Beneficial Effect of Fingolimod in a Lafora Disease Mouse Model by Preventing Reactive Astrogliosis-Derived Neuroinflammation and Brain Infiltration of T-lymphocytes

Lafora disease (LD; OMIM#254780) is a rare, devastating, and fatal form of progressive myoclonus epilepsy that affects young adolescents and has no treatment yet. One of the hallmarks of the disease is the accumulation of aberrant poorly branched forms of glycogen (polyglucosans, PGs) in the brain and peripheral tissues. The current hypothesis is that this accumulation is causative of the pathophysiology of the disease. Another hallmark of LD is the presence of neuroinflammation. We have recently reported the presence of reactive glia-derived neuroinflammation in LD mouse models and defined the main inflammatory pathways that operate in these mice, mainly TNF and IL-6 signaling pathways. In addition, we described the presence of infiltration of peripheral immune cells in the brain parenchyma, which could cooperate and aggravate the neuroinflammatory landscape of LD. In this work, we have checked the beneficial effect of two compounds with the capacity to ameliorate neuroinflammation and reduce leukocyte infiltration into the brain, namely fingolimod and dimethyl fumarate. Our results indicate a beneficial effect of fingolimod in reducing reactive astrogliosis-derived neuroinflammation and T-lymphocyte infiltration, which correlated with the improved behavioral performance of the treated Epm2b-/- mice. On the contrary, dimethyl fumarate, although it was able to reduce reactive astrogliosis, was less effective in preventing neuroinflammation and T-lymphocyte infiltration and in modifying behavioral tests.

Impaired malin expression and interaction with partner proteins in Lafora disease

Lafora disease (LD) is an autosomal recessive myoclonus epilepsy with onset in the teenage years leading to death within a decade of onset. LD is characterized by the overaccumulation of hyperphosphorylated, poorly branched, insoluble, glycogen-like polymers called Lafora bodies. The disease is caused by mutations in either EPM2A, encoding laforin, a dual specificity phosphatase that dephosphorylates glycogen, or EMP2B, encoding malin, an E3-ubiquitin ligase. While glycogen is a widely accepted laforin substrate, substrates for malin have been difficult to identify partly due to the lack of malin antibodies able to detect malin in vivo. Here we describe a mouse model in which the malin gene is modified at the C-terminus to contain the c-myc tag sequence, making an expression of malin-myc readily detectable. Mass spectrometry analyses of immunoprecipitates using c-myc tag antibodies demonstrate that malin interacts with laforin and several glycogen-metabolizing enzymes. To investigate the role of laforin in these interactions we analyzed two additional mouse models: malin-myc/laforin knockout and malin-myc/LaforinCS, where laforin was either absent or the catalytic Cys was genomically mutated to Ser, respectively. The interaction of malin with partner proteins requires laforin but is not dependent on its catalytic activity or the presence of glycogen. Overall, the results demonstrate that laforin and malin form a complex in vivo, which stabilizes malin and enhances interaction with partner proteins to facilitate normal glycogen metabolism. They also provide insights into the development of LD and the rescue of the disease by the catalytically inactive phosphatase.

Prognostic value of pathogenic variants in Lafora Disease: systematic review and meta-analysis of patient-level data

BACKGROUND

Lafora disease (LD) is a fatal form of progressive myoclonic epilepsy caused by biallelic pathogenic variants in EPM2A or NHLRC1. With a few exceptions, the influence of genetic factors on disease progression has yet to be confirmed. We present a systematic review and meta-analysis of the known pathogenic variants to identify genotype-phenotype correlations.

METHODS

We collected all reported cases with genetically-confirmed LD containing data on disease history. Pathogenic variants were classified into missense (MS) and protein-truncating (PT). Three genotype classes were defined according to the combination of the variants: MS/MS, MS/PT, and PT/PT. Time-to-event analysis was performed to evaluate survival and loss of autonomy.

RESULTS

250 cases described in 70 articles were included. The mutated gene was NHLRC1 in 56% and EPM2A in 44% of cases. 114 pathogenic variants (67 EPM2A; 47 NHLRC1) were identified. The NHLRC1 genotype PT/PT was associated with shorter survival [HR 2.88; 95% CI 1.23-6.78] and a trend of higher probability of loss of autonomy [HR 2.03, 95% CI 0.75-5.56] at the multivariable Cox regression analysis. The population carrying the homozygous p.Asp146Asn variant of NHLRC1 genotype was confirmed to have a more favourable prognosis in terms of disease duration.

CONCLUSIONS

This study demonstrates the existence of prognostic genetic factors in LD, namely the genotype defined according to the functional impact of the pathogenic variants. Although the reasons why NHLRC1 genotype PT/PT is associated with a poorer prognosis have yet to be fully elucidated, it may be speculated that malin plays a pivotal role in LD pathogenesis.

Role of Astrocytes in the Pathophysiology of Lafora Disease and Other Glycogen Storage Disorders

Lafora disease is a rare disorder caused by loss of function mutations in either the EPM2A or NHLRC1 gene. The initial symptoms of this condition are most commonly epileptic seizures, but the disease progresses rapidly with dementia, neuropsychiatric symptoms, and cognitive deterioration and has a fatal outcome within 5-10 years after onset. The hallmark of the disease is the accumulation of poorly branched glycogen in the form of aggregates known as Lafora bodies in the brain and other tissues. Several reports have demonstrated that the accumulation of this abnormal glycogen underlies all the pathologic traits of the disease. For decades, Lafora bodies were thought to accumulate exclusively in neurons. However, it was recently identified that most of these glycogen aggregates are present in astrocytes. Importantly, astrocytic Lafora bodies have been shown to contribute to pathology in Lafora disease. These results identify a primary role of astrocytes in the pathophysiology of Lafora disease and have important implications for other conditions in which glycogen abnormally accumulates in astrocytes, such as Adult Polyglucosan Body disease and the buildup of Corpora amylacea in aged brains.

P-Rex1 is a novel substrate of the E3 ubiquitin ligase Malin associated with Lafora disease

Laforin and Malin are two proteins that are encoded by the genes EPM2A and EPM2B, respectively. Laforin is a glucan phosphatase and Malin is an E3-ubiquitin ligase, and these two proteins function as a complex. Mutations occurring at the level of one of the two genes lead to the accumulation of an aberrant form of glycogen meant to cluster in polyglucosans that go under the name of Lafora bodies. Individuals affected by the appearance of these polyglucosans, especially at the cerebral level, experience progressive neurodegeneration and several episodes of epilepsy leading to the manifestation of a fatal form of a rare disease called Lafora disease (LD), for which, to date, no treatment is available. Despite the different dysfunctions described for this disease, many molecular aspects still demand elucidation. An effective way to unknot some of the nodes that prevent the achievement of better knowledge of LD is to focus on the substrates that are ubiquitinated by the E3-ubiquitin ligase Malin. Some substrates have already been provided by previous studies based on protein-protein interaction techniques and have been associated with some alterations that mark the disease. In this work, we have used an unbiased alternative approach based on the activity of Malin as an E3-ubiquitin ligase. We report the discovery of novel bonafide substrates of Malin and have characterized one of them more deeply, namely PIP3-dependent Rac exchanger 1 (P-Rex1). The analysis conducted upon this substrate sets the genesis of the delineation of a molecular pathway that leads to altered glucose uptake, which could be one of the origin of the accumulation of the polyglucosans present in the disease.

