Aging and polyamine acetylation in rat kidney

The Spermine Oxidase/Spermine Axis Coordinates ATG5-Mediated Autophagy to Orchestrate Renal Senescence and Fibrosis

Decreased plasma spermine levels are associated with kidney dysfunction. However, the role of spermine in kidney disease remains largely unknown. Herein, it is demonstrated that spermine oxidase (SMOX), a key enzyme governing polyamine metabolism, is predominantly induced in tubular epithelium of human and mouse fibrotic kidneys, alongside a reduction in renal spermine content in mice. Moreover, renal SMOX expression is positively correlated with kidney fibrosis and function decline in patients with chronic kidney disease. Importantly, supplementation with exogenous spermine or genetically deficient SMOX markedly improves autophagy, reduces senescence, and attenuates fibrosis in mouse kidneys. Further, downregulation of ATG5, a critical component of autophagy, in tubular epithelial cells enhances SMOX expression and reduces spermine in TGF-β1-induced fibrogenesis in vitro and kidney fibrosis in vivo. Mechanically, ATG5 readily interacts with SMOX under physiological conditions and in TGF-β1-induced fibrogenic responses to preserve cellular spermine levels. Collectively, the findings suggest SMOX/spermine axis is a potential novel therapy to antagonize renal fibrosis, possibly by coordinating autophagy and suppressing senescence.

Mechanisms of spermidine-induced autophagy and geroprotection

Aging involves the systemic deterioration of all known cell types in most eukaryotes. Several recently discovered compounds that extend the healthspan and lifespan of model organisms decelerate pathways that govern the aging process. Among these geroprotectors, spermidine, a natural polyamine ubiquitously found in organisms from all kingdoms, prolongs the lifespan of fungi, nematodes, insects and rodents. In mice, it also postpones the manifestation of various age-associated disorders such as cardiovascular disease and neurodegeneration. The specific features of spermidine, including its presence in common food items, make it an interesting candidate for translational aging research. Here, we review novel insights into the geroprotective mode of action of spermidine at the molecular level, as we discuss strategies for elucidating its clinical potential.

Histone deacetylase-10 liberates spermidine to support polyamine homeostasis and tumor cell growth

Cytosolic histone deacetylase-10 (HDAC10) specifically deacetylates the modified polyamine N8-acetylspermidine (N8-AcSpd). Although intracellular concentrations of N8-AcSpd are low, extracellular sources can be abundant, particularly in the colonic lumen. Extracellular polyamines, including those from the diet and microbiota, can support tumor growth both locally and at distant sites. However, the contribution of N8-AcSpd in this context is unknown. We hypothesized that HDAC10, by converting N8- AcSpd to spermidine, may provide a source of this growth-supporting polyamine in circumstances of reduced polyamine biosynthesis, such as in polyamine-targeting anticancer therapies. Inhibitors of polyamine biosynthesis, including α-difluoromethylornithine (DFMO), inhibit tumor growth, but compensatory uptake of extracellular polyamines has limited their clinical success. Combining DFMO with inhibitors of polyamine uptake have improved the antitumor response. However, acetylated polyamines may use different transport machinery than the parent molecules. Here, we use CRISPR/Cas9-mediated HDAC10-knockout cell lines and HDAC10-specific inhibitors to investigate the contribution of HDAC10 in maintaining tumor cell proliferation. We demonstrate inhibition of cell growth by DFMO-associated polyamine depletion is successfully rescued by exogenous N8-AcSpd (at physiological concentrations), which is converted to spermidine and spermine, only in cell lines with HDAC10 activity. Furthermore, we show loss of HDAC10 prevents both restoration of polyamine levels and growth rescue, implicating HDAC10 in supporting polyamine-associated tumor growth. These data suggest the utility of HDAC10-specific inhibitors as an antitumor strategy that may have value in improving the response to polyamine-blocking therapies. Additionally, the cell-based assay developed in this study provides an inexpensive, high-throughput method of screening potentially selective HDAC10 inhibitors.

Regional and temporal alterations of ODC/polyamine system during ALS-like neurodegenerative motor syndrome in G93A transgenic mice

Natural polyamines (putrescine, spermidine and spermine) are ubiquitous molecules known to regulate a number of physiological processes and suspected to play a role also in various pathological conditions. Changes in polyamine levels and in their biosynthetic enzymes have been described for some neurodegenerative diseases but the available data are incomplete and somewhat contradictory. We report here alterations of the key enzyme of the polyamine pathway, ornithine decarboxylase (ODC) catalytic activity and polyamine levels in different CNS areas from SOD1 G39A transgenic mice, an animal model for amyotrophic lateral sclerosis (ALS). ODC catalytic activity, was found significantly increased both in the cervical and lumbar spinal cord and, to a lesser extent in the brain stem of transgenic mice at a symptomatic stage of the disease (125-day-old mice), while no differences were present at a pre-symptomatic stage (55-day-old mice). In parallel with the increase of ODC activity putrescine levels were several times increased in both cervical and lumbar spinal cord and in the brain stem of 125-day-old SOD1 G39A mice. Higher order polyamines were not increased except for a significant increase of spermidine in the cervical spinal cord. The present data demonstrate considerable alterations of the ODC/polyamine system in a reliable animal model of ASL, consistent with their role in neurodegeneration and in particular in motor neuron diseases.

