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Scientists at Johns Hopkins have shown in laboratory experiments in mice that blocking the action of a signaling protein deep inside the heart’s muscle cells blunts the most serious ill effects of high blood pressure on the heart. These include heart muscle enlargement, scar tissue formation and loss of blood vessel growth.

Specifically, the Johns Hopkins team found that their intervention halted transforming growth factor beta (TGF-beta) secretion at a precise location called cell receptor type 2 in cardiac muscle cells. Blocking its action in this cell type forestalled pathways for hypertrophy, fibrosis, and angiogenesis by stopping the unbridled TGF-beta signaling, which is typically observed in heart failure, in all other non-muscle types of cells in blood vessels and fibrous tissue. However, blocking TGF-beta signaling in non-muscle cells did not stop disease progression.

In several dozen different experiments, using genetically altered mice or chemicals to selectively block different TGF-beta pathways, researchers were able to pinpoint where the signaling protein had its greatest impact on heart function and determine how its unimpeded activity promoted heart disease.

“Now that we know about the pivotal and specific bad roles played by TGF-beta in a common form of heart disease, we can try to mimic our lab experiments to develop cell-specific drug therapies that stop the chain reactions in the heart muscle at the TGF-beta type 2 cell receptor location,” says senior study investigator and cardiologist, David Kass, M.D. Kass is a professor at the Johns Hopkins University School of Medicine and its Heart and Vascular Institute.

The Kass team study, to be published in the June edition of the Journal of Clinical Investigation, is believed to show the first evidence of how TGF-beta is stimulated differently by various cell types in the heart and which resulting pathways promote heart failure, the most common kind of heart disease. Nearly 6 million Americans are estimated to have the condition.

Kass says previous research showed TGF-beta played a mixed role in various heart diseases, reducing arterial inflammation in some while harming valve and blood vessel function in others, such as people with Marfan syndrome. Until now, however, no explanation existed as to why any of these differences occurred, which cells controlled the TGF-beta signal, and which enzymes are stimulated as a result.

In the new study, researchers also found that in mice with hypertension-induced disease, blocking TGF-beta type 2 cell receptor stopped activities of another kind of regulating protein, called TGF-beta activated kinase (TAK-1). Its activation appears to play a key role in heart enlargement and in secreting proteins tied to scarring, as well as others tied to blood vessel formation.

Researchers began the study with injections of TGF-beta neutralizing antibodies to see if they could rein in heart-failing TGF-beta signaling. But the disease got worse in mice whose hearts had induced high blood pressure, and TGF-beta signaling persisted inside the muscle cells even though it was suppressed in other cells in the heart. The action of two other kinds of proteins closely tied to TGF-beta was similarly split, with the activity of Smad proteins suppressed only outside muscle cells, while TAK-1 production continued. This led Kass and his team to investigate what was happening differently inside muscle cells.

Subsequent testing in mice selectively bred to lack either one of the two TGF-beta receptors in the muscle cells revealed that blocking only the TGF-beta type 2 cell receptor shut down both Smad and TAK-1 activity, stalling enlargement and scarring. Blocking only the TGF-beta type 1 receptor, however, failed to block TAK-1 activity, and disease-accelerating TGF-beta signaling persisted in non-muscle heart cells.

Researchers plan further tests in animals of chemicals that block TAK-1 as potential treatments for heart failure or other kinds of heart disease.

Funding for the study, which took three years to complete, was provided by the National Institutes of Health, with additional support from the American Heart Association, the Japan Heart Foundation, the Peter Belfer Laboratory Foundation, and the Fondation Leducq.

Besides Kass, other Hopkins researchers involved in this study were study lead investigator Norimichi Koitabashi, M.D., Ph.D.; Thomas Danner; Ari Zaiman, M.D., Ph.D.; Janelle Rowell, M.Sc.; Joseph Mankowski, D.V.M., Ph.D.; Dou Zang, M.D., Ph.D.; Eiki Takimoto, M.D., Ph.D. Kass is also the Abraham and Virginia Weiss Professor of Cardiology at Hopkins. Additional research assistance was provided from Yigal Pinto, M.D., Ph.D., from the University of Amsterdam, in the Netherlands.

PHILADELPHIA—During embryonic development, cells migrate to their eventual location in the adult body plan and begin to differentiate into specific cell types. Thanks to new research at the University of Pennsylvania, there is new insight into how these processes regulate tissues formation in the heart.

A developmental biologist at Penn’s School of Veterinary Medicine, Jean-Pierre Saint-Jeannet, along with a colleague, Young-Hoon Lee of South Korea’s Chonbuk National University, has mapped the embryonic region that becomes the part of the heart that separates the outgoing blood in Xenopus, a genus of frog.

Xenopus is a commonly used model organism for developmental studies, and is a particularly interesting for this kind of research because amphibians have a single ventricle and the outflow tract septum is incomplete.

In higher vertebrates, chickens and mice, the cardiac neural crest provides the needed separation for both circulations at the level of the outflow tract, remodeling one vessel into two. In fish, where there is no separation at all between the two circulations, the cardiac neural crest contributes to all regions of the heart.

“In the frog, we were expecting to find something that was in between fish and higher vertebrates, but that’s not the case at all,” said Saint-Jeannet. “It turns out that cardiac neural crest cells do not contribute to the outflow tract septum, they stop their migration before entering the outflow tract. The blood separation comes from an entirely different part of the embryo, known as the ‘second heart field.’”

“As compared to other models the  migration of the cardiac neural crest in amphibians has been dramatically changed through evolution,“ he said.

Saint-Jeannet’s research will be published in the May 15 edition of the journal Development.

To determine where the neural crest cells migrated during development, the researchers labeled the embryonic cells with a fluorescent dye, then followed the path those marked cells took under a microscope. “We label the cardiac neural crest cells in one embryo and then graft them onto an embryo that is unlabeled. We let the embryo develop normally and look where those cells end up in the developing heart,” said Saint-Jeannet.

Knowing these paths, and the biological signals that govern them, could have implications for human health.

“There are a number of pathologies in humans that have been associated with abnormal deployment of the cardiac neural crest, such as DiGeorge Syndrome,” said Saint-Jeannet. “Among other developmental problems, these patients have an incomplete blood separation at the level of the outflow tract, because the cardiac neural crest does not migrate and differentiate at the proper location.”

DiGeorge syndrome is present in about 1 in 4,000 live births, and often requires cardiac surgery to correct.

“Xenopus could be a great model to study the signals that cause those cells to migrate into the outflow tract of the heart,’ said Saint-Jeannet. “If you can understand the signals that prevent or promote the colonization of this tissue, you can understand the pathology of something like DiGeorge syndrome and perhaps figure out what kind of molecule we can introduce there to force those cells to migrate further down.”

This research was supported by Bridge Funds from the University of Pennsylvania and the School of Veterinary Medicine and by a grant from the National Institutes of Health.