"Drugs we currently use for heart failure are not very effective," explained lead investigator Walter J. Koch, PhD, Professor and Chairman of the Department of Pharmacology at TUSM, and Director of the Center for Translational Medicine at TUSM. But, he added, "The more we learn about the disease mechanism, the more drug targets we'll find."
That is what Koch and colleagues at Thomas Jefferson University and the University of California, Davis, achieved in their latest study, which appears in the March 5 issue of the online journal PLOS ONE. The report is the first to show that an enzyme called GRK5 (G-protein coupled receptor kinase 5) can gain access to a heart cell's nucleus – its command center, where control of its genes is maintained – by way of a transport mechanism involving calcium and a protein known as calmodulin. Once calcium and calmodulin deliver GRK5 to the nucleus, the enzyme usurps control over specific genes, ultimately causing hypertrophy, in which heart cells grow larger in size. Hypertrophy is a biological hallmark of heart failure.
GRK5 had previously been identified as a key player in maladaptive cardiac hypertrophy, which is the end stage of heart failure, when the heart muscle becomes enlarged and unable to pump enough blood to keep vital organs functioning. While GRK5's ability to get inside the nucleus was known, Koch and colleagues worked to fill in the missing links in its transport mechanism. Those links, they hope, will not only allow them to better understand GRK5's role in causing heart cells to increase in size but also find ways to block that process to more effectively treat heart failure.
The GRK5 enzyme is a unique member of the GRK family, owing to its presence in the nucleus. Its journey begins at the cell membrane, where signals received by a molecule at the cell surface known as a Gq-coupled receptor prompt "escorts" – one of which is calmodulin, as the researchers discovered – to attach to GRK5 and guide it to the nucleus.
The team found that GRK5's transport requires calmodulin after examining different places on the enzyme where various escort molecules attach. They then introduced mutations that altered the attachment sites. Only when calmodulin-binding residues on GRK5 were mutated was the enzyme prevented from reaching the nucleus. Those mutations led to dramatic decreases in nuclear GRK5 levels and corresponding declines in the activity of genes known to drive cardiac hypertrophy. Calmodulin's ability to bind to GRK5 is in turn dependent on calcium. The same results were obtained both in vitro, using human heart muscle cells cultivated under laboratory conditions, and in vivo, in mice.
The team's research also marks a breakthrough in scientists' understanding of the role of neurohormones in hypertrophy. Released by specialized neurons into the bloodstream, neurohormones have long been cited as a cause of heart cell enlargement.
"One of the novel findings to fall out of this paper is that not all hypertrophic signals from neurohormones are the same," Koch explained. "That's something to keep in mind as we move forward."
The next step, according to Koch, is to test the ability of different agents to keep GRK5 out of the nucleus. "We are now discussing a trial on inhibition of another cardiac GRK, GRK2," he said. He cautioned, however, that trials in patients with GRK5 inhibition are years away. First, agents capable of blocking GRK5 transport must be identified and tested in animals.
The work is an important advance for Temple's Center for Translational Medicine. GRK5 enters the pipeline of novel drug targets under investigation by the Center's scientists and clinicians, who share the common goal of coordinating clinical practice and basic research to speed the delivery of new therapies to patients.
"It's another entry into larger, pre-clinical animal studies," Koch said. "Something new to start down the path of translational medicine."
Other researchers contributing to the work include Jessica I. Gold, Jeffrey S. Martini, and Jonathan Hullmann at the Center for Translational Medicine at Thomas Jefferson University; Erhe Gao, J. Kurt Chuprun, Douglas G. Tilley, and Joseph E. Rabinowitz at TUSM; and Julie Bossuyt and Donald M. Bers at the University of California, Davis.
The research was supported by NIH grants P01 HL091799 and P01 HL075443 and by a pre-doctoral Fellowship from the Great Rivers Affiliate of the American Heart Association.About Temple Health
Jeremy Walter | EurekAlert!
Second cause of hidden hearing loss identified
20.02.2017 | Michigan Medicine - University of Michigan
Prospect for more effective treatment of nerve pain
20.02.2017 | Universität Zürich
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
22.02.2017 | Power and Electrical Engineering
22.02.2017 | Life Sciences
22.02.2017 | Innovative Products