Posts

Cholesterol plaque in artery

Looking for atherosclerosis’ root cause

Cholesterol plaque in artery

A multi-institutional team led by research faculty at Children’s National in Washington, D.C., finds that extracellular vesicles derived from kids’ fat can play a pivotal role in ratcheting up risk for atherosclerotic cardiovascular disease well before any worrisome symptoms become visible.

According to the Centers for Disease Control and Prevention, about one in five U.S. kids aged 6 to 19 is obese, boosting their risk for a variety of other health problems now and later in life.

One of these is atherosclerosis, a term that translates literally as hardening of the arteries. Atherosclerosis causes blood vessels that carry oxygen-rich blood throughout the body to become inflamed. White blood cells called macrophages settle in the vessel wall, which becomes overloaded with cholesterol. A plaque forms that restricts blood flow. But it remains a mystery how fat cells residing in one place in the body can trigger mayhem in cells and tissues located far away.

Small, lipid-lined sacs called extracellular vesicles (EVs), released by cells into the bloodstream, are likely troublemakers since they enable intercellular communication. Now, a multi-institutional team led by research faculty at Children’s National in Washington, D.C., finds that EVs derived from kids’ fat can play a pivotal role in ratcheting up risk for atherosclerotic cardiovascular disease well before any worrisome symptoms become visible. What’s more, the team showed that EVs found in the body’s fat stores can disrupt disposal of cholesterol in a variety of kids, from lean to obese, the team reports online July 22, 2019, in the Journal of Translational Medicine.

“We found that seven specific small sequences of RNA (microRNA) carried within the extracellular vesicles from human fat tissue impaired the ability of white blood cells called macrophages to eliminate cholesterol,” says Robert J. Freishtat, M.D., MPH, senior scientist at the Center for Genetic Medicine Research at Children’s National and the study’s senior author. “Fat isn’t just tissue. It can be thought of as a metabolic organ capable of communicating with types of cells that predispose someone to develop atherosclerotic cardiovascular disease, the leading cause of death around the world.”

Research scientists and clinicians from Children’s National, the George Washington University, NYU Winthrop Hospital and the National Heart, Lung and Blood Institute collaborated to examine the relationship between the content of EVs and their effect on macrophage behavior. Their collaborative effort builds on previous research that found microRNA derived from fat cells becomes pathologically altered by obesity, a phenomenon reversed by weight-loss surgery.

Because heart disease can have its roots in adolescence, they enrolled 93 kids aged 12 to 19 with a range of body mass indices (BMIs), including the “lean” group, 15 youth whose BMI was lower than 22 and the “obese” group, 78 youths whose BMI was in the 99th percentile for their age. Their median age was 17. Seventy-one were young women. They collected visceral adipose tissue during abdominal surgeries and visited each other’s respective labs to perform the experiments.

“We were surprised to find that EVs could hobble the macrophage cholesterol outflow system in adolescents of any weight,” says Matthew D. Barberio, Ph.D., the study’s lead author, a former Children’s National scientist who now is an assistant professor at the George Washington University’s Milken Institute School of Public Health. “It’s still an open question whether young people who are healthy can tolerate obesity—or whether there are specific differences in fat tissue composition that up kids’ risk for heart disease.”

The team plans to build on the current findings to safeguard kids and adults against future cardiovascular risk.

“This study was a huge multi-disciplinary undertaking,” adds Allison B. Reiss, M.D., of NYU Winthrop Hospital and the study’s corresponding author. “Ultimately, we hope to learn which properties belonging to adipose tissue EVs make them friendly or unfriendly to the heart, and we hope that gaining that knowledge will help us decrease morbidity and mortality from heart disease across the lifespan.”

In addition to Dr. Freishtat, additional study co-authors include Samuel B. Epstein, Madeleine Goldberg, Sarah C. Ferrante, and Evan P. Nadler, M.D., director of the Bariatric Surgery Program, all of Children’s National’s Center for Genetic Medicine Research; Lead Author, Matthew D. Barberio, of Millken Institute School of Public Health at the George Washington University; Lora J. Kasselman, Heather A. Renna, Joshua DeLeon, Iryna Voloshyna, Ashley Barlev, Michael Salama and Allison B. Reiss, all of NYU Winthrop Hospital; and Martin P. Playford and Nehal Mehta, of the National Heart, Lung and Blood Institute.

Financial support for research described in this post was provided by the National Institutes of Health National Center for Advancing Translational Sciences under award number UL1TR000075, the National Heart, Lung and Blood Institute under award number Z1AHL-06193-4, the American Heart Association under award number 17POST33670787, the Clark Charitable Foundation, the Elizabeth Daniel Research Fund, and Robert Buescher.

Robert J. Freishtat working in the lab

Detecting early signs of type 2 diabetes through microRNA

Robert J. Freishtat working in the lab

Obesity is a major risk factor for insulin resistance and type 2 diabetes. Now researchers understand the pathogenesis better among teens with mid-level obesity, thanks to clues released from circulating adipocyte-derived exosomes.

