. The cornerstone of scrapie eradication programs is the selection of scrapie-resistant genotypes to eliminate classical scrapie. Transmission of classical scrapie in sheep occurs during the prenatal and periparturient periods when lambs are highly susceptible. Initially, the scrapie agent is disseminated throughout the lymphoid system and into the CNS. Shedding of the scrapie agent occurs before the onset of clinical signs. In contrast to classical scrapie, atypical scrapie is believed to be a spontaneous disease that occurs in isolated instances in older animals within a flock. The agent that causes atypical scrapie is not considered to be naturally transmissible. Transmission of the scrapie agent to species other than sheep, including deer, has been experimentally demonstrated as has the transmission of nonscrapie prion agents to sheep. The purpose of this review is to outline the current methods for diagnosing scrapie in sheep and the techniques used for studying the pathogenesis and host range of the scrapie agent. Also discussed is the US scrapie eradication program including recent updates.

Infectious Prions in the Pregnancy Microenvironment of Chronic Wasting Disease-Infected Reeves' Muntjac Deer

Ample evidence exists for the presence of infectious agents at the maternal-fetal interface, often with grave outcomes to the developing fetus (i.e., Zika virus, brucella, cytomegalovirus, and toxoplasma). While less studied, pregnancy-related transmissible spongiform encephalopathies (TSEs) have been implicated in several species, including humans. Our previous work has shown that prions can be transferred from mother to offspring, resulting in the development of clinical TSE disease in offspring born to muntjac dams infected with chronic wasting disease (CWD) (1). We further demonstrated protein misfolding cyclic amplification (PMCA)-competent prions within the female reproductive tract and in fetal tissues harvested from CWD experimentally and naturally exposed cervids (1, 2). To assess whether the PMCA-competent prions residing at the maternal-fetal interface were infectious and to determine if the real-time quaking-induced conversion (RT-QuIC) methodology may enhance our ability to detect amyloid fibrils within the pregnancy microenvironment, we employed a mouse bioassay and RT-QuIC. In this study, we have demonstrated RT-QuIC seeding activity in uterus, placentome, ovary, and amniotic fluid but not in allantoic fluids harvested from CWD-infected Reeves' muntjac dams showing clinical signs of infection (clinically CWD-infected) and in some placentomes from pre-clinically CWD-infected dams. Prion infectivity was confirmed within the uterus, amniotic fluid, and the placentome, the semipermeable interface that sustains the developing fetus, of CWD-infected dams. This is the first report of prion infectivity within the cervid pregnancy microenvironment, revealing a source of fetal CWD exposure prior to the birthing process, maternal grooming, or encounters with contaminated environments.IMPORTANCE The facile dissemination of chronic wasting disease within captive and free-range cervid populations has led to questions regarding the transmission dynamics of this disease. Direct contact with infected animals and indirect contact with infectious prions in bodily fluids and contaminated environments are suspected to explain the majority of this transmission. A third mode of transmission, from mother to offspring, may be underappreciated. The presence of pregnancy-related prion infectivity within the uterus, amniotic fluid, and the placental structure reveals that the developing fetus is exposed to a source of prions long before exposure to the infectious agent during and after the birthing process or via contact with contaminated environments. These findings have impact on our current concept of CWD disease transmission.

Prenatal transmission of scrapie in sheep and goats: A case study for veterinary public health

Unsettled knowledge as to whether scrapie transmits prenatally in sheep and goats and transmits by semen and preimplantation embryos has a potential to compromise measures for controlling, preventing and eliminating the disease. The remedy may be analysis according to a systematic review, allowing comprehensive and accessible treatment of evidence and reasoning, clarifying the issue and specifying the uncertainties. Systematic reviews have clearly formulated questions, can identify relevant studies and appraise their quality and can summarise evidence and reasoning with an explicit methodology. The present venture lays a foundation for a possible systematic review and applies three lines of evidence and reasoning to two questions. The first question is whether scrapie transmits prenatally in sheep and goats. It leads to the second question, which concerns the sanitary safety of artificial breeding technologies, and is whether scrapie transmits in sheep and goats by means of semen and washed or unwashed in vivo derived embryos. The three lines of evidence derive from epidemiological, field and clinical studies, experimentation, and causal reasoning, where inferences are made from the body of scientific knowledge and an understanding of animal structure and function. Evidence from epidemiological studies allow a conclusion that scrapie transmits prenatally and that semen and embryos are presumptive hazards for the transmission of scrapie. Evidence from experimentation confirms that semen and washed or unwashed in vivo derived embryos are hazards for the transmission of scrapie. Evidence from causal reasoning, including experience from other prion diseases, shows that mechanisms exist for prenatal transmission and transmission by semen and embryos in both sheep and goats.

Oral inoculation of neonatal Suffolk sheep with the agent of classical scrapie results in PrP(Sc) accumulation in sheep with the PRNP ARQ/ARQ but not the ARQ/ARR genotype

Scrapie is a transmissible spongiform encephalopathy that can be transmitted amongst susceptible sheep. The prion protein gene (PRNP) profoundly influences the susceptibility of sheep to the scrapie agent. This study reports the failure to detect PrP(Sc) in nervous or lymphoid tissues of Suffolk sheep of the PRNP ARQ/ARR genotype after oral inoculation with a U.S. scrapie isolate. Lambs were inoculated within the first 24 h of birth with 1 ml of a 10% (wt./vol.) brain homogenate derived from a clinically affected ARQ/ARQ sheep. The inoculated sheep were observed daily throughout the experiment for clinical signs suggestive of scrapie until they were necropsied at 86 months post inoculation. Tissues were collected for examination by immunohistochemistry and enzyme immunoassay, but all failed to demonstrate evidence of scrapie infection. Neonatal sheep of the ARQ/ARQ genotype receiving the same inoculum developed scrapie within 24 months. Lambs of the ARQ/ARR genotype that received the same inoculum by intracranial inoculation develop scrapie with a prolonged incubation period and with abnormal prion present within the central nervous system, but not peripheral lymphoid tissues. Results of this study suggest that ARQ/ARR sheep are resistant to oral infection with the scrapie isolate used even during the neonatal period.

