Connexins in congenital heart disease

• Main Author: Rowlinson, Giselle Victoria
• Format: Dissertation
• Language: English
• Published: Imperial College London 2011

Gap junctions are clusters of transmembrane channels, composed of connexins (Cx), that facilitate electrical and chemical communication between the cytoplasmic compartments of contiguous cells. Three connexins are expressed in cardiac myocytes, Cx40, Cx43 and Cx45. Targeted deletion of these connexin genes in mice results in cardiac malformations and conduction abnormalities. From this background, the question arises as to whether connexins play a role in human congenital heart disease. Atrial and ventricular tissue samples were studied from patients undergoing cardiac surgery. Immunoconfocal microscopy and western blot analysis of atrial tissue revealed that expression of CX40 and CX43 in children and adults with congenital heart disease is the same as that in the normal adult atrium, irrespective of the underlying malformation. Normal adult ventricular working myocytes express only CX43. Study of control ventricular samples in children confirmed that, as in adults, CX43 only is expressed. However, immunoconfocal microscopy of samples from patients with right ventricular outflow obstruction (tetralogy of Fallot and double chambered right ventricle) revealed that in addition to CX43, CX40 is also highly expressed. Expression is heterogeneous and CX40 is eo-localised with CX43. Quantitative western blot analysis showed that up to 10% of the total connexin expressed in these samples is CX40. As patients re-operated following previous repair (with markedly different underlying haemodynamics) still demonstrated high CX40 expression in the working myocardium, these results suggest that a lack of normal CX40 repression during development leads to heart malformations . . Gap junction channels formed from each connexin isofonn have distinctive biophysical properties. Connexin eo-expression further alters these properties. To investigate the functional consequences of the connexin eo-expression patterns observed in the ventricular samples, in vitro cell models were used. Intercellular communication was assessed using cell-to-cell Lucifer Yellow dye transfer in an inducible RLE cell line and conducjion properties were studied in an atrial myocyte (HL-l) cell line. The findings are consistent with the idea that altered function arising from abnormal embryonic connexin expression is a contributor to some types of human cardiac malformation.