Impairment of serine transport across the blood-brain barrier by deletion of Slc38a5 causes developmental delay and motor dysfunction.

Brain L-serine is critical for neurodevelopment and is thought to be synthesized solely from glucose. In contrast, we found that the influx of L-serine across the blood-brain barrier (BBB) is essential for brain development. We identified the endothelial Slc38a5, previously thought to be a glutamine transporter, as an L-serine transporter expressed at the BBB in early postnatal life. Young Slc38a5 knockout (KO) mice exhibit developmental alterations and a decrease in brain L-serine and D-serine, without changes in serum or liver amino acids. Slc38a5-KO brains exhibit accumulation of neurotoxic deoxysphingolipids, synaptic and mitochondrial abnormalities, and decreased neurogenesis at the dentate gyrus. Slc38a5-KO pups exhibit motor impairments that are affected by the administration of L-serine at concentrations that replenish the serine pool in the brain. Our results highlight a critical role of Slc38a5 in supplying L-serine via the BBB for proper brain development.

Serine starvation silences estrogen receptor signaling through histone hypoacetylation.

Loss of estrogen receptor (ER) pathway activity promotes breast cancer progression, yet how this occurs remains poorly understood. Here, we show that serine starvation, a metabolic stress often found in breast cancer, represses estrogen receptor alpha (ERα) signaling by reprogramming glucose metabolism and epigenetics. Using isotope tracing and time-resolved metabolomic analyses, we demonstrate that serine is required to maintain glucose flux through glycolysis and the TCA cycle to support acetyl-CoA generation for histone acetylation. Consequently, limiting serine depletes histone H3 lysine 27 acetylation (H3K27ac), particularly at the promoter region of ER pathway genes including the gene encoding ERα, ESR1. Mechanistically, serine starvation impairs acetyl-CoA-dependent gene expression by inhibiting the entry of glycolytic carbon into the TCA cycle and down-regulating the mitochondrial citrate exporter SLC25A1, a critical enzyme in the production of nucleocytosolic acetyl-CoA from glucose. Consistent with this model, total H3K27ac and ERα expression are suppressed by SLC25A1 inhibition and restored by acetate, an alternate source of acetyl-CoA, in serine-free conditions. We thus uncover an unexpected role for serine in sustaining ER signaling through the regulation of acetyl-CoA metabolism.

A new type of blood-brain barrier aminoacidopathy underlies metabolic microcephaly associated with SLC1A4 mutations.

Mutations in the SLC1A4 transporter lead to neurodevelopmental impairments, spastic tetraplegia, thin corpus callosum, and microcephaly in children. SLC1A4 catalyzes obligatory amino acid exchange between neutral amino acids, but the physiopathology of SLC1A4 disease mutations and progressive microcephaly remain unclear. Here, we examined the phenotype and metabolic profile of three Slc1a4 mouse models, including a constitutive Slc1a4-KO mouse, a knock-in mouse with the major human Slc1a4 mutation (Slc1a4-K256E), and a selective knockout of Slc1a4 in brain endothelial cells (Slc1a4tie2-cre). We show that Slc1a4 is a bona fide L-serine transporter at the BBB and that acute inhibition or deletion of Slc1a4 leads to a decrease in serine influx into the brain. This results in microcephaly associated with decreased L-serine content in the brain, accumulation of atypical and cytotoxic 1-deoxysphingolipids in the brain, neurodegeneration, synaptic and mitochondrial abnormalities, and behavioral impairments. Prenatal and early postnatal oral administration of L-serine at levels that replenish the serine pool in the brain rescued the observed biochemical and behavioral changes. Administration of L-serine till the second postnatal week also normalized brain weight in Slc1a4-E256 K mice. Our observations suggest that the transport of "non-essential" amino acids from the blood through the BBB is at least as important as that of essential amino acids for brain metabolism and development. We proposed that SLC1A4 mutations cause a BBB aminoacidopathy with deficits in serine import across the BBB required for optimal brain growth and leads to a metabolic microcephaly, which may be amenable to treatment with L-serine.

Altered serine metabolism promotes drug tolerance in Mycobacterium abscessus via a WhiB7-mediated adaptive stress response.

