(p)ppGpp/GTP and Malonyl-CoA Modulate Staphylococcus aureus Adaptation to FASII Antibiotics and Provide a Basis for Synergistic Bi-Therapy.

Fatty acid biosynthesis (FASII) enzymes are considered valid targets for antimicrobial drug development against the human pathogen Staphylococcus aureus However, incorporation of host fatty acids confers FASII antibiotic adaptation that compromises prospective treatments. S. aureus adapts to FASII inhibitors by first entering a nonreplicative latency period, followed by outgrowth. Here, we used transcriptional fusions and direct metabolite measurements to investigate the factors that dictate the duration of latency prior to outgrowth. We show that stringent response induction leads to repression of FASII and phospholipid synthesis genes. (p)ppGpp induction inhibits synthesis of malonyl-CoA, a molecule that derepresses FapR, a key regulator of FASII and phospholipid synthesis. Anti-FASII treatment also triggers transient expression of (p)ppGpp-regulated genes during the anti-FASII latency phase, with concomitant repression of FapR regulon expression. These effects are reversed upon outgrowth. GTP depletion, a known consequence of the stringent response, also occurs during FASII latency, and is proposed as the common signal linking these responses. We next showed that anti-FASII treatment shifts malonyl-CoA distribution between its interactants FapR and FabD, toward FapR, increasing expression of the phospholipid synthesis genes plsX and plsC during outgrowth. We conclude that components of the stringent response dictate malonyl-CoA availability in S. aureus FASII regulation, and contribute to latency prior to anti-FASII-adapted outgrowth. A combinatory approach, coupling a (p)ppGpp inducer and an anti-FASII, blocks S. aureus outgrowth, opening perspectives for bi-therapy treatment.IMPORTANCEStaphylococcus aureus is a major human bacterial pathogen for which new inhibitors are urgently needed. Antibiotic development has centered on the fatty acid synthesis (FASII) pathway, which provides the building blocks for bacterial membrane phospholipids. However, S. aureus overcomes FASII inhibition and adapts to anti-FASII by using exogenous fatty acids that are abundant in host environments. This adaptation mechanism comprises a transient latency period followed by bacterial outgrowth. Here, we use metabolite sensors and promoter reporters to show that responses to stringent conditions and to FASII inhibition intersect, in that both involve GTP and malonyl-CoA. These two signaling molecules contribute to modulating the duration of latency prior to S. aureus adaptation outgrowth. We exploit these novel findings to propose a bi-therapy treatment against staphylococcal infections.

Isoflavone malonyl-CoA acyltransferase GmMaT2 is involved in nodulation of soybean by modifying synthesis and secretion of isoflavones.

Malonyl-CoA:flavonoid acyltransferases (MaTs) modify isoflavones, but only a few have been characterized for activity and assigned to specific physiological processes. Legume roots exude isoflavone malonates into the rhizosphere, where they are hydrolyzed into isoflavone aglycones. Soybean GmMaT2 was highly expressed in seeds, root hairs, and nodules. GmMaT2 and GmMaT4 recombinant enzymes used isoflavone 7-O-glucosides as acceptors and malonyl-CoA as an acyl donor to generate isoflavone glucoside malonates. GmMaT2 had higher activity towards isoflavone glucosides than GmMaT4. Overexpression in hairy roots of GmMaT2 and GmMaT4 produced more malonyldaidzin, malonylgenistin, and malonylglycitin, and resulted in more nodules than control. However, only GmMaT2 knockdown (KD) hairy roots showed reduced levels of malonyldaidzin, malonylgenistin, and malonylglycitin, and, likewise, reduced nodule numbers. These were consistent with the up-regulation of only GmMaT2 by rhizobial infection, and higher expression levels of early nodulation genes in GmMaT2- and GmMaT4-overexpressing roots, but lower only in GmMaT2-KD roots compared with control roots. Higher malonyl isoflavonoid levels in transgenic hairy roots were associated with higher levels of isoflavones in root exudates and more nodules, and vice versa. We suggest that GmMaT2 participates in soybean nodulation by catalyzing isoflavone malonylation and affecting malonyl isoflavone secretion for activation of Nod factor and nodulation.

