Nickel allergy is one of the most common causes of allergic contact dermatitis and a team led by researchers at the University of Giessen have now shown that the response is linked to activation of a single receptor, toll-like receptor 4 (TLR4).

The family of toll-like receptors normally recognizes structurally similar molecules derived from microbial pathogens and plays a key role in host defense. The team showed that nickel directly activated human, but not mouse, TLR4 and studies with mutant proteins showed that non-conserved histidine residues at positions 456 and 458 were necessary for activation of human TLR4. Wild type mice do not show an allergy to nickel but transgenic mice expressing human, rather than mouse, TLR4 could be efficiently sensitized to the metal. This is the first time that an inorganic substance has been shown to activate this innate immune pathway and, since histidines 456 and 458 are not essential for responses to microbial lipopolysaccharide, the authors suggest that site-specific inhibition of TLR4 could provide a potential strategy for treatment of nickel allergy, which would not compromise normal immune responses. Nickel allergy affects millions of people and is often associated with earrings and jewellery for other body piercings.

The study is published in the journal Nature Immunology.

Huntington’s disease is an inherited neurodegenerative disorder associated with mutations in the huntingtin gene on human chromosome 4. Although the functions of normal huntingtin protein are not entirely clear, it is known that abnormal huntingtin (mutantHtt, or mHtt) – and especially small proteolytic fragments of the protein – are toxic to neurons, particularly those in the striatum and cortex. Previous studies into the cleavage of huntingtin have focussed on the role of the cysteine protease families of caspases and calpains, but scientists at the Buck Institute for Age Research have now discovered that a metalloprotease also cleaves huntingtin into highly toxic fragments.

The team used a set of small interfering RNA (siRNA) pools targeting the 514 known and predicted human protease genes to identify those proteases involved in the cleavage of huntingtin. Eleven proteases were found to alter huntingtin fragment accumulation, and knockdown of the nine which are expressed in striatal cells significantly reduced huntingtin-mediated striatal cell death in a cellular toxicity screen. Amongst the proteases associated with huntingtin cleavage were three metalloproteases, MMP-10, MMP-14 and MMP-23B. Subsequent experiments showed that only MMP-10 directly cleaves huntingtin, suggesting that knockdown of MMP-10 reduces toxicity by directly altering proteolysis of huntingtin whereas knockdown of MMP-14 or MMP-23B modulates toxicity indirectly through proteolysis of cytokines or components of the extracellular matrix. Whilst matrix metalloproteases are generally thought to be secreted as proenzymes which are processed to the active forms extracellularly, MMP-10 was found to be activated inside the cell and to co-localise with huntingtin, suggesting that cleavage may occur intracellularly.

The study, which is published in the journal Neuron, suggests a role for matrix metalloproteases in the progression of Huntington’s disease and that development of inhibitors of MMP-10 may be a useful therapeutic strategy.

Alopecia areata is a type of hair loss that typically begins with one or more small bald patches on the scalp, beard area or elsewhere. The patches appear quite quickly and the hair may re-grow after a few months – or the condition may persist for several years with recurrences of patchy baldness and hair re-growth. The condition can also result in total loss of scalp hair (alopecia totalis) and, in a small number of cases, total loss of all body hair (alopecia universalis).

Alopecia areata is thought to be an autoimmune disease in which the immune system attacks the hair follicle, although the follicle is not destroyed since hair can re-grow. There also appears to be a hereditary component to the disease and a team lead by investigators at Columbia University Medical Center has now identified eight regions in the genome that are linked to the condition. The associated regions include some that have been linked to other autoimmune diseases including type I diabetes, rheumatoid arthritis, systemic lupus erythematosus, celiac disease, and systemic sclerosis. Of particular interest for its potential role in the onset of disease is the ULBP (cytomegalovirus UL16-binding protein) gene cluster that has not previously been associated with autoimmune disease. Expression of ULBP3 proteins, which act as activating ligands for the NKG2D receptor on natural killer cells, is markedly upregulated in hair follicles affected by alopecia areata.

