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Archive for category: E-News

E-News

The Heart-Brain Connection: The link between LQTS and seizures

, 26 August 2020/in E-News /by 3wmedia

Researchers at the University of Rochester Medical Center recently discovered a genetic link between Long QT Syndrome (LQTS), a rare cardiac rhythm disease, and an increased risk for seizures. The study also found that people with LQTS who experience seizures are at greater risk of sudden cardiac death.

According to research, there is a clear association between the heart and the brain of LQTS patients. Patients carrying LQTS genetic mutations were three times more likely to have experienced seizures in their past, compared to their family members who did not carry those mutations. Interestingly, LQTS patients who had a history of seizures also tended to have worse cardiac symptoms.

David Auerbach, Ph.D., senior instructor of Medicine in the Aab Cardiovascular Research Institute of the University of Rochester Medical Center, and lead author of the study found seizure status to be the strongest predictor of cardiac arrhythmias – the abnormal heart rhythms characteristic of LQTS. In fact, about 20% of the LQTS patients in the study who had a history of seizures had survived at least one lethal cardiac arrhythmia. 

You could begin applying these findings to patients today by telling physicians treating LQTS patients to look outside the heart.
Auerbach’s study set a new clinical precedence for the link between seizures and LQTS and provides a case for doctors to pay more attention to what is happening in LQTS patients’ brains or, more broadly, to “look outside the classic organ of interest” in any disease.

As a postdoctoral fellow, Auerbach studied the heart-brain connection in a severe genetic form of epilepsy, and found that cardiac arrhythmias were one cause of sudden unexplained death in people with epilepsy. Now, he investigates the converse – whether a genetic heart disorder is also associated with issues in the brain. 

Auerbach tapped into the Rochester-based LQTS Patient Registry to answer this question. This unique resource was developed 40 years ago by the senior author of the study, Arthur Moss, M.D., the Bradford C. Berk, MD, PhD, Distinguished Professor of Medicine at URMC. The registry contains information about more than 18,000 people including LQTS patients and their affected and unaffected family members, who provide a nearly ideal group of controls. “In essence, they have the same genetic makeup, except theoretically, the LQTS-causing mutation,” says Auerbach.

To ensure that the seizures reported in the registry were not merely misdiagnosed cardiac arrhythmias, Auerbach investigated the effect of beta blockers, drugs often prescribed to LQTS patients to prevent cardiac arrhythmias. While the drugs effectively reduced patients’ arrhythmias, they had no effect on seizures, minimizing the chance that the seizures were simply misdiagnosed cardiac side effects.

Looking at the patients’ genetic information, Auerbach and his colleagues found that patients with the three different types of LQTS (LQTS1-3) showed similar heart rhythm symptoms, but vastly different prevalence of seizures. LQTS1 and LQTS2 patients had much higher prevalence of seizures than LQTS3 or no mutation – with LQTS2 at the greatest risk.

Further investigation of the LQTS-causing mutation showed that the specific location of the mutation greatly affected the risk of cardiac arrhythmias and seizures.  In one location on the gene, the mutation protected against these symptoms, but in another location on the same gene, the mutation increased the risk of those symptoms. Understanding what each of these mutations does may shed new light on a basic mechanism of seizures and may provide viable therapeutic targets to treat LQTS.

The University of Rochester Medical Center www.urmc.rochester.edu/news/story/4612/the-heart-brain-connection-the-link-between-lqts-and-seizures.aspx

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A key gene in the development of coeliac disease has been found in ‘junk’ DNA

, 26 August 2020/in E-News /by 3wmedia

Coeliac disease is a chronic, immunological disease that is manifested as intolerance to gluten proteins present in wheat, rye and barley. This intolerance leads to an inflammatory reaction in the small intestine that hampers the absorption of nutrients. The only treatment is a strict, life-long, gluten-free diet.

It has been known for some time that coeliac disease develops in people who have a genetic susceptibility, but despite the fact that 40% of the population carry the most decisive risk factor (the HLA-DQ2 and DQ8 polymorphisms), only 1% go on to develop the disease. ‘What we have here is a complex genetic disease in which many polymorphisms play a role, each making a very small contribution to its development,’ explained the UPV/EHU researcher Ainara Castellanos, who has led the work published in Science.

