Genome-scale target identification in Escherichia coli for high-titer production of free fatty acids

To construct a superior microbial cell factory for chemical synthesis, a major challenge is to fully exploit cellular potential by identifying and engineering beneficial gene targets in sophisticated metabolic networks. Here, we take advantage of CRISPR interference (CRISPRi) and omics analyses to systematically identify beneficial genes that can be engineered to promote free fatty acids (FFAs) production in Escherichia coli. CRISPRi-mediated genetic perturbation enables the identification of 30 beneficial genes from 108 targets related to FFA metabolism. Then, omics analyses of the FFAs-overproducing strains and a control strain enable the identification of another 26 beneficial genes that are seemingly irrelevant to FFA metabolism. Combinatorial perturbation of four beneficial genes involving cellular stress responses results in a recombinant strain ihfAL−-aidB+-ryfAM−-gadAH−, producing 30.0 g L−1 FFAs in fed-batch fermentation, the maximum titer in E. coli reported to date. Our findings are of help in rewiring cellular metabolism and interwoven intracellular processes to facilitate high-titer production of biochemicals.

Insulin Action, Glucose Homeostasis and Free Fatty Acid Metabolism: Insights From a Novel Model

Glucose and free fatty acids (FFA) are essential nutrients that are both partly regulated by insulin. Impaired insulin secretion and insulin resistance are hallmarks of aberrant glucose disposal, and type 2 diabetes (T2DM). In the current study, a novel model of FFA kinetics is proposed to estimate the role insulin action on FFA lipolysis and oxidation allowing estimation of adipose tissue insulin sensitivity (SIFFA). Twenty-five normal volunteers were recruited for the current study. To participate, volunteers had to be less than 40 years of age and have a body mass index (BMI) < 30 kg/m2, and be free of medical comorbidity. The proposed model of FFA kinetics was used to analyze the data derived from the insulin-modified FSIGT. Mean fractional standard deviations of the parameter estimates were all less than 20%. Standardized residuals of the fit of the model to the FFA temporal data were randomly distributed, with only one estimated point lying outside the 2-standard deviation range, suggesting an acceptable fit of the model to the FFA data. The current study describes a novel one-compartment non-linear model of FFA kinetics during an FSIGT that provides an FFA metabolism insulin sensitivity parameter (SIFFA). Furthermore, the models suggest a new role of glucose as the modulator of FFA disposal. Estimates of SIFFA confirmed previous findings that FFA metabolism is more sensitive to changes in insulin than glucose metabolism. Novel derived indices of insulin sensitivity of FFA (SIFFA) were correlated with minimal model indices. These associations suggest a cooperative rather than competitive interplay between the two primary nutrients (glucose and FFA) and allude to the FFA acting as the buffer, such that glucose homeostasis is maintained.

Mangiferin Improved Palmitate-Induced-Insulin Resistance by Promoting Free Fatty Acid Metabolism in HepG2 and C2C12 Cells via PPARα: Mangiferin Improved Insulin Resistance

Elevated free fatty acid (FFA) is a key risk factor for insulin resistance (IR). Our previous studies found that mangiferin could decrease serum FFA levels in obese rats induced by a high-fat diet. Our research was to determine the effects and mechanism of mangiferin on improving IR by regulating FFA metabolism in HepG2 and C2C12 cells. The model was used to quantify PA-induced lipid accumulation in the two cell lines treated with various concentrations of mangiferin simultaneously for 24 h. We found that mangiferin significantly increased insulin-stimulated glucose uptake, via phosphorylation of protein kinase B (P-AKT), glucose transporter 2 (GLUT2), and glucose transporter 4 (GLUT4) protein expressions, and markedly decreased glucose content, respectively, in HepG2 and C2C12 cells induced by PA. Mangiferin significantly increased FFA uptake and decreased intracellular FFA and triglyceride (TG) accumulations. The activity of the peroxisome proliferator-activated receptor α (PPARα) protein and its downstream proteins involved in fatty acid translocase (CD36) and carnitine palmitoyltransferase 1 (CPT1) and the fatty acid β-oxidation rate corresponding to FFA metabolism were also markedly increased by mangiferin in HepG2 and C2C12 cells. Furthermore, the effects were reversed by siRNA-mediated knockdown of PPARα. Mangiferin ameliorated IR by increasing the consumption of glucose and promoting the FFA oxidation via the PPARα pathway in HepG2 and C2C12 cells.

