Modelling Metabolic Shifts during Cardiomyocyte Differentiation, Iron Deficiency and Transferrin Rescue Using Human Pluripotent Stem Cells

Cardiomyocytes rely on specialised metabolism to meet the high energy demand of the heart. During heart development, metabolism matures and shifts from the predominant utilisation of glycolysis and glutamine oxidation towards lactate and fatty acid oxidation. Iron deficiency (ID) leads to cellular metabolism perturbations. However, the exact alterations in substrate metabolism during ID are poorly defined. Using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM), the present study investigated changes in major metabolic substrate utilisation in the context of ID or upon transferrin rescue. Typically, during hiPSC-CM differentiation, the greatest increase in total metabolic output and rate was seen in fatty acid metabolism. When ID was induced, hiPSC-CMs displayed increased reliance on glycolytic metabolism, and six TCA cycle, five amino acid, and four fatty acid substrates were significantly impaired. Transferrin rescue was able to improve TCA cycle substrate metabolism, but the amino acid and fatty acid metabolism remained perturbed. Replenishing iron stores partially reverses the adverse metabolic changes that occur during ID. Understanding the changes in metabolic substrate utilisation and their modification may provide potential for discovery of new biomarkers and therapeutic targets in cardiovascular diseases.

Coping with extremes: lowered myocardial phosphofructokinase activities and glucose content but increased fatty acids content in highland Eurasian Tree Sparrows

Background Efficient and selective utilization of metabolic substrates is one of the key strategies in high-altitude animals to cope with hypoxia and hypothermia. Previous findings have shown that the energy substrate utilization of highland animals varies with evolutionary history and phylogeny. The heart is a proxy for the cardiopulmonary system, and the metabolic substrate utilization in the myocardium is also under the strong selective pressure of chronically hypoxic and hypothermic environments. However, little information is available on the physiological adjustments in relation to metabolic substrate utilization in the myocardium for coping with high-altitude environments. Methods We compared the metabolic enzyme activities, including hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), citrate synthase (CS), carnitine palmitoyl transferase 1 (CPT-1), lactic dehydrogenase (LDH), and creatine kinase (CK), and metabolic substrate contents including glucose (Glu), triglyceride (TG), and free fatty acid (FFA) in the myocardium of a typical human commensal species, Eurasian Tree Sparrows (Passermontanus) between the Qinghai-Tibet Plateau (the QTP, 3230 m) and low altitude population (Shijiazhuang, 80 m), and between sexes. Results Among the seven metabolic enzymes and three substrates investigated, we identified no significant differences in PK, CPT-1, HK, CS, LDH, and CK activities and TG content of the myocardium between high and low altitude populations. However, the QTP sparrows had significantly lower Glu content and PFK activities but higher FFA content relative to their lowland counterparts. In addition, male sparrows had higher myocardial HK and CS activities relative to females, independent of altitude. Conclusions Our results showed that the QTP sparrows elevated fatty acid utilization rather than glucose preference in the myocardium relative to lowland counterpart, which contributes to uncovering both the physiological adjustments for adapting to the extreme conditions of the QTP, intraspecifically.

gbpA and chiA genes are not uniformly distributed amongst diverse Vibrio cholerae

Members of the bacterial genus Vibrio utilize chitin both as a metabolic substrate and a signal to activate natural competence. Vibrio cholerae is a bacterial enteric pathogen, sub-lineages of which can cause pandemic cholera. However, the chitin metabolic pathway in V. cholerae has been dissected using only a limited number of laboratory strains of this species. Here, we survey the complement of key chitin metabolism genes amongst 195 diverse V. cholerae . We show that the gene encoding GbpA, known to be an important colonization and virulence factor in pandemic isolates, is not ubiquitous amongst V. cholerae . We also identify a putatively novel chitinase, and present experimental evidence in support of its functionality. Our data indicate that the chitin metabolic pathway within V. cholerae is more complex than previously thought, and emphasize the importance of considering genes and functions in the context of a species in its entirety, rather than simply relying on traditional reference strains.