Genital and Urinary Tracts and Mesothelial Cells as Hyaluronan Producers

The expression of hyaluronan in the simple epithelia of the male reproductive tract and its accessory glands is more active than that in the gut and intestine. Distal epididymis, vas deferens, seminal vesicle, prostate, and Cowper's gland epithelium from the cervix of uterus. Stratified epithelia (a,b,i) show strong hyaluronan expression, while normal intestinal epithelia contain little hyaluronan. Poorly differentiated squamous carcinoma is practically hyaluronan-negative, while adenocar-inomas have acquired hyaluronan expression. Small arrows indicate the location of the basal lamina, large arrows in (e) and (h) indicate positive staining in cancer cells and lack of staining in (f). The asterisk in (a) indicates cornified cell layer.

show hyaluronan located mainly on the lower basolateral surface, but with little on the apical surface (Fig. 2c-f) (38). In these epithelia, the location of CD44 correlates with that of hyaluronan on the basolateral surfaces. This distribution suggests that hyaluronan is mostly synthesized and remains bound on the basal side of the adjacent epithelial cells. However, the lumen of the seminal vesicle, prostate and Cowper's gland (Fig. 2c-e) contain hyaluronan, suggesting that it is either secreted from the apical surface, or passes the cell junctions in the lateral sides of the cells. There is an extensive pool of hyaluronan in the underlying stroma of these glands, a potential source of the epithelial and lumenal hyaluronan. Interestingly, testis seems almost devoid of hyaluronan (38), perhaps a finding related to the high level of hyaluronidase in the sperm cells. At ejaculation, the hyaluronan in the product of the accessory sex glands comes in contact with sperm cells.

In the female genital tract, the stratified epithelium of the cervix shows strong hyaluronan expression similar to other stratified epithelia (Fig. 3i), while the simple columnar epithelium covering the lumen of the uterus and the fallopian tubes show little hyaluronan, except the tubal cells close to the uterotubal junction, showing an apical hyaluronan signal (39). The pig tubal fluid contains soluble hyaluronan (39) and some cells in this part of the tuba are positive for CD44, with an elevated expression before ovulation, suggesting that the enrichment of CD44 and hyaluronan may enhance the viability and functionality of sperm stored at this site (40). The sperm cells are thus both in the seminal fluid and in the upper female genital tract in a milieu containing hyaluronan. Interestingly, epithelial cells scraped from the luminal surface of pig oviduct express Has3 mRNA (but not that of Has2 or Has1), suggesting that hyaluronan in the oviduct may be produced by the epithelial cells rather than by the underlying stroma (41).

Most of the normal epithelial cells in the adult kidney, including the loop of Henle, proximal and distal tubules, collecting ducts, and calices of different sizes are completely negative in staining with a probe specific for hyaluronan. The mesenchymal compartment in the kidney cortex and outer medulla is also very weak in hyaluronan staining, in striking contrast to the inner medulla where hyaluronan resides in high concentrations, perhaps as part of the urine concentration process. There is also little, if any, expression of the hyaluronan receptor CD44 in normal kidney. However, both CD44 and hyaluronan are highly upregulated in the kidney cortex after immunological (42) and ischemic (43) injury, CD44 particularly in the tubular epithelial cells, and hyaluronan in the interstitium. Cultured cortical tubular epithelial cells are also capable of hyaluronan synthesis (44) induced by cytokines, high glucose (45), and cell dispersal, while downregulated by cell density-dependent epithelial integrity (46). The inducible hyaluronan synthesis appears a result of increased Has2 expression (45). Hyaluronan is one of the molecules on tubular epithelium supposed to bind developing crystals that may eventually lead to kidney stone formation (47).

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