One of the added risk factors is to be found, according to this research, in the so-called ‘junk’ DNA, in other words, in 95% of the DNA. It is the least-known part because, unlike the remaining 5%, it is not involved in synthesising proteins. Nevertheless, light is gradually being shed on its role in the control of the overall functioning of the genome, in other words, it regulates important processes in our organism such as immune response and that is where it might be possible to find the causes of auto-immune diseases such as coeliac disease.

A key gene in the regulating of the inflammatory response observed in coeliac patients has been found in one of the regions of the junk genome: it is the 1nc13. The ribonucleic acid produced by this gene belongs to the family of long, non-coding RNAs or lncRNA and is responsible for maintaining the normal levels of expression of pro-inflammatory genes. In coeliacs, this non-coding RNA is hardly produced at all so the levels of these inflammatory genes are not properly regulated and their expression is increased. But besides being produced in low quantities, the 1nc13 produced by coeliac patients has a variant that alters the way it functions. ‘That way an inflammatory environment is created and the development of the disease is encouraged,’ said Ainara Castellanos.

‘This study confirms the importance of the regions of the genome previously regarded as ‘junk’ in the development of common complaints such as coeliac disease and opens up the door to a new possibility for diagnosis. Right now, we are interested in finding out whether the low levels of this RNA are an early feature of coeliac disease (and of other immune diseases), which could be used as a diagnostic tool before its onset,’ explained the UPV/EHU’s lecturer in Genetics José Ramón Bilbao, another of the authors of the work. University of the Basque Country

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Clues to altered brain wiring in autism

, 26 August 2020/in E-News /by 3wmedia

Autism is an agonizing puzzle, a complex mixture of genetic and environmental factors. One piece of this puzzle that has emerged in recent years is a biochemical cascade called the mTOR pathway that regulates growth in the developing brain. A mutation in one of the genes that controls this pathway, PTEN (also known as phosphatase and tensin homolog), can cause a particular form of autism called macrocephaly/autism syndrome.

Using an animal model of this syndrome, scientists from the Florida campus of The Scripps Research Institute (TSRI) have discovered that mutations in PTEN affect the assembly of connections between two brain areas important for the processing of social cues: the prefrontal cortex, an area of the brain associated with complex cognitive processes such as moderating social behavior, and the amygdala, which plays a role in emotional processing.

 “When PTEN is mutated, we find that neurons that project from the prefrontal cortex to the amygdala are overgrown and make more synapses,” said TSRI Associate Professor Damon Page. “In this case, more synapses are not necessary a good thing because this contributes to abnormal activity in the amygdala and deficits in social behavior.”

The study also showed that targeting the activity of the mTOR pathway shortly after birth, a time when neurons are forming connections between these brain areas, can block the emergence of abnormal amygdala activity and social behavioral deficits. Likewise, reducing activity neurons that project between these areas in adulthood can also reverse these symptoms.

‘Given that the functional connectivity between the prefrontal cortex and amygdala is largely conserved between mice and humans,” said TSRI Graduate Student Wen-Chin Huang, the first author of the study, “we anticipate the therapeutic strategies suggested here may be relevant for individuals on the autism spectrum.”

Although caution is warranted in extrapolating findings from animal models to humans, these findings have implications for individualized approaches to treating autism. “Even within individuals exposed to the same risk factor, different strategies may be appropriate to treat the symptoms of autism in early development versus maturity,” said Page.

The Scripps Research Institute www.scripps.edu/news/press/2016/20161115page.html

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Discovery of a novel gene for hereditary colon cancer

, 26 August 2020/in E-News /by 3wmedia

The formation of large numbers of polyps in the colon has a high probability of developing into colon cancer, if left untreated. The large-scale appearance of polyps is often due to a hereditary cause; in this case the disease can occur in multiple family members. Under the leadership of human geneticists of the University Hospital Bonn, a team of researchers discovered genetic changes in the MSH3 gene in patients and identified a new rare form of hereditary colon cancer.

Colon polyps form like mushroom-shaped growths from the mucosa and are several millimetres to several centimetres in size. They are benign and generally do not cause any symptoms – however, they can turn into malignant tumours (colon cancer). Physicians refer to the development of a large number of polyps in the colon as ‘polyposis.’ Scientists have already discovered several genes associated with a polyposis. ‘However, about one-third of families affected by the disease do not have any abnormalities in these genes,’ says Prof. Dr. Stefan Aretz, head of the working group at the Institute of Human Genetics at the University of Bonn Hospital. Therefore, there would have to be even more genes involved in the formation of polyps in the colon.