Mycobacterium abscessus is an emerging opportunistic pathogen responsible for chronic lung diseases, especially in patients with cystic fibrosis. Treatment failure of M. abscessus infections is primarily associated with intrinsic or acquired antibiotic resistance. However, there is growing evidence that antibiotic tolerance, i.e., the ability of bacteria to transiently survive exposure to bactericidal antibiotics through physiological adaptations, contributes to the relapse of chronic infections and the emergence of acquired drug resistance. Yet, our understanding of the molecular mechanisms that underlie antibiotic tolerance in M. abscessus remains limited. In the present work, a mutant with increased cross-tolerance to the first- and second-line antibiotics cefoxitin and moxifloxacin, respectively, has been isolated by experimental evolution. This mutant harbors a mutation in serB2, a gene involved in L-serine biosynthesis. Metabolic changes caused by this mutation alter the intracellular redox balance to a more reduced state that induces overexpression of the transcriptional regulator WhiB7 during the stationary phase, promoting tolerance through activation of a WhiB7-dependant adaptive stress response. These findings suggest that alteration of amino acid metabolism and, more generally, conditions that trigger whiB7 overexpression, makes M. abscessus more tolerant to antibiotic treatment.

Serine metabolism in macrophage polarization.

OBJECTIVE: Emerging studies have revealed that macrophages possess different dependences on the uptake, synthesis, and metabolism of serine for their activation and functionalization, necessitating our insight into how serine availability and utilization impact macrophage activation and inflammatory responses. METHODS: This article summarizes the reports published domestically and internationally about the serine uptake, synthesis, and metabolic flux by the macrophages polarizing with distinct stimuli and under different pathologic conditions, and particularly analyzes how altered serine metabolism rewires the metabolic behaviors of polarizing macrophages and their genetic and epigenetic reprogramming. RESULTS: Macrophages dynamically change serine metabolism to orchestrate their anabolism, redox balance, mitochondrial function, epigenetics, and post-translation modification, and thus match the distinct needs for both classical and alternative activation. CONCLUSION: Serine metabolism coordinates multiple metabolic pathways to tailor macrophage polarization and their responses to different pathogenic attacks and thus holds the potential as therapeutic target for types of acute and chronic inflammatory diseases.

Serine metabolism contributes to cell survival by regulating extracellular pH and providing an energy source in Saccharomyces cerevisiae.

Changes in extracellular pH affect the homeostasis and survival of unicellular organisms. Supplementation of culture media with amino acids can extend the lifespan of budding yeast, Saccharomyces cerevisiae, by alleviating the decrease in pH. However, the optimal amino acids to use to achieve this end, and the underlying mechanisms involved, remain unclear. Here, we describe the specific role of serine metabolism in the regulation of pH in a medium. The addition of serine to synthetic minimal medium suppressed acidification, and at higher doses increased the pH. CHA1, which encodes a catabolic serine hydratase that degrades serine into ammonium and pyruvate, is essential for serine-mediated alleviation of acidification. Moreover, serine metabolism supports extra growth after glucose depletion. Therefore, medium supplementation with serine can play a prominent role in the batch culture of budding yeast, controlling extracellular pH through catabolism into ammonium and acting as an energy source after glucose exhaustion.

Hypoxia-induced circSTT3A enhances serine synthesis and promotes H3K4me3 modification to facilitate breast cancer stem cell formation.

