Abstract. To ascertain the role of spermidine/spermine N-1-acetyl-transferase (SSAT; the rate-limiting enzyme in polyamine catabolism) in cell injury, cultured kidney (HEK 293) cells conditionally overexpressing SSAT were generated. The SSAT expression was induced and its enzymatic activity increased 24 h after addition of tetracycline and remained elevated over the length of the experiments. Induction of SSAT upregulated the expression of polyamine oxidase and resulted in the reduction of cellular concentration of spermidine and spermine, increased concentration of putrescine, and inhibited cell growth. SSAT overexpression increased the expression of heme oxygenase-1 (HO-1) by 350% 24 h after addition of tetracycline, indicating the induction of oxidative stress. The presence of catalase significantly prevented the upregulation of HO-1 in SSAT overexpressing cells, indicating that generation of H 2 O 2 is partially responsible for the induction of oxidative stress. Overexpression of SSAT caused rounding and loss of cell anchorage and significantly altered the morphology of actin-containing filopodia, suggesting an adhesion defect. SSAT upregulation may mediate majority of the oxidative stress in kidney ischemia-reperfusion injury (IRI) as manifested by decreased cell growth, generation of toxic metabolites (H 2 O 2 and putrescine), upregulation of HO-1, disruption of cell anchorage, and defect in cell adhesion. These data point to the inhibition of polyamine catabolism as a therapeutic approach for the prevention of tissue injury in kidney IRI.Ischemia-reperfusion injury (IRI) is the major cause of morbidity and mortality in diseases such as stroke, myocardial infarction, and acute renal tubular necrosis. Ischemic conditions result in ATP depletion and accumulation of toxic metabolites. Reperfusion results in the production of reactive oxygen intermediates (1,2). The resulting alteration in cellular metabolism and generation of toxic molecules contribute to tissue damage in IRI (1,2), which is characterized by the presence of necrotic and apoptotic areas in the affected organs (1,3). Despite important developments in our understanding of the pathophysiology of IRI in kidney, heart, and other organs, there is no specific therapy for patients except for supportive care.Polyamines (spermidine, spermine, and putrescine) are aliphatic cations derived from ornithine (4,5). They play a fundamental role in the stabilization of DNA structure; they modulate gene expression and regulate protein synthesis, signal transduction, and cell growth and differentiation (4,6 -8). Spermidine/spermine N-1-acetyl-transferase (SSAT; the rate-limiting enzyme in polyamine catabolism) acetylates both spermidine and spermine. As a result, the cellular contents of spermidine and spermine are decreased and the concentrations of N-acetyl spermidine and N-acetyl spermine are increased (9). The subsequent activity of polyamine oxidase (PAO) on acetylated polyamines results in the production of spermidine or putrescine (depending on the startin...

Induction of Zf9 and its transactivating factor TGF-beta1 may play a critical and hitherto unrecognized role in the early apoptotic response to ischemic renal injury.

. Identification of stathmin as a novel marker of cell proliferation in the recovery phase of acute ischemic renal failure.

In kidneys subjected to ischemic reperfusion injury (IRI) stathmin, a tubulin-binding protein involved in the regulation of mitosis, is expressed in dedifferentiated and proliferating renal tubule cells during the recovery phase. To ascertain the role of stathmin in the recovery from ischemic kidney injury, stathmin-deficient (OP18-/-) and wild-type (WT) animals were subjected to experimental IRI. At 3, 7, and 14 days after reperfusion serum samples and kidneys were collected for the examination of parameters of renal function, morphology, and recovery. Our studies indicate that on day 14 after reperfusion OP18-/- mice have significant renal failure, whereas the creatinine levels of WT animals have returned to baseline. Compared with WT animals OP18-/- mice had more extensive tubular fibrosis. The examination of proliferating cell nuclear antigen expression indicated that OP18-/- animals have increased proliferative or DNA repair activity for a more prolonged duration. The OP18-/- animals also had an increased number of tubules with apoptotic cells. These results suggest that in stathmin-deficient mice subjected to IRI, the aberrant regulation of cell cycle progression, not observed under normal conditions, impairs or at least delays the process of tubular repair and recovery after acute renal injury.