Effects of chronic mild food restriction on behavior and the hypothalamic malonyl-CoA signaling pathway.

Depression induces anorexia, leading to suppressed feeding behaviors and energy intake. Previously, we revealed that chronic social defeat induced a mild suppression of feeding in rats with elevated levels of hypothalamic malonyl-CoA which regulates feeding. Therefore, we attempted to elucidate the effects of chronic mild food restriction on behavior and on hypothalamic malonyl-CoA. The chronic mild food restricted rats were fed a restricted diet approximately 80% to 90% amount of diet compared to the control for 5 weeks. Ratios of restriction were adjusted with feed consumption in the chronic social defeat stressed rats. Chronic mild food restricted rats exhibited a suppression of body weight gain similar to that of the chronic social defeat stressed rats. Also these rats showed increased time spent in the center area of an open field (OF), prolonged immobility time in forced swim, increased phosphorylation of hypothalamic adenosine monophosphate-activated protein kinase (AMPK) and acetyl-CoA carboxylase and a decreased concentration of hypothalamic malonyl-CoA. Weight of the adrenal glands, locomotion in an OF, mitogen-activated protein kinase cascade and calcium/calmodulin-dependent protein kinases II in the hippocampus were not affected by chronic mild food restriction. Our findings suggest that chronic mild food restriction activates AMPK following a decreased hypothalamic malonyl-CoA.

Important role of ventromedial hypothalamic carnitine palmitoyltransferase-1a in the control of food intake.

Carnitine palmitoyltransferase-1 (CPT-1) liver isoform, or CPT-1a, is implicated in CNS control of food intake. However, the exact brain nucleus site(s) in mediating this action of CPT-1a has not been identified. In this report, we assess the role of CPT-1a in hypothalamic ventromedial nucleus (VMN). We stereotaxically injected an adenoviral vector containing CPT-1a coding sequence into the VMN of rats to induce overexpression and activation of CPT-1a. The VMN-selective activation of CPT-1a induced an orexigenic effect, suggesting CPT-1a in the VMN is involved in the central control of feeding. Intracerebroventricular administration of etomoxir, a CPT-1 inhibitor, decreases food intake. Importantly, in the animals with VMN overexpression of a CPT-1a mutant that antagonizes the CPT-1 inhibition by etomoxir, the anorectic response to etomoxir was attenuated. This suggests that VMN is involved in mediating the anorectic effect of central inhibition of CPT-1a. In contrast, arcuate nucleus (Arc) overexpression of the mutant did not alter etomoxir-induced inhibition of food intake, suggesting that Arc CPT-1a does not play significant roles in this anorectic action. Furthermore, in the VMN, CPT-1a appears to act downstream of hypothalamic malonyl-CoA action of feeding. Finally, we show that in the VMN CPT-1 activity was altered in concert with fasting and refeeding states, supporting a physiological role of CPT-1a in mediating the control of feeding. All together, CPT-1a in the hypothalamic VMN appears to play an important role in central control of food intake. VMN-selective modulation of CPT-1a activity may therefore be a promising strategy in controlling food intake and maintaining normal body weight.

Malonyl-CoA mediates leptin hypothalamic control of feeding independent of inhibition of CPT-1a.

