Overexpression of SSAT in kidney cells recapitulates various phenotypic aspects of kidney ischemia-reperfusion injury

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 H₂O 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 (H₂O₂ 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.