Mitochondrial Protein in Cardiac Muscle Cells Linked to Heart Failure, Study Finds

Reducing a protein found in the mitochondria of cardiac muscle cells initiates cardiac dysfunction and heart failure, a finding that could provide insight for new treatments for cardiovascular diseases, a study led by Georgia State University has shown.

The researchers discovered that reducing an outer mitochondrial membrane protein, FUN14 domain containing 1 (FUNDC1), in cardiac muscle cells, also known as cardiomyocytes, activates and worsens cardiac dysfunction. Also, disrupting how FUNDC1 binds to a particular receptor inhibited the release of calcium from another cell structure, the endoplasmic reticulum (ER), into the mitochondria of these cells and resulted in mitochondrial dysfunction, cardiac dysfunction and heart failure. The findings are published in the journal Circulation.

Mitochondria play numerous roles in the body, including energy production, reactive oxygen species generation and signal transduction. Because the myocardium, the muscular wall of the heart, is a high-energy-demand tissue, mitochondria play a central role in maintaining optimal cardiac performance. Growing evidence suggests deregulated mitochondrial activity plays a causative role in cardiovascular diseases.

In the body, mitochondria and ER are interconnected and form their own endomembrane networks. The points where mitochondria and ER make physical contact and communicate are known as mitochondria-associated ER membranes (MAMs). MAMs play a major role in regulating the transfer of calcium between ER and mitochondria. Dysfunctional MAMs are involved in several neuronal disorders, including Alzheimer’s disease and Parkinson’s disease. Until now, the role of MAMs in cardiac pathologies has not been well understood.

“Our study found the formation of MAMs mediated by the mitochondrial membrane protein FUNDC1 was significantly suppressed in patients with heart failure, which provides evidence that FUNDC1 and MAMs actively participate in the development of heart failure,” said Dr. Ming-Hui Zou, director of the Center for Molecular and Translational Medicine at Georgia State and a Georgia Research Alliance Eminent Scholar in Molecular Medicine. “This work has important clinical implications and provides support that restoring proper function of MAMs may be a novel target for treating heart failure.”

The researchers used mouse neonatal cardiomyocytes, mice with a genetic deletion of the FUNDC1 gene, control mice with no genetic deficiencies and the cardiac tissues of patients with heart failure.

The cardiac functions of the mice were monitored using echocardiography at 10 weeks of age. Mice with the genetic deletion of FUNDC1 had markedly reduced ventricular filling velocities, prolonged left ventricular isovolumic relaxation time, diastolic dysfunction, decreased cardiac output (which indicates impaired systolic functions) and interstitial fibrosis of the myocardium, among other issues. The mitochondria in the hearts of mice with FUNDC1 gene deletion were larger and more elongated, a 2.5-fold increase of size compared to mitochondria in the control mice.

To determine if FUNDC1 reduction occurred in human hearts and contributed to heart failure in patients, the researchers examined four heart specimens from heart failure patients and four heart specimens from control donors. They found the levels of FUNDC1 were significantly reduced in patients with heart failure compared to control donors. Also, the contact between ER and mitochondria in failed hearts was significantly reduced. In addition, the mitochondria in heart failure hearts were more elongated compared to those in control donors.

Cancer-cardiac connection illuminates promising new drug for heart failure

A team of researchers at the Gladstone Institutes uncovered a new strategy to treat heart failure, a leading contributor to mortality and healthcare costs in the United States. Despite widespread use of currently-approved drugs, approximately 40% of patients with heart failure die within 5 years of their initial diagnosis.

“The current standard of care is clearly not sufficient, which highlights the urgent need for new therapeutic approaches,” said Saptarsi Haldar, MD, an associate investigator at Gladstone and senior author of a new study featured on the cover of the scientific journal Science Translational Medicine. “In our previous work, we found that a drug-like small molecule called JQ1 can prevent the development of heart failure in mouse models when administered at the very onset of the disease. However, as the majority of patients requiring treatment already have longstanding cardiac dysfunction, we needed to determine if our strategy could also treat established heart failure.”

