This review focuses on the biological role and clinical relevance of relatively poor studied enzymes known as sialidases. We describe structure and function of sialic acid, in particular as a component of gangliosides and plasma lipoproteins. Several types of sialidases are known in mammals, of which trans-sialidase is of special interest, since it is capable of removing sialic acid from low density lipoprotein (LDL) particles and transferring it to different acceptors in blood plasma. Desialylation of LDL, in turn, endows it a capacity to accumulate in the smooth muscle cells of human aortic intima, and therefore is important for atherogenesis. Moreover, sialidases appear to be involved in a variety of pathological processes, including viral infections and cancer, which makes these enzymes an attractive therapeutic target.
Cells isolated from a fixed adult human aorta by alcoholic-alkaline dissociation retain their intrinsic shape. They are represented by four major morphological types: stellate, elongated, elongated with side processes, and irregularly shaped cells. All the four types of cells were found in the elastic-hyperplastic intimal sublayer; elongated and irregularly shaped cells were mainly observed in the musculoelastic sublayer and in the media. Cell density in the atherosclerotic lesion is higher than normal, the number of stellate cells being increased more substantially compared to other cell types. The origin of stellate cells and other morphological cell types, and reasons for their disproportionate accumulation in the atherosclerotic intima are discussed.
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