Purine Biosynthesis Enzymes in Hippocampal Neurons

The Role of Purine Metabolism and Uric Acid in Postnatal Neurologic Development

This review explores the essential roles of purine metabolism including the catabolic product, uric acid, in the development of dopaminergic neurons of the substantia nigra pars compacta. The high energy requirements of the substantia nigra pars compacta alongside necessary purinergic neurotransmission and the influence of oxidative stress during development makes these neurons uniquely susceptible to changes in purine metabolism. Uric acid's role as a central nervous system antioxidant may help to ameliorate these effects in utero. Understanding the mechanisms by which purines and uric acid influence development of the substantia nigra pars compacta can help further explain neurologic consequences of inborn errors of purine metabolism, such as Lesch-Nyhan disease.

Targeting purine metabolism-related enzymes for therapeutic intervention: A review from molecular mechanism to therapeutic breakthrough

Purines are ancient metabolites with established and emerging metabolic and non-metabolic signaling attributes. The expression of purine metabolism-related genes is frequently activated in human malignancies, correlating with increased cancer aggressiveness and chemoresistance. Importantly, under certain stimulating conditions, the purine biosynthetic enzymes can assemble into a metabolon called "purinosomes" to enhance purine flux. Current evidence suggests that purine flux is regulated by a complex circuit that encompasses transcriptional, post-translational, metabolic, and association-dependent regulatory mechanisms. Furthermore, purines within the tumor microenvironment modulate cancer immunity through signaling mediated by purinergic receptors. The deregulation of purine metabolism has significant metabolic consequences, particularly hyperuricemia. Herbal-based therapeutics have emerged as valuable pharmacological interventions for the treatment of hyperuricemia by inhibiting the activity of hepatic XOD, modulating the expression of renal urate transporters, and suppressing inflammatory responses. This review summarizes recent advancements in the understanding of purine metabolism in clinically relevant malignancies and metabolic disorders. Additionally, we discuss the role of herbal interventions and the interaction between the host and gut microbiota in the regulation of purine homeostasis. This information will fuel the innovation of therapeutic strategies that target the disease-associated rewiring of purine metabolism for therapeutic applications.

Purinosomes and Purine Metabolism in Mammalian Neural Development: A Review

Neural stem/progenitor cells (NSPCs) in specific brain regions require precisely regulated metabolite production during critical development periods. Purines-vital components of DNA, RNA, and energy carriers like ATP and GTP-are crucial metabolites in brain development. Purine levels are tightly controlled through two pathways: de novo synthesis and salvage synthesis. Enzymes driving de novo pathway are assembled into a large multienzyme complex termed the "purinosome." Here, we review purine metabolism and purinosomes as spatiotemporal regulators of neural development. Notably, around postnatal day 0 (P0) during mouse cortical development, purine synthesis transitions from the de novo pathway to the salvage pathway. Inhibiting the de novo pathway affects mTORC1 pathway and leads to specific forebrain malformations. In this review, we also explore the importance of protein-protein interactions of a newly identified NSPC protein-NACHT and WD repeat domain-containing 1 (Nwd1)-in purinosome formation. Reduced Nwd1 expression disrupts purinosome formation, impacting NSPC proliferation and neuronal migration, resulting in periventricular heterotopia. Nwd1 interacts directly with phosphoribosylaminoimidazole-succinocarboxamide synthetase (PAICS), an enzyme involved in de novo purine synthesis. We anticipate this review will be valuable for researchers investigating neural development, purine metabolism, and protein-protein interactions.

Analysis of the mechanism of Buyang Huanwu Decoction against cerebral ischemia-reperfusion by multi-omics

ETHNOPHARMACOLOGICAL RELEVANCE

Buyang Huanwu Decoction (BYHW) is a classic representative formula for treating qi deficiency and the blood stasis syndrome of stroke in the Qing Dynasty physician Wang Qingren's Correction on the Errors of Medical Works. However, the research on the mechanism of BYHW in the treatment of stroke is not systematic and comprehensive.

AIM OF THE STUDY

Combined with multi-omics analysis methods to explore the potential targets of BYHW in the treatment of cerebral ischemia-reperfusion (I/R).

MATERIALS AND METHODS

The rat middle cerebral artery occlusion (MCAO) model was established to study the effect of BYHW on cerebral I/R injury in rats. Then, the potential targets and pathways of BYHW in the treatment of cerebral I/R injury were analyzed by proteomic, transcriptomic, and metabolomic methods. Finally, 4D-PRM was used to validate potential targets.

RESULTS

BYHW effectively improved the neurological function scores of MCAO rats and significantly reduced the rate of cerebral infarction in MCAO rats. Multi-omics analysis had identified 15 potential targets and 4 potential signaling pathways. The results of 4D-PRM targeted proteomics verification showed that Pde1b was reversed up-regulated, and Aprt, Gpd1, Glb1, HEXA, and HEXB were reversed down-regulated.