Alterations in branched-chain amino acid kinetics in nonobese but insulin-resistant Asian men

ABSTRACT Background Branched-chain amino acids (BCAAs) are elevated in the insulin-resistant (IR) state. The reasons for this increase remain unclear, but it may be related to abnormalities in BCAA metabolism and free fatty acid (FFA) metabolism. Objective In this study, we quantified BCAA and FFA kinetics of IR and insulin-sensitive (IS) nonobese Asian men with the use of stable-isotope tracers. We hypothesized that in addition to greater substrate flux, the BCAA oxidative pathway is also impaired to account for the higher plasma BCAA concentration in the IR state. Design We recruited 12 IR and 14 IS nonobese and healthy Asian men. Oral-glucose-tolerance tests (OGTTs) were performed to quantify insulin sensitivity, and subjects underwent 2 stable-isotope infusion studies. [U-13C6]Leucine was infused to measure leucine flux and oxidation as indexes of BCAA metabolism, whereas [U-13C16]palmitate was infused to measure palmitate flux and oxidation to represent FFA metabolism, The 2H2O dilution method was used to estimate body composition. Results IR subjects had greater adiposity and significantly higher fasting and post-OGTT glucose and insulin concentrations compared with the IS group. However, none of the subjects were diabetic. Despite similar dietary protein intake, IR subjects had a significantly higher plasma BCAA concentration and greater leucine flux. Leucine oxidation was also greater in the IR group, but the relation between leucine oxidation and flux was significantly weaker in the IR group than in the IS group (r = 0.530 compared with 0.695, P < 0.0388 for differences between slope). FFA oxidation was, however, unaffected despite higher FFA flux in the IR group. Conclusion The higher plasma BCAA concentration in healthy nonobese individuals with IR is associated with a weaker relation between BCAA oxidation and BCAA flux and this occurs in the presence of accelerated FFA flux and oxidation.

