Mechanisms of anoxic survival

In this project we have studied an animal that naturally can survive anoxia (no oxygen) for extended periods to find out how evolution has solved the problem of living without oxygen. This is something biomedical science has struggled with for decades with limited success although anoxia related diseases like stroke and heart infarction are among the most common causes of death and disabilities in the human population. The animal in focus is the crucian carp, a fish that in nature survives many months without oxygen every winter. We have examined physiological mechanisms that allows the crucian carp to survive anoxia, including its exotic ability to produce ethanol as the major metabolic end product when it has no access to oxygen. Our studies of the ethanol producing system have revealed that the crucian carp has an extra copy of a key enzyme in the metabolism, the pyruvate dehydrogenase which normally links glycolysis with the citric acid cycle. This extra copy has evolved to gain a new function, which is to turn pyruvate into acetaldehyde. The acetaldehyde is then transformed into ethanol. This new function makes this enzyme a pyruvate decarboxylase, an enzyme never found in a vertebrate but well known from brewers yeast. This new function was made possible by a genome duplication a few million years ago. Our publication of these findings in 2017 attracted much international media attention. We have also analysed the effect of anoxia and reoxygenation on the transcriptome (the levels of all different mRNA expressed) of the crucian carp brain. The results show that surviving anoxia is a very active process where more genes are turned on than turned off, and the changes involves thousands of genes. This contradicts the old notion that a key strategy for surviving energy limiting situations like anoxia is to shut down as much as possible. A somewhat surprising finding that we have made lately is that the crucian car actually shows signs of brain damage and memory loss after regaining access to oxygenated water after an anoxic episode. It appears to be the reoxygenation rather than the anoxia that causes the damage. Most interesting, it appears to effectively repair the damage, which makes it even more attractive as a model from a biomedical point of view. These results for the basis of a Young Research Talent grant that was recently awarded to one of the postdoctoral researchers in the project.

Very few animals can survive without oxygen (anoxia). By studying anoxia tolerant vertebrates we can find out how evolution has solved the problem of anoxic survival. It can be pointed out that anoxia is a major biomedical problem, playing a key role in d iseases like stroke, heart infarction and cancer. This project plan describes new directions in the research on the extremely anoxia tolerant crucian carp (Carassius carassius), while building on our successful research efforts in this area over several y ears. Now we set out to (1) explore the roles of recently discovered signaling pathways, two of which are related to the gaseous transmitters NO and H2S. This include identifying target proteins for S-nitrosylation, S-sulfhydration and O-GlcNAcylation. Th ese are novel types of protein modifications, that may play similar roles as classical phosphorylation. Our initial studies suggest that they are prevalent in the anoxic brain and heart of crucian carp, with S-nitrosylation even massively up-regulated, su ggesting an important role in anoxia defense mechanisms. Moreover, (2) we will charter the molecular and evolutionary background of the ethanol-producing pathway of crucian carp. Our results indicate that a genome duplication event has allowed for the evo lution of a novel enzyme, the first vertebrate pyruvate decarboxylase with analogous function to that of brewers yeast. As a final proof of principle we will use the crucian carp pyruvate decarboxylase genes to make a daring attempt to create the first et hanol producing mammalian cell.