Early Treatment with Metformin Improves Neurological Outcomes in Lafora Disease

Lafora disease is a fatal form of progressive myoclonic epilepsy caused by mutations in the EPM2A or NHLRC1/EPM2B genes that usually appears during adolescence. The Epm2a-/- and Epm2b-/- knock-out mouse models of the disease develop behavioral and neurological alterations similar to those observed in patients. The aim of this work is to analyze whether early treatment with metformin (from conception to adulthood) ameliorates the formation of Lafora bodies and improves the behavioral and neurological outcomes observed with late treatment (during 2 months at 10 months of age). We also evaluated the benefits of metformin in patients with Lafora disease. To assess neurological improvements due to metformin administration in the two mouse models, we evaluated the effects on pentylenetetrazol sensitivity, posturing, motor coordination and activity, and memory. We also analyzed the effects on Lafora bodies, neurodegeneration, and astrogliosis. Furthermore, we conducted a follow-up study of an initial cohort of 18 patients with Lafora disease, 8 treated with metformin and 10 untreated. Our results indicate that early metformin was more effective than late metformin in Lafora disease mouse models improving neurological alterations of both models such as neuronal hyperexcitability, motor and memory alterations, neurodegeneration, and astrogliosis and decreasing the formation of Lafora bodies. Moreover, patients receiving metformin had a slower progression of the disease. Overall, early treatment improves the outcome seen with late metformin treatment in the two knock-out mouse models of Lafora disease. Metformin-treated patients exhibited an ameliorated course of the disease with slower deterioration of their daily living activities.

TNF and IL6/Jak2 signaling pathways are the main contributors of the glia-derived neuroinflammation present in Lafora disease, a fatal form of progressive myoclonus epilepsy

Lafora disease (LD; OMIM#254780) is a rare form of progressive myoclonus epilepsy (prevalence <1:1,000,000) characterized by the accumulation of insoluble deposits of aberrant glycogen (polyglucosans), named Lafora bodies, in the brain but also in peripheral tissues. LD is the most severe form of the group of progressive myoclonus epilepsies, since patients present a rapid deterioration and dementia with amplification of seizures, leading to death after a decade from the onset of the first symptoms. We have recently described that reactive glia-derived neuroinflammation should be considered a novel hallmark of LD since we observed a florid upregulation of differentially expressed genes in both LD mouse lines, which were mainly related to mediators of inflammatory response. In this work, we define an upregulation of the expression of mediators of the TNF and IL6/JAK2 signaling pathways in LD. In addition, we describe the activation of the non-canonical form of the inflammasome. Furthermore, we describe the infiltration of peripheral immune cells in the brain parenchyma, which could aggravate glia-derived neuroinflammation. Finally, we describe CXCL10 and S100b as blood biomarkers of the disease, which will allow the study of the progression of the disease using serum blood samples. We consider that the identification of these initial inflammatory changes in LD will be very important to implement possible anti-inflammatory therapeutic strategies to prevent the development of the disease.

Laforin targets malin to glycogen in Lafora progressive myoclonus epilepsy

Glycogen is the largest cytosolic macromolecule and is kept in solution through a regular system of short branches allowing hydration. This structure was thought to solely require balanced glycogen synthase and branching enzyme activities. Deposition of overlong branched glycogen in the fatal epilepsy Lafora disease (LD) indicated involvement of the LD gene products laforin and the E3 ubiquitin ligase malin in regulating glycogen structure. Laforin binds glycogen, and LD-causing mutations disrupt this binding, laforin-malin interactions and malin's ligase activity, all indicating a critical role for malin. Neither malin's endogenous function nor location had previously been studied due to lack of suitable antibodies. Here, we generated a mouse in which the native malin gene is tagged with the FLAG sequence. We show that the tagged gene expresses physiologically, malin localizes to glycogen, laforin and malin indeed interact, at glycogen, and malin's presence at glycogen depends on laforin. These results, and mice, open the way to understanding unknown mechanisms of glycogen synthesis critical to LD and potentially other much more common diseases due to incompletely understood defects in glycogen metabolism.

Management of plant central metabolism by SnRK1 protein kinases

SUCROSE NON-FERMENTING1 (SNF1)-RELATED KINASE 1 (SnRK1) is an evolutionarily conserved protein kinase with key roles in plant stress responses. SnRK1 is activated when energy levels decline during stress, reconfiguring metabolism and gene expression to favour catabolism over anabolism, and ultimately to restore energy balance and homeostasis. The capacity to efficiently redistribute resources is crucial to cope with adverse environmental conditions and, accordingly, genetic manipulations that increase SnRK1 activity are generally associated with enhanced tolerance to stress. In addition to its well-established function in stress responses, an increasing number of studies implicate SnRK1 in the homeostatic control of metabolism during the regular day-night cycle and in different organs and developmental stages. Here, we review how the genetic manipulation of SnRK1 alters central metabolism in several plant species and tissue types. We complement this with studies that provide mechanistic insight into how SnRK1 modulates metabolism, identifying changes in transcripts of metabolic components, altered enzyme activities, or direct regulation of enzymes or transcription factors by SnRK1 via phosphorylation. We identify patterns of response that centre on the maintenance of sucrose levels, in an analogous manner to the role described for its mammalian orthologue in the control of blood glucose homeostasis. Finally, we highlight several knowledge gaps and technical limitations that will have to be addressed in future research aiming to fully understand how SnRK1 modulates metabolism at the cellular and whole-plant levels.

Genome-Wide Association Study of Growth Traits in a Four-Way Crossbred Pig Population

Growth traits are crucial economic traits in the commercial pig industry and have a substantial impact on pig production. However, the genetic mechanism of growth traits is not very clear. In this study, we performed a genome-wide association study (GWAS) based on the specific-locus amplified fragment sequencing (SLAF-seq) to analyze ten growth traits on 223 four-way intercross pigs. A total of 227,921 highly consistent single nucleotide polymorphisms (SNPs) uniformly dispersed throughout the entire genome were used to conduct GWAS. A total of 53 SNPs were identified for ten growth traits using the mixed linear model (MLM), of which 18 SNPs were located in previously reported quantitative trait loci (QTL) regions. Two novel QTLs on SSC4 and SSC7 were related to average daily gain from 30 to 60 kg (ADG30–60) and body length (BL), respectively. Furthermore, 13 candidate genes (ATP5O, GHRHR, TRIM55, EIF2AK1, PLEKHA1, BRAP, COL11A2, HMGA1, NHLRC1, SGSM1, NFATC2, MAML1, and PSD3) were found to be associated with growth traits in pigs. The GWAS findings will enhance our comprehension of the genetic architecture of growth traits. We suggested that these detected SNPs and corresponding candidate genes might provide a biological foundation for improving the growth and production performance of pigs in swine breeding.

