| First Author | Kim JC | Year | 2019 |
| Journal | Circulation | Volume | 140 |
| Issue | 12 | Pages | 1015-1030 |
| PubMed ID | 31315456 | Mgi Jnum | J:298052 |
| Mgi Id | MGI:6457184 | Doi | 10.1161/CIRCULATIONAHA.119.039710 |
| Citation | Kim JC, et al. (2019) Disruption of Ca(2+)i Homeostasis and Connexin 43 Hemichannel Function in the Right Ventricle Precedes Overt Arrhythmogenic Cardiomyopathy in Plakophilin-2-Deficient Mice. Circulation 140(12):1015-1030 |
| abstractText | BACKGROUND: Plakophilin-2 (PKP2) is classically defined as a desmosomal protein. Mutations in PKP2 associate with most cases of gene-positive arrhythmogenic right ventricular cardiomyopathy. A better understanding of PKP2 cardiac biology can help elucidate the mechanisms underlying arrhythmic and cardiomyopathic events consequent to PKP2 deficiency. Here, we sought to capture early molecular/cellular events that can act as nascent arrhythmic/cardiomyopathic substrates. METHODS: We used multiple imaging, biochemical and high-resolution mass spectrometry methods to study functional/structural properties of cells/tissues derived from cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mice (PKP2cKO) 14 days post-tamoxifen injection, a time point preceding overt electrical or structural phenotypes. Myocytes from right or left ventricular free wall were studied separately. RESULTS: Most properties of PKP2cKO left ventricular myocytes were not different from control; in contrast, PKP2cKO right ventricular (RV) myocytes showed increased amplitude and duration of Ca(2+) transients, increased Ca(2+) in the cytoplasm and sarcoplasmic reticulum, increased frequency of spontaneous Ca(2+) release events (sparks) even at comparable sarcoplasmic reticulum load, and dynamic Ca(2+) accumulation in mitochondria. We also observed early- and delayed-after transients in RV myocytes and heightened susceptibility to arrhythmias in Langendorff-perfused hearts. In addition, ryanodine receptor 2 in PKP2cKO-RV cells presented enhanced Ca(2+) sensitivity and preferential phosphorylation in a domain known to modulate Ca(2+) gating. RNAseq at 14 days post-tamoxifen showed no relevant difference in transcript abundance between RV and left ventricle, neither in control nor in PKP2cKO cells. Instead, we found an RV-predominant increase in membrane permeability that can permit Ca(2+) entry into the cell. Connexin 43 ablation mitigated the membrane permeability increase, accumulation of cytoplasmic Ca(2+), increased frequency of sparks and early stages of RV dysfunction. Connexin 43 hemichannel block with GAP19 normalized [Ca(2+)]i homeostasis. Similarly, protein kinase C inhibition normalized spark frequency at comparable sarcoplasmic reticulum load levels. CONCLUSIONS: Loss of PKP2 creates an RV-predominant arrhythmogenic substrate (Ca(2+) dysregulation) that precedes the cardiomyopathy; this is, at least in part, mediated by a Connexin 43-dependent membrane conduit and repressed by protein kinase C inhibitors. Given that asymmetric Ca(2+) dysregulation precedes the cardiomyopathic stage, we speculate that abnormal Ca(2+) handling in RV myocytes can be a trigger for gross structural changes observed at a later stage. |
