By tracking brain activity when an animal stops to look around its environment, neuroscientists at the Johns Hopkins University believe they can mark the birth of a memory.
Using lab rats on a circular track, James Knierim, professor of neuroscience in the Zanvyl Krieger Mind/Brain Institute at Johns Hopkins, and a team of brain scientists noticed that the rats frequently paused to inspect their environment with head movements as they ran. The scientists found that this behavior activated a place cell in their brain, which helps the animal construct a cognitive map, a pattern of activity in the brain that reflects the animal’s internal representation of its environment.
In a paper recently published in the journal Nature Neuroscience, the researchers state that when the rodents passed that same area of the track seconds later, place cells fired again, a neural acknowledgement that the moment has imprinted itself in the brain’s cognitive map in the hippocampus.
The hippocampus is the brain’s warehouse for long- and short-term processing of episodic memories, such as memories of a specific experience like a trip to Maine or a recent dinner. What no one knew was what happens in the hippocampus the moment an experience imprints itself as a memory.
“This is like seeing the brain form memory traces in real time,” said Knierim, senior author of the research. “Seeing for the first time the brain creating a spatial firing field tied to a specific behavioral experience suggests that the map can be updated rapidly and robustly to lay down a memory of that experience.”
A place cell is a type of neuron within the hippocampus that becomes active when an animal or human enters a particular place in its environment. The activation of the cells helps create a spatial framework much like a map, that allows humans and animals to know where they are in any given location. Place cells can also act like neural flags that “mark” an experience on the map, like a pin that you drop on Google maps to mark the location of a restaurant.
“We believe that the spatial coordinates of the map are delivered to the hippocampus by one brain pathway, and the information about the things that populate the map, like the restaurant, are delivered by a separate pathway,” Knierim said. “When you experience a new item in the environment, the hippocampus combines these inputs to create a new spatial marker of that experience.”
In the experiments, researchers placed tiny wires in the brains of the rats to monitor when and where brain activity increased as they moved along the track in search of chocolate rewards. About every seven seconds, the rats stopped moving forward and turned their heads to the perimeter of the room as they investigated the different landmarks, behavior called “head-scanning.”
“We found that many cells that were previously silent would suddenly start firing during a specific head-scanning event,” Knierim said. “On the very next lap around the track, many of these cells had a brand new place field at that exact same location and this place field remained usually for the rest of the laps. We believe that this new place field marks the site of the head scan and allows the brain to form a memory of what it was that the rat experienced during the head scan.”
Knierim said the formation and stability of place fields and the newly activated place cells requires further study. The research is primarily intended to understand how memories are formed and retrieved under normal circumstances, but it could be applicable to learning more about people with brain trauma or hippocampal damage due to aging or Alzheimer’s.
“There are strong indications that humans and rats share the same spatial mapping functions of the hippocampus, and that these maps are intimately related to how we organize and store our memories of prior life events,” Knierim said. “Since the hippocampus and surrounding brain areas are the first parts of the brain affected in Alzheimer’s, we think that these studies may lend some insight into the severe memory loss that characterizes the early stages of this disease.”
Johns Hopkins researchers identify set of genes that can be turned back on and potentially allow for more effective treatment
Johns Hopkins researchers say they have identified a set of genes that appear to predict which tumors can evade detection by the body’s immune system, a step that may enable them to eventually target only the patients most likely to respond best to a new class of treatment.
Immune therapy for ovarian, breast and colorectal cancer — treatments that encourage the immune system to attack cancer cells as the foreign invaders they are — has so far had limited success, primarily because the immune system often can’t destroy the cancer cells. In a report published online Feb. 16 in the journal Oncotarget, the Johns Hopkins team says it has identified genes that have been repressed through so-called epigenetic changes — modifications that alter the way genes function without changing their DNA sequence — which help the cells to evade the immune system. The researchers were able to reverse these epigenetic changes with the use of an FDA-approved drug, forcing the cancer cells out of hiding and potentially making them better targets for the same immune therapy that in the past may have failed.