Hypoxia is a key feature of tumor microenvironment that contributes to the development of breast cancer stem cells (BCSCs) with strong self-renewal properties. However, the specific mechanism underlying hypoxia in BCSC induction is not completely understood. Herein, we provide evidence that a novel hypoxia-specific circSTT3A is significantly upregulated in clinical breast cancer (BC) tissues, and is closely related to the clinical stage and poor prognosis of patients with BC. The study revealed that hypoxia-inducible factor 1 alpha (HIF1α)-regulated circSTT3A has a remarkable effect on mammosphere formation in breast cancer cells. Mechanistically, circSTT3A directly interacts with nucleotide-binding domain of heat shock protein 70 (HSP70), thereby facilitating the recruitment of phosphoglycerate kinase 1 (PGK1) via its substrate-binding domain, which reduces the ubiquitination and increases the stability of PGK1. The enhanced levels of PGK1 catalyze 1,3-diphosphoglycerate (1,3-BPG) into 3-phosphoglycerate (3-PG) leading to 3-PG accumulation and increased serine synthesis, S-adenosylmethionine (SAM) accumulation, and trimethylation of histone H3 lysine 4 (H3K4me3). The activation of the H3K4me3 contributes to BCSCs by increasing the transcriptional level of stemness-related factors. Especially, our work reveals that either loss of circSTT3A or PGK1 substantially suppresses tumor initiation and tumor growth, which dramatically increases the sensitivity of tumors to doxorubicin (DOX) in mice. Injection of PGK1-silenced spheroids with 3-PG can significantly reverse tumor initiation and growth in mice, thereby increasing tumor resistance to DOX. In conclusion, our study sheds light on the functional role of hypoxia in the maintenance of BCSCs via circSTT3A/HSP70/PGK1-mediated serine synthesis, which provides new insights into metabolic reprogramming, tumor initiation and growth. Our findings suggest that targeting circSTT3A alone or in combination with chemotherapy has potential clinical value for BC management.

Mitochondrial FAD shortage in SLC25A32 deficiency affects folate-mediated one-carbon metabolism.

The SLC25A32 dysfunction is associated with neural tube defects (NTDs) and exercise intolerance, but very little is known about disease-specific mechanisms due to a paucity of animal models. Here, we generated homozygous (Slc25a32Y174C/Y174C and Slc25a32K235R/K235R) and compound heterozygous (Slc25a32Y174C/K235R) knock-in mice by mimicking the missense mutations identified from our patient. A homozygous knock-out (Slc25a32-/-) mouse was also generated. The Slc25a32K235R/K235R and Slc25a32Y174C/K235R mice presented with mild motor impairment and recapitulated the biochemical disturbances of the patient. While Slc25a32-/- mice die in utero with NTDs. None of the Slc25a32 mutations hindered the mitochondrial uptake of folate. Instead, the mitochondrial uptake of flavin adenine dinucleotide (FAD) was specifically blocked by Slc25a32Y174C/K235R, Slc25a32K235R/K235R, and Slc25a32-/- mutations. A positive correlation between SLC25A32 dysfunction and flavoenzyme deficiency was observed. Besides the flavoenzymes involved in fatty acid ß-oxidation and amino acid metabolism being impaired, Slc25a32-/- embryos also had a subunit of glycine cleavage system-dihydrolipoamide dehydrogenase damaged, resulting in glycine accumulation and glycine derived-formate reduction, which further disturbed folate-mediated one-carbon metabolism, leading to 5-methyltetrahydrofolate shortage and other folate intermediates accumulation. Maternal formate supplementation increased the 5-methyltetrahydrofolate levels and ameliorated the NTDs in Slc25a32-/- embryos. The Slc25a32K235R/K235R and Slc25a32Y174C/K235R mice had no glycine accumulation, but had another formate donor-dimethylglycine accumulated and formate deficiency. Meanwhile, they suffered from the absence of all folate intermediates in mitochondria. Formate supplementation increased the folate amounts, but this effect was not restricted to the Slc25a32 mutant mice only. In summary, we established novel animal models, which enabled us to understand the function of SLC25A32 better and to elucidate the role of SLC25A32 dysfunction in human disease development and progression.

Perfluorooctanoic acid alters the developmental trajectory of female germ cells and embryos in rodents and its potential mechanism.

The epidemiological studies regarding perfluorooctanoic acid (PFOA) suggests that its exposure causes reproductive health issues, the underlying mechanisms of which are still in its infancy. Here, we report that PFOA deteriorates female reproduction at multiple development stages. Oocyte meiosis and preimplantation development are severely impaired by PFOA with oxidative stress being a contributor. Supplementing with antioxidant melatonin partially rescues oocyte meiotic maturation and non-apoptotic demise. The attenuation in ovarian follicle development however can be improved by metformin but not melatonin. Importantly, metformin blunts PFOA-induced fetal growth retardation (FGR) and such protective effect could be recapitulated by transplantation of fecal material and pharmacological activation of AMPK. Mechanistically, PFOA causes gut microbiota dysbiosis, which might thereby rewire host metabolism of L-phenylalanine, histamine and L-palmitoylcarnitine that triggers hyperphenylalaninaemia, inflammation and ferroptosis to initiate FGR. Deregulated serine metabolism by the gut microbe constitutes an alternative mechanism underlying PFOA-induced FGR in that modulation of serine in dam's diet phenocopied the FGR. Our study expands the understanding of risk factors that impair human reproductive health, and proposes restoration of gut microbiota diversity and intervention of metabolism as therapeutics mitigating health risks predisposed by environmental perturbation.

