The secret to building a strong heart lies in blood vessels

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By IMPC

Published 9th July 2018

Research using IMPC resources offers new insight into congenital heart disease and may allow new therapies to be developed for human patients. The research is  published in Nature Communications, and is summarised below.

By Nathan Collins,

Every year, a small number of babies are born with hearts whose muscles are spongy and thin, although exactly what causes this condition isn’t clear. Now, Stanford biologists think they may have found a clue: spongy heart muscles could be the result of improperly developed blood vessels surrounding the heart.

Apart from a deeper understanding of congenital heart disease, the results could shed light on how heart muscle forms in the first place. Until now, no one realised what an important role newly-forming blood vessels played in supporting the growth of heart muscle – or that the support is more than just a matter of supplying oxygen.

Yet the study’s two senior authors, Ashby Morrison and Kristy Red-Horse, and their colleagues did not set out to understand congenital heart disease or to change how people thought about heart development in utero. Instead, they attribute the project to something altogether more random: their offices are right next to each other.

Next door and miles away

Apart from the fact that both are biologists, Morrison and Red-Horse don’t have that much in common as researchers. For one thing, Red-Horse, who is a member of Stanford Bio-X, the Cardiovascular Institute and the Child Health Research Institute, studies the development of tissues and whole organs, often by breeding her own genetically modified mice. Much of Morrison’s research, meanwhile, centers on the basic molecular machinery that reads out messages in the DNA and uses it to build functioning cells – usually in yeast.

“Kristy’s on the opposite side,” said Morrison, a member of Stanford Bio-X, the Child Health Research Institute and the Stanford Cancer Institute.

Still, their physical proximity got them talking, and among the topics of conversation was a particular molecule that Morrison had been looking at, one that turns out to be present not just in yeast but also in mice and many other living things, too. That got them wondering: what did that molecule do in those other living things, and what would happen if it disappeared?

Time to make some mice

In yeast, the molecule, called Ino80, is pretty important – without it, yeast get sick and die off – but in other organisms, “we didn’t know what to expect,” Morrison said.

To find out, Red-Horse and her lab started the years-long process of genetically modifying mice to lack Ino80, either throughout their bodies or in specific areas of the body or specific cell types. To do this they utilised IMPC resources.

The most intriguing results, Red-Horse said, came from mice which didn’t produce Ino80 in certain heart cells – called endothelial cells – that are the progenitors of blood vessels that feed the muscles of the heart. Without Ino80, the network doesn’t develop properly, and as a result, cardiac muscles couldn’t develop properly either – instead remaining spongy and weak.

It was at this point that the team noticed the similarity between their mice and a form of heart disease called left ventricular non-compaction, the third most common disease of the heart muscle. “It was a complete surprise,” Morrison said.

Growing hearts

Curiously, blood flow through those missing vessels – and the oxygen it provides – is only part of the story. In a follow-up experiment, the researchers grew heart muscles in a dish along with endothelial cells that had not yet formed into blood vessels. The team found that when those endothelial cells produced no Ino80, the heart muscle didn’t develop properly. Apparently, Red-Horse said, “endothelial cells are producing something that’s a growth factor” for cardiac muscle cells. “The next step is to identify that factor.”

Still, what they’ve found already should change how both doctors and biologists think about how the heart forms. In both cases, taking into account the role of blood vessels could help explain normal muscle development in mice and then humans or lead to new therapies for diseases like left ventricular non-compaction. Farther down the road, the research could also have implications for regenerative medicine specialists working to grow hearts and other organs in the lab, Red-Horse and Morrison said.

 

Research article: Endothelial deletion of Ino80 disrupts coronary angiogenesis and causes congenital heart disease

Article edited from a press release for Stanford News

A team of researchers at the Harvard T. H. Chan School of Public Health has illuminated a critical player in cholesterol metabolism that acts as a molecular guardian in cells to help maintain cholesterol levels within a safe, narrow range. Known as Nrf1, it both senses and responds to excess cholesterol, and could represent a potential new therapeutic target in a multitude of diseases where cholesterol metabolism is disrupted.

The study is published in the journal Cell. To produce mice deficient in Nrf1 or Nrf2, the research used alleles from the International Mouse Phenotyping Consortium.