As part of an emerging treatment strategy, drugs derived from JQ1 are currently under study in early-phase human cancer trials. These drugs act by inhibiting a protein called BRD4, a member of a family of proteins called BET bromodomains, which directly influences heart failure. With this study, the scientists found that JQ1 can effectively treat severe, pre-established heart failure in both small animal and human cell models by blocking inflammation and fibrosis (scarring of the heart tissue).

“It has long been known that inflammation and fibrosis are key conspirators in the development of heart failure, but targeting these processes with drugs has remained a significant challenge,” added Haldar, who is also a practicing cardiologist and an associate professor in the Department of Medicine at the University of California, San Francisco. “By inhibiting the function of the protein BRD4, an approach that simultaneously blocks both of these processes, we are using a new and different strategy altogether to tackle the problem.”

Currently available drugs used for heart failure work at the surface of heart cells. In contrast, Haldar’s approach goes to the root of the problem and blocks destructive processes in the cell’s command center, or nucleus.

“We treated mouse models of heart failure with JQ1, similarly to how patients would be treated in a clinic,” said Qiming Duan, MD, PhD, postdoctoral scholar in Haldar’s lab and co-first author of the study. “We showed that this approach effectively treats pre-established heart failure that occurs both after a massive heart attack or in response to persistent high blood pressure (mechanical overload), suggesting it could be used to treat a wide array of patients.”

Using Gladstone’s unique expertise, the scientists then used induced pluripotent stem cells (iPSCs), generated from adult human skin cells, to create a type of beating heart cell known as cardiomyocytes.

“After testing the drug in mice, we wanted to check whether JQ1 would have the same effect in humans,” explained co-first author Sarah McMahon, a UCSF graduate student in Haldar’s lab. “We tested the drug on human cardiomyocytes, as they are cells that not only beat, but can also trigger the processes of inflammation and fibrosis, which in turn make heart failure progressively worse. Similar to our animal studies, we found that JQ1 was also effective in human heart cells, reaffirming the clinical relevance of our results.”

The study also showed that, in contrast to several cancer drugs that have been documented to cause cardiac toxicity, BRD4 inhibitors may be a class of anti-cancer therapeutics that has protective effects in the human heart.

“Our study demonstrates a new therapeutic approach to successfully target inflammation and fibrosis, representing a major advance in the field,” concluded Haldar. “We also believe our current work has important near-term translational impact in human heart failure. Given that drugs derived from JQ1 are already being tested in cancer clinical trials, their safety and efficacy in humans are already being defined. This key information could accelerate the development of a new heart failure drug and make it available to patients more quickly.”

Photo caption: Saptarsi Haldar (right), Qiming Duan (left) and Sarah McMahon (center) find a new strategy to treat heart failure. [Photo: Chris Goodfellow, Gladstone Institutes]

Rare Type of Immune Cell Responsible for Progression of Heart Inflammation to Heart Failure in Mice

A new study in mice reveals that eosinophils, a type of disease-fighting white blood cell, appear to be at least partly responsible for the progression of heart muscle inflammation to heart failure in mice.

In a report on the findings, published in The Journal of Experimental Medicine on March 16, researchers found that while eosinophils are not required for heart inflammation to occur, they are needed for it to progress to a condition known as inflammatory dilated cardiomyopathy (DCMi) in mice. The discovery, they say, advances information about the impact of eosinophils on heart function.

“Other studies have shown that people with high levels of eosinophils develop a number of heart diseases. This new work has provided more details about how these immune system cells may lead to deterioration of heart muscle function in mice in a way that lets us draw some parallels to human disease processes,” says Daniela Cihakova, M.D., Ph.D., associate professor of pathology at the Johns Hopkins University School of Medicine and the paper’s senior author.

Heart inflammation, or myocarditis, is rarely diagnosed because it doesn’t always cause severe symptoms and it requires a biopsy to be taken from the patient’s heart. This makes it difficult to study the outcomes of the disease. “We don’t understand why the hearts of some people will heal while those of others develop chronic disease,” says Cihakova.

