Virus enables heart cells to become 'biological pacemakers'
17 Dec 2012
Cedars-Sinai Heart Institute researchers have reprogrammed ordinary heart cells to become exact replicas of pacemaker cells.
The achievement was made by injecting a virus carrying a single gene (Tbx18) to directly reprogramme heart muscle cells.
Researchers claim this is major step forward in the decade-long search for a biological therapy to correct erratic and failing heartbeats.
“Although we and others have created primitive biological pacemakers before, this study is the first to show that a single gene can direct the conversion of heart muscle cells to genuine pacemaker cells,” said Hee Cheol Choo, a Heart Institute research scientist.
“The new cells generated electrical impulses spontaneously and were indistinguishable from native pacemaker cells.”
This is major step forward in the decade-long search for a biological therapy to correct erratic and failing heartbeats
Pacemaker cells generate electrical activity that spreads to other heart cells in an orderly pattern to create rhythmic muscle contractions.
If these cells go awry, the heart pumps erratically at best; patients healthy enough to undergo surgery often look to an electronic pacemaker as the only option for survival.
The heartbeat originates in the sinoatrial node (SAN) of the heart’s right upper chamber, where pacemaker cells are clustered. Of the heart’s 10 billion cells, fewer than 10,000 are pacemaker cells, often referred to as SAN cells.
Once reprogrammed by the Tbx18 gene, the newly created pacemaker cells - “induced SAN cells” or iSAN cells - had all key features of native pacemakers and maintained their SAN-like characteristics even after the effects of the Tbx18 gene had faded.
But the Cedars-Sinai researchers, employing a virus engineered to carry a single gene (Tbx18) that plays a key role in embryonic pacemaker cell development, directly reprogrammed heart muscle cells (cardiomyocytes) to specialised pacemaker cells.
The new cells took on the distinctive features and function of native pacemaker cells, both in lab cell reprogramming and in guinea pig studies.
Previous efforts to generate new pacemaker cells resulted in heart muscle cells that could beat on their own.
Still, the modified cells were closer to ordinary muscle cells than to pacemaker cells. Other approaches employed embryonic stem cells to derive pacemaker cells.
But, the risk of contaminating cancerous cells is a persistent hurdle to realising a therapeutic potential with the embryonic stem cell-based approach.
The new work, with astonishing simplicity, creates pacemaker cells that closely resemble the native ones free from the risk of cancer.
If subsequent research confirms and supports findings of the pacemaker cell studies, the researchers said they believe therapy might be administered by injecting Tbx18 into a patient’s heart or by creating pacemaker cells in the laboratory and transplanting them into the heart.
