Dimethyl fumarate targets GAPDH and aerobic glycolysis to modulate immunity

Activated immune cells undergo a metabolic switch to aerobic glycolysis akin to the Warburg effect, thereby presenting a potential therapeutic target in autoimmune disease. Dimethyl fumarate (DMF), a derivative of the Krebs cycle intermediate fumarate, is an immunomodulatory drug used to treat multiple sclerosis and psoriasis. Although its therapeutic mechanism remains uncertain, DMF covalently modifies cysteine residues in a process termed succination. We found that DMF succinates and inactivates the catalytic cysteine of the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in mice and humans, both in vitro and in vivo. It thereby down-regulates aerobic glycolysis in activated myeloid and lymphoid cells, which mediates its anti-inflammatory effects. Our results provide mechanistic insight into immune modulation by DMF and represent a proof of concept that aerobic glycolysis is a therapeutic target in autoimmunity.

Nitric oxide-induced nuclear GAPDH activates p300/CBP and mediates apoptosis

Besides its role in glycolysis, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) initiates a cell death cascade. Diverse apoptotic stimuli activate inducible nitric oxide synthase (iNOS) or neuronal NOS (nNOS), with the generated nitric oxide (NO) S-nitrosylating GAPDH, abolishing its catalytic activity and conferring on it the ability to bind to Siah1, an E3-ubiquitin-ligase with a nuclear localization signal (NLS). The GAPDH-Siah1 protein complex, in turn, translocates to the nucleus and mediates cell death; these processes are blocked by procedures that interfere with GAPDH-Siah1 binding. Nuclear events induced by GAPDH to kill cells have been obscure. Here we show that nuclear GAPDH is acetylated at Lys 160 by the acetyltransferase p300/CREB binding protein (CBP) through direct protein interaction, which in turn stimulates the acetylation and catalytic activity of p300/CBP. Consequently, downstream targets of p300/CBP, such as p53 (Refs 10,11,12,13,14,15), are activated and cause cell death. A dominant-negative mutant GAPDH with the substitution of Lys 160 to Arg (GAPDH-K160R) prevents activation of p300/CBP, blocks induction of apoptotic genes and decreases cell death. Our findings reveal a pathway in which NO-induced nuclear GAPDH mediates cell death through p300/CBP.

The immunologic Warburg effect: Evidence and therapeutic opportunities in autoimmunity

Pro‐inflammatory signals induce metabolic reprogramming in innate and adaptive immune cells of both myeloid and lymphoid lineage, characterized by a shift to aerobic glycolysis akin to the Warburg effect first described in cancer. Blocking the switch to aerobic glycolysis impairs the survival, differentiation, and effector functions of pro‐inflammatory cell types while favoring anti‐inflammatory and regulatory phenotypes. Glycolytic reprogramming may therefore represent a selective vulnerability of inflammatory immune cells, providing an opportunity to modulate immune responses in autoimmune disease without broad toxicity in other tissues of the body. The mechanisms by which aerobic glycolysis and the balance between glycolysis and oxidative phosphorylation regulate immune responses have only begun to be understood, with many additional insights expected in the years to come. Immunometabolic therapies targeting aerobic glycolysis include both pharmacologic inhibitors of key enzymes and glucose‐restricted diets, such as the ketogenic diet. Animal studies support a role for these pharmacologic and dietary therapies for the treatment of autoimmune diseases, and in a few cases proof of concept has been demonstrated in human disease. Nonetheless, much more work is needed to establish the clinical safety and efficacy of these treatments.