Effect of selectively knocking down key metabolic genes in Müller glia on photoreceptor health.

The importance of Müller glia for retinal homeostasis suggests that they may have vulnerabilities that lead to retinal disease. Here, we studied the effect of selectively knocking down key metabolic genes in Müller glia on photoreceptor health. Immunostaining indicated that murine Müller glia expressed insulin receptor (IR), hexokinase 2 (HK2) and phosphoglycerate dehydrogenase (PHGDH) but very little pyruvate dehydrogenase E1 alpha 1 (PDH-E1α) and lactate dehydrogenase A (LDH-A). We crossed Müller glial cell-CreER (MC-CreER) mice with transgenic mice carrying a floxed IR, HK2, PDH-E1α, LDH-A, or PHGDH gene to study the effect of selectively knocking down key metabolic genes in Müller glia cells on retinal health. Selectively knocking down IR, HK2, or PHGDH led to photoreceptor degeneration and reduced electroretinographic responses. Supplementing exogenous l-serine prevented photoreceptor degeneration and improved retinal function in MC-PHGDH knockdown mice. We unexpectedly found that the levels of retinal serine and glycine were not reduced but, on the contrary, highly increased in MC-PHGDH knockdown mice. Moreover, dietary serine supplementation, while rescuing the retinal phenotypes caused by genetic deletion of PHGDH in Müller glial cells, restored retinal serine and glycine homeostasis probably through regulation of serine transport. No retinal abnormalities were observed in MC-CreER mice crossed with PDH-E1α- or LDH-A-floxed mice despite Cre expression. Our findings suggest that Müller glia do not complete glycolysis but use glucose to produce serine to support photoreceptors. Supplementation with exogenous serine is effective in preventing photoreceptor degeneration caused by PHGDH deficiency in Müller glia.

Epilepsy in inherited neurotransmitter disorders: Spotlights on pathophysiology and clinical management.

Inborn errors of neurotransmitter metabolism are ultrarare disorders affecting neurotransmitter biosynthesis, breakdown or transport or their essential cofactors. Neurotransmitter dysfunctions could also result from the impairment of neuronal receptors, intracellular signaling, vesicle release or other synaptic abnormalities. Epilepsy is the main clinical hallmark in some of these diseases (e.g. disorders of GABA metabolism, glycine encephalopathy) while it is infrequent in others (e.g. all the disorders of monoamine metabolism in exception for dihydropteridine reductase deficiency). This review analyzes the epileptogenic mechanisms, the epilepsy phenotypes and the principle for the clinical management of epilepsy in primary and secondary inherited disorders of neurotransmitter metabolism (disorders of GABA, serine and glycine metabolism, disorders of neurotransmitter receptors and secondary neurotransmitter diseases).

Effects of arsenic exposure on D-serine metabolism in the hippocampus of offspring mice at different developmental stages.

The main purpose of this study was to verify the hypothesis that cognitive dysfunctions induced by arsenic exposure were related to the changes of D-serine metabolism in the hippocampus of offspring mice. Mother mice and their offsprings were exposed to 0, 15, 30 or 60 mg/L sodium arsenite (NaAsO2) through drinking water from the first day of gestation until the end of lactation. D-serine levels in the hippocampus of mice of postnatal day (PND) 10, 20 and 40 were examined by high-performance liquid chromatography. Expressions of serine racemase (SR), D-amino acid oxidase (DAAO), alanine-serine-cysteine transporter-1 (asc-1) and subunits of N-methyl-D-aspartate receptors (NMDARs) in the hippocampus of mice were measured by Western blot and Real-time RT-PCR. Results showed that arsenic exposure significantly decreased D-serine levels of mice exposed to 60 mg/L NaAsO2. Exposure to 60 mg/L NaAsO2 could inhibit both mRNA and protein expression of SR, whereas increase in the protein expression of DAAO, only enhances the mRNA levels of DAAO of PND 20 mice. In addition, arsenic exposure could upregulate protein expression of asc-1. The mRNA and protein levels of NR1, NR2A and NR2B in the hippocampus of mice were down-regulated by arsenic. Findings from this study suggested that SR might play an important role in the reduction of D-serine levels caused by arsenic exposure, which might further influence the levels of NMDAR subunits especially on PND20, and then might disturb the function of NMDARs and cause the deficits of learning and memory ability of offspring mice.