Different types of myocarditis are distinguished based on the type of immune cell that predominates the inflammation of the heart. For example, in eosinophilic myocarditis, numerous eosinophils infiltrate the heart. It is not known if some types of myocarditis are more likely to progress to DCMi than others. “Our studies show that the presence of eosinophils in the heart makes mice more likely to get DCMi following myocarditis. And if there are a lot of eosinophils, the mice develop even more severe heart failure,” says Nicola Diny, a Ph.D. student in the Bloomberg School of Public Health and the study’s first author. “It will be important to test if the same is true in patients. That way, we may be able to intervene early and prevent DCMi.”

This study, says Cihakova, is the first to examine the role eosinophils play in the development and severity of heart inflammation, and the subsequent progression of inflammation to DCMi. The study addresses a National Institutes of Health-identified need for preclinical models and a clearer understanding of how eosinophils drive heart damage.

For the study, Cihakova and her team first induced myocarditis in two groups of mice: normal mice and a group of mice genetically modified to be eosinophil-deficient. Myocarditis was induced through a process called experimental autoimmune myocarditis, in which mice are immunized with a peptide from heart muscle cells to initiate an immune response against the heart. After 21 days, the researchers found similar levels of acute inflammation in the hearts of both groups by studying the hearts’ tissue. But when the team checked the mice’s hearts later on for evidence of heart failure, the differences between the eosinophil-deficient and the normal mice were striking. The normal mice developed heart failure, while the eosinophil-deficient mice showed no signs of reduced heart function.

“These surprising results told us that it is not the overall severity of inflammation but rather the types of immune cells in the heart that decide whether myocarditis develops into heart failure,” says Diny.

The researchers also examined the hearts for fibrosis, or scar tissue, which develops when mammalian (including human) heart muscles die. This type of scar tissue is also found in DCMi. Although both groups of mice had similar degrees of scar tissue, the eosinophil-deficient mice’s heart functions weren’t negatively affected, while the normal mice developed DCMi.

“This told us that in the absence of eosinophils, heart function can be preserved despite scar tissue formation,” Cihakova says. “It’s also important to note that although eosinophils accounted for just 1 to 3 percent of all heart-infiltrating cells in normal mice, this small percentage can still drive heart failure.”

In another set of experiments, the research team used genetically modified mice, called IL5Tg mice, which have an excess of the protein IL5 that causes the body to make eosinophils. The IL5Tg mice had more inflammation in the atria, or upper chambers of the heart, compared to normal mice in the acute stage and more atrial scar tissue in the chronic stage. IL5Tg mice also had more heart-infiltrating cells in general. Eosinophils accounted for more than 60 percent of heart-infiltrating cells in the IL5Tg mice’s hearts, compared to only 3 percent in normal mice. When the team examined the heart function some 45 days after the start of the experiment, the IL5Tg mice had developed severe DCMi.

To examine whether humans with eosinophil-driven myocarditis also developed inflammation in the atria, the researchers obtained heart tissue samples and cardiac MRI scans from three patients seen at The Johns Hopkins Hospital, all of whom had confirmed eosinophil-driven inflammation.

The images showed that two patients had either inflammation or scar tissue in the atria, which suggests that atrial inflammation and/or scar tissue may also be a feature in humans with eosinophil-driven inflammation, Cihakova says.

To determine whether the IL5 protein is necessary for DCMi development, the research team next examined IL5-deficient mice. The scientists found that they had both inflammation and DCMi severity similar to that of normal mice, suggesting that the IL5 protein is not necessary for DCMi to develop.

Finally, to confirm the differences between the effects of IL5 and eosinophils, the team bred the eosinophil-deficient mice to have excess IL5. Compared to normal mice, these mice showed no decrease in heart function and appeared completely protected from DCMi, which confirms that it is the eosinophils themselves, not high levels of IL5, that are responsible for DCMi development, the investigators say.

To learn more about how eosinophils might drive DCMi progression, the investigators built on the knowledge that eosinophils harbor granules, some of which can kill cells, while others change the function of cells.

“We didn’t see any differences in cell death between the normal mice and those with or without too many eosinophils, so we became interested in the molecules that can change the function of other cells,” says Diny.

In particular, one protein, called IL4, caught the researchers’ attention. Other studies had shown that IL4 made by eosinophils has diverse functions in liver repair and fat tissue. “We wondered if this protein from eosinophils may also be important in the heart,” Cihakova says.

