Therapeutic benefits of the methyl donor S-adenosylmethionine on nerve injury–induced mechanical hypersensitivity and cognitive impairment in mice

Dysfunction of Small-Conductance Ca2+-Activated Potassium (SK) Channels Drives Amygdala Hyperexcitability and Neuropathic Pain Behaviors: Involvement of Epigenetic Mechanisms

Neuroplasticity in the amygdala and its central nucleus (CeA) is linked to pain modulation and pain behaviors, but cellular mechanisms are not well understood. Here, we addressed the role of small-conductance Ca2+-activated potassium (SK) channels in pain-related amygdala plasticity. The facilitatory effects of the intra-CeA application of an SK channel blocker (apamin) on the pain behaviors of control rats were lost in a neuropathic pain model, whereas an SK channel activator (NS309) inhibited pain behaviors in neuropathic rats but not in sham controls, suggesting the loss of the inhibitory behavioral effects of amygdala SK channels. Brain slice electrophysiology found hyperexcitability of CeA neurons in the neuropathic pain condition due to the loss of SK channel-mediated medium afterhyperpolarization (mAHP), which was accompanied by decreased SK2 channel protein and mRNA expression, consistent with a pretranscriptional mechanisms. The underlying mechanisms involved the epigenetic silencing of the SK2 gene due to the increased DNA methylation of the CpG island of the SK2 promoter region and the change in methylated CpG sites in the CeA in neuropathic pain. This study identified the epigenetic dysregulation of SK channels in the amygdala (CeA) as a novel mechanism of neuropathic pain-related plasticity and behavior that could be targeted to control abnormally enhanced amygdala activity and chronic neuropathic pain.

Clemastine-induced enhancement of hippocampal myelination alleviates memory impairment in mice with chronic pain

Patients with chronic pain often experience memory impairment, but the underlying mechanisms remain elusive. The myelin sheath is crucial for rapid and accurate action potential conduction, playing a pivotal role in the development of cognitive abilities in the central nervous system. The study reveals that myelin degradation occurs in the hippocampus of chronic constriction injury (CCI) mice, which display both chronic pain and memory impairment. Using fiber photometry, we observed diminished task-related neuronal activity in the hippocampus of CCI mice. Interestingly, the repeated administration with clemastine, which promotes myelination, counteracts the CCI-induced myelin loss and reduced neuronal activity. Notably, clemastine specifically ameliorates the impaired memory without affecting chronic pain in CCI mice. Overall, our findings highlight the significant role of myelin abnormalities in CCI-induced memory impairment, suggesting a potential therapeutic approach for treating memory impairments associated with neuropathic pain.

The Epigenetics of Neuropathic Pain: A Systematic Update

Epigenetics deals with alterations to the gene expression that occur without change in the nucleotide sequence in the DNA. Various covalent modifications of the DNA and/or the surrounding histone proteins have been revealed, including DNA methylation, histone acetylation, and methylation, which can either stimulate or inhibit protein expression at the transcriptional level. In the past decade, an exponentially increasing amount of data has been published on the association between epigenetic changes and the pathomechanism of pain, including its most challenging form, neuropathic pain. Epigenetic regulation of the chromatin by writer, reader, and eraser proteins has been revealed for diverse protein targets involved in the pathomechanism of neuropathic pain. They include receptors, ion channels, transporters, enzymes, cytokines, chemokines, growth factors, inflammasome proteins, etc. Most work has been invested in clarifying the epigenetic downregulation of mu opioid receptors and various K+ channels, two types of structures mediating neuronal inhibition. Conversely, epigenetic upregulation has been revealed for glutamate receptors, growth factors, and lymphokines involved in neuronal excitation. All these data cannot only help better understand the development of neuropathic pain but outline epigenetic writers, readers, and erasers whose pharmacological inhibition may represent a novel option in the treatment of pain.

Integration of microbiota and metabolomics reveals the analgesic mechanisms of emodin against neuropathic pain

BACKGROUND AND OBJECTIVE

Neuropathic pain (NeP) induced dysbiosis of intestinal microbiota in chronic constriction injury (CCI) rats. Emodin has analgesic effect but the detailed mechanism is not clear at the present time. This study aims to explore the underling mechanism of action of emodin against NeP with in CCI model.

METHODS

Male SD rats (180-220 g) were randomly divided into three groups: sham group, CCI group, and emodin group. Behavioral tests were performed to evaluate the therapeutic effects of emodin on CCI model. Feces and spinal cords of all rats were collected 15 days after surgery. 16S rDNA sequencing, untargeted metabolomics, qPCR and ELISA were performed.

RESULTS

Mechanical withdrawal thresholds (MWT), thermal withdrawal latency (TWL) and Sciatic functional index (SFI) in emodin group were significantly higher than CCI group (P < 0.05). Emodin not only inhibited the expression of pro-inflammatory cytokines in the spinal cords and colonic tissue, but also increased the expression of tight junction protein in colonic tissue. 16S rDNA sequencing showed that emodin treatment changed the community structure of intestinal microbiota in CCI rats. Untargeted metabolomics analysis showed that 33 differential metabolites were screened out between CCI group and emodin group. After verification, we found that emodin increased the level of S-adenosylmethionine (SAM) and Histamine in the spinal cord of CCI rats.

CONCLUSION

Emodin was effective in relieving neuropathic pain, which is linked to inhibition inflammatory response, increasing the proportion of beneficial bacteria and beneficial metabolites.

Characterization and designing of an SAM riboswitch to establish a high-throughput screening platform for SAM overproduction in Saccharomyces cerevisiae

S-adenosyl- l-methionine (SAM) is a high-value compound widely used in the treatment of various diseases. SAM can be produced through fermentation, but further enhancing the microbial production of SAM requires novel high-throughput screening methods for rapid detection and screening of mutant libraries. In this work, an SAM-OFF riboswitch capable of responding to the SAM concentration was obtained and a high-throughput platform for screening SAM overproducers was established. SAM synthase was engineered by semirational design and directed evolution, which resulted in the SAM2S203F,W164R,T251S,Y285F,S365R mutant with almost twice higher catalytic activity than the parental enzyme. The best mutant was then introduced into Saccharomyces cerevisiae BY4741, and the resulting strain BSM8 produced a sevenfold higher SAM titer in shake-flask fermentation, reaching 1.25 g L-1 . This work provides a reference for designing biosensors to dynamically detect metabolite concentrations for high-throughput screening and the construction of effective microbial cell factories.