This article is categorized under:

Biological Mechanisms > Metabolism

Translational, Genomic, and Systems Medicine > Translational Medicine

Biological Mechanisms > Cell Signaling

Multi-omic evaluation of metabolic alterations in multiple sclerosis identifies shifts in aromatic amino acid metabolism

The circulating metabolome provides unique insights into multiple sclerosis (MS) pathophysiology, but existing studies are relatively small or characterized limited metabolites. We test for differences in the metabolome between people with MS (PwMS; n = 637 samples) and healthy controls (HC; n = 317 samples) and assess the association between metabolomic profiles and disability in PwMS. We then assess whether metabolic differences correlate with changes in cellular gene expression using publicly available scRNA-seq data and whether identified metabolites affect human immune cell function. In PwMS, we identify striking abnormalities in aromatic amino acid (AAA) metabolites (p = 2.77E-18) that are also strongly associated with disability (p = 1.01E-4). Analysis of scRNA-seq data demonstrates altered AAA metabolism in CSF and blood-derived monocyte cell populations in PwMS. Treatment with AAA-derived metabolites in vitro alters monocytic endocytosis and pro-inflammatory cytokine production. We identify shifts in AAA metabolism resulting in the reduced production of immunomodulatory metabolites and increased production of metabotoxins in PwMS.

Dimethyl fumarate treatment induces lipid metabolism alterations that are linked to immunological changes

Objective

Identify metabolic changes produced by dimethyl fumarate (DMF) treatment and link them to immunological effects.

Methods

We enrolled 18 MS patients and obtained blood prior to DMF and 6 months postinitiation. We also enrolled 18 healthy controls for comparison. We performed global metabolomics on plasma and used weighted correlation network analysis (WGCNA) to identify modules of correlated metabolites. We identified modules that changed with treatment, followed by targeted metabolomics to corroborate changes identified in global analyses. We correlated changes in metabolite modules and individual metabolites with changes in immunological parameters.

Results

We identified alterations in lipid metabolism after DMF treatment – increases in two modules (phospholipids, lysophospholipids and plasmalogens) and reduction in one module (saturated and poly‐unsaturated fatty acids) eigen‐metabolite values (all P < 0.05). Change in the fatty acid module was greater in participants who developed lymphopenia and was strongly associated with both reduction in absolute lymphocyte counts (r = 0.65; P = 0.005) and change in CD8+ T cell subsets. We also noted significant correlation of change in lymphocyte counts with multiple fatty acid levels (measured by targeted or untargeted methods).

Interpretation

This study demonstrates that DMF treatment alters lipid metabolism and that changes in fatty acid levels are related to DMF‐induced immunological changes.

Inositol hexakisphosphate kinase-2 non-catalytically regulates mitophagy by attenuating PINK1 signaling

Inositol pyrophosphates, such as 5-diphosphoinositol pentakisphosphate (IP7), are generated by a family of inositol hexakisphosphate kinases (IP6Ks), of which IP6K2 has been implicated in various cellular functions including neuroprotection. Absence of IP6K2 causes impairment of oxidative phosphorylation regulated by creatine kinase-B. In the present study, we show that IP6K2 is involved in attenuation of PINK1-mediated mitochondrial autophagy (mitophagy) in the brain. Up-regulation of dynamin-related protein (Drp-1), as well as increased expression of mitochondrial biogenesis markers (PGC1-α and NRF-1) in the cerebella of IP6K2-deleted mice (IP6K2-knockout), point to the involvement of IP6K2 in the regulation of mitochondrial fission. Knockdown of IP6K2 also leads to augmented glycolysis, potentially as a compensatory mechanism for decreased mitochondrial respiration. Overexpressing IP6K2 as well as IP6K2-kinase dead mutant in IP6K2-knockdown N2A cells reverses the expression of mitophagy markers, demonstrating that IP6K2-induced mitoprotection is catalytically/kinase independent. IP6K2 supplementation in K2-PINK1 double-knockdown N2A cells fails to reverse the expression of the mitophagic marker, LC3-II, indicating that the mitoprotective effect of IP6K2 is dependent on PINK1. Overall, our study reveals a key neuroprotective role of IP6K2 in the prevention of PINK1-mediated mitophagy in the brain.