The study is published in the journal Nature.

Since drugs that target some of the pathways involved in alopecia areata have already been developed to treat other autoimmune diseases, the researchers hope that their discovery will lead quickly to treatments for hair loss caused by alopecia areata. The team are also developing a genetic test that should be able to help predict the likely course of the disease in a particular individual.

Regular use of NSAIDS has been linked to reduced incidence of certain types of cancer but the underlying protective mechanisms are unclear. Some of the anticancer effects are believed to be mediated through inhibition of COX-2, but a study led by investigators at Sanford-Burnham Medical Research Institute has now identified another mechanism by which the sulindac sulfide (the NSAID metabolite of sulindac) inhibits tumour growth. The team found that sulindac sulfide induces apoptosis by binding to retinoid X receptor-α (RXRα), a member of the nuclear hormone receptor family which had been already been identified as a potential target for cancer therapy. In cancer cells, levels of RXRα are often reduced, at least in part because of proteolytic processing to a truncated form, tRXRα. As with other nuclear receptors, RXRα regulates transcription of target genes by binding to DNA response elements but accumulating evidence suggests that RXRα may also have extranuclear activity. Both RXRα and tRXRα can exist in the cytoplasm and the study showed that cytoplasmic tRXRα can activate the PI3K/AKT survival pathway by interaction with the p85a subunit of PI3K, leading to anchorage-independent cell growth in vitro, and tumour growth in animals. Sulindac sulfide was found to inhibit the tRXRα-mediated PI3K/AKT activation, suggesting that the compound could provide a useful lead for anti-cancer drugs targeting this pathway.

The use of NSAIDs to reduce the incidence of cancer has been limited by the risk of major cardiovascular events and the Sanford-Burnham have identified an analogue of sulindac sulfide, K-80003 which has improved affinity for RXRα but lacks significant COX-2 inhibitory activity. K-80003 inhibited the growth of cancer cells in vitro and in animals and would be expected to have reduced COX-2-associated side effects.

The study is published in the journal Cancer Cell.

New research has shown that compounds that affect cellular energy status could also be used to treat hepatitis C virus (HCV) infections. Metformin, which is used to treat type II diabetes, and 5-amino-1-β-D-ribofuranosyl-1H-imidazole-4-carboxamide (AICAR), which has been shown to mimic the beneficial effects of exercise in mice, stimulate AMP-activated protein kinase (AMPK). AMPK is a key sensor of cellular energy status and regulates both lipid and glucose metabolism to maintain cellular energy balance and protect against metabolic stress. An increase in the AMP/ATP ratio initiates an AMPK-mediated switch from activities that consume ATP, such as lipid production, to activities that produce ATP, such as lipid and glucose oxidation.

Infection with viruses might be expected to activate AMPK because of the energy demands put on the cell by viral replication, but research led by scientists at the University of Leeds has shown instead that HCV switches off AMPK so that the cell continues to produce the lipids needed to provide new viral particles with a protective outer coat. When the team treated HCV-infected cells with metformin or AICAR, AMPK activity was restored and viral replication was inhibited.

The team plan to carry out a small scale clinical trial to investigate the effects of AMPK activators in HCV infection and hope that such drugs may provide much-needed new treatments for HCV.

The study is published in the Proceedings of the National Academy of Science.

Cholesterol is essential for all animal life but high levels of cholesterol – when associated with low density lipoprotein (LDL) – are linked to an increased risk of atherosclerosis, heart disease and stroke. Circulating cholesterol can also be transported by high density lipoprotein (HDL); HDL is believed to be able to remove cholesterol from atheroma within arteries and cholesterol associated with HDL is considered to be beneficial for cardiovascular health. Cholesterol levels are determined by dietary intake, de novo synthesis and secretion by the liver: cholesterol absorption blockers and HMG-CoA reductase inhibitors (statins), which block cholesterol synthesis, are used clinically to reduce cholesterol levels.