Analysis of glucose-derived amino acids involved in one-carbon and cancer metabolism by stable-isotope tracing gas chromatography mass spectrometry.

A major hallmark of cancer is a perturbed metabolism resulting in high demand for various metabolites, glucose being the most well studied. While glucose can be converted into pyruvate for ATP production, the serine synthesis pathway (SSP) can divert glucose to generate serine, glycine, and methionine. In the process, the carbon unit from serine is incorporated into the one-carbon pool which makes methionine and maintains S-adenosylmethionine levels, which are needed to maintain the epigenetic landscape and ultimately controlling what genes are available for transcription. Alternatively, the carbon unit can be used for purine and thymidylate synthesis. We present here an approach to follow the flux through this pathway in cultured human cells using stable isotope enriched glucose and gas chromatography mass spectrometry analysis of serine, glycine, and methionine. We demonstrate that in three different cell lines this pathway contributes only 1-2% of total intracellular methionine. This suggests under high extracellular methionine conditions, the predominance of carbon units from this pathway are used to synthesize nucleic acids.

Rethinking the evolution of eukaryotic metabolism: novel cellular partitioning of enzymes in stramenopiles links serine biosynthesis to glycolysis in mitochondria.

BACKGROUND: An important feature of eukaryotic evolution is metabolic compartmentalization, in which certain pathways are restricted to the cytosol or specific organelles. Glycolysis in eukaryotes is described as a cytosolic process. The universality of this canon has been challenged by recent genome data that suggest that some glycolytic enzymes made by stramenopiles bear mitochondrial targeting peptides. RESULTS: Mining of oomycete, diatom, and brown algal genomes indicates that stramenopiles encode two forms of enzymes for the second half of glycolysis, one with and the other without mitochondrial targeting peptides. The predicted mitochondrial targeting was confirmed by using fluorescent tags to localize phosphoglycerate kinase, phosphoglycerate mutase, and pyruvate kinase in Phytophthora infestans, the oomycete that causes potato blight. A genome-wide search for other enzymes with atypical mitochondrial locations identified phosphoglycerate dehydrogenase, phosphoserine aminotransferase, and phosphoserine phosphatase, which form a pathway for generating serine from the glycolytic intermediate 3-phosphoglycerate. Fluorescent tags confirmed the delivery of these serine biosynthetic enzymes to P. infestans mitochondria. A cytosolic form of this serine biosynthetic pathway, which occurs in most eukaryotes, is missing from oomycetes and most other stramenopiles. The glycolysis and serine metabolism pathways of oomycetes appear to be mosaics of enzymes with different ancestries. While some of the noncanonical oomycete mitochondrial enzymes have the closest affinity in phylogenetic analyses with proteins from other stramenopiles, others cluster with bacterial, plant, or animal proteins. The genes encoding the mitochondrial phosphoglycerate kinase and serine-forming enzymes are physically linked on oomycete chromosomes, which suggests a shared origin. CONCLUSIONS: Stramenopile metabolism appears to have been shaped through the acquisition of genes by descent and lateral or endosymbiotic gene transfer, along with the targeting of the proteins to locations that are novel compared to other eukaryotes. Colocalization of the glycolytic and serine biosynthesis enzymes in mitochondria is apparently necessary since they share a common intermediate. The results indicate that descriptions of metabolism in textbooks do not cover the full diversity of eukaryotic biology.

Structure-function relationships in human d-amino acid oxidase variants corresponding to known SNPs.