Ibrutinib Disrupts the Metabolic Program of CLL Cells in-Vivo

Introduction: Unlike their normal resting B cell counterparts, chronic lymphocytic leukemia (CLL) cells proliferate. Approximately 1% of the total CLL cell clone expands daily. To adjust for the increase in energetic demands imposed by continuous proliferation, CLL cells undergo metabolic reprogramming and, as recently shown (Rozovski U, et al. Mol Cancer Res. 2015; 13:944-53), CLL cells utilize fat in a manner similar to that of adipocytes. The recent introduction of the oral Bruton tyrosine kinase inhibitor (BTK) ibrutinib revolutionized the treatment of CLL. Because the proliferation of CLL cells is driven by lipid metabolism and ibrutinib inhibits the B cell receptor-induced proliferation of CLL cells, we sought to determine whether ibrutinib also disrupts the metabolic program that provides CLL cells with their unique energy requirements. Methods: We prospectively studied serial peripheral blood samples from 16 patients with CLL. The patients' peripheral blood CLL cells were analyzed prior to and during treatment with ibrutinib. All patients received a daily dose of 420 mg ibrutinib. In addition, we performed in vitro studies using CLL cells from 3 ibrutinib-naïve patients. CLL cells were analyzed for free-fatty acids (FFA) consumption and for the rate of cellular apoptosis using propiduim iodide (PI) and annexin V staining analyzed by flow cytometry. Results: To study lipid metabolism of CLL cells we incubated peripheral blood CLL cells from 3 randomly selected ibrutinib-naïve patients in the presence or absence of FFA and measured the concentration of culture media-dissolved O2 (dO2). Like in our previous study (Rozovski U, et al. Mol Cancer Res. 2015; 13:944-53), we found that CLL cells metabolized FFA and, as a result, the levels of dO2 decreased. However when the cells were co-cultured with FFA and ibrutinib, the delta dO2 (dO2 with FFA minus dO2 without FFA) remained unchanged, suggesting that ibrutinib blocked FFA metabolism in CLL cells.Then, to determine whether ibrutinib also inhibited CLL-cell lipid metabolism in patients treated with ibrutinib, we collected 2 to 5 consecutive PB samples (median: 5) from 16 CLL patients prior to and during treatment with ibrutinib. Unlike the 12% reduction in delta dO2 detected in untreated patients' CLL cells incubated with FFA in vitro, a 6% reduction in delta dO2 was detected in CLL cells of patients treated with ibrutinib 4 days into treatment and after a median of 147 days of ibrutinib treatment a change in delta dO2 was no longer detected. These data suggest that ibrutinib-treated cells lost their capacity to utilize FFA or that the number of FFA consuming circulating CLL cells declined until they were no longer detected. In addition, whereas ibrutinib induced apoptosis of CLL cells in a dose-dependent manner in vitro, ibrutinib did not induce apoptosis at the same time points in vivo, suggesting that interruption of FFA metabolism does not lead to apoptotic cell death and that the metabolic and proapoptotic pathways are not linearly intertwined in CLL cells. In conclusion: Treatment with ibrutinib changes the metabolic profile CLL cells. Even after short exposure to the drug the cells were less capable of utilizing FFA, and after longer exposure, the cells could no longer utilize FFA. Whether ibrutinib induced reduction in FFA metabolism decreases the proliferation capacity of CLL cells remains to be determined. Disclosures Burger: Pharmacyclics: Research Funding. O'Brien:Janssen: Consultancy, Honoraria; Pharmacyclics, LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding. Jain:Pfizer: Consultancy, Honoraria, Research Funding; Celgene: Research Funding; Abbvie: Research Funding; Novimmune: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Incyte: Research Funding; ADC Therapeutics: Consultancy, Honoraria, Research Funding; Seattle Genetics: Research Funding; Genentech: Research Funding; BMS: Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Infinity: Research Funding; Novartis: Consultancy, Honoraria. Wierda:Novartis: Research Funding; Abbvie: Research Funding; Acerta: Research Funding; Gilead: Research Funding; Genentech: Research Funding.

Myocardial FFA metabolism during rest and atrial pacing in humans

There is limited in vivo data in humans evaluating myocardial fat utilization during increased heart work. This study was done to determine myocardial free fatty acid (FFA) metabolism during rest and atrial pacing, which increases cardiac work without changing arterial substrate concentration. We studied seven healthy men and women (age = 49.7 ± 3.9 yr, BMI = 23.4 ± 1.1 kg/m2, V̇o2max = 35.5 ± 3.0 ml·kg−1·min−1, ejection fraction = 68 ± 3%). After 3 days of dietary control, coronary sinus, femoral arterial and venous, and peripheral venous catheters were placed. Subjects received [13C]bicarbonate followed by a continuous infusion of [1-13C]palmitate through the end of the study. Arterial and coronary sinus blood sampling and measurements of resting coronary sinus blood flow were made during rest and atrial pacing to 120 beats/min. MV̇o2 increased ( P < 0.05) from rest to atrial pacing. Coronary sinus FFA concentration was significantly lower than arterial through rest and atrial pacing ( P = 0.007). Isotopically measured myocardial palmitate uptake increased significantly from rest to atrial pacing ( P = 0.03). Approximately one-third of palmitate delivery was extracted by the myocardium during rest and atrial pacing. Myocardial V13CO2 production and palmitate oxidation increased significantly from rest ( P < 0.01) to atrial pacing. Net glycerol balance was significantly greater than zero during rest ( P = 0.04) but not different from zero during atrial pacing ( P = 0.13). These data suggest that myocardial lipid uptake and oxidation increase with greater heart work during atrial pacing, with a similar relative proportion of fat oxidation to total myocardial energy expenditure.

