In obesity and type 2 diabetes, Glut4 glucose transporter expression is decreased selectively in adipocytes1. Adipose-specific knockout or overexpression of Glut4 alters systemic insulin sensitivity2. Here we show, using DNA array analyses, that nicotinamide N-methyltransferase (Nnmt) is the most strongly reciprocally regulated gene when comparing gene expression in white adipose tissue (WAT) from adipose-specific Glut4-knockout or adipose-specific Glut4-overexpressing mice with their respective controls. NNMT methylates nicotinamide (vitamin B3) using S-adenosylmethionine (SAM) as a methyl donor3,4. Nicotinamide is a precursor of NAD+, an important cofactor linking cellular redox states with energy metabolism5. SAM provides propylamine for polyamine biosynthesis and donates a methyl group for histone methylation6. Polyamine flux including synthesis, catabolism and excretion, is controlled by the rate-limiting enzymes ornithine decarboxylase (ODC) and spermidine–spermine N1-acetyltransferase (SSAT; encoded by Sat1) and by polyamine oxidase (PAO), and has a major role in energy metabolism7,8. We report that NNMT expression is increased in WAT and liver of obese and diabetic mice. Nnmt knockdown in WAT and liver protects against diet-induced obesity by augmenting cellular energy expenditure. NNMT inhibition increases adipose SAM and NAD+ levels and upregulates ODC and SSAT activity as well as expression, owing to the effects of NNMT on histone H3 lysine 4 methylation in adipose tissue. Direct evidence for increased polyamine flux resulting from NNMT inhibition includes elevated urinary excretion and adipocyte secretion of diacetylspermine, a product of polyamine metabolism. NNMT inhibition in adipocytes increases oxygen consumption in an ODC-, SSAT- and PAO-dependent manner. Thus, NNMT is a novel regulator of histone methylation, polyamine flux and NAD+-dependent SIRT1 signalling, and is a unique and attractive target for treating obesity and type 2 diabetes.

Alzheimer's disease (AD) is a neurodegenerative pathology in which amyloid-beta (Abeta) peptide accumulates in different brain areas leading to deposition of plaques and a progressive decline of cognitive functions. After a decade in which a number of transgenic (Tg) mouse models mimicking AD-like amyloid-deposition pathology have been successfully generated, few rat models have been reported that develop intracellular and extracellular Abeta accumulation, together with impairment of cognition. The generation of a Tg rat reproducing the full AD-like amyloid pathology has been elusive. Here we describe the generation and characterization of a new transgenic rat line, coded McGill-R-Thy1-APP, developed to express the human amyloid-beta precursor protein (AbetaPP) carrying both the Swedish and Indiana mutations under the control of the murine Thy1.2 promoter. The selected mono-transgenic line displays an extended phase of intraneuronal Abeta accumulation, already apparent at 1 week after birth, which is widespread throughout different cortical areas and the hippocampus (CA1, CA2, CA3, and dentate gyrus). Homozygous Tg animals eventually produce extracellular Abeta deposits and, by 6 months of age, dense, thioflavine S-positive, amyloid plaques are detected, associated with glial activation and surrounding dystrophic neurites. The cognitive functions in transgenic McGill-R-Thy1-APP rats, as assessed using the Morris water maze task, were found already altered as early as at 3 months of age, when no CNS plaques are yet present. The spatial cognitive impairment becomes more prominent in older animals (13 months), where the behavioral performance of Tg rats positively correlates with the levels of soluble Abeta (trimers) measured in the cortex.

