Concurrent overexpression of ornithine decarboxylase and spermidine/spermine N1-acetyltransferase further accelerates the catabolism of hepatic polyamines in transgenic mice

Abstract

We have generated a hybrid transgenic mouse line overexpressing both ornithine decarboxylase (ODC) and spermidine/spermine N1-acetyltransferase (SSAT) under the control of the mouse metallothionein (MT) I promoter. In comparison with singly transgenic animals overexpressing SSAT, the doubly transgenic mice unexpectedly displayed much more striking signs of activated polyamine catabolism, as exemplified by a massive putrescine accumulation and an extreme reduction of hepatic spermidine and spermine pools. Interestingly, the profound depletion of the higher polyamines in the hybrid animals occurred in the presence of strikingly high ODC activity and tremendous putrescine accumulation. Polyamine catabolism in the doubly transgenic mice could be enhanced further by administration of zinc or the polyamine analogue N1,N11-diethylnorspermine. In tracer experiments with [14C]spermidine we found that, in comparison with syngenic animals, both MT-ODC and MT-SSAT mice possessed an enhanced efflux mechanism for hepatic spermidine. In the MT-ODC animals this mechanism apparently operated in the absence of measurable SSAT activity. In the hybrid animals, spermidine efflux was stimulated further in comparison with the singly transgenic animals. In spite of a dramatic accumulation of putrescine and a profound reduction of the spermidine and spermine pools, only marginal changes were seen in the level of ODC antizyme. Even though the hybrid animals showed no liver or other organ-specific overt toxicity, except an early and permanent loss of hair, their life span was greatly reduced. These results can be understood from the perspective that catabolism is the overriding regulatory mechanism in the metabolism of the polyamines and that, even under conditions of severe depletion of spermidine and spermine, extremely high tissue pools of putrescine are not driven further to replenish the pools of the higher polyamines.

Spermidine/spermine-N1-acetyltransferase ablation protects against liver and kidney ischemia-reperfusion injury in mice

“…The role of SSAT in this regard is supported by in vivo and in vitro evidence showing that its expression leads to oxidative stress and that it is detrimental to the integrity of tissues and organs (1-3, 28 -30, 34, 36, 37). Studies examining the effect of transgenic expression of SSAT in mice indicate that it adversely effects the integrity and function of various tissues (28,30,34). These results are complemented by in vitro observations indicating that SSAT expression leads to alterations in cell physiology, cell cycle arrest, and apoptosis (36,37).…”

Transgenic mouse models for studies of the role of polyamines in normal, hypertrophic and neoplastic growth

“…Transgenic mice and rats in which ODC, AdoMetDC, spermidine synthase or SSAT has been increased generally in multiple tissues have been described (see [17][18][19][20][21] and references therein). In these studies, either a metallothionein promoter was used or the inserted transgene was a fragment of DNA containing the entire gene with its own associated promoter.…”

Genetic approaches to the cellular functions of polyamines in mammals

“…In an attempt to correct SSAT‐induced perturbations in polyamine homeostasis, we generated a hybrid transgenic mouse line overexpressing both ODC and SSAT under the control of mouse metallothionein I promoter. Unexpectedly, these animals showed much more striking signs of activated hepatic polyamine catabolism than the SSAT overexpressing animals [80]. Even under the condition of severe depletion of spermidine and spermine pools, tremendously high tissue putrescine was not driven further to replenish the reduced pool of spermidine.…”

“…Even under the condition of severe depletion of spermidine and spermine pools, tremendously high tissue putrescine was not driven further to replenish the reduced pool of spermidine. We understand from these results that catabolism is the overriding control mechanism in polyamine metabolism [80].…”