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Expression of multiple gap junction proteins in human fetal and infant hearts
S C Chen1, L M Davis, E M Westphale
1Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110.
Insights
Human cardiac connexin expression changes during development. Connexin40 (Cx40) is abundant in fetal atria, while connexin43 (Cx43) and connexin45 (Cx45) show developmental regulation in cardiac myocytes.
Area of Science:
- Cardiovascular Biology
- Developmental Biology
- Molecular Cardiology
Background:
- Mammalian cardiac myocytes utilize various connexins for gap junction channels.
- Avian connexin expression changes during cardiac development, impacting myocyte electrophysiology.
- Understanding human cardiac connexin developmental regulation is crucial.
Purpose of the Study:
- To investigate the developmental regulation of cardiac connexin (Cx40, Cx43, Cx45) mRNA and protein in human hearts.
- To characterize the spatial and temporal distribution of these connexins throughout human cardiac development.
Main Methods:
- Northern blot analysis to quantify connexin mRNA levels in fetal, child, and adult human heart samples.
- Immunofluorescence microscopy to determine the protein distribution of connexins in cardiac myocytes and associated structures.
- Analysis of heart samples from different gestational ages and age groups.
Main Results:
- All three connexin transcripts (Cx40, Cx43, Cx45) were detected in all analyzed human hearts.
- Cx40 mRNA was significantly higher in fetal hearts, likely due to atrial contributions, and abundant in adult atrial appendages.
- Cx43 and Cx45 mRNA levels showed no significant developmental variation. Cx43 was abundant in all hearts, while Cx45 staining increased with age. Cx40 was localized to ventricular coronary arteries and atrial myocyte junctions.
Conclusions:
- Human cardiac connexin expression is developmentally regulated, particularly Cx40 and Cx45.
- Cx40's abundance in fetal atria and adult atrial junctions suggests a specific role in atrial function.
- Cx45 expression increases with age, indicating a role in mature cardiac myocyte function.
Abstract:
Mammalian cardiac myocytes express multiple gap junction channel proteins or connexins. Expression patterns of the avian homologues of the mammalian cardiac connexins change during cardiac morphogenesis in association with changes in the electrophysiologic properties of intercellular junctions in chick cardiac myocytes. To determine whether expression of cardiac connexins is developmentally regulated in humans, we characterized connexin mRNA and protein content and distribution in hearts of 11 human fetuses (74 to 122 d gestational age), seven children (0.5 mo to 3 y of age), and two adults. Northern blot analysis identified transcripts of connexin40 (Cx40), connexin43 (Cx43), and connexin45 (Cx45) genes in all hearts analyzed. Cx40 mRNA was approximately 5-fold more abundant in samples from fetal hearts than in hearts of children or adults. However, fetal samples used for RNA extraction included atrial as well as ventricular myocardium, whereas samples from children and adults were exclusively ventricular. Northern analysis of adult human right atrial appendages revealed abundant Cx40 mRNA, thus suggesting that the greater amount of Cx40 signal seen on Northern blots from fetal hearts could have been attributable to atrial contributions. Neither Cx43 nor Cx45 mRNA varied significantly in amount in samples from the different developmental stages analyzed. Immunofluorescence identified abundant Cx43 in the known distribution of gap junctions in myocytes in sections of all hearts. Cx45 staining was inconspicuous in fetal hearts but was readily apparent in cardiac myocytes in hearts of older subjects. In contrast, Cx40 staining in the ventricle was confined to mural coronary arteries, apparently in endothelial cells, whereas in the atrium Cx40 staining at myocyte junctions was abundant.(ABSTRACT TRUNCATED AT 250 WORDS)