The normal programmed development of a multicellular organism from the germ cell is a synchronized series of events driven by genetic instructions acquired during conception. During the early critical periods in life the organism also has the ability to respond to environmental situations that are alien to normal development by adaptations at the cellular, molecular, and biochemical levels. Such early adaptations to a nutritional stress/stimulus permanently change the physiology and metabolism of the organism and continue to be expressed even in the absence of the stimulus/stress that initiated them, a process termed "metabolic programming" (1). A brief summary of the findings from human epidemiological and animal studies is presented below in support of the concept of metabolic programming induced by nutritional experiences during critical periods in development with consequences later in adulthood. For detailed accounts the reader is referred to excellent reviews on this subject (2-5). This minireview will focus on metabolic programming with reference to a novel rat model developed in our laboratory. Evidence for Metabolic Programming from Human Epidemiological DataExtensive epidemiological findings indicate that metabolic programming occurs in humans. Barker (6) was the first to suggest from epidemiological studies that the disproportionate size of the newborn resulting from maternal malnutrition correlated with an increased risk for adverse health outcomes (type II diabetes, hypertension, and cardiovascular diseases) later in adult life. These primary observations resulted in the now widely recognized "fetal origins" hypothesis emphasizing the importance of adequate maternal nutrition during pregnancy (4). Evidence for Metabolic Programming in AnimalsNutritional programming has been demonstrated in animal studies. In pioneering studies with rodents, McCance (7) demonstrated by adjusting litter size that the quantity of food consumed during early periods of postnatal life has long term consequences on growth. The consequences of maternal malnutrition induced by either a low protein diet or caloric restriction during gestation and lactation cause major changes in the structure and function of several organs in the offspring. Pregnant rats fed a low protein diet produced pups with alterations in pancreatic islets (8, 9). These include reduced islet vascularization, ␤ cell proliferative capacity, and islet size with rightward shift (decreased sensitivity) in glucose-stimulated insulin secretion and altered sensitivity to insulin in muscle (8, 9). Furthermore, hypothalamic nuclei are malformed in these weanling rats; this is accompanied by reduced vascularization of the cerebral cortex in the progeny (10). Metabolic capacities of the liver, muscle, and adipose tissue are compromised by maternal protein restriction during gestation and lactation with adverse adult onset outcomes (11). Elevated insulin concentrations during critical periods of development, as occurs perinatally in the offspring of gestationally dia...

A protein geranylgeranyltransferase (PGT) that catalyzes the transfer of a 20-carbon prenyl group from geranylgeranyl pyrophosphate to a cysteine residue in protein and peptide acceptors was detected in bovine brain cytosol and partially purified. The enzyme was shown to be distinct from a previously characterized protein farnesyltransferase (PFT). The PGT selectively geranylgeranylated a synthetic peptide corresponding to the C terminus of the y6 subunit of bovine brain G proteins, which have previously been shown to contain a 20-carbon prenyl modification. Likewise, a peptide corresponding to the C terminus of human lamin B, a known farnesylated protein, selectively served as a substrate for farnesylation by the PFT. However, with high concentrations of peptide acceptors, both prenyl transferases were able to use either peptide as substrates and the PGT was able to catalyze farnesyl transfer. Among the prenyl acceptors tested, peptides and proteins with leucine or phenylalanine at their C termini served as geranylgeranyl acceptors, whereas those with C-terminal serine were preferentially farnesylated. These results suggest that the C-terminal amino acid is an important structural determinant in controlling the specificity of protein prenylation.

In pressure overload-induced hypertrophy, the heart increases its reliance on glucose as a fuel while decreasing fatty acid oxidation. A key regulator of this substrate switching in the hypertrophied heart is peroxisome proliferator-activated receptor ␣ (PPAR␣). We tested the hypothesis that down-regulation of PPAR␣ is an essential component of cardiac hypertrophy at the levels of increased mass, gene expression, and metabolism by pharmacologically reactivating PPAR␣. Pressure overload (induced by constriction of the ascending aorta for 7 days in rats) resulted in cardiac hypertrophy, increased expression of fetal genes (atrial natriuretic factor and skeletal ␣-actin), decreased expression of PPAR␣ and PPAR␣-regulated genes (medium chain acyl-CoA dehydrogenase and pyruvate dehydrogenase kinase 4), and caused substrate switching (measured ex vivo in the isolated working heart preparation). Treatment of rats with the specific PPAR␣ agonist WY-14,643 (8 days) did not affect the trophic response or atrial natriuretic factor induction to pressure overload. However, PPAR␣ activation blocked skeletal ␣-actin induction, reversed the down-regulation of measured PPAR␣-regulated genes in the hypertrophied heart, and prevented substrate switching. This PPAR␣ reactivation concomitantly resulted in severe depression of cardiac power and efficiency in the hypertrophied heart (measured ex vivo). Thus, PPAR␣ down-regulation is essential for the maintenance of contractile function of the hypertrophied heart.Pressure overload of the heart activates a complex series of interconnected signaling cascades resulting in adaptive responses for the maintenance of a normal cardiac output (1, 2). This adaptation includes alterations in cardiomyocyte mass (trophic response), gene expression, and metabolism (1-6). At the trophic level, the heart hypertrophies (1, 7). At the transcriptional level, the heart reexpresses fetal genes (such as atrial natriuretic factor (ANF) 1 and skeletal ␣-actin) while depressing the expression of various adult isoforms (e.g. cardiac ␣-actin) (4, 8). At the level of metabolism, the hypertrophied heart increases reliance on glucose as a fuel and depresses fatty acid oxidation (the dominant energy source for the normal heart) (5, 6, 9).A key regulator of substrate switching in the heart is postulated to be PPAR␣ (10). This nuclear receptor regulates the expression of several genes involved in both fatty acid and glucose oxidation. These include the fatty acid transporter (FAT/CD36), fatty acid-binding protein, malonyl-CoA decarboxylase, muscle-specific carnitine palmitoyltransferase I, medium and long chain acyl-CoA dehydrogenases, as well as pyruvate dehydrogenase kinase 4 (11-16). For example, increased fatty acids in the diabetic milieu result in activation of PPAR␣, induction of PPAR␣-regulated genes, and increased fatty acid oxidation with depression of glucose oxidation (17, 18). In contrast, increased reliance of the hypertrophied heart on glucose as a fuel is associated with decreased PPAR␣ expression and ...

