Thomas Jefferson University-led group creates first 3D map of heart neurons

02 Jun 2020

New imaging technique Knife-Edge Scanning Microscopy gives insight into neurons' role in heart attacks and other conditions.

The normal functioning of the human heart is maintained by the the brain via an intricate network of nerves. When this communication is disrupted, it can result in heart disease, including heart attacks, sudden cardiac death and problems in blood supply.

As an added layer of control, the heart has its own “little brain”, called the intracardiac nervous system (ICN), which monitors and corrects any local disturbances in communication. The ICN can even protect cardiac muscle during a heart attack.

How the ICN carries out these roles has not been well understood because the organization and location of neurons was not known. But now, in a study published in iScience, researchers at Thomas Jefferson University, Philadelphia, PA, and collaborators have been able to answer these questions in significant detail.

“The ICN represents a big void in our understanding that falls between neurology and cardiology,” said co-senior author James Schwaber, PhD, director of the Daniel Baugh Institute for Functional Genomics and Computational Biology (DBI) and co-senior author of the study.

“The only other organ for which such a detailed high-resolution 3D map exists is the brain,” commented co-senior author Raj Vadigepalli, PhD, Professor of Pathology, Cell Biology and Anatomy. “What we have created is the first comprehensive roadmap of the heart’s nervous system that can be referenced by other researchers for a range of questions about the function, physiology, and connectivity of different neurons in the ICN.”

The study drew on technologies and expertise from different research groups (from Jefferson and University of Central Florida) and industry partners Strateos and MBF Bioscience, eventually creating a dual-approach pipeline.

Novel imaging technique

One approach involved a novel imaging technique called Knife-Edge Scanning Microscopy (KSEM) that allowed the researchers to build a precise 3D model of the entire rodent heart; it is the first use of this technology for cardiac research.

The second approach used a technique called laser capture microdissection to sample single neurons for gene expression analysis, as well as to precisely map their individual positions within the 3D structure of the heart.

The 3D map revealed hitherto unknown complexity of the ICN. The researchers found that the neurons that make up the ICN are found in a coherent band of clusters on the base (top) of the heart, where the heart’s veins and arteries enter and leave, but also extend down the length of the left atrium on the back of the heart.

Co-author Jonathan Gorky, a recently graduated MD/PhD student and now a resident at the Massachusetts General Hospital, commented, “Seeing the clustering of neurons around it was something we had always suspected but had never known for sure. It is really interesting to see the physical evidence of the ICN’s function and the precise distribution of the neurons.”

The gene expression analysis of individual neurons also pointed to previously unknown diversity of molecular identities or phenotypes. “We found that there are several different types of neuromodulators and receptors present,” said Dr. Vadigepalli. “This means that we don’t just have neurons in the heart that shut on and off activity, but also those that can fine-tune ICN activity.”

Sex-specific differences

When comparing male and female rat hearts, the researchers also found sex-specific differences in the way neurons were organized. Co-authors Alison Moss, PhD Candidate in Biochemistry and Molecular Pharmacology, and Shaina Robbins, a senior research assistant, are pursuing further analyses based on these findings.

“It could help us explain some of the differences in heart disease in men and women,” says Moss. “We’re now trying to create a 3D model of the intrinsic nervous system of the pig heart, which is even more anatomically comparable to the human heart, to explore those questions further.”

This project is part of a NIH research program called ‘Stimulating Peripheral Activity to Relieve Conditions’, or SPARC, which aims to promote development of therapeutic devices that modulate electrical activity in nerves to improve organ function. “Eventually the hope is to create a 3D map for the human heart, both in health and disease,” concluded Dr. Schwaber. “We’ve created the foundation for an endless possibility of future studies.”