Non-lysine ubiquitylation: Doing things differently

The post-translational modification of proteins with ubiquitin plays a central role in nearly all aspects of eukaryotic biology. Historically, studies have focused on the conjugation of ubiquitin to lysine residues in substrates, but it is now clear that ubiquitylation can also occur on cysteine, serine, and threonine residues, as well as on the N-terminal amino group of proteins. Paradigm-shifting reports of non-proteinaceous substrates have further extended the reach of ubiquitylation beyond the proteome to include intracellular lipids and sugars. Additionally, results from bacteria have revealed novel ways to ubiquitylate (and deubiquitylate) substrates without the need for any of the enzymatic components of the canonical ubiquitylation cascade. Focusing mainly upon recent findings, this review aims to outline the current understanding of non-lysine ubiquitylation and speculate upon the molecular mechanisms and physiological importance of this non-canonical modification.

Genome-wide association study for four measures of epigenetic age acceleration and two epigenetic surrogate markers using DNA methylation data from Taiwan biobank

To highlight the genetic architecture for epigenetic aging, McCartney et al. recently identified 137 significant SNPs based on genome-wide association study (GWAS) meta-analyses of four epigenetic clocks and two epigenetic surrogate markers. However, none Asian ancestry studies have been included in this or previous meta-analyses. I performed a GWAS on blood DNA methylation (DNAm) levels of 2309 Taiwan Biobank (TWB) participants. Owing to the fact that the sample size of an individual GWAS of DNAm data is still not large, I adopted the "prioritized subset analysis" (PSA) method to boost the power of a GWAS. The four epigenetic clocks and the two epigenetic surrogate markers were investigated, respectively. I replicated 21 out of the 137 aging-associated genetic loci by applying the PSA method to the TWB DNAm data. Moreover, I identified five novel loci, including rs117530284 that was associated with the "epigenetic age acceleration" (EAA) according to Lu et al.'s GrimAge (called "GrimEAA"). Considering 16 covariates (sex, BMI, smoking status, drinking status, regular exercise, educational attainment, and the first 10 ancestry principal components), each "A" allele of rs117530284 in the IBA57 gene was found to be associated with a 1.5943-year GrimEAA (95% C.I. = [1.0748, 2.1138]). IBA57 is a protein coding gene and is associated with multiple mitochondrial dysfunctions syndromes. A decline in mitochondrial activity and quality is associated with aging and many age-related diseases. This is one of the first DNAm GWAS for individuals of Asian ancestry.

An empirical pipeline for personalized diagnosis of Lafora disease mutations

Lafora disease (LD) is a fatal childhood dementia characterized by progressive myoclonic epilepsy manifesting in the teenage years, rapid neurological decline, and death typically within ten years of onset. Mutations in either EPM2A, encoding the glycogen phosphatase laforin, or EPM2B, encoding the E3 ligase malin, cause LD. Whole exome sequencing has revealed many EPM2A variants associated with late-onset or slower disease progression. We established an empirical pipeline for characterizing the functional consequences of laforin missense mutations in vitro using complementary biochemical approaches. Analysis of 26 mutations revealed distinct functional classes associated with different outcomes that were supported by clinical cases. For example, F321C and G279C mutations have attenuated functional defects and are associated with slow progression. This pipeline enabled rapid characterization and classification of newly identified EPM2A mutations, providing clinicians and researchers genetic information to guide treatment of LD patients.

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Lafora disease (LD) patients present with varying clinical progression

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LD missense mutations differentially affect laforin function

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An empirical in vitro pipeline is used to classify laforin missense mutations

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Patient progression can be predicted based on mutation class

Modulators of Neuroinflammation Have a Beneficial Effect in a Lafora Disease Mouse Model

Lafora disease (LD; OMIM#274780) is a fatal rare neurodegenerative disorder characterized by generalized epileptic seizures and the presence of polyglucosan inclusions (PGs), called Lafora bodies (LBs), typically in the brain. LD is caused by mutations in two genes EPM2A or EPM2B, which encode respectively laforin, a glucan phosphatase, and malin, an E3-ubiquitin ligase. Much remains unknown about the molecular bases of LD and, unfortunately, appropriate treatment is still missing; therefore patients die within 10 years from the onset of the disease. Recently, we have identified neuroinflammation as one of the initial determinants in LD. In this work, we have investigated anti-inflammatory treatments as potential therapies in LD. With this aim, we have performed a preclinical study in an Epm2b-/- mouse model with propranolol, a β-adrenergic antagonist, and epigallocatechin gallate (EGCG), an antioxidant from green tea extract, both of which displaying additional anti-inflammatory properties. In vivo motor and cognitive behavioral tests and ex vivo histopathological brain analyses were used as parameters to assess the therapeutic potential of propranolol and EGCG. After 2 months of treatment, we observed an improvement not only in attention defects but also in neuronal disorganization, astrogliosis, and microgliosis present in the hippocampus of Epm2b-/- mice. In general, propranolol intervention was more effective than EGCG in preventing the appearance of astrocyte and microglia reactivity. In summary, our results confirm the potential therapeutic effectiveness of the modulators of inflammation as novel treatments in Lafora disease.

TRIM32 and Malin in Neurological and Neuromuscular Rare Diseases

Tripartite motif (TRIM) proteins are RING E3 ubiquitin ligases defined by a shared domain structure. Several of them are implicated in rare genetic diseases, and mutations in TRIM32 and TRIM-like malin are associated with Limb-Girdle Muscular Dystrophy R8 and Lafora disease, respectively. These two proteins are evolutionary related, share a common ancestor, and both display NHL repeats at their C-terminus. Here, we revmniew the function of these two related E3 ubiquitin ligases discussing their intrinsic and possible common pathophysiological pathways.

TRIM32: A Multifunctional Protein Involved in Muscle Homeostasis, Glucose Metabolism, and Tumorigenesis

Human tripartite motif family of proteins 32 (TRIM32) is a ubiquitous multifunctional protein that has demonstrated roles in differentiation, muscle physiology and regeneration, and tumor suppression. Mutations in TRIM32 result in two clinically diverse diseases. A mutation in the B-box domain gives rise to Bardet–Biedl syndrome (BBS), a disease whose clinical presentation shares no muscle pathology, while mutations in the NHL (NCL-1, HT2A, LIN-41) repeats of TRIM32 causes limb-girdle muscular dystrophy type 2H (LGMD2H). TRIM32 also functions as a tumor suppressor, but paradoxically is overexpressed in certain types of cancer. Recent evidence supports a role for TRIM32 in glycolytic-mediated cell growth, thus providing a possible mechanism for TRIM32 in the accumulation of cellular biomass during regeneration and tumorigenesis, including in vitro and in vivo approaches, to understand the broad spectrum of TRIM32 functions. A special emphasis is placed on the utility of the Drosophila model, a unique system to study glycolysis and anabolic pathways that contribute to the growth and homeostasis of both normal and tumor tissues.