“Chemotherapy often works, but in most cases, it eventually stops working,” says one of the study leaders, Nita Ahuja, M.D., an associate professor of surgery, oncology and urology at the Johns Hopkins University School of Medicine. “What if we could get the immune system itself to fight the tumors and keep the cancer in check forever? That is the ultimate goal, and this gene panel may get us closer.” The other study leader is Cynthia Zahnow, Ph.D., an associate professor of oncology at Johns Hopkins.
The researchers treated 63 cancer cell lines (26 breast, 14 colorectal and 23 ovarian) with low-dose 5-azacitidine (AZA), an FDA-approved drug for myelodysplastic syndrome, that reverses epigenetic changes by stripping off the methyl group that silences the gene. They identified a panel of 80 biological pathways commonly increased in expression by AZA in all three cancers, finding that 16 of them (20 percent) are related to the immune system. These pathways appeared to be dialed down in the cancer cells, allowing for evasion. After treatment with AZA, the epigenetic changes were reversed, rendering the cancer cells unable to evade the immune system any longer.
The researchers found that these immune system pathways were suppressed in a large number of primary tumors — roughly 50 percent of ovarian cancers studied, 40 percent of colorectal cancers and 30 percent of breast cancers. The findings may be applicable to other cancer types such as lung cancer or melanoma, they say.
After looking in cell lines, the Johns Hopkins team extended their work to human tumor samples. Again they found evidence that these immune system pathways are turned down in some patients and, that these immune genes can be turned back up in a small number of patients with breast and colorectal cancer who had been treated with epigenetic therapies.
“Most of us haven’t thought of these common cancers as being immune-driven,” Ahuja says. “We haven’t held out much hope for immune therapy to work in them because before you can enter cancer cells to knock them down, you have to be able to get inside. They were locked and now we may have identified a key.”
The hope is that clinicians could eventually pinpoint which patients with these common cancers would benefit from a dose of AZA followed by an immune therapy that stimulates the immune system to attack cancer cells.
“This would tell us which patients’ tumors are hiding from the immune system and will allow us to use all of our tools to flush that cancer out,” she says.
While most of the work was done in the lab, Ahuja says her colleagues have already started to put the panel into use in a lung cancer trial. Six patients were treated first with epigenetic therapy followed by immune therapy. Though the sample is small and time has been short, four of the patients have had their cancer suppressed for many months.
“If this works — and we don’t know yet if it will — this could have the potential to control someone’s cancer for good,” she says.
A way of using nanoparticles to investigate the mechanisms underlying ‘mystery’ cases of infertility has been developed by scientists at Oxford University.
The technique, published in Nanomedicine: Nanotechnology, Biology and Medicine, could eventually help researchers to discover the causes behind cases of unexplained infertility and develop treatments for affected couples. The method involves loading porous silica nanoparticle ‘envelopes’ with compounds to identify, diagnose or treat the causes of infertility.
The researchers demonstrated that the nanoparticles could be attached to boar sperm with no detrimental effects on their function.
‘An attractive feature of nanoparticles is that they are like an empty envelope that can be loaded with a variety of compounds and inserted into cells,’ says Dr Natalia Barkalina, lead author of the study from the Nuffield Department of Obstetrics and Gynaecology at Oxford University. ‘The nanoparticles we use don’t appear to interfere with the sperm, making them a perfect delivery vessel.
‘We will start with compounds to investigate the biology of infertility, and within a few years may be able to explain or even diagnose rare cases in patients. In future we could even deliver treatments in a similar way.’
Sperm are difficult to study due to their small size, unusual shape and short lifetime outside of the body. Yet this is a vital part of infertility research, as senior author Dr Kevin Coward explains: ‘To discover the causes of infertility, we need to investigate sperm to see where the problems start. Previous methods involved complicated procedures in animals and introduced months of delays before the sperm could be used.
‘Now, we can simply expose sperm to nanoparticles in a petri dish. It’s so simple that it can all be done quickly enough for the sperm to survive perfectly unharmed.’
The team, based at the Institute of Reproductive Sciences, used boar sperm because of its similarities to human sperm, as study co-author Celine Jones explains: ‘It is similar in size, shape and activity. Now that we have proven the system in boar sperm, we hope to replicate our findings in human sperm and eventually see if we can use them to deliver compounds to eggs as well.’
