TRPA1 in ischemic cardiovascular disease (Resubmission)

Cardiovascular disease represents the leading cause of death in developed countries and can inflict serious complications in non-fatal cases. In acute myocardial infarction, the blood supply to the cardiac muscle is interrupted. Timely restoration of blood supply (reperfusion) reduces the occurrence of acute heart failure. Reperfusion is necessary to save tissue, but it is the reperfusion during which cellular stress and death occurs. Therefore, an aim addressed here is to limit the cell damage during ischemia/reperfusion. We hypothesize that the same channel in the cell membrane detects but also contributes to the caused damage. This channel, called TRPA1, is found in nervous tissue, but also in the active cells of the heart, where its role is unclear. The channel is activated by a variety of substances which arise during the time without blood supply and immediately thereafter. Thus, TRPA1 could be an important sensor for myocardial infarctions. However, activation of the channel admits further calcium to cells of the heart, which could worsen the inflicted damage. In this respect, in the acute situation, inhibition of TRPA1 is expected to limit damage. However, the channel can also activate protective mechanisms, and can be reduced in relevance by prior activation, which is why activation of the channel at the right time and location might also be a beneficial option to be considered. In this respect, preplanned cardiac surgery should be considered, where, in contrast to unexpected events, such therapy could be used with a preplanned schedule ahead. The project will investigate crosstalk between nerve cells and the heart in case of a cardiac event. A particular focus will be given to diabetic conditions, where the nervous system is at least partially damaged. In summary, the project will clarify the role of TRPA1 in cardiac ischemia, and explore potential therapeutic applications, as we consider it an attractive drug target in cardiovascular disease.

The whole project has developed into four completed lines of research, which are each reflected by their dedicated paper: Paper 1 investigated the TRPA1 ion channel, which is known to respond to various stimuli, in heart cells (cardiomyocytes). TRPA1 is present in very low amounts in these cells, making its functional role negligible. Despite previous studies suggesting some activity, the authors conclude that TRPA1 does not significantly influence heart cell behavior. This was verified by various techniques, including RNA analysis and calcium imaging, to support their findings. Overall, the study suggests that TRPA1 is not functionally relevant in cardiomyocytes, contrasting with its more prominent role in other cell types like sensory neurons. Paper 2 investigated the role of the TRPA1 ion channel in myocardial infarction, a condition where blood flow to the heart is blocked. Although TRPA1 activation on neurons might influence heart cell survival and damage during this event, the in vivo experiments to measure heart injury and cell survival after lack of and restoration of blood flow suggest at best a limited role of targeting TRPA1. Therefore, it is questionable whether this could offer new treatment options to protect the heart during heart attacks or improving recovery and reducing damage to heart tissue. Paper 3 investigates the ability to detect the TRPA1 channel in tissue. Given that all publicly available antibodies are questionable, we turned to a technique called RNAscope to visualize TRPA1's RNA in specific cells. This was compared to the ground truth of function, provided by functional responses measured through calcium imaging. RNAscope clearly shows a positive correlation to the functional response, however, the association is not as high as expected. The study helps to decide which technique should be used for further investigations. Paper 4 is a study on ischemia-reperfusion injury, in which a new model was established. This demonstrates that neurons secrete factors into fluid, which can be transferred to heart cells and protect them. When exposed to ischemia, the conditioned supernatant from sensory neurons increased the tolerance of heart muscle cells to ischemia and reperfusion. The protective effect persisted even after removal of extracellular vesicles and exposure to protease activity. This research sheds light on potential mechanisms for improving cardiomyocyte survival during heart-related stress.