Loss of mTORC2 Activity in Neutrophils Impairs Fusion of Granules and Affects Cellular Metabolism Favoring Increased Bacterial Burden in Sepsis

Sepsis is a complex infectious syndrome in which neutrophil participation is crucial for patient survival. Neutrophils quickly sense and eliminate the pathogen by using different effector mechanisms controlled by metabolic processes. The mammalian target of rapamycin (mTOR) pathway is an important route for metabolic regulation, and its role in neutrophil metabolism has not been fully understood yet, especially the importance of mTOR complex 2 (mTORC2) in the neutrophil effector functions. In this study, we observed that the loss of Rictor (mTORC2 scaffold protein) in primary mouse-derived neutrophils affects their chemotaxis by fMLF and their microbial killing capacity, but not the phagocytic capacity. We found that the microbicidal capacity was impaired in Rictor-deleted neutrophils because of an improper fusion of granules, reducing the hypochlorous acid production. The loss of Rictor also led to metabolic alterations in isolated neutrophils, increasing aerobic glycolysis. Finally, myeloid-Rictor-deleted mice (LysMRic Δ/Δ) also showed an impairment of the microbicidal capacity, increasing the bacterial burden in the Escherichia coli sepsis model. Overall, our results highlight the importance of proper mTORC2 activation for neutrophil effector functions and metabolism during sepsis.

Sex-Dependent Effects of Eicosapentaenoic Acid and UCP1 Deficiency on Hepatic Steatosis in Diet-Induced Obese Mice

Objectives

Nonalcoholic fatty liver disease (NAFLD), characterized by hepatic triglyceride (TG) accumulation, is associated with expansion of white adipose tissue (WAT). By contrast, brown adipose tissue (BAT) may prevent obesity and NAFLD through activity of mitochondrial uncoupling protein 1 (UCP1), which is involved in energy dissipation. Previous studies in our lab have shown that eicosapentaenoic acid (EPA) ameliorates obesity and hepatic steatosis in high-fat (HF) fed male, B6 mice at thermoneutral conditions, independent of UCP1. However, it is unknown whether similar effects of EPA and UCP1 deficiency will be observed at ambient temperature, and whether they differ by sex. Thus, the goal of this project was to investigate sex-dependent mechanisms of EPA in the livers of diet-induced obese, wild type (WT) and UCP1 knockout (KO) mice housed at ambient temperature.

Methods

WT and UCP1 KO B6 male and female mice were fed a HF diet (45% kcal fat; WT-HF, KO-HF) or HF diet supplemented with 36g/kg EPA (WT-EPA, KO-EPA) for 14 weeks. Body weight (BW), liver histology, and specific metabolic gene expression profiles were assessed.

Results

Although BW significantly varied by sex, diet, and genotype, UCP1 inactivation did not significantly increase BW compared to WT in either sex. Hepatic TG accumulation varied significantly by genotype with no significant differences seen with EPA supplementation in either sex. However, markers of lipogenesis were sex-dependently impacted by genotype and diet: there were no significant differences in markers of lipogenesis (Fasn and Acaca) with UCP1 KO or EPA supplementation in males; while these markers were reduced in female KO mice compared to female WT with no response to EPA. By contrast, lipogenic markers were reduced with EPA in female WT mice.

Conclusions

Our findings reveal an association between NAFLD and UCP1 deficiency, indicating the importance of this mitochondrial protein in limiting hepatic lipid accumulation, particularly in females. These findings also suggest a genotypic difference in response to dietary EPA supplementation on the livers of male and female mice, with beneficial effects reported in the female WT group.

Funding Sources

Funded by NIH/NCCIH grant #R15AT008879-01A1.

Thermoneutrality Reduces the Beneficial Metabolic Effects of Eicosapentaenoic Acid on White Adipose Tissue in Diet-Induced Obese Mice

Objectives

At ambient temperature (23°C), eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid reduces visceral adipose tissue (VAT) inflammation, adipocyte size and improves overall metabolic profile in diet-induced obese (DIO) mice, potentially through upregulation of uncoupling protein 1 (UCP-1). The goal of this study is to determine whether effects of EPA are maintained at thermoneutrality, and/or mediated by UCP-1, and if so through which cellular mechanisms.

Methods

Wild type (WT) and UCP-1 knockout (KO) B6 male mice were housed at thermoneutral temperature (28–30°C) and fed high fat (HF, 45% kcal fat) supplemented with or without EPA (36 g/kg diet). Serum, VAT (epididymal fat) and cecal microbiome specimens were analyzed.

