Posted on NIH. 7 July, 2021
The National Institutes of Health (NIH) is our nation’s medical research agency. Its mission focuses on scientific discoveries that improve health and save lives. Founded in 1870, the NIH conducts its own scientific research through its Intramural Research Program (IRP), which supports approximately 1,200 principal investigators and more than 4,000 postdoctoral fellows conducting basic, translational and clinical research. In this blog, we will highlight recent innovative NIH research.
In a recent study at the National Eye Institute (NEI), a team of IRP scientists have discovered that certain peptides have the ability to protect neuronal cells found in the light-sensing retina layer at the back of the eye. The peptides, which are short fragments of proteins, have the potential to be used to treat degenerative retinal diseases, such as age-related macular degeneration (AMD).
The peptides were derived from a protein called pigment epithelium-derived factor (PEDF), which is produced by retinal pigment epithelial cells that line the back of the eye. The research team, led by Dr. Patricia Becerra, chief of the NEI Section on Protein Structure and Function, used a well-known cell culture model using immature retinal cells isolated from the eyes of newborn rats. The model includes not only the retina’s light-sensing photoreceptors, but additional types of neurons that help the retina process and transmit visual information to the brain.
“In the eye, PEDF protects neurons from dying. It prevents the invasion of blood vessels, it prevents inflammation, it has antioxidant properties—all these are beneficial properties,” said Dr. Becerra, the senior author of the study. Her studies suggest that PEDF is part of the eye’s natural mechanism for maintaining eye health. “PEDF may have a role for treating eye disease. If we want to exploit the protein for therapeutics, we need to separate out the regions responsible for its various properties and determine how each of them works.”
In prior work, the research team determined that the PEDF protein has functionally distinct domains that can work function independently. One PEDF domain, called the 34-mer because it is formed by 34 amino acid building blocks, halts blood vessel growth. Aberrant blood vessel growth is central to retinal diseases such as AMD and diabetic retinopathy. The second PEDF domain, called the 44-mer, provides anti-death signals to retinal neurons and can also stimulate neurons to grow neurites which are finger-like projections that help the neurons communicate with their neighbors. A shorter version of the 44-mer, with only 17 amino acids (17-mer), has identical activities.
Germán Michelis, predoctoral fellow at NEI and the study’s first author, along with colleagues tested whether the 44-mer could protect immature retinal cells in a dish. Without the presence of proteins and other cells in their usual retinal environment, immature photoreceptors quickly die but can be preserved with PEDF. They found that both the 44-mer and 17-mer were as capable of saving these photoreceptors as full-length PEDF. The PEDF activity appeared to be most needed at a specific point in photoreceptor cell development. Light detection takes place in a part of the photoreceptor known as the outer segment, where light-sensing opsin proteins are concentrated. The scientists found that when a photoreceptor cell is just beginning to create its outer segments, PEDF triggers the movement of opsin into the budding outer segment, where it belongs.
Along with photoreceptors, the retina is packed with several other types of neurons, which work in conjunction to process visual signals. Via neurites, amacrine neurons form connections, called synapses, to the cells that forward these visual signals to the brain. The team discovered that PEDF stimulates amacrine cells to develop neurites using their cell culture model. The 44-mer and 17-mer were as effective or better at stimulating these connections than the native protein. These peptides work by binding to a protein receptor (PEDF-R) on the surface of neurons. PEDF activates PEDF-R, which processes molecules like docosahexaenoic acid (DHA), an omega-3 fatty acid critical for babies’ development and for eye health.
“We’ve known for a long time that DHA is important for retinal health. We think PEDF signaling might be a key component of regulating omega-3 fatty acids like DHA, both during eye development and in maintaining the eye’s health over time,” said Becerra. “We’re hoping that we can harness some of these protective effects in a peptide-based therapeutic approach in the near future.”
In a study of healthy volunteers conducted at the NIH Clinical Center, IRP researchers discovered that our brains may replay compressed memories of learning new skills when we rest, suggesting that taking short breaks during practice is a key to effective learning. The researchers found that during rest the volunteers’ brains rapidly and repeatedly replayed faster versions of the activity seen while they practiced typing a code. The more times a volunteer replayed the activity, the better they performed during subsequent practice sessions, indicating rest strengthened memories.
