Evolution under juvenile malnutrition impacts adult metabolism and fitness

Juveniles are often first to suffer from nutrient shortage, and juvenile undernutrition is likely an important force of natural selection shaping animal physiology, with consequences potentially extending into adulthood. We combined RNAseq, targeted metabolomics and genomics to study the consequences of experimental evolution under juvenile undernutrition for metabolism of reproductively active adult females of Drosophila melanogaster. Compared to six Control populations maintained on standard diet, six Selected populations evolved for over 230 generations on a nutrient-poor larval diet showed major changes in adult gene expression and metabolite abundance. In particular, Selected flies were relatively deficient in essential amino acids and purine nucleotides, but showed overabundance of several non-essential amino-acids involved in purine synthesis and overexpression of multiple enzymes catalyzing this pathway. Selected flies also accumulated medium-chain acylcarnitines suggestive of congestion in beta-oxidation, possibly linked to deficiency of electron transporters. Some aspects of the metabolic profile of Selected flies resembled that of flies subject to starvation. Furthermore, differences between Selected and Control populations in adult gene expression were in general positively correlated with differences in larval expression, consistent with pleiotropy in gene regulation between the life stages. Finally, Selected flies were less fit in terms of fecundity than Controls even when both were raised under the conditions under which the Selected populations evolved. These results suggest that evolutionary adaptation to juvenile undernutrition has large pleiotropic consequences for adult metabolism, and that they are costly rather than adaptive for adult fitness.

In Silico-guided Metabolic Engineering of Bacillus Subtilis for Efficient Biosynthesis of Purine Nucleosides by Blocking the Key Backflow Nodes

Background: Purine nucleosides play essential roles in cellular physiological processes and have a wide range of applications in the fields of antitumor/antiviral drugs and food. However, microbial overproductions of purine nucleosides by de novo metabolic engineering have been a great challenge due to their strict and complex regulatory machinery involved in the biosynthetic pathways. Results: In this study, we designed an in silico-guided strategy for overproducing purine nucleosides based on the genome-scale metabolic network model in Bacillus subtilis. The metabolic flux was analyzed to predict two key backflow nodes Drm (Purine nucleotides toward PPP) and YwjH (PPP-EMP) for resolving the competitive relationship between biomass and purine nucleotides synthesis. In terms of the purine synthesis pathway, the first backflow node Drm was inactivated to block the degradation of purine nucleotides and greatly increased the inosine production to 13.98–14.47 g/L without affecting cell growth. Furthermore, releasing feedback inhibition of purine operon by promoter replacement further enhanced the accumulation of purine nucleotides. In terms of the central carbon metabolic pathways, deleting the second backflow node YwjH and overexpressing Zwf were combined to increase the inosine production to 22.01±1.18 g/L by enhancing the metabolic flow of PPP. Through switching on the flux node of the glucose-6- phosphate to PPP or EMP, the final inosine engineered strain produced up to 25.81±1.23 g/L of inosine by a pgi-based metabolic switch in shake-flask cultivation, suggesting the highest yield in de novo engineered inosine bacteria. Under the guidance of the in silico-designed strategy, a general chassis bacterium was generated for the first time to efficiently synthesize inosine, adenosine, guanosine, IMP, and GMP, providing the sufficient precursor for the synthesis of various purine intermediates. Conclusions: Overall, in silico-guided metabolic engineering successfully optimized the purine synthesis pathway by exploring the efficient targets, representing a superior strategy for efficient biosynthesis of the biotechnological products.

The Role of Uric Acid in Acute and Chronic Coronary Syndromes

Uric acid (UA) is the final product of the catabolism of endogenous and exogenous purine nucleotides. While its association with articular gout and kidney disease has been known for a long time, new data have demonstrated that UA is also related to cardiovascular (CV) diseases. UA has been identified as a significant determinant of many different outcomes, such as all-cause and CV mortality, and also of CV events (mainly Acute Coronary Syndromes (ACS) and even strokes). Furthermore, UA has been related to the development of Heart Failure, and to a higher mortality in decompensated patients, as well as to the onset of atrial fibrillation. After a brief introduction on the general role of UA in CV disorders, this review will be focused on UA’s relationship with CV outcomes, as well as on the specific features of patients with ACS and Chronic Coronary Syndrome. Finally, two issues which remain open will be discussed: the first is about the identification of a CV UA cut-off value, while the second concerns the possibility that the pharmacological reduction of UA is able to lower the incidence of CV events.

