Enhanced triglyceride clearance with intraperitoneal human acylation stimulating protein in C57BL/6 mice

Complement Properdin Regulates the Metabolo-Inflammatory Response to a High Fat Diet

Background and objectives: Overnutrition leads to a metabolic and inflammatory response that includes the activation of Complement. Properdin is the only amplifier of complement activation and increases the provision of complement activation products. Its absence has previously been shown to lead to increased obesity in mice on a high fat diet. The aim of this study was to determine ways in which properdin contributes to a less pronounced obese phenotype. Materials and Methods: Wild type (WT) and properdin deficient mice (KO) were fed a high-fat diet (HFD) for up to 12 weeks. Results: There was a significant increase in liver triglyceride content in the KO HFD group compared to WT on HFD. WT developed steatosis. KO had an additional inflammatory component (steatohepatitis). Analysis of AKT signalling by phosphorylation array supported a decrease in insulin sensitivity which was greater for KO than WT in liver and kidney. There was a significant decrease of C5L2 in the fat membranes of the KO HFD group compared to the WT HFD group. Circulating microparticles in KO HFD group showed lower presence of C5L2. Expression of the fatty acid transporter CD36 in adipose tissue was increased in KO on HFD and was also significantly increased in plasma of KO HFD mice compared to WT on HFD. CD36 was elevated on microparticles from KO on HFD. Ultrastructural changes consistent with obesity-associated glomerulopathy were observed for both HFD fed genotypes, but tubular strain was greater in KO. Conclusion: Our work demonstrates that complement properdin is a dominant factor in limiting the severity of obesity-associated conditions that impact on liver and kidney. The two receptors, C5L2 and CD36, are downstream of the activity exerted by properdin.

Role of Complement and Complement-Related Adipokines in Regulation of Energy Metabolism and Fat Storage

Adipose tissue releases many cytokines and inflammatory factors described as adipokines. In obesity, adipokines released from expanding adipose tissue are implicated in disease progression and metabolic dysfunction. However, mechanisms controlling the progression of adiposity and metabolic complications are not fully understood. It has been suggested that expanding fat mass and sustained release of inflammatory adipokines in adipose tissue lead to hypoxia, oxidative stress, apoptosis, and cellular damage. These changes trigger an immune response involving infiltration of adipose tissue with immune cells, complement activation and generation of factors involved in opsonization and clearance of damaged cells. Abundant evidence now indicates that adipose tissue is an active secretory source of complement and complement-related adipokines that, in addition to their inflammatory role, contribute to the regulation of metabolic function. This article highlights advances in knowledge regarding the role of these adipokines in energy regulation of adipose tissue through modulating lipogenic and lipolytic pathways. Several adipokines will be discussed including adipsin, Factor H, properdin, C3a, Acylation-Stimulating Protein, C1q/TNF-related proteins, and response gene to complement-32 (RGC-32). Interactions between these factors will be described considering their immune-metabolic roles in the adipose tissue microenvironment and their potential contribution to progression of adiposity and metabolic dysfunction. The differential expression and the role of complement factors in gender-related fat partitioning will also be addressed. Identifying lipogenic adipokines and their specific autocrine/paracrine roles may provide means for adipose-tissue-targeted therapeutic interventions that may disrupt the vicious circle of adiposity and disease progression. © 2019 American Physiological Society. Compr Physiol 9:1411-1429, 2019.

The role of complement system in adipose tissue-related inflammation

As the common factor linking adipose tissue to the metabolic context of obesity, insulin resistance and atherosclerosis are associated with a low-grade chronic inflammatory status, to which the complement system is an important contributor. Adipose tissue synthesizes complement proteins and is a target of complement activation. C3a-desArg/acylation-stimulating protein stimulates lipogenesis and affects lipid metabolism. The C3a receptor and C5aR are involved in the development of adipocytes' insulin resistance through macrophage infiltration and the activation of adipose tissue. The terminal complement pathway has been found to be instrumental in promoting hyperglycemia-associated tissue damage, which is characteristic of the major vascular complications of diabetes mellitus and diabetic ketoacidosis. As a mediator of the effects of the terminal complement complex C5b-9, RGC-32 has an impact on energy expenditure as well as lipid and glucose metabolic homeostasis. All of this evidence, taken together, indicates an important role for complement activation in metabolic diseases.

Serum Adipsin Levels throughout Normal Pregnancy and Preeclampsia

Adipsin is a protease produced at high levels by adipose tissue. It is involved in complement activation and metabolic control. The objective of this study was to determine the changes in adipsin levels during different stages of normal pregnancy, and its association with obstetric outcomes, such as preeclampsia. This nested case-control study in a longitudinal cohort included normal pregnant (n = 54) and preeclamptic (n = 18) women, both followed throughout pregnancy. Additionally, some of the normal pregnant women were followed up three months postpartum (n = 18). Healthy non-pregnant women were also studied during their menstrual cycle (n = 20). The results of this study show that in healthy non-pregnant women, adipsin levels did not change significantly during the menstrual cycle. In normal pregnant women, adipsin levels were lower (p < 0.01) when compared with non-pregnant healthy women, but these serum levels increased again during postpartum (p < 0.001). Adipsin levels were significantly elevated in preeclamptic women in late pregnancy (P < 0.01). A significant correlation was not found between leptin and adipsin during the three periods of gestation studied in healthy pregnant and preeclamptic women. Our results suggest that adipsin may be involved in pregnancy-associated metabolic changes. Moreover, the increase of adipsin levels towards late gestation in preeclamptic women could be related to the pathophysiology of this disease.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Elevated fetal adipsin/acylation-stimulating protein (ASP) in obese pregnancy: novel placental secretion via Hofbauer cells

CONTEXT AND OBJECTIVE

Obesity in pregnancy is associated with increased risks of obesity in the offspring. We investigated the relationship between obesity in pregnancy and circulating maternal and fetal levels of adipose tissue-derived factors adipsin and acylation stimulating protein (ASP) in lean and obese mothers.

DESIGN

Paired peripheral and cord blood samples were taken. Paired fat and placenta tissue were taken for explant culture. Media were assayed for secreted adipsin and ASP. Clinical parameters assayed included fasting insulin, glucose, and adipsin.

SETTING

The study was conducted at a university hospital maternity unit.

PATIENTS

Patients included 35 lean [body mass index (BMI) 19-25 kg/m(2), mean age 32 years and 39 obese (BMI) > 30 kg/m(2), mean age 32.49 years] pregnant Caucasian women, delivered by cesarean section at term.

MAIN OUTCOME MEASURE

Identification of placental macrophages [Hofbauer cells (HBCs)], as a source of adipsin and ASP was determined.

RESULTS

HBCs secreted both adipsin and ASP. Cord levels of adipsin (1663.78 ± 52.76 pg/mL) and ASP (354.48 ± 17.17 ng/mL) were significantly elevated in the offspring of obese mothers compared with their lean controls [1354.66 ± 33.87 pg/mL and 302.63 ± 14.98 ng/mL, respectively (P < .05 for both)]. Placentae from obese mothers released significantly more adipsin and ASP than placentae from lean mothers [546.0 ± 44 pg/mL · g vs 284.56 ± 43 pg/mL · g and 5485.75 ± 163.32 ng/mL · g vs 2399.16 ± 181.83 ng/mL · g, respectively (P < .05 for both)]. Circulating fetal adipsin and ASP positively correlated with maternal BMI (r = 0.611, P < .0001, and r = 0.391, P < .05, respectively). Fetal adipsin correlated positively with maternal (r = 0.482, P < .01) and fetal homeostasis model assessment of insulin resistance (r = 0.465, P < .01).

