Serotonin activates glycolysis and mitochondria biogenesis in human breast cancer cells through activation of the Jak1/STAT3/ERK1/2 and adenylate cyclase/PKA, respectively.

BACKGROUND: Although produced by several types of tumours, the role of serotonin on cancer biology is yet to be understood. METHODS: The effects of serotonin (5-HT) on human breast cancer cells proliferation, signalling pathways and metabolic profile were evaluated by cytometry, western blotting, qPCR, enzymology and confocal microscopy. RESULTS: Our results revealed that incubation of MCF-7 cells with 10 µM 5-HT increased cell growth rate by 28%, an effect that was prevented by the 5-HTR2A/C antagonist, ketanserin. Conversely, increasing concentrations of 5-HT promoted glucose consumption and lactate production by MCF-7 cells. We also showed that increased glucose metabolism is provoked by the upregulation of pyruvate kinase M2 (PKM2) isoform through 5-HTR2A/C-triggered activation of Jak1/STAT3 and ERK1/2 subcellular pathways. However, we noticed a decrease in the rate of produced lactate per consumed glucose as a function of the hormone concentration, suggesting a disruption of the Warburg effect. The latter effect is due to 5-HTR2A/C-dependent mitochondrial biogenesis and metabolism, which is triggered by adenylyl cyclase/PKA, enhancing the oxidation of lactate within these cells. CONCLUSIONS: We showed that serotonin, through 5-HTR2A/C, interferes with breast cancer cells proliferation and metabolism by triggering two distinct signalling pathways: Jak1/STAT3 that boosts glycolysis through upregulation of PKM2, and adenylyl cyclase/PKA that enhances mitochondrial biogenesis.

Keto analogues and amino acid supplementation and its effects on ammonaemia during extenuating endurance exercise in ketogenic diet-fed rats.

Keto analogues and amino acids (KAAA) supplementation can reduce blood ammonia concentrations in athletes undergoing high-intensity exercise under both ketogenic and thermoneutral conditions. This study evaluated the acute effects of KAAA supplementation on ammonia metabolism during extenuating endurance exercise in rats fed a ketogenic diet. In all, eighty male Fischer rats at 90 d of age were divided into eight groups, and some were trained using a swimming endurance protocol. A ketogenic diet supplemented with keto analogues was administered for 10 d. Administration of the ketogenic diet ended 3 d before the exhaustion test (extenuating endurance exercise). A ketogenic diet plus KAAA supplementation and extenuating endurance exercise (trained ketogenic diet supplemented with KAAA (TKKa)) increased blood ammonia concentrations by approximately 50 % compared with the control diet (trained control diet supplemented with KAAA (TCKa)) and similar training (effect size=1·33; statistical power=0·50). The KAAA supplementation reduced blood urea concentrations by 4 and 18 % in the control and ketogenic diet groups, respectively, compared with the groups fed the same diets without supplementation. The trained groups had 60 % lower blood urate concentrations after TCKa treatment than after TKKa treatment. Our results suggest that KAAA supplementation can reduce blood ammonia concentrations after extenuating endurance exercise in rats fed a balanced diet but not in rats fed a ketogenic diet.

Metformin reverses hexokinase and phosphofructokinase downregulation and intracellular distribution in the heart of diabetic mice.

Diabetes mellitus is characterized by hyperglycemia and its associated complications, including cardiomyopathy. Metformin, in addition to lowering blood glucose levels, provides cardioprotection for diabetic subjects. Glycolysis is essential to cardiac metabolism and its reduction may contribute to diabetic cardiomyopathy. Hexokinase (HK) and phosphofructokinase (PFK), rate-limiting enzymes of glycolysis, are downregulated in cardiac muscle from diabetic subjects, playing a central role on the decreased glucose utilization in the heart of diabetic subjects. Thus, the aim of this study was to determine whether metformin modulates heart HK and PFK from diabetic mice. Diabetes was induced by streptozotocin injection on male Swiss mice, which were treated for three consecutive days with 250 mg/kg metformin before evaluating HK and PFK activity, expression, and intracellular distribution on the heart of these subjects. We show that metformin abrogates the downregulation of HK and PFK in the heart of streptozotocin-induced diabetic mice. This effect is not correlated to alteration on the enzymes' transcription and expression. However, the intracellular distribution of both enzymes is altered in diabetic hearts that show increased activity of the soluble fraction when compared to the particulate fraction. Moreover, this pattern is reversed upon the treatment with metformin, which is correlated with the effects of the drug on the enzymes activity. Altogether, our results support evidences that metformin alter the intracellular localization of HK and PFK augmenting glucose utilization by diabetic hearts and, thus, conferring cardiac protection to diabetic subjects.

Lactate downregulates the glycolytic enzymes hexokinase and phosphofructokinase in diverse tissues from mice.

We examined the effects of lactate on the enzymatic activity of hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK) in various mouse tissues. Our results showed that lactate inhibited PFK activity in all the analyzed tissues. This inhibitory effect was observed in skeletal muscle even in the presence of insulin. Lactate directly inhibited the phosphorylation of PFK tyrosine residues in skeletal muscle, an important mechanism of the enzyme activation. Moreover, lactate indirectly inhibited HK activity, which resulted from its cellular redistribution, here attributed to alterations of HK structure. PK activity was not affected by lactate. The activity of HK and PFK is directly related to glucose metabolism. Thus, it is conceivable that lactate exposure can induce inhibition of glucose consumption in tissues.

Regulation of mammalian muscle type 6-phosphofructo-1-kinase and its implication for the control of the metabolism.

Phosphofructokinase (PFK) is a major regulatory glycolytic enzyme and is considered to be the pacemaker of glycolysis. This enzyme presents a puzzling regulatory mechanism that is modulated by a large variety of metabolites, drugs, and intracellular proteins. To date, the mammalian enzyme structure has not yet been resolved. However, it is known that PFK undergoes an intricate oligomerization process, shifting among monomers, dimers, tetramers, and more complex oligomeric structures. The equilibrium between PFK dimers and tetramers is directly correlated with the enzyme regulation, because the dimer exhibits very low catalytic activity, whereas the tetramer is fully active. Several PFK ligands modulate the enzyme, favoring the formation of its dimers or tetramers. The present review integrates recent findings regarding the regulatory aspects of muscle type PFK and discusses their relation to the control of metabolism.