| Abstrakt: |
Cells exist within a complex and ever-changing environment, which includes soluble molecules such as growth factors, an extracellular matrix that includes adhesive proteins and carbohydrates, and other neighboring cells. They actively sense and respond to changes in this environment, existing in a state of physiological equilibrium with it. Thus, it has been said, ". . . the unit of function in higher organisms is larger than the cell itself " [10]. The information content in the adhesive environment is encoded both in its composition and its organization on the nanometer to micrometer length scales. When taken out of this physiological context and cultured in plastic tissue culture dishes, cells lose the cues that maintain their in vivo identity or phenotype, and dedifferentiate. For example, hepatocytes— the principal cell type in the liver—perform several critical liver-specific functions such as production of bile, metabolism of urea, and the synthesis of important serum proteins such as albumin, fibrinogen, and transferrin [27]. When cultured in vitro and isolated from the liver microenvironment, they rapidly downregulate liver-specific phenotype [54]. Similarly, chondrocytes, which are required for the secretion and maintenance of cartilage, lose their differentiated function when cultured in vitro downregulating the synthesis and secretion of cartilage-specific collagens and proteoglycans [88]. Thus, tissue-specific cell function appears to be closely related to the microstructural organization of the tissue itself [11]. [ABSTRACT FROM AUTHOR] |