CONCLUSIONS

We demonstrate novel secretion of adipsin and ASP by placental HBCs.

Paradoxical glucose-sensitizing yet proinflammatory effects of acute ASP administration in mice

Acylation stimulating protein (ASP) is an adipokine derived from the immune complement system, which stimulates fat storage and is typically increased in obesity, type 2 diabetes, and cardiovascular disease. Using a diet-induced obesity (DIO) mouse model, the acute effects of ASP on energy metabolism and inflammatory processes in vivo were evaluated. We hypothesized that ASP would specifically exert proinflammatory effects. C57Bl/6 wild-type mice were put on a high-fat-high-sucrose diet for 12 weeks. Mice were then subjected to both glucose and insulin tolerance tests, each manipulation being preceded by recombinant ASP or vehicle (control) bolus injection. ASP supplementation increased whole-body glucose excursion, and this was accomplished with reduced concomitant insulin levels. However, ASP did not directly alter insulin sensitivity. ASP supplementation induced a proinflammatory phenotype, with higher levels of cytokines including IL-6 and TNF-α in plasma and in adipose tissue, liver, and skeletal muscle mRNA. Additionally, ASP increased M1 macrophage content of these tissues. ASP exerted a direct concentration-dependent role in the migration and M1 activation of cultured macrophages. Altogether, the in vivo and in vitro experiments demonstrate that ASP plays a role in both energy metabolism and inflammation, with paradoxical whole-body glucose-sensitizing yet proinflammatory effects.

C5L2 receptor disruption enhances the development of diet-induced insulin resistance in mice

INTRODUCTION

Acylation stimulating protein (ASP) is a hormone secreted by the adipose tissue that has been shown to increase triglyceride storage and glucose transport in adipocytes. These effects are mediated by C5L2 receptor, which has also been associated with inflammatory effects. C5L2 deficient mice on a low-fat diet are hyperphagic yet lean due to increased energy expenditure. The present study assessed insulin sensitivity and metabolic and inflammatory changes in C5L2KO mice vs WT in diet-induced obesity.

METHODS

We placed C5L2KO and WT mice on a diabetogenic diet for 12 weeks and examined in vivo and ex vivo metabolism.

RESULTS

C5L2KO mice on a diabetogenic diet exhibit decreased insulin sensitivity. Whole body substrate partitioning is evidenced through increased glucose uptake by the liver and decreased uptake by adipose tissue and skeletal muscle. Lipid content of both liver and skeletal muscle was higher in C5L2KO mice vs WT. Furthermore, elevated levels of macrophage markers were found in adipose tissue, liver and skeletal muscle of C5L2KO mice vs WT. Several inflammatory cytokines such as IL-6, MIP-1α and KC were also elevated in plasma of C5L2KO mice vs WT.

CONCLUSIONS

Overall, we demonstrated that C5L2KO mice fed a diabetogenic diet develop more severe insulin resistance than WT mice through altered substrate partitioning, ectopic fat deposition and a pro-inflammatory phenotype.

CD55 deficiency protects against atherosclerosis in ApoE-deficient mice via C3a modulation of lipid metabolism

Atherosclerosis, the leading cause of death in the Western world, is driven by chronic inflammation within the artery wall. Elements of the complement cascade are implicated in the pathogenesis, because complement proteins and their activation products are found in the atherosclerotic plaque. We examined the role of CD55, a membrane inhibitor of the complement component 3 (C3) convertase, which converts C3 into C3a and C3b, in atherosclerosis. CD55-deficient (CD55^−/−) mice were crossed onto the atherosclerosis-prone apolipoprotein E (apoE)-deficient (apoE^−/−) background. High fat–fed male apoE^−/−/CD55^−/− mice were strongly protected from developing atherosclerosis compared with apoE^−/− controls. Lipid profiling showed significantly lower levels of triglycerides, nonesterified fatty acids, and cholesterol in apoE^−/−/CD55^−/− mice than that in controls after high-fat feeding, whereas body fat in apoE^−/−/CD55^−/− mice content was increased. Plasma levels of C3 fell, whereas concentrations of C3adesArg (alias acylation stimulating protein; ASP), produced by serum carboxypeptidase N–mediated desargination of C3a, increased in nonfasted high fat–fed apoE^−/−/CD55^−/− mice, indicating complement activation. Thus, complement dysregulation in the absence of CD55 provoked increased C3adesArg production that, in turn, caused altered lipid handling, resulting in atheroprotection and increased adiposity. Interventions that target complement activation in adipose tissue should be explored as lipid-decreasing strategies.

Acute injection of ASP in the third ventricle inhibits food intake and locomotor activity in rats

Acylation-stimulating protein (ASP; also known as C3adesArg) stimulates triglyceride synthesis and glucose transport via interaction with its receptor C5L2, which is expressed peripherally (adipose tissue, muscle) and centrally. Previous studies have shown that ASP-deficient mice (C3KO) and C5L2-deficient mice (C5L2KO) are hyperphagic (59 to 229% increase, P < 0.0001), which is counterbalanced by increased energy expenditure measured as oxygen consumption (Vo(2)) and a lower RQ. The aim of the present study was to evaluate ASP's effect on food intake, energy expenditure, and neuropeptide expression. Male rats were surgically implanted with intracerebroventricular (icv) cannulas directed toward the third ventricle. After a 5-h fast, rats were injected, and food intake was assessed at 0.5, 1, 2, 4, 16, 24, and 48 h, with a 5- to 7-day washout period between each injection. Acute icv injections of ASP (0.3-1,065 pmol) had a time-dependent effect on decreasing food intake by 20 to 57% (P < 0.05). Decreases were detected by 30 min (maximum 57%, P < 0.01) and at the highest dose effects extended to 48 h (19%, P < 0.05, 24- to 48-h period). Daily body weight gain was decreased by 131% over the first 24 h and 29% over the second 24 h (P < 0.05). A conditioned taste aversion test indicated that there was no malaise. Furthermore, acute ASP injection affected energy substrate usage, demonstrated by decreased Vo(2) and RQ (P < 0.05; implicating greater fatty acid usage), with a 49% decrease in total activity over 24 h (P < 0.05). ASP administration also increased anorexic neuropeptide POMC expression (44%) in the arcuate nucleus, with no change in NPY. Altogether ASP may have central in addition to peripheral effects.

Long-term cardiac-targeted RNA interference for the treatment of heart failure restores cardiac function and reduces pathological hypertrophy

BACKGROUND

RNA interference (RNAi) has the potential to be a novel therapeutic strategy in diverse areas of medicine. Here, we report on targeted RNAi for the treatment of heart failure, an important disorder in humans that results from multiple causes. Successful treatment of heart failure is demonstrated in a rat model of transaortic banding by RNAi targeting of phospholamban, a key regulator of cardiac Ca(2+) homeostasis. Whereas gene therapy rests on recombinant protein expression as its basic principle, RNAi therapy uses regulatory RNAs to achieve its effect.

