BK channels as targets of cGMP signalling in myocardial pre- and postconditioning and survival

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This project covers various aspects of cardioprotective cGMP signalling opposing ischaemia and reperfusion (I/R) damages via mitochondrial K+ channels of the KATP (mitoKATP) and BK type (mitoBK). Previously we studied hearts obtained from global BK-null mice in an ex vivo Langendorff perfusion setup and found evidence for mitoBKs in cardiac myocytes (CMs) as infarct-limiting factors. In the absence of BK, post-anoxic reactive oxygen species (ROS) production from isolated CM mitochondria was elevated indicating that mitoBK fine-tune the oxidative state at hypoxia and re-oxygenation. In collaboration with members of this research unit we further demonstrated that brief episodes of ischaemia applied directly after an ischemic insult (iPost) and cGMP-elevating drugs such as sildenafil render the heart less susceptible to the I/R injury, but only if NO-stimulated guanylyl cyclase (NO-GC) and mitoBKs were present in the CM. Because it is well established that canonical BK channels usually present at the plasma membrane of cells are directly stimulated by cGMP/cGMP-dependent protein kinase type I (cGKI) it seems possible that cardioprotection afforded by iPost and/or cGMP-elevating compounds require mitoBKs in CMs to prevent cell death in vivo. Our ongoing studies will now reveal the dynamics of local and global cGMP prior, during and upon a period of ischaemia following reperfusion. cGMP in the CMs and in different non-myocyte cell types will be visualized by FRET imaging in the presence and absence of i.) cGMP-elevating drugs and ii.) endogenous CM NO-GC, cGKI and BK using established single cell assays and intact beating hearts derived from transgenic redDE5 or cGi500 cGMP indicator mouse models. Finally, we aim to study the response of our time- and tissue-specific mutants lacking either NO-GC, cGKI and BK in CMs to acute I/R setups and to models involving post-infarction remodeling processes of the myocardium to uncover how NO-GC/cGMP and mitoBK oppose e.g. ROS overproduction and cell death. This subproject will also reveal if long-term survival, functional recovery and/or wound healing/regenerative processes in the post-infarcted heart require a functional cGMP pathway in CMs. To answer all major questions of our project, we strongly interact with the other groups of this research unit. By continuing exchange in tools and techniques we will improve our understanding of local/compartmentalized vs global cGMP signalling and the role of NO-GC, cGKI and mitoBKs in ischemic hearts with either timely reperfusion or during long-term follow up after MI, which should validate the different factors of this pathway as potentially druggable targets.