Four separate types of Creutzfeldt-Jakob disease?

Researchers from the UK and France have identified four separate biochemical subgroups in a selection of cases of Creutzfeldt-Jakob disease. The study suggests that these subgroups could represent distinct prion strains in what is the most common human prion disease. Prion diseases are transmissible neurodegenerative disorders characterized by accumulation of an abnormal isoform (PrP^Sc) of a host-encoded protein (PrP^C) in affected tissues. According to the prion hypothesis, PrP^Sc alone constitutes the infectious agent. Sporadic Creutzfeldt-Jakob disease (sCJD) is the commonest human prion disease. Although considered as a spontaneous disorder, the clinicopathological phenotype of sCJD is variable and substantially influenced by the methionine/valine polymorphism at codon 129 of the prion protein gene (PRNP). Based on these clinicopathological and genetic criteria, a subclassification of sCJD has been proposed. Two new biochemical assays identified four distinct biochemical PrP^Sc subgroups in a cohort of 41 sCJD cases. These subgroups correlate with the current sCJD subclassification and could therefore represent distinct prion strains. Iatrogenic CJD (iCJD) occurs following presumed accidental human-to-human sCJD transmission. Our biochemical investigations on 12 iCJD cases from different countries found the same four subgroups as in sCJD. However, in contrast to the sCJD cases, no particular correlation between the PRNP codon 129 polymorphism and biochemical PrP^Sc phenotype could be established in iCJD cases. This study provides an alternative biochemical definition of PrP^Sc diversity in human prion diseases and new insights into the perception of agent variability.
Sporadic Creutzfeldt-Jakob disease (sCJD) cases are currently subclassified according to the methionine/valine polymorphism at codon 129 of the PRNP gene and the proteinase K (PK) digested abnormal prion protein (PrP^res) identified on Western blotting (type 1 or type 2). These biochemically distinct PrP^res types have been considered to represent potential distinct prion strains. However, since cases of CJD show co-occurrence of type 1 and type 2 PrP^res in the brain, the basis of this classification system and its relationship to agent strain are under discussion. The identification of four different PrP^Sc biochemical subgroups in sCJD and iatrogenic CJD (iCJD), irrespective of the PRNP polymorphism at codon 129 and the PrP^res isoform, provides an alternative biochemical definition of PrP^Sc diversity and new insight in the perception of Human TSE agents variability.

Beyond PrP^res Type 1/Type 2 Dichotomy in Creutzfeldt-Jakob Disease. PLoS Pathog 4(3): e1000029

Related:

• Drugs for treatment of prion infections
• Fears over new wave of vCJD deaths
• A General Model of Prion Strains and Their Pathogenicity
• Prions, Proteasomes, and Mad Cows

Drugs for treatment of prion infections

Prion diseases are fatal and at present there are neither cures nor therapies available to delay disease onset or progression in humans. Inspired in part by therapeutic approaches in the fields of Alzheimer’s disease and amyotrophic lateral sclerosis, researchers tested five different drugs which are known to efficiently pass through the blood-brain barrier in a mouse prion system. Groups of intracerebrally prion-challenged mice were treated with the drugs curcumin, dapsone, ibuprofen, memantine and minocycline. Treatment with antibiotics dapsone and minocycline had no therapeutic benefit. Ibuprofen-treated mice showed severe adverse effects, which prevented assessment of therapeutic efficacy. Mice treated with low- but not high-dose curcumin and mice treated with memantine survived infections significantly longer than untreated controls. These results encourage further research efforts to improve the therapeutic effect of these drugs.