Neuroinflammation and progressive myoclonus epilepsies: from basic science to therapeutic opportunities

Progressive myoclonus epilepsies (PMEs) are a group of genetic neurological disorders characterised by the occurrence of epileptic seizures, myoclonus and progressive neurological deterioration including cerebellar involvement and dementia. The primary cause of PMEs is variable and alterations in the corresponding mutated genes determine the progression and severity of the disease. In most cases, they lead to the death of the patient after a period of prolonged disability. PMEs also share poor information on the pathophysiological bases and the lack of a specific treatment. Recent reports suggest that neuroinflammation is a common trait under all these conditions. Here, we review similarities and differences in neuroinflammatory response in several PMEs and discuss the window of opportunity of using anti-inflammatory drugs in the treatment of several of these conditions.

Reactive Glia-Derived Neuroinflammation: a Novel Hallmark in Lafora Progressive Myoclonus Epilepsy That Progresses with Age

Lafora disease (LD) is a rare, fatal form of progressive myoclonus epilepsy. The molecular basis of this devastating disease is still poorly understood, and no treatment is available yet, which leads to the death of the patients around 10 years from the onset of the first symptoms. The hallmark of LD is the accumulation of insoluble glycogen-like inclusions in the brain and peripheral tissues, as a consequence of altered glycogen homeostasis. In addition, other determinants in the pathophysiology of LD have been suggested, such as proteostasis impairment, with reduction in autophagy, and oxidative stress, among others. In order to gain a general view of the genes involved in the pathophysiology of LD, in this work, we have performed RNA-Seq transcriptome analyses of whole-brain tissue from two independent mouse models of the disease, namely Epm2a-/- and Epm2b-/- mice, at different times of age. Our results provide strong evidence for three major facts: first, in both models of LD, we found a common set of upregulated genes, most of them encoding mediators of inflammatory response; second, there was a progression with the age in the appearance of these inflammatory markers, starting at 3 months of age; and third, reactive glia was responsible for the expression of these inflammatory genes. These results clearly indicate that neuroinflammation is one of the most important traits to be considered in order to fully understand the pathophysiology of LD, and define reactive glia as novel therapeutic targets in the disease.

Regulation of the autophagic PI3KC3 complex by laforin/malin E3-ubiquitin ligase, two proteins involved in Lafora disease

Lafora progressive myoclonus epilepsy is a fatal rare neurodegenerative disorder characterized by the accumulation of insoluble abnormal glycogen deposits in the brain and peripheral tissues. Mutations in at least two genes are responsible for the disease: EPM2A, encoding the glucan phosphatase laforin, and EPM2B, encoding the RING-type E3-ubiquitin ligase malin. Both laforin and malin form a functional complex in which laforin recruits the substrates to be ubiquitinated by malin. We and others have described that, in cellular and animal models of this disease, there is an autophagy impairment which leads to the accumulation of dysfunctional mitochondria. In addition, we established that the autophagic defect occurred at the initial steps of autophagosome formation. In this work, we present evidence that in cellular models of the disease there is a decrease in the amount of phosphatidylinositol-3P. This is probably due to defective regulation of the autophagic PI3KC3 complex, in the absence of a functional laforin/malin complex. In fact, we demonstrate that the laforin/malin complex interacts physically and co-localizes intracellularly with core components of the PI3KC3 complex (Beclin1, Vps34 and Vps15), and that this interaction is specific and results in the polyubiquitination of these proteins. In addition, the laforin/malin complex is also able to polyubiquitinate ATG14L and UVRAG. Finally, we show that overexpression of the laforin/malin complex increases PI3KC3 activity. All these results suggest a new role of the laforin/malin complex in the activation of autophagy via regulation of the PI3KC3 complex and explain the defect in autophagy described in Lafora disease.

Nuclear Glycogenolysis Modulates Histone Acetylation in Human Non-Small Cell Lung Cancers

Nuclear glycogen was first documented in the early 1940s, but its role in cellular physiology remained elusive. In this study, we utilized pure nuclei preparations and stable isotope tracers to define the origin and metabolic fate of nuclear glycogen. Herein, we describe a key function for nuclear glycogen in epigenetic regulation through compartmentalized pyruvate production and histone acetylation. This pathway is altered in human non-small cell lung cancers, as surgical specimens accumulate glycogen in the nucleus. We demonstrate that the decreased abundance of malin, an E3 ubiquitin ligase, impaired nuclear glycogenolysis by preventing the nuclear translocation of glycogen phosphorylase and causing nuclear glycogen accumulation. Re-introduction of malin in lung cancer cells restored nuclear glycogenolysis, increased histone acetylation, and decreased growth of cancer cells transplanted into mice. This study uncovers a previously unknown role for glycogen metabolism in the nucleus and elucidates another mechanism by which cellular metabolites control epigenetic regulation.

Lafora disease - from pathogenesis to treatment strategies

Lafora disease is a severe, autosomal recessive, progressive myoclonus epilepsy. The disease usually manifests in previously healthy adolescents, and death commonly occurs within 10 years of symptom onset. Lafora disease is caused by loss-of-function mutations in EPM2A or NHLRC1, which encode laforin and malin, respectively. The absence of either protein results in poorly branched, hyperphosphorylated glycogen, which precipitates, aggregates and accumulates into Lafora bodies. Evidence from Lafora disease genetic mouse models indicates that these intracellular inclusions are a principal driver of neurodegeneration and neurological disease. The integration of current knowledge on the function of laforin-malin as an interacting complex suggests that laforin recruits malin to parts of glycogen molecules where overly long glucose chains are forming, so as to counteract further chain extension. In the absence of either laforin or malin function, long glucose chains in specific glycogen molecules extrude water, form double helices and drive precipitation of those molecules, which over time accumulate into Lafora bodies. In this article, we review the genetic, clinical, pathological and molecular aspects of Lafora disease. We also discuss traditional antiseizure treatments for this condition, as well as exciting therapeutic advances based on the downregulation of brain glycogen synthesis and disease gene replacement.

Lafora Disease: A Ubiquitination-Related Pathology

Lafora disease (LD, OMIM254780) is a rare and fatal form of progressive myoclonus epilepsy (PME). Among PMEs, LD is unique because of the rapid neurological deterioration of the patients and the appearance in brain and peripheral tissues of insoluble glycogen-like (polyglucosan) inclusions, named Lafora bodies (LBs). LD is caused by mutations in the EPM2A gene, encoding the dual phosphatase laforin, or the EPM2B gene, encoding the E3-ubiquitin ligase malin. Laforin and malin form a functional complex that is involved in the regulation of glycogen synthesis. Thus, in the absence of a functional complex glycogen accumulates in LBs. In addition, it has been suggested that the laforin-malin complex participates in alternative physiological pathways, such as intracellular protein degradation, oxidative stress, and the endoplasmic reticulum unfolded protein response. In this work we review the possible cellular functions of laforin and malin with a special focus on their role in the ubiquitination of specific substrates. We also discuss here the pathological consequences of defects in laforin or malin functions, as well as the therapeutic strategies that are being explored for LD.

