Scientists have recently noticed disturbances in a newly discovered type of heart cell. They now believe that these may underlie certain congenital heart abnormalities and a broader array of autonomic nervous system conditions. As for the cells discovered, they are called cardiac nexus glia. They were shown to have a vital role in both heart rate and heart rhythm. Previously, scientists only knew that nexus glia occurred just in the central nervous system.
Glial cells are cells found throughout the nervous system. They are also critical for normal development and function. According to experts, these cells are categorized according to their primary function in the nervous system. There are also subtypes which are ensheathing glia, microglia, and astroglia.
There are several parts of the nervous system. These are the central nervous system (CNS), the peripheral nervous system (PNS), and the autonomic nervous system (ANS). The PNS and ANS work in tandem to control nonbrain organ systems and functions. Such functions are muscle movement, digestion, “fight-or-flight” responses, breathing, circulation, and heart rate.
As of late, researchers have discovered a new type of glial cell found in the heart. This is vital for both development and function. This cell may also hold the secret behind specific congenital abnormalities and other cardiac diseases. Researcher Cody Smith, Ph.D. is associate professor in the Department of Biological Sciences at the University of Notre Dame, IN. He and his colleagues reported what they discovered in PLOS Biology. They also made time to make an outline of the cell’s function and its location in the heart.
In order to explain their findings, they used tissue from zebrafish, mice, and humans. Dr. Smith then pointed out a region of the heart called the outflow tract (OT). The OT held the cells in his search for astroglial-like cells. The researchers discovered that this novel discovery of the cardiac nexus glia was consistent with all the species. Interestingly enough, this region is also what affects the carrier’s heart health.
From a developmental point of view, neuronal cells in the CNS typically precede those in the PNS and ANS. Hence, the doctor and his colleagues looked for the origin of these astroglial cell populations before they traversed into the heart. The doctor made use of the zebrafish model where he was able to confirm the source of these glial cells. He discovered that it was actually the neural crest located in the hindbrain.
The doctor fertilized the zebrafish embryos and within 24 hours, the glial cells started to migrate into the heart. By the fourth day, they had populated the OT. This is the area where a certain group of the cells differentiated into cardiac nexus glia. The other group differentiated into cardiomyocytes and smooth muscles cells. The entire team then confirmed the presence of these astroglia in both the mice and the human cardiac tissue. Unlike the previous research made, it was the astroglia that preceded neuronal development. This process was a challenge to explain provided that the axonal branching of neurons only happens when the glia isn’t there.
The Astroglia and Heart Function
The team started out with a hypothesis. They believed that these cardiac nexus glia regulate heart-related autonomic functions. To see if this was accurate, Dr. Smith and his colleagues removed or ablated the cells across the species they observed. On average, the ablated samples had increased the heart rates to more than 20 beats each minute. This rhythmic increase is often referred to as ventricular tachycardia.
Ventricular tachycardia happens as a result of an imbalance of ionic activity in the OT. The team of scientists wanted to further see if whether the absence of cardiac nexus glia in the region was its chief cause. In order to find out, they extirpated the cardiac nexus glia in other regions, most notably the atrium, which was the upper chamber of the heart. They found that in terms of heart rate, there was no effect. This validated their belief in the value of the cardiac nexus glia in the OT region.
Moreover, they discovered the significant downstream effects of this cardiac nexus glia disruption on the sympathetic and parasympathetic branches of the ANS. The chemical manipulation of cardiac nexus glia brought about a substantial increase in the duration of ventricular fibrillation, which is an irregular heartbeat. This spoke of its reactive role of the sympathetic nervous system in dysrhythmia.
Dr. Smith also noted that 30 percent of congenital heart abnormalities have an immediate relationship to OT dysfunction. But the question on whether or not this is particularly because of an anomaly of cardiac nexus glia in the developmental process has yet to be fully understood and clarified.
Understanding the Neurons Found in the Cardiovascular System
Even with the new experimental data on astroglial manipulation and cardiac function, how or if this translates to heart diseases in humans remains to be a mystery. On the other hand, congenital heart abnormalities are can already be identified in utero during pregnancy, later-life cardiovascular problems are multifactorial because these involve the dynamic connection between genetics and lifestyle.
When the doctor was asked whether this discovery of astroglia in the heart may underlie a possible connection between extreme stress or emotional states and cardiac problems, Dr. Smith believed that this new research was not yet translational. He spoke to Medical News Today and said, “I think it is way too early to know the physiological role of these cells. We really are at the earliest phases of understanding their role. […] As for the clinical observations you mentioned, my hope is that as we begin to study them more in model systems like zebrafish, we will know which narrower set of questions the field can investigate for humans.”
Nonetheless, this cellular discovery may have been unexpected, but this may also herald future discoveries, particularly in the field of cardiac neurobiology. Dr. Smith said, “We started this project because we were fascinated with the unknown of neurobiology but perhaps stumbled on a cell that is relevant to having a healthy heart. The investment in basic science was the spark, though.” He further explained, “As with other glial cells in the nervous system, it seems like we are just at the tip of the iceberg with the role of glia in nervous system function. It is an exciting time to be in the field.”