Evaluation of drugs for treatment of prion infections of the central nervous system. 2008 J Gen Virol. 89: 594-597

Related:

• Fears over new wave of vCJD deaths
• A General Model of Prion Strains and Their Pathogenicity
• Prions, Proteasomes, and Mad Cows

Fears over new wave of vCJD deaths

Sensitivity to vCJD, the human form of mad cow disease (BSE) is determined by many factors. One of these is a genetic polymorphism at codon 129 of the human prion gene PrP. Individuals may have either a methionine (M) or valine (V) codon at this position. People who are heterozygous at this codon, that is, have different codons on each of the two alleles (copies) of the PrP gene in every cell, show resistance to sporadic CJD as well as to acquired prion diseases such as kuru and vCJD. The extent of the resistance is such that to date, all of the 162 known victims of vCJD have been homozygous at codon 129, and all have had two methionine codons (genotype 129MM).

Until now.

The first reported case of vCJD involving a victim who is homozygous for valine (129VV) at codon 129 has just been published. Why does that matter? It’s too early to say for sure, but this cases raises the possibility of a new wave of human vCJD cases with a longer incubation period in the 10% of the population with the 129VV phenotype, in addition to the previously at risk 30-40% of the population with the 129MM phenotype.

Related:

• Creutzfeldt-Jakob Disease, Prion Protein Gene Codon 129VV, and a Novel PrPSc Type in a Young British Woman
• Prion Disease Update

MicrobiologyBytes 2007: Year in Review

2007 has been a record breaking year for MicrobiologyBytes, so here’s a look back at some of the highlights:

We started January off with noroviruses and ancient plague, then relaxed a bit by playing with Lego and brewing beer.

In February, we looked at yaws and Mimivirus, then went green by reducing our carbon footprint with microdiesel.

And in March we marked World Tuberculosis Day by looking at new drugs for an old foe.

April started off with an exploration of whether viruses evolve to protect their hosts, then we took out first look at colony collapse disorder affecting bees.

May was dominated by news about extreme drug resistant tuberculosis (XDR-TB) and chikungunya, then later looked at probiotics.

In June we looked at the origins of yellow fever and quorum sensing in Serratia (quorum sensing remains one of the most popular topics on MicrobiologyBytes).

July began with flesh eating bacteria and finished up with prions and Alzheimers disease.

In August, most people took a holiday and this was the quietest month of the year in terms of visitors, but we still managed to fit in Hendra, chikungunya and Marburg viruses.

September brought lots of bad news for UK farmers, so we looked at the biology of the bluetongue and foot and mouth disease virus outbreaks in the UK.

In October we covered the bacterial SOS system and debated the strategy for HPV vaccination in the UK.

November started with the terrorist threat posed by glanders and melioidosis then considered the dangers of Chlamydia infection and the opportunities presented by DNA microarrays.

We finished up the year with bacteriocins and bacterial morphology.

Phew. Overall, the most popular posts of the year were:

1. Hepatitis C Virus: a mountain to climb
2. Fungal Infections and All About Fungi
3. Infectobesity
4. Toll-Like Receptors
5. DNA microarrays

See you next year!

A General Model of Prion Strains and Their Pathogenicity

Prions are lethal mammalian pathogens composed of aggregated conformational isomers of a host-encoded glycoprotein and which appear to lack nucleic acids. Their unique biology, allied with the public-health risks posed by prion zoonoses such as bovine spongiform encephalopathy, has focused much attention on the molecular basis of prion propagation and the “species barrier” that controls cross-species transmission. Both are intimately linked to understanding how multiple prion “strains” are encoded by a protein-only agent. The underlying mechanisms are clearly of much wider importance, and analogous protein-based inheritance mechanisms are recognized in yeast and fungi. Recent advances suggest that prions themselves are not directly neurotoxic, but rather their propagation involves production of toxic species, which may be uncoupled from infectivity.