In the brain, d-amino acid oxidase plays a key role in modulating the N-methyl-d-aspartate receptor (NMDAR) activation state, catalyzing the stereospecific degradation of the coagonist d-serine. A relationship between d-serine signaling deregulation, NMDAR dysfunction, and CNS diseases is presumed. Notably, the R199W substitution in human DAAO (hDAAO) was associated with familial amyotrophic lateral sclerosis (ALS), and further coding substitutions, i.e., R199Q and W209R, were also deposited in the single nucleotide polymorphism database. Here, we investigated the biochemical properties of these different hDAAO variants. The W209R hDAAO variant shows an improved d-serine degradation ability (higher activity and affinity for the cofactor FAD) and produces a greater decrease in cellular d/(d+l) serine ratio than the wild-type counterpart when expressed in U87 cells. The production of H2O2 as result of excessive d-serine degradation by this hDAAO variant may represent the factor affecting cell viability after stable transfection. The R199W/Q substitution in hDAAO altered the protein conformation and enzymatic activity was lost under conditions resembling the cellular ones: this resulted in an abnormal increase in cellular d-serine levels. Altogether, these results indicate that substitutions that affect hDAAO functionality directly impact on d-serine cellular levels (at least in the model cell system used). The pathological effect of the expression of the R199W hDAAO, as observed in familial ALS, originates from both protein instability and a decrease in kinetic efficiency: the increase in synaptic d-serine may be mainly responsible for the neurotoxic effect. This information is expected to drive future targeted treatments.

Organ-Specific Cancer Metabolism and Its Potential for Therapy.

Targeting cancer metabolism has the potential to lead to major advances in tumor therapy. Numerous promising metabolic drug targets have been identified. Yet, it has emerged that there is no singular metabolism that defines the oncogenic state of the cell. Rather, the metabolism of cancer cells is a function of the requirements of a tumor. Hence, the tissue of origin, the (epi)genetic drivers, the aberrant signaling, and the microenvironment all together define these metabolic requirements. In this chapter we discuss in light of (epi)genetic, signaling, and environmental factors the diversity in cancer metabolism based on triple-negative and estrogen receptor-positive breast cancer, early- and late-stage prostate cancer, and liver cancer. These types of cancer all display distinct and partially opposing metabolic behaviors (e.g., Warburg versus reverse Warburg metabolism). Yet, for each of the cancers, their distinct metabolism supports the oncogenic phenotype. Finally, we will assess the therapeutic potential of metabolism based on the concepts of metabolic normalization and metabolic depletion.

Identification of a premature stop codon mutation in the PHGDH gene in severe Neu-Laxova syndrome-evidence for phenotypic variability.

In some cases Neu-Laxova syndrome (NLS) is linked to serine deficiency due to mutations in the phosphoglycerate dehydrogenase (PHGDH) gene. We describe the prenatal and postnatal findings in a fetus with one of the most severe NLS phenotypes described so far, caused by a homozygous nonsense mutation of PHGDH. Serial ultrasound (US) and pre- and postnatal magnetic resonance imaging (MRI) evaluations were performed. Prenatally, serial US evaluations suggested symmetric growth restriction, microcephaly, hypoplasia of the cerebellar vermis, micrognathia, hydrops, shortened limbs, arthrogryposis, and talipes equinovarus. The prenatal MRI confirmed these findings prompting a diagnosis of NLS. After birth, radiological imaging did not detect any gross bone abnormalities. DNA was extracted from fetal and parental peripheral blood, all coding exons of PHGDH were PCR-amplified and subjected to Sanger sequencing. Sequencing of PHGDH identified a homozygous premature stop codon mutation (c.1297C>T; p.Gln433*) in fetal DNA, both parents (first-cousins) being heterozygotes. Based on previous associations of mutations in this gene with a milder NLS phenotype, as well as cases of serine deficiency, these observations lend further support to a genotype-phenotype correlation between the degree of PHGDH inactivation and disease severity.

The enzymes of serine synthesis pathway in cancer metastasis.

Metastasis, the major cause of cancer mortality, requires cancer cells to reprogram their metabolism to adapt to and thrive in different environments, thereby leaving metastatic cells metabolic characteristics different from their parental cells. Mounting research has revealed that the de novo serine synthesis pathway (SSP), a glycolytic branching pathway that consumes glucose carbons for serine makeup and α-ketoglutarate generation and thus supports the proliferation, survival, and motility of cancer cells, is one such reprogrammed metabolic pathway. During different metastatic cascades, the SSP enzyme proteins or their enzymatic activity are both dynamically altered; manipulating their expression or catalytic activity could effectively prevent the progression of cancer metastasis; and the SSP enzymatic proteins could even conduce to metastasis via their nonenzymatic functions. In this article we overview the SSP dynamics during cancer metastasis and put the focuses on the regulatory role of the SSP in metastasis and the underlying mechanisms that mainly involve cellular anabolism/catabolism, redox balance, and epigenetics, aiming to provide a theoretical basis for the development of therapeutic strategies for targeting metastatic lesions.

