ROS and hypoxia signaling regulate periodic metabolic arousal during insect dormancy to coordinate glucose, amino acid, and lipid metabolism

Metabolic suppression is a hallmark of animal dormancy that promotes overall energy savings. Some diapausing insects and some mammalian hibernators have regular cyclic patterns of substantial metabolic depression alternating with periodic arousal where metabolic rates increase dramatically. Previous studies, largely in mammalian hibernators, have shown that periodic arousal is driven by an increase in aerobic mitochondrial metabolism and that many molecules related to energy metabolism fluctuate predictably across periodic arousal cycles. However, it is still not clear how these rapid metabolic shifts are regulated. We first found that diapausing flesh fly pupae primarily use anaerobic glycolysis during metabolic depression but engage in aerobic respiration through the tricarboxylic acid cycle during periodic arousal. Diapausing pupae also clear anaerobic by-products and regenerate many metabolic intermediates depleted in metabolic depression during arousal, consistent with patterns in mammalian hibernators. We found that decreased levels of reactive oxygen species (ROS) induced metabolic arousal and elevated ROS extended the duration of metabolic depression. Our data suggest ROS regulates the timing of metabolic arousal by changing the activity of two critical metabolic enzymes, pyruvate dehydrogenase and carnitine palmitoyltransferase I by modulating the levels of hypoxia inducible transcription factor (HIF) and phosphorylation of adenosine 5′-monophosphate-activated protein kinase (AMPK). Our study shows that ROS signaling regulates periodic arousal in our insect diapasue system, suggesting the possible importance ROS for regulating other types of of metabolic cycles in dormancy as well.

Apigenin Attenuates Acetaminophen-Induced Hepatotoxicity by Activating AMP-Activated Protein Kinase/Carnitine Palmitoyltransferase I Pathway

Overuse of acetaminophen (APAP) is a major cause of drug-induced liver failure at the clinics. Apigenin (API) is a natural flavonoid derived from Matricaria chamomilla. The aim of the present study was to investigate the amelioration function of API in APAP-induced hepatotoxicity both in vitro and in vivo and investigate its potential mechanisms. Analysis results of the activities of serum alanine and aspartate aminotransferases (ALT and AST), malondialdehyde, myeloperoxidase (MPO), and reactive oxygen species (ROS) demonstrated therapeutic effects of API. MTT assay results revealed that API attenuated APAP and its metabolic product, N-acetyl-p-benzoquinone imine (NAPQI) induced cytotoxicity in a dose-dependent manner in human liver cells, L-02 cells. Subsequently, metabolomic results of cells and serum analyses demonstrated an aberrant level of carnitine palmitoyltransferase I (CPT1A). We established that API stimulated CPT1A activity in mice liver tissues and L-02 cells. Molecular docking analyses revealed potential interaction of API with CPT1A. Further investigation of the role of CPT1A in L0-2 cells revealed that API reversed cytotoxicity via the AMP-activated protein kinase (AMPK)/GSK-3β signaling pathway and compound C, which is a selective AMPK inhibitor, inhibited activation of CPT1A induced by API. API was bound to the catalytic region of AMPK as indicated by molecular docking results. In addition, compound C suppressed nuclear translocation of nuclear factor erythroid 2–related factor 2 (NRF2) that is enhanced by API and inhibited the antioxidative function of API. In summary, the study demonstrates that API attenuates APAP-induced hepatotoxicity by activating the AMPK/GSK-3β signaling pathway, which subsequently promotes CPT1A activity and activates the NRF2 antioxidant pathway.

Abstract 505: Diabetes Mellitus-Induced Metabolic Remodeling is Alleviated by Transgenic Overexpression of Mir-133a in the Heart

Diabetic mellitus (DM) cardiomyopathy is a DM-induced metabolic disorder where energy dependence on fatty acid (FA) metabolism causes FA influx overload. While we reported that miR-133a overexpression prevented deleterious lipid accumulation in the diabetic Akita heart, it is unclear whether miR-133a regulates diabetes-induced metabolic remodeling in the DM heart. Thus, we performed deep sequencing on the heart from DM Akita (Ak), cardiac-specific miR-133aTg (Tg), Ak/Tg mice, and sibling wild-type (WT) mice. Ingenuity pathway analysis showed that FAO was the highest activated pathway in the DM heart (p-value=4.59E-11). Therefore, we hypothesized that miR-133a overexpression in the DM heart improves cardiac metabolism by increasing FA clearance via enhancing FA oxidation (FAO). Notably, mitochondrial FA transport protein carnitine palmitoyltransferase I (CPT1) was upregulated (WT: 0.02±0.01, Ak: 0.06±0.02, Ak/Tg: 0.17±0.02, Tg: 0.06±0.01) while changes in the intracellular FA transport protein CD36 were not significant. Interestingly, the rate-limiting enzyme of ketogenesis, the FAO spillover pathway, 3-Hydroxy-3-Methylglutaryl-CoA Synthase 2 (HMGCS2) was downregulated (WT: 0.13±0.02, Ak: 0.74±0.13, Ak/Tg: 0.39±0.07, Tg: 0.05±0.01) in Ak/Tg mice. These results support that increased miR-133a in the diabetic heart contributes to improved FAO and FA metabolism in addition to downregulating FA deposition and ketogenesis in the diabetic heart.

