Subcellular Localization of Connexin 26 in Cardiomyocytes and in Cardiomyocyte-Derived Extracellular Vesicles.

Alessandra Falleni,Stefania Moscato,Letizia Mattii,Francesco Bianchi,Antonietta R M Sabbatini,Antonella Cecchettini,Margherita Bernardeschi

doi:10.3390/molecules26216726

Alessandra Falleni, Stefania Moscato + Show 5 more

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https://doi.org/10.3390/molecules26216726

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Abstract

Connexins (Cxs) are a family of membrane-spanning proteins, expressed in vertebrates and named according to their molecular weight. They are involved in tissue homeostasis, and they function by acting at several communication levels. Cardiac Cxs are responsible for regular heart function and, among them, Cx26 and Cx43 are widely expressed throughout the heart. Cx26 is present in vessels, as well as in cardiomyocytes, and its localization is scattered all over the cell aside from at the intercalated discs as is the case for the other cardiac Cxs. However, having been found in cardiomyocytes only recently, both its subcellular localization and its functional characterization in cardiomyocytes remain poorly understood. Therefore, in this study we aimed to obtain further data on the localization of Cx26 at the subcellular level. Our TEM immunogold analyses were performed on rat heart ventricles and differentiated H9c2 cardiac cell sections as well as on differentiated H9c2 derived extracellular vesicles. The results confirmed the absence of Cx26 at intercalated discs and showed the presence of Cx26 at the level of different subcellular compartments. The peculiar localization at the level of extracellular vesicles suggested a specific role for cardiac Cx26 in inter-cellular communication in an independent gap junction manner.

Highlights

Connexins (Cxs) are a family of membrane-spanning proteins, expressed in vertebrates and named according to their molecular weight, which can range from 26 to 60 KDa
The subcellular distribution of Cx26 was analysed on ultrathin sections from both rat heart tissue and cardiomyocytes obtained from the differentiation of a rat H9c2 myoblast cell line
Our electron micrographs show that, Molecules 2021, 26, x FOR PEER REVIfEoWr the dH9c2 cytoplasm, Cx26 was found in vesicles of size ranging from 50 to 6040onf m15 (Figure 2), including multivesicular bodies (MVBs), which are large endosomal vesicles where exosomes are formed [12]

Summary

Introduction

Connexins (Cxs) are a family of membrane-spanning proteins, expressed in vertebrates and named according to their molecular weight, which can range from 26 to 60 KDa. Over twenty identified isoforms of mammalian Cxs have a shared sequence and topological homology. Over twenty identified isoforms of mammalian Cxs have a shared sequence and topological homology The latter consists of 4 transmembrane regions, 2 extracellular loops, 1 cytosolic loop, 1 cytosolic amino terminal tail and 1 cytosolic carboxy terminal tail [1]. Six assembled Cxs can form pores, which are named hemichannels or connexons, thereby allowing for the exchange of small molecules, such as ions, nucleotides, amino acids, sugars, mRNAs and miRNAs, with both intracellular and extracellular compartments. The connexons of adjacent cells can align to form gap junctions, allowing communication from cell to cell [1,2]

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