CONCLUSION

BYHW may improve cerebral I/R through Aprt, Pde1b, Gpd1, Glb1, HEXA and HEXB targets, and Glycerophospholipid metabolism, Purine metabolism and Glycosphingolipid biosynthesis - globoseries pathway.

The mammalian purine salvage pathway as an exploitable route for cerebral bioenergetic support after brain injury

Purine-based molecules play ancient, fundamental, and evolutionarily-conserved roles across life on Earth, ranging from DNA and RNA, to the universal energy currency, ATP. In mammals, the two primary routes for the synthesis of the adenine nucleotides ATP, ADP and AMP, and, as a consequence, the major bioactive metabolite adenosine, are the de novo purine biosynthesis (DNPB) pathway, and the purine salvage pathway (PSP). Of the two, the PSP dominates in both the mammalian brain and heart. This is because the PSP utilizes the breakdown products of ATP, occasioned by the high energy demands of these organs, to rapidly regenerate adenine nucleotides. This resynthesis route, while efficient and energetically favourable, leaves these organs vulnerable to loss of salvageable metabolites, with the potential for protracted depletion of the means to synthesize ATP, and the ability to deploy neuro- and cardioprotective adenosine. Having previously shown that hippocampal cellular ATP and adenosine release can be increased by supplying substrates for the PSP (d-ribose and adenine), we now explore the expression of DNPB and PSP enzymes in hippocampal neurons and astrocytes based on available transcriptomic data. We find that key enzymes of the PSP are expressed at higher levels than those in the DNPB pathway, and that PSP enzymes are expressed at higher levels in neurons than in astrocytes. These data reflect the importance of the PSP in the mammalian brain and imply that pharmacological targeting of the PSP may be particularly beneficial to neurons at times of metabolic stress. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

The Purinosome: A Case Study for a Mammalian Metabolon

Over the past fifteen years, we have unveiled a new mechanism by which cells achieve greater efficiency in de novo purine biosynthesis. This mechanism relies on the compartmentalization of de novo purine biosynthetic enzymes into a dynamic complex called the purinosome. In this review, we highlight our current understanding of the purinosome with emphasis on its biophysical properties and function and on the cellular mechanisms that regulate its assembly. We propose a model for functional purinosomes in which they consist of at least ten enzymes that localize near mitochondria and carry out de novo purine biosynthesis by metabolic channeling. We conclude by discussing challenges and opportunities associated with studying the purinosome and analogous metabolons. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Induced pluripotent stem cells from subjects with Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is an inherited disorder caused by pathogenic variants in the HPRT1 gene, which encodes the purine recycling enzyme hypoxanthine-guanine phosphoribosyltransferase (HGprt). We generated 6 induced pluripotent stem cell (iPSC) lines from 3 individuals with LND, along with 6 control lines from 3 normal individuals. All 12 lines had the characteristics of pluripotent stem cells, as assessed by immunostaining for pluripotency markers, expression of pluripotency genes, and differentiation into the 3 primary germ cell layers. Gene expression profiling with RNAseq demonstrated significant heterogeneity among the lines. Despite this heterogeneity, several anticipated abnormalities were readily detectable across all LND lines, including reduced HPRT1 mRNA. Several unexpected abnormalities were also consistently detectable across the LND lines, including decreases in FAR2P1 and increases in RNF39. Shotgun proteomics also demonstrated several expected abnormalities in the LND lines, such as absence of HGprt protein. The proteomics study also revealed several unexpected abnormalities across the LND lines, including increases in GNAO1 decreases in NSE4A. There was a good but partial correlation between abnormalities revealed by the RNAseq and proteomics methods. Finally, functional studies demonstrated LND lines had no HGprt enzyme activity and resistance to the toxic pro-drug 6-thioguanine. Intracellular purines in the LND lines were normal, but they did not recycle hypoxanthine. These cells provide a novel resource to reveal insights into the relevance of heterogeneity among iPSC lines and applications for modeling LND.

Human de novo purine biosynthesis

The focus of this review is the human de novo purine biosynthetic pathway. The pathway enzymes are enumerated, as well as the reactions they catalyze and their physical properties. Early literature evidence suggested that they might assemble into a multi-enzyme complex called a metabolon. The finding that fluorescently-tagged chimeras of the pathway enzymes form discrete puncta, now called purinosomes, is further elaborated in this review to include: a discussion of their assembly; the role of ancillary proteins; their locus at the microtubule/mitochondria interface; the elucidation that at endogenous levels, purinosomes function to channel intermediates from phosphoribosyl pyrophosphate to AMP and GMP; and the evidence for the purinosomes to exist as a protein condensate. The review concludes with a consideration of probable signaling pathways that might promote the assembly and disassembly of the purinosome, in particular the identification of candidate kinases given the extensive phosphorylation of the enzymes. These collective findings substantiate our current view of the de novo purine biosynthetic metabolon whose properties will be representative of how other metabolic pathways might be organized for their function.

