Macrophages typically protect the body against invading pathogens, but a new study published in April of this year, shows their role in helping to keep the heart beating. It has been known for a couple years that macrophages live in healthy heart tissue but their role was not known, until now.
Cardiomyocytes, the heart muscle cells, are responsible for contracting in response to electrical signals, pumping blood through the heart. It is thought that macrophages squeeze in between the cardiomyocytes and help them receive the signals and stay on beat. A cell biologist at Harvard Medical School performed an experiment to test their role. He genetically engineered a mouse to not have macrophages and then performed a cardiac MRI. What he found to be interesting was that the heartbeat was too slow and too irregular to even perform the scan. Isolating an individual heart macrophage and testing it for electrical activity did not lead to any answers either. It wasn't until the macrophage was coupled with a cardiomyocyte that researchers saw what they were looking for. When they were coupled, the two cells began communicating electrically.
When in their resting state, cardiomyocytes have more positive ions outside the cell than in. When the cardiomyocyte receives an electrical signal from a neighboring cell, positive ions rush in causing a depolarization and the ability for this cell to contract and send the signal on to the next cardiomyocyte. Previously, it was thought that cardiomyocytes could conduct these electrical signals on their own, but now it is being demonstrated that this might not be the case. Macrophages link to cardiomyocytes by a protein which allows the macrophages to transfer positive charges making it easier for the heart cells to depolarize.
The next step is to determine if macrophages play the same role in humans.
References:
Eaton, Elizabeth. “Immune Cells Play Surprising Role in Steady Heartbeat.” Science News, 16 May 2017, www.sciencenews.org/article/immune-cells-play-surprising-role-steady-heartbeat.
This is fascinating information Taylor, Thank you for sharing it. Beyond this new found role, cardiac macrophages are also responsible for the inflammatory response in the heart, myocardial reconstruction, and left vertical remodeling. For this reason scientist have been looking at cardiac macrophages for post Myocardial infarction recover. Knowing now that they are critical for electrical signaling might make their role in post MI recovery even more critical.
ReplyDeleteReferences:
Frantz, S., & Nahrendorf, M. (2014, May 01). Cardiac macrophages and their role in ischaemic heart disease. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3989449/