Results

EPA reduced adiposity and improved glucose tolerance in EPA-fed KO mice (P < 0.05), but not in EPA-fed WT mice. EPA supplementation lowered VAT mass in both genotypes (P < 0.05); however, there were no diet or genotype-related differences in adipocyte size or serum triglyceride levels. Both genotypes fed EPA had lower serum resistin levels compared to respective HF (P < 0.01). EPA showed trends towards increased serum adiponectin levels compared to HF fed mice in both genotypes, with KO-EPA group having the highest concentration. There was no significant difference in the expression of IL-6 in VAT among the groups, while MCP-1 mRNA was expressed more in KO groups compared to WT groups (P < 0.01). Diet had no effect on expression of anti-inflammatory markers in both WT and KO mice. There were no genotype or diet effects on expression of genes involved in lipid metabolism and mitochondrial energy metabolism. Cecal microbiome showed no differences in the species diversity (Shannon index) between genotypes or diet types. However, only in the KO group, the Bacteroidetes/Firmicutes ratio was increased by EPA.

Conclusions

Compared to previous work at ambient temperatures, VAT does not mediate protective effects of EPA in DIO mice at thermoneutral temperature. Moreover, EPA effects are independent of UCP-1 as it produced beneficial effects on glucose tolerance and adiposity in KO mice, which may be in part mediated by changes in microbiome. Further mechanistic studies are ongoing to understand the mechanisms mediating EPA and UCP-1 effects in VAT.

Funding Sources

Funded by NIH (NCCIH and NIA).

Lipoatrophy-Associated Insulin Resistance and Hepatic Steatosis are Attenuated by Intake of Diet Rich in Omega 3 Fatty Acids

SCOPE

Glucose homeostasis and progression of nonalcoholic fatty liver disease (NAFLD) and hepatomegaly in severe lipoatrophic mice and their modulation by intake of a diet rich in omega 3 (n-3) fatty acids (HFO) are evaluated.

METHODS AND RESULTS

Severe lipoatrophic mice induced by PPAR-γ deletion exclusively in adipocytes (A-PPARγ KO) and littermate controls (A-PPARγ WT) are evaluated for glucose homeostasis and liver mass, proteomics, lipidomics, inflammation, and fibrosis. Lipoatrophic mice are heavier than controls, severely glucose intolerant, and hyperinsulinemic, and develop NAFLD characterized by increased liver glycogen, triacylglycerol, and diacylglycerol contents, mitotic index, apoptosis, inflammation, steatosis score, fibrosis, and fatty acid synthase (FAS) content and activity. Lipoatrophic mice also display liver enrichment with monounsaturated in detriment of polyunsaturated fatty acids including n-3 fatty acids, and increased content of cardiolipin, a tetracyl phospholipid exclusively found at the mitochondria inner membrane. Administration of a high-fat diet rich in n-3 fatty acids (HFO) to lipoatrophic mice enriches liver with n-3 fatty acids, reduces hepatic steatosis, FAS content and activity, apoptosis, inflammation, and improves glucose homeostasis.

CONCLUSION

Diet enrichment with n-3 fatty acids improves glucose homeostasis and reduces liver steatosis and inflammation without affecting hepatomegaly in severe lipoatrophic mice.

Sympathetic Regulation of Slc2a4 Gene Expression: Participation of a Putative cAMP Responsive Element (CRE) Site in the Slc2a4 Promoter

BACKGROUND/AIMS

Studies have indicated that sympathetic activity enhances GLUT4 expression (Slc2a4 gene) by activating beta-adrenergic receptors. This could be mediated by a direct enhancer effect of cyclic AMP-responsive element binding protein (CREB) and family members upon Slc2a4 gene. However, a cAMP responsive element (CRE) in Slc2a4 promoter has never been demonstrated.

METHODS

Slc2a4 CRE-site was searched by in silico analysis. In skeletal muscles from rats displaying high sympathetic activity (SHR), Slc2a4 CRE-site was investigated by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay; and Slc2a4 expression was analyzed by RT-qPCR. Functional activity of the CRE-site was investigated by luciferase assay, 2 hours after 8-br-cAMP stimulation, in 3T3L1 adipocytes transientely transfected with native and mutated CRE-sites.

RESULTS

In silico analysis indicated the -480/-473 segment as a putative CRE-site, with 62.5% of identity to CRE consensus sequence, and highly preserved in mouse, rat and human. CREB/CREM binding in this CRE-site was confirmed to occur in vitro (EMSA) and in vivo (ChIP assay). Enhancer activity of this segment in Slc2a4 transcription was confirmed in 3T3-L1 cells. Finally, in extensor digitorum longus muscle from SHR, 80% increase in Slc2a4 mRNA expression was observed to be accompanied by increased CREB/CREM binding into the CRE-site both in vitro and in vivo.

CONCLUSION

This study demonstrates the presence of a functional CRE-site at -480/-473 sequence of the Slc2a4 gene. This CRE-site has an enhancing activity on Slc2a4 expression and participates in the Slc2a4 increased expression observed in glycolytic muscles of rats displaying high sympathetic activity.

