Changes in membrane lipid composition cause alterations in epithelial cell-cell adhesion structures in renal papillary collecting duct cells.

In epithelial tissues, adherens junctions (AJ) mediate cell-cell adhesion by using proteins called E-cadherins, which span the plasma membrane, contact E-cadherin on other cells and connect with the actin cytoskeleton inside the cell. Although AJ protein complexes are inserted in detergent-resistant membrane microdomains, the influence of membrane lipid composition in the preservation of AJ structures has not been extensively addressed. In the present work, we studied the contribution of membrane lipids to the preservation of renal epithelial cell-cell adhesion structures. We biochemically characterized the lipid composition of membranes containing AJ complexes. By using lipid membrane-affecting agents, we found that such agents induced the formation of new AJ protein-containing domains of different lipid composition. By using both biochemical approaches and fluorescence microscopy we demonstrated that the membrane phospholipid composition plays an essential role in the in vivo maintenance of AJ structures involved in cell-cell adhesion structures in renal papillary collecting duct cells.

Stratification of sphingosine kinase-1 expression and activity in rat kidney.

Sphingosine-1-phosphate, the product of sphingosine kinase (SK) activity, is a sphingolipid metabolite that regulates cell growth, survival and migration. It is also known to affect diuresis, natriuresis and renovascular contraction in rats, although the mechanisms through which it affects these processes are not known. No previous report has addressed the differences among the kidney zones regarding endogenous SK expression and activity. Therefore, we examined SK1 distribution and activity in the various kidney zones: cortex, medulla and papilla. We found that SK1 expression does not correlate with enzyme activity. Study of the expression showed that the enzyme is highly expressed in cortex, followed by medulla and papilla. However, medulla had the highest enzyme activity. In all kidney zones, SK1 expression was mainly cytosolic. Regarding enzyme activity, whereas we found no difference between cytosol, membrane and nucleus in renal medulla, the membrane-bound enzyme presented the highest activity in cortex and papilla. SK1 distribution observed by immunohistochemical staining showed higher expression in cortical proximal convoluted epithelial cells. In medulla, immunostaining was observed as patches of staining, whereas in papilla, positive immunostaining was exclusively restricted to collecting duct cells. We also evaluated the effects of bradykinin and angiotensin II on SK1 activity.