ApoE is a lipid transport protein with roles in transport of dietary lipids, regulation of plasma cholesterol, and protection from atherosclerosis. In humans, there are three variants of ApoE (ApoE2, ApoE3 and ApoE4) and one of these, ApoE4, has been linked to earlier onset of Alzheimer’s disease. The mechanisms underlying the increased risk of Alzheimer’s disease remain unclear but researchers at UT Southwestern Medical Center have now shown that the ApoE4 variant reduces surface expression of receptors involved in synaptic plasticity by sequestering the receptors inside the cell.

ApoE interacts with members of the LDL receptor family and one of the receptors for ApoE, Apoer2, also acts as a signalling receptor for reelin, a protein that is important in the developing brain but also enhances NMDA receptor activity and increases long-term potentiation (LTP) in the adult brain. ApoE4 was found to reduce surface expression of NMDA and AMPA receptors as well as Apoer2 receptors, thereby impairing glutamatergic neurotransmission. β-Amyloid peptide, a hallmark of Alzheimer’s disease, suppresses LTP and the ability of reelin to counter the effects of β-amyloid peptide was almost completely abolished in mice expressing human ApoE4. The team are now trying to understand whether it is possible to build on their findings to develop new treatments for Alzheimer’s disease.

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

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.

Multiple sclerosis (MS) is an autoimmune disorder in which T-cells attack and damage the fatty myelin sheaths around the axons of the brain and spinal cord, disrupting the conduction of electrical signals along the nerve fibres. Although both genetic factors and viral infections have been suggested to contribute to the development of MS, no single virus has been conclusively linked to the disease and other mechanisms could also play a role. Animal models induced by CD8⁺ T-cells show similarities to human MS, and researchers at the University of Washington investigating the causes of MS have engineered mice that over-express CD8⁺ T-cells that recognise myelin basic protein (MBP), a candidate autoantigen in MS.

When infected with vaccinia virus engineered to produce MBP, the infection should activate the CD8⁺ T-cells to attack virally infected cells and also other cells that produce MBP. As expected, mice infected with the engineered virus developed MS-like disease but, surprisingly, symptoms were also triggered by infection with wild-type virus. This suggested that the engineered CD8⁺ T cells expressed a second receptor that recognised wild-type virus and subsequent cross-breeding experiments confirmed that some of the CD8⁺ T cells did indeed have receptors for both MBP and wild-type virus. Once activated by the virus, the dual-receptor CD8⁺ T cells were than able to attack cells producing MBP.

The study suggests a role for dual-receptor cells in autoimmune diseases and could explain how infection with a common virus triggers MS in genetically predisposed people, whilst having no lasting effects in most of the population. In the ‘dual-receptor model’, autoimmune activation could be triggered by a chance event leading to T-cells that recognise both MBP and a viral antigen. The prevalence of dual-receptor T cells is presently unclear and the team plan to assess whether they are more common in MS patients.

The study is published in Nature Immunology.

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.

The cytoskeleton plays a key role in regulating many cellular functions; it maintains cell shape, protects the cell, enables cellular motion, and has important roles in proliferation and differentiation. Metastasising cancer cells exploit the cytoskeleton to produce protrusions that allow them to invade surrounding tissue and enter the blood system from where they can spread to distant tissues and seed new tumours.

The protrusions, known as pseudopodia, are highly specialised ‘feet’ that the cell uses to pull itself forward across the underlying surface. A team led by researchers at the University of California, San Diego has now identified a previously unknown kinase – termed pseudopodium-enriched atypical kinase one or PEAK1 – that regulates the cytoskeleton and plays a central role in the formation of pseudopodia. Preliminary studies in mice suggest that PEAK1 is important during tumour growth and the team also showed that PEAK1 levels are increased in primary and metastatic samples from human colon cancer patients. Whether PEAK1 is capable of transforming non-tumour cells into cancer cells has not yet been determined but the fact that PEAK1 has kinase activity suggests that it may be possible to design specific inhibitors which could help to elucidate its role in both normal and cancer cells. PEAK1, which is a 190-kDa non-receptor tyrosine kinase, could serve as a clinical biomarker that predicts whether a cancer is likely to metastasise and could also be a target for future cancer treatments.