Hypothalamic fatty acid metabolism is involved in central nervous system controls of feeding and energy balance. Malonyl-CoA, an intermediate of fatty acid biosynthesis, is emerging as a significant player in these processes. Notably, hypothalamic malonyl-CoA has been implicated in leptin's feeding effect. Leptin treatment increases malonyl-CoA level in the hypothalamic arcuate nucleus (Arc), and this increase is required for leptin-induced decrease in food intake. However, the intracellular downstream mediators of malonyl-CoA's feeding effect have not been identified. A primary biochemical action of malonyl-CoA is the inhibition of the acyltransferase activity of carnitine palmitoyltransferase-1 (CPT-1). In the hypothalamus, the predominant isoform of CPT-1 that possesses the acyltransferase activity is CPT-1 liver type (CPT-1a). To address the role of CPT-1a in malonyl-CoA's anorectic action, we used a recombinant adenovirus expressing a mutant CPT-1a that is insensitive to malonyl-CoA inhibition. We show that Arc overexpression of the mutant CPT-1a blocked the malonyl-CoA-mediated inhibition of CPT-1 activity. However, the overexpression of this mutant did not affect the anorectic actions of leptin or central cerulenin for which an increase in Arc malonyl-CoA level is also required. Thus, CPT-1a does not appear to be involved in the malonyl-CoA's anorectic actions induced by leptin. Furthermore, long-chain fatty acyl-CoAs, substrates of CPT-1a, dissociate from malonyl-CoA's actions in the Arc under different feeding states. Together, our results suggest that Arc intracellular mechanisms of malonyl-CoA's anorectic actions induced by leptin are independent of CPT-1a. The data suggest that target(s), rather than CPT-1a, mediates malonyl-CoA action on feeding.

Regulation of food intake and energy expenditure by hypothalamic malonyl-CoA.

Energy balance is monitored by the hypothalamus. Malonyl-CoA, an intermediate in fatty acid synthesis, serves as an indicator of energy status in the hypothalamic neurons. The cellular malonyl-CoA level is determined by its rate of synthesis, catalyzed by acetyl-CoA carboxylase (ACC), and rate of removal, by fatty acid synthase (FAS). Malonyl-CoA functions in the hypothalamic neurons that express orexigenic and anorexigenic neuropeptides. Inhibitors of FAS, administered systemically or intracerebroventricularly to mice, increase hypothalamic malony-CoA and suppress food intake. Recent evidence suggests that the changes of hypothalamic malonyl-CoA during feeding and fasting cycles are caused by changes in the phosphorylation state and activity of ACC mediated via 5'-AMP-activated protein kinase (AMPK). Stereotactic delivery of a viral malonyl-CoA decarboxylase (MCD) vector into the ventral hypothalamus lowers malonyl-CoA and increases food intake. Fasting decreases hypothalamic malonyl-CoA and refeeding increases hypothalamic malonyl-CoA, to alter feeding behavior in the predicted manner. Malonyl-CoA level is under the control of AMP kinase which phosphorylates/inactivates ACC. Malonyl-CoA is an inhibitor of carnitine palmitoyl-CoA transferase-1 (CPT1), an outer mitochondrial membrane enzyme that regulates entry into, and oxidation of fatty acids, by mitochondria. CPT1c, a recently discovered, brain-specific enzyme expressed in the hypothalamus, has high sequence similarity to liver/muscle CPT1a/b and binds malonyl-CoA, but does not catalyze the prototypical reaction. This suggests that CPT1c has a unique function or activation mechanism. CPT1c knockout (KO) mice have lower food intake, weigh less and have less body fat, consistent with the role as an energy-sensing malonyl-CoA target. Paradoxically, CPT1c protects against the effects of a high-fat diet. CPT1cKO mice exhibit decreased rates of fatty acid oxidation, consistent with their increased susceptibility to diet-induced obesity. We suggest that CPT1c may be a downstream target of malonyl-CoA that regulates energy homeostasis.

Malonyl-CoA, a key signaling molecule in mammalian cells.

Malonyl-CoA can be formed within the mitochondria, peroxisomes, and cytosol of mammalian cells. Besides being an intermediate in the pathways of de novo fatty acid biosynthesis and fatty acid elongation, malonyl-CoA has an important signaling function through its allosteric inhibition of carnitine palmitoyltransferase 1, the enzyme that normally exerts flux control over mitochondrial beta-oxidation. Malonyl-CoA is rapidly turned over in mammalian cells, and the activities of acetyl-CoA carboxylase and malonyl-CoA decarboxylase are important determinants of its cytosolic concentration. It is now recognized that malonyl-CoA participates in a diverse range of physiological or pathological responses and systems. These include the ketogenic response of the liver to fasting and diabetes, carbohydrate versus fat fuel selection in muscle tissues, metabolic changes in muscle during contracture, alterations in fatty acid metabolism during cardiac ischemia and postischemic reperfusion, stimulation of B cell insulin secretion by glucose, and the hypothalamic control of appetite.

