Super-resolution microscopy reveals that Na+/K+-ATPase signaling protects against glucose-induced apoptosis by deactivating Bad

Activation of the apoptotic pathway is a major cause of progressive loss of function in chronic diseases such as neurodegenerative and diabetic kidney diseases. There is an unmet need for an anti-apoptotic drug that acts in the early stage of the apoptotic process. The multifunctional protein Na+,K+-ATPase has, in addition to its role as a transporter, a signaling function that is activated by its ligand, the cardiotonic steroid ouabain. Several lines of evidence suggest that sub-saturating concentrations of ouabain protect against apoptosis of renal epithelial cells, a common complication and major cause of death in diabetic patients. Here, we induced apoptosis in primary rat renal epithelial cells by exposing them to an elevated glucose concentration (20mM) and visualized the early steps in the apoptotic process using super-resolution microscopy. Treatment with 10nM ouabain interfered with the onset of the apoptotic process by inhibiting the activation of the BH3-only protein Bad and its translocation to mitochondria. This occurred before the pro-apoptotic protein Bax had been recruited to mitochondria. Two ouabain regulated and Akt activating Ca2+/calmodulin-dependent kinases were found to play an essential role in the ouabain anti-apoptotic effect. Our results set the stage for further exploration of ouabain as an anti-apoptotic drug in diabetic kidney disease as well as in other chronic diseases associated with excessive apoptosis.

Automated summary

Activation of the apoptotic pathway is a major factor in the progression of chronic diseases, and ouabain, a cardiotonic steroid, has shown potential as an anti-apoptotic drug by interfering with early steps in the apoptotic process. The activation of Ca2+/calmodulin-dependent kinases by ouabain plays a crucial role in its anti-apoptotic effect. This research paves the way for further exploration of ouabain as a treatment for diabetic kidney disease and other chronic conditions associated with excessive apoptosis.