A General Model of Prion Strains and Their Pathogenicity
Science 2007 318: 930-936

Related:

• Variant Creutzfeldt-Jacob disease (vCJD) update
• Prions, Proteasomes, and Mad Cows
• New forms of bovine spongiform encephalopathy
• Prions and Alzheimers disease

Variant Creutzfeldt-Jacob disease (vCJD) update

Definite and probable CJD cases in the UK as of 28 Sep 2007

Summary of vCJD cases:
Deaths from definite vCJD (confirmed): 114
Deaths from probable vCJD (without neuropathological confirmation): 47
Deaths from probable vCJD (neuropathological confirmation pending): 0
Number of deaths from definite or probable vCJD (as above): 161
Number of probable vCJD cases still alive: 5
Total number of definite or probable vCJD (dead and alive): 166

This data are consistent with the view that the vCJD outbreak n the UK is in decline. The peak number of deaths was 28 in the year 2000, followed by 20 in 2001, 17 in 2002, 18 in 2003, 9 in 2004, 5 in 2005, 5 in 2006, and so far 3 in 2007.The UK Department of Health will stop issuing monthly CJD press notices because the same data is published by the National CJD Surveillance Unit in Edinburgh.Related:

• The Origin of BSE
• Prions and Alzheimers disease
• New forms of bovine spongiform encephalopathy
• BSE in France

Prions, Proteasomes, and Mad Cows

All cells have the capacity to selectively degrade misfolded intracellular proteins, which, if they accumulated, could interfere with normal function and could be toxic. Such proteins may arise by mutation, errors in gene expression, failure to fold correctly, spontaneous denaturation, or postsynthetic damage (for example, by oxygen radicals). How often such events occur in cells is uncertain, largely because the ubiquitin–proteasome pathway rapidly degrades such aberrant proteins, including those that cause various inherited diseases, such as cystic fibrosis and certain hemoglobinopathies. This pathway also protects against neurodegenerative diseases. Direct evidence that the abnormal toxic proteins in these various diseases can inhibit the functioning of the proteasome pathway has been lacking. Recently, Kristiansen et al presented strong evidence that soluble aggregates of the toxic protein may cause prion disease by specifically inhibiting the function of the 26S proteasome. A major gap in our understanding has been how the conversion of PrPC to PrPSc eventually kills neurons. Kristiansen et al showed that neurons and neuroblastoma cells infected with prions have reduced proteasomal activity against model substrates. Loss of proteasomal function affects many critical cellular processes and can induce apoptosis.

On Prions, Proteasomes, and Mad Cows
NEJM 2007 357:1150-1152

Happy Birthday PLoS Pathogens

PLoS Pathogens is two years old, and to celebrate, they’ve just published a list of the top ten papers downloaded from September 2005 to July 2007, so if you need to catch up on your reading:

1. Carrageenan Is a Potent Inhibitor of Papillomavirus Infection
   Sexually transmitted human papillomavirus (HPV) infections are very common. Although most HPV infections don’t cause noticeable symptoms, persistent infection with some genital HPV types can lead to cervical cancer or other anal/genital cancers. Another subset of HPV types can cause genital warts. Recent studies have suggested that condoms are not highly effective in preventing HPV infection. Although HPV vaccines will soon become available, they probably will not protect against all genital HPV types and will be too expensive for use in the developing world. Inexpensive HPV-inhibitory compounds (known as topical microbicides) might be useful for blocking the spread of HPV. Using a newly developed cell culture–based HPV inhibition test, we have discovered that an inexpensive gelling agent called carrageenan is an unexpectedly potent HPV infection inhibitor. Carrageenan is also under investigation as a topical microbicide targeting HIV and herpes viruses, but it is a thousand times more effective against HPV in cell culture tests. Interestingly, carrageenan is used as a thickener in some commercially available sexual lubricants and lubricated condoms. Several of these commercial lubricant products are potent HPV inhibitors in our cell culture–infection system. Clinical trials are needed to determine the effectiveness of carrageenan as a topical microbicide against HPV.
2. Modulation of Tumor Necrosis Factor by Microbial Pathogens
   In response to invasion by microbial pathogens, host defense mechanisms get activated by both the innate and adaptive arms of the immune responses. TNF (tumor necrosis factor) is a potent proinflammatory cytokine expressed by activated macrophages and lymphocytes that induces diverse cellular responses that can vary from apoptosis to the expression of genes involved in both early inflammatory and acquired immune responses. A wide spectrum of microbes has acquired elegant mechanisms to overcome or deflect the host responses mediated by TNF. For example, modulatory proteins encoded by multiple families of viruses can block TNF and TNF-mediated responses at multiple levels, such as the inhibition of the TNF ligand or its receptors, or by modulating key transduction molecules of the TNF signaling pathway. Bacteria, on the other hand, tend to modify TNF-mediated responses specifically by regulating components of the TNF signaling pathway. Investigation of these diverse strategies employed by viral and bacterial pathogens has significantly advanced our understanding of both host TNF responses and microbial pathogenesis. This review summarizes the diverse microbial strategies to regulate TNF and how such insights into TNF modulation could benefit the treatment of inflammatory or autoimmune diseases.
3. Identification of a Novel Gammaretrovirus in Prostate Tumors of Patients Homozygous for R462Q RNASEL Variant
   Prostate cancer is the most frequent cancer and the second leading cause of cancer deaths in US men over the age of 50. Several genetic factors have been proposed as potential risk factors for the development of prostate cancer, including a viral defense gene called RNASEL. A common genetic variant in this gene, R462Q, was recently implicated in up to 13% of prostate cancer cases. Given the antiviral role of RNASEL, the authors sought to examine if a virus might be present in prostate cancers associated with the R462Q variant. Using a DNA microarray designed to detect all known viral families, the authors identified a novel virus, named XMRV, in a subset of prostate tumor samples. Polymerase chain reaction testing of 86 prostate tumors for the presence of XMRV revealed a strong association between the presence of the virus and being homozygous for the R462Q variant. Cloning and sequencing of the virus showed that XMRV is a close relative of several known xenotropic murine leukemia viruses. This report presents the first documented cases of human infection with a xenotropic retrovirus. Future work will address the potential connection between XMRV infection and the increased prostate cancer risk in patients with the R462Q RNASEL variant.
4. Human Neutrophils Kill Bacillus anthracis
   Bacillus anthracis is the bacterium that causes anthrax, a disease that can occur through natural infections and also through intentional release. B. anthracis makes spores, which are in a dormant state, similar to seeds of a plant, and are extremely resistant to the environment. B. anthracis spores can infect through the skin or the lung. Lung infections disseminate through the body and are lethal. In contrast, skin infections often remain localized, and patients survive even without treatment. It is not well understood why these bacteria cause a localized infection through the skin and a lethal disease through the lung. Little is known about how B. anthracis is controlled. Neutrophils are the first white blood cells recruited to a site of infection and are specialized in killing microbes. Previous studies show that neutrophils are abundant in the skin form, but not in the lung form of anthrax. The researchers report that human neutrophils can take up B. anthracis spores. Once inside, the spores germinate to form vegetative bacteria. The vegetative bacteria are extremely susceptible to neutrophil-killing mechanisms. The B. anthracis virulence factors (molecules that make bacteria cause diseases) manipulate other human cells but do not deter neutrophils. B. anthracis is indeed exquisitely sensitive to the neutrophil protein α-defensin. These data support a new model where B. anthracis skin, but not lung, infections are controlled by the antimicrobial activity of neutrophils.
5. A Novel Bacterium Associated with Lymphadenitis in a Patient with Chronic Granulomatous Disease
   As new bacteria continue to be discovered every year, it is inevitable that some of them will be found to cause human disease. The authors describe the isolation and characterization of a new bacterium, grown from a patient with chronic granulomatous disease (CGD). In this genetic disease, one of the main lines of defense against infection, the neutrophil, has a discrete defect in the generation of superoxide, leading to recurrent infections with a narrow spectrum of bacteria and fungi. This new organism was cultured from lymph nodes that had been inflamed for several months. To prove that this new bacterium was indeed a pathogen, Greenberg and colleagues measured specific antibody response in the patient: they inoculated CGD mice with this organism and reproduced the appearance of the human infection; they recovered the organism in pure growth from infected mouse spleens. This new bacterium belongs to the family Acetobacteraceae, bacteria that are found widely in the environment. They have a variety of industrial uses, such as the production of vinegar, but have never been reported to cause invasive human disease. Disease-causing organisms remain to be discovered. The researchers outline some of the steps that can be taken to verify the pathogenicity of novel organisms.
