Mutations linked to genetic disorders shed light on a crucial DNA repair pathway

Dividing cells are prone to errors, and so they must be prepared to summon sophisticated emergency systems to deal with potential damage. One type of division-derailing mishap can occur when assault by certain chemicals causes two strands of DNA to permanently connect when they shouldn't, in what scientists call interstrand crosslinks (ICLs). Properly fixing these crosslinks is crucial to preventing cancer, maintaining tissues, and fertility.

To better understand how a cell finds and fixes these misplaced crosslinks, researchers at The Rockefeller University and their colleagues are examining the genomes of patients in whom the repair process is defective. In two separate studies, the most recent described in Molecular Cellon August 6, they have identified two new genes in which mutations can produce one such rare genetic disorder, Fanconi anemia, and so revealed new insights on this critical repair pathway.

"Our work began, as it often does, with samples and histories from patients. In these cases, we had two patients who each represented a sort of mystery: They had symptoms of Fanconi anemia, but no genetic cause yet identified," says senior author Agata Smogorzewska, associate professor and head of the Laboratory of Genome Maintenance. "Our investigation led us to discover a defective RAD51 protein in one patient, and a similarly dysfunctional protein UBE2T in the other."

The genes that code for RAD51 and UBE2T -- along with many other genes linked to Fanconi anemia in previous studies -- contribute to a repair process known as interstrand crosslink repair, which fixes a misplaced attachment between two strands of DNA. Caused by chemical agents, including often used chemotherapies like cisplatin; chemicals called aldehydes that occur naturally within cells, and nitrous acid formed after eating nitrates, ICLs block the replication of DNA, making it impossible for cells to accurately copy their genomes as they divide. The ICL repair process is very sophisticated and uses multiple enzymes that cut away the connection between the DNA strands, freeing them up and allowing the cells to grow.

The genome is at constant risk of forming ICLs, and defects in the ICL repair pathway can produce a constellation of symptoms associated with Fanconi anemia: a predisposition to cancer, failure of the stem cells in bone marrow responsible for producing blood cells, infertility, as well as developmental defects.

In the RAD51 research, supported by the Starr Cancer Consortium, first author Anderson Wang, a postdoctoral fellow in the Smogorzewska laboratory and his colleagues set out to determine the cause of the Fanconi anemia-like symptoms of a girl in the university's International Fanconi Anemia Registry. When they sequenced the protein-coding genes in her genome, they found mutations in one of two copies of the gene for the protein RAD51 -- a surprising culprit. This protein was already known to be important for another DNA repair process, called homologous recombination, in which a missing section of DNA is replaced using its sister strand as a template. Homologous recombination is thought to be used during the last step of ICL repair, after the crosslink has been cut.

But because only one copy of the RAD51 gene was partially defective, her cells could still perform homologous recombination, but not ICL repair. If both copies of RAD51, which is essential for life, had been defective, the girl would never have been born.

To show that the defective copy of the RAD51 gene was indeed responsible for her symptoms, the researchers genetically engineered the patient's own cells to remove the defect, which restored their ability to fix ICLs. Further experiments on the patient's cells --including biochemical work conducted by coauthor Stephen Kowalczykowski's lab at the University of California, Davis -- lead the researchers to suspect that RAD51 plays a role outside of homologous recombination, by tamping down the activity of two enzymes that degrade the DNA at the ICL. When RAD51 is defective, these enzymes (DNA2 and WRN) become overly destructive.

In the UBE2T study, published July 7 in in Cell Reports, the team, including first author Kimberly Rickman, a biomedical fellow in Smogorzewska's lab, found that mutations in a gene for a protein named UBE2T explained the Fanconi anemia symptoms seen in another registry patient. While it was already known that UBE2T is involved in activating ICL repair, the discovery that these mutations could produce Fanconi anemia revealed the protein is an irreplaceable player in the pathway.

