2 min readScientists Discover a Key to Mending Broken Hearts

La Jolla, CA — Researchers at the Salk Institute have healed injured hearts of living mice by reactivating long dormant molecular machinery found in the animals’ cells, a finding that could help pave the way to new therapies for heart disorders in humans.

The new results, published November 6 in the journal Cell Stem Cell, suggest that although adult mammals don’t normally regenerate damaged tissue, they may retain a latent ability as a holdover from development like their distant ancestors on the evolutionary tree. When the Salk researchers blocked four molecules thought to suppress these programs for regenerating organs, they saw a drastic improvement in heart regeneration and healing in the mice.

The findings provide proof-of-concept for a new type of clinical treatment in the fight against heart disease, which kills about 600,000 people each year in the United States—more than AIDS and all cancer types combined, according to the U.S. Centers for Disease Control and Prevention.

“Organ regeneration is a fascinating phenomenon that seemingly recapitulates the processes observed during development. However, despite our current understanding of how embryogenesis and development proceeds, the mechanisms preventing regeneration in adult mammals have remained elusive,” says the study’s senior author Juan Carlos Izpisua Belmonte, a professor in the Gene Expression Laboratory at Salk.

Within the genomes of every cell in our bodies, we have what information we need to generate an organ. Izpisua Belmonte’s group has for many years focused on elucidating the key molecules involved in embryonic development as well as those potentially underlying healing responses in regenerative organisms such as the zebrafish.

Indeed, back in 2003, Izpisua Belmonte’s laboratory first identified the signals preceding zebrafish heart regeneration. And in a 2010 Nature paper, the researchers described how regeneration occurred in the zebrafish. Rather than stem cells invading injured heart tissue, the cardiac cells themselves were reverting to a precursor-like state (a process called ‘dedifferentiation’), which, in turn, allowed them to proliferate in tissue.

Although in theory it might have seemed like the next logical step to ask whether mammals had evolutionarily conserved any of the right molecular players for this kind of regenerative reprogramming, in practice it was a scientific risk, recalls Ignacio Sancho-Martinez, a postdoctoral researcher in Izpisua Belmonte’s lab.

“When you speak about these things, the first thing that comes to peoples’ minds is that you’re crazy,” he says. “It’s a strange sounding idea, since we associate regeneration with salamanders and fish, but not mammals.”

Most other studies have looked to the hearts of neonatal mammals for molecular clues about proliferation, to no avail. “Instead, we thought, ‘If fish know how to do it, there must be something they can teach us about it,’” says the study’s first author Aitor Aguirre, a postdoctoral researcher in Izpisua Belmonte’s group.

The team decided to focus on microRNAs, in part because these short strings of RNA control the expression of many genes. They performed a comprehensive screen for microRNAs that were changing in their expression levels during the healing of the zebrafish heart and that were also conserved in the mammalian genome.

Article adapted from a Salk Institute for Biological Studies news release.

Publication: In vivo reprogramming with conserved regenerative effectors promotes robust mammalian heart regeneration. Aitor Aguirre, Nuria Montserrat, Serena Zachiggna, Emmanuel Nivet, Tomoaki Hishida, Marie Nicole Krause, Leo Kurian, Alejandro Ocampo, Eric Vazquez-Ferrer, Concepcion Rodriguez-Esteban, Sachin Kumar, James J. Moresco, John R. Yates III, Josep Maria Campistol, Ignacio Sancho-Martinez, Mauro Giacca and Juan Carlos Izpisua Belmonte Cell Stem Cell (2014): Click here to view.

Regenerative Medicine

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