The research was an interdisciplinary effort, involving reproductive biologists from the Nuffield Department of Obstetrics & Gynaecology and nanoscientists from the Department of Engineering Science led by Dr Helen Townley.
The study was funded by the Nuffield Department of Obstetrics & Gynaecology at Oxford University and the Engineering and Physical Sciences Research Council (EPSRC). This technique is the subject of patent applications held by Isis Innovation, Oxford University’s technology transfer arm.
You might not think to look to a urine test to diagnose an eye disease.
But a new Duke University study says it can link what is in a patient’s urine to gene mutations that cause retinitis pigmentosa, or RP, an inherited, degenerative disease that results in severe vision impairment and often blindness. The findings appear online in the Journal of Lipid Research.
“My collaborators, Dr. Rong Wen and Dr. Byron Lam at the Bascom Palmer Eye Institute in Florida first sought my expertise in mass spectrometry to analyze cells cultured from a family in which three out of the four siblings suffer from RP,” said Ziqiang Guan, an associate research professor of biochemistry in the Duke University Medical School and a contributing author of the study.
Guan’s collaborators had previously sequenced the genome of this family and found that the children with RP carry two copies of a mutation at the dehydrodolichol diphosphate synthase (DHDDS) gene, which makes the enzyme that synthesizes organic compounds called dolichols. In humans, dolichol-19, containing 19 isoprene units, is the most abundant species.
The DHDDS mutation, which was found in 2011, is the latest addition to more than 60 gene mutations that have been implicated in RP. This mutation appears to be prevalent in RP patients of the Ashkenazi Jewish origin, and 1 in 322 Ashkenazi carries one copy of the mutation.
“I knew from my previous experience in analyzing urine samples from liver disease patients that I can readily detect dolichols by liquid chromatography and mass spectrometry,” Guan said. Using these techniques, he analyzed urine and blood samples from the six family members and found that instead of dolichol-19, the profiles from the three siblings with RP showed dolichol-18 as the dominant species. The parents, who each carry one copy of the mutated DHDDS gene, showed intermediate levels of dolichol-19 and higher levels of dolichol-18 than their healthy child. Guan believes dolichol profiling could effectively distinguish RP caused by DHDDS mutation from that caused by other mutations.
Guan and his collaborators hope to develop the dolichol profiling method as a first-line diagnostic test to identify RP patients with abnormal dolichol metabolism. They think this mass spectrometry-based detection method will help physicians provide more personalized care to RP patients, especially to young children whose retinal degeneration has not fully developed.
“Since the urine samples gave us more distinct profiles than the blood samples, we think that urine is a better clinical material for dolichol profiling,” he said. Urine collection is also easier than a blood draw and the samples can be conveniently stored with a preservative. The team is now pursuing a patent for this newl diagnostic test for the DHDDS mutation.
There are currently no treatments for RP, but Guan hopes his research will shed light on potential drug design strategies for treating RP caused by DHDDS mutation. “We are now researching ways to manipulate the dolichol synthesis pathway in RP patients with the DHDDS mutation so that the mutated enzyme can still produce enough dolichol-19, which we believe may be important for the rapid renewal of retinal tissue in a healthy individual.”
Researchers discover that an important clue to diagnosing Parkinson’s disease may lie just beneath the skin.
Although Parkinson’s disease is the second most prevalent neurodegenerative disorder in the U.S., there are no standard clinical tests available to identify this widespread condition. As a result, Parkinson’s disease often goes unrecognized until late in its progression, when the brain’s affected neurons have already been destroyed and telltale motor symptoms such as tremor and rigidity have already appeared.
Now researchers from Beth Israel Deaconess Medical Center (BIDMC) have discovered that an important clue to diagnosing Parkinson’s may lie just beneath the skin.
In a study scheduled to appear in the October 29 print issue of the journal Neurology and currently published on-line, the investigators report that elevated levels of a protein called alpha-synuclein can be detected in the skin of Parkinson’s patients, findings that offer a possible biomarker to enable clinicians to identify and diagnose PD before the disease has reached an advanced stage.