“Our results support the idea that wakeful rest plays just as important a role as practice in learning a new skill. It appears to be the period when our brains compress and consolidate memories of what we just practiced,” said Dr. Leonardo Cohen, senior investigator at the National Institute of Neurological Disorders and Stroke (NINDS) and senior author of the study. “Understanding this role of neural replay may not only help shape how we learn new skills but also how we help patients recover skills lost after neurological injury like stroke.”
The research team used magnetoencephalography, a highly sensitive scanning technique, to record the brain waves of 33 healthy, right-handed volunteers as they learned to type a five-digit test code with their left hands. The subjects sat in a chair and under the scanner’s long, cone-shaped cap. Each experiment began when a subject was shown the code “41234” on a screen and asked to type it out as many times as possible for 10 seconds, followed by a 10 second break. The subjects were asked to repeat this cycle of alternating practice and rest sessions a total of 35 times.
Throughout the first few trials, the speed at which subjects correctly typed the code improved dramatically, levelling off around the 11th cycle. In a previous study, led by former NIH postdoctoral fellow Dr. Marlene Bönstrup, the team showed that most of these gains occurred during the short rests, and not when the subjects were typing. These gains were greater than those made after a night’s sleep and correlated with a decrease in the size of brain waves, called beta rhythms.
“We wanted to explore the mechanisms behind memory strengthening seen during wakeful rest. Several forms of memory appear to rely on the replaying of neural activity, so we decided to test this idea out for procedural skill learning,” said Dr. Ethan Buch, staff scientist on Dr. Cohen’s team and leader of the study. To do this, Dr. Leonardo Claudino, a former postdoctoral fellow in Dr. Cohen’s lab, helped Dr. Buch develop a computer program which allowed the team to decipher the brain wave activity associated with typing each number in the test code. The program helped them discover that a much faster version, about 20 times faster, of the brain activity seen during typing was replayed during the rest periods. Over the course of the first eleven practice trials, these compressed versions of the activity were replayed approximately 25 times per rest period.
“During the early part of the learning curve we saw that wakeful rest replay was compressed in time, frequent, and a good predictor of variability in learning a new skill across individuals,” said Dr. Buch. “This suggests that during wakeful rest the brain binds together the memories required to learn a new skill.”
The team concluded that the frequency of replay during rest predicted memory strengthening. The subjects whose brains replayed the typing activity more often showed greater jumps in performance after each trial than those who replayed it less often. The replay activity often happened in the sensorimotor regions of the brain, which are responsible for controlling movements. However, they also saw activity in other brain regions, namely the hippocampus and entorhinal cortex.
“We were a bit surprised by these last results. Traditionally, it was thought that the hippocampus and entorhinal cortex may not play such a substantive role in procedural memory. In contrast, our results suggest that these regions are rapidly chattering with the sensorimotor cortex when learning these types of skills,” said Dr. Cohen. “Overall, our results support the idea that manipulating replay activity during waking rest may be a powerful tool that researchers can use to help individuals learn new skills faster and possibly facilitate rehabilitation from stroke.”
The ketogenic diet is a low-carbohydrate, high fat diet with its origins dating back to the early 1900’s and has been used as a dietary based treatment for epilepsy in the 1920’s and 30’s. The ‘keto’ diet has steadily gained in popularity in recent years and continues to catch the attention of scientists seeking natural and alternative treatments for an array of health ailments. A recent IRP study suggests that a keto diet might make it easier for people with alcohol use disorder to stop drinking by reducing withdrawal symptoms.
When consuming a diet of carbohydrate-rich foods like grains and fruits, the brain runs on the sugar, called glucose, that is produced when the digestive system breaks down those carbohydrates. However, the keto diet is so low in carbohydrates that the liver must produce molecules called ketone bodies to supply the brain with energy when glucose is not readily available.
Brain cells can also convert acetate, produced when the liver breaks down alcohol, into energy through the same processes they use to burn ketone bodies for fuel. In people who habitually consume large amounts of alcohol, brain cells switch to running primarily on acetate instead of glucose. Brain cells cannot immediately resume running on glucose when people stop drinking and cut off the supply of acetate, contributing to the symptoms of alcohol withdrawal which include headache, nausea, anxiety, difficulty sleeping, and in severe cases, extreme distress or dangerous seizures.
