Investigating the secretome: lessons about the cells that comprise the heart.

The cell/environment interface is composed of the proteins of plasma membrane which face the extracellular space and by the proteins secreted directly by the cell of origin or by neighboring cells. The secreted proteins can act as extracellular matrix proteins and/or autocrine/paracrine proteins. This report discusses the technical aspects involved in the identification and characterization of the secreted proteins of specific cell types that comprise the heart. These aspects include the culturing of the cells, cell co-culturing and quantitative labeling, conditioned media collection and dealing with high abundant serum proteins, post-translational modification enrichment, the use of protein separation methods and mass spectrometry, protein identification and validation and the incorporation of pathway analysis to better understand the novel discovery on the background of already known experimental biological systems. The proteomic methods have the solid emplacement in cardiovascular research and the identification of proteins secreted by cardiac cells has been used in various applications such as determination the specificity between secretomes of different cell types, e.g. cardiac stem cells and cardiac myocytes, for the global secretome screening of e.g. human arterial smooth muscle cells, for the mapping of the beneficial effect of conditioned medium of one cell type on the other cell type, e.g. conditioned medium of human mesenchymal stem cells on cardiac myocytes, and for the searching the candidate paracrine factors and potential biomarkers.