The placenta shed from goats with classical scrapie is infectious to goat kids and lambs

The placenta of domestic sheep plays a key role in horizontal transmission of classical scrapie. Domestic goats are frequently raised with sheep and are susceptible to classical scrapie, yet potential routes of transmission from goats to sheep are not fully defined. Sparse accumulation of disease-associated prion protein in cotyledons casts doubt about the role of the goat's placenta. Thus, relevant to mixed-herd management and scrapie-eradication efforts worldwide, we determined if the goat's placenta contains prions orally infectious to goat kids and lambs. A pooled cotyledon homogenate, prepared from the shed placenta of a goat with naturally acquired classical scrapie disease, was used to orally inoculate scrapie-naïve prion genotype-matched goat kids and scrapie-susceptible lambs raised separately in a scrapie-free environment. Transmission was detected in all four goats and in two of four sheep, which importantly identifies the goat's placenta as a risk for horizontal transmission to sheep and other goats.

Clinical effect of bovine amniotic membrane and hydrocolloid on wound by laser treatment: prospective comparative randomized clinical trial

Bovine amniotic membrane (BAM) has been regarded as an ideal dressing material because it accelerates epithelization and has anti-inflammatory, anti-angiogenic, and strong analgesic effects. To evaluate the clinical effects of BAM and compare them to that of hydrocolloid dressings on wounds created by ablative laser treatments, 49 subjects with nevi or scars requiring ablative laser treatment were evaluated. To compare efficacy, we divided the body into six areas and included patients with two or more similar skin lesions in the same body area. After ablative laser treatments, BAM and hydrocolloid dressing were applied to the wounds with random allocation. Clinical assessments were performed at baseline, 1, 4, 6, 8, 11, and 13 days after treatment. Histologic changes were assessed by skin biopsy. BAM treatment induced faster epithelization than hydrocolloid treatment (6.7 vs. 9.2 days). Erythema and oozing faded more quickly, and the satisfaction score was higher in BAM-treated sites than it was in hydrocolloid-treated sites, without severe adverse effects. Histologic analysis confirmed epithelization and immunohistochemistry revealed different growth factor profiles between the two treatment modalities. BAM benefits wound healing following ablative laser treatment.

Role of the prion protein family in the gonads

The prion-gene family comprises four members named PRNP (PRP^c), PRND (Doppel), PRNT (PRT), and SPRN (Shadoo). According to species, PRND is located 16–52 kb downstream from the PRNP locus, whereas SPRN is located on another chromosome. The fourth prion-family gene, PRNT, belongs to the same genomic cluster as PRNP and PRND in humans and bovidae. PRNT and PRND possibly resulted from a duplication event of PRND and PRNP, respectively, that occurred early during eutherian species divergence. Although most of the studies concerning the prion-family has been done on PRP^c and its involvement in transmissible neurodegenerative disorders, different works report some potential roles of these proteins in the reproductive function of both sexes. Among them, a clear role of PRND, that encodes for the Doppel protein, in male fertility has been demonstrated through gene targeting studies in mice. In other species, Doppel seems to play a role in testis and ovary development but its cellular localization is variable according to the gonadal developmental stage and to the mammalian species considered. For the other three genes, their roles in reproductive function appear ill-defined and/or controversial. The present review aimed to synthesize all the available data on these prion-family members and their relations with reproductive processes, mainly in the gonad of both sexes.

Obstetric dilemma on the most appropriate management of Creutzfeldt-Jakob disease in pregnancy: seventh case presentation, literature review and new insight

Prion diseases (PDs) are fatal neurological disorders that are thought to be caused by the accumulation of an altered variant of a benign, widely expressed protein (PrPC) into a distinct pathological conformation(s) (PrPSc). The PDs are so rare but lethal pathologies that need an early diagnosis to adequately support the infected patient. A maternal-fetal transmission during pregnancy has been supposed to be on the basis of animal studies, but till now the effective vertical transmission in humans has not been proved. We present a case of infected pregnant woman with a peculiar pregnancy course and outcome. We also provided a systematic literature review to find the best obstetrical management of women affected by prionic disease during pregnancy. The available data underline the potential risk of prenatal and postnatal transmission of the disease but do not permit to define the exact molecular mechanism of transmission, the best follow-up and recommendations that are useful in both obstetrical and neonatal practice. At present awaiting for further clarifications about this topic, it is mandatory to personalize the management of this rare pregnancy complication according to the maternal-fetal well-being status.

Prion (PrPC) expression in ovine uteroplacental tissues increases after estrogen treatment of ovariectomized ewes and during early pregnancy

Scrapie in sheep is spread laterally by placental transmission of an infectious misfolded form (PrPSc) of a normal prion protein (PrPC) used as a template in PrPSc formation. We hypothesized that PrPC would be expressed in uterine and placental tissues and estradiol-17β (E2) would affect uterine PrPC expression. PrPC expression was evaluated in the uterus of long-term ovariectomized (OVX) ewes treated with an E2 implant for 2-24 h and in uteroplacental tissues from day 20 to day 30 of pregnancy. Expression of PrPC mRNA and PrPC protein increased in the uterus after E2 treatment of OVX ewes. In the maternal placenta, expression of PrPC mRNA and PrPC protein were unchanged, but in the fetal membranes (FM) PrPC mRNA and PrPC protein expression increased from day 20 to day 28. In the nonpregnant uterus, PrPC protein was immunolocalized at apical borders of the surface epithelium, in outer smooth muscle layers of large blood vessels, and in scattered stromal cells of the deep intercaruncular areas of the uterus. In the maternal placenta, PrPC protein was immunolocalized in the cytoplasm of flattened luminal epithelial cells apposed to the FM, whereas in the FM PrPC protein was in trophoblast cells and was also in several tissues of the developing embryo during early pregnancy. These data linking estrogen stimulation to increases in PrPC expression in uteroplacental tissues suggest that PrPC has a specific function during the estrous cycle and early pregnancy. Future studies should determine whether or not estrogen influences PrPC expression in other tissues, such as the nervous system and brain.