A comprehensive method for determining cellular uptake of purine nucleoside phosphorylase and adenylosuccinate synthetase inhibitors by H. pylori

Due to the growing number of Helicobacter pylori strains resistant to currently available antibiotics, there is an urgent need to design new drugs utilizing different molecular mechanisms than those that have been used up to now. Enzymes of the purine salvage pathway are possible targets of such new antibiotics because H. pylori is not able to synthetize purine nucleotides de novo. The bacterium’s recovery of purines and purine nucleotides from the environment is the only source of these essential DNA and RNA building blocks. We have identified formycins and hadacidin as potent inhibitors of purine nucleoside phosphorylase (PNP) and adenylosuccinate synthetase (AdSS) from H. pylori — two key enzymes of the purine salvage pathway. However, we have found that these compounds are not effective in H. pylori cell cultures. To address this issue, we have developed a universal comprehensive method for assessing H. pylori cell penetration by drug candidates, with three alternative detection assays. These include liquid chromatography tandem mass spectrometry, UV absorption, and inhibition of the target enzyme by the tested compound. Using this approach, we have shown that cellular uptake by H. pylori of formycins and hadacidin is very poor, which reveals why their in vitro inhibition of PNP and AdSS and their effect on H. pylori cell cultures are so different. The cell penetration assessment method developed here will be extremely useful for validating the cellular uptake of other drug candidates, facilitating the design of new potent therapeutic agents against H. pylori. Key points • A method for assessing H. pylori cells penetration by drug candidates is described. • Three alternative detection assays that complement each other can be used. • The method may be adapted for other bacteria as well.

Geoffrey Burnstock. 10 May 1929—3 June 2020

Geoffrey Burnstock was a biomedical scientist who gained renown for his discovery that adenosine 5′-triphosphate (ATP) functions as an extracellular signalling molecule. Born in London and educated at King's and University colleges, he did postdoctoral work at Mill Hill and Oxford. He moved in 1959 to the Department of Zoology at the University of Melbourne because he sensed there a greater freedom to challenge established thinking in physiology. His group found that transmission from sympathetic and parasympathetic autonomic nerves to smooth muscle was in some places not mediated by the accepted chemical messengers (noradrenaline and acetylcholine). He amassed evidence that ATP was this non-adrenergic, non-cholinergic transmitter, using biochemical, histological and electrophysiological approaches: heretically, he styled this ‘purinergic transmission’. Geoff further upset dogma in the 1970s by proposing ‘co-transmission’ in which some nerves released ATP in addition to either noradrenaline or acetylcholine. He distinguished pharmacologically P1 receptors (activated best by adenosine and blocked by xanthines) and P2 receptors (activated best by purine nucleotides such as ATP) and he proposed in 1985 that the latter embraced P2X (ion channel) and P2Y (G protein-coupled) subtypes: about 10 years later these categories were substantiated by cDNA cloning. From 1975 until his retirement in 1997, Geoff was head of the Department of Anatomy and Embryology at University College London (UCL), which he developed energetically into a large and strong research department. Later, as head of the Autonomic Research Institute at the Royal Free (part of UCL), he continued to collaborate extensively, and founded several journals and international professional societies. He widely sought clinical benefit for his discoveries, and both P2X and P2Y receptors have been developed as the targets of useful therapeutics (gefapixant, clopidogrel). Geoff was proud of his modest, rather humble, background and eschewed formality. He may have smiled when his early discoveries were met with cynicism, even ridicule (‘pure-imagine’ transmission noted one amusing critic), but this just reinforced his resolve and encouraged his encyclopaedic oeuvre.