METHODS AND RESULTS

We describe structural requirements to obtain high RNAi activity from adenoviral and adeno-associated virus (AAV9) vectors and show that an adenoviral short hairpin RNA vector (AdV-shRNA) silenced phospholamban in cardiomyocytes (primary neonatal rat cardiomyocytes) and improved hemodynamics in heart-failure rats 1 month after aortic root injection. For simplified long-term therapy, we developed a dimeric cardiotropic adeno-associated virus vector (rAAV9-shPLB) to deliver RNAi activity to the heart via intravenous injection. Cardiac phospholamban protein was reduced to 25%, and suppression of sacroplasmic reticulum Ca(2+) ATPase in the HF groups was rescued. In contrast to traditional vectors, rAAV9 showed high affinity for myocardium but low affinity for liver and other organs. rAAV9-shPLB therapy restored diastolic (left ventricular end-diastolic pressure, dp/dt(min), and tau) and systolic (fractional shortening) functional parameters to normal ranges. The massive cardiac dilation was normalized, and cardiac hypertrophy, cardiomyocyte diameter, and cardiac fibrosis were reduced significantly. Importantly, no evidence was found of microRNA deregulation or hepatotoxicity during these RNAi therapies.

CONCLUSIONS

Our data show for the first time the high efficacy of an RNAi therapeutic strategy in a cardiac disease.

Cord blood ASP is predicted by maternal lipids and correlates with fetal birth weight

BACKGROUND

The acylation stimulating protein (ASP) is a potent lipogenic adipokine that correlates with postprandial triglyceride (TG) clearance and is linked to the pathophysiology of obesity and related disorders.

OBJECTIVE

To investigate ASP levels in cord blood and its relation to maternal and cord blood lipid parameters and fetal birth weight.

METHODS AND PROCEDURES

Thirty nondiabetic pregnant women, their newborns, and thirty-three nonpregnant controls were included in this study. Fasting maternal and cord blood ASP, TGs, nonesterified fatty acids (NEFAs), cholesterol, glucose levels, in addition to maternal BMI and fetal birth weight were measured.

RESULTS

No significant difference was found between cord blood ASP (16.3 +/- 0.96 nmol/l) and ASP levels in the adult controls (15.7 +/- 1.0 nmol/l). Cord blood ASP, however, was lower than maternal plasma ASP levels (25.4 +/- 1.6 nmol/l, P < 0.001). Yet, lipid levels in cord blood, particularly TGs were markedly decreased compared to control and maternal TG levels (threefold and 7.4-fold, P < 0.001 respectively). Maternal TGs significantly correlated with fetal birth weight (r = 0.54, P = 0.002). Multiple regression analysis showed that maternal TGs (beta = 0.57, P = 0.01) and NEFAs (beta = 0.43, P = 0.024) predicted 45% variation in cord blood ASP levels, independent of all measured maternal and cord blood parameters. Cord blood ASP showed a positive correlation with fetal birth weight (r = 0.524, P = 0.037) in neonates above average fetal birth weight of the studied population.

DISCUSSION

This is the first study investigating ASP in cord blood. We suggest that maternal hypertriglyceridemia is associated with increased fetal ASP production, thus enhancing fetal fat storage independent of maternal glucose variations in nondiabetic women.

Shift in metabolic fuel in acylation-stimulating protein-deficient mice following a high-fat diet

ASP-deficient mice (C3 KO) have delayed postprandial TG clearance, are hyperphagic, and display increased energy expenditure. Markers of carbohydrate and fatty acid metabolism in the skeletal muscle and heart were examined to evaluate the mechanism. On a high-fat diet, compared with wild-type mice, C3 KO mice have increased energy expenditure, decreased RQ, lower ex vivo glucose oxidation (-39%, P = 0.018), and higher ex vivo fatty acid oxidation (+68%, P = 0.019). They have lower muscle glycogen content (-25%, P < 0.05) and lower activities for the glycolytic enzymes glycogen phosphorylase (-31%, P = 0.005), hexokinase (-43%, P = 0.007), phosphofructokinase (-51%, P < 0.0001), and GAPDH (-15%, P = 0.04). Analysis of mitochondrial enzyme activities revealed that hydroxyacyl-coenzyme A dehydrogenase was higher (+25%, P = 0.004) in C3 KO mice. Furthermore, Western blot analysis of muscle revealed significantly higher fatty acid transporter CD36 (+40%, P = 0.006) and cytochrome c (a marker of mitochondrial content; +69%, P = 0.034) levels in C3 KO mice, whereas the activity of AMP kinase was lower (-48%, P = 0.003). Overall, these results demonstrate a shift in the metabolic potential of skeletal muscle toward increased fatty acid utilization. Whether this is 1) a consequence of decreased adipose tissue storage with repartitioning toward muscle or 2) a direct result of the absence of ASP interaction with the receptor C5L2 in muscle remains to be determined. However, these in vivo data suggest that ASP inhibition could be a potentially viable approach in correcting muscle metabolic dysfunction in obesity.

Acylation-stimulating protein/C5L2-neutralizing antibodies alter triglyceride metabolism in vitro and in vivo

Acylation-stimulating protein (ASP), a lipogenic hormone, stimulates triglyceride (TG) synthesis and glucose transport upon activation of C5L2, a G protein-coupled receptor. ASP-deficient mice have reduced adipose tissue mass due to increased energy expenditure despite increased food intake. The objective of this study was to evaluate the blocking of ASP-C5L2 interaction via neutralizing antibodies (anti-ASP and anti-C5L2-L1 against C5L2 extracellular loop 1). In vitro, anti-ASP and anti-C5L2-L1 blocked ASP binding to C5L2 and efficiently inhibited ASP stimulation of TG synthesis and glucose transport. In vivo, neither anti-ASP nor anti-C5L2-L1 altered body weight, adipose tissue mass, food intake, or hormone levels (insulin, leptin, and adiponectin), but they did induce a significant delay in TG clearance [P < 0.0001, 2-way repeated-measures (RM) ANOVA] and NEFA clearance (P < 0.0001, 2-way RM ANOVA) after a fat load. After treatment with either anti-ASP or anti-C5L2-L1 antibody there was no change in adipose tissue AMPK activity, but neutralizing antibodies decreased perirenal TG mass (-38.4% anti-ASP, -18.8% anti-C5L2, P < 0.01-0.001) and perirenal LPL activity (-75.6% anti-ASP, -72.5% anti-C5L2, P < 0.05). In liver, anti-C5L2-L1 decreased TG mass (-42.8%, P < 0.05), whereas anti-ASP increased AMPK activity (+34.6%, P < 0.001). In the muscle, anti-C5L2-L1 significantly increased TG mass (+128.0%, P < 0.05), LPL activity (+226.1%, P < 0.001), and AMPK activity (+71.1%, P < 0.01). In addition, anti-ASP increased LPL activity (+164.4, P < 0.05) and AMPK activity (+53.9%, P < 0.05) in muscle. ASP/C5L2-neutralizing antibodies effectively block ASP-C5L2 interaction, altering lipid distribution and energy utilization.

Rosiglitazone decreases postprandial production of acylation stimulating protein in type 2 diabetics

Background

We evaluated plasma ASP and its precursor C3 in type 2 diabetic men with/without rosiglitazone (ROSI) treatment compared to healthy non-obese men. We tested (1) whether plasma ASP or C3 are altered postprandially in subcutaneous adipose tissue or forearm muscle effluent assessed by arteriovenous (A-V) differences in healthy lean men and older obese diabetic men and (2) whether treatment with ROSI changes the arteriovenous gradient of ASP and/or C3.

