Laforin, a dual-specificity phosphatase involved in Lafora disease, is phosphorylated at Ser25 by AMP-activated protein kinase

Lafora progressive myoclonus epilepsy [LD (Lafora disease)] is a fatal autosomal recessive neurodegenerative disorder caused by loss-of-function mutations in either the EPM2A gene, encoding the dual-specificity phosphatase laforin, or the EPM2B gene, encoding the E3-ubiquitin ligase malin. Previously, we and others showed that laforin and malin form a functional complex that regulates multiple aspects of glycogen metabolism, and that the interaction between laforin and malin is enhanced by conditions activating AMPK (AMP-activated protein kinase). In the present study, we demonstrate that laforin is a phosphoprotein, as indicated by two-dimensional electrophoresis, and we identify Ser(25) as the residue involved in this modification. We also show that Ser(25) is phosphorylated both in vitro and in vivo by AMPK. Lastly, we demonstrate that this residue plays a critical role for both the phosphatase activity and the ability of laforin to interact with itself and with previously established binding partners. The results of the present study suggest that phosphorylation of laforin-Ser(25) by AMPK provides a mechanism to modulate the interaction between laforin and malin. Regulation of this complex is necessary to maintain normal glycogen metabolism. Importantly, Ser(25) is mutated in some LD patients (S25P), and our results begin to elucidate the mechanism of disease in these patients.     

Laforin, a dual specificity phosphatase that dephosphorylates complex carbohydrates

Laforin is the only phosphatase in the animal kingdom that contains a carbohydrate-binding module. Mutations in the gene encoding laforin result in Lafora disease, a fatal autosomal recessive neurodegenerative disorder, which is diagnosed by the presence of intracellular deposits of insoluble complex carbohydrates known as Lafora bodies. We demonstrate that laforin interacts with proteins known to be involved in glycogen metabolism and rule out several of these proteins as potential substrates. Surprisingly, we find that laforin displays robust phosphatase activity against a phosphorylated complex carbohydrate. Furthermore, this activity is unique to laforin, since several other phosphatases are unable to dephosphorylate polysaccharides. Finally, fusing the carbohydrate-binding module of laforin to the dual specific phosphatase VHR does not result in the ability of this phosphatase to dephosphorylate polysaccharides. Therefore, we hypothesize that laforin is unique in its ability to utilize a phosphorylated complex carbohydrate as a substrate and that this function may be necessary for the maintenance of normal cellular glycogen.     

Malin decreases glycogen accumulation by promoting the degradation of protein targeting to glycogen (PTG)

Lafora disease (LD) is an autosomal recessive neurodegenerative disease that results in progressive myoclonus epilepsy and death. LD is caused by mutations in either the E3 ubiquitin ligase malin or the dual specificity phosphatase laforin. A hallmark of LD is the accumulation of insoluble glycogen in the cytoplasm of cells from most tissues. Glycogen metabolism is regulated by phosphorylation of key metabolic enzymes. One regulator of this phosphorylation is protein targeting to glycogen (PTG/R5), a scaffold protein that binds both glycogen and many of the enzymes involved in glycogen synthesis, including protein phosphatase 1 (PP1), glycogen synthase, phosphorylase, and laforin. Overexpression of PTG markedly increases glycogen accumulation, and decreased PTG expression decreases glycogen stores. To investigate if malin and laforin play a role in glycogen metabolism, we overexpressed PTG, malin, and laforin in tissue culture cells. We found that expression of malin or laforin decreased PTG-stimulated glycogen accumulation by 25%, and co-expression of malin and laforin abolished PTG-stimulated glycogen accumulation. Consistent with this result, we found that malin ubiquitinates PTG in a laforin-dependent manner, both in vivo and in vitro, and targets PTG for proteasome-dependent degradation. These results suggest an additional mechanism, involving laforin and malin, in regulating glycogen metabolism.     