The role of epigenetic modification in postoperative cognitive dysfunction

With the ageing of the population, the health problems of elderly individuals have become particularly important. Through a large number of clinical studies and trials, it has been confirmed that elderly patients can experience postoperative cognitive dysfunction after general anesthesia/surgery. However, the mechanism of postoperative cognitive dysfunction is still unknown. In recent years, the role of epigenetics in postoperative cognitive dysfunction has been widely studied and reported. Epigenetics includes the genetic structure and biochemical changes of chromatin not involving changes in the DNA sequence. This article summarizes the epigenetic mechanism of cognitive impairment after general anesthesia/surgery and analyses the broad prospects of epigenetics as a therapeutic target for postoperative cognitive dysfunction.

Understanding the initiation, delivery and processing of bone cancer pain from the peripheral to the central nervous system

Bone cancer pain is a complex condition characterized by persistent, sudden, spontaneous pain accompanied by hyperalgesia that typically arises from bone metastases or primary bone tumors, causing severe discomfort and significantly diminishing cancer patients' quality of life and confidence in their ability to overcome the disease. It is widely known that peripheral nerves are responsible for detecting harmful stimuli, which are then transmitted to the brain via the spinal cord, resulting in the perception of pain. In the case of bone cancer, tumors and stromal cells within the bone marrow release various chemical signals, including inflammatory factors, colony-stimulating factors, chemokines, and hydrogen ions. Consequently, the nociceptors located at the nerve endings within the bone marrow sense these chemical signals, generating electrical signals that are then transmitted to the brain through the spinal cord. Subsequently, the brain processes these electrical signals in a complex manner to create the sensation of bone cancer pain. Numerous studies have investigated the transmission of bone cancer pain from the periphery to the spinal cord. However, the processing of pain information induced by bone cancer within the brain remains unclear. With the continuous advancements in brain science and technology, the brain mechanism of bone cancer pain would become more clearly understood. Herein, we focus on summarizing the peripheral nerve perception of the spinal cord transmission of bone cancer pain and provide a brief overview of the ongoing research regarding the brain mechanisms involved in bone cancer pain.

The pro-resolving lipid mediator Maresin 1 ameliorates pain responses and neuroinflammation in the spared nerve injury-induced neuropathic pain: A study in male and female mice

Specialized pro-resolving mediators (SPMs) have recently emerged as promising therapeutic approaches for neuropathic pain (NP). We evaluated the effects of oral treatment with the SPM Maresin 1 (MaR1) on behavioral pain responses and spinal neuroinflammation in male and female C57BL/6J mice with spared nerve injury (SNI)-induced NP. MaR1, or vehicle, was administered once daily, on post-surgical days 3 to 5, by voluntary oral intake. Sensory-discriminative and affective-motivational components of pain were evaluated with von Frey and place escape/avoidance paradigm (PEAP) tests, respectively. Spinal microglial and astrocytic activation were assessed by immunofluorescence, and the spinal concentration of cytokines IL-1β, IL-6, IL-10, and macrophage colony-stimulating factor (M-CSF) were evaluated by multiplex immunoassay. MaR1 treatment reduced SNI-induced mechanical hypersensitivity on days 7 and 11 in both male and female mice, and appeared to ameliorate the affective component of pain in males on day 11. No definitive conclusions could be drawn about the impact of MaR1 on the affective-motivational aspects of pain in female mice, since repeated suprathreshold mechanical stimulation of the affected paw in the dark compartment did not increase the preference of vehicle-treated SNI females for the light side, during the PEAP test session (a fundamental assumption for PAEP's validity). MaR1 treatment also reduced ipsilateral spinal microglial and astrocytic activation in both sexes and marginally increased M-CSF in males, while not affecting cytokines IL-1β, IL-6 and IL-10 in either sex. In summary, our study has shown that oral treatment with MaR1 (i) produces antinociception even in an already installed peripheral NP mouse model, and (ii) this antinociception may extend for several days beyond the treatment time-frame. These therapeutic effects are associated with attenuated microglial and astrocytic activation in both sexes, and possibly involve modulation of M-CSF action in males.

Intraperitoneal 5-Azacytidine Alleviates Nerve Injury-Induced Pain in Rats by Modulating DNA Methylation

To investigate the role of DNA methylation in modulating chronic neuropathic pain (NPP), identify possible target genes of DNA methylation involved in this process, and preliminarily confirm the medicinal value of the DNA methyltransferases (DNMTs) inhibitor 5-azacytidine (5-AZA) in NPP by targeting gene methylation. Two rat NPP models, chronic constriction injury (CCI) and spinal nerve ligation (SNL), were used. The DNA methylation profiles in the lumbar spinal cord were assayed using an Arraystar Rat RefSeq Promoter Array. The underlying genes with differential methylation were then identified and submitted to Gene Ontology and pathway analysis. Methyl-DNA immunoprecipitation quantitative PCR (MeDIP-qPCR) and quantitative reverse transcription-PCR (RT-qPCR) were used to confirm gene methylation and expression. The protective function of 5-AZA in NPP and gene expression were evaluated via behavioral assays and RT-qPCR, respectively. Analysis of the DNA methylation patterns in the lumbar spinal cord indicated that 1205 differentially methylated fragments in CCI rats were located within DNA promoter regions, including 638 hypermethylated fragments and 567 hypomethylated fragments. The methylation levels of Grm4, Htr4, Adrb2, Kcnf1, Gad2, and Pparg, which are associated with long-term potentiation (LTP) and glutamatergic synapse pathways, were increased with a corresponding decrease in their mRNA expression, in the spinal cords of CCI rats. Moreover, we found that the intraperitoneal injection of 5-AZA (4 mg/kg) attenuated CCI- or SNL-induced mechanical allodynia and thermal hyperalgesia. Finally, the mRNA expression of hypermethylated genes such as Grm4, Htr4, Adrb2, Kcnf1, and Gad2 was reversed after 5-AZA treatment. CCI induced widespread methylation changes in the DNA promoter regions in the lumbar spinal cord. Intraperitoneal 5-AZA alleviated hyperalgesia in CCI and SNL rats, an effect accompanied by the reversed expression of hypermethylated genes. Thus, DNA methylation inhibition represents a promising epigenetic strategy for protection against chronic NPP following nerve injury. Our study lays a theoretical foundation for 5-AZA to become a clinical targeted drug.