"Although we have discovered new causes for this devastating but very rare genetic disease, the implications of this work go much further. By identifying new disruptions to this repair pathway, we can better understand the mechanisms of an event that is crucial to every cell division -- a process that occurs constantly within the human body throughout a lifetime," Smogorzewska says.

Source:ROCKEFELLER UNIVERSITY

How white blood cells limit muscle regeneration

Researchers have identified a protein produced by white blood cells that puts the brakes on muscle repair after injury.

By removing the protein CD163 from mice, scientists at Emory University School of Medicine could boost muscle repair and recovery of blood flow after ischemic injury (damage caused by restriction of blood flow).

The findings point to a target for potential treatments aimed at enhancing muscle regeneration. Muscle breakdown occurs in response to injury or inactivity -- during immobilization in a cast, for example -- and in several diseases such as diabetes and cancer.

The results are scheduled for publication online by Nature Communications on August 5.

CD163 was known to scientists, mostly as a molecule involved in scavenging excess hemoglobin from the body, but its role in regulating muscle repair was not, says senior author Aloke Finn, MD, assistant professor of medicine (division of cardiology) at Emory University School of Medicine.

Mice lacking CD163 showed increased blood flow and muscle repair, compared with controls, after an injury coming from a restriction of blood flow in one leg. Examining the mice lacking CD163, Finn and his colleagues were surprised to find that blood vessels and muscle fibers also grew substantially (roughly 10 percent) in their uninjured legs.

"We were astonished," Finn says. "Why would something we did, which caused an injury to one leg, help tissue in the other leg regenerate when it wasn't injured in the first place?"

Potentially, researchers could try to achieve the effect of removing CD163 in humans by giving patients an antibody against CD163, but more research is needed to know how this might work. CD163 levels have been found to increase in aging humans in multiple studies.

Finn and his colleagues found that macrophages, which are a type of white blood cell, appear to release a soluble form of CD163 in response to injury. In the blood, CD163 soaks up and counteracts another protein called TWEAK, which stimulates muscle cells to multiply.

In CD163's absence, TWEAK can have a greater effect, and can apparently stimulate muscle growth distant from the site of injury. When infused into normal mice, TWEAK does not have any effect on muscle growth, possibly because of circulating CD163.

Scientists that study muscle cells have been interested in TWEAK for several years, but some studies have suggested that TWEAK negatively regulates muscle regeneration - the opposite of what Finn's team observed. To prove that TWEAK was needed for the extra repair seen in mice lacking CD163, the Emory researchers showed that if they injected an antibody against TWEAK, thus removing it from the blood, it eliminated the extra repair activity.

"I think our results show a specific mechanism by which muscle regeneration takes place. TWEAK can be a pro-regenerative factor," Finn says, "but its effects have to be transient and limited."

TWEAK is thought of as transmitting inflammatory signals because it activates a master regulator of inflammation called NF-kB. While chronic inflammation is bad for muscle growth, in the mice lacking CD163, the signals coming from increased TWEAK are helpful for regeneration.

"Ischemic injury is a situation in which TWEAK can stimulate muscle progenitor cells to proliferate," Finn says. "But if you have lots of TWEAK around all the time, the muscle cells don't know when it's time to differentiate and mature. "

TWEAK has also been shown to be connected to liver regeneration and stroke. Finn says his team is currently investigating CD163's effects on atherosclerosis.

Source:EMORY HEALTH SCIENCE

Balancing Omega-6 and Omega-3 Fatty Acids in Ready-to-use Therapeutic Foods

Omega 6 and 3 fatty acids are both types of polyunsaturated fats and they are extremely important to the health and wellbeing of various bodily functions.

 In children, long-chain polyunsaturated fatty acids are essential for the healthy development of the brains and eyes, while they are also essential to all of us because they are needed for the production of powerful regulatory hormones. There are two classes of long-chain polyunsaturated fatty acids, namely omega-6 and 3, linoleic acid (LA), an omega-6 fatty acid, and alpha-linolenic acid (ALA), an omega-3 fatty acid. Omega 6 fats are essential for the production of numerous pro-inflammatory hormones, while omega 3 fats are needed for the production of anti-inflammatory hormones. 

