ABSTRACT
Th e expression of adhesion molecules in the normal human kidney is summarized in Table 1.
Th e apical junctional complex has been considered to consist of two primary units. Occludin and the claudins are the structural components of the tight junction (TJ) and are the main determinants of paracellular permeability in the tubular segments of the nephron (Gonzalez-Mariscal et al. 2003). Occludin and zonula occludens-1 (ZO), ZO-2 and ZO-3 are integral membrane proteins that interact with each other and anchor the junctional complex to the cytoskeletal elements of adjacent cells (Van Itallie et al. 2006). Claudins, but not occludin, are thought to constitute the backbone of TJ. In the kidney, the claudin expression pattern
is tissue-and segment-specifi c: the glomerulus expresses claudin-1, the proximal tubule expresses relatively high levels of claudin 2, the thick ascending limb of the loop of Henle expresses claudin-16 (paracellin-1), the distal nephron expresses claudin-7 and -8, the collecting tubule contains claudin-4, and claudin-5 is localized in endothelial cells. Claudin-6 in the glomeruli is distributed along the glomerular capillary wall and co-localized with ZO-1. Claudin-6 is a transmembrane protein of TJ in podocytes present during development and under pathological conditions. Two isoforms of claudin-10 (a and b) are expressed in many tissues, but claudin10a is unique to the kidney. It is diffi cult to assign the expression of claudin-10a
and -10b to specifi c nephron segments, while their mRNAs are preferentially expressed in either the medulla or cortex, respectively (Table 1).