The study is published in the Early Edition of the Proceedings of the National Academy of Sciences.

Although the recent sporadic outbreaks of influenza A virus H5N1 and of a new variant of H1N1 in 2009 were less serious than initially feared, public health responses gave an indication of the potential for pandemic influenza A to wreak havoc amongst human populations. Timely development of vaccines should help to contain future outbreaks, but effective antiviral medicines will also be needed. Circulating strains of influenza A virus with resistance to existing neuraminidase inhibitors have already been discovered, and new molecular targets would provide additional protection in the event of a fresh outbreak.

Researchers led by a team at the University of Hong Kong have now identified a compound, nucleozin, which can aggregate the viral nucleoprotein and prevent its transport into the nucleus. The nucleoprotein plays critical roles in viral RNA replication and genome assembly, and nucleozin was shown to block replication of H1N1, H3N2, and H5N1 viruses in cell culture experiments and also to protect mice from lethal challenge with highly pathogenic avian influenza virus A H5N1.

The study, which is published in Nature Biotechnology, shows that the nucleoprotein is a viable drug target and could lead to the development of new treatments to control the impact of future influenza A outbreaks. Potential binding sites for nucleozin on the influenza nucleoprotein were also predicted using molecular docking models.

The origins of acupuncture are lost in antiquity and, today, the effectiveness of such treatment remains controversial. Despite the sometimes extravagant claims of proponents, there is little scientific basis to explain how acupuncture works and many researchers believe that the effects are attributable to a placebo effect. In a study published in Nature Neuroscience, researchers led by a team at the University of Rochester Medical Center have now suggested a physiological mechanism that may explain the analgesic effects of acupuncture.

The team found that adenosine was released during acupuncture in mice and that the analgesic effect of acupuncture could be replicated by direct injection of an adenosine A1 receptor agonist, 2-chloro-N(6)-cyclopentyladenosine (CCPA). Adenosine, which is released in response to injury or inflammation, has known pain-relieving properties and acupuncture was found to be ineffective in A1 receptor knock-out mice. 2′-Deoxycoformycin (dCF), a potent inhibitor of adenosine deaminase, was found to boost the effects of acupuncture, increasing the accumulation of adenosine in tissue as well as the duration of analgesia.

It will be interesting to see whether similar effects are observed in human subjects and also whether adenosine is also released during ‘sham’ acupuncture treatment in which needles are pressed against the skin without puncturing it – lack of differentiation from sham treatment is one of the main reasons that detractors cite for the placebo effect of acupuncture.

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.

Programmed cell death (apoptosis) is essential to maintain homeostasis within living organisms and is controlled by a variety of intra- and extra-cellular signals. Activation of the death receptor CD95 (also known as Fas or Apo-1) by its physiological ligand, CD95 ligand (Fas ligand), leads to apoptosis in many tissues and is especially important in the immune system.

Resistance to apoptosis is also key to the survival of malignant cells but the role of CD95 in cancer progression is complex: although the down-regulation of CD95 that is frequently observed in tumour cells could contribute to their survival, complete loss of CD95 is rare in human cancers. On the other hand, many cancer cells express large quantities of CD95 and are highly sensitive to CD95-mediated apoptosis in vitro. Cancer patients often have high levels of CD95 ligand, suggesting that CD95 could perhaps promote the growth of tumours through non-apoptotic activities. Scientists from the University of Chicago and Northwestern University Feinberg School of Medicine have further investigated the role of CD95 in several human cancer cell lines and in mouse models of liver and ovarian cancer. Cancer cells – regardless of their sensitivity to CD95-mediated apotosis – were found to produce CD95 ligand and to depend on constitutive activity of CD95 for optimal growth. In the mouse models, deletion of CD95 reduced both the incidence and size of tumours. In further studies, the tumour promoting activity of CD95 was shown to be mediated by pathways involving JNK and Jun but not caspase-8.

The study, which is published in Nature, suggests that, paradoxically, reducing rather than enhancing activity of the death receptor CD95 may be an effective way to control the growth and proliferation of cancer cells. Further research is needed to understand the switch between signalling ‘die’ and ‘grow’, but eventually soluble CD95 or antibodies against CD95 ligand could find a role in the treatment of cancer.