Mother to offspring transmission of chronic wasting disease in reeves' muntjac deer

The horizontal transmission of prion diseases has been well characterized in bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD) of deer and elk and scrapie of sheep, and has been regarded as the primary mode of transmission. Few studies have monitored the possibility of vertical transmission occurring within an infected mother during pregnancy. To study the potential for and pathway of vertical transmission of CWD in the native cervid species, we used a small cervid model-the polyestrous breeding, indoor maintainable, Reeves' muntjac deer-and determined that the susceptibility and pathogenesis of CWD in these deer reproduce that in native mule and white-tailed deer. Moreover, we demonstrate here that CWD prions are transmitted from doe to fawn. Maternal CWD infection also appears to result in lower percentage of live birth offspring. In addition, evolving evidence from protein misfolding cyclic amplification (PMCA) assays on fetal tissues suggest that covert prion infection occurs in utero. Overall, our findings demonstrate that transmission of prions from mother to offspring can occur, and may be underestimated for all prion diseases.

Estimating prion adsorption capacity of soil by BioAssay of Subtracted Infectivity from Complex Solutions (BASICS)

Prions, the infectious agent of scrapie, chronic wasting disease and other transmissible spongiform encephalopathies, are misfolded proteins that are highly stable and resistant to degradation. Prions are known to associate with clay and other soil components, enhancing their persistence and surprisingly, transmissibility. Currently, few detection and quantification methods exist for prions in soil, hindering an understanding of prion persistence and infectivity in the environment. Variability in apparent infectious titers of prions when bound to soil has complicated attempts to quantify the binding capacity of soil for prion infectivity. Here, we quantify the prion adsorption capacity of whole, sandy loam soil (SLS) typically found in CWD endemic areas in Colorado; and purified montmorillonite clay (Mte), previously shown to bind prions, by BioAssay of Subtracted Infectivity in Complex Solutions (BASICS). We incubated prion positive 10% brain homogenate from terminally sick mice infected with the Rocky Mountain Lab strain of mouse-adapted prions (RML) with 10% SLS or Mte. After 24 hours samples were centrifuged five minutes at 200×g and soil-free supernatant was intracerebrally inoculated into prion susceptible indicator mice. We used the number of days post inoculation to clinical disease to calculate the infectious titer remaining in the supernatant, which we subtracted from the starting titer to determine the infectious prion binding capacity of SLS and Mte. BASICS indicated SLS bound and removed ≥ 95% of infectivity. Mte bound and removed lethal doses (99.98%) of prions from inocula, effectively preventing disease in the mice. Our data reveal significant prion-binding capacity of soil and the utility of BASICS to estimate prion loads and investigate persistence and decomposition in the environment. Additionally, since Mte successfully rescued the mice from prion disease, Mte might be used for remediation and decontamination protocols.

Factors influencing temporal variation of scrapie incidence within a closed Suffolk sheep flock

Several studies have shown that transmission of natural scrapie can occur vertically and horizontally, and that variations in scrapie incidence between and within infected flocks are mostly due to differences in the proportion of sheep with susceptible and resistant PRNP genotypes. This report presents the results of a 12-year period of scrapie monitoring in a closed flock of Suffolk sheep, in which only animals of the ARQ/ARQ genotype developed disease. Among a total of 120 of these, scrapie attack rates varied between birth cohorts from 62.5 % (5/8) to 100 % (9/9), and the incidence of clinical disease among infected sheep from 88.9 % (8/9) to 100 % (in five birth cohorts). Susceptible sheep born to scrapie-infected ewes showed a slightly higher risk of becoming infected (97.2 %), produced earlier biopsy-positive results (mean 354 days) and developed disease at a younger age (median 736 days) than those born to non-infected dams (80.3 %, 451 and 782 days, respectively). Taken together, this was interpreted as evidence of maternal transmission. However, it was also observed that, for the birth cohorts with the highest incidence of scrapie (90-100 %), sheep born to infected and non-infected dams had a similar risk of developing scrapie (97.1 and 95.3 %, respectively). Compared with moderate-attack-rate cohorts (62.5-66.7 %), high-incidence cohorts had greater numbers of susceptible lambs born to infected ewes, suggesting that increased rates of horizontal transmission in these cohorts could have been due to high levels of environmental contamination caused by infected placentas.

Sparse PrP(Sc) accumulation in the placentas of goats with naturally acquired scrapie

Background

Domestic goats (Capra hircus) are a natural and experimental host of scrapie and bovine spongiform encephalopathy, the transmissible spongiform encephalopathies (TSE) of sheep and cattle. Goats are also susceptible to experimental infection with the agents of TSEs of deer and elk (chronic wasting disease) and humans (Creutzfeldt Jakob disease). Distribution of PrP^Sc, the abnormal prion protein, is similar in the tissues of scrapie-infected sheep and goats but no data are available on the potential shedding of the agent through the placenta, the presumed route of transmission of ovine scrapie. We describe the sparse accumulation of PrP^Sc in the placentas of goats with naturally acquired classical scrapie in comparison to field cases of classical ovine scrapie.

Results

PrP^Sc was detected in the shed placentas from a sample of U.S. goats with naturally occurring scrapie, diagnosed by antemortem lymphoid tissue biopsy or identified as high risk progeny of infected dams. PrP^Sc accumulation patterns in the intact placentome and western blot banding was similar in the caprine and ovine samples. However, levels of PrP^Sc estimated from ELISA and immunohistochemistry assays were generally lower in goats than in sheep, although wide variation was noted in both species.

Conclusions

PrP^Sc accumulates in the shed placentas of goats with naturally acquired scrapie. Although these levels were low in most caprine samples, the caprine placenta may contribute to prion contamination of kidding facilities and transmission to co-housed sheep or goats.

Prion transmission: prion excretion and occurrence in the environment

Prion diseases range from being highly infectious, for example scrapie and CWD, which show facile transmission between susceptible individuals, to showing negligible horizontal transmission, such as BSE and CJD, which are spread via food or iatrogenically, respectively. Scrapie and CWD display considerable in vivo dissemination, with PrP(Sc) and infectivity being found in a range of peripheral tissues. This in vivo dissemination appears to facilitate the recently reported excretion of prion through multiple routes such as from skin, feces, urine, milk, nasal secretions, saliva and placenta. Furthermore, excreted scrapie and CWD agent is detected within environmental samples such as water and on the surfaces of inanimate objects. The cycle of "uptake of prion from the environment--widespread in vivo prion dissemination--prion excretion--prion persistence in the environment" is likely to explain the facile transmission and maintenance of these diseases within wild and farmed populations over many years.