Malonyl coenzyme A affects insulin-stimulated glucose transport in myotubes.

There seems to be an association between increased concentrations of malonyl coenzyme A (malonyl CoA) in skeletal muscle and diabetes and/or insulin resistance. The purpose of the current study was to test the hypothesis that treatments designed to manipulate malonyl CoA concentrations would affect insulin-stimulated glucose transport in cultured C2C12 myotubes. We assessed glucose transport after polyamine-mediated delivery of malonyl CoA to myotubes, after incubation with dichloroacetate (which reportedly increases malonyl CoA levels), or after exposure of myotubes to 2-bromopalmitate, a carnitine palmitoyl transferase I inhibitor. All three of these treatments prevented stimulation of glucose transport by insulin. We also assayed glucose transport after 30 min of inhibition of acetyl coenzyme A carboxylase (ACC), the enzyme which catalyzes the production of malonyl CoA. Three unrelated ACC inhibitors (diclofop, clethodim, and Pfizer CP-640186) all enhanced insulin-stimulated glucose transport. However, none of the treatments designed to manipulate malonyl CoA concentrations altered markers of proximal insulin signaling through Akt. The findings support the hypothesis that acute changes in malonyl CoA concentrations affect insulin action in muscle cells but suggest that the effects do not involve alterations in proximal insulin signaling.

Role of malonyl-CoA in heart disease and the hypothalamic control of obesity.

Obesity is an important contributor to the risk of developing insulin resistance, diabetes, and heart disease. Alterations in tissue levels of malonyl-CoA have the potential to impact on the severity of a number of these disorders. This review will focus on the emerging role of malonyl-CoA as a key "metabolic effector" of both obesity and cardiac fatty acid oxidation. In addition to being a substrate for fatty acid biosynthesis, malonyl-CoA is a potent inhibitor of mitochondrial carnitine palmitoyltransferase (CPT) 1, a key enzyme involved in mitochondrial fatty acid uptake. A decrease in myocardial malonyl-CoA levels and an increase in CPT1 activity contribute to an increase in cardiac fatty acid oxidation. An increase in malonyl-CoA degradation due to increased malonyl-CoA decarboxylase (MCD) activity may be one mechanism responsible for this decrease in malonyl-CoA. Another mechanism involves the inhibition of acetyl-CoA carboxylase (ACC) synthesis of malonyl-CoA, due to AMP-activated protein kinase (AMPK) phosphorylation of ACC. Recent studies have demonstrated a role of malonyl-CoA in the hypothalamus as a regulator of food intake. Increases in hypothalamic malonyl-CoA and inhibition of CPT1 are associated with a decrease in food intake in mice and rats, while a decrease in hypothalamic malonyl-CoA increases food intake and weight gain. The exact mechanism(s) responsible for these effects of malonyl-CoA are not clear, but have been proposed to be due to an increase in the levels of long chain acyl CoA, which occurs as a result of malonyl-CoA inhibition of CPT1. Both hypothalamic and cardiac studies have demonstrated that control of malonyl-CoA levels has an important impact on obesity and heart disease. Targeting enzymes that control malonyl-CoA levels may be an important therapeutic approach to treating heart disease and obesity.

Fatty acid signaling in the beta-cell and insulin secretion.