Purinergic Signaling in the Pathophysiology and Treatment of Huntington’s Disease

Huntington’s disease (HD) is a devastating, progressive, and fatal neurodegenerative disorder inherited in an autosomal dominant manner. This condition is characterized by motor dysfunction (chorea in the early stage, followed by bradykinesia, dystonia, and motor incoordination in the late stage), psychiatric disturbance, and cognitive decline. The neuropathological hallmark of HD is the pronounced neuronal loss in the striatum (caudate nucleus and putamen). The striatum is related to the movement control, flexibility, motivation, and learning and the purinergic signaling has an important role in the control of these events. Purinergic signaling involves the actions of purine nucleotides and nucleosides through the activation of P2 and P1 receptors, respectively. Extracellular nucleotide and nucleoside-metabolizing enzymes control the levels of these messengers, modulating the purinergic signaling. The striatum has a high expression of adenosine A2A receptors, which are involved in the neurodegeneration observed in HD. The P2X7 and P2Y2 receptors may also play a role in the pathophysiology of HD. Interestingly, nucleotide and nucleoside levels may be altered in HD animal models and humans with HD. This review presents several studies describing the relationship between purinergic signaling and HD, as well as the use of purinoceptors as pharmacological targets and biomarkers for this neurodegenerative disorder.

Purine Nucleotides Metabolism and Signaling in Huntington’s Disease: Search for a Target for Novel Therapies

Huntington’s disease (HD) is a multi-system disorder that is caused by expanded CAG repeats within the exon-1 of the huntingtin (HTT) gene that translate to the polyglutamine stretch in the HTT protein. HTT interacts with the proteins involved in gene transcription, endocytosis, and metabolism. HTT may also directly or indirectly affect purine metabolism and signaling. We aimed to review existing data and discuss the modulation of the purinergic system as a new therapeutic target in HD. Impaired intracellular nucleotide metabolism in the HD affected system (CNS, skeletal muscle and heart) may lead to extracellular accumulation of purine metabolites, its unusual catabolism, and modulation of purinergic signaling. The mechanisms of observed changes might be different in affected systems. Based on collected findings, compounds leading to purine and ATP pool reconstruction as well as purinergic receptor activity modulators, i.e., P2X7 receptor antagonists, may be applied for HD treatment.

Detailed Study of HPRT1 Gross Deletions Found in 10 Italian Lesch-Nyhan Families

Background: Lesch-Nyhan disease (LND) is an X-linked rare pathology involving the purine nucleotides salvage pathway. Its incidence is estimated in 1:350.000 born. The condition is due to mutations in the HPRT1 (hypoxanthine phosphoribosyl transferase 1) gene of which in our cohort 28% (10/35) are large deletions. In order to better assess the nature of the observed deletions in our LND population we analyzed 10 families carrying large deletions in the HPRT1 gene region and studied the underlying pathogenic mechanisms. Methods: We performed PCR based localization of the break points and sequenced the gap-junction fragments. Bioinformatics analysis was performed through several web tools on the 5’ and 3’ break points to determine the factors involved in the deletion mechanism. Results: We precisely mapped 10 unique large deletions involving the HPRT1 gene region that span from 300 bp to 64 kbp. No common breakpoints were found and each deletion appears to be family specific. Conclusions: The deletions in the HPRT1 gene area are consistent with the Micro homology-Mediated Break-Induced Replication (MMBIR) mechanism. There are strong links with Alu-s and no recurrent break points with all of the observed deletions being unique. The relatively large amount of deletions in the HPRT1 region is peculiar and linked with the almost absolute lack of polymorphic sites in the HPRT1 gene making it a very interesting region for further studies.