First, the research team used a mouse in which cells that make IL4 turned fluorescent green, thereby allowing researchers to tell where IL4 is made. The team found that eosinophils accounted for the majority of IL4-producing cells. When they used mice that lacked IL4 in all cells, these mice were completely protected from DCMi, just like the eosinophil-deficient mice.

Finally, to determine whether IL4 specifically from eosinophils is necessary for DCMi development, the team used genetically modified mice with no IL4 in their eosinophils but with IL4 in other heart-infiltrating cells. These mice developed less severe DCMi compared to normal mice, which confirms that eosinophils are responsible for DCMi development through IL4.

“The take-home message is that inflammation severity doesn’t necessarily determine long-term disease progression, but specific infiltrating cell types — eosinophils, in this case — do,” says Cihakova. Because eosinophil-driven inflammation is so clinically rare, the percentage of people who develop DCMi is unknown, she notes.

While no drugs are currently available to stop or delay the development of DCMi, the researchers hope their findings will help establish a novel target for IL4-blocking medicines that might be used to treat people with myocarditis, possibly preventing disease progression and the need for heart transplantation.

Cancer Drug Could Double as a Weapon Against Heart Disease, Promoting Regeneration of Damaged Heart Tissue

An anticancer agent in development promotes regeneration of damaged heart muscle – an unexpected research finding that may help prevent congestive heart failure in the future.

Many parts of the body, such as blood cells and the lining of the gut, continuously renew throughout life. Others, such as the heart, do not. Because of the heart’s inability to repair itself, damage caused by a heart attack causes permanent scarring that frequently results in serious weakening of the heart, known as heart failure.
For years, Dr. Lawrence Lum, Associate Professor of Cell Biology at UT Southwestern Medical Center, has worked to develop a cancer drug targeting Wnt signaling molecules. These molecules are crucial for tissue regeneration, but also frequently contribute to cancer. Essential to the production of Wnt proteins in humans is the porcupine (Porcn) enzyme, so-named because fruit fly embryos lacking this gene resemble a porcupine. In testing the porcupine inhibitor researchers developed, they noted a curiosity.

“We saw many predictable adverse effects – in bone and hair, for example – but one surprise was that the number of dividing cardiomyocytes (heart muscle cells) was slightly increased,” said Dr. Lum, senior author of the paper, and a member of UTSW’s Hamon Center for Regenerative Science and Medicine. “In addition to the intense interest in porcupine inhibitors as anticancer agents, this research shows that such agents could be useful in regenerative medicine.”

Based on their initial results, the researchers induced heart attacks in mice and then treated them with a porcupine inhibitor. Their hearts’ ability to pump blood improved by nearly twofold compared to untreated animals.

The study findings were published online this week in Proceedings of the National Academy of Sciences.

“Our lab has been studying heart repair for several years, and it was striking to see that administration of a Wnt inhibitor significantly improved heart function following a heart attack in mice,” said Dr. Rhonda Bassel-Duby, Professor of Molecular Biology and Associate Director of the Hamon Center for Regenerative Science and Medicine.
Importantly, in addition to the improved pumping ability of hearts in the mice, the researchers noticed a reduction in fibrosis, or scarring in the hearts. Collagen-laden scarring that occurs following a heart attack can cause the heart to inappropriately increase in size, and lead to heart failure.

“While fibrotic responses may be immediately beneficial, they can overwhelm the ability of the heart to regenerate in the long run. We think we have an agent that can temper this fibrotic response, thus improving wound healing of the heart,” said Dr. Lum, a Virginia Murchison Linthicum Scholar in Medical Research and Associate Director of Basic Research at the Harold C. Simmons Comprehensive Cancer Center.
Additionally, Dr. Lum said, preliminary experiments indicate that the porcupine inhibitor would only need to be used for a short time following a heart attack, suggesting that the unpleasant side effects typically caused by cancer drugs might be avoided.

“We hope to advance a Porcn inhibitor into clinical testing as a regenerative agent for heart disease within the next year,” Dr. Lum said.