Fatty acids (FAs) and other lipid molecules are important for many cellular functions, including vesicle exocytosis. For the pancreatic beta-cell, while the presence of some FAs is essential for glucose-stimulated insulin secretion, FAs have enormous capacity to amplify glucose-stimulated insulin secretion, which is particularly operative in situations of beta-cell compensation for insulin resistance. In this review, we propose that FAs do this via three interdependent processes, which we have assigned to a "trident model" of beta-cell lipid signaling. The first two arms of the model implicate intracellular metabolism of FAs, whereas the third is related to membrane free fatty acid receptor (FFAR) activation. The first arm involves the AMP-activated protein kinase/malonyl-CoA/long-chain acyl-CoA (LC-CoA) signaling network in which glucose, together with other anaplerotic fuels, increases cytosolic malonyl-CoA, which inhibits FA partitioning into oxidation, thus increasing the availability of LC-CoA for signaling purposes. The second involves glucose-responsive triglyceride (TG)/free fatty acid (FFA) cycling. In this pathway, glucose promotes LC-CoA esterification to complex lipids such as TG and diacylglycerol, concomitant with glucose stimulation of lipolysis of the esterification products, with renewal of the intracellular FFA pool for reactivation to LC-CoA. The third arm involves FFA stimulation of the G-protein-coupled receptor GPR40/FFAR1, which results in enhancement of glucose-stimulated accumulation of cytosolic Ca2+ and consequently insulin secretion. It is possible that FFA released by the lipolysis arm of TG/FFA cycling is partly "secreted" and, via an autocrine/paracrine mechanism, is additive to exogenous FFAs in activating the FFAR1 pathway. Glucose-stimulated release of arachidonic acid from phospholipids by calcium-independent phospholipase A2 and/or from TG/FFA cycling may also be involved. Improved knowledge of lipid signaling in the beta-cell will allow a better understanding of the mechanisms of beta-cell compensation and failure in diabetes.

The regulation of food intake by hypothalamic malonyl-coenzyme A: the MaloA hypothesis.

In animals, food intake and therefore energy balance is regulated by a center in the hypothalamus of the brain. Neurons there release appetite-inhibiting (anorexigenic) or appetite-stimulating (orexigenic) peptide hormones according to whether energy intake exceeds or is less than expenditure, respectively. Recent evidence for the "malonyl coenzyme A hypothesis" showed that the level of malonyl coenzyme A (MalCoA) in the arcuate nucleus of the hypothalamus determines the stimulation or inhibition of food intake. A high level of MalCoA, indicative of energy surplus, signals the release of anorexigenic neuropeptides, resulting in decreased food intake; a low level of MalCoA, due to an energy deficit such as during fasting, signals the release of orexigenic neuropeptides, stimulating food intake.

Control of energy homeostasis: role of enzymes and intermediates of fatty acid metabolism in the central nervous system.

The regulation of energy homeostasis is critical for normal physiology and survival. Energy flux must be rigorously monitored and adjusted to ensure that fuel intake and expenditure remain within acceptable limits. The central nervous system (CNS) is, in large part, responsible for conducting this energy-monitoring function and for integrating the numerous inputs. It has become evident that neurons of the CNS monitor and respond to levels of metabolic intermediates that reflect peripheral energy status. Intermediates in the fatty acid biosynthetic pathway have been implicated as hypothalamic signaling mediators that sense and respond to changes in circulating fuels. Genetic and pharmacologic manipulation of the enzymes of fatty acid metabolism have led to the hypothesis that neuronal metabolic intermediates affect neural outputs that modify both feeding behavior and energy expenditure. This review focuses on the regulatory roles of these enzymes and intermediates in the regulation of food intake and energy balance.

Role of malonyl-CoA in the hypothalamic control of food intake and energy expenditure.