Methods

In this ongoing placebo-controlled, crossover, double-blinded study, AV differences following a mixed meal were measured in diabetic men (n = 6) as compared to healthy men (n = 9).

Results

Postprandial arterial and adipose venous TG and venous NEFA were increased in diabetics vs. controls (p < 0.05–0.0001). ROSI treatment decreased postprandial arterial TG (p < 0.001), adipose venous NEFA (p < 0.005), reduced postprandial glucose (p < 0.0001) and insulin concentrations (p < 0.006). In healthy men, there was no change in postprandial C3, but an increase in adipose venous ASP vs. arterial ASP (p < 0.02), suggesting ASP production, with no change in forearm muscle. In older, obese diabetic subjects, arterial C3 was greater than in controls (p < 0.001). Arterial C3 was greater than venous C3 (p < 0.05), an effect that was lost with ROSI treatment. In diabetics, postprandial venous ASP was greater than arterial (p < 0.05), indicating ASP production, an effect that was lost with ROSI treatment (p < 0.01).

Conclusion

Increased postprandial venous production of ASP is specific for adipose tissue (absent in forearm muscle). Increased postprandial C3 and ASP in diabetic subjects is consistent with an ASP resistant state, this state is partially normalized by treatment with ROSI.

Increased plasma acylation-stimulating protein correlates with hyperlipidemia at late gestation

OBJECTIVES

Obesity is often associated with negative consequences, including hyperlipidemia and insulin resistance. Weight gain during pregnancy is also associated with major lipid alterations. Fat storage is enhanced in early pregnancy. At late gestation, hyperlipidemia becomes a major manifestation. The acylation-stimulating protein (ASP) is a potent lipogenic adipocytokine that correlates with postprandial triglyceride (TG) clearance in vivo and has been linked to hyperlipidemic disorders. The role of ASP during a normal pregnancy is unknown. The objective of this study was to investigate plasma ASP levels in correlation with the lipid profile during late gestation.

RESEARCH METHODS AND PROCEDURES

Seventy healthy women at late gestation and 60 non-pregnant controls of similar age and prepregnancy BMI were included in a cross-sectional study. Fasting plasma ASP levels and the lipid profile of all of the women were measured.

RESULTS

ASP levels were markedly elevated in the pregnant women (66%, p < 0.001). ASP levels correlated strongly with the elevated levels of TGs (r = 0.608, p < 0.000), apolipoprotein B (0.519, p < 0.000), and low-density lipoprotein-cholesterol (r = 0.405, p < 0.000). Multivariate analysis adjusting for BMI and age showed that changes in ASP levels at late gestation were best predicted by TG and apoB levels, accounting for 53.8% of plasma ASP variation. For the controls, ASP strongly correlated with BMI, which was the only significant predictor of ASP levels.

DISCUSSION

Gestational hormone alterations during pregnancy may affect ASP function as a lipogenic factor. Increased plasma ASP levels at late gestation and their strong correlation with parameters reflecting very low-density lipoprotein accumulation are suggestive of ASP resistance, which may further contribute to the hyperlipidemic state, shifting energy in the form of TGs to the rapidly growing fetus.

Relationships among acylation stimulating protein, adiponectin and complement C3 in lean vs obese type 2 diabetes

OBJECTIVE

The purpose of this study was to determine the relationships between adipocyte hormones acylation stimulating protein (ASP), adiponectin, complement C3 (C3) (ASP precursor) and insulin, C-reactive protein (CRP), lipid profiles and insulin resistance in lean vs obese type 2 diabetes subjects.

SUBJECTS

Lean type 2 diabetes subjects (DL n = 27) vs obese type 2 diabetes subjects (DO n = 55) were compared to age-matched nondiabetic groups (Obese, OB n = 55 and control, CTL n = 50).

RESULTS

The DO group demonstrated significant increases in plasma ASP and C3 with decreases in plasma adiponectin as compared to CTL. Interestingly, these increases in ASP and C3 were as high, or greater, in the DL group in spite of normal weight. By contrast adiponectin in the DL group was comparable to CTL, in spite of marked insulin resistance. C3 correlated with insulin, glucose and homeostasis model assessment of insulin resistance (HOMA-IR); ASP correlated with body mass index (BMI), glucose, insulin and plasma lipid parameters (non-esterified fatty acids (NEFA), triglyceride, cholesterol and apolipoprotein B). Adiponectin correlated with BMI, glucose, NEFA, triglyceride, high-density lipoprotein cholesterol and apolipoprotein A1 but not HOMA-IR, ASP or C3. CRP correlated only with HOMA-IR.

CONCLUSION

Increased ASP and C3 are both associated with diabetes and related lipid factors but are not regulated coordinately. Adiponectin appears to be more closely related to body size (decreased in obese subjects) than insulin resistance in these subjects.

Characterization of a novel PKA phosphorylation site, serine-2030, reveals no PKA hyperphosphorylation of the cardiac ryanodine receptor in canine heart failure

Hyperphosphorylation of the cardiac Ca2+ release channel (ryanodine receptor, RyR2) by protein kinase A (PKA) at serine-2808 has been proposed to be a key mechanism responsible for cardiac dysfunction in heart failure (HF). However, the sites of PKA phosphorylation in RyR2 and their phosphorylation status in HF are not well defined. Here we used various approaches to investigate the phosphorylation of RyR2 by PKA. Mutating serine-2808, which was thought to be the only PKA phosphorylation site in RyR2, did not abolish the phosphorylation of RyR2 by PKA. Two-dimensional phosphopeptide mapping revealed two major PKA phosphopeptides, one of which corresponded to the known serine-2808 site. Another, novel, PKA phosphorylation site, serine 2030, was identified by Edman sequencing. Using phospho-specific antibodies, we showed that the novel serine-2030 site was phosphorylated in rat cardiac myocytes stimulated with isoproterenol, but not in unstimulated cells, whereas serine-2808 was considerably phosphorylated before and after isoproterenol treatment. We further showed that serine-2030 was stoichiometrically phosphorylated by PKA, but not by CaMKII, and that mutations of serine-2030 altered neither the FKBP12.6-RyR2 interaction nor the Ca2+ dependence of [3H]ryanodine binding. Moreover, the levels of phosphorylation of RyR2 at serine-2030 and serine-2808 in both failing and non-failing canine hearts were similar. Together, our data indicate that serine-2030 is a major PKA phosphorylation site in RyR2 responding to acute beta-adrenergic stimulation, and that RyR2 is not hyperphosphorylated by PKA in canine HF.