Sex-specific effects of neuropathic pain on long-term pain behavior and mortality in mice

ABSTRACT

Human epidemiological studies suggest that chronic pain can increase mortality risk. We investigated whether this was true in mice so that underlying mechanisms might be identified. At 10 weeks of age, C57BL/6 mice of both sexes received sham or spared nerve injury (SNI) surgery producing neuropathic pain. Mice were weighed monthly, tested behaviorally for mechanical and cold sensitivity and guarding behavior every 3 months postsurgery, and otherwise left undisturbed in their cages until death by natural causes. Evidence of pain over the lifespan displayed a strikingly sex-specific pattern. Male mice displayed largely stable mechanical and cold hypersensitivity and guarding at 6 to 30 months post-SNI. By contrast, female mice displayed a biphasic temporal pattern of mechanical hypersensitivity and guarding behavior, with a complete resolution of SNI-induced pain behavior at 6 to 9 months post-SNI followed by the return of pain thereafter. Mouse lifespan was not significantly altered by SNI in either sex nor was frailty as assessed by cage inspection in the last 6 months of life. However, in male mice with SNI, we observe a significant correlation between average lifetime mechanical hypersensitivity and lifespan, such that death occurred sooner in male mice exhibiting more evidence of chronic pain. This relationship was not observed in female SNI mice nor in sham-operated mice of either sex. This experiment is the first to investigate pain behavior over an entire adult lifetime and suggests that biology of relevance to human chronic pain is being ignored by the very short timespans of most extant preclinical pain research.

Transient Receptor Potential Ankyrin 1 (TRPA1) Methylation and Chronic Pain: A Systematic Review

BACKGROUND AND OBJECTIVE

Chronic pain represents a major global health issue in terms of psycho-physiological, therapeutic, and economic burden, not limited to adults but also to the pediatric age. Despite its great impact, its molecular mechanisms have still not been completely unraveled. Focusing on the impact of epigenetics in the pain complex trait, we assessed the association between chronic pain and the methylation pattern of TRPA1, a key gene related to pain sensitivity.

METHODS

We conducted a systematic review retrieving articles from three different databases. After deduplication, 431 items were subjected to manual screening, and then 61 articles were selected and screened again. Of these, only six were maintained for meta-analysis and analyzed using specific R packages.

RESULTS

Six articles were divided into two groups (group 1: comparison of mean methylation levels between healthy subjects and patients with chronic pain; group 2: correlation between mean methylation levels and pain sensation). A non-significant mean difference was obtained from the analysis of group 1 with a value of 3.97 (95% C.I. -7.79; 15.73). Analysis of group 2 showed a high level of variability between studies (correlation = 0.35, 95% C.I. -0.12; 0.82) due to their heterogeneity (I2 = 97%, p < 0.01).

CONCLUSIONS

Despite the high variability observed in the different studies analyzed, our results suggest that hypermethylation and increased pain sensitivity could be connected, possibly due to the variation of TRPA1 expression.

Development of a synthetic transcription factor-based S-adenosylmethionine biosensor in Saccharomyces cerevisiae

S-Adenosylmethionine (SAM) is a crucial small-molecule metabolite widely used in food and medicine. The development of high-throughput biosensors for SAM biosynthesis can significantly improve the titer of SAM. This paper constructed a synthetic transcription factor (TF)-based biosensor for SAM detecting in Saccharomyces cerevisiae. The synthetic TF, named MetJ-hER-VP16, consists of an Escherichia coli-derived DNA-binding domain MetJ, GS linker, the human estrogen receptor binding domain hER, and the viral activation domain VP16. The synthetic biosensor is capable of sensing SAM in a dose-dependent manner with fluorescence as the output. Additionally, it is tightly regulated by the inducer SAM and β-estradiol, which means that the fluorescence output is only available when both are present together. The synthetic SAM biosensor could potentially be applied for high-throughput metabolic engineering and is expected to improve SAM production.

A decrease in NR2B expression mediated by DNA hypermethylation induces perioperative neurocognitive disorder in aged mice

AIMS

This study was designed to investigate the role of NR2B and the contribution of DNA methylation to NR2B expression in the pathogenesis of PND.

METHODS

Eighteen-month-old C57BL/6J mice were subjected to experimental laparotomy under 1.4% isoflurane anesthesia. Hippocampus-dependent learning and memory were evaluated by using the Barnes maze and contextual fear conditioning tests. The protein and mRNA expression levels of NR2B were evaluated by western blotting and qRT-PCR respectively, and the methylation of the NR2B gene was examined by using targeted bisulfite sequencing. Long-term synaptic plasticity (LTP) was measured by electrophysiology.

RESULTS

Mice that underwent laparotomy exhibited hippocampus-dependent cognitive deficits accompanied by decreased NR2B expressions and LTP deficiency. The overexpression of NR2B in the dorsal hippocampus could improve learning and memory in mice subjected to laparotomy. In particular, the decreased NR2B expressions induced by laparotomy was attributed to the NR2B gene hypermethylation. Preoperative administration of S-adenosylmethionine (SAM) could hypomethylate the NR2B gene, upregulate NR2B expression and improve LTP, exerting a dose-dependent therapeutic effect against PND. Moreover, inhibiting NR2B abrogated the benefits of SAM pretreatment.

CONCLUSIONS

Laparotomy cause hippocampus-dependent cognitive decline by hypermethylating the NR2B gene, allowing us to understand the pathogenesis of PND in an epigenetic landscape.

Effects of S-Adenosylmethionine on Cognition in Animals and Humans: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

There is increasing evidence that supplementation of S-adenosylmethionine (SAM) can improve cognitive function in animals and humans, although the outcomes are not always inconsistent.

OBJECTIVE

We conducted a systematic review and meta-analysis to evaluate the correlation between SAM supplementation and improved cognitive function.

METHODS

We searched studies in the PubMed, Cochrane Library, Embase, Web of Science, and Clinical Trials databases from January 1, 2002 to January 1, 2022. Risk of bias was assessed using the Cochrane risk of bias 2.0 (human studies) and the Systematic Review Center for Laboratory Animal Experimentation risk of bias (animal studies) tools; and evidence quality was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation. STATA software was employed to perform meta-analysis, and the random-effects models was used to evaluate the standardized mean difference with 95% confidence intervals.

RESULTS

Out of the 2,375 studies screened, 30 studies met the inclusion criteria. Meta-analyses of animal (p = 0.213) and human (p = 0.047) studies showed that there were no significant differences between the SAM supplementation and control groups. The results of the subgroup analyses showed that the animals aged ≤8 weeks (p = 0.027) and the intervention duration >8 weeks (p = 0.009) were significantly different compared to the controls. Additionally, the Morris water maze test (p = 0.005) used to assess the cognitive level of the animals revealed that SAM could enhance spatial learning and memory in animals.

