Abstract 507: The Glycome Is Functionally Remodeled Throughout The Developing Myocardium
Cell surfaces are replete with complex, biologically important glycan structures responsible for multiple cellular functions including cell adhesion and cellular communication. Proper protein glycosylation is essential for normal development and physiology with the effects of improper glycosylation being severe and even lethal. Gene products involved in glycan formation (glycosylation-associated genes) comprise 1–2% of the genome, resulting in a glycome of thousands of structures; possibly more extensive than the proteome. Using GeneChip microarray analyses, we provide evidence that glycosylation-associated gene expression is highly regulated throughout the developing myocardium. Nearly one-third of the glycosylation-associated genes were significantly differentially expressed in neonatal atria versus neonatal ventricles while 46.8% of these same genes were differentially expressed in neonate versus adult ventricles. Quantitative-PCR of individual genes confirmed the microarray analyses. Such gross glycosylation-associated gene expression remodeling likely modifies the complexity and size of glycosylation structures attached to cell surface proteins. To confirm this, glycan structures were determined and compared among myocyte types using mass spectrometry. The data indicated that the observed regulation in gene expression translated into a change in glycan structure. Further, we report that remodeled glycans are likely responsible for alterations in voltage-gated sodium channel activity and action potential waveforms, suggesting a physiological role for regulation of glycosylation-associated genes in the heart. Specifically, differences in sodium channel gating in neonatal atria versus neonatal ventricles were abolished by knocking out a single polysialyltransferase expressed only in neonatal atria. Atrial action potential duration and the rate of depolarization were altered in the absence of this polysialyltransferase, while ventricle action potential waveforms were unaffected. Together, these data indicate that the glycome is tightly controlled in the heart, and proper glycosylation is apparently essential for normal myocyte functions.