Transmembrane signaling in kidney health and disease

The development of pediatric nephrology

Pediatric nephrology, as a discipline, arose from descriptive studies of childhood glomerulonephritis in Europe and the field of pediatric metabolism in the United States. While pediatric scientists before 1950 were concerned with fluid and electrolyte metabolism, regulation of intracellular and extracellular fluid, acid-base homeostasis, and parenteral fluid therapy, the defined field of nephrology developed after the Second World War around six major advances: ACTH and glucocorticoid therapy for nephrotic syndrome; renal biopsy to diagnose glomerular disease; the role of immunologic factors in glomerular injury; the use of dialysis as renal replacement therapy; renal transplantation as the optimal form of therapy in children with end stage renal failure; and recognition of renal disease in the etiology of 80% of cases of childhood hypertension. These discoveries led to focused research, the definition of specific training in nephrology, establishment of an American, European, and an International Society of Pediatric Nephrology, as well as an American Sub-Board of Pediatric Nephrology, and the inception of a journal, Pediatric Nephrology, now in its 15th year. Major research themes have included developmental nephrology, transplantation immunology, and concerns about growth in children with renal disease. Many clinical entities have been described in detail, some of which are almost confined to children. The scientific basis of pediatric nephrology, ongoing patient care needs, and its technical aspects - renal biopsy, dialysis and transplantation - assure its continuing future as a major pediatric discipline on all continents.

Localization of cytosolic phospholipase A2 messenger RNA mainly in neurons in the rat brain

Ca2(+)-sensitive 85,000 mol. wt cytosolic phospholipase A2 plays an essential role in the selective and stimulus-dependent release of arachidonic acid from membrane phospholipids. Cytosolic phospholipase A2-catalysed lipid mediators including arachidonic acid and its metabolites have been suggested to be involved in a variety of neuronal functions in the CNS. Since the cellular localization of cytosolic phospholipase A2 is still controversial and obscure, we tried an improved method of rapid processing of each specimens and succeeded in obtaining intense signals of cytosolic phospholipase A2 messenger RNA in the normal rat brain by northern blot analysis and in situ hybridization. Northern blot analysis showed the abundant distribution of cytosolic phospholipase A2 messenger RNA in most regions of the brain, with intense signals observed in the pineal gland and pons. Macroautoradiographs prepared after in situ hybridization with three different antisense riboprobes gave essentially similar patterns of localization; significant signals were widely detected in the gray matter of various regions, i.e. the olfactory bulb, cerebral cortex, hippocampus, amygdala, several thalamic and hypothalamic nuclei and cerebellum. Microautoradiographs showed that most of the intense signals were predominant in neurons, and that faint signals were from glial cells and other non-neuronal cells in the choroid plexus, inner surface cells of veins and the leptomeninges. In addition, the cycloheximide treatment increased the cytosolic phospholipase A2 messenger RNA level in the same cell populations originally possessing messenger RNA signals. Predominant expression of cytosolic phospholipase A2 messenger RNA in neurons may provide the basis for the contribution of cytosolic phospholipase A2-catalysed lipid mediators to a variety of neurotransmission and synaptic functions in the CNS.

Structure, function and regulation of Ca2+-sensitive cytosolic phospholipase A2 (cPLA2)

The 85-kDa cytosolic PLA2 (cPLA2) is present in many cells and tissues and its unusual functional properties and catalytic mechanism are being elucidated. Notably, cPLA2 becomes catalytically active in the presence of free Ca2+ concentrations as present in stimulated cells and preferentially cleaves arachidonic acid-containing phospholipids. A variety of agonists, growth factors and cytokines, as well as stressful stimuli activate cPLA2 to hydrolyze cellular phospholipids thereby liberating fatty acids and lysophospholipids and providing the precursor substrates for the biosynthesis of eicosanoids and platelet-activating factor. These products of cPLA2 contribute to inflammatory and degenerative disease states and cPLA2 is therefore an attractive target for the development of novel therapies.

20-Hydroxyeicosa-tetraenoic acid (20 HETE) activates protein kinase C. Role in regulation of rat renal Na+,K+-ATPase

It is well documented that the activity of Na+,K+-ATPase can be inhibited by the arachidonic acid metabolite, 20-hydroxyeicosa-tetraenoic acid (20 HETE). Evidence is presented here that this effect is mediated by protein kinase C (PKC). PKC inhibitors abolished 20 HETE inhibition of rat Na+,K+-ATPase in renal tubular cells. 20 HETE caused translocation of PKC alpha from cytoplasm to membrane in COS cells. It also inhibited Na+,K+-ATPase activity in COS cells transfected with rat wild-type renal Na+,K+-ATPase alpha1 subunit, but not in cells transfected with Na+,K+-ATPase alpha1, where the PKC phosphorylation site, serine 23, had been mutated to alanine. PKC-induced phosphorylation of rat renal Na+,K+-ATPase, as well as of histone was strongly enhanced by 20 HETE at the physiologic calcium concentration of 1.3 microM, but not at the calcium concentration of 200 microM. The results indicate that phospholipase A2-arachidonic acid-20 HETE pathway can exert important biological effects via activation of PKC and that this effect may occur in the absence of a rise in intracellular calcium.