Crossing the Species Line: From Hearing Genes to Pig Livers
Hepsin, Hearing, and Cross-Species Medicine Hearing loss is way more common than people realize, and it usually starts with something breaking down inside the inner ear. Scientists already know that tiny proteins in the ear turn sound waves into electrical signals, but full knowledge on how those proteins form and interact is still a mystery. The research paper “Critical role of hepsin/TMPRSS1 in hearing and tectorial membrane morphogenesis” (Yang et al., 2024) caught my attention because it found that a liver enzyme plays an important role in hearing. The gene is called hepsin, and what they showed was that if you take mice that were deaf because they didn’t have hepsin, and give them the human version of the same gene, their hearing partly comes back.
Chinese scientists also pulled off another crazy milestone. They were able to transplant a genetically modified pig liver segment into a person with cancer. Totally different organs from Dr Yang's research, but both are examples of how scientists are starting to play with the boundaries between species to fix human problems. In the study by Dr. Yang et al (2024), they deleted the hepsin gene in mice, and those mice basically went deaf. When they looked at their inner ears, the tectorial membrane, which is the thin sheet that lets sound vibrations move hair cells, was damaged. They then put the human hepsin gene back in, and the membrane was able to rebuild itself enough for the mice to start hearing again. The issue was that it only worked if the enzyme’s protease activity was still working. That’s what activates other proteins like α- and β-tectorin, which hold the whole structure together. So a protein that’s normally doing stuff in the liver turned out to be essential for hearing. That idea of using something human to restore another species’ function connects directly to what the Chinese team did. According to “Gene-modified pig-to-human liver xenotransplantation” (Wang et al., 2025, Nature), they used a gene-edited pig whose DNA was tweaked to make it “look” human enough for the immune system to tolerate it. They removed three pig genes that trigger rejection and added three human genes that help blood flow and prevent clotting. They didn’t replace the patient’s real liver, but hooked up the pig liver alongside it just to see if it could work. And it did, for ten days. It made bile, kept blood flowing, and even produced albumin, which is a big deal for an organ that’s not supposed to survive in a human body. The patient’s family ended the experiment early, but it still proved something major. An animal organ can function inside a person if you tweak the genetics enough.
Both of these studies are really about the same question: how far can biology stretch across species lines? The mouse experiment used a human protein to restore hearing; the transplant used a genetically reprogrammed pig organ to keep a human alive. They’re different scales of the same idea. And it’s very interesting that hepsin is a liver enzyme, the same organ at the center of both stories. The enzyme fixes hearing in mice, and a pig liver modified with human genes works in a human. Two separate projects, both rewriting what “compatible” even means in biology. These are the early pieces of a new kind of medicine, one that isn’t just human-only anymore. It’s both amazing and unsettling, because it forces us to rethink what’s natural versus what’s possible. But if a human gene can help a deaf mouse hear, and a pig liver can function in a person, then the line between species isn’t as fixed as we may think.
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