Re-oxygenation resilience - the overlooked element of anoxic survival

It is well known that the crucian carp (Carassius carassius) has a unique ability to survive without oxygen. The fish use this ability in the winter when the small lakes, their habitat, gets a thick layer of ice that restricts the flow of oxygen from air into water, and the formation of oxygen from plants. The crucian carp matches its energy demand to the availability, and it can convert lactic acid to
alcohol. This allows it to survive longer using anaerobic metabolism without accumulating lactic acid that would otherwise acidify the blood. But the lack of oxygen is not only a problem from an energetic perspective - total lack of oxygen interferes with the balance of mitochondria (the organelles responsible for respiration and the formation of ATP), and this disturbance makes the cell emit a "death signal" that lead to the death of that cell. Preliminary results shows that there is an increased incidence of cell death in the brain of crucian carp during the first day of re-oxygenation, but not during anoxia. As the crucian carp survive repeated periods of anoxia and re-oxygenation in the wild, it must be able to repair and even limit the amount of damage. This makes crucian carp an interesting fish not only from a physiological, but also biomedical, perspective. When humans get a blood clot in the brain or the heart, something that affects many people every year, the lack of blood supply leads to lack of oxygen and when blood flow and thereby oxygen supply is restored it leads to long-term damage to the tissue. In this project, I will examine the processes that contribute to the ability of the crucian carp to survive re-oxygenation.The understanding arising from studies on crucian carp can expand our understanding of the general physiological mechanisms, an understanding that may even be useful in biomedical research.

The ability of the crucian carp (Carassius carassius) to survive anoxia for
several months makes this animal a unique model. This anoxia tolerance
is gained by matching ATP demand with ATP production. Nevertheless,
without oxygen, the respiratory chain may be at a full stop, resulting in
mitochondrial depolarization - a death signal in other animals. Moreover, it
is often overlooked that when oxygen is restored, free oxygen radicals are
bound to be produced, damaging mitochondria and DNA. Indeed, preliminary
data reveal an increased occurrence of apoptotic cells in the crucian carp
brain after re-oxygenation, but not in anoxia. Thus, the crucian carp must
posses effective repair mechanisms, as it evidently survives many years
of repeated re-oxygenation episodes in nature. This makes crucian carp
interesting even from a biomedical perspective, as reperfusion after the
ischemia associated with stroke and heart attack can be as detrimental
as the ischemia itself. Furthermore, recent analyses reveals that a large
proportion of the crucian carp brain transcriptome is differentially regulated
in anoxia and re-oxygenation, revealing very active molecular responses
rather than shutting down and waiting for 'better times'. At the same time,
post-transcriptional mechanisms may be at work to modulate or even
dampen the transcriptional response. Using an array of methods, from
real-time quantitative PCR and western blotting, to the recently developed
ribosome footprint profiling, I will examine and identify the pathways that are
keys to the re-oxygenation response. I will look at the damage of the brain
in more detail, to determine if the processes are restricted to certain areas,
and also look at different stages of recovery. Lastly, to be able to quantify the
functional consequences of anoxia/re-oxygenation damage, I will investigate
if increased cell death also occurs in the heart, another sensitive organ, and
measure its effects on cardiac performance.