Metabolic Tools for Identification of New Mutations of Enzymes Engaged in Purine Synthesis Leading to Neurological Impairment

The cellular pool of purines is maintained by de novo purine synthesis (DNPS), recycling and degradation. Mutations in genes encoding DNPS enzymes cause their substrates to accumulate, which has detrimental effects on cellular division and organism development, potentially leading to neurological impairments. Unspecified neurological symptoms observed in many patients could not be elucidated even by modern techniques. It is presumable that some of these problems are induced by dysfunctions in DNPS enzymes. Therefore, we determined the concentrations of dephosphorylated DNPS intermediates by LC-MS/MS as markers of yet unpublished mutations in PFAS and PAICS genes connected with dysfunctions of carboxylase/phosphoribosylaminoimidazolesuccinocarboxamide synthase (PAICS) or phosphoribosylformylglycinamidine synthase (PFAS). We determined the criteria for normal values of metabolites and investigated 1,447 samples of urine and 365 dried blood spots of patients suffering from various forms of neurological impairment. We detected slightly elevated aminoimidazole riboside (AIr) concentrations in three urine samples and a highly elevated 5-formamidoimidazole-4-carboxamide riboside (FGAr) concentration in one urine sample. The accumulation of AIr or FGAr in body fluids can indicate PAICS or PFAS deficiency, respectively, which would be new disorders of DNPS caused by mutations in the appropriate genes. Measurement of DNPS intermediates in patients with neurological symptoms can uncover the cause of serious cellular and functional impairments that are otherwise inaccessible to detection. Further genetic and molecular analysis of these patients should establish the causal mutations for prenatal diagnosis, genetic consultation, and reinforce the DNPS pathway as a therapeutic target.

Utilizing Optimized Tools to Investigate PTM Crosstalk: Identifying Potential PTM Crosstalk of Acetylated Mitochondrial Proteins

Post-translational modification (PTM) crosstalk is recognized as a major cell-regulatory mechanism, and studies of several proteins have validated the premise that PTMs work in concert. Previous work by our group investigated the potential PTM crosstalk on proteins in the EGFR-Ras-c-Fos axis by utilizing a comprehensive set of PTM reagents termed Signal-Seeker toolkits. In this study, these tools were used to investigate the potential PTM crosstalk that occurs in acetylated mitochondrial proteins in response to a mitochondrial stress-inducing agent hydrogen peroxide (H₂O₂). Mitochondrial protein acetylation has been shown to participate in PTM crosstalk as exemplified by the regulation of the pyruvate dehydrogenase complex via kinase, phosphatase, acetyltransferase, and deacetylase activities. Changes in the acetylated state of mitochondrial proteins were investigated, in response to H₂O₂, using a novel anti acetyl lysine (Ac-K) antibody. Signal-Seeker PTM detection tools were used to validate the acetylation state of ten mitochondrial targets, as well as their endogenous acetylation state in response to H₂O₂. Importantly, the endogenous acetylation, ubiquitination, SUMOylation 2/3, and tyrosine phosphorylation state of four target mitochondrial proteins were also investigated with the toolkit. Each of the four proteins had unique PTM profiles, but diverging acetylation and ubiquitin or SUMO 2/3 signals appeared to be a common theme. This proof-of-concept study identifies the Signal-Seeker toolkits as a useful tool to investigate potential PTM crosstalk.

Expression of the purine biosynthetic enzyme phosphoribosyl formylglycinamidine synthase in neurons

Purines are metabolic building blocks essential for all living organisms on earth. De novo purine biosynthesis occurs in the brain and appears to play important roles in neural development. Phosphoribosyl formylglycinamidine synthase (FGAMS, also known as PFAS or FGARAT), a core enzyme involved in the de novo synthesis of purines, may play alternative roles in viral pathogenesis. To date, no thorough investigation of the endogenous expression and localization of de novo purine biosynthetic enzymes has been conducted in human neurons or in virally infected cells. In this study, we characterized expression of FGAMS using multiple neuronal models. In differentiated human SH-SY5Y neuroblastoma cells, primary rat hippocampal neurons, and in whole-mouse brain sections, FGAMS immunoreactivity was distributed within the neuronal cytoplasm. FGAMS immunolabeling in vitro demonstrated extensive distribution throughout neuronal processes. To investigate potential changes in FGAMS expression and localization following viral infection, we infected cells with the human pathogen herpes simplex virus 1. In infected fibroblasts, FGAMS immunolabeling shifted from a diffuse cytoplasmic location to a mainly perinuclear localization by 12 h post-infection. In contrast, in infected neurons, FGAMS localization showed no discernable changes in the localization of FGAMS immunoreactivity. There were no changes in total FGAMS protein levels in either cell type. Together, these data provide insight into potential purine biosynthetic mechanisms utilized within neurons during homeostasis as well as viral infection. Cover Image for this Issue: doi: 10.1111/jnc.14169.