Tufts scientists use advance bioelectric signals to repair alcohol-induced defects in embryos

Exposure to nicotine, alcohol or disruptions of a protein necessary for cell communication can cause the organs to develop improperly in an embryo. It's one reason why pregnant women are urged not to smoke or drink.

The mechanism by which the damage is caused has been the subject of investigation by Tufts University scientists for several years. In particular, they have been looking at the role of bioelectrical signals in organ patterning defects and the potential use of HCN2 ion channels as a repair technology.

Ion channels regulate cell communication electrically or chemically. HCN2 is the gene that encodes for a particular ion channel protein. The name is an acronym for potassium/sodium hyperpolarization-activated cyclic nucleotide-gated ion channel 2.

Vaibhav P. Pai and Michael Levin of the Allen Discovery Center at Tufts summarize their latest research in the journal Wound Repair and Regeneration June 4. Their article focuses on how HCN2 channels can restore malformed organs and other defects caused by nicotine, alcohol, or disruptions of the Notch protein.

Their research was done with the African clawed frog, Xenopus laevis, a popular model system for improving understanding of diverse human diseases. Their results suggest that molecular bioelectric repair methods should be explored for human applications in regenerative medicine, including birth defects and traumatic injury.

The amazing role of HCN2 channels

Professor Levin, who directs both the Allen Discovery Center and the Center for Regenerative and Developmental Biology at Tufts, described in an interview with Current Science Daily how his team came to focus on HCN2 channels:

"In 2018, we built a computer model of bioelectric signaling in normal embryos, and in those treated with various disruptive drugs or those receiving mutant Notch protein. We asked this model: What channels would we have to open or close, to make the incorrect bioelectrical pattern into the correct one?"

"The model, created and analyzed by our collaborator Alexis Pietak, suggested we try HCN2. We did, and saw an amazing repair of many defects, including brain, heart, face, and gut," Levin continued. "So, even `hardware' problems, like a broken Notch machinery, can sometimes be fixed `in software,' by physiological means, like increasing HCN2 activity."

Levin explained what broken Notch signaling is. "Notch is protein used by cells to communicate with other cells. It is especially important during creation of the nervous system. Errors in signaling by this protein lead to many developmental problems, including really strong birth defects of the brain."

"What Pai and I did," Levin said, "was introduce a mutated version of the Notch protein into frog embryos, which interfered with the ability of these cells to use Notch to signal to each other, and thus they had very malformed brains and no behavior."

The experiments

The researchers were exploring how HCN2 channels might rescue other organ systems and teratogenic defects (those caused in the embryo) beyond what they had found in their prior work. "Our goal was not to focus on one specific aspect of HCN2," they write, "which we have already done with nicotine neuroteratogenesis, but to explore the breadth of HCN2 rescue effect and its applicability to other organ systems."

They found that HCN2 expression rescued heart and gut defects caused by nicotine, alcohol, and Notch disruption, and that it worked even at a distance when injected on the opposite side of the animal. As the researchers summarize in the article: "Together, these data identify HCN2 as a tractable and potent regulator of organogenesis from all three germ layers [ectodermal, mesodermal, and ectodermal], reveal ion channel-dependent long-range coordination of organogenesis, and suggest molecular bioelectric strategies for repair in a roadmap for regenerative medicine applications."

This work was done with tadpoles in which four levels of defect severity were induced by disrupting voltage patterns in cells. When HCN2 channel activity was added to the bioelectric circuits, it was able to prevent and to rescue the damage.

Future human applications

In answer to a question about whether it was possible to activate the HCN2 channels in humans for repair, Levin said: "We have not done work in humans yet, but it will be with drugs; there are pharmaceuticals, already taken by human patients for epilepsy, that open HCN2 channels."

He added that "In animal models we also did it by introducing new HCN2 channels, a kind of gene therapy, but this is mostly for the experiments--to be certain of the mechanism. It won't be necessary for biomedical purposes."

As for future development of this embryonic defect repair, Levin said, "We hope to understand better the bioelectric code--which patterns code for correct anatomical structures--and develop new ways to induce those patterns in many different kinds of disease states."

Levin concluded, "Bioelectricity is an exciting path for not just birth defects --genetic and teratogen-caused--but also for regeneration after damage, and cancer. We have many papers on this and are actively researching therapeutics."

-----

Vaibhav P. Pai & Michael Levin, HCN2 Channel-induced Rescue of Brain, Eye, Heart, and Gut Teratogenesis Caused by Nicotine, Ethanol, and Aberrant Notch Signaling, Wound Repair and Regeneration, June 4, 2022.

DOI: https://doi.org/10.1111/wrr.13032