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Ontogeny of membrane cofactor protein: phenotypic divergence in the fetal heart
A Gorelick1, T Oglesby, W Rashbaum
1Department of Rheumatology, Hospital for Joint Diseases, New York University School of Medicine, New York 10003, USA.
Insights
Fetal hearts show a unique pattern of membrane cofactor protein (MCP, CD46) expression, with lower molecular weight isoforms being more prominent. This suggests tissue-specific regulation may impact autoantibody-mediated diseases like neonatal lupus.
Area of Science:
- Immunology
- Developmental Biology
- Genetics
Background:
- Human adult cells utilize membrane cofactor protein (MCP, CD46) for protection against complement-induced damage.
- Understanding fetal characteristics is crucial for studying in utero acquired autoantibody-mediated diseases, such as neonatal lupus.
- MCP (CD46) is a key regulator of complement activation on cell surfaces.
Purpose of the Study:
- To investigate the tissue-specific expression of MCP (CD46) in human fetuses.
- To identify potential differences in MCP (CD46) expression patterns between fetal organs and correlate these with susceptibility to autoimmune diseases.
- To examine MCP (CD46) isoforms during early gestational development.
Main Methods:
- Immunoblotting techniques were employed to analyze MCP (CD46) expression in fetal tissues.
- Tissues from six fetuses (19-24 weeks gestation) were examined.
- High-resolution acrylamide:bisacrylamide ratios were used to resolve MCP (CD46) isoforms.
Main Results:
- A novel 60 KD MCP (CD46) band was detected alongside the known 65 KD and 55 KD isoforms.
- Most fetuses (5/6) displayed a common MCP (CD46) polymorphism (alpha-phenotype) in kidney, spleen, liver, and lung.
- Fetal hearts predominantly showed lower molecular weight MCP (CD46) bands (beta-isoform accentuation), differing from other organs in 5 out of 6 fetuses.
Conclusions:
- MCP (CD46) is expressed in fetal tissues during early gestational life.
- Preferential expression of MCP (CD46) beta-isoforms in fetal hearts suggests tissue-specific regulation (RNA splicing or post-translational modification).
- This unique fetal heart MCP (CD46) expression pattern may be relevant to autoantibody-mediated injury in conditions like neonatal lupus.
Abstract:
Human adult cells are protected from complement-induced damage in part by membrane cofactor protein (MCP, CD46). To examine fetal characteristics which might influence autoantibody-mediated diseases acquired in utero, such as heart block in neonatal lupus, the tissue expression of MCP was studied. Using a high ratio of acrylamide:bisacrylamide, immunoblots of tissues from six fetuses (aged 19-24 weeks) probed with rabbit anti-MCP antibodies revealed a band at 60 KD in addition to the known 65 KD and 55 KD isoforms which comprise the codominant allelic system of MCP. Five fetuses expressed the most common MCP polymorphism (predominance of the 65 KD isoform, upper band alpha-phenotype) in the kidney, spleen, liver and lung. In contrast, all hearts from these five fetuses demonstrated a different pattern in which there was a marked decrease in the intensity of the 65 KD band and accentuation of the lower molecular weight bands. In a sixth fetus, which expressed the second most common polymorphism (equal expression of the 65 KD and 55 KD MCP isoforms, alpha beta-phenotype), the heart was similar to the other tissues. These studies confirm the expression of MCP in early gestational life. Preferential expression of the MCP beta-isoform in the majority of fetal hearts irrespective of the phenotype of other organs, suggests tissue-specific RNA splicing or post-translational modification which may relate to autoantibody-mediated injury in diseases such as neonatal lupus.