Abstract P1-08-08: Reduction of HER2-associated lipogenic phenotype by docosahexaenoic acid (DHA) induces apoptosis in breast tumor cells harboring HER2 overexpression

The lipogenic phenotype is associated with oncogenic transformation and malignancy in the cancer setting. Our hypothesis is that the oncogenic nature of lipogenesis depends on the expression of HER2 oncogene, and its modulation by docosahexaenoic acid-DHA, might induce apoptosis in breast tumor cells with HER2 overexpression. To evaluate if the lipogenic phenotype might be induced by HER2 overexpression, we used a oncogenic transformation cell model in which, cells were engineered to overexpress HER-2 receptor (HB4aC5.2), but are identical to their parental strain (HB4a) in all other aspects, permitting an specific analysis of enhanced HER-2 effects. Toward this end the lipogenesis profiling was characterized, evaluating several molecular features, including synthesis (FASN), uptake(CD36), transport(FABP4) and storage(DGAT) of FA by RT-PCR and lipogenic regulatory pathways (mTOR, DEPTOR, SREBP1 and PPARγ) in both cells. Lipogenic contribution to lipid rafts formation, which is necessary to HER2 receptor location and activation in the cell membrane, was evaluated by gas chromatography and confocal microscopy. The influence of HER2 overexpression and lipogenic phenotype on proteins activated by HER-2 (AKT, ERK1/2 and FASN) was analyzed by western blot. Next, HB4a and HB4aC5.2 cells were treated, alone or in combination, with DHA, Trastuzumab (anti-HER2), and GW9662 (PPARγ inhibitor) for 72h, and the above experiments were repeated. Cell death was analyzed by flow cytometry and confocal microscopy. Results: In HB4aC5.2 cells, the oncogenic transformation by HER2 overexpression was associated with a lipogenic phenotype, which contributed to increase of lipid rafts formation, activation of survival and proliferation signals, as compared to HB4a normal cells (p<0.001). It is believed that PPARγ is the main regulator of cell lipogenesis. However, our data have shown that mTOR/SREBP pathway, exclusively mTORC1, was decreased concomitantly to increase of DEPTOR gene expression and AKT activation, in HB4aC5.2 cells. Also, the treatment with GW9662 did not change the expression of lipogenic genes, suggesting that lipogenesis seems independent of PPARγ activation, and that HER-2 overexpressing cells may use alternative mechanisms to maintain the lipogenic phenotype. DEPTOR is overexpressed in white adipose tissue and is associated with regulation of lipogenesis. Moreover, DEPTOR overexpression suppresses S6K1 but, by relieving feedback inhibition from mTORC1 to PI3K signaling, activates Akt. In HB4aC5.2 cells, only the DHA treatment decreased the lipogenic phenotype, DEPTOR expression, disrupted lipid raft, inhibited HER-2 signaling, and induced apoptosis (p<0.001). In addition the combined treatment using DHA and Trastuzumab increased cell death. Conclusion: We show that lipogenic phenotype was associated with HER-2 in breast cancer, can be induced early in the oncogenic transformation, and it seems important to promote survival and proliferation. Otherwise, Its modulation by DHA increased death in tumor cells, suggesting this kind of FA may represent a useful tool for controlling the HER2-positive breast cancer.

Citation Format: Graziela R Ravacci, Maria M Brentani, William Festuccia, Tharcisio Tortelli, Angela F Waitzberg, Dan L Waitzberg. Reduction of HER2-associated lipogenic phenotype by docosahexaenoic acid (DHA) induces apoptosis in breast tumor cells harboring HER2 overexpression [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-08-08.

Depot-specific modulation of rat intraabdominal adipose tissue lipid metabolism by pharmacological inhibition of 11beta-hydroxysteroid dehydrogenase type 1

The metabolic consequences of visceral obesity have been associated with amplification of glucocorticoid action by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in adipose tissue. This study aimed to assess in a rat model of diet-induced obesity the effects of pharmacological 11beta-HSD1 inhibition on the morphology and expression of key genes of lipid metabolism in intraabdominal adipose depots. Rats fed a high-sucrose, high-fat diet were treated or not with a specific 11beta-HSD1 inhibitor (compound A, 3 mg/kg.d) for 3 wk. Compound A did not alter food intake or body weight gain but specifically reduced mesenteric adipose weight (-18%) and adipocyte size, without significantly affecting those of epididymal or retroperitoneal depots. In mesenteric fat, the inhibitor decreased (to 25-50% of control) mRNA levels of genes involved in lipid synthesis (FAS, SCD1, DGAT1) and fatty acid cycling (lipolysis/reesterification, ATGL and PEPCK) and increased (30%) the activity of the fatty acid oxidation-promoting enzyme carnitine palmitoyltransferase 1. In striking contrast, in the epididymal depot, 11beta-HSD1 inhibition increased (1.5-5-fold) mRNA levels of those genes related to lipid synthesis/cycling and slightly decreased carnitine palmitoyltransferase 1 activity, whereas gene expression remained unaffected in the retroperitoneal depot. Compound A robustly reduced liver triacylglycerol content and plasma lipids. The study demonstrates that pharmacological inhibition of 11beta-HSD1, at a dose that does not alter food intake, reduces fat accretion specifically in the mesenterical adipose depot, exerts divergent intraabdominal depot-specific effects on genes of lipid metabolism, and reduces steatosis and lipemia.