A study led by researchers at the University of Cincinnati has now identified a new potential target for the control of cholesterol. The study, carried out in mice, found that circulation of cholesterol is regulated in the brain by the ‘hunger hormone’, ghrelin, which inhibits the melanocortin 4 receptor (MC4R) in the hypothalamus and is important for the regulation of food intake and energy expenditure. Increased levels of ghrelin were associated with increased levels of circulating HDL cholesterol, which the authors attribute to a reduction in the uptake of cholesterol by the liver. Genetically deleting or chemically blocking MCR4 in the CNS also led to increased levels of HDL cholesterol, suggesting that MCR4 is key to central control of cholesterol.

More studies are need to determine whether the effects observed in mice can be applied to humans but the finding that a neural circuit may be directly involved in the control of cholesterol metabolism by the liver could provide a target for new treatments to control cholesterol.

The study is published in the journal Nature Neuroscience.

Apicomplexan parasites such as Toxoplasma gondii and Plasmodium species can cause serious diseases in humans and domestic animals. Because the parasites are eukaryotes and share many metabolic pathways with their hosts, it has proved difficult to develop safe and effective treatments but researchers at Washington University School of Medicine in St. Louis have now identified an essential kinase in T. gondii which is unlike human kinases and more closely resembles those found in plants. In a study published in Nature, the team used conditional suppression to show that T. gondii calcium-dependent protein kinase 1 (TgCDPK1) is essential for survival of the parasite. The enzyme controls the ability of T. gondii parasites to secrete microneme proteins which allow the parasites to control their movement and move in and out of host cells.

It should be possible to exploit the differences between the parasite kinase and human kinases to develop potent and selective inhibitors of the parasite enzyme and the team have already identified compounds that block CDPK1 signalling without affecting human cells. Pyrazolopyrimidine-derived compounds such as 3-MB-PPI were found to specifically inhibit TgCDPK1 and disrupt the parasite’s life cycle at stages dependent on microneme secretion. The disruption was dependent on TgCDPK1 inhibition since parasites expressing a mutant kinase not sensitive to the inhibitors.

Calcium-dependent protein kinases have a kinase domain similar to that of calmodulin-dependent kinase, regulated by a calcium-binding domain in the C terminus. X-ray structures of TgCDPK1, published in Nature Structural and Molecular Biology, showed that, in the auto-inhibited (apo) form, the C-terminal activation domain resembles a calmodulin protein with an unexpected long helix in the N terminus that inhibits the kinase domain in the same manner as calmodulin-dependent kinase II. Calcium binding triggers reorganization of the C-terminal activation domain into a highly intricate fold, leading to its relocation around the base of the kinase domain to a site remote from the substrate binding site. This large conformational change constitutes a distinct mechanism in calcium signal-transduction pathways.

CDPK1 may play a similar role in Plasmodium species which cause malaria, but the researchers predict that it may be harder to selectively inhibit the Plasmodium enzymes.

The eukaryotic translation initiation factor eIF5A, which exists in two isoforms, was originally thought to be involved in formation of the first peptide bond during mRNA translation, but more recent work has implicated it as a translation elongation factor. In mammalian cells it has variously been associated with mediation of proliferation, apoptosis and inflammatory responses, although its mechanisms of action have remained vague. It has also been identified as a cofactor of the Rev trans-activator protein of HIV-1. eIF5A is unique in that it is the only known protein to contain the amino acid hypusine, formed posttranslationally via the sequential action of deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) acting at a specific lysine residue.