We postulate that metabolic conditions that develop systemically during exercise (high blood lactate and high nonesterified fatty acids) are favorable for energy homeostasis of the heart during contractile stimulation. We used working rat hearts perfused at physiological workload and levels of the major energy substrates and compared the metabolic and contractile responses to an acute low-to-high work transition under resting versus exercising systemic metabolic conditions (low vs. high lactate and nonesterified fatty acids in the perfusate). Glycogen preservation, resulting from better maintenance of high-energy phosphates, was a consequence of improved energy homeostasis with high fat and lactate. We explained the result by tighter coupling between workload and total beta-oxidation. Total fatty acid oxidation with high fat and lactate reflected increased availability of exogenous and endogenous fats for respiration, as evidenced by increased long-chain fatty acyl-CoA esters (LCFA-CoAs) and by an increased contribution of triglycerides to total beta-oxidation. Triglyceride turnover (synthesis and degradation) also appeared to increase. Elevated LCFA-CoAs caused high total beta-oxidation despite increased malonyl-CoA. The resulting bottleneck at mitochondrial uptake of LCFA-CoAs stimulated triglyceride synthesis. Our results suggest the following. First, both malonyl-CoA and LCFA-CoAs determine total fatty acid oxidation in heart. Second, concomitant stimulation of peripheral glycolysis and lipolysis should improve cardiac energy homeostasis during exercise. We speculate that high lactate contributes to the salutary effect by bypassing the glycolytic block imposed by fatty acids, acting as an anaplerotic substrate necessary for high tricarbocylic acid cycle flux from fatty acid-derived acetyl-CoA.

We postulated that glycogen is a significant energy substrate compared with fatty acids and glucose in response to adrenergic stimulation of working rat hearts. Oxidation rates were determined at 1-min intervals by release of3H2O from [9,10-3H]oleate (0.4 mM, 1% albumin) and14CO2from exogenous [U-14C]glucose (5 mM) or, by a pulse-chase method, from [14C]glycogen. We estimated the 14C enrichment of glycogen metabolized at each time point to determine true rates of glycogen use. Based on the pattern of glycogen enrichment over time, glycogenolysis did not exhibit a high degree of preference for newly synthesized glycogen. Epinephrine (1 μM) increased contractile performance 86% but did not stimulate oleate oxidation. The increased energy demand was supplied by carbohydrates, initially by a burst of glycogenolysis (contributing 35% to total ATP synthesis for 5 min) and followed by delayed increase in the use of exogenous glucose (eventually contributing 29% to ATP synthesis). On the basis of the release of14CO2and [14C]lactate specifically from glucose or glycogen, we found that a larger portion of glycogen was oxidized compared with exogenous glucose, augmenting the yield of ATP from glycogen. Thus the heart responds to an acute increase in energy demand by selective oxidation of glycogen.

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We tested the hypothesis that the level of malonyl-CoA, as well as the corresponding rate of total fatty acid oxidation of the heart, is regulated by the opposing actions of acetyl-CoA carboxylase (ACC) and malonyl-CoA decarboxylase (MCD). We used isolated working rat hearts perfused under physiological conditions. MCD in heart homogenates was measured specifically by14CO2production from [3-14C]malonyl-CoA, and ACC was measured specifically based on the portion of total carboxylase that is citrate sensitive. Increased heart work (1 μM epinephrine + 40% increase in afterload) elicited a 40% increase in total β-oxidation of exogenous plus endogenous lipids, accompanied by a 33% decrease in malonyl-CoA. The basal activity and citrate sensitivity of ACC (reflecting its phosphorylation state) and citrate content were unchanged. AMP levels were also unchanged. MCD activity, when measured at a subsaturating concentration of malonyl-CoA (50 μM), was increased by 55%. We conclude that physiological increments in AMP during the work transition are insufficient to promote ACC phosphorylation by AMP-stimulated protein kinase. Rather, increased fatty acid oxidation results from increased malonyl-CoA degradation by MCD.

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