A new type of cell has been identified in the heart that is linked to regulating heart rate – and the discovery promises to advance our understanding of cardiovascular defects and diseases, once these cells have been more extensively studied.
The new cell is a type of glial cell – cells that support nerve cells – like astrocytes in the central nervous system (the brain and spinal cord). Named nexus glia, they're located in the outflow tract of the heart, the place where many congenital heart defects are found.
The new cell type was first found in zebrafish, before being confirmed in mouse and human hearts too. Experiments on zebrafish found that when the cells were removed, heart rate increased; and when genetic editing blocked glial development, the heartbeat became irregular.
"We don't completely know the function of these cells, but the concept that if you get rid of them, heart rates increase, could link it to certain disease cases," says biologist Cody Smith from the University of Notre Dame in Indiana.
"I think these glial cells could play a pretty important role in regulating the heart. This is another example of how studying basic neurobiology can lead to the understanding of many different disorders."
Finding the nexus glia cells took plenty of detective work. It was previously thought that star-shaped glia (astroglia) such as astrocytes could only be found in the brain and spinal cord, although "glial-like processes" had already been spotted in the heart.
Astroglia cells are important to the central nervous system because they help maintain the cellular environment for neurons and provide support and nutrients for them as well. So it seems plausible that they should be found in the peripheral nervous system (the remaining nerves in the body) too, the researchers reasoned.
Different types of glial cells with astroglia properties have been found in other organs – including the pancreas and the lungs – but their function isn't yet well understood. That led the team to the heart in their search for new types of cells.
"I thought that if we could find a new cellular piece to the cardiovascular puzzle, it could be foundational for future work," says biologist Nina Kikel-Coury from the University of Notre Dame.
Sure enough, a combination of scientific techniques – including time-lapse imaging and single-cell sequencing – revealed the presence of nexus glia in zebrafish, mouse, and human tissue, in cells which appear to support heart function and regulation.
Having only just discovered these cells, it's going to take more time to learn about their roles and functions, but they could potentially be linked to a variety of medical conditions – including something called dysautonomia, caused by breakdowns in the normal workings of the autonomic nervous system, which the brain uses to control involuntary physiological processes like heart rhythm and breathing.
Another possible avenue for future research is analyzing other key organs in the body for cells similar to nexus glia – they could be hidden away, secretly providing crucial support to the way that our biological systems function.
"For me the definition of great science is something that you discover that opens up even more questions, and this, I think, is the definition of that," says Smith.
"It's a discovery that now we have 100 questions we didn't even know existed, so we're following up on them to explore this path that has never been studied before."
The research has been published in PLOS Biology.