Together with pathologists from the University Hospital Bonn, scientists from the Yale University School of Medicine in New Haven (USA), and the Frankfurt University Hospital, the team working with Prof. Aretz investigated the genetic material (DNA) of more than 100 polyposis patients using blood samples. In each patient, all of the about 20,000 protein-coding genes known were simultaneously examined. In this process, the scientists filtered the rare, possibly relevant genetic changes out of the gigantic quantity of data, like the proverbial needle in a haystack. In two patients, genetic changes (mutations) were discovered in the MSH3 gene on chromosome 5.

Proof of causes is like a trial based on circumstantial evidence

‘The challenge is proving the causal connection between the mutations in this gene and the disease,’ says Prof. Aretz. The process is similar to that of a trial based on circumstantial evidence. Family members also play a role here: The siblings with the disease have to have these same MSH3 mutations as the patient who was first examined, but not the healthy relatives. That was the case. In addition, the scientists investigated the consequences for patients resulting from the loss of function of the MSH3 gene. ‘It involves a gene for the repair of the genetic material,’ reports Dr. Ronja Adam, one of the two lead authors from Prof. Aretz’s team. ‘The mutations cause the MSH3 protein to not be formed.’ Since the protein is missing in the cell nucleus of the patient´s tissues, there is an accumulation of genetic defects. The mutations which are not repaired then predispose to the more frequent occurrence of polyps in the colon.

The newly discovered type of polyposis, in contrast to many other forms of hereditary colon cancer, is not inherited dominantly, but instead recessively. ‘This means that siblings have a 25 percent chance of developing the disease; however, the parents and children of affected persons only have a very low risk of developing the disease,’ explains Dr. Isabel Spier from the Institute of Human Genetics, who was also very involved in the study.

The annual colonoscopy is the most effective cancer screening method for polyposis patients. As a result, the development of colon cancer can be effectively prevented. By investigating the MSH3 gene, a clear diagnosis can be made prospectively in some other, previously unexplained polyposis cases. Afterwards, healthy persons at risk in the family can be tested for the mutations. ‘Only proven carriers would need to take part in the intensive surveillance program,’ says the human geneticist. In addition, science would gain new insights into the development and biological foundations of tumours through the identification of mutations in the MSH3 gene. Prof. Aretz: ‘The knowledge about molecular mechanisms which lead to cancer is also a precondition for the development of new targeted drugs.’

University of Bonn www.uni-bonn.de/Press-releases/discovery-of-a-novel-gene-for-hereditary-colon-cancer

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Changes in benign tissue next to prostate tumours may predict biomedical recurrence of cancer

, 26 August 2020/in E-News /by 3wmedia

Changes in benign tissues next to prostate tumours may provide an early warning for patients at higher risk for biochemical recurrence after a radical prostatectomy, a study by researchers at Case Western Reserve University and Johns Hopkins Medical Institutions shows.

Biochemical recurrence, which is increasing prostate-specific antigen (PSA) levels, can be used to predict which prostate cancer patients will develop local recurrence, distant metastases and death.
In a small sampling, image analysis of the adjacent tissue was a better predictor than the current standard for prognosis following the prostatectomy.
If preliminary findings are confirmed by further studies, they may help doctors decide sooner which patients need more follow-up therapies after surgery or should return for more regular monitoring.
“In a sense, this study is validating what a lot of people think regarding these cancers—that there is a field effect, as if the tumour has hard-to-see tentacles that can affect the patient and outcomes,” said Anant Madabhushi, the F. Alex Nason professor II of biomedical engineering at Case Western Reserve and leader of the research.

Madabhushi worked with Case Western Reserve’s George Lee, a research assistant professor, and Sahirzeeshan Ali, a PhD student, and Johns Hopkins Medical Institutions’ Robert W. Veltri, associate professor of urology, and Jonathan I. Epstein, the Reinhard Professor of Urologic Pathology. Their study is published in the journal European Urology Focus.

The researchers analyzed records from 70 patients who underwent radical prostatectomies from 2000 to 2004 with up to 14 years follow-up. They digitized images of the resected prostate specimens and analysed the tumour regions and surrounding tissue that appeared to be benign.
Of the group studied, 22 suffered from biochemical recurrence, metastasis or died.

The scientists used computers to search for and identify image features that may be undetectable with the human eye, but which may correlate with a biochemical recurrence. They used the top 10 features to develop a risk score.