To maintain optimum health, it is absolutely necessary that a proper balance is maintained between levels of the two fatty acids. Over the millennia, our diets have changed dramatically, with the shift being even more pronounced in recent decades. This change is in the ratio of Omega 6 to Omega 3 polyunsaturated fatty acids that we ingest through our diet. Omega 6 levels have spiraled because of an abundance of omega 6 fats in chemically extracted vegetable oils, margarine and salad oil, while there has been a corresponding decrease in omega 3 intake, which in the past was available abundantly from cold water fish and grass-fed or wild meat. While the ideal ratio of omega 6 to omega 3 fatty acids is 4:1 to 1:1, the average ratio in the American diet today is a shocking 20:1. These figures are just as bad in most urbanized parts of the world. The high intake of peanuts in most urban diets also contributes to the high levels of omega 3 fatty acids. 

Findings of Recent Study

Our bodies can produce all of the fatty acids that we need with the exception of linoleic acid and alpha-linolenic acid. These fatty acids must be absorbed through the food we eat which is why health care experts and nutritionists have been concerned with the role and scope for ready-to-use therapeutic foods or RUTFs. It should also be pointed out that while our bodies can de-saturate and elongate both linoleic acid and alpha-linolenic acid to produce long-chain polyunsaturated fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), our cells are not very efficient when it comes to converting alpha-linolenic acid to EPA and then DHA. It is advisable to obtain these long chain polyunsaturated fatty acids directly from food. 

Dr. J. Thomas Brenna of Cornell University recently led a team of researchers who reviewed the findings of studies this far into the role of ready-to-use therapeutic foods (RUTFs). Based on their analysis of the data, it is apparent that maintaining an optimal balance of omega-6 and omega-3 fatty acids through the foods we ingest is of the utmost importance, especially in children. Ready-to-use therapeutic foods are high energy density foods that are used to treat severe malnutrition, which is most common among children in underdeveloped and developing parts of the world. A decrease in the intake of linoleic acid through the diet, with or without simultaneous increases in omega 3 intake from the diet, results in an increase of EPA and DHA content in red blood cells. Researchers point out that the most suitable strategy would be to increase DHA and EPA intake. 

While the study may have focused on role of ready-to-use therapeutic foods when dealing with acute malnutrition, the problem of an omega 6 and omega 3 imbalance is typical of all industrial diets across the world. Many nutritionists and experts therefore recommend 500 mg EPA and DHA supplementation for adults and 250 mg for children. Before taking any supplements or making any drastic dietary changes however, make it a point to consult with your pediatrician and other health care providers. 

Consequences of Omega 3 - Omega 6 Imbalance 
As mentioned earlier, omega 6 and omega 3 aren't just used as a source of energy, but they are biologically active and needed for the creation of other fatty acids and hormones, with Omega-6s being pro-inflammatory and omega-3s producing an anti-inflammatory effect. Most diets today are imbalanced in favor of omega-6. While inflammation is essential and inflammatory responses help to protect against infection and injuries, an excessive or disproportionate inflammatory response can be counterproductive, causing severe damage and contributing to the development of various health conditions. Such a lopsided response is believed to be a contributing factor in the incidence of heart disease, diabetes, arthritis, Alzheimer's and even in some types of cancer. In other words, the consequences of an omega3-omega6 imbalance can severely threaten your health. 

How to Maintain Balance

The best way to maintain that balance of omega-6 and omega-3 intake is by cutting down on food sources that are high in omega-6. This does pose some problem as many of the most widely consumed foods and food products contain omega-6. To start with, avoid processed seed- and vegetable oils that have high omega-6 content. Most of these foods are not really natural to the human diet but were only introduced in the last century, completely distorting the balance of omega-6 and omega-3 fatty acids. It's not necessary or desirable to eliminate every food that is rich in omega-6 because many of these foods are extremely healthy, like nuts, seeds and certain grains. It is important that such foods are consumed in moderation however. 