Alterations in early action potential repolarization causes localized failure of sarcoplasmic reticulum Ca2+ release

Depressed contractility of failing myocytes involves a decreased rate of rise of the Ca2+ transient. Synchronization of Ca2+ release from the junctional sarcoplasmic reticulum (SR) is responsible for the rapid rise of the normal Ca2+ transient. This study examined the idea that spatially and temporally dyssynchronous SR Ca2+ release slows the rise of the cytosolic Ca2+ transient in failing feline myocytes. Left ventricular hypertrophy (LVH) with and without heart failure (HF) was induced in felines by constricting the ascending aorta. Ca2+ transients were measured in ventricular myocytes using confocal line scan imaging. Ca2+ transients were induced by field stimulation, square wave voltage steps, or action potential (AP) voltage clamp. SR Ca2+ release was significantly less well spatially and temporally synchronized in field-stimulated HF versus control or LVH myocytes. Surprisingly, depolarization of HF cells to potentials where Ca2+ currents (ICa) were maximal resynchronized SR Ca2+ release. Correspondingly, decreases in the amplitude of ICa desynchronized SR Ca2+ release in control, LVH, and HF myocytes to the same extent. HF myocytes had significant loss of phase 1 AP repolarization and smaller ICa density, which should both reduce Ca2+ influx. When normal myocytes were voltage clamped with HF AP profiles SR Ca2+ release was desynchronized. SR Ca2+ release becomes dyssynchronized in failing feline ventricular myocytes because of reductions in Ca2+ influx induced in part by alterations in early repolarization of the AP. Therefore, therapies that restore normal early repolarization should improve the contractility of the failing heart.

Novel roles for acylation stimulating protein/C3adesArg: a review of recent in vitro and in vivo evidence

Recent experimental evidence is shedding more light on the physiological actions of acylation-stimulating protein (ASP)/C3adesArg. The role of ASP in regulating lipid metabolism has primarily focused on its participation in the stimulation of triglyceride synthesis (TGS) and glucose transport. Although there is no doubt that ASP, an adipocyte-produced hormone, plays a key physiological role, accumulating evidence suggests that the effects of ASP go beyond its acute effects on lipid metabolism. In this review, we present novel findings of ASP/C3adesArg effects on preadipocyte differentiation. In 3T3-L1 and 3T3-F442A cells, ASP can substitute for insulin and enhance differentiation as measured by intracellular lipid droplet accumulation, clonal expansion, and increased expression of differentiation markers. Specifically, ASP increased basal TGS by 250% after 9 days differentiation, with similar effects induced by insulin. With ASP treatment, expression of C/EBPdelta was up-regulated early in differentiation (day 2) and decreased thereafter. Expression of PPARgamma and late markers of differentiation, such as adipsin and diacylglycerol acyltransferase-1, were also increased. Effects on clonal expansion were indicated by a twofold increase in [(3)H] thymidine incorporation in 3T3-L1 cells compared to treatment with IBMX + DX alone. Further, the effects of ASP extended beyond adipose tissue to endocrine effects on hormone secretion of insulin (pancreatic cells); cytokines TNFalpha, IL-1beta, and IL-6 (myeloid cells); prolactin, growth hormone, and adrenocorticotropin (pituitary cells). Finally, the potential implication of C5L2, the newly discovered ASP receptor, and its expression profile in various tissues are discussed relative to ASP function.

Diabetes, lipids, and adipocyte secretagogues

That obesity is associated with insulin resistance and type II diabetes mellitus is well accepted. Overloading of white adipose tissue beyond its storage capacity leads to lipid disorders in non-adipose tissues, namely skeletal and cardiac muscles, pancreas, and liver, effects that are often mediated through increased non-esterified fatty acid fluxes. This in turn leads to a tissue-specific disordered insulin response and increased lipid deposition and lipotoxicity, coupled to abnormal plasma metabolic and (or) lipoprotein profiles. Thus, the importance of functional adipocytes is crucial, as highlighted by the disorders seen in both "too much" (obesity) and "too little" (lipodystrophy) white adipose tissue. However, beyond its capacity for fat storage, white adipose tissue is now well recognised as an endocrine tissue producing multiple hormones whose plasma levels are altered in obese, insulin-resistant, and diabetic subjects. The consequence of these hormonal alterations with respect to both glucose and lipid metabolism in insulin target tissues is just beginning to be understood. The present review will focus on a number of these hormones: acylation-stimulating protein, leptin, adiponectin, tumour necrosis factor alpha, interleukin-6, and resistin, defining their changes induced in obesity and diabetes mellitus and highlighting their functional properties that may protect or worsen lipid metabolism.

Differential regulation of fatty acid trapping in mouse adipose tissue and muscle by ASP

Acylation-stimulating protein (ASP) is a lipogenic hormone secreted by white adipose tissue (WAT). Male C3 knockout (KO; C3(-/-)) ASP-deficient mice have delayed postprandial triglyceride (TG) clearance and reduced WAT mass. The objective of this study was to examine the mechanism(s) by which ASP deficiency induces differences in postprandial TG clearance and body composition in male KO mice. Except for increased (3)H-labeled nonesterified fatty acid (NEFA) trapping in brown adipose tissue (BAT) of KO mice (P = 0.02), there were no intrinsic tissue differences between wild-type (WT) and KO mice in (3)H-NEFA or [(14)C]glucose oxidation, TG synthesis or lipolysis in WAT, muscle, or liver. There were no differences in WAT or skeletal muscle hydrolysis, uptake, and storage of [(3)H]triolein substrate [in situ lipoprotein lipase (LPL) activity]. ASP, however, increased in situ LPL activity in WAT (+64.8%, P = 0.02) but decreased it in muscle (-35.0%, P = 0.0002). In addition, after prelabeling WAT with [(3)H]oleate and [(14)C]glucose, ASP increased (3)H-lipid retention, [(3)H]TG synthesis, and [(3)H]TG-to-[(14)C]TG ratio, whereas it decreased (3)H-NEFA release, indicating increased NEFA trapping in WAT. Conversely, in muscle, ASP induced effects opposite to those in WAT and increased lipolysis, indicating reduced NEFA trapping within muscle by ASP (P < 0.05 for all parameters). In conclusion, novel data in this study suggest that 1) there is little intrinsic difference between KO and WT tissue in the parameters examined and 2) ASP differentially regulates in situ LPL activity and NEFA trapping in WAT and skeletal muscle, which may promote optimal insulin sensitivity in vivo.

Myocyte Nitric Oxide Synthase 2 Contributes to Blunted β-Adrenergic Response in Failing Human Hearts by Decreasing Ca 2+ Transients

BACKGROUND

Human heart failure (HF) usually exhibits blunted response to beta-adrenergic receptor (AR) stimulation. Here, we examined whether expression of nitric oxide synthase-2 (NOS2, or inducible NOS) contributes to this loss of inotropic reserve in human HF.

METHODS AND RESULTS

Failing human hearts were obtained at transplantation. Contraction and [Ca2+]i measurements were performed in isolated cardiac myocytes and trabeculae. In HF myocytes and muscle, isoproterenol (ISO), a beta-AR agonist, led to small inotropic and lusitropic responses. Specific inhibition of NOS2 by aminoguanidine (AG) or L-NIL dramatically increased the ISO-induced inotropy and lusitropy, such that the ISO+AG response in HF approached that seen with ISO alone in nonfailing human myocytes or muscles. Ca2+ transient data directly paralleled these results, indicating that altered cellular Ca2+ handling is responsible. In nonfailing human hearts, NOS2 inhibition had no effects. In addition, NOS2 inhibition also had no effect in 30% of failing hearts, but in these myocytes and muscles, the ISO response alone was similar to that of nonfailing hearts. In line with these functional findings, NOS2 protein expression measured by Western blotting was induced in HF when AG/L-NIL had a functional effect but not when AG/L-NIL had no effect on contractility and Ca2+ transients.