A novel EPM2A mutation yields a slow progression form of Lafora disease

Lafora disease (LD, OMIM 254780) is a rare disorder characterized by epilepsy and neurodegeneration leading patients to a vegetative state and death, usually within the first decade from the onset of the first symptoms. In the vast majority of cases LD is related to mutations in either the EPM2A gene (encoding the glucan phosphatase laforin) or the EPM2B gene (encoding the E3-ubiquitin ligase malin). In this work, we characterize the mutations present in the EPM2A gene in a patient displaying a slow progression form of the disease. The patient is compound heterozygous with Y112X and N163D mutations in the corresponding alleles. In primary fibroblasts obtained from the patient, we analyzed the expression of the mutated alleles by quantitative real time PCR and found slightly lower levels of expression of the EPM2A gene respect to control cells. However, by Western blotting we were unable to detect endogenous levels of the protein in crude extracts from patient fibroblasts. The Y112X mutation would render a truncated protein lacking the phosphatase domain and likely degraded. Since minute amounts of laforin-N163D might still play a role in cell physiology, we analyzed the biochemical characteristics of the N163D mutation. We found that recombinant laforin N163D protein was as stable as wild type and exhibited near wild type phosphatase activity towards biologically relevant substrates. On the contrary, it showed a severe impairment in the interaction profile with previously identified laforin binding partners. These results lead us to conclude that the slow progression of the disease present in this patient could be either due to the specific biochemical properties of laforin N163D or to the presence of alternative genetic modifying factors separate from pathogenicity.

Aging-associated changes in hippocampal glycogen metabolism in mice. Evidence for and against astrocyte-to-neuron lactate shuttle

Lactate derived from astrocytic glycogen has been shown to support memory formation in hippocampi of young animals, inhibiting it in old animals. Here we show, using quantitative mass spectrometry-based proteomics, immunofluorescence, and qPCR that aging is associated with an increase of glycogen metabolism enzymes concentration and shift in their localization from astrocytes to neurons. These changes are accompanied with reorganization of hippocampal energy metabolism which is manifested by elevated capacity of aging neurons to oxidize glucose in glycolysis and mitochondria, and decreased ability for fatty acids utilization. Our observations suggest that astrocyte-to-neuron lactate shuttle may operate in young hippocampi, however, during aging neurons become independent on astrocytic lactate and the metabolic crosstalk between the brain's cells is disrupted.

Degradation of altered mitochondria by autophagy is impaired in Lafora disease

Lafora disease (LD) is a fatal neurodegenerative disorder caused mostly by mutations in either of two genes encoding laforin and malin. LD is characterized by accumulation of a poorly branched form of glycogen in the cytoplasm of neurons and other cells. We previously reported dysfunctional mitochondria in different LD models. Now, using mitochondrial uncouplers and respiratory chain inhibitors, we have investigated with human fibroblasts a possible alteration in the selective degradation of damaged mitochondria (mitophagy) in LD. By flow cytometry of MitoTracker-labelled cells and measuring the levels of various mitochondrial proteins by western blot, we found in LD fibroblasts a partial impairment in the increased mitochondrial degradation produced by these treatments. In addition, colocalization of mitochondrial and lysosomal markers decreased in LD fibroblasts. All these results are consistent with a partial impairment in the induced autophagic degradation of dysfunctional mitochondria in LD fibroblasts. However, canonical recruitment of Parkin to mitochondria under these conditions remained unaffected in LD fibroblasts, and also in SH-SY5Y cells after malin and laforin overexpression. Neither mitochondrial localization nor protein levels of Bcl-2-like protein 13, another component of the mitophagic machinery that operates under these conditions, were affected in LD fibroblasts. In contrast, although these treatments raised autophagy in both control and LD fibroblasts, this enhanced autophagy was clearly lower in the latter cells. Therefore, the autophagic degradation of altered mitochondria is impaired in LD, which is due to a partial defect in the autophagic response and not in the canonical mitophagy signalling pathways.

Lafora disease offers a unique window into neuronal glycogen metabolism

Lafora disease (LD) is a fatal, autosomal recessive, glycogen-storage disorder that manifests as severe epilepsy. LD results from mutations in the gene encoding either the glycogen phosphatase laforin or the E3 ubiquitin ligase malin. Individuals with LD develop cytoplasmic, aberrant glycogen inclusions in nearly all tissues that more closely resemble plant starch than human glycogen. This Minireview discusses the unique window into glycogen metabolism that LD research offers. It also highlights recent discoveries, including that glycogen contains covalently bound phosphate and that neurons synthesize glycogen and express both glycogen synthase and glycogen phosphorylase.

Diabetes Mellitus in a Patient With Lafora Disease: Possible Links With Pancreatic β-Cell Dysfunction and Insulin Resistance

Lafora disease (LD) is a rare autosomal recessive disorder characterized by progressive myoclonic epilepsy followed by continuous neurological decline, culminating in death within 10 years. LD leads to accumulation of insoluble, abnormal, glycogen-like structures called Lafora bodies (LBs). It is caused by mutations in the gene encoding glycogen phosphatase (EPM2A) or the E3 ubiquitin ligase malin (EPM2B/NHLRC1). These two proteins are involved in an intricate, however, incompletely elucidated pathway governing glycogen metabolism. The formation of EPM2A and malin signaling complex promotes the ubiquitination of proteins participating in glycogen metabolism, where dysfunctional mutations lead to the formation of LBs. Herein, we describe a 13-years-old child with LD due to a NHLRC1 (c.386C > A, p.Pro129His) mutation, who has developed diabetes mellitus and was treated with metformin. We discuss how basic mechanisms of LD could be linked to β-cell dysfunction and insulin resistance.

AMPK Protein Interaction Analyses by Yeast Two-Hybrid

Mammalian AMP-activated protein kinase (AMPK) is a Ser/Thr protein kinase that acts as a crucial energy sensor in the cell. Since AMPK plays a key role in a multitude of different pathways in the cell, major efforts have been concentrated to elucidate its signaling network, mainly by the identification of AMPK downstream targets. In this chapter we describe a yeast two-hybrid method for the direct evaluation of the interaction between an AMPK subunit and putative substrates.

