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Linkermann et al. provide the first evidence for a possible biochemical mechanism of necrotic kidney cell death associated with renal ischemia/reperfusion-induced acute kidney injury. The mechanisms of several pathways resulting in programmed necrosis were recently elucidated and rely on receptor-interacting protein kinases 1 and 3. Using an inhibitor of one of these kinases, Linkermann et al. were able to ameliorate functional and morphologic kidney damage after ischemia/reperfusion.

Cell-cycle proteins influence almost all aspects of embryogenesis and differentiation. In adults, these proteins control cell division and regeneration after injury. During the past several years, their roles in controlling reaction to stress have been demonstrated in several organ systems. In the kidney, the cell types affected include both tubular and glomerular compartments. Now a novel cell cycle-related protein is shown to influence podocyte biology.

Acute kidney injury (AKI) activates pathways of cell death and cell proliferation. Although seemingly discrete and unrelated mechanisms, these pathways can now be shown to be connected and even to be controlled by similar pathways. The dependence of the severity of renal-cell injury on cell cycle pathways can be used to control and perhaps to prevent acute kidney injury. This review is written to address the correlation between cellular life and death in kidney tubules, especially in acute kidney injury.

One complication of diabetes is a pronounced renal cellular hypertrophy, inevitably resulting in chronic fibrotic changes. Chuang and colleagues demonstrate that hypertrophy in vitro is dependent on an increased phosphoinositide 3-kinase (PI3K) activity and is correlated with increased levels of p21(WAF1/Cip1), a cell-cycle regulator that was previously associated with renal fibrosis and sclerosis from nondiabetic causes.

Research into mechanisms of acute renal failure has begun to reveal molecular targets for possible therapeutic intervention. Much useful knowledge into the causes and prevention of this syndrome has been gained by the study of animal models. Most recently, investigation of the effects on acute renal failure of selected gene knock-outs in mice has contributed to our recognition of many previously unappreciated molecular pathways. Particularly, experiments have revealed the protective nature of two highly induced genes whose functions are to inhibit and control the cell cycle after acute renal failure. By use of these models we have started to understand the role of increased cell cycle activity after renal stress, and the role of proteins induced by these stresses that limit this proliferation.

Background: The p21 protein is found in the nucleus of most cells where it modulates cell cycle activity. At low levels, p21 stabilizes interactions between D cyclins and their cyclin-dependent kinases (cdks), but at high levels after induction by several different stress pathways, it causes cell cycle arrest. The p21 mRNA is induced in murine kidney after several types of acute renal failure, including cisplatin administration, ischemia-reperfusion, and ureteral obstruction. We reported that after cisplatin injection, mice with a p21 gene deletion developed much more severe renal damage than wild-type mice. To dissociate the effects of cisplatin-induced DNA damage and subsequent initiation of DNA damage-dependent cell death pathways from effects of acute renal failure, we have now examined mice after ischemia-reperfusion, a model of renal failure not associated with genotoxin-induced DNA damage early after the injury., Methods: Wild-type and p21(-/-) mice were made ischemic by clamping both renal hila for 30 or 50 minutes. At various times after reflow, mortality and parameters of renal function and morphology were quantified. Also, the nuclear proteins p21 and proliferating cell nuclear antigen (PCNA) were localized in kidney sections by immunohistochemistry., Results: Kidney function was more impaired and mortality increased significantly in p21(-/-) mice as compared with p21(+/+) mice. We found more cell cycle activity, indicated by increased number of mitotic cells and nuclear PCNA-positive cells, in kidney of p21(-/-) mice., Conclusions: In this study, p21(-/-) mice were more susceptible to ischemia-induced acute renal failure, with similarly elevated levels of parameters of cell cycle activity. We propose that the increased and inappropriate cell cycle activity in kidney cells is responsible for the increased kidney impairment and mortality.

The response of the kidney to ischemic injury includes increased DNA synthesis, which is preceded by rapid and brief expression of the c-fos proto-oncogene. While the timing of these two events would suggest that c-Fos participates in an immediate-early gene program leading to proliferation, no direct test of this hypothesis exists. The purpose of these studies was (1) to determine whether c-fos is expressed as part of a typical immediate-early (IE) gene response, which would require co-expression of c-jun and sensitivity to cycloheximide, and (2) to determine whether the cells expressing c-Fos are the same as those undergoing DNA synthesis. Northern analysis was performed on renal mRNA at different times following release of a 50 minute period of renal hilar clamping. c-jun and c-fos mRNA were rapidly and briefly expressed following renal ischemia and their expression was superinduced by cycloheximide in a manner typical of an immediate-early gene response. 3H-thymidine autoradiography performed on semi-thin sections from intravascularly perfusion fixed kidneys 24 hours following induction of ischemia showed labeled nuclei in cells lining the damaged proximal tubules of the outer stripe of the outer medulla, as well as proximal tubules in the cortex and interstitial cells throughout the kidney. However, immunohistochemical localization of c-Fos and c-Jun protein occurred predominantly in nuclei of the thick ascending limb, distal tubule and collecting duct cells. The studies demonstrate that c-fos and c-jun are expressed following renal ischemia as a typical immediate-early gene response, but they are expressed in cells that do not enter the cell cycle. The failure of the cells to enter the cell cycle may depend on the co-expression of jun-B and jun-D, which suppress the mitogenic activity of c-Jun in other cells. The data suggest that the IE response following renal ischemia is part of the stress response, which is antiproliferative rather than proliferative. The role of the stress response during renal ischemia and the fate of the cells undergoing it are unknown.