They were surprised to find that nuclear shape and architecture in the benign-looking tissue were greater predictors of recurrence than features found in the tumour, Madabhushi said. “Its an amazing finding, completely unexpected.”
Among the risk calculators used to assess prostate cancer recurrence is a nomogram of variables known to influence recurrence, and a Gleason score, which is based on the cancer tissue pattern compared to normal tissue.
“We were able to do better than nomograms and the Gleason score,” Madabhushi said.
But by combining the benign-field features with tumour features extracted from patient’s pathology images and Gleason scoring, they were able to further improve the prediction of recurrence.

Case Western Reserve University blog.case.edu/think/2016/07/06/changes_in_benign_tissue_next_to_prostate_tumours_may_predict_biomedical_recurrence_of_cancer_scientists_find

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Activation of 2 genes linked to development of atherosclerosis

, 26 August 2020/in E-News /by 3wmedia

Researchers at Brigham and Women’s Hospital have found two new potential drug targets for treating arterial diseases such as atherosclerosis. By using proteomics to screen a vast number of molecules, the researchers identified PARP9 and PARP14 – two members of the PARP family of proteins – as regulators of macrophage activation, which has been linked to arterial disease by systems biology.

Though the mechanisms that activate macrophages, a type of digestive white blood cell that targets foreign cells, remain incompletely understood, previous research shows that macrophages play an important role in the development of atherosclerosis and its thrombotic complications. Masanori Aikawa, MD, PhD, director of the Center for Interdisciplinary Cardiovascular Sciences (CICS) at the Brigham, his research fellow Hiroshi Iwata, MD, PhD, and colleagues studied atherosclerosis on the protein-level to determine which molecules were most involved in the regulation of macrophages.

Once Aikawa and his colleagues narrowed down their search to these two proteins, they silenced each gene in cultured macrophages and found that tamping down PARP14 increased macrophage activation while tamping down PARP9 had the opposite effect.

Aikawa founded CICS and hopes that this hypothesis-generating method can be used to streamline the lengthy process of drug development. Aikawa and CICS are using a more systematic approach which hinges on network analysis; this analysis predicts which pathways are most likely to control their studied effect so that they can prioritize these pathways. Ideally, this process would take a fraction of the time in comparison to searching through each individual pathway unaware of their likelihood of affecting their studied effect.

Aikawa and his colleagues plan to augment these findings to develop targeted therapeutics for atherosclerosis and other diseases.

‘Macrophage activation plays a role in not only vascular disorders but also various inflammatory and autoimmune diseases,’ said Aikawa. ‘These results could provide important information about the mechanisms of these diseases and help to develop much needed new therapeutics.’

EurekAlert www.eurekalert.org/pub_releases/2016-10/bawh-aot102516.php

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Correcting metabolic deficiencies may improve depression symptoms

, 26 August 2020/in E-News /by 3wmedia

Identifying and treating metabolic deficiencies in patients with treatment-resistant depression can improve symptoms and in some cases even lead to remission, according to new research from the University of Pittsburgh School of Medicine.

“What’s really promising about these new findings is that they indicate that there may be physiological mechanisms underlying depression that we can use to improve the quality of life in patients with this disabling illness,” said David Lewis, M.D., Thomas Detre Professor and Chair of Pitt’s Department of Psychiatry.

Major depressive disorder, also referred to simply as depression, affects nearly 15 million American adults and is one of the most common mental disorders. Unfortunately, at least 15 percent of patients don’t find relief from conventional treatments such as antidepressant medications and psychotherapy, explained lead study investigator Lisa Pan, M.D., professor of psychiatry, and clinical and translational science, Pitt School of Medicine. Depression also is the cause of more than two-thirds of suicides that occur annually.

The groundwork for the current study was laid five years ago when Dr. Pan and David Brent, M.D., Endowed Chair in suicide studies at Pitt, treated a teen with a history of suicide attempts and long-standing depression. “Over a period of years, we tried every treatment available to help this patient, and yet he still found no relief from his depression symptoms,” she explained.

Searching for answers, Dr. Pan contacted Jerry Vockley, M.D., Ph.D., chair of genetics, Children’s Hospital of Pittsburgh of UPMC, and David Finegold, M.D., professor of human genetics at Pitt’s Graduate School of Public Health, and through a series of biochemical tests, the three discovered that the patient had a cerebrospinal fluid deficiency in biopterin, a protein involved in the synthesis of several brain signalling chemicals called neurotransmitters.