Parkinson’s disease affects more than 1 million individuals throughout the U.S. Diagnosis is currently made through neurological history and examination, often by a patient’s primary care physician.
“Even the experts are wrong in diagnosing Parkinson’s disease a large percentage of the time,” says senior author Roy Freeman, MD, Director of the Autonomic and Peripheral Nerve Laboratory at BIDMC and Professor of Neurology at Harvard Medical School. “A reliable biomarker could help doctors in more accurately diagnosing Parkinson’s disease at an earlier stage and thereby offer patients therapies before the disease has progressed.”
Alpha-synuclein is a protein found throughout the nervous system. Although its function is unknown, it is the primary component of protein clumps known as Lewy bodies, which are considered the hallmark of Parkinson’s disease. There is accumulating evidence that the protein plays a role in Parkinson’s disease development.
“Alpha-synuclein deposition occurs early in the course of Parkinson’s disease and precedes the onset of clinical symptoms,” explains Freeman, who with his coauthors suspected that the protein was elevated in the skin’s structures with autonomic innervation.
“Symptoms related to the autonomic nervous system, including changes in bowel function, temperature regulation, and blood pressure control may antedate motor symptoms in Parkinson’s patients,” he explains. “Skin-related autonomic manifestations, including excessive and diminished sweating and changes in skin color and temperature, occur in almost two-thirds of patients with Parkinson’s disease. The skin can provide an accessible window to the nervous system and based on these clinical observations, we decided to test whether examination of the nerves in a skin biopsy could be used to identify a PD biomarker.”
To test this hypothesis, the research team enrolled 20 patients with Parkinson’s disease and 14 control subjects of similar age and gender. The participants underwent examinations, autonomic testing and skin biopsies in three locations on the leg. Alpha-synuclein deposition and density of cutaneous sensory, sudomotor and pilomotor nerve fibers were measured.
As predicted, their results showed that alpha-synuclein was increased in the cutaneous nerves supplying the sweat glands and pilomotor muscles in the Parkinson’s patients. Higher alpha-synuclein deposition in the nerves supplying the skin’s autonomic structures was associated with more advanced Parkinson’s disease and worsening autonomic function.
“There is a strong and unmet need for a biomarker for Parkinson’s disease,” says Freeman. “Alpha-synuclein deposition within the skin has the potential to provide a safe, accessible and repeatable biomarker. Our next steps will be to test whether this protein is present in the cutaneous nerves of individuals at risk for Parkinson’s disease, and whether measurement of alpha-synuclein deposition in the skin can differentiate Parkinson’s disease from other neurodegenerative disorders.”
Study coauthors include BIDMC investigators Ningshan Wang, PhD and Christopher Gibbons, MD (co-first authors) and Jacob Lafo.
This study was supported by National Institutes of Health grant K23NS020509 and grants from the Langer Family Foundation and the RJG Foundation.
‘Optic flow’ is especially important for people with low vision, says study in optometry and vision science
Blurred images that are unidentifiable as still pictures become understandable once the images are set in motion. That’s because of a phenomenon called “optic flow”—which may be especially relevant as a source of visual information in people with low vision, reports a study ‘With an Eye to Low Vision: Optic Flow Enables Perception Despite Image Blur‘ (published online ahead of print, September 3, 2013) in the October issue of Optometry and Vision Science official journal of the American Academy of Optometry. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.
The concept of optic flow “has important implications for understanding of the daily functioning of observers with low vision,” according to the report by Jing Samantha Pan, MA, and Geoffrey P. Bingham, PhD, of Indiana University, Bloomington. “For low-vision observers, static image information is not the only (or perhaps even the primary) source of information about [their] surroundings.”
Despite Blur, Motion Improves Perception of Events
The researchers designed a study to assess the contributions of static images and optic flow to identifying events in the environment. They took short videos of everyday activities, such as a woman pouring a drink, a man bowling, and two people dancing. The black-and-white videos were then blurred—similar to what might be seen by a person with low vision—and split into 20 frames.