[Acquired human prion diseases--past and present issues]

Transmissible spongiform encephalopathies, or prion diseases, are fatal neurodegenerative disorders. In aetiological viewpoint, human prion diseases are classified into 1) sporadic Creutzfeldt-Jakob disease (CJD) which comprises 80-90% of the total population of human prion disaeses, 2) inherited forms, and 3) acquired types by prion-contaminated surgical instruments, biopharmaceuticals or foodstuffs. The diseases cause an accumulation of the disease-associated form(s) of prion protein (PrP(Sc)) in the central nervous system. PrP(Sc) is regarded as the entity of prion agents and generally exerts infectivity, irrespective of its origin being from the sporadic cases or the inherited cases. Variant CJD (vCJD), first identified in the United Kingdom (UK) in 1996, is an acquired type of human CJD by oral intake of BSE prion. Cumulative numbers of 215 patients in the world have been reported for definite or probable vCJD cases according to the UK National Creutzfeldt-Jakob Disease Surveillance Unit by September, 2009. Different from sporadic CJD cases, vCJD patients show an accumulation of PrP(Sc) in spleen and tonsils. Such distribution of PrP(Sc) in lymphoid tissues raised clinical concern about the potential infectivity in the blood or blood components used for blood transfusion. To date, five instances of probable transfusion-mediated transmission of vCJD prion have been found in UK. Here we review the past and the present issues about the acquired human prion diseases.

Experimental oral transmission of United States origin scrapie to neonatal sheep

Scrapie, a transmissible spongiform encephalopathy (TSE), is a naturally occurring fatal neurodegenerative disease of sheep and goats. The current study documents incubation periods, pathologic findings, and distribution of abnormal prion proteins (PrP(Sc)) by immunohistochemistry and Western blot in tissues of genetically susceptible and resistant neonatal lambs inoculated with pooled brain homogenates from 13 U.S. origin scrapie-affected ewes. Nine Suffolk lambs with genotypes AA/RR/QQ (n = 5) and AA/RR/QR (n = 4) at codons 136, 154, and 171, respectively) were orally inoculated, within 12 hr of birth, with 1 ml of a 10% (w/v) brain homogenate prepared from scrapie-affected sheep brains. Inoculated animals were euthanized when advanced clinical signs of scrapie were observed. All QQ sheep developed clinical signs of scrapie, with a mean survival time of 24 months. Spongiform lesions in the brains and PrP(Sc) deposits in the central nervous system and lymphoid tissues were present in these sheep. None of the QR sheep succumbed to the disease. A previous study that used a larger volume (30 ml of 10% brain suspension) of the same inoculum in 4-month-old Suffolk lambs of susceptible genotype documented longer survival periods (average 32 months), and only 5 of 9 inoculated sheep developed scrapie. Findings of this study suggest that orally exposed neonatal lambs of a susceptible (QQ) genotype exhibit a higher attack rate and shorter incubation period than older (4-month-old) lambs exposed to a larger dose (30x) of the same inoculum.

Failure to detect the presence of prions in the uterine and gestational tissues from a Gravida with Creutzfeldt-Jakob disease

The vertical transmission of a prion disease from infected mothers to their offspring is believed to be one of the routes for the natural spread of animal prion diseases. Supporting this notion is the observation that prion infectivity occurs in the placenta of infected ewes. Furthermore, the prion protein (PrP), both in its cellular form (PrP(C)) and its pathological isoform (PrP(Sc)), has been observed at the fetal-maternal interface of scrapie-infected sheep. However, whether these features of prion infectivity also hold true for human prion diseases is currently unknown. To begin to address such an important question, we examined PrP in the uterus as well as gestational tissues, including the placenta and amniotic fluid, in a pregnant woman with sporadic Creutzfeldt-Jakob disease (CJD). Although the proteinase K (PK)-resistant prion protein, PrP27-30, was present in the brain tissues of the mother, the PrP detected in the uterus, placenta, and amniotic fluid was sensitive to PK digestion. Unlike PrP(C) in the brain and adjacent cerebrospinal fluid, the predominant PrP species in the reproductive and gestational tissues were N-terminally truncated, similar to urine PrP. Our study did not detect abnormal PrP in the reproductive and gestational tissues in this case of CJD. Nevertheless, examination by a highly sensitive bioassay is ongoing to ascertain possible prion infectivity from CJD in the amniotic fluid.

Molecular mechanisms of prion pathogenesis

Prion diseases are infectious neurodegenerative diseases occurring in humans and animals with an invariably lethal outcome. One fundamental mechanistic event in prion diseases is the aggregation of aberrantly folded prion protein into large amyloid plaques and fibrous structures associated with neurodegeneration. The cellular prion protein (PrPC) is absolutely required for disease development, and prion knockout mice are not susceptible to prion disease. Prions accumulate not only in the central nervous system but also in lymphoid organs, as shown for new variant and sporadic Creutzfeldt-Jakob patients and for some animals. To date it is largely accepted that prions consist primarily of PrPSc, a misfolded and aggregated beta-sheet-rich isoform of PrPC. However, PrPSc may or may not be completely congruent with the infectious moiety. Here, we discuss the molecular mechanisms leading to neurodegeneration, the role of the immune system in prion pathogenesis, and the existence of prion strains that appear to have different tropisms and biochemical characteristics.

Effects of nutrition and genotype on prion protein (PrPC) gene expression in the fetal and maternal sheep placenta

For placental transmission of scrapie to occur, the normal cellular prion protein (PrPC) must be converted to an abnormal infectious form known as PrPSc. PrPC genotype influences susceptibility to contracting scrapie, but we still do not understand whether genotype or expression levels of PrPC are important in transmission of scrapie. Some evidence exists that nutrition affects expression levels of PrPC. Thus, we evaluated the effects of genotype and nutrition on PrPC mRNA and protein expression in adolescent ewes fed at control (100% of National Research Council [NRC] requirements) or restricted (60% of NRC) levels of diet intake during two periods of pregnancy (days 50-90 and days 90-130)]. Gravid uteri (n=50) from singleton pregnancies were collected at day 130, and placentomes were either separated into caruncular (CAR; maternal) or cotyledonary (COT; fetal) placenta and snap-frozen for PrPC mRNA expression or perfusion fixed for PrPC protein expression. PrPC genotypes were determined (codons 136 and 171) using SNP assay. There were no genotype effects on PrPC mRNA expression in CAR or on PrPC protein expression in either CAR or COT, but PrPC mRNA expression in COT was greater (P<0.02) when codon 136 was homozygous for alanine. Some PrPC protein-positive cells were found in the epithelium of CAR, but most were found in trophoblast binucleate and mononucleate cells of COT. In CAR, from days 90 to 130, PrPC protein abundance was greater (P=0.003) in diet-restricted ewes than in control ewes, but was less uniformly distributed (P<0.007). Additionally, in COT, from days 90 to 130, PrPC protein was less uniformly distributed (P<0.01) in diet-restricted ewes. The localized increase in PrPC protein expression, found in ewes diet-restricted late in pregnancy, may suggest a protective role for PrPC in placental biology. Further study is needed to evaluate whether nutrition, PrPC genotype, and PrPC expression levels influence placental transmission of scrapie.