After receiving an analogue of biopterin to correct the deficiency, the patient’s depression symptoms largely disappeared and today he is a thriving college student.

The success prompted the researchers to examine other young adults with depression who were not responding to treatment, explained Dr. Pan.

In the published trial, the researchers looked for metabolic abnormalities in 33 adolescents and young adults with treatment-resistant depression and 16 controls. Although the specific metabolites affected differed among patients, the researchers found that 64 percent of the patients had a deficiency in neurotransmitter metabolism, compared with none of the controls.

In almost all of these patients, treating the underlying deficiency improved their depression symptoms, and some patients even experienced complete remission. In addition, the further along the patients progress in the treatment, the better they are getting, Dr. Pan added.

University of Pittsburgh School of Medicine www.upmc.com/media/NewsReleases/2016/Pages/l-pan.aspx

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Genes that control smooth muscle contraction in digestive system identified

, 26 August 2020/in E-News /by 3wmedia

Researchers at UMass Medical School have identified a new molecular pathway critical for maintaining the smooth muscle tone that allows the passage of materials through the digestive system. This finding, based on studying calcium ion-controlled pathways in mice, may lead to new treatments for a host of digestive disorders ranging from common gastroesophageal reflux disease (GERD), to swallowing disorders, incontinence and pancreatitis.
“We are excited about the potential to target identified genes to treat disorders such as reflux and incontinence,” said Ronghua ZhuGe, PhD, associate professor of microbiology and physiological systems and a senior author of the study. “Knowing how these muscles stay contracted for such long periods of time will allow us to develop potential new treatments for these diseases. The next step is to see whether this molecular mechanism in mice also operates in humans.”

The human body, and those of other mammals, contains a number of ring-shaped structures made of smooth muscle encircling openings in hollow organs such as the intestines and bladder called sphincters. Smooth muscle is involuntarily controlled, unlike the muscles we use to walk, for example, so that we don’t need to consciously move digested food from stomach to small intestine. Dysfunction in the sphincters, either structurally or functionally, can have severe consequences leading to diseases that impair the ability of the muscle to contract or relax. This can lead to achalasia, which makes it difficult to swallow; gastroesophageal reflux disease (GERD), which allows stomach acid to enter the oesophagus or incontinence of the bowels.

“A healthy sphincter opens transiently but remains closed most of the time, maintaining a basal tone. This basal tone requires constant generation of force produced by the contraction of smooth muscle cells that make up the sphincters,” said Dr. ZhuGe. “However, the genetics governing how the sphincter smooth muscle stays contracted for such long periods of time remains unknown.”

Smooth muscle operates by generating force as the muscle motor protein myosin and actin filaments move past each other. This happens after a molecule called the myosin regulatory light chain (MLC) is turned on through a common molecular transformation called phosphorylation. How much phosphorylation takes place is controlled by the relative amounts of two enzymes; calcium dependent MLC kinase (MLCK), which promotes phosphorylation, and calcium independent MLC phosphatase (MLCP), which reverses phosphorylation. Through this process, contraction and relaxation of the muscle is achieved.

To understand the molecular mechanism responsible for the involuntary and continuous contraction of the sphincter muscle, Dr. ZhuGe and colleagues examined the internal anal sphincter that controls bowel continence in mice. They showed that genetic deletion of the MLCP enzyme in the smooth muscle had no effect on the basal tone of the mouse sphincter, but deletion of MLCK essentially abolishes the basal tone and mice become incontinent as a result.

“Although previous biochemical studies suggested that lower MLCP activity may be related to the basal tone of this sphincter, our genetic study indicates this doesn’t seem to be the case. It turns out MLCK is essential for the tone formation,” said ZhuGe. “This prompted us to look for specific calcium signals that regulate MLCK.”

Co-author Lawrence Lifshitz, PhD, associate professor of molecular medicine, said, “Calcium signalling is our favourite subject. We originally hypothesized that localized releases of calcium inside the cell, near target ion channels, might do the trick, as we knew that such releases can regulate the contraction of smooth muscle in blood vessels and airways.”

But experiments showed that these local calcium releases have no direct role in muscle tone. Instead, three types of ion channels act in concert to generate a rise in cytosolic calcium which eventually results in MLCK activation and muscle tone.