CONCLUSION

SAM supplementation showed no significant improvement in cognition. Therefore, further studies are needed to assess the effectiveness of SAM supplementation.

STING Contributes to Cancer-Induced Bone Pain by Promoting M1 Polarization of Microglia in the Medial Prefrontal Cortex

The medial prefrontal cortex (mPFC) is the main cortical area for processing both sensory and affective aspects of pain. Recently, mPFC was reported to participate in cancer-induced bone pain (CIBP) via the mechanism of central inflammation. STING is a key component of neuroinflammation in the central neuron system by activating downstream TBK1 and NF-κB signaling pathways. We aimed to investigate whether STING regulated neuroinflammation in the mPFC in rat models of CIBP. It is worth noting that we found a significant upregulation of STING in the mPFC after CIBP, accompanied by activation of TBK1 and NF-κB signaling pathways. In addition, pain and anxiety-like behaviors were alleviated by intraperitoneal injection of the STING inhibitor C-176. Furthermore, in microglia GMI-R1 cells, C-176 reversed LPS-induced M1 polarization. Collectively, this evidence indicated that STING may contribute to cancer-induced bone pain by activating TBK1 and NF-κB, and by promoting M1 polarization of microglia in the mPFC.

Epigenetic Mechanisms of Postoperative Cognitive Impairment Induced by Anesthesia and Neuroinflammation

Cognitive impairment after surgery is a common problem, affects mainly the elderly, and can be divided into postoperative delirium and postoperative cognitive dysfunction. Both phenomena are accompanied by neuroinflammation; however, the precise molecular mechanisms underlying cognitive impairment after anesthesia are not yet fully understood. Anesthesiological drugs can have a longer-term influence on protein transcription, thus, epigenetics is a possible mechanism that impacts on cognitive function. Epigenetic mechanisms may be responsible for long-lasting effects and may implicate novel therapeutic approaches. Hence, we here summarize the existing literature connecting postoperative cognitive impairment to anesthesia. It becomes clear that anesthetics alter the expression of DNA and histone modifying enzymes, which, in turn, affect epigenetic markers, such as methylation, histone acetylation and histone methylation on inflammatory genes (e.g., TNF-alpha, IL-6 or IL1 beta) and genes which are responsible for neuronal development (such as brain-derived neurotrophic factor). Neuroinflammation is generally increased after anesthesia and neuronal growth decreased. All these changes can induce cognitive impairment. The inhibition of histone deacetylase especially alleviates cognitive impairment after surgery and might be a novel therapeutic option for treatment. However, further research with human subjects is necessary because most findings are from animal models.

Persistent inflammatory pain is linked with anxiety-like behaviors, increased blood corticosterone, and reduced global DNA methylation in the rat amygdala

Chronic pain increases the risk of developing anxiety, with limbic areas being likely neurological substrates. Despite high clinical relevance, little is known about the precise behavioral, hormonal, and brain neuroplastic correlates of anxiety in the context of persistent pain. Previous studies have shown that decreased nociceptive thresholds in chronic pain models are paralleled by anxiety-like behavior in rats, but there are conflicting ideas regarding its effects on the stress response and circulating corticosterone levels. Even less is known about the molecular mechanisms through which the brain encodes pain-related anxiety. This study examines how persistent inflammatory pain in a rat model would impact anxiety-like behaviors and corticosterone release, and whether these changes would be reflected in levels of global DNA methylation in brain areas involved in stress regulation. Complete Freund's adjuvant (CFA) or saline was administered in the right hindpaw of adult male Wistar rats. Behavioral testing included the measurement of nociceptive thresholds (digital anesthesiometer), motor function (open field test), and anxiety-like behaviors (elevated plus maze and the dark-light box test). Corticosterone was measured via radioimmunoassay. Global DNA methylation (enzyme immunoassay) as well as DNMT3a levels (western blotting) were quantified in the amygdala, prefrontal cortex, and ventral hippocampus. CFA administration resulted in persistent reduction in nociceptive threshold in the absence of locomotor abnormalities. Increased anxiety-like behaviors were observed in the elevated plus maze and were accompanied by increased blood corticosterone levels 10 days after pain induction. Global DNA methylation was decreased in the amygdala, with no changes in DNMT3a abundance in any of the regions examined. Persistent inflammatory pain promotes anxiety -like behaviors, HPA axis activation, and epigenetic regulation through DNA methylation in the amygdala. These findings describe a molecular mechanism that links pain and stress in a well-characterized rodent model.

Epigenetic modifications from arsenic exposure: A comprehensive review

Arsenic is a notorious element with the potential to harm exposed individuals in ways that include cancerous and non-cancerous health complications. Millions of people across the globe (especially in South and Southeast Asian countries including China, Vietnam, India and Bangladesh) are currently being unknowingly exposed to precarious levels of arsenic. Among the diverse effects associated with such arsenic levels of exposure is the propensity to alter the epigenome. Although a large volume of literature exists on arsenic-induced genotoxicity, cytotoxicity, and inter-individual susceptibility due to active research on these subject areas from the last millennial, it is only recently that attention has turned on the ramifications and mechanisms of arsenic-induced epigenetic changes. The present review summarizes the possible mechanisms involved in arsenic induced epigenetic alterations. It focuses on the mechanisms underlying epigenome reprogramming from arsenic exposure that result in improper cell signaling and dysfunction of various epigenetic components. The mechanistic information articulated from the review is used to propose a number of novel therapeutic strategies with a potential for ameliorating the burden of worldwide arsenic poisoning.

DNA Methylation and Non-Coding RNAs during Tissue-Injury Associated Pain

While about half of the population experience persistent pain associated with tissue damages during their lifetime, current symptom-based approaches often fail to reduce such pain to a satisfactory level. To provide better patient care, mechanism-based analgesic approaches must be developed, which necessitates a comprehensive understanding of the nociceptive mechanism leading to tissue injury-associated persistent pain. Epigenetic events leading the altered transcription in the nervous system are pivotal in the maintenance of pain in tissue injury. However, the mechanisms through which those events contribute to the persistence of pain are not fully understood. This review provides a summary and critical evaluation of two epigenetic mechanisms, DNA methylation and non-coding RNA expression, on transcriptional modulation in nociceptive pathways during the development of tissue injury-associated pain. We assess the pre-clinical data and their translational implication and evaluate the potential of controlling DNA methylation and non-coding RNA expression as novel analgesic approaches and/or biomarkers of persistent pain.

