Induction of stress response proteins and experimental renal ischemia/reperfusion.

BACKGROUND: The induction of stress response (heat shock) proteins (HSPs) is a highly conserved response that protects many cell types from diverse physiological and environmental stressors. We tested the hypothesis that the induction of HSPs is protective in experimental renal ischemia/reperfusion injury. METHODS: The effect of prior heat stress was examined in a rat model of renal ischemia. Postischemic renal function, histopathology, myeloperoxidase activity, and mortality were determined in hyperthermia and sham hyperthermia groups. RESULTS: HSP84, HSP70, and HSP22 mRNA were increased after eight minutes but not four minutes of hyperthermia. The induction of HSP84 and HSP70 was blocked by pretreatment with quercetin. Improvement in renal function, mortality, and histologic abnormalities was seen with eight minutes of hyperthermia six hours before ischemia. Protection was dependent on the timing of ischemia relative to heat stress and was not observed when HSPs were not induced. Postischemic increases in renal myeloperoxidase activity were markedly attenuated in the hyperthermia compared with the sham hyperthermia group. CONCLUSION: Endogenous protective mechanisms may be important in renal ischemia/reperfusion injury.

Molecular cloning, genomic organization, and functional expression of Na+/H+ exchanger isoform 5 (NHE5) from human brain.

To isolate a cDNA encoding Na+/H+ exchanger isoform 5 (NHE5), we screened a human spleen library using exon sequences of the NHE5 gene. Clones spanning 2.9 kilobase pairs were isolated; however, they contained several introns and were missing coding sequences at both the 5' and 3' ends. The missing 5' sequences were obtained by 5'-rapid amplification of cDNA ends and by analysis of an NHE5 genomic clone, and the missing 3' sequences were obtained by 3'-rapid amplification of cDNA ends. Polymerase chain reaction amplification of brain cDNA yielded products in which each of the introns had been correctly excised, whereas the introns were retained in products from spleen and testis, suggesting that the NHE5 transcripts expressed in these organs do not encode a functional transporter. The intron/exon organization of the NHE5 gene was analyzed and found to be very similar to that of the NHE3 gene. The NHE5 cDNA, which encodes an 896-amino acid protein that is most closely related to NHE3, was expressed in Na+/H+ exchanger-deficient fibroblasts and shown to mediate Na+/H+ exchange activity. Northern blot analysis demonstrated that the mRNA encoding NHE5 is expressed in multiple regions of the brain, including hippocampus, consistent with the possibility that it regulates intracellular pH in hippocampal and other neurons.

Amplification of the arachidonic acid cascade: implications for pharmacologic intervention.

The signal transduction pathway that results in prostaglandin production is thought to occur in a stepwise manner that involves agonist-stimulated action of a phospholipase that releases the second messenger arachidonic acid from membrane phospholipids. Prostaglandin endoperoxide synthase (PGH synthase) then converts arachidonic acid to the prostaglandin precursors. Further delineation of this cascade has recently occurred with the identification of two distinct prostaglandin endoperoxide synthases, PGH synthase-1 and PGH synthase-2. There is evidence that PGH synthase-1 may have broad cellular expression and may be constitutively expressed in most cells. In contrast, PGH synthase-2 expression may be more limited and has been shown to be stimulated by a variety of cytokines and growth factors. Dexamethasone inhibits the expression of an early response gene, TIS10, which is homologous to PGH synthase-2. The exact mechanism of PGH synthase-2 gene regulation in mesangial cells is unknown; however, it may be a potential site for pharmacologic intervention. Regulation of PGH synthase-2 could in turn modulate prostaglandin production and temper the production of extracellular matrix and thus scar formation that occurs in a wide variety of inflammatory renal diseases.