To test this hypothesis, ZhuGe’s group teamed up with Minsheng Zhu, PhD, at Nanjing University in China, to generate a line of mice in which one of these channels could be turned off in smooth muscle only. “These mice were a powerful tool for establishing our hypothesis,” said ZhuGe. “They helped us identify the Tmem16a (also called Ano1) gene as a critical component for basal tone formation and fecal continence. When we were able to turn off the TMEM16A channels in these mice, they lost the majority of the basal tone and became incontinent. ”

UMass Medical School www.umassmed.edu/news/news-archives/2016/04/umms-scientists-identify-genes-that-control-smooth-muscle-contraction-in-digestive-system/

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Culprit found in breast cancer resistance to tamoxifen

, 26 August 2020/in E-News /by 3wmedia

Researchers have discovered that a protein found naturally in cells that provides some protection from viruses is responsible for creating mutations that drive resistance to tamoxifen treatment in breast cancer. Because the protein, known as APOBEC3B, is found in elevated quantities in other kinds of cancer cells, the finding explains differential responses to treatment and opens the door to boosting the effectiveness of tamoxifen and related breast cancer therapies that inhibit the ability of oestrogen to stimulate tumour growth.

As they report, University of Minnesota Professor and Howard Hughes Medical Institute Investigator Reuben Harris, Ph.D., Professor of Medicine and Masonic Cancer Center Director Douglas Yee, M.D., and colleagues analysed primary breast cancers from human patients along with studies of human breast cancer cell lines growing in mice to elucidate the relationship between presence of APOBEC3B and development of tamoxifen resistance. They found that 1) the more APOBEC3B a breast cancer contained, the less benefit patients received from tamoxifen for treatment of their recurrent disease; 2) depletion of APOBEC3B in a cancer cell line results in delayed development of tamoxifen resistance; and 3) increased production of active APOBEC3B by a cancer cell line accelerates development of resistance.

Previous studies had linked higher concentrations of the protein APOBEC3B with increased levels of mutation and poorer outcomes for patients with breast cancer, but a causal connection had not been established between this enzyme and the development of therapy resistance. By using both clinical data and mouse models, Harris, Yee and colleagues were able to show that APOBEC3B is responsible for the reduced response to tamoxifen therapy in breast cancer.

The findings open a new door for improving the effectiveness of tamoxifen in treating breast cancer by discovering ways to prevent APOBEC3B from mutating the cancer cell’s DNA. Because APOBEC3B has been implicated as a major cause of mutations in bladder, lung and other cancer types, the results could potentially be applied to boosting the success of therapies against other tumours as well.

“It’s not just breast cancer,” Yee said. “In treatment of all metastatic cancer, patients will eventually develop resistance and progress. What are the mechanisms of resistance? [APOBEC3B] is proving to be a major driver of resistance and something we’re continuing to actively investigate.”

The big challenge now is to try to identify exactly how APOBEC3B alters a cell’s DNA to induce tamoxifen resistance. “We know how it mutates DNA, but we don’t know exactly which genes are mutated to confer tamoxifen resistance,” Harris said. “If it turns out APOBEC3B mutates a known pathway, such a result may point to additional therapies.”

University of Minnesota twin-cities.umn.edu/news-events/culprit-found-breast-cancer-resistance-tamoxifen

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Similarities unite three distinct gene mutations of Treacher Collins Syndrome

, 26 August 2020/in E-News /by 3wmedia

Scientists at the Stowers Institute for Medical Research have reported a detailed description of how function-impairing mutations in polr1c and polr1d genes cause Treacher Collins syndrome (TCS), a rare congenital craniofacial development disorder that affects an estimated 1 in 50,000 live births.
Collectively the results of the study reveal that a unifying cellular and biochemical mechanism underlies the etiology and pathogenesis of TCS and its possible prevention, irrespective of the causative gene mutation.