We have generated a transgenic mouse line that overexpresses the rate-controlling enzyme of polyamine catabolism, spermidine/spermine N 1 -acetyltransferase. Tissues of these mice showed markedly distorted polyamine pools, which in most cases were characterized by the appearance of N 1 -acetylspermidine, not normally found in mouse tissues, a massive accumulation of putrescine, and decreases in spermidine and/or spermine pools. The most striking phenotypic change was permanent hair loss at the age of 3 to 4 weeks which was typified histologically by the appearance of extensive follicular cysts in the dermis. The effect seemed attributable to putrescine interference with hair development, possibly with differentiation/proliferation of epidermal cells located in hair follicles. Female members of the transgenic line were found to be infertile apparently due to ovarian hypofunction and hypoplastic uteri. The findings demonstrate the utility of spermidine/spermine N 1 -acetyltransferase overexpression as an effective means for genetically modulating total tissue polyamine pools in transgenic animals and examining the developmental and oncogenic consequences.The well recognized association of polyamines with cell growth (1-3) is best illustrated by findings related to the key polyamine biosynthetic enzyme, ornithine decarboxylase (ODC).1 Although ODC is sharply but transiently increased by growth stimuli, it is constitutively activated during cell transformation induced by carcinogens, viruses, or oncogenes. Overexpression of ODC has been correlated with increased proliferative potential (4), tissue invasiveness (5), and in certain cell types, with oncogene-like transforming capabilities (6 -8). Thus far, ODC appears to be the only growth-related gene activated by the transcription factors c-myc (9 -11) and n-myc (12), suggesting a critical role for the enzyme in growth control. However, as indicated below, findings obtained in cell culture may not be directly applicable to conditions prevailing in vivo.To define the role of polyamines in proliferative processes associated with the whole animal, we have generated a number of transgenic mouse and rat lines that overexpress ODC and/or other polyamine biosynthetic enzymes. Given the importance of polyamine biosynthetic activity to cell growth, the phenotypic changes were unexpectedly mild. In transgenic mice overexpressing ODC, the most marked effect was inhibition of meiotic DNA synthesis during spermatogenesis (13) ultimately leading to male infertility (14). It is also noteworthy that lifelong overexpression of ODC in mouse tissues did not seem to increase the incidence of spontaneous tumors (15). The absence of more profound phenotypic changes in these mice may be attributable to the relatively minor changes observed in higher polyamine pools. Despite severalfold increases in ODC activity, polyamine pool disturbances were mainly confined to putrescine accumulation, and the pools of those polyamines considered to be more significantly involved in cell growth, spermidi...

The polyamines putrescine, spermidine and spermine are organic cations shown to participate in a bewildering number of cellular reactions, yet their exact functions in intermediary metabolism and specific interactions with cellular components remain largely elusive. Pharmacological interventions have demonstrated convincingly that a steady supply of these compounds is a prerequisite for cell proliferation to occur. The last decade has witnessed the appearance of a substantial number of studies, in which genetic engineering of polyamine metabolism in transgenic rodents has been employed to unravel their cellular functions. Transgenic activation of polyamine biosynthesis through an overexpression of their biosynthetic enzymes has assigned specific roles for these compounds in spermatogenesis, skin physiology, promotion of tumorigenesis and organ hypertrophy as well as neuronal protection. Transgenic activation of polyamine catabolism not only profoundly disturbs polyamine homeostasis in most tissues, but also creates a complex phenotype affecting skin, female fertility, fat depots, pancreatic integrity and regenerative growth. Transgenic expression of ornithine decarboxylase antizyme has suggested that this unique protein may act as a general tumor suppressor. Homozygous deficiency of the key biosynthetic enzymes of the polyamines, ornithine and S-adenosylmethionine decarboxylase, as achieved through targeted disruption of their genes, is not compatible with murine embryogenesis. Finally, the first reports of human diseases apparently caused by mutations or rearrangements of the genes involved in polyamine metabolism have appeared.Keywords: antizyme; ornithine decarboxylase; putrescine; spermidine/spermine N 1 -acetyltransferase; spermidine; spermine; transgenic mouse; transgenic rat. IntroductionThe cellular functions of the natural polyamines (putrescine, spermidine and spermine) are still largely unknown, although a vast number of studies have shown that these polycationic compounds are crucial to the growth and proliferation of mammalian cells. Pharmacological approaches are applied typically in studies aimed to unravel their functions in cellular metabolism and, admittedly, much valuable information has been generated with the use of specific inhibitors of polyamine biosynthesis. However, the last decade has produced a substantial number of experimental studies in which genetic engineering of polyamine metabolism has been used as a tool to elucidate their cellular functions. Studies with genetically engineered mice and rats have not only brought entirely new information about the involvement of polyamines in various physiological and pathophysiological processes but they have likewise challenged some of the conventional wisdoms. Mainly, four different approaches have been applied in the genetic engineering of experimental animals: (a) activation of polyamine biosynthesis through the overexpression of their biosynthetic enzymes; (b) activation of polyamine catabolism through the overexpression of the enzymes i...

