Engineered Hot Fat Implants Reduce Weight Gain in Mice


UC Berkeley scientists have discovered a new way to engineer the growth and expansion of energy-burning “good” fat. Subsequently they showed that this fat helped reduce weight gain and lower blood glucose levels in mice. According to Andreas Stahl, the senior author of this study, this technique could potentially lead to new approaches to combat obesity, diabetes and other metabolic disorders.

Stahl and his coworkers devised a specifically tailored hydrogel that acted as a scaffold for stem cells that are able to form brown fat. Implantation of this stem cell-laced scaffold could form a functional brown-fat-like tissue. White fat, which is associated with obesity, stores excess energy, but brown fat is a heat generator and burns calories in order to heat your body.

“What is truly exciting about this system is its potential to provide plentiful supplies of brown fat for therapeutic purposes,” said study lead author Kevin Tharp, a doctoral student in the Department of Nutritional Sciences and Toxicology. “The implant is made from the stem cells that reside in white fat, which could be made from tissue obtained through liposuction.”

“This is figuratively and literally a hot area of research right now,” said Stahl, who is an associate professor of nutritional sciences and toxicology. “We are the first to implant in mice an artificial brown-fat depot and show that it has the expected effects on body temperature and beneficial effects on metabolism.”

Several studies have shown that cold temperatures can increase the metabolic activity of brown fat. However, Stahl pointed out that exposure to cold usually leads to increases in food intake, as well, which potentially negating any calorie-burning benefits from brown-fat activity.

There are three basic types of fat tissue in our bodies. These include energy-storing white fat that many of us are most familiar with, and two kinds of energy-burning fat used to generate heat, which include brown fat, which arises during fetal development, and beige fat, which is brown-like fat that is formed within white fat tissue after exposure to cold and other stressful situations.

For this experiment, Stahl teamed up with Kevin Healy, a UC Berkeley professor of bioengineering. The goal was to increase brown-like beige fat without exposing the animals to cold temperatures. Stahl and Healy wanted to develop a system of physical cues to guide stem cell differentiation.

“It’s already known that for a number of organs, including the heart, the extracellular matrix in which a cell resides provides signals to guide growth and development,” said Dr. Healy. “We applied this concept to stem cells isolated from white-fat tissue.”

The specific matrix recipe for converting white-fat stem cells to brown fat was quite unclear but Stahl and Healy noted that previous studies suggested that stiffness of the surrounding environment was a factor. If white-fat stem cells are placed in a 3D environment that is soft, with little resistance, they become fat. However, if the surrounding environment is rather stiff, the stem cells grew into bone.
Healy and his postdoctoral research fellow Amit Jha generated a tightly knit 3D mesh that consisted of hydrogel, water, hyaluronic acid and short protein sequences associated with brown-fat growth and function. Hyaluronic acid is a naturally occurring acidic carbohydrate that helps make water thicker and gel-like (stiffer in other words). They then took white-fat stem cells (adipose tissue-derived multipotent stem cells or ADMSCs) from mice that had been genetically engineered to express an enzyme from fireflies that made the cells luminescent. Because these cells glowed when incubated with the right substrate, they could be easily traced.

These ADMSCs were then added to the hydrogel and, before the mixture thickened, injected them under the skin of genetically identical mice.

The gel polymerized after injection and stiffens up under the skin of the animal. These labeled cells were then monitored to determine how well they stayed put, how long they persisted in the body and whether they were metabolically functional.

Stahl and Healy and their colleagues noticed an increase in the core body temperature of the mice at ambient temperatures of 21 degrees Celsius and after 24 hours at 4 degrees Celsius. In both cases, the mice with the implanted cells were up to half a degree Celsius warmer than a control group of mice with no injection. The higher the concentration of cells, the larger the effect on temperature.

Next, they put these experimental mice on a high-fat diet. By the end of three weeks, the mice with injected beige fat gained half as much weight and had lower levels of blood glucose and circulating fatty acids compared with control mice.

“This is a feasibility study, but the results were very encouraging,” said Dr. Stahl. “It is the first time an optimized 3D environment has been created to stimulate the growth of brown-like fat. Given the negative health effects of obesity, research into the role of brown fat should continue to see if these findings would be effective in humans.”

The study was published Aug. 20 in Diabetes.

Brown Fat Stem Cells for Treating Diabetes and Obesity


Mammals have two main types of fat: brown fat and white fat.  Brown fat is especially abundant in newborns and in mammals undergoing hibernation.  The primary function of brown fat is to produce body heat so that the animal does not shiver.  In contrast to white fat cells, which contain a single lipid droplet, brown fat cells contain numerous smaller droplets and a higher number of mitochondria, and it is these mitochondria and their high iron content that makes this fat tissue brown.  Brown fat also contains more small blood vessels than white fat, since it has a greater need for oxygen than most tissues.

Recently, researchers at the University of Utah School of Medicine have identified stem cells from brown fat.  The principal researcher of this project, Amit Patel, associate professor of medicine, refuted an old dogma – that adult humans do not possess brown fat.  Children have large amounts of brown fat that is highly metabolically active.  Children can eat a great deal and not gain any weight, relative to adults.  Adults, on the other hand, have an abundance of white fat, and accumulation of white fat leads to weight gain and cardiovascular disease (something not seen in brown fat).  As people age, the amount of white fat increases and the amount of brown fat decreases, which contributes to the onset of diabetes and high cholesterol.

