A new study contradicts controversial findings from a 2017 study that had suggested around two-thirds of myenteric neurons replicate within 1 week under normal conditions, which – if true – would have an impact on research into several GI diseases and pathologies.
Previous research had suggested that enteric nerve cells, which help control peristalsis throughout the digestive tract, do not replicate in the small intestine under normal conditions, with some limited potential for it observed only after injury, wrote Heikki Virtanen, MD, of the University of Helsinki (Finland), and colleagues. Their report is in Cellular and Molecular Gastroenterology and Hepatology. However, a study by Subhash Kulkarni, PhD, published in 2017, “challenged this dogma, suggesting that almost 70% of myenteric neurons are replaced within 1 week under normal physiological conditions.” These findings were reportedly considered controversial and presented “possibly far-reaching impact on future research,” Dr. Virtanen and colleagues explained.
According to the researchers, the difference between the controversial study findings and other research results may be partially explained by differences in methodology such as DNA labeling times, antigen retrieval methods, and analyzed portions of the small intestine. Dr. Virtanen and colleagues initiated the current study because no systematic evaluation of those potential confounding variables or attempt at independently replicating the findings had been undertaken.
For example, Dr. Virtanen and colleagues administered the nucleoside analogue 5-iodo-2’-deoxyuridine (IdU) in drinking water with the same concentration and labeling period, DNA denaturation steps, and antibodies as Dr. Kulkarni’s 2017 study had used. However, they also examined additional areas of the small intestine, employed paraffin embedding, performed parallel analysis using “click chemistry”-based detection of 5-ethynyl-2’-deoxyuridine (EdU), and more.
The gut’s epithelial cells turn over within 1 week “and serve as an internal positive control for DNA replication,” the researchers noted. In this study, IdU-positive enteric nerve cells were not revealed in microscopic analysis of immunohistochemically labeled small intestines of both cryosections and paraffin-embedded sections or in measurement of 300 ganglia in the small intestine. In contrast, the researchers wrote that the epithelium demonstrated label retention.
In their discussion section of their paper, Dr. Virtanen and colleagues wrote that while “proliferating epithelial cells were readily detectable” in the study, they were unable to detect enteric neuronal proliferation. Although noting that they could not identify reasons for the observations by Kulkarni and colleagues, Dr. Virtanen and colleagues continued to suspect unnoticed variables in the 2017 study affected its findings.
“The fact that the repeat of exactly the same experiment with the same reagents and methods did not reproduce the finding, not even partially, supports this interpretation and is further supported by the same conclusion using EdU-based click chemistry data and previous studies.”
The authors disclose no conflicts.