“We’ve uncovered a key missing piece in our understanding of how cells can precisely control their cholesterol levels,” said senior author Gökhan S. Hotamisligil, J.S. Simmons Professor of Genetics and Metabolism and head of the Sabri Ülker Center for Nutrient, Genetic, and Metabolic Research at Harvard Chan School. “That piece forms part of a molecular yin-yang that is critical for keeping cholesterol levels in proper balance and ensuring proper cellular function.”

It has been accepted for decades that high cholesterol in the blood can set the stage for cardiovascular disease and other significant health problems. But elevated cholesterol is even more dangerous at the cellular level, leading to toxicity, inflammation, and eventually cell death. “The cell must guard against any rise in cholesterol — it cannot tolerate levels that are too high or too low,” said Hotamisligil. While there are well known cellular factors that send and receive signals when cholesterol is in short supply (orchestrated by a protein called SREBP2), it has been unclear how cells handle some crucial aspects of the converse problem of too much cholesterol.

To explore the mechanisms that defend cells against cholesterol, first author Scott Widenmaier, research fellow in the Department of Genetic and Complex Diseases and Sabri Ülker Center, and colleagues focused their attention on an area of the cell known as the endoplasmic reticulum or ER, which is surrounded by a membrane notoriously low in cholesterol — lower, in fact, than any other cellular membrane. “This would be a particularly vulnerable place in the cell, where a small increase in cholesterol would make a significant impact,” explained Hotamisligil. As an intracellular structure, the ER requires fluidity, and adding more cholesterol to its membrane makes it more brittle.

Based on their assumption, the scientists set out to find molecules that reside in the ER membrane and that might play a role in detecting or responding to cellular cholesterol levels; they homed in on a handful of likely suspects. In initial experiments, Nrf1 protein stood out because it responds to cholesterol — when cholesterol is added to cells, the levels of Nrf1 increase, indicating that the protein can react to high cholesterol. And when Nrf1 function is disrupted in mice, the liver becomes dramatically enlarged and overrun with excess cholesterol, suggesting that it normally acts to protect the liver from cholesterol accumulation.

To dig more deeply into Nrf1’s protective role in cholesterol metabolism, the researchers set out to determine how it works at the molecular level. They discovered that Nrf1 has the capacity to bind to cholesterol directly, and pinpointed specific regions of the protein that mediate this binding. Moreover, the binding of cholesterol triggers a cascade of molecular events that suppress inflammation and promote cholesterol removal from the cell.

Taken together, these findings highlight a novel program for responding to high cholesterol in the cell that operates alongside other molecular components that guard against low cholesterol.

“This discovery really teaches us a lot about how cells maintain cholesterol homeostasis,” said Hotamisligil. “Now, we demonstrate that there is a molecular yin-yang– formed by NRF1 and SREBP2 — that together keep cellular cholesterol within a safe, narrow range. That’s an exciting finding that could have broad, new therapeutic applications.”

Research article: NRF1 Is an ER Membrane Sensor that Is Central to Cholesterol Homeostasis

A study led by Kevin King, a bioengineer and physician at the University of California San Diego, has found that the immune system plays a surprising role in the aftermath of heart attacks. The research could lead to new therapeutic strategies for heart disease. Mice for this study originated from the Jackson Laboratory and the European Conditional Mouse Mutagenesis Program (EUCOMM).

The team, which also includes researchers from the Center for Systems Biology at Massachusetts General Hospital (MGH), Brigham and Women’s Hospital, Harvard Medical School, and the University of Massachusetts, presents the findings in the journal Nature Medicine. Ischemic heart disease is the most common cause of death in the world and it begins with a heart attack. During this process, heart cells die, prompting immune cells to enter the dead tissue, clear debris and orchestrate stabilization of the heart wall.

But what is it about dying cells in the heart that stimulates the immune system? To answer this, researchers looked deep inside thousands of individual cardiac immune cells and mapped their individual transcriptomes using a method called single cell RNA-Seq. This led to the discovery that after a heart attack, DNA from dying cells masquerades as a virus and activates an ancient antiviral program called the type I interferon response in specialized immune cells. The researchers named these “interferon inducible cells (IFNICs).”

