High-energy guanine nucleotides as a signal capable of linking growth to cellular energy status via the control of gene transcription

Exercise-induced changes in myocardial glucose utilization during periods of active cardiac growth

Exercise training can promote physiological cardiac growth, which has been suggested to involve changes in glucose metabolism to facilitate hypertrophy of cardiomyocytes. In this study, we used a dietary, in vivo isotope labeling approach to examine how exercise training influences the metabolic fate of carbon derived from dietary glucose in the heart during acute, active, and established phases of exercise-induced cardiac growth. Male and female FVB/NJ mice were subjected to treadmill running for up to 4 weeks and cardiac growth was assessed by gravimetry. Cardiac metabolic responses to exercise were assessed via in vivo tracing of [13C6]-glucose via mass spectrometry and nuclear magnetic resonance. We found that the half-maximal cardiac growth response was achieved by approximately 1 week of daily exercise training, with near maximal growth observed in male mice with 2 weeks of training; however, female mice were recalcitrant to exercise-induced cardiac growth and required a higher daily intensity of exercise training to achieve significant, albeit modest, increases in cardiac mass. We also found that increases in the energy charge of adenylate and guanylate nucleotide pools precede exercise-induced changes in cardiac size and were associated with higher glucose tracer enrichment in the TCA pool and in amino acids (aspartate, glutamate) sourced by TCA intermediates. Our data also indicate that the activity of collateral biosynthetic pathways of glucose metabolism may not be markedly altered by exercise. Overall, this study provides evidence that metabolic remodeling in the form of heightened energy charge and increased TCA cycle activity and cataplerosis precedes cardiac growth caused by exercise training in male mice.

Environmental organic contaminant body burdens and GC-MS based untargeted metabolomics in mediterranean mussels from Port Phillip Bay, Australia☆

Mussels were collected from four coastal sites around Port Phillip Bay, Australia in Mar and Apr 2021). Body burdens of Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) were measured and the possible sources of toxicants discussed. In addition, a gas chromatography-mass spectrometry (GC-MS) based untargeted metabolomics analysis was performed using the mantle tissues of mussels. Correlations between the results of contaminant body burdens and metabolic variations were investigated. The results demonstrated that high accumulations of low-molecular-weight PAHs were found in mussels. High body burdens of PCBs and OCPs were only found at mussels from the site close to the river mouth. Some of the metabolic pathways were correlated with the accumulation of PAHs. No correlations were found between PCB and OCP accumulations and metabolic abundances. According to the food and environmental standards of the European Union (EU), the PAH, PCB, and OCP accumulation in mussels in this study are a serious food safety concern.

Sports Participation Promotes Beneficial Adaptations in the Erythrocyte Guanylate Nucleotide Pool in Male Athletes Aged 20-90 Years

Introduction

The guanine nucleotide pool (GTP, guanosine-5'-triphosphate; GDP, guanosine-5'-diphosphate, and GMP, guanosine-5'-monophosphate) is an essential energy donor in various biological processes (eg protein synthesis and gluconeogenesis) and secures several vital regulatory functions in the human body. The study aimed to predict the trends of age-related changes in erythrocyte guanine nucleotides and examine whether competitive sport and related physical training promote beneficial adaptations in erythrocyte guanylate concentrations.

Methods

The study included 86 elite endurance runners (EN) aged 20-81 years, 58 sprint-trained athletes (SP) aged 21-90 years, and 62 untrained individuals (CO) aged 20-68 years.

Results

The concentration of erythrocyte GTP and total guanine nucleotides (TGN) were highest in the SP group, lower in the EN group, and lowest in the CO group. Both athletic groups had higher guanylate energy charge (GEC) values than the CO group (p = 0.012). Concentrations of GTP, TGN, and GEC value significantly decreased, while GDP and GMP concentrations progressively increased with age.

Conclusion

Such a profile of change suggests a deterioration of the GTP-related regulatory function in older individuals. Our study explicitly shows that lifelong sports participation, especially of sprint-oriented nature, allows for maintaining a higher erythrocyte guanylate pool concentration, supporting cells' energy metabolism, regulatory and transcription properties, and thus more efficient overall body functioning.

Effects of different levels of inosine-5'-monophosphate (5'-IMP) supplementation on the growth performance and meat quality of finishing pigs (75 to 100 kg)

This study aimed to assess the effects of dietary supplementation of inosine-5'-monophosphate (5'-IMP) on energy efficiency, growth performance, carcass characteristics, meat quality, oxidative status, and biochemical profile of blood plasma in finishing pigs. Fifty-four crossbred castrated male pigs were distributed in a randomized block design consisting of nine blocks, with six treatments per block and one animal per treatment per block. Experimental diets were as follows: positive control diet (PC, 3300 kcal ME/kg), negative control diet (NC, 3200 kcal ME/kg), and four diets prepared by supplementing the NC diet with 0.050%, 0.100%, 0.150%, or 0.200% 5'-IMP. Based on regression analysis, supplementation with 0.129% 5'-IMP increased average daily weight gain (1.30 kg). Backfat thickness, pH45minutes and redness of m. Longissimus Lumborum (LL) increased linearly with 5'-IMP supplementation level. Drip loss and pH at 24 h post-slaughter had a quadratic response to 5'-IMP supplementation. It is concluded that 5'-IMP supplementation positively influenced growth performance, carcass characteristics and LL meat quality in finishing barrows.