Designed PKC-targeting bryostatin analogs modulate innate immunity and neuroinflammation

Neuroinflammation characterizes multiple neurologic diseases, including primary inflammatory conditions such as multiple sclerosis and classical neurodegenerative diseases. Aberrant activation of the innate immune system contributes to disease progression, but drugs modulating innate immunity, particularly within the central nervous system (CNS), are lacking. The CNS-penetrant natural product bryostatin-1 attenuates neuroinflammation by targeting innate myeloid cells. Supplies of natural bryostatin-1 are limited, but a recent scalable good manufacturing practice (GMP) synthesis has enabled access to it and its analogs (bryologs), the latter providing a path to more efficacious, better tolerated, and more accessible agents. Here, we show that multiple synthetically accessible bryologs replicate the anti-inflammatory effects of bryostatin-1 on innate immune cells in vitro, and a lead bryolog attenuates neuroinflammation in vivo, actions mechanistically dependent on protein kinase C (PKC) binding. Our findings identify bryologs as promising drug candidates for targeting innate immunity in neuroinflammation and create a platform for evaluation of synthetic PKC modulators in neuroinflammatory diseases.

DNA methylation patterns in bladder tumors of African American patients point to distinct alterations in xenobiotic metabolism

Racial/ethnic disparities have a significant impact on bladder cancer outcomes with African American patients demonstrating inferior survival over European-American patients. We hypothesized that epigenetic difference in methylation of tumor DNA is an underlying cause of this survival health disparity. We analyzed bladder tumors from African American and European-American patients using reduced representation bisulfite sequencing (RRBS) to annotate differentially methylated DNA regions. Liquid chromatography-mass spectrometry (LC-MS/MS) based metabolomics and flux studies were performed to examine metabolic pathways that showed significant association to the discovered DNA methylation patterns. RRBS analysis showed frequent hypermethylated CpG islands in African American patients. Further analysis showed that these hypermethylated CpG islands in patients are commonly located in the promoter regions of xenobiotic enzymes that are involved in bladder cancer progression. On follow-up, LC-MS/MS revealed accumulation of glucuronic acid, S-adenosylhomocysteine, and a decrease in S-adenosylmethionine, corroborating findings from the RRBS and mRNA expression analysis indicating increased glucuronidation and methylation capacities in African American patients. Flux analysis experiments with 13C-labeled glucose in cultured African American bladder cancer cells confirmed these findings. Collectively, our studies revealed robust differences in methylation-related metabolism and expression of enzymes regulating xenobiotic metabolism in African American patients indicate that race/ethnic differences in tumor biology may exist in bladder cancer.

Biliverdin reductase bridges focal adhesion kinase to Src to modulate synaptic signaling

Synapses connect discrete neurons into vast networks that send, receive, and encode diverse forms of information. Synaptic function and plasticity, the neuronal process of adapting to diverse and variable inputs, depend on the dynamic nature of synaptic molecular components, which is mediated in part by cell adhesion signaling pathways. Here, we found that the enzyme biliverdin reductase (BVR) physically links together key focal adhesion signaling molecules at the synapse. BVR-null (BVR-/-) mice exhibited substantial deficits in learning and memory on neurocognitive tests, and hippocampal slices in which BVR was postsynaptically depleted showed deficits in electrophysiological responses to stimuli. RNA sequencing, biochemistry, and pathway analyses suggested that these deficits were mediated through the loss of focal adhesion signaling at both the transcriptional and biochemical level in the hippocampus. Independently of its catalytic function, BVR acted as a bridge between the primary focal adhesion signaling kinases FAK and Pyk2 and the effector kinase Src. Without BVR, FAK and Pyk2 did not bind to and stimulate Src, which then did not phosphorylate the N-methyl-d-aspartate (NMDA) receptor, a critical posttranslational modification for synaptic plasticity. Src itself is a molecular hub on which many signaling pathways converge to stimulate NMDAR-mediated neurotransmission, thus positioning BVR at a prominent intersection of synaptic signaling.