The polyamines putrescine, spermidine and spermine represent a group of naturally occurring compounds exerting a bewildering number of biological effects, yet despite several decades of intensive research work, their exact physiological function remains obscure. Chemically these compounds are organic aliphatic cations with two (putrescine), three (spermidine) or four (spermine) amino or amino groups that are fully protonated at physiological pH values. Early studies showed that the polyamines are closely connected to the proliferation of animal cells. Their biosynthesis is accomplished by a concerted action of four different enzymes: ornithine decarboxylase, adenosylmethionine decarboxylase, spermidine synthase and spermine synthase. Out of these four enzyme, the two decarboxylases represent unique mammalian enzymes with an extremely short half life and dramatic inducibility in response to growth promoting stimuli. The regulation of ornithine decarboxylase, and to some extent also that of adenosylmethionine decarboxylase, is complex, showing features that do not always fit into the generally accepted rules of molecular biology. The development and introduction of specific inhibitors to the biosynthetic enzymes of the polyamines have revealed that an undisturbed synthesis of the polyamines is a prerequisite for animal cell proliferation to occur. The biosynthesis of the polyamines thus offers a meaningful target for the treatment of certain hyperproliferative diseases, most notably cancer. Although most experimental cancer models responds strikingly to treatment with polyamine antimetabolites--namely, inhibitors of various polyamine synthesizing enzymes--a real breakthrough in the treatment of human cancer has not yet occurred. It is, however, highly likely that the concept is viable. An especially interesting approach is the chemoprevention of cancer with polyamine antimetabolites, a process that appears to work in many experimental animal models. Meanwhile, the inhibition of polyamine accumulation has shown great promise in the treatment of human parasitic diseases, such as African trypanosomiasis.

The acetylating enzyme, spermidine/spermine N 1 -acetyltransferase, participates in polyamine homeostasis by regulating polyamine export and catabolism. Previously, we reported that overexpression of the enzyme in cultured tumor cells and mice activates metabolic flux through the polyamine pathway and depletes the N 1 -acetyltransferase coenzyme and fatty acid precursor, acetyl-CoA. Here, we investigate this possibility in spermidine/spermine N 1 -acetyltransferase transgenic mice in which the enzyme is systemically overexpressed and in spermidine/spermine N 1 -acetyltransferase knock-out mice. Tissues of the former were characterized by increased N 1 -acetyltransferase activity, a marked elevation in tissue and urinary acetylated polyamines, a compensatory increase in polyamine biosynthetic enzyme activity, and an increase in metabolic flux through the polyamine pathway. These polyamine effects were accompanied by a decrease in white adipose acetyl-and malonyl-CoA pools, a major (20-fold) increase in glucose and palmitate oxidation, and a distinctly lean phenotype. In SSAT-ko mice, the opposite relationship between polyamine and fat metabolism was observed. In the absence of N 1 -acetylation of polyamines, there was a shift in urinary and tissue polyamines indicative of a decline in metabolic flux. This was accompanied by an increase in white adipose acetyl-and malonyl-CoA pools, a decrease in adipose palmitate and glucose oxidation, and an accumulation of body fat. The latter was further exaggerated under a high fat diet, where knock-out mice gained twice as much weight as wild-type mice. A model is proposed whereby the expression status of spermidine/spermine N 1 -acetyltransferase alters body fat accumulation by metabolically modulating tissue acetyl-and malonyl-CoA levels, thereby influencing fatty acid biosynthesis and oxidation.The polyamines putrescine (Put), 3 spermidine (Spd), and spermine (Spm) are known for their critical role in supporting cell proliferation, albeit in ways that have not yet been clearly defined. For the most part, polyamines do not incorporate into macromolecules but rather bind electrostatically to negatively charged molecules, such as DNA, RNA, and phospholipids. Thus, as metabolically distinct entities, homeostatic control of intracellular polyamines is critical to their role in supporting cell proliferation. This is achieved by effector systems that regulate biosynthesis, catabolism, uptake, and export of these molecules. The enzyme, spermidine/spermine N 1 -acetyltransferase (SSAT), catalyzes the transfer of acetyl groups from acetyl-CoA to the terminal amines of polyamines and, thus, readies the molecule for export or catabolism via polyamine oxidase. The enzyme is short lived, sensitively regulated by intracellular polyamine pools, and highly inducible by polyamine analogues and various cytotoxic agents (1, 2).Although most antiproliferative strategies targeting the polyamine pathway seek to deplete intracellular pools by inhibiting biosynthesis, we have been investigating t...