CONCLUSIONS

NOS2 expression strongly limited ISO-induced increases in contraction, twitch Delta[Ca2+]i, and lusitropy in trabeculae and isolated myocytes from failing human hearts. Thus, the beta-AR hyporesponsiveness in human HF is mediated in large part by NO (or related congeners) produced within cardiac myocytes via NOS2.

Lack of complement factor C3, but not factor B, increases hyperlipidemia and atherosclerosis in apolipoprotein E-/- low-density lipoprotein receptor-/- mice

OBJECTIVE

To investigate the effect of complement deficiency on atherogenesis and lipidemia, we used mice deficient in the third complement component (C3-/-) or factor B (FB-/-).

METHODS AND RESULTS

Complement-deficient mice were crossed with mice deficient in both apolipoprotein E and the low-density lipoprotein receptor (Apoe-/- LDLR-/-). The percent lesion area in the aorta at 16 weeks, determined by en face analysis, was 84% higher in C3-/- mice than in controls (11.8%+/-0.4% versus 6.4%+/-0.8%, mean+/-SEM, P<0.00005). The C3-/- mice also had 58% higher serum triglyceride levels (P<0.05) and a more proatherogenic lipoprotein profile, with significantly more low-density lipoprotein cholesterol and very-low-density lipoprotein triglycerides than control mice. The C3-/- mice weighed 13% less (P<0.01) and had a lower body fat content (3.5%+/-1.0% versus 13.1%+/-3.0%, P<0.01). There were no differences between FB-/- mice and controls.

CONCLUSIONS

Complement activation by the classical or lectin pathway exerts atheroprotective effects, possibly through the regulation of lipid metabolism.

Update on adipocyte hormones: regulation of energy balance and carbohydrate/lipid metabolism

Hormones produced by adipose tissue play a critical role in the regulation of energy intake, energy expenditure, and lipid and carbohydrate metabolism. This review will address the biology, actions, and regulation of three adipocyte hormones-leptin, acylation stimulating protein (ASP), and adiponectin-with an emphasis on the most recent literature. The main biological role of leptin appears to be adaptation to reduced energy availability rather than prevention of obesity. In addition to the well-known consequences of absolute leptin deficiency, subjects with heterozygous leptin gene mutations have low circulating leptin levels and increased body adiposity. Leptin treatment dramatically improves metabolic abnormalities (insulin resistance and hyperlipidemia) in patients with relative leptin deficiency due to lipoatrophy. Leptin production is primarily regulated by insulin-induced changes of adipocyte metabolism. Dietary fat and fructose, which do not increase insulin secretion, lead to reduced leptin production, suggesting a mechanism for high-fat/high-sugar diets to increase energy intake and weight gain. ASP increases the efficiency of triacylglycerol synthesis in adipocytes leading to enhanced postprandial lipid clearance. In mice, ASP deficiency results in reduced body fat, obesity resistance, and improved insulin sensitivity. Adiponectin production is stimulated by thiazolidinedione agonists of peroxisome proliferator-activated receptor-gamma and may contribute to increased insulin sensitivity. Adiponectin and leptin cotreatment normalizes insulin action in lipoatrophic insulin-resistant animals. These effects may be mediated by AMP kinase-induced fat oxidation, leading to reduced intramyocellular and liver triglyceride content. The production of all three hormones is influenced by nutritional status. These hormones, the pathways controlling their production, and their receptors are promising targets for managing obesity, hyperlipidemia, and insulin resistance.

ASP enhances in situ lipoprotein lipase activity by increasing fatty acid trapping in adipocytes

Acylation-stimulating protein (ASP) increases triglyceride (TG) storage (fatty acid trapping) in adipose tissue and plays an important role in postprandial TG clearance. We examined the capacity of ASP and insulin to stimulate the activity of lipoprotein lipase (LPL) and the trapping of LPL-derived nonesterified fatty acid (NEFA) in 3T3-L1 adipocytes. Although insulin increased total LPL activity (secreted and cell-associated; P < 0.001) in 3T3-L1 adipocytes, ASP moderately stimulated secreted LPL activity (P = 0.04; 5% of total LPL activity). Neither hormone increased LPL translocation from adipocytes to endothelial cells in a coculture system. However, ASP and insulin increased the V(max) of in situ LPL activity ([(3)H]TG synthetic lipoprotein hydrolysis and [(3)H]NEFA incorporation into adipocytes) by 60% and 41%, respectively (P </= 0.01) without affecting K(m). Tetrahydrolipstatin (LPL inhibitor) diminished baseline, ASP-, and insulin-stimulated in situ LPL activity, resulting in [(3)H]TG accumulation (P < 0.0001). Unbound oleate inhibited in situ LPL activity (P < 0.0001) but did not eliminate the ASP stimulatory effect. Therefore, 1) the clearance of TG-rich lipoproteins is enhanced by ASP through increasing TG storage and relieving NEFA inhibition of LPL; and 2) the effectiveness of adipose tissue trapping of LPL-derived NEFAs determines overall LPL activity, which in turn determines the efficiency of postprandial TG clearance.

Fasting acylation-stimulating protein is predictive of postprandial triglyceride clearance

Postprandial plasma triglyceride (ppTG) and NEFA clearance were stratified by plasma acylation-stimulating protein (ASP) and gender to determine the contribution of fasting ASP in a normal population (70 men; 71 women). In the highest ASP tertile only, ASP decreased over 8 h (90 +/- 9.7 nM to 70 +/- 5.9 nM, P<0.05 males; 61.9 +/- 4.0 nM to 45.6 +/- 6.2 nM, P<0.01 females). Fasting ASP correlated positively with ppTG response. ppTG (P<0.0001, 2-way ANOVA, both genders) and NEFA levels progressively increased from lowest to highest ASP tertile, with the greatest differences in males. By stepwise multiple regression, the best prediction of ppTG was: (fasting ASP + apolipoprotein B + insulin + TG; r=0.806) for men and (fasting ASP + total cholesterol; r=0.574) for women. Leptin, body mass index, and other fasting variables did not improve the prediction. Thus, in men and women, ASP significantly predicted ppTG and NEFA clearance and, based on lower ASP, women may be more ASP sensitive than men. Plasma ASP may be useful as a fasting variable that will provide additional information regarding ppTG and NEFA clearance.

Chronic SR Ca2+-ATPase inhibition causes adaptive changes in cellular Ca2+ transport

Phospholamban, the critical regulator of the cardiac SERCA2a Ca2+ affinity, is phosphorylated at Ser16 and Thr17 during beta-adrenergic stimulation (eg, isoproterenol). To assess the impact of nonphosphorylatable phospholamban, a S16A, T17A double-mutant (DM) was introduced into phospholamban knockout mouse hearts. Transgenic lines expressing DM phospholamban at levels similar to wild types (WT) were identified. In vitro phosphorylation confirmed that DM phospholamban could not be phosphorylated, but produced the same shift in EC50 of SERCA2a for Ca2+ as unphosphorylated WT phospholamban. Rates of basal twitch [Ca2+]i decline were not different in DM versus WT cardiomyocytes. Isoproterenol increased the rates of twitch [Ca2+]i decline in WT, but not DM myocytes, confirming the prominent role of phospholamban phosphorylation in this response. Increased L-type Ca2+ current (ICa) density, with unaltered characteristics, was the major compensation in DM myocytes. Consequently, the normal beta-adrenergic-induced increase in ICa caused larger dynamic changes in absolute ICa density. Isoproterenol increased Ca2+ transients to a comparable amplitude in DM and WT. There were no changes in myofilament Ca2+ sensitivity, or the expression levels and Ca2+ removal activities of other Ca2+-handling proteins. Nor was there evidence of cardiac remodeling up to 10 months of age. Thus, chronic inhibition of SERCA2a by ablation of phospholamban phosphorylation (abolishing its adrenergic regulation) results in a unique cellular adaptation involving greater dynamic ICa modulation. This ICa modulation may partly compensate for the loss in SERCA2a responsiveness and thereby partially normalize beta-adrenergic inotropy in DM phospholamban mice.