Giant cell arteritis mimicking infiltrative leptomeningeal disease of the optic nerves

A 67-year-old man presented with several days of progressive, painless left eye vision loss. He reported mild jaw claudication but denied headache, scalp tenderness or constitutional symptoms. Examination revealed palpable temporal arteries, blurring of the left optic disc, and 20/100 vision in the left eye with mild relative afferent pupillary defect. Inflammatory markers were sent, and methylprednisolone was initiated for presumptive giant cell arteritis (GCA). Erythrocyte sedimentation rate was normal, however, and C reactive protein was only mildly elevated, prompting further investigation. Orbital MRI revealed nodular enhancement of the optic nerve sheaths bilaterally from optic nerve head to chiasm, raising concern for an infiltrative leptomeningeal process such as sarcoidosis or lymphoma. Methylprednisolone was temporarily stopped while a broad work up for inflammatory and neoplastic causes was pursued. Fluorodeoxyglucose-positron emission tomography ultimately revealed hypermetabolism in the temporal, ophthalmic and occipital arteries suggesting GCA, which was confirmed by temporal artery biopsy. Steroids were restarted, and the patient's vision stabilised.

PKC modulator bryostatin-1 therapeutically targets CNS innate immunity to attenuate neuroinflammation and promote remyelination

In multiple sclerosis (MS), microglia and macrophages within the central nervous system (CNS) play an important role in determining the balance between myelin repair and demyelination/neurodegeneration. Phagocytic and regenerative functions of these CNS innate immune cells support remyelination, whereas chronic and maladaptive inflammatory activation promotes lesion expansion and disability, particularly in the progressive forms of MS. No currently approved drugs convincingly target microglia and macrophages within the CNS, contributing to the critical lack of therapies promoting remyelination and slowing progression in MS. Here, we found that the protein kinase C (PKC)-modulating drug bryostatin-1 (bryo-1), a CNS-penetrant compound with an established human safety profile, produces a shift in microglia and CNS macrophage transcriptional programs from pro-inflammatory to regenerative phenotypes, both in vitro and in vivo. Treatment of microglia with bryo-1 prevented the activation of neurotoxic astrocytes while stimulating scavenger pathways, phagocytosis, and secretion of factors that promote oligodendrocyte differentiation. In line with these findings, systemic treatment with bryo-1 augmented remyelination following a focal demyelinating injury in vivo. Our results demonstrate the potential of bryo-1 and functionally related PKC modulators as myelin regenerative and neuroprotective agents in MS and other neurologic diseases through therapeutic targeting of microglia and CNS-associated macrophages.

The role of multiple sclerosis subtype in microvascular decompression outcomes for patients with trigeminal neuralgia

OBJECTIVES

While patients with concomitant trigeminal neuralgia (TN) and multiple sclerosis (MS) are understood to experience a more intractable pain phenotype, whether TN pain outcomes differ by the presenting MS subtype is not well characterized. This study's objective is to compare post-operative pain and numbness outcomes following microvascular decompression (MVD) in TN patients with either relapsing-remitting MS (RRMS) or progressive MS.

METHODS

We retrospectively reviewed all TN patients who underwent MVDs at our institution from 2007 to 2020. Of the 1044 patients reviewed, 45 (4.3%) patients with MS were identified. Patient demographics, procedural characteristics, and post-operative pain and numbness scores were recorded and compared. Factors associated with pain recurrence were assessed using survival analyses and multivariate regressions.

RESULTS

Of the resulting 45 MS patients, 34 (75.6%) patients presented with the RRMS subtype, whereas 11 (24.4%) patients exhibited progressive MS. Using an adjusted multivariate ordinal regression, the subtype of MS was not significantly associated with the Barrow Neurological Institute (BNI) pain score at final follow-up. Using a Kaplan-Meier survival analysis and a multivariate Cox proportional hazards regression, respectively, RRMS was significantly associated with a shorter post-operative pain-free interval (p = 0.04) as well as a greater risk for pain recurrence (p = 0.02).

CONCLUSIONS

Although the degree of pain at final follow-up may not differ, RRMS patients are at increased risk for pain recurrence following MVD for TN. These results align with a growing understanding that neuroinflammation may play a significant role in TN pain.