Loss of hepatic AMP-activated protein kinase impedes the rate of glycogenolysis but not gluconeogenic fluxes in exercising mice

Pathologies including diabetes and conditions such as exercise place an unusual demand on liver energy metabolism, and this demand induces a state of energy discharge. Hepatic AMP-activated protein kinase (AMPK) has been proposed to inhibit anabolic processes such as gluconeogenesis in response to cellular energy stress. However, both AMPK activation and glucose release from the liver are increased during exercise. Here, we sought to test the role of hepatic AMPK in the regulation of in vivo glucose-producing and citric acid cycle-related fluxes during an acute bout of muscular work. We used ²H/¹³C metabolic flux analysis to quantify intermediary metabolism fluxes in both sedentary and treadmill-running mice. Additionally, liver-specific AMPK α1 and α2 subunit KO and WT mice were utilized. Exercise caused an increase in endogenous glucose production, glycogenolysis, and gluconeogenesis from phosphoenolpyruvate. Citric acid cycle fluxes, pyruvate cycling, anaplerosis, and cataplerosis were also elevated during this exercise. Sedentary nutrient fluxes in the postabsorptive state were comparable for the WT and KO mice. However, the increment in the endogenous rate of glucose appearance during exercise was blunted in the KO mice because of a diminished glycogenolytic flux. This lower rate of glycogenolysis was associated with lower hepatic glycogen content before the onset of exercise and prompted a reduction in arterial glucose during exercise. These results indicate that liver AMPKα1α2 is required for maintaining glucose homeostasis during an acute bout of exercise.

Pathogenesis of Lafora Disease: Transition of Soluble Glycogen to Insoluble Polyglucosan

Lafora disease (LD, OMIM #254780) is a rare, recessively inherited neurodegenerative disease with adolescent onset, resulting in progressive myoclonus epilepsy which is fatal usually within ten years of symptom onset. The disease is caused by loss-of-function mutations in either of the two genes EPM2A (laforin) or EPM2B (malin). It characteristically involves the accumulation of insoluble glycogen-derived particles, named Lafora bodies (LBs), which are considered neurotoxic and causative of the disease. The pathogenesis of LD is therefore centred on the question of how insoluble LBs emerge from soluble glycogen. Recent data clearly show that an abnormal glycogen chain length distribution, but neither hyperphosphorylation nor impairment of general autophagy, strictly correlates with glycogen accumulation and the presence of LBs. This review summarizes results obtained with patients, mouse models, and cell lines and consolidates apparent paradoxes in the LD literature. Based on the growing body of evidence, it proposes that LD is predominantly caused by an impairment in chain-length regulation affecting only a small proportion of the cellular glycogen. A better grasp of LD pathogenesis will further develop our understanding of glycogen metabolism and structure. It will also facilitate the development of clinical interventions that appropriately target the underlying cause of LD.

Ubiquitin Ligases and Posttranslational Regulation of Energy in the Heart: The Hand that Feeds

Heart failure (HF) is a costly and deadly syndrome characterized by the reduced capacity of the heart to adequately provide systemic blood flow. Mounting evidence implicates pathological changes in cardiac energy metabolism as a contributing factor in the development of HF. While the main source of fuel in the healthy heart is the oxidation of fatty acids, in the failing heart the less energy efficient glucose and glycogen metabolism are upregulated. The ubiquitin proteasome system plays a key role in regulating metabolism via protein-degradation/regulation of autophagy and regulating metabolism-related transcription and cell signaling processes. In this review, we discuss recent research that describes the role of the ubiquitin-proteasome system (UPS) in regulating metabolism in the context of HF. We focus on ubiquitin ligases (E3s), the component of the UPS that confers substrate specificity, and detail the current understanding of how these E3s contribute to cardiac pathology and metabolism. © 2017 American Physiological Society. Compr Physiol 7:841-862, 2017.

Lafora disease

Lafora disease (LD) is an autosomal recessive progressive myoclonus epilepsy due to mutations in the EPM2A (laforin) and EPM2B (malin) genes, with no substantial genotype-phenotype differences between the two. Founder effects and recurrent mutations are common, and mostly isolated to specific ethnic groups and/or geographical locations. Pathologically, LD is characterized by distinctive polyglucosans, which are formations of abnormal glycogen. Polyglucosans, or Lafora bodies (LB) are typically found in the brain, periportal hepatocytes of the liver, skeletal and cardiac myocytes, and in the eccrine duct and apocrine myoepithelial cells of sweat glands. Mouse models of the disease and other naturally occurring animal models have similar pathology and phenotype. Hypotheses of LB formation remain controversial, with compelling evidence and caveats for each hypothesis. However, it is clear that the laforin and malin functions regulating glycogen structure are key. With the exception of a few missense mutations LD is clinically homogeneous, with onset in adolescence. Symptoms begin with seizures, and neurological decline follows soon after. The disease course is progressive and fatal, with death occurring within 10 years of onset. Antiepileptic drugs are mostly non-effective, with none having a major influence on the progression of cognitive and behavioral symptoms. Diagnosis and genetic counseling are important aspects of LD, and social support is essential in disease management. Future therapeutics for LD will revolve around the pathogenesics of the disease. Currently, efforts at identifying compounds or approaches to reduce brain glycogen synthesis appear to be highly promising.

Activation of Wnt Signaling in Cortical Neurons Enhances Glucose Utilization through Glycolysis

The Wnt signaling pathway is critical for a number of functions in the central nervous system, including regulation of the synaptic cleft structure and neuroprotection against injury. Deregulation of Wnt signaling has been associated with several brain pathologies, including Alzheimer's disease. In recent years, it has been suggested that the Wnt pathway might act as a central integrator of metabolic signals from peripheral organs to the brain, which would represent a new role for Wnt signaling in cell metabolism. Energy metabolism is critical for normal neuronal function, which mainly depends on glucose utilization. Brain energy metabolism is important in almost all neurological disorders, to which a decrease in the capacity of the brain to utilize glucose has been linked. However, little is known about the relationship between Wnt signaling and neuronal glucose metabolism in the cellular context. In the present study, we found that acute treatment with the Wnt3a ligand induced a large increase in glucose uptake, without changes in the expression or localization of glucose transporter type 3. In addition, we observed that Wnt3a treatment increased the activation of the metabolic sensor Akt. Moreover, we observed an increase in the activity of hexokinase and in the glycolytic rate, and both processes were dependent on activation of the Akt pathway. Furthermore, we did not observe changes in the activity of glucose-6-phosphate dehydrogenase or in the pentose phosphate pathway. The effect of Wnt3a was independent of both the transcription of Wnt target genes and synaptic effects of Wnt3a. Together, our results suggest that Wnt signaling stimulates glucose utilization in cortical neurons through glycolysis to satisfy the high energy demand of these cells.