Approaches to investigating transmission of spongiform encephalopathies in domestic animals using BSE as an example

Bovine spongiform encephalopathy was a novel spongiform encephalopathy, in an hitherto unaffected species, that had characteristics of a point source epidemic, with an agent that could have been incorporated into a wide variety of feedstuffs and iatrogenically administered to naïve populations, and there was early evidence that it was not restricted to bovines. It was vital to establish, albeit experimentally, which other species might be affected, and whether the epidemic could be maintained by natural transmission, if the source was removed. In contrast, scrapie has been endemic throughout Great Britain for centuries, is maintained naturally (even if we don't know exactly how) and has a known host range. The principles, process and integration of evidence from different types of studies, however, are similar for both of these transmissible spongiform encephalopathies (TSE) and can be applied to any emerging or suspected spongiform encephalopathy. This review discusses the experimental approaches used to determine TSE transmissibility and infectivity and how they relate to natural disease and control measures.

Scrapie: uncertainties, biology and molecular approaches

The study of the biology of scrapie in sheep is irretrievably associated with the genetics of the PrP gene in sheep. Control of susceptibility and resistance is so closely linked to certain alleles of the sheep PrP gene that no review on scrapie can avoid PrP genetics. Before the importance of PrP protein was discovered and before the influence of the gene itself on disease incidence was understood, it was clear there were some sheep which were more susceptible to natural scrapie than others and that this feature was heritable. These early observations have led to the development and use of PrP genotyping in sheep in what is probably the biggest genetic selection process ever attempted. The accompanying increase in surveillance has also discovered a novel type of scrapie, the subject of much speculation about its origin.

What veterinary practitioners should know about scrapie

Scrapie is the longest known and most widely spread of the transmissible spongiform encephalopathies and remains the model for much of the research regarding these diseases. Because scrapie is a reportable disease and the subject of an active eradication program in the United States, veterinary practitioners should have a basic understanding of the disease.

Association of the prion protein and its expression with ovarian follicle development in cattle

The cellular form of the prion protein (PrP(C)) has been detected in many tissues including reproductive tissues. While its function is unclear, it has been suggested to act as a receptor for an unidentified ligand and/or as an antioxidant agent. We tested the hypothesis that PrP(C) is differentially expressed in dominant, growing, compared to subordinate bovine ovarian follicles. Using both microarray analysis and quantitative real-time PCR, the level of prion protein mRNA (Prnp) in both theca and granulosa cells was measured. We found that levels of Prnp were significantly higher in the theca cells of dominant compared to subordinate follicles but similar among granulosa cells from different follicles. This difference was apparent immediately after selection of the dominant follicle and continued to the dominance stage of the follicle wave. Levels of the protein for PrP(C) were also higher (P < 0.05) in theca cells of dominant compared to subordinate follicles. In conclusion, elevated PrP(C) was associated with ovarian follicle growth and development and we suggest that it may play a role in the success of follicle development.

Expression of the prion protein gene (PRNP) and cellular prion protein (PrPc) in cattle and sheep fetuses and maternal tissues during pregnancy

We investigated the expression of prion protein gene both on mRNA and protein levels in bovine and ovine female reproductive organs during gestation and various tissues of their fetuses. The fetal tissues of both species included brain, cotyledon, heart, intestine, kidney, liver, lung, and muscle. In cattle, prion protein gene (PRNP) transcripts were detected by semiquantitative RT-PCR in reproductive tissues such as ovary, oviduct, endometrium, myometrium, follicles, and granulosa cells. In various tissues of 2-month-old fetuses, higher expression levels were found in brain and cotyledon compared to the other tissues. To detect the expression of the gene transcript in in vivo preimplantation embryos and 1-month-old fetuses, real-time PCR was performed showing that the level of gene expression in zygote stage was significantly higher (p < or = 0.05) than that of the other stages. Sheep were categorized as resistant (RI) or high susceptible (R5) to scrapie according to their PRNP genotype. In both genotype groups, the PRNP mRNA was detectable in all tissues studied including ovary, oviduct, endometrium, myometrium, and caruncle of ewes and all tissues of 2-month-old fetuses of both groups. Comparison between reproductive organs demonstrates the highest expression level in caruncle tissue of R1 ewes, whereas the level was high in brain and low in liver of both R1 and R5 fetuses. In addition, real-time RT-PCR was performed in immature oocytes, mature oocytes, in vivo embryos at morula stage, and 1-month-old fetuses. The results showed that the relative expression levels of the ovine PRNP mRNA in mature oocytes and morula stage embryos were significantly lower than those in immature oocytes and 1-month-old fetuses (p < or = 0.05). Western blot analyses revealed the immunoreactive bands corresponding to the cellular prion protein (PrPc) in all maternal and fetal tissues examined of both cattle and sheep. Moreover, immunohistochemical staining implicated localization of the PrPc in ovarian cortex and ovarian medulla of both species. However, PrPc was not detected in oocyte, granulosa cells, theca cells, and corpus luteum in this study.

Pathogenesis of prion diseases: current status and future outlook

The prion, a conformational variant of a host protein, is the infectious particle responsible for transmissible spongiform encephalopathy (TSE), a fatal neurodegenerative disease of humans and animals. The principal target of prion pathology is the brain, yet most TSEs also display prion replication at extra-cerebral locations, including secondary lymphoid organs and sites of chronic inflammation. Despite significant progress in our understanding of this infectious agent, many fundamental questions relating to the nature of the prion, including the mechanism of replication and the molecular events underlying brain damage, remain unanswered. Here we focus on the unresolved issues pertaining to prion pathogenesis, particularly on the role played by the immune system.

