Bioengineered Nanofiber Patch to Treat Heart Failure

Stem cells have the capacity to heal damaged tissues and replace death cells. However, harvesting and employing the right stem cell for the right job, at the right dose, and under the right conditions has proven to be a difficult puzzle to solve.

In particular, the damaged heart has proven rather difficult to heal with stem cells. Many different clinical trials have administered stem cells by direct injection, intracoronary delivery in coronary vessels, or injection into the surface of the heart. These studies have examined the efficacy of stem cells from fat, bone marrow, the heart itself, and other sources. The upshot of these studies is that some strategies work and others do not, but even those that work only work modestly well.

The biggest obstacle is overcoming the hostile environment into which stem cells are introduced when they are administered into the heart after a heart attack. The post-heart attack heart suffers from lots of inflammation, low oxygen concentrations, and the pervasive presence of dangerous molecules. Several laboratories have discovered that preconditioning stem cells by growing them in low-oxygen culture conditions can increase their survival in the post-heart attack heart as can genetically engineering cells to resist increased levels of cell stress. Now, a research team from Ohio State University has designed a different strategy to beat the hostility of the post-heart attack heart.

After a heart attack, oxygen-deprived tissues die and various chemical messengers instruct damaged cells to die. However, data from a host of clinical trials strongly suggests that this dangerous time is the best time to introduce stem cells into the heart. Thus, this window of opportunity is the “best of times and the worst of times” for cell therapy.

As it turns out, about 30% of all mammalian protein-encoding genes are regulated by small molecules called microRNAs (miRNAs). MiRNAs are single-stranded RNA molecules approximately 22 nucleotides in length that bind to messenger RNAs and regulate their translation into protein or half-life. Research has shown that miRNAs have substantial potential as a therapeutic target for the treatment of many diseases, including cardiovascular disease. A good deal of research in laboratory animals and in cultured heart cells that altered expression of miRNAs such as miR-1, miR-133, miR-21 and miR-208 contribute to the development of heart disease. The laboratory of Mahmood Khan, a scientist at the Davis Heart and Lung Research Institute at The Ohio State University Wexner Medical Center, has focused on miR-133a which seems to play a role in slowing fibrosis and cardiac remodeling. Importantly, levels of miR-133a are reduced in the heart tissues of patients who have suffered a heart attack.

Khan and his group predicted that increasing the levels of miR-133a in stem cells as they are cultured might preprogram the cells to survive in the hostile environment of the post-heart attack heart.

Khan’s team began by bioengineering a molecule to induce mesenchymal stem cells (MSCs) to produce miRNA-133a. When transplanted into an animal model of cardiac ischemia, the pre-treated MSCs showed improved survival over non-treated MSCs. These pre-treated MSCs also did a better job at decreasing the global damage to the heart, and increasing the thickness of the left ventricle, the main pumping chamber of the heart.

“We found that the pre-treated MSCs did a better job at decreasing the global damage to the heart, along with improvement in the left-ventricular wall thickness compared to the untreated MSCs,” said Dr. Angelos. “MSCs are a commonly used cell type in current heart failure studies, so our findings are definitely relevant to that work.”

The results of these experiments were published in the March issue of the Journal of Cardiovascular Pharmacology.

While trying to increase cell survival, Khan and his colleagues also addressed the problems surviving stem cells face in the heart – how to help them function along existing heart tissue without getting in the way or fouling things up.

To date, most stem cells are grown in flat culture plates and either injected directly into the heart muscle (typically on the periphery of scar tissue), or infused into the heart via an artery. While most of these stem cells either die or diffuse throughout the body, successfully transplanted stem cells sometimes inadvertently disrupt heart function.

“The heart is a constantly moving, connected matrix of muscle fibers working together to make the heart pump in sync,” said Dr. Angelo’s, an emergency medicine researcher and collaborator of Dr Khan. “Transplanted stem cells may not align with native tissue, potentially disrupting or attenuating signals that keep a steady heartbeat. There’s evidence that this could contribute to arrhythmias.”

To create a more secure environment that allows implanted stem cells successfully engraft into the heart, Drs. Khan and Angelos have used a biodegradeable nanofiber “patch” seeded with human inducible pluripotent stem cells derived cardiomyocytes (hiPSC-CMs). Khan and Angelos chose hiPSC-CMs because these cells are patient derived and can be used to model the heart disease of patients and for autologous stem cell transplantation in patients with failing hearts.