When investigators blocked the interferon response, either genetically or with a neutralizing antibody given after the heart attack, there was less inflammation, less heart dysfunction, and improved survival. Specifically, blocking antiviral responses in mice improved survival from 60 percent to over 95 percent. These findings reveal a new potential therapeutic opportunity to prevent heart attacks from progressing to heart failure in patients.

“We are interested to learn whether interferons contribute to adverse cardiovascular outcomes after heart attacks in humans,” said King, who did most of the work on the study while he was a cardiology fellow at Brigham and Women’s Hospital and at the Center for Systems Biology at MGH in Boston.

The immune system has evolved innate antiviral programs to defend against a diverse range of invading pathogens. Immune cells do this by detecting molecular fingerprints of pathogens, activating a protein called IRF3, and secreting interferons, which orchestrate a defense program mediated by hundreds of interferon-stimulated genes. Investigators found that surprisingly, the antiviral interferon response is also turned on after a heart attack despite the absence of any infection. Their results point to dying cell DNA as the cause of this confusion because the immune system interprets it as the molecular signature of a virus.

Surprisingly, the immune cells participating in the interferon response were a previously unrecognized subset of cardiac macrophages. These cells could not be identified by conventional flow sorting because unique markers on the cell surface were not known. By using single cell RNA Seq, an emerging technique that combines microfluidic nanoliter droplet reactors with single cell barcoding and next generation sequencing, the researchers were able to examine expression of every gene in over 4,000 cardiac immune cells and found the specialized IFNIC population of responsible cells.

Future studies will aim to better understand the interferon response and the IFNIC cell type and explore their roles in the infarcted and remodeling heart. The team is also working to understand the interferon response in other tissues and diseases where cell death occurs.

 

Research article: IRF3 and type I interferons fuel a fatal response to myocardial infarction

Scientists from the University of Cambridge have identified a potential therapeutic target in the devastating genetic disease Hutchinson-Gilford Progeria Syndrome (HGPS), which is characterised by premature ageing. The research utilises IMPC resources through the use of mouse phenotypic data.

The paper is published in Nature Communications, with preclinical data showing that chemical inhibition or genetic deregulation of the enzyme N-acetyltransferase 10 (NAT10) leads to significant health and lifespan gains in a mouse model of HGPS.

HGPS is a rare condition: patients have an average life expectancy of around 15 years, suffering a variety of symptoms including short stature, low body weight, hair loss, skin thickening, problems with fat storage, osteoporosis, and cardiovascular disease, typically dying of a heart attack.

The disease arises from specific mutations in the gene for the protein Lamin A, which lead to production of a shorter, dysfunctional protein that accumulates in cells, specifically in the membranes surrounding the nucleus. This causes disorganisation of chromatin (the ‘packaging’ around DNA), deregulated transcription, accumulation of DNA damage and defective cell proliferation.

By screening candidate molecules for an effect on nuclear membranes in human HGPS patient-derived cells in vitro, the authors have previously identified a small molecule called remodelin as an effective ameliorative agent. They then identified which component of the cells was being affected by remodelin: an enzyme with a variety of cell functions, called NAT10.

Their aim in the new study was to take these findings into a mouse model with the same genetic defect as HGPS patients, to see whether inhibiting NAT10 – either chemically by administration of remodelin or genetically by engineering reduced production of NAT10 – could ameliorate the disease. The results show that these approaches indeed significantly improved the health of the diseased mice, increased their lifespan, and reduced the effects of the HGPS mutation across a variety of measures in body tissues and at the cellular level.

The research was led by Dr Gabriel Balmus from the Wellcome Trust/ Cancer Research UK Gurdon Institute and Dr Delphine Larrieu from the Cambridge Institute for Medical Research, University of Cambridge; and Dr David Adams from the Wellcome Sanger Institute.

 

Senior author Professor Steve Jackson commented: “We’re very excited by the possibility that drugs targeting NAT10 may, in future, be tested on people suffering from HGPS. I like to describe this approach as a ‘re-balancing towards the healthy state’.