An evaluation of the links between microRNA, autophagy, and epilepsy

Epilepsy is a serious chronic neurologic disorder characterized by recurrent unprovoked seizures resulting from abnormal and highly synchronous neuronal discharges within the brain. Small noncoding RNAs, called microRNAs, play vital roles in epileptogenesis, with potential contributions as valuable biomarkers and targets for the treatment of epilepsy. To maintain cellular homeostasis, cellular components, such as organelles, proteins, protein complexes/oligomers, and pathogens, are delivered to the lysosome for degradation through a process called autophagy, which plays either a protective or a harmful role under epileptic stress. Several autophagic mechanisms have been implicated in epileptogenesis, including the mammalian target of rapamycin pathway, aberrant substrate accumulation, and the formation of epileptic networks. In addition, the regulation of autophagy through microRNAs (miRNAs) represents a novel posttranscriptional regulatory mechanism through 'autophagamiRNAs'. The correlation between autophagy and miRNA has increased our understanding of the underlying pathogenesis of human diseases. Here, we review the current findings regarding the correlations between miRNA, autophagy, and epilepsy to provide a solid foundation for further examination of the miRNA-autophagy pathway involved in epilepsy pathophysiology.

Cadmium inhibits mouse sperm motility through inducing tyrosine phosphorylation in a specific subset of proteins

Cadmium (Cd) has been reported to impair male fertility, primarily by disrupting sperm motility, but the underlying molecular mechanism remains unclear. Here we investigated the effects of Cd on sperm motility, tyrosine phosphorylation, AMP-activated protein kinase (AMPK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, and ATP levels in vitro. Our results demonstrated that Cd inhibited sperm motility, GAPDH activity, AMPK activity and ATP production, and induced tyrosine phosphorylation of 55-57KDa proteins. Importantly, all the parameters affected by Cd were restored to normal levels when incubated with 10μM Cd in the presence of 30μM ethylene diamine tetraacetic acid (EDTA). Interestingly, changes of tyrosine phosphorylation levels of 55-57KDa proteins are completely contrary to that of other parameters. These results suggest that Cd-induced tyrosine phosphorylation of 55-57KDa proteins might act as an engine to block intracellular energy metabolism and thus decrease sperm motility.

Inflammation in Lafora Disease: Evolution with Disease Progression in Laforin and Malin Knock-out Mouse Models

Lafora progressive myoclonus epilepsy (Lafora disease, LD) is a fatal rare autosomal recessive neurodegenerative disorder characterized by the accumulation of insoluble ubiquitinated polyglucosan inclusions in the cytoplasm of neurons, which is most commonly associated with mutations in two genes: EPM2A, encoding the glucan phosphatase laforin, and EPM2B, encoding the E3-ubiquitin ligase malin. The present study analyzes possible inflammatory responses in the mouse lines Epm2a ^-/- (laforin knock-out) and Epm2b ^-/- (malin knock-out) with disease progression. Increased numbers of reactive astrocytes (expressing the GFAP marker) and microglia (expressing the Iba1 marker) together with increased expression of genes encoding cytokines and mediators of the inflammatory response occur in both mouse lines although with marked genotype differences. C3ar1 and CxCl10 messenger RNAs (mRNAs) are significantly increased in Epm2a ^-/- mice aged 12 months when compared with age-matched controls, whereas C3ar1, C4b, Ccl4, CxCl10, Il1b, Il6, Tnfα, and Il10ra mRNAs are significantly upregulated in Epm2b ^-/- at the same age. This is accompanied by increased protein levels of IL1-β, IL6, TNFα, and Cox2 particularly in Epm2b ^-/- mice. The severity of inflammatory changes correlates with more severe clinical symptoms previously described in Epm2b ^-/- mice. These findings show for the first time increased innate inflammatory responses in a neurodegenerative disease with polyglucosan intraneuronal deposits which increase with disease progression, in a way similar to what is seen in neurodegenerative diseases with abnormal protein aggregates. These findings also point to the possibility of using anti-inflammatory agents to mitigate the degenerative process in LD.

Homeostasis of the astrocytic glutamate transporter GLT-1 is altered in mouse models of Lafora disease

Lafora disease (LD, OMIM 254780) is a fatal rare disorder characterized by epilepsy and neurodegeneration. Although in recent years a lot of information has been gained on the molecular basis of the neurodegeneration that accompanies LD, the molecular basis of epilepsy is poorly understood. Here, we present evidence indicating that the homeostasis of glutamate transporter GLT-1 (EAAT2) is compromised in mouse models of LD. Our results indicate that primary astrocytes from LD mice have reduced capacity of glutamate transport, probably because they present a reduction in the levels of the glutamate transporter at the plasma membrane. On the other hand, the overexpression in cellular models of laforin and malin, the two proteins related to LD, results in an accumulation of GLT-1 (EAAT2) at the plasma membrane and in a severe reduction of the ubiquitination of the transporter. All these results suggest that the laforin/malin complex slows down the endocytic recycling of the GLT-1 (EAAT2) transporter. Since, defects in the function of this transporter lead to excitotoxicity and epilepsy, we suggest that the epilepsy that accompanies LD could be due, at least in part, to deficiencies in the function of the GLT-1 (EAAT2) transporter.

Biophysical characterization of laforin–carbohydrate interaction

Laforin, a key regulator of glycogen metabolism, is a low-affinity glycan binder. In the present work, we thoroughly biophysically characterized its glycan interaction.

Assessing the Biological Activity of the Glucan Phosphatase Laforin

Glucan phosphatases are a recently discovered family of enzymes that dephosphorylate either starch or glycogen and are essential for proper starch metabolism in plants and glycogen metabolism in humans. Mutations in the gene encoding the only human glucan phosphatase, laforin, result in the fatal, neurodegenerative, epilepsy known as Lafora disease. Here, we describe phosphatase assays to assess both generic laforin phosphatase activity and laforin's unique glycogen phosphatase activity.

Regulation of Carbohydrate Metabolism, Lipid Metabolism, and Protein Metabolism by AMPK

This chapter summarizes AMPK function in the regulation of substrate and energy metabolism with the main emphasis on carbohydrate and lipid metabolism, protein turnover, mitochondrial biogenesis, and whole-body energy homeostasis. AMPK acts as whole-body energy sensor and integrates different signaling pathway to meet both cellular and body energy requirements while inhibiting energy-consuming processes but also activating energy-producing ones. AMPK mainly promotes glucose and fatty acid catabolism, whereas it prevents protein, glycogen, and fatty acid synthesis.

Oxidative stress, a new hallmark in the pathophysiology of Lafora progressive myoclonus epilepsy

Lafora disease (LD; OMIM 254780, ORPHA501) is a devastating neurodegenerative disorder characterized by the presence of glycogen-like intracellular inclusions called Lafora bodies and caused, in most cases, by mutations in either the EPM2A or the EPM2B gene, encoding respectively laforin, a phosphatase with dual specificity that is involved in the dephosphorylation of glycogen, and malin, an E3-ubiquitin ligase involved in the polyubiquitination of proteins related to glycogen metabolism. Thus, it has been reported that laforin and malin form a functional complex that acts as a key regulator of glycogen metabolism and that also plays a crucial role in protein homeostasis (proteostasis). Regarding this last function, it has been shown that cells are more sensitive to ER stress and show defects in proteasome and autophagy activities in the absence of a functional laforin-malin complex. More recently, we have demonstrated that oxidative stress accompanies these proteostasis defects and that various LD models show an increase in reactive oxygen species and oxidative stress products together with a dysregulated antioxidant enzyme expression and activity. In this review we discuss possible connections between the multiple defects in protein homeostasis present in LD and oxidative stress.