6. Gene-Specific Countermeasures against Ebola Virus Based on Antisense Phosphorodiamidate Morpholino Oligomers
   Ebola virus (EBOV) causes a highly lethal hemorrhagic fever that results in up to 50%–90% mortality in humans. There are currently no available vaccines or therapeutics to treat EBOV infection. To date, multiple pre- and post-exposure therapeutic strategies, primarily focused on bolstering the host immune response or inhibiting viral replication, have been undertaken with limited success. Here, Bavari and colleagues report the development of a successful therapeutic regimen for EBOV infection based on antisense phosphorodiamidate morpholino oligomers (PMOs). PMOs are a subclass of chemically modified antisense oligonucleotides that interfere with the translation of viral mRNA, thus inhibiting viral amplification. Using a cell-free translation system, a cell-based assay, and survival studies in rodents, we identified several efficacious EBOV-specific PMOs. Further, prophylactic administration of a combination of three EBOV-specific PMOs specifically targeting VP24, VP35, and the viral polymerase L protected rhesus macaques from lethal EBOV infection. This is the first successful antiviral intervention against filoviruses in nonhuman primates. These findings may serve as the basis for a new strategy to quickly develop virus-specific therapies in defense against known, emerging, and genetically engineered bioterrorism threats.
7. The Role of Innate Immune Responses in the Outcome of Interspecies Competition for Colonization of Mucosal Surfaces
   Bacterial infection commonly begins with organisms that colonize and proliferate on mucosal surfaces. These microenvironments may be occupied by multiple microbial species, suggesting that successful colonizers are distinguished by their capacity to prevail over their competitors. This study examines interactions between two bacterial species that both colonize and infect the human upper respiratory tract. In a mouse model, strains of both Haemophilus influenzae and Streptococcus pneumoniae efficiently colonize the nasal mucosa when tested individually. In contrast, following co-inoculation, H. influenzae rapidly and completely outcompetes S. pneumoniae. This competitive effect is dependent on the local responses from the host in the form of a specific type of white blood cell (neutrophil) that acts to engulf and kill microorganisms that have been labeled by proteins that bind to microbial surfaces (complement). The results of this study show that recognition of microbial products from one species may activate inflammatory responses that promote the clearance of another competing species. This study also demonstrates how manipulations such as antibiotics or vaccines, which are meant to diminish the presence of a single pathogen, may inadvertently alter the competitive interactions of complex microbial communities.
8. Prions Adhere to Soil Minerals and Remain Infectious
   Transmissible spongiform encephalopathies (TSEs) are a group of incurable diseases likely caused by a misfolded form of the prion protein (PrP^Sc). TSEs include scrapie in sheep, bovine spongiform encephalopathy (“mad cow” disease) in cattle, chronic wasting disease (CWD) in deer and elk, and Creutzfeldt-Jakob disease in humans. Scrapie and CWD are unique among TSEs because they can be transmitted between animals, and the disease agents appear to persist in environments previously inhabited by infected animals. Soil has been hypothesized to act as a reservoir of infectivity, because PrP^Sc likely enters soil environments through urinary or alimentary shedding and decomposition of infected animals. In this manuscript, the authors test the potential for soil to serve as a reservoir for PrP^Sc and TSE infectivity. They demonstrate that PrP^Sc binds to a variety of soil minerals and to whole soils. They also quantitate the levels of protein binding to three common soil minerals and show that the interaction of PrP^Sc with montmorillonite, a common clay mineral, is remarkably strong. PrP^Sc bound to Mte remained infectious to laboratory animals, suggesting that soil can serve as a reservoir of TSE infectivity.
9. The Expanding Universe of Prion Diseases
   Prions cause fatal and transmissible neurodegenerative disease. These etiological infectious agents are formed in greater part from a misfolded cell-surface protein called PrP^C. Several mammalian species are affected by the diseases, and in the case of “mad cow disease” (BSE) the agent has a tropism for humans, with negative consequences for agribusiness and public health. Unfortunately, the known universe of prion diseases is expanding. At least four novel prion diseases—including human diseases variant Creutzfeldt-Jakob disease (vCJD) and sporadic fatal insomnia (sFI), bovine amyloidotic spongiform encephalopathy (BASE), and Nor98 of sheep—have been identified in the last ten years, and chronic wasting disease (CWD) of North American deer (Odocoileus Specis) and Rocky Mountain elk (Cervus elaphus nelsoni) is undergoing a dramatic spread across North America. While amplification (BSE) and dissemination (CWD, commercial sourcing of cervids from the wild and movement of farmed elk) can be attributed to human activity, the origins of emergent prion diseases cannot always be laid at the door of humankind. Instead, the continued appearance of new outbreaks in the form of “sporadic” disease may be an inevitable outcome in a situation where the replicating pathogen is host-encoded.
10. Crossing the Line: Selection and Evolution of Virulence Traits
    The evolution of pathogens presents a paradox. Pathogenic species are often absolutely dependent on their host species for their propagation through evolutionary time, yet the pathogenic lifestyle requires that the host be damaged during this dependence. It is clear that pathogenic strategies are successful in evolutionary terms because a diverse array of pathogens exists in nature. Pathogens also evolve using a broad range of molecular mechanisms to acquire and modulate existing virulence traits in order to achieve this success. Detailing the benefit of enhanced selection derived through virulence and understanding the mechanisms through which virulence evolves are important to understanding the natural world and both have implications for human health.