Cellular basis of abnormal calcium transients of failing human ventricular myocytes

Depressed contractility is a central feature of the failing human heart and has been attributed to altered [Ca2+]i. This study examined the respective roles of the L-type Ca2+ current (ICa), SR Ca2+ uptake, storage and release, Ca2+ transport via the Na+-Ca2+ exchanger (NCX), and Ca2+ buffering in the altered Ca2+ transients of failing human ventricular myocytes. Electrophysiological techniques were used to measure and control V(m) and measure I(m), respectively, and Fluo-3 was used to measure [Ca2+]i in myocytes from nonfailing (NF) and failing (F) human hearts. Ca2+ transients from F myocytes were significantly smaller and decayed more slowly than those from NF hearts. Ca2+ uptake rates by the SR and the amount of Ca2+ stored in the SR were significantly reduced in F myocytes. There were no significant changes in the rate of Ca2+ removal from F myocytes by the NCX, in the density of NCX current as a function of [Ca2+]i, ICa density, or cellular Ca2+ buffering. However, Ca2+ influx during the late portions of the action potential seems able to elevate [Ca2+]i in F but not in NF myocytes. A reduction in the rate of net Ca2+ uptake by the SR slows the decay of the Ca2+ transient and reduces SR Ca2+ stores. This leads to reduced SR Ca2+ release, which induces additional Ca2+ influx during the plateau phase of the action potential, further slowing the decay of the Ca2+ transient. These changes can explain the defective Ca2+ transients of the failing human ventricular myocyte.

Targeting phospholamban by gene transfer in human heart failure

BACKGROUND

Myocardial cells from failing human hearts are characterized by abnormal calcium handling, a negative force-frequency relationship, and decreased sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) activity. In this study, we tested whether contractile function can be improved by decreasing the inhibitory effects of phospholamban on SERCA2a with adenoviral gene transfer of antisense phospholamban (asPL).

METHODS AND RESULTS

Myocardial cells isolated from 9 patients with end-stage heart failure and 18 donor nonfailing hearts were infected with adenoviruses encoding for either the antisense of phospholamban (Ad.asPL), the SERCA2a gene (Ad.SERCA2a), or the reporter genes beta-galactosidase and green fluorescent protein (Ad.betagal-GFP). Adenoviral gene transfer with Ad.asPL decreased phospholamban expression over 48 hours, increasing the velocity of both contraction and relaxation. Compared with cardiomyocytes infected with Ad.asPL (n=13), human myocytes infected with Ad.betagal-GFP (n=8) had enhanced contraction velocity (20.3 +/- 3.9% versus 8.7 +/- 2.6% shortening/second; P<0.01) and relaxation velocity (26.0 +/- 6.2% versus 8.6 +/- 4.3% shortening/second; P<0.01). The improvement in contraction and relaxation velocities was comparable to cardiomyocytes infected with Ad.SERCA2a. Failing human cardiomyocytes had decreased contraction and Ca2+ release with increasing frequency (0.1 to 2 Hz). Phospholamban ablation restored the frequency response in the failing cardiomyocytes to normal; increasing frequency resulted in enhanced sarcoplasmic reticulum Ca2+ release and contraction.

CONCLUSION

These results show that gene transfer of asPL can improve the contractile function in failing human myocardium. Targeting phospholamban may provide therapeutic benefits in human heart failure.

Improvement in survival and cardiac metabolism after gene transfer of sarcoplasmic reticulum Ca(2+)-ATPase in a rat model of heart failure

BACKGROUND

In heart failure, sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a) activity is decreased, resulting in abnormal calcium handling and contractile dysfunction. We have previously shown that increasing SERCA2a expression by gene transfer improves ventricular function in a rat model of heart failure created by ascending aortic constriction.

METHODS AND RESULTS

In this study, we tested the effects of gene transfer of SERCA2a on survival, left ventricular (LV) volumes, and metabolism. By 26 to 27 weeks after aortic banding, all animals developed heart failure (as documented by >25% decrease in fractional shortening) and were randomized to receive either an adenovirus carrying the SERCA2a gene (Ad.SERCA2a) or control virus (Ad.betagal-GFP) by use of a catheter-based technique. Sham-operated rats, uninfected or infected with either Ad.betagal-GFP or Ad.SERCA2a, served as controls. Four weeks after gene transfer, survival in rats with heart failure treated with Ad.betagal-GFP was 9%, compared with 63% in rats receiving Ad.SERCA2a. LV volumes were significantly increased in heart failure (0.64+/-0.05 versus 0.35+/-0.03 mL, P<0.02). Overexpression of SERCA2a normalized LV volumes (0.46+/-0.07 mL) in the failing hearts. (31)P NMR analysis showed a reduced ratio of phosphocreatine to ATP content in failing+Ad.betagal-GFP compared with sham+Ad.betagal-GFP (0.82+/-0.13 versus 1.38+/-0.14, P<0.01). Overexpression of SERCA2a in failing hearts improved the phosphocreatine/ATP ratio (1.23+/-0.28).

CONCLUSIONS

In this study, we show that unlike inotropic agents that improve contractile function at the expense of increased mortality and worsening metabolism, gene transfer of SERCA2a improves survival and the energy potential in failing hearts.

Regulation by retinoic acid of acylation-stimulating protein and complement C3 in human adipocytes

Acylation-stimulating protein (ASP), a product of complement C3, stimulates triacylglycerol synthesis in adipocytes. Previous studies have identified transthyretin, associated with chylomicrons, as a stimulator of C3 and ASP production. Since both transthyretin and chylomicrons transport retinyl ester/retinol, our goal was to investigate whether retinoic acid (RA) could be a potential hormonal mediator of the effect. Inhibitors of protein synthesis and protein secretion eliminated the stimulatory effects of chylomicrons on both C3 and ASP production in human differentiated adipocytes, suggesting that de novo protein synthesis and secretion are both required. Incubation with chylomicrons increased C3 mRNA levels (37+/-1.5%). RA alone or with chylomicrons had a stimulatory effect on C3 production (29-fold at 16.6 nM RA) and ASP production. An RA receptor antagonist blocked stimulation of C3 mRNA and C3 secretion by both RA and chylomicrons. Finally, RA and chylomicrons activated a 1.8 kb C3-promoter-luciferase construct transfected into 3T3-F442 and 3T3-L1 cells (by 41+/-0.2% and 69+/-0.3% respectively), possibly via RA receptor half-sites identified by sequence analysis. This is the first evidence documenting stimulation by RA of the C3 gene. Thus we propose RA as a novel cellular trigger in chylomicrons that subsequently results in increased ASP production by adipocytes after a meal.