“In the early stages of alcohol withdrawal, patients’ brains have very low uptake of glucose — the levels are equivalent to what you see in patients with mild to moderate Alzheimer’s dementia,” explains Dr. Nora Volkow, director of the National Institute on Drug Abuse (NIDA) and the study’s senior author.
Dr. Volkow’s research team theorized that putting patients with alcohol use disorder (AUD) on a keto diet as they attempted to quit drinking might temper withdrawal symptoms by providing their brains with a fuel similar to the acetate they had grown accustomed to using. The scientists put 19 such individuals on a keto diet for three weeks and another 14 on a diet with macronutrient proportions resembling those of the standard American diet. Liquid diets were used so the study participants would not know which diet they were on.
The keto diet increased the levels of ketone bodies in participants’ blood and brains, but in addition, those on the keto diet required much lower levels of benzodiazepine medications than the control group to alleviate their alcohol withdrawal symptoms.
As part of the study, functional magnetic resonance imaging (fMRI) was used to measure participants brain activity when viewing alcohol and food related images. Those on the keto diet reported that the alcohol-related images triggered weaker feelings of ‘wanting’ compared to the control group, whereas there were no such differences for the food-related images. This correlated to more activation than the control group in a region of the brain involved in self-control called the dorsal anterior cingulate cortex (dACC), which the scientists think may reflect a greater ability to use self-control when confronted with alcohol-related cues. Finally, the brains of patients on the keto diet had lower levels of two markers of brain inflammation than the control participants.
“We believe that neuroinflammation modulates neuronal activities and that these effects contribute to alcohol withdrawal symptoms,” explains Dr. Leandro Vendruscolo, IRP staff scientist and one of the study’s lead authors. “We think that neuroinflammation makes people feel sick, which may contribute to the negative emotional state that drives dependence.”
The IRP study shows promising evidence that supplying the brain with an alternative energy source via a keto diet can aid in easing alcohol withdrawal. Unfortunately, a keto diet can be difficult to stick with. It may also be possible to design a modified ketogenic diet that eases symptoms without restricting carbohydrate consumption as much as a typical keto diet.
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a degenerative neuromuscular disease affecting nerve cells in the brain and spinal cord, resulting in the progressive loss of muscle control and gradual increasing weakness and muscle wasting. There are two classifications of the disease. Sporadic is the most common form of ALS, affecting 90 to 95% of all patients. Familial is an inherited form of the disease accounting for 5 to 10% of ALS cases. Children of a parent with the dominant mutation have a 50% chance of inheriting the gene mutation and developing ALS.
Studies have shown that families with a history of ALS also had a history of frontotemporal dementia (FTD), which occurs when nerve cells in the frontal and temporal lobes of the brain are lost, causing changes in behavior and personality. Dr. Bryan Traynor, senior investigator and neurologist at the National Institute on Aging (NIA) led an international consortium of researchers that uncovered a genetic mutation linking the most common ‘familial’ cause of both ALS and FTD to the same segment of DNA on chromosome 9.
In 2009, Dr. Traynor’s NIH research team began a genetic study of ALS in Finland, a country with below-average genetic diversity for historical reasons and an unusually high incidence of ALS. After testing samples from about 300 Finnish ALS and FTD patients and 300 people with neither condition, the IRP scientists noticed a common genetic haplotype that exists in the Finnish population. A haplotype is a set of genetic information that is inherited together as a set from a single parent, rather than having a mix of DNA from both parents. The study concluded that the vast majority of ALS and FTD patients across Europe and North America had this Finnish haplotype, which included specific variations of three genes: MOBKL2b, IFNK, and C9ORF72.
“One of the things about genetics is you can use it as a kind of time machine,” Dr. Traynor says. “What this finding indicates to us is there was probably a one-off genetic event that occurred about 1500 years ago, around the time of the fall of the Roman Empire. We think it was actually the Vikings on their summer holidays who spread this version of the C9ORF72 gene around the rest of Europe.”
Having identified the genetic site where a disease-causing mutation must exist and a common set of variations in the genetic profile, researchers had yet to identify the specific gene that was at the root of the cause. With a relatively rare disease like ALS, even after narrowing the search to a particular location on a single chromosome, finding a mutation among 7 million base pairs proved difficult. To aid in this effort, Dr. Traynor’s research team reached out to other scientists globally and invited them to send their DNA samples to them for sequencing. The resulting data was also shared with the collaborators for analysis at the same time. The global team of scientists narrowed the area down to about 200,000 base pairs, “a blink of the eye in genetic terms,” according to Dr. Traynor.