Lactylation-Driven IGF2BP3-Mediated Serine Metabolism Reprogramming and RNA m6A-Modification Promotes Lenvatinib Resistance in HCC.

Acquired resistance remains a bottleneck for molecular-targeted therapy in advanced hepatocellular carcinoma (HCC). Metabolic adaptation and epigenetic remodeling are recognized as hallmarks of cancer that may contribute to acquired resistance. In various lenvatinib-resistant models, increased glycolysis leads to lactate accumulation and lysine lactylation of IGF2BP3. This lactylation is crucial for capturing PCK2 and NRF2 mRNAs, thereby enhancing their expression. This process reprograms serine metabolism and strengthens the antioxidant defense system. Additionally, altered serine metabolism increases the availability of methylated substrates, such as S-adenosylmethionine (SAM), for N6-methyladenosine (m6A) methylation of PCK2 and NRF2 mRNAs. The lactylated IGF2BP3-PCK2-SAM-m6A loop maintains elevated PCK2 and NRF2 levels, enhancing the antioxidant system and promoting lenvatinib resistance in HCC. Treatment with liposomes carrying siRNAs targeting IGF2BP3 or the glycolysis inhibitor 2-DG restored lenvatinib sensitivity in vivo. These findings highlight the connection between metabolic reprogramming and epigenetic regulation and suggest that targeting metabolic pathways may offer new strategies to overcome lenvatinib resistance in HCC.

Classical swine fever virus inhibits serine metabolism-mediated antiviral immunity by deacetylating modified PHGDH.

Classical swine fever virus (CSFV), an obligate intracellular pathogen, hijacks cellular metabolism to evade immune surveillance and facilitate its replication. The precise mechanisms by which CSFV modulates immune metabolism remain largely unknown. Our study reveals that CSFV infection disrupts serine metabolism, which plays a crucial role in antiviral immunity. Notably, we discovered that CSFV infection leads to the deacetylation of PHGDH, a key enzyme in serine metabolism, resulting in autophagic degradation. This deacetylation impairs PHGDH's enzymatic activity, reduces serine biosynthesis, weakens innate immunity, and promotes viral proliferation. Molecularly, CSFV infection induces the association of HDAC3 with PHGDH, leading to deacetylation at the K364 site. This modification attracts the E3 ubiquitin ligase RNF125, which facilitates the addition of K63-linked ubiquitin chains to PHGDH-K364R. Subsequently, PHGDH is targeted for lysosomal degradation by p62 and NDP52. Furthermore, the deacetylation of PHGDH disrupts its interaction with the NAD+ substrate, destabilizing the PHGDH-NAD complex, impeding the active site, and thereby inhibiting de novo serine synthesis. Additionally, our research indicates that deacetylated PHGDH suppresses the mitochondria-MAVS-IRF3 pathway through its regulatory effect on serine metabolism, leading to decreased IFN-ß production and enhanced viral replication. Overall, our findings elucidate the complex interplay between CSFV and serine metabolism, revealing a novel aspect of viral immune evasion through the lens of immune metabolism. IMPORTANCE: Classical swine fever (CSF) seriously restricts the healthy development of China's aquaculture industry, and the unclear pathogenic mechanism and pathogenesis of classical swine fever virus (CSFV) are the main obstacle to CSF prevention, control, and purification. Therefore, it is of great significance to explore the molecular mechanism of CSFV and host interplay, to search for the key signaling pathways and target molecules in the host that regulate the replication of CSFV infection, and to elucidate the mechanism of action of host immune dysfunction and immune escape due to CSFV infection for the development of novel CSFV vaccines and drugs. This study reveals the mechanism of serine metabolizing enzyme post-translational modifications and antiviral signaling proteins in the replication of CSFV and enriches the knowledge of CSFV infection and immune metabolism.