Acylation stimulating protein (ASP) acute effects on postprandial lipemia and food intake in rodents

BACKGROUND

In vitro studies have shown that acylation stimulating protein (ASP) stimulates triglyceride (TG) synthesis and storage in adipocytes. We have previously demonstrated that intraperitoneal (i.p.) injection of ASP in C57BL/6J mice accelerated TG clearance following an orally-administered fat load as well as reducing postprandial glucose levels.

RESULTS

In the present study, we first examined the effect of i.p. and intracerebroventricular (i.c.v.) injection of ASP on food intake in Sprague-Dawley rats. Intraperitoneal injection resulted in a short-term increase in food intake (maximum increase 29.3% within the first hour, P<0.025) decreasing thereafter as compared to vehicle alone. i.c.v. Administration of a comparable dose of ASP resulted in a similar but delayed increase in food intake with a maximum at 2-4 h, suggesting that the actions of ASP are peripherally mediated. However, there was no significant difference in 24 h food intake with either i.p. or i.c.v. injection. We also examined the effects of ASP on TG clearance in two obese mouse strains with different metabolic profiles: ob/ob (C57BL/6J-Lep(ob)) and db/db (C57BLKS/J-Lepr(db)). In a crossover design, the response to an oral fat load was determined with and without i.p. injection of exogenous ASP. In ob/ob mice, there was a 44% greater clearance of postprandial TG (area under the curve (AUC)=245+/-49 control vs 138+/-43 mg/dl h with ASP; P<0.05 by RM ANOVA). The db/db mice showed a greater response, with a 62% decrease in postprandial TG (AUC=4080+/-1489 control vs 1540+/-719 mg/dl h with ASP; P=0.004 by RM ANOVA). In addition there were decreases in postprandial glucose and non-esterified fatty acid (NEFA) levels in response to ASP.

CONCLUSION

These results are the first to report that ASP can increase food intake in rats and also enhance postprandial TG clearance in obese animals. These data therefore support previous in vitro evidence pointing to ASP as a regulator of lipid metabolism.

Mechanisms of nutritional and hormonal regulation of lipogenesis

Fat build-up is determined by the balance between lipogenesis and lipolysis/fatty acid oxidation. In the past few years, our understanding of the nutritional, hormonal and particularly transcriptional regulation of lipogenesis has expanded greatly. Lipogenesis is stimulated by a high carbohydrate diet, whereas it is inhibited by polyunsaturated fatty acids and by fasting. These effects are partly mediated by hormones, which inhibit (growth hormone, leptin) or stimulate (insulin) lipogenesis. Recent research has established that sterol regulatory element binding protein-1 is a critical intermediate in the pro- or anti-lipogenic action of several hormones and nutrients. Another transcription factor implicated in lipogenesis is the peroxisome proliferator activated receptor gamma. Both transcription factors are attractive targets for pharmaceutical intervention of disorders such as hypertriglyceridemia and obesity.

Contractile reserve and intracellular calcium regulation in mouse myocytes from normal and hypertrophied failing hearts

Mouse myocyte contractility and the changes induced by pressure overload are not fully understood. We studied contractile reserve in isolated left ventricular myocytes from mice with ascending aortic stenosis (AS) during compensatory hypertrophy (4-week AS) and the later stage of early failure (7-week AS) and from control mice. Myocyte contraction and [Ca(2+)](i) transients with fluo-3 were measured simultaneously. At baseline (0.5 Hz, 1.5 mmol/L [Ca(2+)](o), 25 degrees C), the amplitude of myocyte shortening and peak-systolic [Ca(2+)](i) in 7-week AS were not different from those of controls, whereas contraction, relaxation, and the decline of [Ca(2+)](i) transients were slower. In response to the challenge of high [Ca(2+)](o), fractional cell shortening was severely depressed with reduced peak-systolic [Ca(2+)](i) in 7-week AS compared with controls. In response to rapid pacing stimulation, cell shortening and peak-systolic [Ca(2+)](i) increased in controls, but this response was depressed in 7-week AS. In contrast, the responses to both challenge with high [Ca(2+)](o) and rapid pacing in 4-week AS were similar to those of controls. Although protein levels of Na(+)-Ca(2+) exchanger were increased in both 4-week and 7-week AS, the ratio of SR Ca(2+)-ATPase to phospholamban protein levels was depressed in 7-week AS compared with controls but not in 4-week AS. This was associated with an impaired capacity to increase sarcoplasmic reticulum Ca(2+) load during high work states in 7-week AS myocytes. In hypertrophied failing mouse myocytes, depressed contractile reserve is related to an impaired augmentation of systolic [Ca(2+)](i) and SR Ca(2+) load and simulates findings in human failing myocytes.

Of mice and men (and women) and the acylation-stimulating protein pathway

The storage and release of energy by adipocytes is of fundamental biologic importance. Not surprisingly, therefore, the rate at which these processes occur can be modulated by a variety of physiologic molecules. A newly recognized participant is produced by adipocytes themselves: acylation-stimulating protein (ASP). This article focuses on the most recent in-vivo evidence regarding how the ASP pathway may influence energy storage and release. In brief, the rate at which triglycerides are cleared from plasma (i.e. the rate at which they are hydrolysed) is determined by lipoprotein lipase and insulin, which is the principal hormone that regulates lipoprotein lipase. By contrast, the ASP pathway modulates the rate at which fatty acids are taken up and converted to triglycerides by adipocytes. Under certain circumstances, however, reduction of activity of the ASP pathway may negatively impact on the first step of the process. ASP also influences the rate at which fatty acids are released by adipocytes, and it is clear that insulin and ASP interact in a variety of ways that involve energy storage and release. Accordingly, to understand the impact of any intervention on energy storage and release by adipocytes, the effects of both insulin and ASP must be taken into account.

Sarcoplasmic reticulum Ca(2+)/Calmodulin-dependent protein kinase is altered in heart failure

Although Ca(2+)/calmodulin-dependent protein kinase-II (CaMK) is known to phosphorylate different Ca(2+) cycling proteins in the cardiac sarcoplasmic reticulum (SR) and regulate its function, the status of CaMK in heart failure has not been investigated previously. In this study, we examined the hypothesis that changes in the CaMK-mediated phosphorylation of the SR Ca(2+) cycling proteins are associated with heart failure. For this purpose, heart failure in rats was induced by occluding the coronary artery for 8 weeks, and animals with >30% infarct of the left ventricle wall plus septum mass were used. Noninfarcted left ventricle was used for biochemical assessment; sham-operated animals served as control. A significant depression in SR Ca(2+) uptake and release activities was associated with a decrease in SR CaMK phosphorylation of the SR proteins, ryanodine receptor (RyR), Ca(2+) pump ATPase (SR/endoplasmic reticulum Ca(2+) ATPase [SERCA2a]), and phospholamban (PLB) in the failing heart. The SR protein contents for RyR, SERCA2a, and PLB were decreased in the failing hearts. Although the SR Ca(2+)/calmodulin-dependent CaMK activity, CaMK content, and CaMK autophosphorylation were depressed, the SR phosphatase activity was enhanced in the failing heart. On the other hand, the cAMP-dependent protein kinase-mediated phosphorylation of RyR and PLB was not affected in the failing heart. On the basis of these results, we conclude that alterations in SR CaMK-mediated phosphorylation may be partly responsible for impaired SR function in heart failure.