Targeted up-regulation of Drp1 in dorsal horn attenuates neuropathic pain hypersensitivity by increasing mitochondrial fission

Mitochondria play an essential role in pathophysiology of both inflammatory and neuropathic pain (NP), but the mechanisms are not yet clear. Dynamin-related protein 1 (Drp1) is broadly expressed in the central nervous system and plays a role in the induction of mitochondrial fission process. Spared nerve injury (SNI), due to the dysfunction of the neurons within the spinal dorsal horn (SDH), is the most common NP model. We explored the neuroprotective role of Drp1 within SDH in SNI. SNI mice showed pain behavior and anxiety-like behavior, which was associated with elevation of Drp1, as well as increased density of mitochondria in SDH. Ultrastructural analysis showed SNI induced damaged mitochondria into smaller perimeter and area, tending to be circular. Characteristics of vacuole in the mitochondria further showed SNI induced the increased number of vacuole, widened vac-perimeter and vac-area. Stable overexpression of Drp1 via AAV under the control of the Drp1 promoter by intraspinal injection (Drp1 OE) attenuated abnormal gait and alleviated pain hypersensitivity of SNI mice. Mitochondrial ultrastructure analysis showed that the increased density of mitochondria induced by SNI was recovered by Drp1 OE which, however, did not change mitochondrial morphology and vacuole parameters within SDH. Contrary to Drp1 OE, down-regulation of Drp1 in the SDH by AAV-Drp1 shRNA (Drp1 RNAi) did not alter painful behavior induced by SNI. Ultrastructural analysis showed the treatment by combination of SNI and Drp1 RNAi (SNI + Drp1 RNAi) amplified the damages of mitochondria with the decreased distribution density, increased perimeter and area, as well as larger circularity tending to be more circular. Vacuole data showed SNI + Drp1 RNAi increased vacuole density, perimeter and area within the SDH mitochondria. Our results illustrate that mitochondria within the SDH are sensitive to NP, and targeted mitochondrial Drp1 overexpression attenuates pain hypersensitivity. Drp1 offers a novel therapeutic target for pain treatment.

Epigenetic modifications in neuropathic pain

Neuropathic pain (NP) is a common symptom in many diseases of the somatosensory nervous system, which severely affects the patient’s quality of life. Epigenetics are heritable alterations in gene expression that do not cause permanent changes in the DNA sequence. Epigenetic modifications can affect gene expression and function and can also mediate crosstalk between genes and the environment. Increasing evidence shows that epigenetic modifications, including DNA methylation, histone modification, non-coding RNA, and RNA modification, are involved in the development and maintenance of NP. In this review, we focus on the current knowledge of epigenetic modifications in the development and maintenance of NP. Then, we illustrate different facets of epigenetic modifications that regulate gene expression and their crosstalk. Finally, we discuss the burgeoning evidence supporting the potential of emerging epigenetic therapies, which has been valuable in understanding mechanisms and offers novel and potent targets for NP therapy.

Epigenetic signature of chronic low back pain in human T cells

Supplemental Digital Content is Available in the Text.

This study reveals sex-specific DNA methylation signatures in human T cells that discriminate chronic low back pain participants from healthy controls.

Objective:

Determine if chronic low back pain (LBP) is associated with DNA methylation signatures in human T cells that will reveal novel mechanisms and potential therapeutic targets and explore the feasibility of epigenetic diagnostic markers for pain-related pathophysiology.

Methods:

Genome-wide DNA methylation analysis of 850,000 CpG sites in women and men with chronic LBP and pain-free controls was performed. T cells were isolated (discovery cohort, n = 32) and used to identify differentially methylated CpG sites, and gene ontologies and molecular pathways were identified. A polygenic DNA methylation score for LBP was generated in both women and men. Validation was performed in an independent cohort (validation cohort, n = 63) of chronic LBP and healthy controls.

Results:

Analysis with the discovery cohort revealed a total of 2,496 and 419 differentially methylated CpGs in women and men, respectively. In women, most of these sites were hypomethylated and enriched in genes with functions in the extracellular matrix, in the immune system (ie, cytokines), or in epigenetic processes. In men, a unique chronic LBP DNA methylation signature was identified characterized by significant enrichment for genes from the major histocompatibility complex. Sex-specific polygenic DNA methylation scores were generated to estimate the pain status of each individual and confirmed in the validation cohort using pyrosequencing.

Conclusion:

This study reveals sex-specific DNA methylation signatures in human T cells that discriminates chronic LBP participants from healthy controls.

The methyl donor S-adenosyl methionine reverses the DNA methylation signature of chronic neuropathic pain in mouse frontal cortex

Supplemental Digital Content is Available in the Text.

Chronic administration of S-adenosylmethionine reverses neuropathic pain–induced changes in DNA methylation in the mouse frontal cortex.

Chronic pain is associated with persistent but reversible structural and functional changes in the prefrontal cortex (PFC). This stable yet malleable plasticity implicates epigenetic mechanisms, including DNA methylation, as a potential mediator of chronic pain–induced cortical pathology. We previously demonstrated that chronic oral administration of the methyl donor S-adenosyl methionine (SAM) attenuates long-term peripheral neuropathic pain and alters global frontal cortical DNA methylation. However, the specific genes and pathways associated with the resolution of chronic pain by SAM remain unexplored.

Acupuncture alleviates chronic pain and comorbid conditions in a mouse model of neuropathic pain: the involvement of DNA methylation in the prefrontal cortex

ABSTRACT

Chronic pain reduces life quality and is an important clinical problem associated with emotional and cognitive dysfunction. Epigenetic regulation of DNA methylation is involved in the induction of abnormal behaviors and pathological gene expression. We examined whether acupuncture can restore epigenetic changes caused by chronic pain, and identified the underlying mechanisms in neuropathic pain mice. Acupuncture treatment for 6 months (3 days/week) improved mechanical/cold allodynia and the emotional/cognitive dysfunction caused by left partial sciatic nerve ligation (PSNL)-induced neuropathic pain. The effects of acupuncture were associated with global DNA methylation recovery in the prefrontal cortex (PFC). Analysis of DNA methylation patterns in PFC indicated that 1364 overlapping genes among 4442 and 4416 methylated genes in the PSNL vs sham and PSNL vs acupuncture points groups, respectively, were highly associated with the DNA methylation process. Acupuncture restored the reduced expression of 5-methylcytosine, methyl-cytosine-phospho-guanine binding protein 2, and DNA methyltransferase family enzymes induced by PSNL in PFC. Methylation levels of Nr4a1 and Chkb associated with mitochondrial dysfunction were decreased in PFC of the PSNL mice, and increased by acupuncture. By contrast, high expression of Nr4a1 and Chkb mRNA in PSNL mice decreased after acupuncture. We also found that acupuncture inhibited the expression of Ras pathway-related genes such as Rasgrp1 and Rassf1. Finally, the expression of Nr4a1, Rasgrp1, Rassf1, and Chkb mRNA increased in the neuronal cells treated with Mecp2 small interfering RNA. These results suggest that acupuncture can relieve chronic pain-induced comorbid conditions by altering DNA methylation of Nr4a1, Rasgrp1, Rassf1, and Chkb in the PFC.