Other UT Southwestern researchers who contributed to this work include Dr. Jesung Moon, Dr. Wei Tan, and Lorraine Morlock, research scientists; Huanyu Zhou, graduate student; Dr. Lishu Zhang, Instructor of Cell Biology; and Dr. Shanrong Zhang, research engineer. Also participating in this work were Dr. Noelle Williams, Professor of Biochemistry; Dr. James Amatruda, Associate Professor of Pediatrics, Internal Medicine, and Molecular Biology, holder of the Nearburg Family Professorship in Pediatric Oncology Research, and a Horchow Family Scholar in Pediatrics; and Dr. Eric Olson, Chairman of Molecular Biology and Director of the Hamon Center for Regenerative Science and Medicine. Dr. Olson holds the Annie and Willie Nelson Professorship in Stem Cell Research, the Pogue Distinguished Chair in Research on Cardiac Birth Defects, and the Robert A. Welch Distinguished Chair in Science.
This work was supported by grants from the Robert A. Welch Foundation, National Institutes of Health, Cancer Prevention and Research Institute of Texas, the Foundation Leducq Networks of Excellence, and an American Heart Association predoctoral fellowship.

Cancer Drug Could Double as a Weapon Against Heart Disease, Promoting Regeneration of Damaged Heart Tissue

An anticancer agent in development promotes regeneration of damaged heart muscle – an unexpected research finding that may help prevent congestive heart failure in the future.

Many parts of the body, such as blood cells and the lining of the gut, continuously renew throughout life. Others, such as the heart, do not. Because of the heart’s inability to repair itself, damage caused by a heart attack causes permanent scarring that frequently results in serious weakening of the heart, known as heart failure.
For years, Dr. Lawrence Lum, Associate Professor of Cell Biology at UT Southwestern Medical Center, has worked to develop a cancer drug targeting Wnt signaling molecules. These molecules are crucial for tissue regeneration, but also frequently contribute to cancer. Essential to the production of Wnt proteins in humans is the porcupine (Porcn) enzyme, so-named because fruit fly embryos lacking this gene resemble a porcupine. In testing the porcupine inhibitor researchers developed, they noted a curiosity.

“We saw many predictable adverse effects – in bone and hair, for example – but one surprise was that the number of dividing cardiomyocytes (heart muscle cells) was slightly increased,” said Dr. Lum, senior author of the paper, and a member of UTSW’s Hamon Center for Regenerative Science and Medicine. “In addition to the intense interest in porcupine inhibitors as anticancer agents, this research shows that such agents could be useful in regenerative medicine.”

Based on their initial results, the researchers induced heart attacks in mice and then treated them with a porcupine inhibitor. Their hearts’ ability to pump blood improved by nearly twofold compared to untreated animals.

The study findings were published online this week in Proceedings of the National Academy of Sciences.

“Our lab has been studying heart repair for several years, and it was striking to see that administration of a Wnt inhibitor significantly improved heart function following a heart attack in mice,” said Dr. Rhonda Bassel-Duby, Professor of Molecular Biology and Associate Director of the Hamon Center for Regenerative Science and Medicine.
Importantly, in addition to the improved pumping ability of hearts in the mice, the researchers noticed a reduction in fibrosis, or scarring in the hearts. Collagen-laden scarring that occurs following a heart attack can cause the heart to inappropriately increase in size, and lead to heart failure.

“While fibrotic responses may be immediately beneficial, they can overwhelm the ability of the heart to regenerate in the long run. We think we have an agent that can temper this fibrotic response, thus improving wound healing of the heart,” said Dr. Lum, a Virginia Murchison Linthicum Scholar in Medical Research and Associate Director of Basic Research at the Harold C. Simmons Comprehensive Cancer Center.
Additionally, Dr. Lum said, preliminary experiments indicate that the porcupine inhibitor would only need to be used for a short time following a heart attack, suggesting that the unpleasant side effects typically caused by cancer drugs might be avoided.

“We hope to advance a Porcn inhibitor into clinical testing as a regenerative agent for heart disease within the next year,” Dr. Lum said.

Uthealth Researchers Identify Genetic Marker For Heart Failure

A team of scientists at The University of Texas Health Science Center at Houston (UTHealth) and Baylor College of Medicine, led by Eric Boerwinkle, Ph.D., Richard Gibbs, Ph.D., and Bing Yu, Ph.D., have identified powerful predictors of congestive heart failure, a major cause of hospitalization and death in the United States. The discovery, published today in Science Advances, was made through an analysis of how gene mutations affect circulating metabolites in the human body.