Based on the role of eIF5A in inflammation, a multi-institutional research team led by scientists at Indiana University School of Medicine has explored involvement of the protein in pancreatic islet dysfunction during the development of diabetes. In a low-dose streptozotocin mouse model of diabetes the team found that depletion of eIF5A (using siRNA) protected the mice from pancreatic β-cell loss and hyperglycemia. The depletion of eIF5A resulted in impaired translation of inducible nitric oxide synthase (iNOS)-encoding mRNA within islet cells. Further studies using an inhibitor of DHS, N¹-guanyl-1,7-diaminoheptane (GC7), demonstrated a requirement for hypusination in the action of eIF5A.

The study, published in the Journal of Clinical Investigation, demonstrates a role for eIF5A in inflammation-induced damage to islet cells. Since the negative effects of eIF5A depend on hypusination, DHS may represent a viable therapeutic target for diabetes. Further work will be necessary to establish the role of this pathway in development and progression of the human disease.

Mucormycosis is a potentially fatal infection of the sinuses, brain, or lungs, which is most commonly caused by the fungus Rhizopus oryzae. Even if the disease is successfully treated with antifungal agents together with surgery to remove necrotic tissue, survivors are typically left with considerable disfigurement. The condition is seen most often in people with diabetic ketoacidosis (DKA) who have elevated serum glucose and iron levels and a team of researchers at the University of California Los Angeles has now discovered why these individuals are more susceptible to infection. In mucormycosis, fungal invasion of blood vessels results in the formation of blood clots and destruction of local tissue and the team set out to identify the endothelial cell receptor that the fungus uses, and also whether iron and glucose play a role in regulating the expression of the receptor.

In human endothelial cells, glucose-regulated protein 78 (GRP78) was found to play a key role in endocytosis of R. oryzae and subsequent damage; enhanced expression of the protein in the presence of high concentrations of glucose, especially when iron levels are also elevated, offers an explanation of the increased susceptibility of individuals with DKA to mucormycosis. Mice with DKA, which have elevated levels of glucose and available iron, and which are also susceptible to mucormycosis, showed increased expression of GRP78 in sinus, lungs, and brain compared with normal mice. In further studies, treatment of DKA mice with GRP78-specific immune serum was shown to protect them from mucormycosis.

The study, which is published in the Journal of Clinical investigation, provides a new understanding of the pathogenesis of R. oryzae and may lead to new treatments for potentially lethal mucormycosis.

Emotionally resilient people adapt to adversity and bounce back after stressful events; less resilient individuals find it difficult to cope with setbacks and may decline into depression or post-traumatic stress disorder (PTSD). Mice, like humans, vary widely in their reaction to stressful situations and a study led by researchers at Mount Sinai School of Medicine which was funded by the National Institute of Health’s National Institute of Mental Health (NIMH) has now uncovered a mechanism that helps to explain differences in resilience.

Mice experience stress when confronted by an aggressive, larger mouse and about two thirds of animals that repeatedly undergo this ‘social defeat’ have altered behaviours including long-lasting social avoidance and anxiety-like symptoms. The other third of the ‘defeated’ mice showed relatively few behavioural effects and these resilient animals were found to have higher levels of the transcription factor ΔFosB in the nucleus accumbens, an important brain reward-associated region or “pleasure centre”. Social behaviour in ‘defeated’ mice can be normalised by chronic antidepressant treatment and the action of fluoxetine was found to require induction of ΔFosB in the nucleus accumbens. Post-mortem examination shows that ΔFosB is also depleted in the brains of people who suffered from depression, suggesting that induction of this protein is a positive adaptation that provides resilience to stress.

ΔFosB is also known to be involved in regulating responses to both drugs of abuse and natural rewards such as food, sex and exercise, although the cell populations involved in these responses differ somewhat from those involved in protection from stress. The team suggest that concentrations of ΔFosB in the nucleus accumbens are important in setting the level of an individual’s reward-seeking motivation and that reduced concentrations of the protein are linked to the impaired motivation and ability to experience pleasure seen in many people with depression. The team now hope to discover small molecules that will augment the actions of ΔFosB and lead to resilience-boosting treatments for depression.

The study is published in the journal Nature Neuroscience.