Evidence to Support the Use of S-Adenosylmethionine for Treatment of Post-Concussive Sequelae in the Military

INTRODUCTION

Since the year 2000, over 413,000 service members have sustained traumatic brain injury (TBI) and may present with post-concussive sequelae including headaches, fatigue, irritability, cognitive problems, depression, insomnia, and chronic pain. Although the focus of the article is on military TBI, the usefulness of S-adenosylmethionine (SAMe) would extend to both civilian and military populations. This narrative review examines the preclinical and clinical literature of SAMe's metabolism and alterations seen in disease states such as depressive disorders, pain disorders, fatigue, cognition, dementia, use in pregnancy and peripartum, children, adolescents, and adults, to the elderly with and without dementia, stroke, and neurodegeneration, in order to highlight its potential benefit in post-concussive sequelae after TBI.

MATERIALS AND METHODS

A MEDLINE/PubMed and Cochrane Database search was conducted between May 3, 2018 and July 30, 2019 by combining search terms for SAMe with terms for relevant disease states including depression, brain injury, dementia, Alzheimer's disease, Parkinson's disease, cognition, fatigue, and pain. This search retrieved a total of 676 references. 439 were excluded for being over a 10-year publication date, except where clinically relevant. After additional removal of repeated articles, the number of articles were totaled 197. An additional 59 articles were excluded: 10 not in English, 4 duplicates, 4 not original investigations, and 41 outside the scope of this article. The remaining 138 articles were used in this review and included 25 clinical studies, 46 preclinical studies, 63 reviews, and 4 case reports.

RESULTS

This narrative review examined the preclinical and clinical literature of SAMe's metabolism and alterations seen in MDD, pain disorders, fatigue, cognition and memory, dementia, and other disorders to highlight the potential benefit of SAMe in post-concussive sequelae in mTBI. The literature showed potential for improvement, safety, and tolerability in these symptom clusters commonly seen in military mild TBI (mTBI).

CONCLUSION

There is evidence of a potential benefit of SAMe as an intervention to help with symptoms across the range of post-concussive sequelae and syndromes commonly seen in military mTBI. Since the discovery of SAMe in 1952, this pleiotropic molecule has shown the significance of its involvement in several metabolic cascades in such disparate systems as epigenetics, bioenergetics, DNA methylation, neurotransmitter systems, and potential usefulness in military TBI. Significant limitations include disparate presentations seen in patients with mild TBI, those with post-concussive syndrome, as well as those with comorbid depression and posttraumatic stress disorder. Also, over-the-counter medications are not regulated and SAMe products may vary widely in price and quality. Given the potential for mania in patients with bipolar disorder, evaluation and recommendations should be made by a physician able to evaluate the underlying bipolar diathesis. Furthermore, this narrative review serves as the rationale for future open-label and double-blind placebo-controlled trials in military mTBI and SAMe.

The transition from acute to chronic pain: dynamic epigenetic reprogramming of the mouse prefrontal cortex up to 1 year after nerve injury

Supplemental Digital Content is Available in the Text.

DNA methylation undergoes rapid and large changes in mouse prefrontal cortex at multiple time points postinjury, implicating hundreds of genes in a time-dependent manner.

Chronic pain is associated with persistent structural and functional changes throughout the neuroaxis, including in the prefrontal cortex (PFC). The PFC is important in the integration of sensory, cognitive, and emotional information and in conditioned pain modulation. We previously reported widespread epigenetic reprogramming in the PFC many months after nerve injury in rodents. Epigenetic modifications, including DNA methylation, can drive changes in gene expression without modifying DNA sequences. To date, little is known about epigenetic dysregulation at the onset of acute pain or how it progresses as pain transitions from acute to chronic. We hypothesize that acute pain after injury results in rapid and persistent epigenetic remodelling in the PFC that evolves as pain becomes chronic. We further propose that understanding epigenetic remodelling will provide insights into the mechanisms driving pain-related changes in the brain. Epigenome-wide analysis was performed in the mouse PFC 1 day, 2 weeks, 6 months, and 1 year after peripheral injury using the spared nerve injury in mice. Spared nerve injury resulted in rapid and persistent changes in DNA methylation, with robust differential methylation observed between spared nerve injury and sham-operated control mice at all time points. Hundreds of differentially methylated genes were identified, including many with known function in pain. Pathway analysis revealed enrichment in genes related to stimulus response at early time points, immune function at later time points, and actin and cytoskeletal regulation throughout the time course. These results emphasize the importance of considering pain chronicity in both pain research and in treatment optimization.

Epigenetic control of ion channel expression and cell-specific splicing in nociceptors: Chronic pain mechanisms and potential therapeutic targets

Ion channels underlie all forms for electrical signaling including the transmission of information about harmful events. Voltage-gated calcium ion channels have dual function, they support electrical signaling as well as intracellular calcium signaling through excitation-dependent calcium entry across the plasma membrane. Mechanisms that regulate ion channel forms and actions are essential for myriad cell functions and these are targeted by drugs and therapeutics. When disrupted, the cellular mechanisms that control ion channel activity can contribute to disease pathophysiology. For example, alternative pre-mRNA splicing is a major step in defining the precise composition of the transcriptome across different cell types from early cellular differentiation to programmed apoptosis. An estimated 30% of disease-causing mutations are associated with altered alternative splicing, and mis-splicing is a feature of numerous highly prevalent diseases including neurodegenerative, cancer, and chronic pain. Here we discuss the important role of epigenetic regulation of gene expression and cell-specific alternative splicing of calcium ion channels in nociceptors, with emphasis on how these processes are disrupted in chronic pain, the potential therapeutic benefit of correcting or compensating for aberrant ion channel splicing in chronic pain.