The brain plays an important role in the regulation of energy balance in higher animals. Global energy balance is monitored by sets of neurons in the hypothalamus that respond to peripheral hormonal and afferent neural signals that sense the energy status. Malonyl-CoA, an intermediate in the biosynthesis of fatty acids, appears to function in this hypothalamic energy-sensing system. The steady-state level of malonyl-CoA is determined by its rate of synthesis catalysed by ACC (acetyl-CoA carboxylase) relative to its rate of turnover catalysed by FAS (fatty acid synthase). Changes in the level of malonyl-CoA in the hypothalamus alter the expression/secretion of key hypothalamic orexigenic and anorexigenic neuropeptides that regulate the feeding behaviour and energy expenditure. Inhibitors of FAS, administered i.c.v. (intracerebroventricularly) to lean or obese mice, cause a rapid rise in hypothalamic malonyl-CoA level, suppression of food intake, increased fatty acid oxidation in skeletal muscle and profound weight loss. Stereotactic delivery of a viral MCD (malonyl-CoA decarboxylase) expression vector into the ventral hypothalamus lowers malonyl-CoA levels and reverses the anorectic effect of the FAS inhibitors. Fasting decreases, whereas refeeding increases, hypothalamic malonyl-CoA and alters subsequent feeding behaviour accordingly. The level of malonyl-CoA in the hypothalamus appears to be under the control of 5'-AMP kinase, which phosphorylates and thereby inactivates ACC under conditions of energy surplus. Thus malonyl-CoA appears to link the energy-responsive fatty acid synthesis in the hypothalamus to feeding behaviour and peripheral energy expenditure.

A role for hypothalamic malonyl-CoA in the control of food intake.

The cellular level of malonyl-CoA, an intermediate in fatty acid biosynthesis, depends on its rate of synthesis catalyzed by acetyl-CoA carboxylase relative to its rate of utilization and degradation catalyzed by fatty acid synthase and malonyl-CoA decarboxylase, respectively. Recent evidence suggests that hypothalamic malonyl-CoA functions in the regulation of feeding behavior by altering the expression of key orexigenic and anorexigenic neuropeptides. Here we report that 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a 5'-AMP kinase activator, rapidly lowers malonyl-CoA both in GT1-7 hypothalamic neurons and in the hypothalami of mice. These effects correlate closely with the phosphorylation of acetyl-CoA carboxylase, an established target of AMP kinase. Intracerebroventricular (i.c.v.) administration of AICAR rapidly lowers hypothalamic [malonyl-CoA] and increases food intake. Expression of an adenoviral cytosolic malonyl-CoA decarboxylase vector (Ad-cMCD) in hypothalamic GT1-7 cells decreases malonyl-CoA. When delivered by bilateral stereotaxic injection into the ventral hypothalamus (encompassing the arcuate nucleus) of mice, Ad-cMCD increases food intake and body weight. Ad-MCD delivered into the ventral hypothalamus also reverses the rapid suppression of food intake caused by i.c.v.-administered C75, a fatty acid synthase inhibitor that increases hypothalamic [malonyl-CoA]. Taken together these findings implicate malonyl-CoA in the hypothalamic regulation of feeding behavior.

Hypothalamic malonyl-CoA as a mediator of feeding behavior.

Previous studies showed that i.p. administration of C75, a potent inhibitor of fatty acid synthase (FAS), blocked fasting-induced up-regulation of orexigenic neuropeptides and down-regulation of anorexigenic neuropeptides in the hypothalami of mice. As a result, food intake and body weight were drastically reduced. Here we provide evidence supporting the hypothesis that hypothalamic malonyl-CoA, a substrate of FAS, is an indicator of global energy status and mediates the feeding behavior of mice. We use a sensitive recycling assay to quantify malonyl-CoA to show that the hypothalamic malonyl-CoA level is low in fasted mice and rapidly (< or = 2 h) increases (approximately 5-fold) on refeeding. Intracerebroventricular (i.c.v.) administration of C75 to fasted mice rapidly (< or = 2 h) increased (by 4-fold) hypothalamic malonyl-CoA and blocked feeding when the mice were presented with food. Moreover, prior i.c.v. administration of an acetyl-CoA carboxylase inhibitor, 5-(tetradecyloxy)-2-furoic acid, rapidly (although only partially) prevented the C75-induced rise of hypothalamic malonyl-CoA and prevented the C75-induced decrease of food intake. These effects correlated closely with the rapid (< or = 2 h) and reciprocal effects of i.c.v. C75 on the expression of hypothalamic orexigenic (NPY and AgRP) and anorexigenic (proopiomelanocortin) neuropeptide mRNAs. Previous results showing that C75 administered i.c.v. rapidly activates hypothalamic neurons of the arcuate and paraventricular nuclei are consistent with the results reported in this paper. Together these findings suggest that level of hypothalamic malonyl-CoA, which depends on the relative activities of acetyl-CoA carboxylase and FAS, is an indicator of energy status and mediates feeding behavior.