Northern and dot-blot analysis of polyadenylated RNAs of kidney cortical and outer medullary tissue was performed in male Sprague-Dawley rats at varying times up to 24 hours after bilateral ureteral obstruction (BUO), after 24 hours of unilateral obstruction (UUO) and at varying periods after release of BUO or UUO. Pre-proEGF (preproEGF) and Tamm-Horsfall (TH) mRNA declined by four hours of BUO to virtually undetectable levels at 24 hours of ureteral obstruction. Upon release of BUO or UUO, preproEGF and TH mRNA returned slowly toward normal but remained below control levels up to four days after release of ureteral obstruction. Urinary EGF excretion paralleled these changes in renal preproEGF mRNA. Although these changes are similar to those observed during nephrotoxic and ischemic renal failure, where the expression of the immediate early genes precedes the fall in preproEGF and TH expression, no such increase in the expression of these genes occurred after bilateral ureteral obstruction. These changes in preproEGF and TH expression could also be dissociated from uremia and high rates of DNA synthesis, suggesting that ureteral obstruction itself is a sufficient cause of the reduced expression. The increase in ureteral pressure and its functional and humoral effects may each play a role in reduced preproEGF and TH expression during ureteral obstruction.

Temporary renal ischemia is followed by increased DNA synthesis and cell division as the kidney restores the continuity of the renal epithelium. We sought to characterize some of the changes in proto-oncogene and growth factor expression during this proliferative response. Northern analysis of polyadenylated RNAs of kidney cortical and outer stripe of outer medullary tissue from male Sprague-Dawley rats was performed following release of renal hilar clamping of 50 minutes duration. Ischemia produced an increase in c-fos mRNA that reached a peak at one hour and declined rapidly to control levels by four hours after release of the clamp. A similar rapid increase and decrease in early growth response 1 (Egr 1) mRNA was noted. The response of these immediate early genes was typical of their response to mitogens, suggesting that they served a similar role in renal cell regeneration. Levels of c-Ki-ras and glyceraldehyde phosphate dehydrogenase mRNA were unchanged. Renal preproEGF mRNA decreased at two hours, was virtually absent by 24 hours and remained low for at least four days after ischemia. Urinary excretion of EGF fell immediately after release of ischemia and before the decline in preproEGF mRNA or SNGFR, suggesting post-transcriptional affects of ischemia on renal EGF production. EGF excretion returned to only 50% of control by day 21. Specific 125I-EGF binding increased in membrane fractions of cortex, outer medulla and inner medulla as early as 24 hours after release of the clamp. Cortical 125I-EGF binding increased in the proximal tubule but not in the glomerulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Levels of prepro epidermal growth factor (EGF) mRNA in renal cortical tissue and urinary EGF excretion have been determined during cisplatin and ischemia-induced acute renal failure in the rat. Northern analysis of polyadenylated RNAs of kidney cortical tissue showed diminished renal preproEGF mRNA in rats injected with cisplatin (5 mg/kg). The decrease in preproEGF mRNA occurred as early as 12 hours in the kidney and persisted for at least three days after cisplatin injection. The submandibular gland, a major site of EGF synthesis, contained normal levels of preproEGF mRNA. Transplatin, a non-nephrotoxic isomer of cisplatin, did not reduce renal preproEGF mRNA levels. Northern analysis of polyadenylated RNAs of kidney cortical tissue 24 hours after a 50 minute period of renal pedicle clamping also showed reduced preproEGF mRNA levels. By contrast, cisplatin increased renal c-fos mRNA. Urinary EGF excretion was also reduced after cisplatin and ischemia and the decrease in EGF excretion correlated significantly with the degree of renal failure. The data show that nephrotoxic and ischemic renal cell injury reduces preproEGF mRNA and urinary EGF excretion. Reduced preproEGF mRNA and diminished EGF excretion may be important in the functional and regenerative responses to renal injury.