In 2011, Dr. Traynor began analyzing the DNA samples his team had gathered for variations that were not present in unaffected individuals, allowing them to narrow the search to eight potential targets. “I noticed that six of these eight variations were all very close together, within 30 base pairs, which they shouldn’t have been,” says Dr. Traynor. “They should have been distributed randomly across the 200,000 base pairs we were looking at.”
Through comparison of the samples to a normal ‘reference’ genome, Dr. Traynor observed that the C9ORF72 gene located in this genetic segment contained multiple repeats of a specific set of base pairs in the patient samples. The reference genome had three repetitions of this genetic sequence within the C9ORF72 gene, but in the DNA from ALS and FTD patients, there were many more. “I remember sitting in front of the computer looking at this and that’s when the penny dropped,” Dr. Traynor says. “It was an expansion of six base pairs that were being repeated again and again and again.”
Following this discovery, Dr. Traynor is now focusing his efforts on identifying therapies for ALS and FTD. While fixing the C9ORF72, KIF5A, or other mutations through gene editing or CRISPR may be possible one day, Dr. Traynor believes that manipulating the responsible genes’ activity is the most likely direction for therapy, noting that a breakthrough could be possible in just a few years.
Rhabdomyosarcoma (RMS) is a rare type of cancer arising in the muscles and other soft tissues. The disease can occur throughout childhood and may even be present at birth and differs from the form of rhabdomyosarcoma typically seen in adults. The presence of mutations in several genes, including TP53, MYOD1, and CDKN2A, appears to be associated with a more aggressive form of the disease and a poorer chance of survival.
A recent study conducted by an international consortium of scientists and led by the National Cancer Institute’s Center for Cancer Research, offers genetic insights that may lead to more widespread use of tumor genetic testing to predict how individual patients with this childhood RMS will respond to therapy, and contribute to the development of targeted treatments for the disease. “These discoveries change what we do with these patients and trigger a lot of really important research into developing new therapies that target these mutations,” said Dr. Javed Khan, senior investigator at NCI’s Genetics Branch, who led the study.
In patients whose RMS has remained localized, combination chemotherapies have led to a five-year survival rate of 70%-80%. However, in patients whose cancer has spread or returned following treatment, the five-year survival rate remains poor at less than 30%, even with aggressive treatment. Doctors have typically used clinical features, such as the size and location of the tumor in the body, and the extent to which it has spread to predict how patients will respond to treatment, but this approach is imprecise. More recently, scientists have discovered that the presence of the PAX-FOXO1 fusion gene that is found in some patients with RMS is associated with poorer survival. Patients are now being screened for this genetic risk factor to help determine how aggressive their treatment should be. Scientists have also begun using genetic analysis to gain a better understanding of the molecular workings of RMS in search of other genetic markers that lead to a poor survival rate.
In this new study, scientists from NCI and the Institute for Cancer Research in the United Kingdom analyzed DNA from tumor samples from 641 children with RMS enrolled over a two-decade period in several clinical trials. Scientists searched for genetic mutations and other aberrations in genes previously associated with RMS and linked that information with clinical outcomes. Among the patterns that emerged, patients with mutations in the tumor suppressor genes TP53, MYOD1, or CDKN2A had a poorer prognosis than patients without those mutations. Using next-generation sequencing, the research team found a median of one mutation per tumor. Patients with two or more mutations per tumor had even poorer survival outcomes. In patients without the PAX-FOXO1 fusion gene, more than 50% had mutations in the RAS pathway genes, although these mutations did not appear to be associated with survival outcomes in this study.
While the researchers have identified the major mutations that may drive RMS development or provide information about prognosis, they note that more work is needed to identify targeted drugs for those mutations. Future clinical trials could also benefit by incorporating genetic markers to more accurately classify patients into treatment groups. Two NCI-sponsored Children’s Oncology Group clinical trials are currently underway using these markers. The researchers hope that routine tumor genetic testing for rare cancers, such as RMS, will soon be a standard part of the treatment plan, as it is for more common cancers, such as breast cancer.
Wednesday, August 25, 2021, 1:00 pm to 5:00 pm
Tuesday, September 21, 2021, 12:30 pm to Thursday, September 23, 2021, 5:30 pm (registration required)
Copyright (C) 2021