Volunteers with normal vision were then presented with the blurred images and asked to describe what they saw. First, static images were presented one at a time. Next, the images were set in motion by playing the frames in sequence.
When viewing the blurred, static images, the volunteers were usually unable to perceive what was going on. They correctly identify the event pictured in less than 30 percent of attempts.
In contrast, when participants viewed the moving images, the rate of correct identification increased to nearly 90 percent. For an example, see the video illustration at http://links.lww.com/OPX/A137. In the moving images, it’s much easier to perceive the dancing couple—despite the blurring.
Optic Flow Aids Functioning in People with Low Vision
“Our results showed that motion-generated optic flow information compensates for the lack of image details and enables effective event perception,” Pan and Bingham write. The effects of optic flow also appeared to be persistent—when participants viewed the static images again five days later, they could still “see” the activities depicted.
The results illustrate the importance of optic flow as a source of information for perceiving everyday events. Optic flow may be especially vital for the millions of people worldwide with low vision—usually defined as visual acuity of 20/60 or less, even with the best possible correction. In the United States, the main causes of low vision are cataract, glaucoma, age-related macular degeneration, and diabetic eye disease.
In the study, once blurred images were “calibrated” by motion, the depicted events could be easily recognized. The concept of optic flow might help to explain how people with even poor visual acuity can function well even in unfamiliar environments. Optic flow may be generated by the motion of objects around them, or even by their own motions.
The information provided by optic flow contributes to perception not only immediately but also several days later “When the motions stop, the blurry images may continue to inform low vision observers about the surround objects and their layout,” Pan and Bingham write.
“When visual acuity is poor, moving images can become important and make the otherwise imperceptible static images meaningful,” comments Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and Vision Science. “Our authors demonstrate the surprisingly powerful effect of moving images despite blur making the static image unrecognizable. They suggest that in low vision as in normal vision, both static and moving images are probably very important sources of information.”
Diabetes increases risk of developing and dying from breast and colon cancer
Diabetes is linked to an increased risk of developing cancer, and now researchers have performed a unique meta-analysis that excludes all other causes of death and found that diabetic patients not only have an increased risk of developing breast and colon cancer but an even higher risk of dying from them.
Dr Kirstin De Bruijn will tell the 2013 European Cancer Congress (ECC2013) , today (Sunday), that previous studies have examined the association between diabetes and dying from cancer but death from specific types of cancer has not been well-studied. “Our meta-analysis is the first to combine incidence and death from breast and colon cancer, while excluding all other causes of death. We have investigated the link between diabetes and the risk of developing as well as the risk of dying from these cancers,” she will say.
Dr De Bruijn, a PhD student in the Surgery Department at the Erasmus University Medical Center in Rotterdam (The Netherlands), and colleagues analysed results from 20 trials that had taken place between 2007 and 2012, involving more than 1.9 million patients with breast or colon cancer, with or without diabetes.
They found that patients with diabetes had a 23% increased risk of developing breast cancer and a 38% increased risk of dying from the disease compared to non-diabetic patients. Diabetic patients had a 26% increased risk of developing colon cancer and a 30% increased risk of dying from it compared to non-diabetic patients.
Dr De Bruijn will say: “The results for breast and colon cancer incidence in patients with diabetes are consistent with other meta-analyses. Furthermore, this meta-analysis shows a higher risk and a stronger association between diabetes and death from breast and colon cancer than previously reported.
“Cancer patients who are obese and diabetic are an already more vulnerable group of individuals when it comes to surgery, as they have an increased risk of developing complications both during and after surgery. If more obese and diabetic patients have to have an operation because of cancer, healthcare costs will increase.
“Worldwide, the numbers of obese and subsequent diabetic patients are still increasing and it is a cause for concern that these individuals are at a higher risk of developing cancer and dying from it. Studies have already highlighted the increased risk of developing cancer for diabetics. Our meta-analysis, which is unique since it looks at the risks for breast and colon cancer while excluding all other causes of death, provides stronger evidence for the association between diabetes and the risk of developing and dying from these cancers. We want to make people more aware of this problem and we hope that prevention campaigns regarding obese and diabetic patients will focus on highlighting this increased risk.”
