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Desmosomal proteins including desmoglein‐2 (DSG2), plakoglobin (PG), and desmoplakin (DP) are components of the intercalated disc and mediate cardiac myocyte cell‐cell adhesion. Enhancement of cardiac myocyte cohesion, referred to as “positive adhesiotropy”, was demonstrated to be a function of sympathetic signaling in the heart and to be relevant for a sufficient positive inotropic response to adrenergic stimulation. Here we used the positive inotropic agent digitoxin to further investigate the link between inotropy and adhesiotropy in cardiac myocytes. Digitoxin failed to enhance cardiac contractility in Langendorff‐perfused mouse hearts lacking the desmosomal plaque protein PG indicating that a positive inotropic response requires intact desmosomal adhesion. To investigate a potential effect of digitoxin on desmosomal adhesion, atomic force microscopy was applied and revealed that digitoxin increased the binding force of the adhesion molecule DSG2 at cell‐cell contact areas. This was paralleled by enhanced cardiac myocyte cohesion in both HL‐1 cardiac myocytes and murine cardiac slices as determined by dissociation assays as well as by accumulation of DSG2, DP and PG at cell‐cell contact areas. However, total protein levels or cytoskeletal anchorage of desmosomal proteins was not affected. siRNA‐mediated depletion of DSG2, PG or DP abrogated increase of cell cohesion demonstrating that intact desmosomal adhesion is required for positive adhesiotropy. Mechanistically, digitoxin caused activation of ERK1/2 but not of p38MAPK or Src. In line with this, inhibition of ERK1/2 signaling using the inhibitor UO 126 abrogated the effects of digitoxin on cell‐cell adhesion and desmosomal reorganization. These results show that the positive inotropic agent digitoxin enhances cardiac myocyte cohesion with reorganization of desmosomal proteins in an ERK1/2‐dependent manner. Desmosomal adhesion seems to be important for a sufficient positive inotropic response of digitoxin treatment which can be medical relevant for the treatment of heart failure. Support or Funding Information This work was supported by the Ludwig‐Maximilians‐Universität Munich with the Wifomed program and the Deutsche Forschungsgemeinschaft DFG [grant number WA2474/11‐1 to J.W.] This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

No abstract

Desmosomal proteins are components of the intercalated disc and mediate cardiac myocyte adhesion. Enhancement of cardiac myocyte cohesion, referred to as "positive adhesiotropy", was demonstrated to be a function of sympathetic signaling and to be relevant for a sufficient inotropic response. We used the inotropic agent digitoxin to investigate the link between inotropy and adhesiotropy. In contrast to wild-type hearts, digitoxin failed to enhance pulse pressure in perfused mice hearts lacking the desmosomal protein plakoglobin which was paralleled with abrogation of plaque thickening indicating that positive inotropic response requires intact desmosomal adhesion. Atomic force microscopy revealed that digitoxin increased the binding force of the adhesion molecule desmoglein-2 at cell-cell contact areas. This was paralleled by enhanced cardiac myocyte cohesion in both HL-1 cardiac myocytes and murine cardiac slices as determined by dissociation assays as well as by accumulation of desmosomal proteins at cell-cell contact areas. However, total protein levels or cytoskeletal anchorage were not affected. siRNA-mediated depletion of desmosomal proteins abrogated increase of cell cohesion demonstrating that intact desmosomal adhesion is required for positive adhesiotropy. Mechanistically, digitoxin caused activation of ERK1/2. In line with this, inhibition of ERK1/2 signaling abrogated the effects of digitoxin on cell-cell adhesion and desmosomal reorganization. These results show that the positive inotropic agent digitoxin enhances cardiac myocyte cohesion with reorganization of desmosomal proteins in an ERK1/2-dependent manner. Desmosomal adhesion seems to be important for a sufficient positive inotropic response of digitoxin treatment, which can be of medical relevance for the treatment of heart failure. Keywords Cardiomyopathies • Intercellular adhesion • Desmosome • Intercalated disc • Cardiac glycosideCamilla Schinner and Silvana Olivares-Florez contributed equally.