SARS-CoV-2 Nsp14 mediates the effects of viral infection on the host cell transcriptome

Viral infection involves complex set of events orchestrated by multiple viral proteins. To identify functions of SARS-CoV-2 proteins, we performed transcriptomic analyses of cells expressing individual viral proteins. Expression of Nsp14, a protein involved in viral RNA replication, provoked a dramatic remodeling of the transcriptome that strongly resembled that observed following SARS-CoV-2 infection. Moreover, Nsp14 expression altered the splicing of more than 1000 genes and resulted in a dramatic increase in the number of circRNAs, which are linked to innate immunity. These effects were independent of the Nsp14 exonuclease activity and required the N7-guanine-methyltransferase domain of the protein. Activation of the NFkB pathway and increased expression of CXCL8 occurred early upon Nsp14 expression. We identified IMPDH2, which catalyzes the rate-limiting step of guanine nucleotides biosynthesis, as a key mediator of these effects. Nsp14 expression caused an increase in GTP cellular levels, and the effect of Nsp14 was strongly decreased in the presence of IMPDH2 inhibitors. Together, our data demonstrate an unknown role for Nsp14 with implications for therapy.

Viruses are parasites, relying on the cells they infect to make more of themselves. In doing so they change how an infected cell turns its genes on and off, forcing it to build new virus particles and turning off the immune surveillance that would allow the body to intervene. This is how SARS-CoV-2, the virus that causes COVID, survives with a genome that carries instructions to make just 29 proteins.

One of these proteins, known as Nsp14, is involved in both virus reproduction and immune escape. Previous work has shown that it interacts with IMPDH2, the cellular enzyme that controls the production of the building blocks of the genetic code. The impact of this interaction is not clear.

To find out more, Zaffagni et al. introduced 26 of the SARS-CoV-2 proteins into human cells one at a time. Nsp14 had the most dramatic effect, dialing around 4,000 genes up or down and changing how the cell interprets over 1,000 genes. Despite being just one protein, it mimicked the genetic changes seen during real SARS-CoV-2 infection. Blocking IMPDH2 partially reversed the effects, which suggests that the interaction of Nsp14 with the enzyme might be responsible for the effects of SARS-CoV-2 on the genes of the cell.

Understanding how viral proteins affect cells can explain what happens during infection. This could lead to the discovery of new treatments designed to counteract the effects of the virus. Further work could investigate whether interfering with Nsp14 helps cells to overcome infection.

SARS-CoV-2 Nsp14 mediates the effects of viral infection on the host cell transcriptome

Viral infection involves complex set of events orchestrated by multiple viral proteins. To identify functions of SARS-CoV-2 proteins, we performed transcriptomic analyses of cells expressing individual viral proteins. Expression of Nsp14, a protein involved in viral RNA replication, provoked a dramatic remodeling of the transcriptome that strongly resembled that observed following SARS-CoV-2 infection. Moreover, Nsp14 expression altered the splicing of more than 1,000 genes and resulted in a dramatic increase in the number of circRNAs, which are linked to innate immunity. These effects were independent of the Nsp14 exonuclease activity and required the N7-guanine-methyltransferase domain of the protein. Activation of the NFkB pathway and increased expression of CXCL8 occurred early upon Nsp14 expression. We identified IMPDH2, which catalyzes the rate-limiting step of guanine nucleotides biosynthesis, as a key mediator of these effects. Nsp14 expression caused an increase in GTP cellular levels, and the effect of Nsp14 was strongly decreased in presence of IMPDH2 inhibitors. Together, our data demonstrate an unknown role for Nsp14 with implications for therapy.

Dietary supplementation with inosine-5'-monophosphate improves the functional, energetic, and antioxidant status of liver and muscle growth in pigs

Inosine 5'-monophosphate (5'-IMP) is an essential nucleotide for de novo nucleotide biosynthesis and metabolism of energy, proteins, and antioxidants. Nucleotides are conditionally essential, as they cannot be produced sufficiently rapidly to meet the needs of the body in situations of oxidative stress or rapid muscle growth. A deficient intake of nucleotides can result in decreased ATP and GTP synthesis and impaired metabolism. We demonstrated that supplementation of finishing pig diets with 5'-IMP reduces the relative weight of the liver, and increases oxygen consumption during mitochondrial respiration without changing the ADP/O ratio, indicating an increase in the respiratory efficiency of liver mitochondria. We also observed a reduction in liver lipid peroxidation and an increase in muscle creatine. Moreover, 5'IMP supplementation increases slaughter weight, lean meat yield, sarcomere length, and backfat thickness in finishing barrows, demonstrating influence on protein metabolism. We suggest that 5'-IMP supplementation increase the mitochondrial respiratory capacity when the liver metabolic activity is stimulated, enhances antioxidant defense, and promotes muscle growth in finishing barrows.