S-adenosylmethionine: A metabolite critical to the regulation of autophagy

Autophagy is a mechanism that enables cells to maintain cellular homeostasis by removing damaged materials and mobilizing energy reserves in conditions of starvation. Although nutrient availability strongly impacts the process of autophagy, the specific metabolites that regulate autophagic responses have not yet been determined. Recent results indicate that S-adenosylmethionine (SAM) represents a critical inhibitor of methionine starvation-induced autophagy. SAM is primarily involved in four key metabolic pathways: transmethylation, transsulphuration, polyamine synthesis and 5'-deoxyadenosyl 5'-radical-mediated biochemical transformations. SAM is the sole methyl group donor involved in the methylation of DNA, RNA and histones, modulating the autophagic process by mediating epigenetic effects. Moreover, the metabolites of SAM, such as homocysteine, glutathione, decarboxylated SAM and spermidine, also exert important influences on the regulation of autophagy. From our perspective, nuclear-cytosolic SAM is a conserved metabolic inhibitor that connects cellular metabolic status and the regulation of autophagy. In the future, SAM might be a new target of autophagy regulators and be widely used in the treatment of various diseases.

Methionine mediates resilience to chronic social defeat stress by epigenetic regulation of NMDA receptor subunit expression

RATIONALE

Previous studies suggested that methionine (Met) levels are decreased in depressed patients. However, whether the decrease in this amino acid is important for phenotypic behaviors associated with depression has not been deciphered.

OBJECTIVE

The response of individuals to chronic stress is variable, with some individuals developing depression and others becoming resilient to stress. In this study, our objective was to examine the effect of Met on susceptibility to stress.

METHODS

Male C57BL/6J mice were subjected to daily defeat sessions by a CD1 aggressor, for 10 days. On day 11, the behavior of mice was assessed using social interaction and open-field tests. Mice received Met 4 h before each defeat session. Epigenetic targets were assessed either through real-rime RTPCR or through Western Blots.

RESULTS

Met did not modulate anxiety-like behaviors, but rather promoted resilience to chronic stress, rescued social avoidance behaviors and reversed the increase in the cortical expression levels of N-methyl-D-aspartate receptor (NMDAR) subunits. Activating NMDAR activity abolished the ability of Met to promote resilience to stress and to rescue social avoidance behavior, whereas inhibiting NMDAR did not show any synergistic or additive protective effects. Indeed, Met increased the cortical levels of the histone methyltransferase SETDB1, and in turn, the levels of the repressive histone H3 lysine (K9) trimethylation (me3).

CONCLUSIONS

Our data indicate that Met rescues susceptibility to stress by inactivating cortical NMDAR activity through an epigenetic mechanism involving histone methylation.

Behavioral, Biochemical and Electrophysiological Changes in Spared Nerve Injury Model of Neuropathic Pain

Neuropathic pain is a pathological condition induced by a lesion or disease affecting the somatosensory system, with symptoms like allodynia and hyperalgesia. It has a multifaceted pathogenesis as it implicates several molecular signaling pathways involving peripheral and central nervous systems. Affective and cognitive dysfunctions have been reported as comorbidities of neuropathic pain states, supporting the notion that pain and mood disorders share some common pathogenetic mechanisms. The understanding of these pathophysiological mechanisms requires the development of animal models mimicking, as far as possible, clinical neuropathic pain symptoms. Among them, the Spared Nerve Injury (SNI) model has been largely characterized in terms of behavioral and functional alterations. This model is associated with changes in neuronal firing activity at spinal and supraspinal levels, and induces late neuropsychiatric disorders (such as anxious-like and depressive-like behaviors, and cognitive impairments) comparable to an advanced phase of neuropathy. The goal of this review is to summarize current findings in preclinical research, employing the SNI model as a tool for identifying pathophysiological mechanisms of neuropathic pain and testing pharmacological agent.

PCC0208009, an indirect IDO1 inhibitor, alleviates neuropathic pain and co-morbidities by regulating synaptic plasticity of ACC and amygdala

BACKGROUND AND PURPOSE

Indoleamine 2, 3-dioxygenase 1 (IDO1) has been linked to neuropathic pain and IDO1 inhibitors have been shown to reduce pain in animals. Some studies have indicated that IDO1 expression increased after neuropathic pain in hippocampus and spinal cord, whether these changes existing in anterior cingulate cortex (ACC) and amygdala remains obscure and how IDO1 inhibition leads to analgesia is largely unknown. Here, we evaluated the antinociceptive effect of PCC0208009, an indirect IDO1 inhibitor, on neuropathic pain and examined the related neurobiological mechanisms.

EXPERIMENTAL APPROACH

The effects of PCC0208009 on pain, cognition and anxiogenic behaviors were evaluated in a rat model of neuropathic pain. Motor disorder, sedation and somnolence were also assessed. Biochemical techniques were used to measure IDO1-mediated signaling changes in ACC and amygdala.

KEY RESULTS

In rats receiving spinal nerve ligation (SNL), IDO1 expression level was increased in ACC and amygdala. PCC0208009 attenuated pain-related behaviors in the formalin test and SNL model and increased cognition and anxiogenic behaviors in SNL rats at doses that did not affect locomotor activity and sleeping. PCC0208009 inhibited IDO1 expression in ACC and amygdala by inhibiting the IL-6-JAK2/STAT3-IDO1-GCN2-IL-6 pathway. In addition, PCC0208009 reversed synaptic plasticity at the functional and structural levels by suppressing NMDA2B receptor and CDK5/MAP2 or CDK5/Tau pathway in ACC and amygdala.

CONCLUSION AND IMPLICATIONS

These results support the role of IDO1-mediated molecular mechanisms in neuropathic pain and suggest that the IDO1 inhibitor PCC0208009 demonstrates selective pain suppression and could be a useful pharmacological therapy for neuropathic pain.

S-adenosyl-l-methionine (SAMe), cannabidiol (CBD), and kratom in psychiatric disorders: Clinical and mechanistic considerations

Given the limitations of prescription antidepressants, many individuals have turned to natural remedies for the management of their mood disorders. We review three selected natural remedies that may be of potential use as treatments for depressive disorders and other psychiatric or neurological conditions. The best studied and best supported of these three remedies is S-adenosyl-l-methionine (SAMe), a methyl donor with a wide range of physiological functions in the human organism. With the increasing legalization of cannabis-related products, cannabidiol (CBD) has gained popularity for various potential indications and has even obtained approval in the United States and Canada for certain neurological conditions. Kratom, while potentially useful for certain individuals with psychiatric disorders, is perhaps the most controversial of the three remedies, in view of its greater potential for abuse and dependence. For each remedy, we will review indications, doses and delivery systems, potential anti-inflammatory and immunomodulatory action, adverse effects, and will provide recommendations for clinicians who may be considering prescribing these remedies in their practice.