Effect of mitoguazone on polyamine oxidase activity in rat liver

Mitoguazone is a known inhibitor of polyamine biosynthesis through competitive inhibition of S-adenosylmethionine decarboxylase. A recent renewed interest in mitoguazone as an antineoplastic agent prompted us to investigate the effect of the drug on polyamine catabolism in rat liver, since the organ plays an important role in detoxification mechanisms. Thus, the purpose of this work was to evaluate the effect of in vivo mitoguazone administration on polyamine catabolic enzymes. In particular, our interest was directed to the changes in polyamine oxidase activity, since this enzyme has been recently confirmed to exert important functions that until now were underestimated. Mitoguazone administration induced hepatic polyamine oxidase activity starting at 4 h after administration, and the enzyme returned to basal levels 96 h after treatment. The changes in enzyme activity were accompanied by changes in putrescine concentrations, which increased starting at 4 h until 72 h after treatment. We also evaluated the activity of the newly identified spermine oxidase, which was not significantly changed by mitoguazone treatment. Therefore, we hypothesized that the enzyme involved in mitoguazone response of the liver is the polyamine oxidase, which acts on acetylated polyamines as substrate.

Polyamine oxidase activity in lymphoid tissues of glucocorticoid-treated rats

Glucocorticoids are known to negatively affect lymphoid tissues, in which they cause programmed cell death. Polyamine depletion, which occurs in glucocorticoid-treated animals by inhibition of biosynthesis and induction of acetylation, may represent a signal to thymocytes for progression into the apoptotic program. Since catalysis of polyamines by the catabolic pathway produces hydrogen peroxide as a by-product, it has been suggested that the apoptotic process may be, in part, due to oxidative stress as a result of hydrogen peroxide production. In order to verify whether polyamine oxidase (EC 1.5.3.11) may play a role in the process, we examined the activity of the enzyme in the thymus and spleen of glucocorticoid-treated rats. We administered dexamethasone (4 mg/kg) or two different doses of corticosterone (4 mg/kg or 30 mg/kg) to rats, which were killed 8 or 24 hr after hormone injection. We found that corticosterone and dexamethasone affected polyamine oxidase activity in both tissues, with an opposite dose-dependent effect of the natural hormone in the thymus. The decrease and increase in polyamine oxidase after the two doses of corticosterone were correlated with the absence and the occurrence of DNA fragmentation, respectively. Moreover, corticosterone affected polyamine oxidase activity earlier (8 hr) than dexamethasone (24 hr), but the synthetic hormone was more efficient than the natural hormone in thymic polyamine depletion. The polyamine oxidase response may represent an important event in lymphoid tissues after glucocorticoid treatment, suggesting a role of the enzyme in the catabolic effects exerted by the two hormones.

Gender-related differences in polyamine oxidase activity in rat tissues

Variations in level of polyamines and their related enzymes are frequently observed in response to some treatments which affect in a different way male and female. The possibility of a gender-related difference in the oxidation of polyamines was investigated in rats by measuring the activity of polyamine oxidase, a ubiquitous enzyme of vertebrate tissues, which transforms spermine into spermidine and spermidine into putrescine. The study was carried out on thymus, spleen, kidney and liver of young rats of both sexes, and female rats showed a lower polyamine oxidase activity than male rats in all the tissues. We also found higher values of spermidine acetylation in female than male rats in thymus and liver. Owing to these gender-related differences, a higher spermidine N-acetyltransferase/polyamine oxidase ratio was found in female than in male rats. A second gender-related difference was a higher spermidine/spermine ratio in female than in male, the only exception being the thymus. These basal differences possibly account for the gender-related differences of polyamine metabolic enzyme activities in response to some treatments, including drugs or hormones.

Changes in hepatic polyamine catabolism in elderly rats

AIMS/BACKGROUND

Given the important role of polyamines (putrescine, spermidine, spermine) in the modulation of macromolecular syntheses, gene expression and proteolysis, alterations in their metabolic pathways could be relevant during senescence. Since the few existing data address mainly polyamine biosynthesis, we studied the oxidative catabolism of polyamines in the liver of rats 3-36 months of age.

METHODS

Polyamine oxidase activity was fluorimetrically measured using N1-acetylspermine as substrate. Spermidine/spermine N1-acetyltransferase and diamine oxidase were measured by radiochemical methods using labeled acetyl-coenzyme A and putrescine, respectively, as substrate. Polyamines were separated by HPLC and fluorimetrically quantified after post-column derivatization with o-phthaldialdehyde.

RESULTS

Spermidine/spermine N1-acetyltransferase activity increased in 36-month-old rats and polyamine oxidase activity in 24- and 36-month-old rats. A decline in spermine and increases in spermidine and putrescine in elderly rats suggested an activation of the interconversion pathway of higher into lower polyamines. The activity of diamine oxidase, which degrades putrescine, was enhanced starting from 12 months of age.

CONCLUSION

In the liver of aged rats, an increase in the catabolic enzymes leads to a reconversion of the higher polyamines to putrescine. This increased catabolism may represent an important age-related change and may contribute to impairment of the expression of growth-related genes in senescence.