PrPSc accumulation in fetal cotyledons of scrapie-resistant lambs is influenced by fetus location in the uterus

Placentae from scrapie-infected ewes have been shown to accumulate PrPSc when the genotype of the fetus is of a susceptible genotype (VRQ/VRQ, ARQ/VRQ or ARQ/ARQ). Cotyledons from fetuses of genotypes ARR/ARR, ARQ/ARR and ARQ/VRR have previously been shown to be resistant to PrPSc accumulation. By using ewes from a naturally infected scrapie flock, cotyledons from fetuses of multiple births of different genotypes were examined. PrPSc was detected in fetal cotyledons of genotype ARQ/ARQ, but not in cotyledons from their dizygotic twin of genotype ARQ/ARR. This confirms earlier reports of single fetuses of these genotypes, but is the first description of such a finding in twin fetuses, one of each genotype. It is also demonstrated that cotyledons from sibling fetuses of genotypes ARQ/VRQ and ARQ/ARQ have different patterns of PrPSc accumulation depending on whether the dam is of genotype ARQ/ARQ or ARQ/VRQ. Lastly, it is shown that cotyledons from fetuses with resistant genotypes are weakly positive for PrPSc when they have shared the same pregnant uterine horn with a fetus of a susceptible genotype with cotyledons positive for the detection of PrPSc. Additionally, a PCR product for the Sry gene, a product specific to males, was found in cotyledons from female fetuses that had shared a uterine horn with a male fetus. This indicates that some sharing of fetal blood occurs between placentomes and fetuses residing in the same uterine horn, which can result in PrPSc accumulation in cotyledons with resistant genotypes.

Chronic wasting disease

Chronic wasting disease (CWD) is a unique transmissible spongiform encephalopathy (TSE) of mule deer (Odocoileus hemionus), white-tailed deer (O. virginianus), and Rocky Mountain elk (Cervus elaphus nelsoni). The natural history of CWD is incompletely understood, but it differs from scrapie and bovine spongiform encephalopathy (BSE) by virtue of its occurrence in nondomestic and free-ranging species. CWD has many features in common with scrapie, including early widespread distribution of disease-associated prion protein (PrP(d)) in lymphoid tissues, with later involvement of central nervous system (CNS) and peripheral tissues. This distribution likely contributes to apparent efficiency of horizontal transmission and, in this, is similar to scrapie and differs from BSE. Clinical features and lesions of CWD are qualitatively similar to the other animal TSEs. Microscopically, marked spongiform lesions occur in the central nervous system (CNS) after a prolonged incubation period and variable course of clinical disease. During incubation, PrP(d) can be identified in tissues by antibody-based detection systems. Although CWD can be transmitted by intracerebral inoculation to cattle, sheep, and goats, ongoing studies have not demonstrated that domestic livestock are susceptible via oral exposure, the presumed natural route of exposure to TSEs. Surveillance efforts for CWD in captive and free-ranging cervids will continue in concert with similar activities for scrapie and BSE. Eradication of CWD in farmed cervids is the goal of state, federal, and industry programs, but eradication of CWD from free-ranging populations of cervids is unlikely with currently available management techniques.

Assessment of the genetic risk and impact of lateral transmission in a valine-associated scrapie outbreak in sheep

OBJECTIVE

To characterize an outbreak of valine-associated scrapie, assess the relative risk of scrapie infection in relation to allele frequency at codon 136, and investigate lateral transmission of infection in a sheep flock within the United States.

ANIMALS

1,006 sheep.

PROCEDURE

To determine genotypes, blood or semen samples were assessed via commercial testing; in 190 slaughtered sheep, scrapie status was determined via immunohistochemical evaluation of tissues. Scrapie-positive sheep born to scrapie-negative dams and sheep infected after 1 year of age were identified to assess lateral transmission.

RESULTS

Genotypes were determined for codon 171 (164 sheep) or codons 136 and 171 (842 sheep). Forty-four of 160 slaughtered sheep of known genotype were scrapie positive. In these sheep, the presence of at least 1 valine allele at codon 136 (V136) was highly correlated with scrapie-positive status. Lateral transmission was the probable source of infection for 4 scrapie-positive sheep born to scrapie-negative dams and for 11 sheep in which scrapie was diagnosed at > 50 months of age.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that the outbreak of scrapie was associated with a relatively high frequency of V136 in the flock, introduction of a valine-dependent scrapie strain, and the occurrence of lateral transmission. Genotyping of sheep may assist management decisions following diagnosis of scrapie in a sheep with at least 1 V136. It may be prudent to remove sheep of the diploid genotype AVQR (at codons 136 and 171) from infected flocks.

In utero gene therapy: current challenges and perspectives

Over the past few years, considerable progress in prenatal diagnosis and surgery combined with improvements in vector design vindicate a reappraisal of the feasibility of in utero gene therapy for serious monogenetic diseases. As adult gene therapy gathers pace, several apparent obstacles to its application as a treatment may be overcome by pre- or early postnatal treatment. This review will examine the concepts and practice of prenatal vector administration. We aim to highlight the advantages of early therapeutic intervention focusing on diseases that could benefit greatly from a prenatal gene therapy approach. We will pay special attention to the strategies and vectors that are most likely to be used for this application and will speculate on their expected developments for the near future.