Background— Vascular endothelial growth factor-B (VEGF-B) binds to VEGF receptor-1 and neuropilin-1 and is abundantly expressed in the heart, skeletal muscle, and brown fat. The biological function of VEGF-B is incompletely understood. Methods and Results— Unlike placenta growth factor, which binds to the same receptors, adeno-associated viral delivery of VEGF-B to mouse skeletal or heart muscle induced very little angiogenesis, vascular permeability, or inflammation. As previously reported for the VEGF-B 167 isoform, transgenic mice and rats expressing both isoforms of VEGF-B in the myocardium developed cardiac hypertrophy yet maintained systolic function. Deletion of the VEGF receptor-1 tyrosine kinase domain or the arterial endothelial Bmx tyrosine kinase inhibited hypertrophy, whereas loss of VEGF-B interaction with neuropilin-1 had no effect. Surprisingly, in rats, the heart-specific VEGF-B transgene induced impressive growth of the epicardial coronary vessels and their branches, with large arteries also seen deep inside the subendocardial myocardium. However, VEGF-B, unlike other VEGF family members, did not induce significant capillary angiogenesis, increased permeability, or inflammatory cell recruitment. Conclusions— VEGF-B appears to be a coronary growth factor in rats but not in mice. The signals for the VEGF-B–induced cardiac hypertrophy are mediated at least in part via the endothelium. Because cardiomyocyte damage in myocardial ischemia begins in the subendocardial myocardium, the VEGF-B–induced increased arterial supply to this area could have therapeutic potential in ischemic heart disease.

Peroxisome proliferator-activated receptor ␥ coactivator 1␣ (PGC-1␣) is an attractive candidate gene for type 2 diabetes, as genes of the oxidative phosphorylation (OXPHOS) pathway are coordinatively downregulated by reduced expression of PGC-1␣ in skeletal muscle and adipose tissue of patients with type 2 diabetes. Here we demonstrate that transgenic mice with activated polyamine catabolism due to overexpression of spermidine/spermine N 1 -acetyltransferase (SSAT) had reduced white adipose tissue (WAT) mass, high basal metabolic rate, improved glucose tolerance, high insulin sensitivity, and enhanced expression of the OXPHOS genes, coordinated by increased levels of PGC-1␣ and 5-AMP-activated protein kinase (AMPK) in WAT. As accelerated polyamine flux caused by SSAT overexpression depleted the ATP pool in adipocytes of SSAT mice and N 1 ,N 11 -diethylnorspermine-treated wild-type fetal fibroblasts, we propose that low ATP levels lead to the induction of AMPK, which in turn activates PGC-1␣ in WAT of SSAT mice. Our hypothesis is supported by the finding that the phenotype of SSAT mice was reversed when the accelerated polyamine flux was reduced by the inhibition of polyamine biosynthesis in WAT. The involvement of polyamine catabolism in the regulation of energy and glucose metabolism may offer a novel target for drug development for obesity and type 2 diabetes.Type 2 diabetes is a growing epidemic worldwide. Defects in insulin secretion and insulin action are fundamental disorders of this disease (30). Several mechanisms regulating insulin secretion and insulin action have been identified, but none of them is likely to explain completely the risk of type 2 diabetes. Previous studies have revealed novel mechanisms, distinct from the insulin signaling pathway, for type 2 diabetes. Mootha et al. (36) identified a set of genes involved in oxidative phosphorylation (OXPHOS), the expression of which was coordinately decreased in human diabetic muscle. Similarly, Patti et al. (40) found the downregulation of OXPHOS not only in individuals with type 2 diabetes but also in their first-degree relatives. In both of these studies, decreased peroxisome proliferator-activated receptor (PPAR) ␥ coactivator 1␣ (PGC-1␣) expression was responsible for the downregulation of OX PHOS genes. In addition, the expression of PGC-1␣ has been shown to be downregulated in white adipose tissue (WAT) of insulin-resistant (15) and morbidly obese (50) subjects.PGC-1␣ was first identified as a coactivator of PPAR␥ (45), and it plays a critical role in the regulation of adaptive thermogenesis. Subsequent studies have demonstrated that PGC-1␣ regulates mitochondrial biogenesis (49), uncoupling (45, 56), fatty acid oxidation (61), OXPHOS (36), glucose transport in muscle (35), hepatic gluconeogenesis (64), and skeletal muscle fiber-type switching (44). PGC-1␣ is highly expressed in brown adipose tissue (BAT), heart, and skeletal muscle and moderately expressed in liver, but a low expression level is found in WAT. The expression of PGC-1␣ is ind...