Dr De Bruijn and her colleagues intend to follow up their work by investigating what effect other factors associated with diabetes have on cancer risk and death, such as the anti-diabetic medication, metformin, as well as insulin and the duration of diabetes.
“It is extremely important that prevention campaigns on obesity and diabetes are intensified and that they also focus on children, to prevent them from becoming obese and developing cancer later in life,” she will conclude.
Professor Cornelis van de Velde, President of ECCO, said: “With the increase in incidence of both diabetes and breast cancer, this is an important update of the meta-analyses on this subject and an interesting addition to the literature as this study excluded other causes of death. As the results are consistent with earlier meta-analyses, the substantial increased risk of breast cancer should be part of prevention campaigns. For further research, it would be important to study how other, competing risk factors might affect survival, as elderly cancer patients with diabetes are usually diagnosed with other conditions as well. Additionally, the potential role of metformin in relation to improved survival and cancer recurrence needs to be studied.”
Professor Hans-Joerg Senn, scientific director at the Tumor and Breast Centre ZeTuP, St Gallen, Switzerland, said: “The message from the Erasmus Medical Center is disturbing and highly important, for the medical community, as well as for the public and politicians. It highlights once more the importance of the negative interactions between lifestyle, metabolism, overweight and certain frequent types of cancers, such as here between diabetes, obesity and breast cancer as well as colon cancer. It is time for increased and more effective information and prevention campaigns, especially in the economically developed world, where caloric abundance is prevalent.”
Study finds link between commonly prescribed statin and memory impairment
New research that looked at whether two commonly prescribed statin medicines, used to lower low-density lipoprotein (LDL) or ‘bad cholesterol’ levels in the blood, can adversely affect cognitive function has found that one of the drugs tested caused memory impairment in rats.
Between six and seven million people in the UK1 take statins daily and the findings follow anecdotal evidence of people reporting that they feel that their newly prescribed statin is affecting their memory. Last year, the US Food and Drug Administration (FDA) insisted that all manufacturers list in their side effects that statins might affect cognitive function.
The study, led by scientists at the University of Bristol and published in the journal PLOS ONE, tested pravastatin and atorvostatin (two commonly prescribed statins) in rat learning and memory models. The findings show that while no adverse cognitive effects were observed in rat performance for simple learning and memory tasks for atorvostatin, pravastatin impaired their performance.
Rats were treated daily with pravastatin (brand name – pravachol) or atorvostatin (brand name – Lipitor) for 18 days. The rodents were tested in a simple learning task before, during and after treatment, where they had to learn where to find a food reward. On the last day of treatment and following one week withdrawal, the rats were also tested in a task which measures their ability to recognise a previously encountered object (recognition memory).
The study’s findings showed that pravastatin tended to impair learning over the last few days of treatment although this effect was fully reversed once treatment ceased. However, in the novel object discrimination task, pravastatin impaired object recognition memory. While no effects were observed for atorvostatin in either task.
The results suggest that chronic treatment with pravastatin impairs working and recognition memory in rodents. The reversibility of the effects on stopping treatment is similar to what has been observed in patients, but the lack of effect of atorvostatin suggests that some types of statin may be more likely to cause cognitive impairment than others.
Neil Marrion, Professor of Neuroscience at Bristol’s School of Physiology and Pharmacology and the study’s lead author, said: “This finding is novel and likely reflects both the anecdotal reports and FDA advice. What is most interesting is that it is not a feature of all statins. However, in order to better understand the relationship between statin treatment and cognitive function, further studies are needed.”
What are statins used for?
Statins are medicines that are prescribed to help protect healthy, but high-risk, people from heart disease and to prevent repeated problems in people who have already had a heart attack, a stroke or peripheral artery disease.
How do statins work?
The cells in our body make a fatty substance called cholesterol. The liver makes the cholesterol mostly from the saturated fats in the food we eat. Cholesterol plays a vital role in how every cell works, throughout the body, and the body uses cholesterol to make other vital chemicals. However, having too much cholesterol in the blood can increase your risk of getting heart and circulatory disease. Statins reduce the amount of cholesterol produced by cells all over our body. This forces them to get their supply by removing it from the bloodstream. So this lowers the blood cholesterol level.