As Patel put it, “If you have more brown fat, you weigh less, you’re metabolically efficient, and you have fewer instances of diabetes and high cholesterol.  The unique identification of human brown fat stem cells in the chest of patients aged 28-34 years is profound.  We were able to isolate the human stem cells, culture and grow them, and implant them into a pre-human model which has demonstrated positive effects on glucose levels.”

In vitro differentiation of brown adipose derived stem cells (BADSCs). (A) Gene expression profile comparing undifferentiated BADSCs to undifferentiated white adipose derived stem cells derived from subcutaneous adipose tissue. Genes in red are associated with brown fat phenotype. (B) Gene expression profile comparing undifferentiated brown adipose derived stem cells to differentiated brown adipocytes. Biological replicates performed in triplicate from a single clone were used for gene expression profile. (C) Transmission electron microscopy of 21 day brown adipocyte differentiation induced with fibronectin type III domain containing 5 (FNDC5) demonstrate multiocular intracytoplasmic lipid vacuoles and mitochondria (arrows). (D) Alizarian red staining of brown adipose derived stem cells induced to undergo osteogenesis. (E) Alcian blue staining of brown adipose derived stem cells directionally differentiated into chondrocytes. (F) Fatty acid binding protein 4 (FABP4) immunocytochemistry of brown adipose derived stem cells induced to undergo white adipogenesis. (G) Undifferentiated BADSCs. (H) Western blot 21 days post FNDC5 induction. Lane 1 brown adipose derived stem cells directionally differentiated into brown adipocytes. Lane 2 non- FNDC5 cells.
In vitro differentiation of brown adipose derived stem cells (BADSCs). (A) Gene expression
profile comparing undifferentiated BADSCs to undifferentiated white adipose derived stem cells
derived from subcutaneous adipose tissue. Genes in red are associated with brown fat phenotype. (B)
Gene expression profile comparing undifferentiated brown adipose derived stem cells to differentiated
brown adipocytes. Biological replicates performed in triplicate from a single clone were used for gene
expression profile. (C) Transmission electron microscopy of 21 day brown adipocyte differentiation
induced with fibronectin type III domain containing 5 (FNDC5) demonstrate multiocular
intracytoplasmic lipid vacuoles and mitochondria (arrows). (D) Alizarian red staining of brown
adipose derived stem cells induced to undergo osteogenesis. (E) Alcian blue staining of brown adipose
derived stem cells directionally differentiated into chondrocytes. (F) Fatty acid binding protein 4
(FABP4) immunocytochemistry of brown adipose derived stem cells induced to undergo white
adipogenesis. (G) Undifferentiated BADSCs. (H) Western blot 21 days post FNDC5 induction. Lane 1
brown adipose derived stem cells directionally differentiated into brown adipocytes. Lane 2 non-
FNDC5 cells.

This new discovery of finding brown fat stem cells may help in identifying potential drugs that may increase the body’s own ability to make brown fat or find novel ways to directly implant brown fat stem cells into patients.

Turning Muscle Stem Cells into Brown Fat


Michael Rudnicki’s laboratory at the Ottawa Hospital Research Institute has managed to convert stem cells from skeletal muscle into brown fat. Because brown fat burns calories, studies have shown that trimmer people tend to have more brown fat, Therefore, Rudnicki’s findings are being viewed as a potential treatment for obesity.

According to Rudnicki, “This discovery significantly advances our ability to harness this good fat in the battle against bad fat and all the associated health risks that come with being overweight and obese. Rudnicki is a senior scientist and director for the Regenerative Medicine Program and Sprott Center for Stem Cell Research at the Ottawa Hospital Research Institute.

Obesity is the fifth leading risk death, globally speaking, and an estimated 2.8 million people dying every year from the effects of being overweight or obese, according to the World Health Organization. The Public Health Agency of Canada estimates that 25% of Canadian adults are obese.

in 2007, Rudnicki and his research team demonstrated the existence of a stem cell population in skeletal muscle. In this new publication, Rudnicki and others show that these adult muscle stem cells not only have the ability to produce muscle fibers, but can also make brown fat.

An even more important aspect of this paper (Yin, et al., Cell Metabolism 17(2) 2013: 210), is that it shows how adult muscle stem cells become brown fat. The main switch is a regulatory molecule called microRNA-133 or miR-133. When miR-133 is present, the muscle stem cells produce muscle fibers, but when the intracellular concentration of miR-133 is reduced, the muscle stem cells form brown fat.

Graphic Abstract

Rudnicki’s research staff developed a molecule that could reduce the concentration of miR-133 in cells. This molecule an antisense oligonucleotide or ASO that is complementary to miR-133. When injected into mice, the ASO caused the mice to produce more brown fat and prevented obesity. Additionally, when injected into the hind leg muscle, the metabolism of the mouse increased, and this effect lasted for four months after the ASO injection.

Even though antisense oligonucleotides are being used in clinical trials, such trials with miR-133 ASOs are still years away.

Rudnicki noted that “we are very excited by this breakthrough.” He continued: “While we acknowledge that it’s a first step there are still many questions to be answered, such as: Will it help adults who are already obese to lose weight? How should it be administered? How long do the effects last? Are there any adverse effects we have not yet observed?”

Surely these questions will be addressed in good time, and Rudnicki’s lab is probably working on them as you read this entry.