Abstract 5385: Transport of Free Fatty Acids in Cardiac Myocytes is Mediated by a Plasma Membrane Pump as Revealed by Monitoring Cytoplasmic Unbound Free Fatty Acids

The transport of FFA across the plasma membrane represents one of the earliest points at which FFA metabolism can be controlled by cardiac myocytes. Using novel methods to measure the intracellular unbound concentration of FFA ([FFA i ]), the first direct measurements of FFA transport across cardiac plasma membranes have been performed in freshly isolated cardiac myoctyes. Measurements of the unbound concentrations of FFA (FFA u ) in the aqueous phase were performed using the fluorescent ratio probe ADIFAB. Cardiac myocytes were microinjected with ADIFAB, and the transport of oleate and palmitate was determined by monitoring [FFA i ] using fluorescence ratio microscopy. FFA influx was initiated by rapidly increasing the extracellular concentration of FFA u ([FFA o ]) using FFA-BSA complexes, which clamped [FFA o ] at fixed values. The time course of influx was monitored from the change in [FFA i ], which rose exponentially to a steady state level (k influx ~ 0.01 s −1 ). Once steady state was achieved, efflux was initiated by changing the extracellular media back to zero [FFA o ]. Efflux was monitored by the decrease in [FFA i ] which, like influx, revealed exponential behavior (k efflux ~ 0.02 s −1 ). At steady state [FFA i ] was greater than [FFA o ] by a factor of ~3.5, indicating that during influx FFA are pumped up a concentration gradient. Both the initial rate of transport and the gradient ([FFA i ] > [FFA o ]) revealed saturation with increasing [FFA o ]. The initial rate of influx saturated at [FFA o ] > 200 nM, while the [FFA i ] > [FFA o ] gradient was relatively constant (~ 3.5) but began to decrease and approached 1 at [FFA o ] > 200 nM. The efflux rate constant decreased for [FFA o ] > zero, suggesting that efflux may be regulated by a mechanism that senses the level of circulating FFA u . Our results indicate that the mechanism of FFA transport across cardiac myocytes is regulated by the plasma membrane and allows for the efficient storage and release of FFA from cardiac myocytes. We suggest that this mechanism involves an as yet unknown membrane protein pump which enables the cells to accumulate surprisingly high concentrations of FFA. The ability to measure [FFA i ] and the demonstration of efflux are significant steps in understanding cardiac FFA metabolism. This research has received full or partial funding support from the American Heart Association, AHA Western States Affiliate (California, Nevada & Utah).

Deleterious action of FA metabolites on ATP synthesis: possible link between lipotoxicity, mitochondrial dysfunction, and insulin resistance

Insulin resistance is a characteristic feature of type 2 diabetes and obesity. Insulin-resistant individuals manifest multiple disturbances in free fatty acid (FFA) metabolism and have excessive lipid accumulation in insulin target tissues. Although much evidence supports a causal role for altered FFA metabolism in the development of insulin resistance, i.e., “lipotoxicity”, the intracellular mechanisms by which elevated plasma FFA levels cause insulin resistance have yet to be completely elucidated. Recent studies have implicated a possible role for mitochondrial dysfunction in the pathogenesis of insulin resistance in skeletal muscle. We examined the effect of FFA metabolites [palmitoyl carnitine (PC), palmitoyl-coenzyme A (CoA), and oleoyl-CoA] on ATP synthesis in mitochondria isolated from mouse and human skeletal muscle. At concentrations ranging from 0.5 to 2 μM, these FFA metabolites stimulated ATP synthesis; however, above 5 μM, there was a dose-response inhibition of ATP synthesis. Furthermore, 10 μM PC inhibits ATP synthesis from pyruvate. Elevated PC concentrations (≥10 μM) inhibit electron transport chain activity and decrease the mitochondrial inner membrane potential. These acquired mitochondrial defects, caused by a physiological increase in the concentration of FFA metabolites, provide a mechanistic link between lipotoxicity, mitochondrial dysfunction, and muscle insulin resistance.