Researchers know that exosomes, tiny nanoparticles released from fat cells, travel through the bloodstream and body, regulating a variety of processes, from growth and development to metabolism. The exosomes are important in lean, healthy individuals in maintaining homeostasis, but when fat gets ‘sick’ – the most common reason for this is too much weight gain – it can change its phenotype, becoming inflammatory, and disrupts how our organs function, from how our skeletal muscle and liver metabolize sugar to how our blood vessels process cholesterol.

Robert J. Freishtat, M.D., M.P.H., the chief of emergency medicine at Children’s National Health System and a professor of precision medicine and genomics at the George Washington University School of Medicine and Health Sciences, and Sheela N. Magge M.D., M.S.C.E., who is now the director of pediatric endocrinology and an associate professor of medicine at the Johns Hopkins School of Medicine, were curious about what this process looked like in teens who fell in the mid-range of obesity.

Obesity is a major risk factor for insulin resistance and type 2 diabetes, but Dr. Freishtat and Dr. Magge wanted to know: Why do some teens with obesity develop type 2 diabetes over others? Why are some teens in this mid-range of obesity metabolically healthy while others have metabolic syndrome? Can fat in obese people become sick and drive disease?

To test this, Dr. Freishtat and Dr. Magge worked with 55 obese adolescents, ages 12 to 17, as part of a study at Children’s National. The participants – 32 obese normoglycemic youth and 23 obese hyperglycemic youth – were similar in age, sex, race, pubertal stage, body mass index and overall fat mass. The distinguishing factor: The hyperglycemic study participants, the teens with elevated blood sugar, differed in where they stored fat. They had extra visceral fat (or adipose tissue) storage, the type of fat that surrounds the liver, pancreas and intestines, a known risk factor for type 2 diabetes.

Dr. Magge and Dr. Freishtat predicted that circulating exosomes from the teens with elevated blood sugar are enriched for microRNAs targeting carbohydrate metabolism.

They used three tests to examine study participants’ metabolism, body composition and circulating exosomes. The first test, an oral glucose tolerance test, measures how efficiently the body metabolizes sugar; the second test is the whole body DXA, or dual-energy x-ray absorptiometry, which analyzes body composition, including lean tissue, fat mass and bone mineral density; and the third test, the serum adipocyte-derived exosomal microRNA assays, is an analysis of circulating fat signals in the bloodstream.

They found that teens with elevated blood sugar and increased visceral fat had different circulating adipocyte-derived exosomes. These study participants’ exosomes were enriched for 14 microRNAs, targeting 1,304 mRNAs and corresponding to 179 canonical pathways – many of which are directly associated with carbohydrate metabolism and visceral fat.

Dr. Magge will present this research, entitled “Changes in Adipocyte-Derived Exosomal MicroRNAs May Play a Role in the Progression from Obese Normoglycemia to Hyperglycemia/Diabetes,” as an oral abstract at the American Diabetes Association’s 79th Scientific Sessions on Saturday, June 8.

Dr. Freishtat envisions having this information will be especially helpful for a patient in a mid-range of obesity. Exosomes primarily consist of small non-coding RNAs. In the current study, the altered RNAs affect P13K/AKT and STAT3 signaling, vital pathways for metabolic and immune function.

“Instead of waiting until someone has the biochemical changes associated with type 2 diabetes, such as hyperglycemia, hyperlipidemia and insulin resistance, we’re hoping physicians will use this information to work with patients earlier,” says Dr. Freishtat. “Through earlier detection, clinicians can intervene when fat shows sign of illness, as opposed to when the overt disease has occurred. This could be intervening with diet and lifestyle for an obese individual or intervening with medication earlier. The goal is to work with children and teens when their system is more plastic and responds better to intervention.”

As this research evolves, Dr. Freishtat continues to look at the intergenerational effects of circulating adipocyte-derived exosomes. Through ongoing NIH-funded research in India, he finds these exosomes, similar in size to lipoproteins, can travel across the placenta, affecting development of the fetus in utero.

“What we’re finding in our initial work is that these exosomes, or ‘sick’ fat, cross the placenta and affect fetal development,” Dr. Freishtat says. “Some of the things that we’re seeing are a change in body composition of the fetus to a more adipose phenotype. Some of our work in cell cultures shows changes in stem cell function and differentiation, but what’s even more interesting to us is that if the fetus is a female sex that means her ovaries are developing while she’s in utero, which means a mother’s adipocyte-derived exosomes could theoretically be affecting her grandchild’s phenotype – influencing the health of three generations.”

While this research is underway, Dr. Freishtat is working with JPOD @ Boston, co-located with the Cambridge Innovation Center in Cambridge, Massachusetts, to develop a test to provide analyses of adipocyte-derived exosomal microRNAs.

“It’s important for families to know that these studies are designed to help researchers and doctors better understand the development of disease in its earliest stages, but there’s no need for patients to wait for the completion of our studies,” says Dr. Freishtat. “Reaching and maintaining a healthy body weight and exercising are important things teens and families can do today to reduce their risk for obesity and diabetes.”