Meningeal Dissemination and Drop Metastasis From Glioma Presenting With Non-Epileptic Myoclonus and Minipolymyoclonus

We describe the case of a 36-year-old woman with a past medical history of low grade right frontal lobe glioma and focal epilepsy presenting with subacute, progressive, multifocal myoclonus and neck and back pain. Unlike her typical seizures, the myoclonus exhibited a distinct semiology, involving both positive and negative muscle jerks affecting multiple limb muscles while sparing the face. In addition, neurological examination revealed low-amplitude, arrhythmic movements of the hands and fingers, resembling minipolymyoclonus. There were no other neurological exam findings, including mental status changes, extrapyramidal signs or signs of myelopathy. Brain and spine MRI indicated leptomeningeal and spinal "drop" enhancing lesions, suggesting likely malignant evolution of the glioma. EEG ruled out a cortical origin of the myoclonus. Pharmacological trials with benzodiazepines and other antiepileptic medications were ineffective. The patient's myoclonus was most likely spinal segmental in origin from meningeal spread of glioma. The spinal roots or anterior horns of the spinal cord may have represented a focus of hyperexcitability responsible for generating minipolymyoclonus. Our case expands the etiological spectrum of non-epileptic myoclonus and minipolymyoclonus to encompass meningeal carcinomatosis and drop metastases from glioma. These cases may occur even without overt signs of myelopathy. Recognizing such presentations holds significance due to the poor prognosis associated with meningeal spread of glioma and the limited response of non-epileptic myoclonus to symptomatic treatments.

Phosphoglycerate mutase regulates Treg differentiation through control of serine synthesis and one-carbon metabolism

The differentiation and suppressive functions of regulatory CD4 T cells (Tregs) are supported by a broad array of metabolic changes, providing potential therapeutic targets for immune modulation. In this study, we focused on the regulatory role of glycolytic enzymes in Tregs and identified phosphoglycerate mutase (PGAM) as being differentially overexpressed in Tregs and associated with a highly suppressive phenotype. Pharmacologic or genetic inhibition of PGAM reduced Treg differentiation and suppressive function while reciprocally inducing markers of a pro-inflammatory, T helper 17 (Th17)-like state. The regulatory role of PGAM was dependent on the contribution of 3-phosphoglycerate (3PG), the PGAM substrate, to de novo serine synthesis. Blocking de novo serine synthesis from 3PG reversed the effect of PGAM inhibition on Treg polarization, while exogenous serine directly inhibited Treg polarization. Additionally, altering serine levels in vivo with a serine/glycine-free diet increased peripheral Tregs and attenuated autoimmunity in a murine model of multiple sclerosis. Mechanistically, we found that serine limits Treg polarization by contributing to one-carbon metabolism and methylation of Treg-associated genes. Inhibiting one-carbon metabolism increased Treg polarization and suppressive function both in vitro and in vivo in a murine model of autoimmune colitis. Our study identifies a novel physiologic role for PGAM and highlights the metabolic interconnectivity between glycolysis, serine synthesis, one-carbon metabolism, and epigenetic regulation of Treg differentiation and suppressive function.

TPPB modulates PKC activity to attenuate neuroinflammation and ameliorate experimental multiple sclerosis

Protein kinase C (PKC) plays a key role in modulating the activities of the innate immune cells of the central nervous system (CNS). A delicate balance between pro-inflammatory and regenerative activities by microglia and CNS-associated macrophages is necessary for the proper functioning of the CNS. Thus, a maladaptive activation of these CNS innate immune cells results in neurodegeneration and demyelination associated with various neurologic disorders, such as multiple sclerosis (MS) and Alzheimer's disease. Prior studies have demonstrated that modulation of PKC activity by bryostatin-1 (bryo-1) and its analogs (bryologs) attenuates the pro-inflammatory processes by microglia/CNS macrophages and alleviates the neurologic symptoms in experimental autoimmune encephalomyelitis (EAE), an MS animal model. Here, we demonstrate that (2S,5S)-(E,E)-8-(5-(4-(trifluoromethyl)phenyl)-2,4-pentadienoylamino)benzolactam (TPPB), a structurally distinct PKC modulator, has a similar effect to bryo-1 on CNS innate immune cells both in vitro and in vivo, attenuating neuroinflammation and resulting in CNS regeneration and repair. This study identifies a new structural class of PKC modulators, which can therapeutically target CNS innate immunity as a strategy to treat neuroinflammatory and neurodegenerative disorders.