Both aligned nanofiber patch and standard culture plate were seeded with hiPSC-CMs. Both sets of cultures heart muscle cells were compared for calcium signaling (a measure of proper heart muscle function) and synchronous beating. Within two weeks, both stem cell cultures were spontaneously beating like a miniature heart, but the linear grain of the nanofiber formed an aligned pattern of cells that looked and functioned like a healthy heart tissue.

“The cardiomyocytes cultured on a flat plate are scattered and disorganized. Cardiomyocytes grown on the nanofiber scaffolding look more like healthy heart cells, beat more strongly and in greater synchronicity than cells from the flat plate,” said Dr. Khan. “Next, we hope to use what we’ve learned from this study to develop a thicker, multi-layer patch that could help restore thin and weakened heart walls.”

Drs. Khan and Angelos see great potential future clinical applications for their nanofiber bandage. This treatment could potentially bandage the damaged heart muscle of heart patients with the nanofiber cardiac patch. Also, it is possible that they could someday combine the microRNA pre-treatment technique and the patch to give stem cells a survival boost along with a protective structure to improve outcomes.

Khan, his co-workers and his collaborators published this work on May 19 in PLoS ONE.

Adding One Gene to Cells can Regrow Hair, Cartilage, Bone and Soft Tissues

The reactivation of a gene called Lin28a, which is active in embryonic stem cells, can regrow hair and repair cartilage, bone, skin, and other soft tissues in mice.

This study comes from scientists at the Stem Cell Program at Boston Children’s Hospital who found that the Lin28a promotes tissue repair by enhancing metabolism in mitochondria, which are the energy-producing engines in cells. These data suggest that upregulation of common “housekeeping” functions might provide new ways to develop regenerative treatments.

George Q. Daley, the director of Boston Children’s Hospital Stem Cell Transplantation Program, said, “Efforts to improve wound healing and tissue repair have mostly failed, but altering metabolism provides a new strategy which we hope will prove successful.”

One of the first authors of this paper, Shyh-Chang Ng, added, “Most people would naturally think that growth factors are the major players in wound healing, but we found that the core metabolism of cells is rate-limiting in terms of tissue repair. The enhanced metabolic rate we saw when we reactivated Lin28a is typical of embryos during their rapid growth phase.”

Lin28a was first discovered in worms, but the Lin28a gene is found in all animals. It is abundantly expressed in embryonic stem cells and during early embryonic development. Stem cell scientists have even used Lin28a to help reprogram adult cells into induced pluripotent stem cells. Lin28a encodes an RNA-binding protein that regulates the translation of messenger RNAs into protein.

To express more of this protein in mice, Daley and his colleagues attached the Lin28a gene to a piece of DNA that would drive expression when the mice were fed the drug doxycycline. Ng and others noticed that one of the targets of Lin28a was a small RNA molecule called Let-7, which is known to promote aging and cell maturation. Let-7 is a member of a class of non-coding RNA molecules called micro-RNAs that bind to messenger RNAs and prevent their translation.  Let-7 is made as a larger precursor molecule that is processed to a smaller molecule that is functional.  LIN28 binds specifically to the primary and precursor forms of Let-7, and inhibits Let-7 processing.

Lin28a function

Ng said, “We were confident that Let-7 would be the mechanism, but there was something else involved.”

Let-28a is known to activate the translation of several different genes that play a role in basic energy metabolism (e.g., Pfkp, Pdha1, Idh3b, Sdha, Ndufb3, and Ndufb8), Activation of these genes enhances oxidative metabolism and promotes an embryonic bioenergetic state.

In their Lin28a transgenic mice, Daley, Ng and others noticed that Lin28a definitively enhanced the production of metabolic enzymes in mitochondria, and that these “revved up” the mitochondria so that they generated the energy needed to stimulate and grow new tissues.


“We already know that accumulated defects in mitochondria can lead to aging in many cells and tissues,” said Ng. We are showing the converse: enhancement of mitochondrial metabolism can boost tissue repair and regeneration, recapturing the remarkable repair capacity of juvenile animals. ”

Further experiments showed that bypassing Lin28a and directly activating mitochondrial metabolism with small molecules had the same effect on wound healing. This suggests that pharmaceuticals might induce regeneration and enhance tissue repair.

“Since Lin28 itself is difficult to introduce into cells, the fact that we were able to activate mitochondrial metabolism pharmacologically gives us hope,” said Ng.

Lin28a did not cause universal regeneration of all tissues. Heart tissue, for example, was poorly aided by Lin28a. Also, Lin28a induced the regeneration of severed finger tips in newborn mice, but not in adult mice.

Nevertheless, Lin28a could be a key factor in constituting a kind of healing cocktail, in combination with other embryonic factors yet to be found.

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.