Malonyl-CoA and AMP-activated protein kinase (AMPK): possible links between insulin resistance in muscle and early endothelial cell damage in diabetes.

Based on available evidence, we would propose the following. (i) Excesses of glucose and free fatty acids cause insulin resistance in skeletal muscle and damage to the endothelial cell by a similar mechanism. (ii) Key pathogenetic events in this mechanism very likely include increased fatty acid esterification, protein kinase C activation, an increase in oxidative stress (demonstrated to date in endothelium) and alterations in the inhibitor kappa B kinase/nuclear factor kappa B system. (iii) Activation of AMP-activated protein kinase (AMPK) inhibits all of these events and enhances insulin signalling in the endothelial cell. It also enhances insulin action in muscle; however, the mechanism by which it does so has not been well studied. (iv) The reported beneficial effects of exercise and metformin on cardiovascular disease and insulin resistance in humans could be related to the fact that they activate AMPK. (v) The comparative roles of AMPK in regulating metabolism, signalling and gene expression in muscle and endothelial cells warrant further study.

Relative importance of malonyl CoA and carnitine in maturation of fatty acid oxidation in newborn rabbit heart.

After birth, a dramatic increase in fatty acid oxidation occurs in the heart, which has been attributed to an increase in l-carnitine levels and a switch from the liver (L) to muscle (M) isoform of carnitine palmitoyltransferase (CPT)-1. However, because M-CPT-1 is more sensitive to inhibition by malonyl CoA, a potent endogenous regulator of fatty acid oxidation, a switch to the M-CPT-1 isoform should theoretically decrease fatty acid oxidation. Because of this discrepancy, we assessed the contributions of myocardial l-carnitine content and CPT-1 isoform expression and kinetics to the maturation of fatty acid oxidation in newborn rabbit hearts. Although fatty acid oxidation rates increased between 1 and 14 days after birth, myocardial l-carnitine concentrations did not increase. Changes in the expression of L-CPT-1 or M-CPT-1 mRNA after birth also did not parallel the increase in fatty acid oxidation. The K(m) of CPT-1 for carnitine and the IC(50) for malonyl CoA remained unchanged between 1 and 10 days after birth. However, malonyl CoA levels dramatically decreased, due in part to an increase in malonyl CoA decarboxylase activity. Our data suggest that a decrease in malonyl CoA control of CPT-1 is primarily responsible for the increase in fatty acid oxidation seen in the newborn heart.

Malonyl-CoA signaling, lipid partitioning, and glucolipotoxicity: role in beta-cell adaptation and failure in the etiology of diabetes.

Beta-cells possess inherent mechanisms to adapt to overnutrition and the prevailing concentrations of glucose, fatty acids, and other fuels to maintain glucose homeostasis. However, this is balanced by potentially harmful actions of the same nutrients. Both glucose and fatty acids may cause good/adaptive or evil/toxic actions on the beta-cell, depending on their concentrations and the time during which they are elevated. Chronic high glucose dramatically influences beta-cell lipid metabolism via substrate availability, changes in the activity and expression of enzymes of glucose and lipid metabolism, and modifications in the expression level of key transcription factors. We discuss here the emerging view that beta-cell "glucotoxicity" is in part indirectly caused by "lipotoxicity," and that beta-cell abnormalities will become particularly apparent when both glucose and circulating fatty acids are high. We support the concept that elevated glucose and fatty acids synergize in causing toxicity in islets and other organs, a process that may be instrumental in the pleiotropic defects associated with the metabolic syndrome and type 1 and type 2 diabetes. The mechanisms by which hyperglycemia and hyperlipidemia alter insulin secretion are discussed and a model of beta-cell "glucolipotoxicity" that implicates alterations in beta-cell malonyl-CoA concentrations; peroxisome proliferator-activated receptor-alpha and -gamma and sterol regulatory element binding protein-1c expression; and lipid partitioning is proposed.