Roles of GTP and Rho GTPases in pancreatic islet beta cell function and dysfunction

A growing body of evidence implicates requisite roles for GTP and its binding proteins (Rho GTPases) in the cascade of events leading to physiological insulin secretion from the islet beta cell. Interestingly, chronic exposure of these cells to hyperglycaemic conditions appears to result in sustained activation of specific Rho GTPases (e.g. Rac1) leading to significant alterations in cellular functions including defects in mitochondrial function and nuclear collapse culminating in beta cell demise. One of the objectives of this review is to highlight our current understanding of the regulatory roles of GTP and Rho GTPases in normal islet function (e.g. proliferation and insulin secretion) as well potential defects in these signalling molecules and metabolic pathways that could contribute islet beta cell dysfunction and loss of functional beta cell mass leading to the onset of diabetes. Potential knowledge gaps in this field and possible avenues for future research are also highlighted.

ABBREVIATIONS

ARNO: ADP-ribosylation factor nucleotide binding site opener; CML: carboxyl methylation; Epac: exchange protein directly activated by cAMP; ER stress: endoplasmic reticulum stress; FTase: farnesyltransferase; GAP: GTPase activating protein; GDI: GDP dissociation inhibitor; GEF: guanine nucleotide exchange factor; GGTase: geranylgeranyltransferase; GGpp: geranylgeranylpyrophosphate; GGPPS: geranylgeranyl pyrophosphate synthase; GSIS: glucose-stimulated insulin secretion; HGPRTase: hypoxanthine-guanine phosphoribosyltransferase; IMPDH: inosine monophosphate dehydrogenase; α-KIC: α-ketoisocaproic acid; MPA: mycophenolic acid; MVA: mevalonic acid; NDPK: nucleoside diphosphate kinase; NMPK: nucleoside monophosphate kinase; Nox2: phagocyte-like NADPH oxidase; PAK-I: p21-activated kinase-I; β-PIX: β-Pak-interacting exchange factor; PRMT: protein arginine methyltransferase; Rac1: ras-related C3 botulinum toxin substrate 1; Tiam1: T-cell lymphoma invasion and metastasis-inducing protein 1; Trx-1: thioredoxin-1; Vav2: vav guanine nucleotide exchange factor 2.

Genetic investigation of purine nucleotide imbalance in Saccharomyces cerevisiae

Because metabolism is a complex balanced process involving multiple enzymes, understanding how organisms compensate for transient or permanent metabolic imbalance is a challenging task that can be more easily achieved in simpler unicellular organisms. The metabolic balance results not only from the combination of individual enzymatic properties, regulation of enzyme abundance, but also from the architecture of the metabolic network offering multiple interconversion alternatives. Although metabolic networks are generally highly resilient to perturbations, metabolic imbalance resulting from enzymatic defect and specific environmental conditions can be designed experimentally and studied. Starting with a double amd1 aah1 mutant that severely and conditionally affects yeast growth, we carefully characterized the metabolic shuffle associated with this defect. We established that the GTP decrease resulting in an adenylic/guanylic nucleotide imbalance was responsible for the growth defect. Identification of several gene dosage suppressors revealed that TAT1, encoding an amino acid transporter, is a robust suppressor of the amd1 aah1 growth defect. We show that TAT1 suppression occurs through replenishment of the GTP pool in a process requiring the histidine biosynthesis pathway. Importantly, we establish that a tat1 mutant exhibits synthetic sickness when combined with an amd1 mutant and that both components of this synthetic phenotype can be suppressed by specific gene dosage suppressors. Together our data point to a strong phenotypic connection between amino acid uptake and GTP synthesis, a connection that could open perspectives for future treatment of related human defects, previously reported as etiologically highly conserved.

tRNA wobble-uridine modifications as amino acid sensors and regulators of cellular metabolic state

Cells must appropriately sense available nutrients and accordingly regulate their metabolic outputs, to survive. This mini-review considers the idea that conserved chemical modifications of wobble (U34) position tRNA uridines enable cells to sense nutrients and regulate their metabolic state. tRNA wobble uridines are chemically modified at the 2- and 5- positions, with a thiol (s2), and (commonly) a methoxycarbonylmethyl (mcm5) modification, respectively. These modifications reflect sulfur amino acid (methionine and cysteine) availability. The loss of these modifications has minor translation defects. However, they result in striking phenotypes consistent with an altered metabolic state. Using yeast, we recently discovered that the s2 modification regulates overall carbon and nitrogen metabolism, dependent on methionine availability. The loss of this modification results in rewired carbon (glucose) metabolism. Cells have reduced carbon flux towards the pentose phosphate pathway and instead increased flux towards storage carbohydrates-primarily trehalose, along with reduced nucleotide synthesis, and perceived amino acid starvation signatures. Remarkably, this metabolic rewiring in the s2U mutants is caused by mechanisms leading to intracellular phosphate limitation. Thus this U34 tRNA modification responds to methionine availability and integratively regulates carbon and nitrogen homeostasis, wiring cells to a 'growth' state. We interpret the importance of U34 modifications in the context of metabolic sensing and anabolism, emphasizing their intimate coupling to methionine metabolism.