Nice work. Open access publishing has come of age.

Shadoo Prion

Canadian scientists seem to have proved the existence of a second mammalian prion protein. The original cellular prion protein, PrP(C), is neuroprotective in a number of settings. Shadoo (Sho) is a protein found in normal mouse brains which has homology to the N-terminus of PrP. Prion-infected mice exhibit a dramatic reduction in endogenous Sho protein, indicating that there is a relationship between PrP(C) and Sho, and that Sho appears to protect brain cells from harm, so reduced levels in prion infections may exacerbate brain damage. Sho may prove useful in deciphering many unresolved aspects of prion biology.

The CNS glycoprotein Shadoo has PrP(C)-like protective properties and displays reduced levels in prion infections.
EMBO J. 2007 Aug 16

Related:

• Prions of fungi
• New forms of bovine spongiform encephalopathy
• Prions and Alzheimers disease
• The Origin of BSE

Prions of fungi

The term ‘prion’ means an infectious protein that does not need an accompanying nucleic acid. There are six known prions of fungi, including four self-propagating amyloids and two enzymes that are necessary to activate their inactive precursors:

• [URE3] is a prion of the nitrogen catabolism regulator Ure2p
• [PSI+] is a prion of the translation-termination factor Sup35p, which has a parallel beta-sheet structure.
• [PIN+] is a prion of Rnq1p (function unknown)
• [Het-s] is a prion of the heterokaryon incompatibility protein HETs; this prion of apparently benefits its host (Podospora anserina), whereas the [URE3] and [PSI+] prions of Saccharomyces cerevisiae are detrimental.
• [β] is a prion of vacuolar protease B
• [C] is a prion of a mitogen-activated protein kinase kinase kinase

This review explores the scope of the prion phenomenon, the biological and evolutionary roles of prions, the structural basis of the amyloid prions and the prominent role of chaperones (proteins that affect the folding of other proteins) and other cellular components in prion generation and propagation. Chaperones catalyse amyloid filament breakage to form new seeds, and probably have other roles in prion propagation and generation as well. Different prion variants, with the same protein sequence, have different amyloid structures. Variants can determine host range and chaperone effects.

Prions of fungi: inherited structures and biological roles. 2007 Nature Reviews Microbiology 5: 611-618

Related:

• Prions and Alzheimers disease
• Candidate prion disease vaccine
• The Origin of BSE