The human metabolome is a collection of small molecules called metabolites that result from cellular and biological processes in the body and can act as predictors of future disease. Researchers studied how naturally occurring gene mutations can affect metabolites in the genomes of 1,361 African-American participants in the Atherosclerosis Risk in Communities (ARIC) study. ARIC is a longitudinal, population study designed to investigate the origins and predictors of heart disease, stroke and other chronic diseases.

A mutated gene, SLCO1B1, was found to be associated with high levels of blood fatty acid, which is a strong predictor for the development of future heart failure and the mutation itself has a direct effect on heart failure risk.

Because of the aging population, the estimated prevalence and cost of care for heart failure is expected to increase dramatically. By 2030, it’s estimated that more than 8 million people in the United States will have heart failure with $70 billion total costs, according to the American Heart Association. A major risk factor of heart failure is high blood pressure, or hypertension, which is more common among African-Americans.

“The key to heart failure is to identify those at increased risk early. Our hope with this discovery is that we can be more aggressive in treating hypertension if we know someone is genetically predisposed to heart failure,” said Boerwinkle, Kozmetsky Family Chair in Human Genetics and dean of UTHealth School of Public Health.

While the finding was made in a population of African-American participants, the researchers were able to confirm the relationship among European Americans as well.

“African-Americans have higher rates of hypertension, heart failure and mortality. We would expect our findings can help in the prediction and prevention of heart failure among African Americans,” said Yu, assistant professor in the Department of Epidemiology, Human Genetics and Environmental Sciences at UTHealth School of Public Health.

The research builds upon the group’s work on “knockout humans,” which are naturally occurring mutations that inactivate a certain gene. A typical human exome has dozens of these loss-of-function gene variants. Last year, using this technique, the team identified eight new relationships between genes and diseases.

This paper is the first to examine how mutated genes directly affect the metabolome on a genome-wide scale and then go on to influence disease risk. By studying these relationships, the researchers have discovered a new pathway to identify how genes influence disease, according to Boerwinkle.

George Washington University Researchers Receive $1.6 Million to Improve Cardiac Function During Heart Failure

Researchers at the George Washington University (GW) received $1.6 million from the National Heart, Lung, and Blood Institute to study a heart-brain connection that could help the nearly 23 million people suffering from heart failure worldwide. The four-year project will study ways to restore parasympathetic activity to the heart through oxytocin neuron activation, which could improve cardiac function during heart failure.

A distinctive hallmark of heart failure is autonomic imbalance, consisting of increased sympathetic activity and decreased parasympathetic activity. Parasympathetic activity is cardiac protective.

“Parasympathetic activity is what you have when you’re reading a book, or relaxing, and counteracts the sympathetic activity you have when you’re stuck on the metro or have an exam tomorrow,” said David Mendelowitz, Ph.D., vice chair and professor in the Department of Pharmacology and Physiology at the GW School of Medicine and Health Sciences. “Heart failure is a disease that effects both neuro and cardiac function.”

Unfortunately, few effective treatments exist to increase parasympathetic activity to the heart. Based upon exciting preliminary results, this study will examine the activation of neurons in the hypothalamus that release oxytocin, which has shown to increase parasympathetic activity in the heart. While oxytocin is often used to start or increase speed of labor, recent research has uncovered its role in feelings of generosity and bonding. It may also have beneficial effects on the heart.

The project is a collaboration between the GW School of Medicine and Health Sciences and the GW School of Engineering and Applied Science.

“While Dr. Mendelowitz’s research is focused on neuroscience and how the brain works, my work is focused on cardiac function. Heart failure is a disease that affects both, which is why it is imperative for Dr. Mendelowitz and I to use our complimentary expertise to solve this problem,” said Matthew Kay, PE, DSc, associate professor in the Department of Biomedical Engineering at the GW School of Engineering and Applied Science.

Kay and his research team will use high-speed optical assessments of heart function to identify heart-specific benefits of oxytocin nerve activation. Working together, Mendelowitz and Kay have the potential to unravel the complex interaction between the brain and the heart during heart failure.