Species-specific properties of the glomerular mesangium

Mesangial cells play a central role in the physiology and pathophysiology of the glomerulus. To date, most of the in vitro studies have been performed in cultured rat mesangial cells, with only 10% of them performed in human mesangial cells. In this article, the major differences between results obtained with these two types of cultured cells will be reviewed. In rats and in humans, most of the mesangial cells appear to be of smooth muscle origin. In the rat, some of the cultured cells also express a phenotype suggesting a monocyte/macrophage origin. Phagocytosis and synthesis of cytokines or proinflammatory proteins that have been described in cultured rat cells seem mostly linked to this monocyte/macrophage subtype of resident mesangial cells. In humans, macrophages are only detected in pathologic conditions, suggesting that they are not resident but rather infiltrating cells. Mesangial receptors, most notably angiotensin II receptors, are clearly present on mesangial cell membranes and are linked to prostaglandin E2 synthesis and to cell contraction. In humans, spontaneous prostanoid synthesis is low and is increased by the induction of cyclooxygenase by sodium butyrate in the medium. Even so, the amount of prostaglandin E2 synthesized by human mesangial cells is quantitatively low comparatively with that in rats. In rats, accordingly, mesangial cells play a role in the regulation of single-nephron GFR. In humans, angiotensin II also exerts a control on GFR but it is more difficult to demonstrate its contractile effect on human than on rat mesangial cells.(ABSTRACT TRUNCATED AT 250 WORDS)