MitoBK Channels as a Therapeutic Target in Renal Cold Storage and Transplantation
Authors: Shrum Stephen , Parajuli Nirmala , Rusch Nancy , Macmillan‐Crow Lee Ann 
Published: June 2021

Patients with end‐stage renal failure require kidney transplantation to avoid life‐long hemodialysis associated with high mortality. The vast majority of transplanted kidneys come from deceased donors, which are placed in cold storage (CS) preservation solutions until a recipient is identified. Despite its necessity, kidneys exposed to CS undergo ischemic injury. Clinically, patients that receive a CS kidney versus one not exposed to CS are much more likely to have transplant dysfunction and failure. Our lab has shown that kidneys which undergo CS prior to transplantation (CS+Tx) sustain far more severe oxidative stress, mitochondrial damage, and renal dysfunction compared to kidneys transplanted without CS. Thus, there is a critical need to develop strategies to protect donor kidneys from CS ‐induced damage to improve long‐term renal function in transplant recipients. In this regard, the high‐conductance Ca2+‐activated K+ (BK) channel recently was discovered in the mitochondrial inner membrane (mitoBK) of cardiomyocytes and other cell types. When activated pharmacologically, the mitoBK channel reportedly protects against ischemia‐reperfusion injury in the heart by reducing mitochondrial damage and reactive oxygen species (ROS). We show, for the first time, that the mitoBK channel is expressed in the mitochondria of rat renal proximal tubular (NRK) cells in vitro and in rat kidney in vivo. We demonstrate that CS followed by rewarming (CS+RW) in vitro and CS+Tx in vivo reduces expression of the pore‐forming a subunit of the mitoBK channel in NRK cells (n=4) and rat kidney (n=4), respectively. Thus, we hypothesis that: mitoBK channels down‐regulate in response to CS+Tx –induced generation of mitochondrial ROS, which contributes to donor kidney injury after transplantation. Addition of BK activators during CS will protect against mitochondrial and renal injury following transplantation. Using Immunocytochemistry we show that CS+RW markedly alters localization of the mitoBK channel to the plasma membrane in NRK cells, which may be a protective response or may further indicate a deleterious loss of mitoBK. To determine whether mitochondrial‐ROS are responsible, current studies are assessing whether adding mitochondrial‐targeted antioxidants to CS will attenuate CS+RW –induced downregulation and altered localization of mitoBK. Whole‐Cell patch clamping is also being used to determine whether these CS+RW –induced plasmalemmal BK channels in NRK cells are functional. We also show that the specific BK opener, NS11021, attenuates CS+RW –induced mitochondrial superoxide and depolarization in NRK cells, as indicated by MitoSox and JC‐1 staining, respectively. Using high resolution‐respirometry, we are currently assessing whether NS11021 will similarly mitigate CS+RW –induced mitochondrial dysfunction in NRK cells. Future studies with our rat in vivo model of renal CS+Tx will evaluate whether NS11021 protects from CS+Tx ‐induced oxidative stress, mitochondrial dysfunction, and renal dysfunction.Support or Funding InformationFunded by AHA Predoctoral Fellowship #16PRE30830010, NIGMS grant T32 GM106999, and UAMS pilot grantThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.