Loss-of-function mutations in three human genes, TCOF1, POLR1C and POLR1D, have been implicated in TCS and are thought to be responsible for about 90 percent of the diagnoses of this congenital craniofacial condition.
The clinical manifestations of TCS include facial anomalies such as small jaws and cleft palate, hearing loss, and respiratory problems. Patients with TCS typically undergo multiple surgeries, but rarely are they fully corrective. By uncovering a mechanism of action common to all three genes, Stowers scientists have advanced scientific understanding of TCS etiology and pathogenesis and identified possible new avenues for preventing or treating the birth defect. This latest study from the laboratory of Stowers Investigator Paul Trainor, Ph.D., focused on Polr1c and Polr1d, whose roles as a genetic cause of TCS were revealed in a 2011 study of a small group of patients who had been diagnosed with TCS but who did not have the TCOF1 mutation. Unlike POLR1C and POLR1D, TCOF1 has been long recognized as a causative gene in TCS and as a result has been more extensively investigated.
“Before we began the study, nothing was known about the role of Polr1c and Polr1d in craniofacial development,” said Kristin Watt, Ph.D., lead author of the PLoS Genetics paper and postdoctoral scientist in the Trainor Lab. “Using zebrafish as our animal model, we set out to explore the functional roles of polr1c and polr1d during embryogenesis and more specifically in craniofacial development.”
Trainor, Watt and their collaborators compared the results of their findings on polr1c and polr1d with their and other labs’ previous research results on Tcof1. In all three loss-of-function models, the researchers found that the chain of cellular events that led to the TCS phenotype of abnormal craniofacial development originated in ribosomes, the cellular components that translate messenger RNA into proteins. Like the Tcof1 gene, polr1c and polr1d mutations were found to perturb ribosome biogenesis, or production of ribosomes, which affects the generation and survival of progenitor neural crest cells, the precursors of craniofacial bone, cartilage and connective tissue.
In animal models of all three causative genes, the scientists determined that deficient ribosome biogenesis triggered a p53-dependent cell death mechanism in progenitor neural crest cells. As a result of the activation of the p53 gene, developing embryos no longer made the quantity of neural crest cells needed to properly form the craniofacial skeleton.
However, in the polr1c and polr1d models as in the Tcof1 models, Stowers scientists found that by experimentally blocking p53 activation, they could restore the neural crest cell population and thereby rescue the animal models’ cranioskeletal cartilage.
Despite the rescue effect, Trainor said that he does not view the “guardian of the genome,” as the p53 gene is often called due to its ability to suppress cancer, as the basis of a potential therapy to prevent or reduce TCS during embryonic development. The p53 gene’s association with cancer makes inhibiting its function too risky, he said.
A less risky and perhaps more effective target for the prevention or treatment of TCS could be enhancing ribosomes, Trainor said, because the loss-of-function mutations in all three causative genes involve ribosome RNA (rRNA) transcription. Polr1c and Polr1d, for example, are subunits of RNA polymerases I and III that are essential for ribosome biogenesis.
“Rather than blocking p53, a better approach may be to try to prevent TCS by treating the problem in ribosome biogenesis that triggers the activation of p53 and the loss of neural crest cells,” said Trainor.
In their research with zebrafish embryos, Trainor and collaborators also determined that polr1c and polr1d are spatiotemporally and dynamically expressed, particularly during craniofacial development. Furthermore, zebrafish embryos with the polr1c and polr1d loss-of-function mutations develop abnormalities in craniofacial cartilage development that mimic the clinical manifestations of TCS in patients. Trainor said that he and his fellow researchers were surprised that mutations in polr1c and polr1d as well as Tcof1 specifically affected craniofacial development, because ribosome biogenesis occurs in every cell of the body. The mutation of a gene that is part of the ribosome complex would be expected to be detrimental to each of these cells, he said. However, in the zebrafish models, the mutation appears to primarily affect progenitor neural crest cells. Trainor said that he and his team theorize that progenitor neural crest cells may be particularly sensitive to deficiencies in ribosome biogenesis during embryogenesis.
Thus, the study revealed new animal models for TCS: zebrafish with polr1c and polr1d loss-of-function mutations. Moreover, the existence of a common mechanism of action may simplify the research, particularly the search for a therapy to prevent or treat TCS. Because of the similarities among the three causative genes, “we may be able to develop creative ways of preventing TCS that will prove effective in at-risk individuals who have one of the gene mutations,” said Trainor, who has investigated the molecular origins and development of TCS and related craniofacial developmental disorders for 10 years.

Stowers Institute for Medical Research www.stowers.org/media/news/jul-22-2016

https://clinlabint.com/wp-content/uploads/sites/2/2020/06/clinlab-logo.png 0 0 3wmedia https://clinlabint.com/wp-content/uploads/sites/2/2020/06/clinlab-logo.png 3wmedia2020-08-26 09:33:212021-01-08 11:10:03Similarities unite three distinct gene mutations of Treacher Collins Syndrome
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