Multiple Sclerosis and Other Acquired Demyelinating Diseases of the Central Nervous System

Acquired demyelinating diseases of the central nervous system (CNS) comprise inflammatory conditions, including multiple sclerosis (MS) and related diseases, as well as noninflammatory conditions caused by toxic, metabolic, infectious, traumatic, and neurodegenerative insults. Here, we review the spectrum of diseases producing acquired CNS demyelination before focusing on the prototypical example of MS, exploring the pathologic mechanisms leading to myelin injury in relapsing and progressive MS and summarizing the mechanisms and modulators of remyelination. We highlight the complex interplay between the immune system, oligodendrocytes and oligodendrocyte progenitor cells (OPCs), and other CNS glia cells such as microglia and astrocytes in the pathogenesis and clinical course of MS. Finally, we review emerging therapeutic strategies that exploit our growing understanding of disease mechanisms to limit progression and promote remyelination.

DICAM, a molecular passport for TH17 cell entry into the brain

[Figure: see text].

TPPB modulates PKC activity to attenuate neuroinflammation and ameliorate experimental multiple sclerosis

Protein kinase C (PKC) plays a key role in modulating the activities of the innate immune cells of the central nervous system (CNS). A delicate balance between pro-inflammatory and regenerative activities by microglia and CNS-associated macrophages is necessary for the proper functioning of the CNS. Thus, a maladaptive activation of these CNS innate immune cells results in neurodegeneration and demyelination associated with various neurologic disorders, such as multiple sclerosis (MS) and Alzheimer's disease. Prior studies have demonstrated that modulation of PKC activity by bryostatin-1 (bryo-1) and its analogs (bryologs) attenuates the pro-inflammatory processes by microglia/CNS macrophages and alleviates the neurologic symptoms in experimental autoimmune encephalomyelitis (EAE), an MS animal model. Here, we demonstrate that (2S,5S)-(E,E)-8-(5-(4(trifluoromethyl)phenyl)-2,4-pentadienoylamino)benzolactam (TPPB), a structurally distinct PKC modulator, has a similar effect to bryo-1 on CNS innate immune cells both in vitro and in vivo, attenuating neuroinflammation and resulting in CNS regeneration and repair. This study identifies a new structural class of PKC modulators, which can therapeutically target CNS innate immunity as a strategy to treat neuroinflammatory and neurodegenerative disorders.

The protein kinase C modulator bryostatin-1 therapeutically targets microglia to attenuate neuroinflammation and promote remyelination

In multiple sclerosis (MS), microglia and macrophages within the central nervous system (CNS) play an important role in determining the balance among demyelination, neurodegeneration, and myelin repair. Phagocytic and regenerative functions of these CNS innate immune cells support remyelination, whereas chronic and maladaptive inflammatory activation promotes lesion expansion and disability, particularly in the progressive forms of MS. No currently approved drugs convincingly target microglia and macrophages within the CNS, contributing to the lack of therapies aimed at promoting remyelination and slowing disease progression for individuals with MS. Here, we found that the protein kinase C (PKC)-modulating drug bryostatin-1 (bryo-1), a CNS-penetrant compound with an established human safety profile, shifts the transcriptional programs of microglia and CNS-associated macrophages from a proinflammatory phenotype to a regenerative phenotype in vitro and in vivo. Treatment of microglia with bryo-1 stimulated scavenger pathways, phagocytosis, and secretion of factors that prevented the activation of neuroinflammatory reactive astrocytes while also promoting neuroaxonal health and oligodendrocyte differentiation. In line with these findings, systemic treatment of mice with bryo-1 augmented remyelination after a focal demyelinating injury. Our results demonstrate the potential of bryo-1 and possibly a wider class of PKC modulators as myelin-regenerative and supportive agents in MS and other neurologic diseases.