ANT1 Activation and Inhibition Patterns Support the Fatty Acid Cycling Mechanism for Proton Transport

Adenine nucleotide translocase (ANT) is a well-known mitochondrial exchanger of ATP against ADP. In contrast, few studies have shown that ANT also mediates proton transport across the inner mitochondrial membrane. The results of these studies are controversial and lead to different hypotheses about molecular transport mechanisms. We hypothesized that the H+-transport mediated by ANT and uncoupling proteins (UCP) has a similar regulation pattern and can be explained by the fatty acid cycling concept. The reconstitution of purified recombinant ANT1 in the planar lipid bilayers allowed us to measure the membrane current after the direct application of transmembrane potential ΔΨ, which would correspond to the mitochondrial states III and IV. Experimental results reveal that ANT1 does not contribute to a basal proton leak. Instead, it mediates H+ transport only in the presence of long-chain fatty acids (FA), as already known for UCPs. It depends on FA chain length and saturation, implying that FA’s transport is confined to the lipid-protein interface. Purine nucleotides with the preference for ATP and ADP inhibited H+ transport. Specific inhibitors of ATP/ADP transport, carboxyatractyloside or bongkrekic acid, also decreased proton transport. The H+ turnover number was calculated based on ANT1 concentration determined by fluorescence correlation spectroscopy and is equal to 14.6 ± 2.5 s−1. Molecular dynamic simulations revealed a large positively charged area at the protein/lipid interface that might facilitate FA anion’s transport across the membrane. ANT’s dual function—ADP/ATP and H+ transport in the presence of FA—may be important for the regulation of mitochondrial membrane potential and thus for potential-dependent processes in mitochondria. Moreover, the expansion of proton-transport modulating drug targets to ANT1 may improve the therapy of obesity, cancer, steatosis, cardiovascular and neurodegenerative diseases.

The purine nucleoside phosphorylase pnp-1 regulates epithelial cell resistance to infection in C. elegans

Intestinal epithelial cells are subject to attack by a diverse array of microbes, including intracellular as well as extracellular pathogens. While defense in epithelial cells can be triggered by pattern recognition receptor-mediated detection of microbe-associated molecular patterns, there is much to be learned about how they sense infection via perturbations of host physiology, which often occur during infection. A recently described host defense response in the nematode C. elegans called the Intracellular Pathogen Response (IPR) can be triggered by infection with diverse natural intracellular pathogens, as well as by perturbations to protein homeostasis. From a forward genetic screen, we identified the C. elegans ortholog of purine nucleoside phosphorylase pnp-1 as a negative regulator of IPR gene expression, as well as a negative regulator of genes induced by extracellular pathogens. Accordingly, pnp-1 mutants have resistance to both intracellular and extracellular pathogens. Metabolomics analysis indicates that C. elegans pnp-1 likely has enzymatic activity similar to its human ortholog, serving to convert purine nucleosides into free bases. Classic genetic studies have shown how mutations in human purine nucleoside phosphorylase cause immunodeficiency due to T-cell dysfunction. Here we show that C. elegans pnp-1 acts in intestinal epithelial cells to regulate defense. Altogether, these results indicate that perturbations in purine metabolism are likely monitored as a cue to promote defense against epithelial infection in the nematode C. elegans.Author summaryAll life requires purine nucleotides. However, obligate intracellular pathogens are incapable of generating their own purine nucleotides and thus have evolved strategies to steal these nucleotides from host cells in order to support their growth and replication. Using the small roundworm C. elegans, we show that infection with natural obligate intracellular pathogens is impaired by loss of pnp-1, the C. elegans ortholog of the vertebrate purine nucleoside phosphorylase (PNP), which is an enzyme involved in salvaging purines. Loss of pnp-1 leads to altered levels of purine nucleotide precursors and increased expression of Intracellular Pathogen Response genes, which are induced by viral and fungal intracellular pathogens of C. elegans. In addition, we find that loss of pnp-1 increases resistance to extracellular pathogen infection and increases expression of genes involved in extracellular pathogen defense. Interestingly, studies from 1975 found that mutations in human PNP impair T-cell immunity, whereas our findings here indicate C. elegans pnp-1 regulates intestinal epithelial immunity. Overall, our work indicates that host purine homeostasis regulates resistance to both intracellular and extracellular pathogen infection.