Examination of Interaction between the SR Proteins 9G8 and Repressor Splicing Factor 1 in the Alternative Splicing of Carnitine Palmitoyltransferase I in lipid Metabolism

The method of gene regulation underlying lipid metabolism related to obesity is poorly understood, yet alternative splicing (AS) appears to be an important mechanism for proper lipid storage. CPT1 (carnitine palmitoyltransferase I) is a beta-oxidation enzyme required for the breakdown of fatty acids. The gene coding for CPT1 is alternatively spliced to produce two different products that vary in their activity. When the splicing SR protein 9G8 is knocked down in the fat body of Drosophila, the CPT1 splicing pattern is altered. A linear search algorithm was developed that parsed through FASTA files of the CPT1 gene region and sought out sequences that matched known binding sequences of 9G8. We expected a result in exon 6A that would signal its inclusion but unexpectedly found a match in exon 5 of the CPT1 transcript. We theorized that 9G8 and the SR protein competitor RSF1, interact with one another for binding sites on the CPT1 gene to result in different isoforms. Additionally, TG data indicated that 9G8 and RSF1 KD flies displayed statistically significant higher TG levels than their control suggesting a potential cooperative relationship. We next performed a starvation resistance experiment and found that 9G8 and RSF1 KD flies phenocopied starvation resistance suggesting that both proteins interact to result in the same CPT1 product. We are using qPCR to determine if there is a difference in the AS of CPT1 among flies with decreased expression of 9G8, the SR protein antagonist RSF1 and the SR protein shuttle TRN-SR.

Synthesis of new Carnitine Palmitoyltransferase I inhibitors derivatives of C75

Carnitine Palmitoyltransferase (CPT1) is an enzyme that catalyzes the transport of fatty acids from the cytosol into the mitochondria. CPT1 inhibition in the hypothalamus increases fatty acid levels, which produces an increased expression of anorexigenic neuropeptides, a sign of satiety. C75 acts as an antiobesity predrug. In vivo C75, is converted into C75-CoA adduct, which is a potent inhibitor of CPT1 and produces a loss of appetite and body weight. In this work, we present three new derivatives of C75, where the carboxylic group is replaced by a carnitine unit, malonic group, and a hydroxyl group with changes from trans to cis relative stereochemistry. Our results suggest that introducing a bigger group than carboxylic in β position or cis relative configuration of the lactone leads to a decrease of CPT1 inhibitory activity.

High intensity exercise inhibits carnitine palmitoyltransferase-I sensitivity to l-carnitine

The decline in fat oxidation at higher power outputs of exercise is a complex interaction between several mechanisms; however, the influence of mitochondrial bioenergetics in this process remains elusive. Therefore, using permeabilized muscle fibers from mouse skeletal muscle, we aimed to determine if acute exercise altered mitochondrial sensitivity to (1) adenosine diphosphate (ADP) and inorganic phosphate (Pi), or (2) carnitine palmitoyltransferase-I (CPT-I) independent (palmitoylcarnitine, PC) and dependent [palmitoyl-CoA (P-CoA), malonyl-CoA (M-CoA), and l-carnitine] substrates, in an intensity-dependent manner. As the apparent ADP Km increased to a similar extent following low (LI) and high (HI) intensity exercise compared with sedentary (SED) animals, and Pi sensitivity was unaltered by exercise, regulation of phosphate provision likely does not contribute to the well-established intensity-dependent shift in substrate utilization. Mitochondrial sensitivity to PC and P-CoA was not influenced by exercise, while M-CoA sensitivity was attenuated similarly following LI and HI. In contrast, CPT-I sensitivity to l-carnitine was only altered following HI, as HI exercise attenuated l-carnitine sensitivity by ∼40%. Moreover, modeling the in vivo concentrations of l-carnitine and P-CoA during exercise suggests that CPT-I flux is ∼25% lower following HI, attributed equally to reductions in l-carnitine content and l-carnitine sensitivity. Altogether, these data further implicate CPT-I flux as a key event influencing metabolic interactions during exercise, as a decline in l-carnitine sensitivity in addition to availability at higher power outputs could impair mitochondrial fatty acid oxidation.