Biology of PrPsc accumulation in two natural scrapie-infected sheep flocks

Sheep scrapie is a prion disease that requires interaction of exogenous prions with host prion protein (PrP) supporting prion formation. Disease is associated with deposition of a host-generated conformational variant of PrP, PrPsc, in a variety of tissues, including brain, resulting in fatal spongiform encephalopathy. Efficiency of PrPsc formation is determined by polymorphisms in the PrP-coding sequence. This article adds to previous data of natural sheep scrapie, concentrating on the effect of host genotype and age on PrPsc accumulation patterns during preclinical and clinical disease. Two entire scrapie-infected, predominantly Suffolk-cross, sheep flocks euthanized for regulatory purposes were genotyped and analyzed for PrPsc deposition in various tissues using single- and dual-label immunohistochemistry. Scrapie, as defined by PrPsc deposition, occurred in 13/80 sheep. Preclinical disease was evident in nearly 70% of infected sheep, ranging in age from 14 months to 7 years. PrPsc accumulated systemically in the nervous tissue, various lymphoid tissues, both alimentary tract related and non-alimentary tract related, and the placenta. Clinical neurological illness was always associated with spongiform encephalopathy and PrPsc deposition in the brain. Only 6 of 9 sheep with preclinical scrapie had PrPsc deposition in the brain but widespread PrPsc deposition in peripheral lymphoid tissue, supporting previous data showing peripheral PrPsc accumulation preceding deposition in the brain. PrPsc colocalized with a marker for follicular dendritic cells throughout the lymphoid system. PrPsc also accumulated in the peripheral nervous system, particularly the nervous supply of the gastrointestinal tract. Abundant PrPsc was evident in trophoblast cells of placentomes but not in the endometrium, myometrium, or associated nervous plexus. PrPsc deposits were not observed in the mammary parenchyma or bone marrow. Scrapie susceptibility was defined genetically by PrP codon 171: PrPsc deposition was restricted to PrP genotype AA136RR154QQ171 in 12/13 cases or AV136RR154QQ171 in 1/13 cases. The earliest accumulation was observed in the single VRQ/ARQ heterozygous animal, consistent with the reported high scrapie susceptibility and brief incubation period observed in breeds with predominance of the V136R154Q171 allele. Disease occurred within, as well as independent of, mother-daughter lines, suggesting both maternal and nonmaternal transmission in the flocks.

A paired case–control study of risk factors for scrapie in Irish sheep flocks

We did a case-control study of the association of several animal, flock and management factors with scrapie in Irish sheep flocks. The characteristics of 61 sheep flocks with at least one laboratory-confirmed case of scrapie (1990-1998) were compared to 61 flocks with no history of scrapie and matched by geographical location and attending veterinary surgeon. The 61 scrapie-affected flocks were from the database of known scrapie flocks in the Republic of Ireland at the start of the study. In conditional multiple logistic regression, factors associated with increased odds of scrapie in a sheep flock were (i) larger breeding-flock size, (ii) purchasing replacement sheep through the market, (iii) spreading sheep compost on the land and (iv) disposing of the placenta in the compost. Factors associated with decreased odds of scrapie were (i) using cattle slurry on the land and (ii) feeding proprietary concentrates to lambs.

Demonstration of lateral transmission of scrapie between sheep kept under natural conditions using lymphoid tissue biopsy

Scrapie free adult sheep were introduced to a sheep flock specifically maintained to maximise scrapie infection. Native born sheep of the highly susceptible VRQ/VRQ genotype in this flock show highly efficient transmission, evidenced by 100% infection, with an age at death of less than 2 years. Infection in introduced sheep was identified by biopsy of tonsilar and nictitating membrane lymphoid tissue. Progeny of these sheep were monitored and clinical disease confirmed by examination of the brain using routine diagnostic methods. Naïve sheep of New Zealand origin introduced to the flock in adulthood became infected, demonstrating that lateral transmission had occurred. Lambs born to introduced ewes became infected and died at the same age as lambs born to native ewes, consistent with lateral transmission of scrapie to lambs. Although maternal transmission cannot be totally excluded for the lambs in this study, the data are consistent with lateral transmission being the most important means of spread leading to the high incidence of scrapie observed in this flock.

Epidemiological implications of the susceptibility to BSE of putatively resistant sheep

The experimental infection of sheep with bovine spongiform encephalopathy (BSE) by the oral route and the likelihood that sheep were fed BSE-infected meat and bone meal has led to extensive speculation as to whether or not sheep are naturally infected with BSE. In response, the UK government has initiated the National Scrapie Plan (NSP), an ambitious £120 million per year project to create a BSE- and scrapie-resistant national sheep flock, by selectively breeding for a genotype of sheep believed to be resistant to both diseases. This genotype has recently been shown to be susceptible to BSE by intracerebral (i.c.) inoculation. Should these sheep be sufficiently susceptible to BSE via natural transmission, the NSP might fail. Here we estimate the susceptibility of this genotype to horizontal (sheep-to-sheep) transmission of BSE by comparison with more extensive oral and i.c. exposure data for other sheep genotypes. We show that a previous estimate of the risk of BSE transmission to sheep via the feedborne route remains robust. However, using a mathematical model for the within-flock transmission of BSE, we show that, while the best estimate indicates that the NSP should be successful, current data cannot exclude the failure of the NSP.

CD21-positive follicular dendritic cells: A possible source of PrPSc in lymph node macrophages of scrapie-infected sheep

Natural sheep scrapie is a prion disease characterized by the accumulation of PrP(Sc) in brain and lymphoid tissues. Previous studies suggested that lymph node macrophages and follicular dendritic cells (FDC) accumulate PrP(Sc). In this study, lymph nodes were analyzed for the presence of PrP(Sc) and macrophage or FDC markers using dual immunohistochemistry. A monoclonal antibody (mAb) to the C-terminus of PrP reacted with CD172a+ macrophages and CD21+ FDC processes in secondary follicles. However, a PrP N-terminus-specific mAb reacted with CD21+ FDC processes but not CD172a+ macrophages in secondary follicles. Neither the PrP N-terminus nor C-terminus-specific mAb reacted with CD172a+ macrophages in the medulla. These results indicate that lymph node follicular macrophages acquire PrP(Sc) by phagocytosis of CD21+ FDC processes. The results also suggest that follicular macrophages have proteases that process full-length PrP(Sc) to N-terminally truncated PrP(Sc).

PrP(Sc) accumulation in placentas of ewes exposed to natural scrapie: influence of foetal PrP genotype and effect on ewe-to-lamb transmission

Placentas from scrapie-affected ewes are known to be infectious. Nevertheless, placenta infectivity in such ewes is not systematic. Maternal transmission to lambs is highly suspected but contamination of the foetus in utero has not been demonstrated. Using ewes from a naturally scrapie-infected flock, it was demonstrated that abnormal prion protein (PrP(Sc)) accumulation in the placenta (i) is controlled by polymorphisms at codons 136, 154 and 171 of the foetal PrP gene and (ii) is restricted mainly to placentome foetal trophoblastic cells. In order to go deeper into the role of the placenta in scrapie transmission, the pattern of PrP(Sc) dissemination was established in susceptible lambs (genotype VRQ/VRQ) sampled from 140 days post-insemination to the age of 4 months from either VRQ/VRQ ewes with PrP(Sc)-positive placentas or ARR/VRQ ewes with PrP(Sc)-negative placentas. In both VRQ/VRQ lamb groups, PrP(Sc) spatial and temporal accumulation patterns were similar, suggesting post-natal rather than in utero contamination.