Diverse Role of Biological Plasticity in Low Back Pain and Its Impact on Sensorimotor Control of the Spine

Pain is complex. It is no longer acceptable to consider pain solely as a peripheral phenomenon involving activation of nociceptive neurons. The contemporary understanding of pain involves consideration of different underlying pain mechanisms and an increasing awareness of plasticity in all of the biological systems. Of note, recent advances in technology and understanding have highlighted the critical importance of neuroimmune interactions, both in the peripheral and central nervous systems, and the interaction between the nervous system and body tissues in the development and maintenance of pain, including low back pain (LBP). Further, the biology of many tissues changes when challenged by pain and injury, as reported in a growing body of literature on the biology of muscle, fat, and connective tissue. These advances in understanding of the complexity of LBP have implications for our understanding of pain and its interaction with the motor system, and may change how we consider motor control in the rehabilitation of LBP. This commentary provides a state-of-the-art overview of plasticity of biology in LBP. The paper is divided into 4 parts that address (1) biology of pain mechanisms, (2) neuroimmune interaction in the central nervous system, (3) neuroimmune interaction in the periphery, and (4) brain and peripheral tissue interaction. Each section considers the implications for clinical management of LBP. J Orthop Sports Phys Ther 2019;49(6):389-401. doi:10.2519/jospt.2019.8716.

Neuroendocrine aging precedes perimenopause and is regulated by DNA methylation

Perimenopause marks initiation of female reproductive senescence. Age of onset is only 47% heritable suggesting that additional factors other than inheritance regulate this endocrine aging transition. To elucidate these factors, we characterized transcriptional and epigenomic changes across endocrine aging using a rat model that recapitulates characteristics of the human perimenopause. RNA-seq analysis revealed that hypothalamic aging precedes onset of perimenopause. In the hypothalamus, global DNA methylation declined with both age and reproductive senescence. Genome-wide epigentic analysis revealed changes in DNA methylation in genes required for hormone signaling, glutamate signaling, and melatonin and circadian pathways. Specific epignetic changes in these signaling pathways provide insight into the origin of perimenopause-associated neurological symptoms such as insomnia. Treatment with 5-aza-2'-deoxycytidine, a DNA-methyltransferase-1 inhibitor, accelerated transition to reproductive senescence/ whereas supplementation with methionine, a S-adenosylmethionine precursor, delayed onset of perimenopause and endocrine aging. Collectively, these data provide evidence for a critical period of female neuroendocrine aging in brain that precedes ovarian failure and that DNA methylation regulates the transition duration of perimenopause to menopause.

Nerve Injury-Induced Chronic Pain Is Associated with Persistent DNA Methylation Reprogramming in Dorsal Root Ganglion

Nerve injury-induced hyperactivity of primary sensory neurons in the dorsal root ganglion (DRG) contributes to chronic pain development, but the underlying epigenetic mechanisms remain poorly understood. Here we determined genome-wide changes in DNA methylation in the nervous system in neuropathic pain. Spinal nerve ligation (SNL), but not paclitaxel treatment, in male Sprague Dawley rats induced a consistent low-level hypomethylation in the CpG sites in the DRG during the acute and chronic phases of neuropathic pain. DNA methylation remodeling in the DRG occurred early after SNL and persisted for at least 3 weeks. SNL caused DNA methylation changes at 8% of CpG sites with prevailing hypomethylation outside of CpG islands, in introns, intergenic regions, and repetitive sequences. In contrast, SNL caused more gains of methylation in the spinal cord and prefrontal cortex. The DNA methylation changes in the injured DRGs recapitulated developmental reprogramming at the neonatal stage. Methylation reprogramming was correlated with increased gene expression variability. A diet deficient in methyl donors induced hypomethylation and pain hypersensitivity. Intrathecal administration of the DNA methyltransferase inhibitor RG108 caused long-lasting pain hypersensitivity. DNA methylation reprogramming in the DRG thus contributes to nerve injury-induced chronic pain. Restoring DNA methylation may represent a new therapeutic approach to treat neuropathic pain.SIGNIFICANCE STATEMENT Epigenetic mechanisms are critically involved in the transition from acute to chronic pain after nerve injury. However, genome-wide changes in DNA methylation in the nervous system and their roles in neuropathic pain development remain unclear. Here we used digital restriction enzyme analysis of methylation to quantitatively determine genome-wide DNA methylation changes caused by nerve injury. We showed that nerve injury caused DNA methylation changes at 8% of CpG sites with prevailing hypomethylation outside of CpG islands in the dorsal root ganglion. Reducing DNA methylation induced pain hypersensitivity, whereas increasing DNA methylation attenuated neuropathic pain. These findings extend our understanding of the epigenetic mechanism of chronic neuropathic pain and suggest new strategies to treat nerve injury-induced chronic pain.

Enhanced S-Adenosylmethionine Production by Increasing ATP Levels in Baker's Yeast ( Saccharomyces cerevisiae)

In the biosynthesis of S-adenosylmethionine (SAM) in baker's yeast ( Saccharomyces cerevisiae), ATP functions as both a precursor and a driving force. However, few published reports have dealt with the control of ATP concentration using genetic design. In this study we have adopted a new ATP regulation strategy in yeast for enhancing SAM biosynthesis, including altering NADH availability and regulating the oxygen supply. Different ATP regulation systems were designed based on the introduction of water-forming NADH oxidase, Vitreoscilla hemoglobin, and phosphite dehydrogenase in combination with overexpression of the gene SAM2. Via application of this strategy, after 28 h cultivation, the SAM titer in the yeast strain ABYSM-2 reached a maximum level close to 55 mg/L, an increase of 67% compared to the control strain. The results show that the ATP regulation strategy is a valuable tool for SAM production and might further enhance the synthesis of other ATP-driven metabolites in yeast.

Control of ATP concentration in Escherichia coli using an ATP-sensing riboswitch for enhanced S-adenosylmethionine production

We proposed an ATP-sensing riboswitch-based strategy which could be applied to regulate the intracellular ATP concentration dynamically inE. coli. This strategy will be most beneficial for enhancing the production of the ATP-driven metabolites.