The laforin-malin complex negatively regulates glycogen synthesis by modulating cellular glucose uptake via glucose transporters

Lafora disease (LD), an inherited and fatal neurodegenerative disorder, is characterized by increased cellular glycogen content and the formation of abnormally branched glycogen inclusions, called Lafora bodies, in the affected tissues, including neurons. Therefore, laforin phosphatase and malin ubiquitin E3 ligase, the two proteins that are defective in LD, are thought to regulate glycogen synthesis through an unknown mechanism, the defects in which are likely to underlie some of the symptoms of LD. We show here that laforin's subcellular localization is dependent on the cellular glycogen content and that the stability of laforin is determined by the cellular ATP level, the activity of 5'-AMP-activated protein kinase, and the affinity of malin toward laforin. By using cell and animal models, we further show that the laforin-malin complex regulates cellular glucose uptake by modulating the subcellular localization of glucose transporters; loss of malin or laforin resulted in an increased abundance of glucose transporters in the plasma membrane and therefore excessive glucose uptake. Loss of laforin or malin, however, did not affect glycogen catabolism. Thus, the excessive cellular glucose level appears to be the primary trigger for the abnormally higher levels of cellular glycogen seen in LD.     

Dimerization of the Glucan Phosphatase Laforin Requires the Participation of Cysteine 329

Laforin, encoded by a gene that is mutated in Lafora Disease (LD, OMIM 254780), is a modular protein composed of a carbohydrate-binding module and a dual-specificity phosphatase domain. Laforin is the founding member of the glucan-phosphatase family and regulates the levels of phosphate present in glycogen. Multiple reports have described the capability of laforin to form dimers, although the function of these dimers and their relationship with LD remains unclear. Recent evidence suggests that laforin dimerization depends on redox conditions, suggesting that disulfide bonds are involved in laforin dimerization. Using site-directed mutagenesis we constructed laforin mutants in which individual cysteine residues were replaced by serine and then tested the ability of each protein to dimerize using recombinant protein as well as a mammalian cell culture assay. Laforin-Cys329Ser was the only Cys/Ser mutant unable to form dimers in both assays. We also generated a laforin truncation lacking the last three amino acids, laforin-Cys329X, and this truncation also failed to dimerize. Interestingly, laforin-Cys329Ser and laforin-Cys329X were able to bind glucans, and maintained wild type phosphatase activity against both exogenous and biologically relevant substrates. Furthermore, laforin-Cys329Ser was fully capable of participating in the ubiquitination process driven by a laforin-malin complex. These results suggest that dimerization is not required for laforin phosphatase activity, glucan binding, or for the formation of a functional laforin-malin complex. Cumulatively, these results suggest that cysteine 329 is specifically involved in the dimerization process of laforin. Therefore, the C329S mutant constitutes a valuable tool to analyze the physiological implications of laforin’s oligomerization.     

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.     

Co-chaperone CHIP Stabilizes Aggregate-prone Malin, a Ubiquitin Ligase Mutated in Lafora Disease

Lafora disease (LD) is an autosomal recessive neurodegenerative disorder caused by mutation in either the dual specificity phosphatase laforin or ubiquitin ligase malin. A pathological hallmark of LD is the accumulation of cytoplasmic polyglucosan inclusions commonly known as Lafora bodies in both neuronal and non-neuronal tissues. How mutations in these two proteins cause disease pathogenesis is not well understood. Malin interacts with laforin and recruits to aggresomes upon proteasome inhibition and was shown to degrade misfolded proteins. Here we report that malin is spontaneously misfolded and tends to be aggregated, degraded by proteasomes, and forms not only aggresomes but also other cytoplasmic and nuclear aggregates in all transfected cells upon proteasomal inhibition. Malin also interacts with Hsp70. Several disease-causing mutants of malin are comparatively more unstable than wild type and form aggregates in most transfected cells even without the inhibition of proteasome function. These cytoplasmic and nuclear aggregates are immunoreactive to ubiquitin and 20 S proteasome. Interestingly, progressive proteasomal dysfunction and cell death is also most frequently observed in the mutant malin-overexpressed cells compared with the wild-type counterpart. Finally, we demonstrate that the co-chaperone carboxyl terminus of the Hsc70-interacting protein (CHIP) stabilizes malin by modulating the activity of Hsp70. All together, our results suggest that malin is unstable, and the aggregate-prone protein and co-chaperone CHIP can modulate its stability.     

