Engineering Cardiac Cell JunctionsIn Vitroto Study the Intercalated Disc

GJA1-20k Arranges Actin to Guide Cx43 Delivery to Cardiac Intercalated Discs

RATIONALE

Delivery of Cx43 (connexin 43) to the intercalated disc is a continuous and rapid process critical for intercellular coupling. By a pathway of targeted delivery involving microtubule highways, vesicles of Cx43 hemichannels are efficiently trafficked to adherens junctions at intercalated discs. It has also been identified that actin provides rest stops for Cx43 forward trafficking and that Cx43 has a 20 kDa internally translated small C terminus isoform, GJA1-20k (Gap Junction Protein Alpha 1- 20 kDa), which is required for full-length Cx43 trafficking, but by an unknown mechanism.

OBJECTIVE

We explored the mechanism by which the GJA1-20k isoform is required for full-length Cx43 forward trafficking to intercalated discs.

METHODS AND RESULTS

Using an in vivo Adeno-associated virus serotype 9-mediated gene transfer system, we confirmed in whole animal that GJA1-20k markedly increases endogenous myocardial Cx43 gap junction plaque size at the intercalated discs. In micropatterned cell pairing systems, we found that exogenous GJA1-20k expression stabilizes filamentous actin without affecting actin protein expression and that GJA1-20k complexes with both actin and tubulin. We also found that filamentous actin regulates microtubule organization as inhibition of actin polymerization with a low dose of latrunculin A disrupts the targeting of microtubules to cell-cell junctions. GJA1-20k protects actin filament from latrunculin A disruption, preserving microtubule trajectory to the cell-cell border. For therapeutic implications, we found that prior in vivo Adeno-associated virus serotype 9-mediated gene delivery of GJA1-20k to the heart protects Cx43 localization to the intercalated discs against acute ischemic injury.

CONCLUSIONS

The internally translated GJA1-20k isoform stabilizes actin filaments, which guides growth trajectories of the Cx43 microtubule trafficking machinery, increasing delivery of Cx43 hemichannels to cardiac intercalated discs. Exogenous GJA1-20k helps to maintain cell-cell coupling in instances of anticipated myocardial ischemia.

Effects of different doses of 2,3-dimercaptosuccinic acid-modified Fe2 O3 nanoparticles on intercalated discs in engineered cardiac tissues

Although iron oxide nanoparticles (IRONs) were applied in clinical magnetic resonance imaging in vivo and magnetic tissue engineering in vitro widely, the underlying effects of IRONs on the development of cardiomyocytes especially the intercellular junctions, intercalated discs (IDs), remain an unknown issue. Given the critical role of three-dimensional (3D) engineered cardiac tissues (ECTs) in evaluation of nanoparticles toxicology, it remained necessary to understand the effects of IRONs on IDs assembly of cardiomyocytes in 3D environment. In this study, we first reconstituted collagen/Matrigel based ECTs in vitro and prepared IRONs with 2,3-dimercaptosuccinic acid (DMSA-IRONs). We found that the internalization of DMSA-IRONs by cardiac cells in dose-dependent manner was not associated with the cell distribution in 3D environment by determination of Prussian blue staining and transmission electronic microscopy. Significantly, through determination of western blotting and immunofluorescence of connexin 43, N-cadherin, desmoplakin, and plakoglobin, DMSA-IRONs enhanced the assembly of gap junctions, decreased mechanical junctions (adherens junctions and desmosomes) of cardiac cells but not in dose-dependent manner in ECTs at seventh day. In addition, DMSA-IRONs increased the vesicles secretion of cardiac cells in ECTs apparently compared to control groups. Overall, we conclude that the internalization of DMSA-IRONs by cardiac cells in dose-dependent manner enhanced the assembly of electrochemical junctions and decreased the mechanical related microstructures. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 121-130, 2018.