The laforin/malin E3-ubiquitin ligase complex ubiquitinates pyruvate kinase M1/M2

BACKGROUND

Lafora disease (LD, OMIM 254780) is a fatal neurodegenerative disorder produced mainly by mutations in two genes: EPM2A, encoding the dual specificity phosphatase laforin, and EPM2B, encoding the E3-ubiquitin ligase malin. Although it is known that laforin and malin may form a functional complex, the underlying molecular mechanisms of this pathology are still far from being understood.

METHODS

In order to gain information about the substrates of the laforin/malin complex, we have carried out a yeast substrate-trapping screening, originally designed to identify substrates of protein tyrosine phosphatases.

RESULTS

Our results identify the two muscular isoforms of pyruvate kinase (PKM1 and PKM2) as novel interaction partners of laforin.

CONCLUSIONS

We present evidence indicating that the laforin/malin complex is able to interact with and ubiquitinate both PKM1 and PKM2. This post-translational modification, although it does not affect the catalytic activity of PKM1, it impairs the nuclear localization of PKM2.

Glycogen phosphorylation and Lafora disease

Covalent phosphorylation of glycogen, first described 35 years ago, was put on firm ground through the work of the Whelan laboratory in the 1990s. But glycogen phosphorylation lay fallow until interest was rekindled in the mid 2000s by the finding that it could be removed by a glycogen-binding phosphatase, laforin, and that mutations in laforin cause a fatal teenage-onset epilepsy, called Lafora disease. Glycogen phosphorylation is due to phosphomonoesters at C2, C3 and C6 of glucose residues. Phosphate is rare, ranging from 1:500 to 1:5000 phosphates/glucose depending on the glycogen source. The mechanisms of glycogen phosphorylation remain under investigation but one hypothesis to explain C2 and perhaps C3 phosphate is that it results from a rare side reaction of the normal synthetic enzyme glycogen synthase. Lafora disease is likely caused by over-accumulation of abnormal glycogen in insoluble deposits termed Lafora bodies in neurons. The abnormality in the glycogen correlates with elevated phosphorylation (at C2, C3 and C6), reduced branching, insolubility and an enhanced tendency to aggregate and become insoluble. Hyperphosphorylation of glycogen is emerging as an important feature of this deadly childhood disease.

Three patients with lafora disease: different clinical presentations and a novel mutation

Lafora disease is a rare, fatal, autosomal recessive hereditary disease characterized by epilepsy, myoclonus and progressive neurological deterioration. Diagnosis is made by polyglucosan inclusion bodies (Lafora bodies) shown in skin biopsy. Responsible mutations of Lafora disease involves either the EPM2A or NHLRC1 (EPM2B) gene. Mutations in the NHLRC1 gene are described as having a more benign clinical course and a later age of death compared with EPM2A mutations. We report 2 genetic mutations and clinical courses of Lafora disease in 3 adolescents with homozygote NHLRC1 mutation and novel homozygous EPM2A mutation.

Loss of protein targeting to glycogen sensitizes human hepatocellular carcinoma cells towards glucose deprivation mediated oxidative stress and cell death

PTG is a protein that is critical for glycogen accumulation in various tissues such as the liver. Our present study shows that its loss sensitizes liver cancer cells towards metabolic and oxidative stress.

Protein targeting to glycogen (PTG) is a ubiquitously expressed scaffolding protein that critically regulates glycogen levels in many tissues, including the liver, muscle and brain. However, its importance in transformed cells has yet to be explored in detail. Since recent studies have demonstrated an important role for glycogen metabolism in cancer cells, we decided to assess the effect of PTG levels on the ability of human hepatocellular carcinoma (HepG2) cells to respond to metabolic stress. Although PTG expression did not significantly affect the proliferation of HepG2 cells under normal culture conditions, we determined that PTG plays an important role during glucose deprivation. Overexpression of PTG protected cells from cell death in the absence of glucose, whereas knocking down PTG further promoted cytotoxicity, as measured by the release of lactate dehydrogenase (LDH) into the media. Additionally, we demonstrated that PTG attenuates glucose deprivation induced haeme oxygenase-1 (HO-1) expression, suggesting that PTG protects against glucose deprivation-induced oxidative stress. Indeed, treating cells with the antioxidant N-acetyl cysteine (NAC) rescued cells from cytotoxicity caused by glucose deprivation. Finally, we showed that loss of PTG resulted in enhanced autophagy. In control cells, glucose deprivation suppressed autophagy as determined by the increase in the levels of p62, an autophagy substrate. However, in knockdown cells, this suppression was relieved. Blockade of autophagy also attenuated cytotoxicity from glucose deprivation in PTG knockdown cells. Taken together, our findings identify a novel role for PTG in protecting hepatocellular carcinoma cells from metabolic stress, in part by regulating oxidative stress and autophagy.

Pharmacological Interventions to Ameliorate Neuropathological Symptoms in a Mouse Model of Lafora Disease

Lafora disease (LD, OMIM 254780) is a rare fatal neurodegenerative disorder that usually occurs during childhood with generalized tonic-clonic seizures, myoclonus, absences, drop attacks, or visual seizures. Unfortunately, at present, available treatments are only palliatives and no curative drugs are available yet. The hallmark of the disease is the accumulation of insoluble polyglucosan inclusions, called Lafora bodies (LBs), within the neurons but also in heart, muscle, and liver cells. Mouse models lacking functional EPM2A or EPM2B genes (the two major loci related to the disease) recapitulate the Lafora disease phenotype: they accumulate polyglucosan inclusions, show signs of neurodegeneration, and have a dysregulation of protein clearance and endoplasmic reticulum stress response. In this study, we have subjected a mouse model of LD (Epm2b-/-) to different pharmacological interventions aimed to alleviate protein clearance and endoplasmic reticulum stress. We have used two chemical chaperones, trehalose and 4-phenylbutyric acid. In addition, we have used metformin, an activator of AMP-activated protein kinase (AMPK), as it has a recognized neuroprotective role in other neurodegenerative diseases. Here, we show that treatment with 4-phenylbutyric acid or metformin decreases the accumulation of Lafora bodies and polyubiquitin protein aggregates in the brain of treated animals. 4-Phenylbutyric acid and metformin also diminish neurodegeneration (measured in terms of neuronal loss and reactive gliosis) and ameliorate neuropsychological tests of Epm2b-/- mice. As these compounds have good safety records and are already approved for clinical uses on different neurological pathologies, we think that the translation of our results to the clinical practice could be straightforward.