Abstract
Epithelial cells of the thick ascending limb of Henle's loop (TALH cells) play a major role in the urinary concentrating mechanism. They are normally exposed to variable and often very high osmotic stress, which is particularly due to high sodium and chloride reabsorption and very low water permeability of the luminal membrane. It is already established that elevation of the activity of aldose reductase and hence an increase in intracellular sorbitol are indispensable for the osmotic adaptation and stability of the TALH cells. To identify new molecular factors potentially associated with the osmotic stress-resistant phenotype in kidney cells, TALH cells exhibiting low or high levels of resistance to osmotic stress were characterized using proteomic tools. Two-dimensional gel analysis showed a total number of 40 proteins that were differentially expressed in TALH cells under osmotic stress. Twenty-five proteins were overexpressed, whereas 15 proteins showed a down-regulation. Besides the sorbitol pathway enzyme aldose reductase, whose expression was 15 times increased, many other metabolic enzymes like glutathione S-transferase, malate dehydrogenase, lactate dehydrogenase, alpha enolase, glyceraldehyde-3-phosphate dehydrogenase, and triose-phosphate isomerase were up-regulated. Among the cytoskeleton proteins and cytoskeleton-associated proteins vimentin, cytokeratin, tropomyosin 4, and annexins I, II, and V were up-regulated, whereas tubulin and tropomyosins 1, 2, and 3 were down-regulated. The heat shock proteins alpha-crystallin chain B, HSP70, and HSP90 were found to be overexpressed. In contrast to the results in oxidative stress the endoplasmic reticulum stress proteins like glucose-regulated proteins (GRP78, GRP94, and GRP96), calreticulin, and protein-disulfide isomerase were down-regulated under hypertonic stress.
Highlights
Epithelial cells of the thick ascending limb of Henle’s loop (TALH cells) play a major role in the urinary concentrating mechanism
Morphology Changes of TALH Cells under Osmotic Stress—To investigate the effect of elevated osmolarity on the cell morphology, TALH cells were exposed to physiological osmolarity of 300 mosmol/kg or an increased extracellular tonicity of 600 mosmol/kg
We investigated whether TALH cells exhibiting resistance to 600 mosmol/kg were able to adapt to higher osmolarity or not
Summary
Epithelial cells of the thick ascending limb of Henle’s loop (TALH cells) play a major role in the urinary concentrating mechanism. Outer medullary cells of the thick ascending limb of Henle’s loop (TALH) participate to a considerable degree in the regulation of the osmotic gradient due to their strong NaCl transport activity and low water conductivity They have to possess specific osmoregulatory mechanisms to tolerate and counteract changes of extracellular osmolality [4]. It is already established that a high extracellular concentration of NaCl or glucose induces sorbitol accumulation in the cells of the inner renal medulla and TALH cells This increase of intracellular sorbitol content is accompanied and augmented by an induction of aldose reductase (AR), which reduces D-glucose in the polyol pathway [5, 6].
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