Source: British Heart Foundation
The paper ‘Chronic Pravastatin but Not Atorvastatin Treatment Impairs Cognitive Function in Two Rodent Models of Learning and Memory’ by Stuart SA, Robertson JD, Marrion NV, Robinson ESJ is published in PLOS ONE : e75467. doi:10.1371/journal.pone.0075467 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0075467
Study shows how deadly Candida albicans might be rendered harmless
Candida albicans is a double agent: In most of us, it lives peacefully, but for people whose immune systems are compromised by HIV or other severe illnesses, it is frequently deadly. Now a new study from Johns Hopkins and Harvard Medical School shows how targeting a specific fungal component might turn the fungus from a lion back into a kitten. Study results were reported this month in The Journal of Biological Chemistry.
“Treatment options for systemic Candida infections are limited, and a major difficulty in finding new drug targets is that fungi are closely related to us, so we risk hurting the patient as much as the pathogen,” says Rajini Rao, Ph.D., a professor of physiology in the Institute for Basic Biomedical Sciences at the Johns Hopkins University School of Medicine. “What we’ve identified is a function that is critical for virulence. If we could block this through medication, it would leave both the fungus and the host healthy while taking away Candida‘s ability to harm.” Candida lives in the guts of most people as one of many so-called “commensal microbes” — that is, harmlessly. It can sometimes cause local infections of the mouth or genitals, known as thrush, that are treatable with over-the-counter antifungals. But given the opportunity to breach our defenses, Candida can cross into the bloodstream and switch from peaceful coexistence to attack mode, producing long filaments that dig into tissues and destroy them.
Unfortunately, Rao says, “there are only a few antifungal drugs, so it’s particularly dangerous when drug resistance develops in Candida.” For that reason, she says, “we’re always looking for new chinks in its armor.”
In her study, Rao and her collaborators looked for such a new chink in a part of Candida‘s cells known as the vacuole. The vacuole’s main function is as a recycling center that chews up cellular waste, so it was a surprise when a previous study from her group found that a well-known antifungal drug prevented the vacuole from becoming acidic. This led them to suspect that acidification of the vacuole was important for virulence. The research team focused on V-ATPase, the enzyme responsible for making many compartments of the cell, including the vacuoles, acidic. Because humans have a very similar enzyme, the scientists weren’t looking to eliminate it altogether — “that would have been like taking a sledgehammer to cells,” Rao explains. Rather, they homed in on just one of the enzyme’s components, known as subunit a. Like many proteins in fungi and higher animals, there is more than one version of subunit a, which come from different genes — a duplication that gives the organism a backup in case a mutation disables one of the genes.
Rao said first they altered Candida cells so that they could only use one or the other version of the subunit a gene. As expected, they found that inactivating either one had no effect because the other compensates in every function — except one. It turned out that acidification of the vacuole exclusively depended on one version of the gene. This allowed them to test the importance of the vacuole’s acidity on virulence, separate from the many other functions of the V-ATPase. Unable to acidify the vacuole, the fungus could no longer form the tentacle-like filaments that characterize its deadly form. When the researchers injected healthy Candida into the bloodstream of mice, nearly all died within a week. In contrast, mice injected with the strain of fungus that was unable to acidify the vacuole remained healthy and survived.
Rao says that this study reveals a vulnerability that could be exploited using drugs known to alter the pH of the vacuole, rendering Candida harmless while potentially posing little risk to infected patients. For example, previous studies from her lab showed that a drug already in use to treat a heart condition known as arrhythmia had the unexpected effect of blocking acidification of the fungal vacuole. The next step, she says, would be to screen drugs already approved by the U. S. Food and Drug Administration to increase the repertoire of antifungal agents to combat deadly fungal infections.
Link to the paper: http://www.jbc.org/content/288/36/26256.short
Other authors on the report were Cassandra Patenaude, Yongqiang Zhang and Brendan Cormack of the Johns Hopkins University School of Medicine, and Julia Köhler of Harvard Medical School.