While cutting down on your omega-6 intake is the first step to leveling the playing field, this is inadequate if you don't have any omega-3 intake from your diet. Traditionally, animal food products or meats have been the best source of omega-3 fatty acids, but because of unnatural agricultural and livestock practices, necessitated by a growing population, this too has started to change. Most cattle today are raised on grain, not grass, resulting in a decline in omega-3 content in such meat sources. Grass fed or wild meat is therefore the healthiest source of omega-3 but is not always an option. The healthiest way to boost your omega-3 intake is by including fatty fish and other seafood like salmon in your regular diet. If you don't eat much seafood then it would be a good idea to take fish oil supplements instead. Plant sources like flax and chia seeds also contain Omega-3 but not the preformed EPA and DHA and the human body is not very efficient at converting ALA into these active forms. 

Reference:

1. Brenna JT, Akomo P, Bahwere P, Berkley JA, Calder PC, Jones KD, Liu L, Manary M, Trehan I, Briend A. Balancing omega-6 and omega-3 fatty acids in ready-to-use therapeutic foods (RUTF). BMC Med. 2015 May 15;13:117. doi:10.1186/s12916-015-0352-1. PubMed PMID: 25980919; PubMed Central PMCID:PMC4433071. 

2. http://oregonstate.edu/ua/ncs/archives/2013/oct/excess-omega-3-fatty-acids-could-lead-negative-health-effects 
 

Antioxidants In Fruits and Vegetables Slows Down Aging and Boost Immune System

Scientists from the Florida campus of Scripps Research Institute (TSRI) have shown how aging affects the immune system as we grow older.

  The research focuses on an organ called as thymus. It produces T lymphocytes, which are vital to the immune system and needs to be replenished constantly to respond to new threats. 

"The thymus begins to atrophy rapidly in very early adulthood, simultaneously losing its function. This new study shows for the first time a mechanism for the long-suspected connection between normal immune function and antioxidants," said TSRI Professor Howard Petrie. 

The researchers developed a computational method for analyzing the activity of stromal and lymphoid cells, which are the two major thymic cells. Researchers examined these cells on mouse tissues. They found a deficiency of an antioxidant enzyme called catalase in stomal cells, which had resulted in high levels of reactive oxygen by-products of metabolism and metabolic damage. 

The researchers increased the levels of catalase in animal models to confirm the significant role of the enzyme. They found that it preserved the thymus size for a longer period. 

Animals that were given two dietary antioxidants, including vitamin C protected them from age related deterioration of the thymus. 

The findings provide support for the "free-radical-theory" of aging, which proposes that reactive oxygen species produced during animal metabolism such as hydrogen peroxide, cause damage to cells that contributes to aging and age-related diseases. 

"There's no question that the thymus is remarkably responsive to androgens. But our study shows that the fundamental mechanism of aging in the thymus, namely accumulated metabolic damage, is the same as in other body tissues. However, the process is accelerated in the thymus by a deficiency in the essential protective effects of catalase, which is found at higher levels in almost all other body tissues," said Petrie. 

The research is published in the journal Cell 

 

The Indian Institute Of Rice Research Identifies Rice Varieties Beneficial For Diabetics

Three rice varieties with low glycemic index (GI), which is suitable for patients with type 2 diabetes has been identified, said the Central government.

 "Indian Institute of Rice Research under the aegis of Indian Council of Agricultural Research has identified three rice varieties with low glycemic index values," minister of state for agriculture, Sanjeev Kumar Balyan said in the Rajya Sabha. 

According to the IIRR Hyderabad, Lalat (GIS.17), BPT 5204 (GIQ.42) and Sampada (GIQ) are considered suitable for diabetic patients, Balyan said. 

Any variety of rice with glycemic index less than or equal to 55 is considered diabetic-friendly, he added. 