“We first studied the cell biology to understand how the disease affects cells, and then used those findings to identify ways to re-balance the defect at the whole-organism level. Our findings in mice suggest a therapeutic approach to HGPS and other premature ageing diseases.”

 

Research article: https://www.nature.com/articles/s41467-018-03770-3.pdf

Nat10 gene on the IMPC website: http://www.mousephenotype.org/data/genes/MGI:2138939

Glucose is the energy that fuels cells, and the body likes to store glucose for later use. But too much glucose can contribute to obesity, and scientists have long wanted to understand what happens within a cell to tip the balance.

To solve this riddle, researchers at UT Southwestern’s Cecil H. and Ida Green Center for Reproductive Biology Sciences examined specialized compartments inside the cell to reveal the role of a molecule termed NAD+ in turning on genes that make fat cells.

The study utilised IMPC resources for the generation of Nmnat1 conditional knockout mice. Frozen Nmnat1tm1a(EUCOMM)Wtsi embryos on a C57BL/6N background were obtained and recovered at UT Southwestern’s Transgenic Core Facility. The research is reported in the journal Science.

NAD+ is found in every cell of the body and some scientists believe that boosting its production may be tied to better health and to the slowing down of the aging process.

What is NAD+?

NAD+ stands for nicotinamide adenine dinucleotide. It’s a molecule found inside cells in the body that helps transfer energy between molecules.

Why is it important?

NAD+ is believed to play important roles in longevity, aging, and diseases ranging from neurodegenerative disorders to cancer.

UT Southwestern biologists examined individual compartments inside cells that house NAD+ molecules to determine how they control genes that are essential to the fat-storing process – knowledge that could help in a wide range of ailments, including metabolic disorders, neurodegenerative diseases, inflammation and aging, and cancer.

“This compartmentalization ends up having profound effects on gene expression in the nucleus, as well as metabolism in the cytoplasm,” (the jellylike substance outside the cell’s nucleus), said Dr. W. Lee Kraus, Director of the Green Center and senior author on the research. “We found that these processes play key roles in fat cell differentiation and in cancer cells.”

“The previous thinking in the field was that NAD+ was evenly distributed throughout cells and moved freely between different subcellular compartments,” said Dr. Kraus, Professor of Obstetrics and Gynecology and Pharmacology. “We showed that NAD+ is actually compartmentalized – there are separate nuclear and cytoplasmic pools of NAD+ whose levels change under certain cellular conditions.”

Accounting for the levels of NAD+ biosynthesis separately rather than in their totality helped increase the understanding of the biology involved, said first author Dr. Keun Ryu, a postdoctoral researcher in Obstetrics and Gynecology.

“Our study provides a new understanding of NAD+ biology,” he said.

Research article: http://science.sciencemag.org/content/sci/360/6389/eaan5780.full.pdf

Nishanth Ulhas Nair discusses his recent article in Scientific Reports: Putative functional genes in idiopathic dilated cardiomyopathy

Link to article: https://www.nature.com/articles/s41598-017-18524-2

The IMPC recently exhibited at the BCS Annual Conference for the first time. The aim of attending conferences such as this is to engage with clinicians and researchers working on human disease models to raise awareness of the IMPC as a resource. The BCS Annual Conference 2018 was a great example of this and we had many interested attendees visiting the stand. Visitors ranged from researchers that had already used IMPC resources and were keen to hear updates, to those that were unaware of what we do and were interested in understanding how the IMPC may benefit their work.

To highlight how the IMPC could be used as a resource for cardiovascular research we talked attendees through the cardiovaducalr landing page.

More information on cardiovascular research and the IMPC

The cardiovascular system refers to the observable morphological and physiological characteristics of the mammalian heart, blood vessels, or circulatory system that are manifested through development and lifespan.
So far a total of 4804 genes have been tested for cardiovascular phenotypes, ranging from Increased Heart Weight to Increased Cardiac Muscle Contractility.

Genes with phenotype associations relating to the Cardiovascular System

 

There have already been many studies on the cardiovascular system that have featured IMPC data and resources. A full list can be found on the cardiovaducalr landing page, and a selection of highlights listed below:

 

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By IMPC

Published 8th June 2018

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