Active surveillance for scrapie by third eyelid biopsy and genetic susceptibility testing of flocks of sheep in Wyoming

Control of scrapie, an ovine transmissible spongiform encephalopathy or prion disorder, has been hampered by the lack of conventional antemortem diagnostic tests. Currently, scrapie is diagnosed by postmortem examination of the brain and lymphoid tissues for PrP(Sc), the protein marker for this group of disorders. For live, asymptomatic sheep, diagnosis using tonsil or third-eyelid lymphoid tissue biopsy and PrP(Sc) assay has been described. To evaluate the feasibility and efficacy of third-eyelid testing for identification of infected flocks and individual infected sheep, 690 sheep from 22 flocks were sampled by third-eyelid lymphoid tissue biopsy and immunohistochemistry. Sheep were further evaluated for relative genetic susceptibility and potential contact exposure to scrapie. Third-eyelid testing yielded suitable samples for 80% of the sheep tested, with a mean of 18.1 lymphoid follicles (germinal centers) per histologic section. Three hundred eleven of the sheep were sampled through passive surveillance programs, in which only sheep with potential contact with an infected sheep at a lambing event were tested, regardless of their scrapie susceptibility genotype. In addition, 141 genetically susceptible sheep with no record of contact with an infected animal at a lambing event were sampled through a targeted active surveillance program. Ten PrP(Sc)-positive sheep were identified through the passive surveillance program, and an additional three PrP(Sc)-positive sheep, including two from flocks with no history of scrapie, were identified through the active surveillance program. All PrP(Sc)-positive sheep had the highly susceptible PrP genotype. Third-eyelid testing is a useful adjunct to flock monitoring programs, slaughter surveillance, and mandatory disease reporting in a comprehensive scrapie eradication and research program.

Pregnancy status and fetal prion genetics determine PrPSc accumulation in placentomes of scrapie-infected sheep

Ovine scrapie is a fatal neurodegenerative disorder that may be transmitted through exposure to infected uterine and placental tissues. Susceptibility to scrapie is primarily controlled by polymorphisms in the prion protein (PrP) gene. Scrapie in the U.S. Suffolk breed and in many breeds in Europe occurs in sheep homozygous for glutamine (171QQ), but rarely in sheep heterozygous for glutamine and arginine (171QR) or homozygous for arginine (171RR) at codon 171 of the PrP gene. This study demonstrated that accumulation of PrP(Sc) in uterine-placental epithelial cells in the placentome was determined by fetal PrP genotype and the pregnancy status of scrapie-infected ewes. PrP(Sc) was detected in 171QQ placentomes of infected ewes, but not in placentomes of infected ewes pregnant with 171QR conceptuses or in the non-pregnant uterus of infected ewes. The distribution of PrP(Sc) plaques in placentomes was temporally associated with stage of gestation. There was a tendency toward increased size and number of placentomal PrP(Sc) plaques from the endometrial stalk (maternal side) to chorionic plate (fetal side). These results indicate that accumulation of PrP(Sc) is eliminated or reduced to undetectable levels in reproductive and placental tissues if infected ewes are not pregnant or conceive conceptuses with a resistant PrP genotype.

Prion peptide 106-126 modulates the aggregation of cellular prion protein and induces the synthesis of potentially neurotoxic transmembrane PrP

In infectious and familial prion disorders, neurodegeneration is often seen without obvious deposits of the scrapie prion protein (PrP(Sc)), the principal cause of neuronal death in prion disorders. In such cases, neurotoxicity must be mediated by alternative pathways of cell death. One such pathway is through a transmembrane form of PrP. We have investigated the relationship between intracellular accumulation of prion protein aggregates and the consequent up-regulation of transmembrane prion protein in a cell model. Here, we report that exposure of neuroblastoma cells to the prion peptide 106-126 catalyzes the aggregation of cellular prion protein to a weakly proteinase K-resistant form and induces the synthesis of transmembrane prion protein, the proposed mediator of neurotoxicity in certain prion disorders. The N terminus of newly synthesized transmembrane prion protein is cleaved spontaneously on the cytosolic face of the endoplasmic reticulum, and the truncated C-terminal fragment accumulates on the cell surface. Our results suggest that neurotoxicity in prion disorders is mediated by a complex pathway involving transmembrane prion protein and not by deposits of aggregated and proteinase K-resistant PrP alone.

New in vivo and ex vivo models for the experimental study of sheep scrapie: development and perspectives

Sheep scrapie is a prototypical transmissible spongiform encephalopathy (TSE), and the most widespread of these diseases. Experimental study of TSE infectious agents from sheep and other species essentially depends on bioassays in rodents. Transmission of natural sheep scrapie to conventional mice commonly requires one or two years. In an effort to develop laboratory models in which investigations on the sheep TSE agent would be facilitated, we have established mice and cell lines that were genetically engineered to express ovine PrP protein and examined their susceptibility to the infection. A series of transgenic mice lines (tgOv) expressing the high susceptibility allele (VRQ) of the ovine PrP gene from different constructs was expanded. Following intracerebral inoculation with natural scrapie isolates, all animals developed typical TSE neurological signs and accumulated abnormal PrP in their brain. The survival time in the highest expressing tgOv lines ranged from 2 to 7 months, depending on the isolate. It was inversely related to the brain PrP content, and essentially unchanged on further passaging. Ovine PrP transgene expression thus enhanced scrapie disease transmission from sheep to mice. Such tgOv mice may bring new opportunities for analysing the natural variation of scrapie strains and measuring infectivity. As no relevant cell culture models for agents of naturally-occurring TSE exist, we have explored various strategies in order to obtain stable cell lines that would propagate the sheep agent ex vivo without prior adaptation to rodent. In one otherwise refractory rabbit epithelial cell line, a regulable expression of ovine PrP was achieved and found to enable an efficient replication of the scrapie agent in inoculated cultures. Cells derived from sheep embryos or from tgOv mice were also used in an attempt to establish permissive cell lines derived from the nervous system. Cells engineered to express PrP proteins of a specified sequence may thus represent a promising strategy to further explore, at the cellular level, various aspects of TSE diseases.