"Presently, these varieties are under cultivation in different states of India."

Source: IANS

 

Regular Exercise And Healthy Diet May Help Prevent Gestational Diabetes

A simple lifestyle along with physical activity and diet control will prevent gestational diabetes even in high-risk women says a new study.

 A study of 293 women with a history of gestational diabetes or a pre-pregnancy body mass index of less than 30 kg/m2 t less than 20 weeks of gestation was done. They were divided into two groups namely intervention group which received individualized counseling on diet and physical activity and the other was control group which received only standard ante-natal care.

Gestational weight gain was lower in the intervention group.Women in the intervention group also increased their leisure time physical activity more and improved their dietary quality compared to women in the control group.

"A simple and individualized lifestyle intervention reduced the incidence of gestational diabetes by 39 percent in high-risk pregnant women," said one of the researchers Saila Koivusalo from Helsinki University Hospital in Finland

"[Gestational diabetes] is a well-known risk factor for later type 2 diabetes, and prevention of [gestational diabetes] may have positive consequences for the mother in her later life but also for the offspring through the intrauteric programming process,"  said Koivusalo.

"It would be very interesting to focus more on factors within the different subgroups in order to identify the women who benefited most from the intervention. Focusing upon different ethnic groups is of major importance. The long-term consequences of the given prevention on both the women's and children's later health is another important topic." said Koivusalo.

 Source:The findings was published in the Journal Diabetes Care. 
 

Highly Efficient Water Purification Technique Developed By Indian-American Scientist

A self-assembling synthetic membrane that may aid in better gas separation, water purification, drug delivery and DNA recognition has been developed by an Indian American researcher.

 This membrane is composed of lipids, fat molecules, and protein-appended molecules that form water channels that transfer water at the rate of natural membranes, and self-assembles into two-dimensional structures with parallel channels. 

"Nature does things very efficiently and transport proteins are amazing machines present in biological membranes. They have functions that are hard to replicate in synthetic systems," said Manish Kumar, assistant professor of chemical engineering at Pennsylvania State University. 

The most obvious use of the technology is to make highly efficient water purification membranes, Kumar added. 

The researchers developed a second-generation synthetic water channel that improves on earlier attempts to mimic aquaporins - natural water channel proteins -- by being more stable and easier to manufacture. 

"We were surprised to see transport rates approaching the 'holy grail' number of a billion water molecules per channel per second," noted Kumar. 

The team also found that these artificial channels like to associate with each other in a membrane to make 2D arrays with a very high pore density. The researchers consider that these membranes are much better than the first-generation artificial water channels reported to date. 

The results were outlined in the journal Proceedings of the National Academy of Science.

Source: IANS
 

Single Dose Of Concentrated Extract Of Spinach Can Curb Food Craving In Men

A new study says that a compound found in spinach, thylakoids, can slow down fat digestion, leading to reduced hunger and food craving especially in men. A concentrated extract of thylakoids encourage the release of satiety hormones, which is very beneficial in controlling hunger.

 "The reduction in hunger and the desire for salty food that we saw might make thylakoids particularly useful for people with high blood pressure and associated weight problems," said study co-author Frank. L. Greenway from the Pennington Biomedical Research Center in Louisiana. 

The researchers examined the effect of consuming a single dose of concentrated extract of thylakoids from spinach on satiety, food intake, lipids, and glucose compared to a placebo. Sixty people (30 men and 30 women) classified as overweight or obese consumed either the spinach extract or a placebo in random order at least a week apart. 

The results showed that the spinach extract containing thylakoids increased satiety over a two-hour period compared to a placebo. There were no differences in plasma lipids and energy intake at dinner but men showed a trend toward decreased energy intake. 

"Thylakoid consumption may influence gender-specific food craving," the authors said. A previous study had found that in women, a reduced urge for sweets was significant after a single dose of the spinach extract and the reduced urge for sweets was sustained throughout the study. 

The article was published in the Journal of the American College of Nutrition.

Source: IANS