Neuronatin-mediated Aberrant Calcium Signaling and Endoplasmic Reticulum Stress Underlie Neuropathology in Lafora Disease

Lafora disease (LD) is a teenage-onset inherited progressive myoclonus epilepsy characterized by the accumulations of intracellular inclusions called Lafora bodies and caused by mutations in protein phosphatase laforin or ubiquitin ligase malin. But how the loss of function of either laforin or malin causes disease pathogenesis is poorly understood. Recently, neuronatin was identified as a novel substrate of malin that regulates glycogen synthesis. Here we demonstrate that the level of neuronatin is significantly up-regulated in the skin biopsy sample of LD patients having mutations in both malin and laforin. Neuronatin is highly expressed in human fetal brain with gradual decrease in expression in developing and adult brain. However, in adult brain, neuronatin is predominantly expressed in parvalbumin-positive GABAergic interneurons and localized in their processes. The level of neuronatin is increased and accumulated as insoluble aggregates in the cortical area of LD brain biopsy samples, and there is also a dramatic loss of parvalbumin-positive GABAergic interneurons. Ectopic expression of neuronatin in cultured neuronal cells results in increased intracellular Ca²⁺, endoplasmic reticulum stress, proteasomal dysfunction, and cell death that can be partially rescued by malin. These findings suggest that the neuronatin-induced aberrant Ca²⁺ signaling and endoplasmic reticulum stress might underlie LD pathogenesis.     

Increased laforin and laforin binding to glycogen underlie Lafora body formation in malin-deficient Lafora disease

The solubility of glycogen, essential to its metabolism, is a property of its shape, a sphere generated through extensive branching during synthesis. Lafora disease (LD) is a severe teenage-onset neurodegenerative epilepsy and results from multiorgan accumulations, termed Lafora bodies (LB), of abnormally structured aggregation-prone and digestion-resistant glycogen. LD is caused by loss-of-function mutations in the EPM2A or EPM2B gene, encoding the interacting laforin phosphatase and malin E3 ubiquitin ligase enzymes, respectively. The substrate and function of malin are unknown; an early counterintuitive observation in cell culture experiments that it targets laforin to proteasomal degradation was not pursued until now. The substrate and function of laforin have recently been elucidated. Laforin dephosphorylates glycogen during synthesis, without which phosphate ions interfere with and distort glycogen construction, leading to LB. We hypothesized that laforin in excess or not removed following its action on glycogen also interferes with glycogen formation. We show in malin-deficient mice that the absence of malin results in massively increased laforin preceding the appearance of LB and that laforin gradually accumulates in glycogen, which corresponds to progressive LB generation. We show that increasing the amounts of laforin in cell culture causes LB formation and that this occurs only with glycogen binding-competent laforin. In summary, malin deficiency causes increased laforin, increased laforin binding to glycogen, and LB formation. Furthermore, increased levels of laforin, when it can bind glycogen, causes LB. We conclude that malin functions to regulate laforin and that malin deficiency at least in part causes LB and LD through increased laforin binding to glycogen.     

Laforin is required for the functional activation of malin in endoplasmic reticulum stress resistance in neuronal cells

Mutations in either EPM2A, the gene encoding a dual-specificity phosphatase named laforin, or NHLRC1, the gene encoding an E3 ubiquitin ligase named malin, cause Lafora disease in humans. Lafora disease is a fatal neurological disorder characterized by progressive myoclonus epilepsy, severe neurological deterioration and accumulation of poorly branched glycogen inclusions, called Lafora bodies or polyglucosan bodies, within the cell cytoplasm. The molecular mechanism underlying the neuropathogenesis of Lafora disease remains unknown. Here, we present data demonstrating that in the cells expressing low levels of laforin protein, overexpressed malin and its Lafora disease-causing missense mutants are stably polyubiquitinated. Malin and malin mutants form ubiquitin-positive aggregates in or around the nuclei of the cells in which they are expressed. Neither wild-type malin nor its mutants elicit endoplasmic reticulum stress, although the mutants exaggerate the response to endoplasmic reticulum stress. Overexpressed laforin impairs the polyubiquitination of malin while it recruits malin to polyglucosan bodies. The recruitment and activities of laforin and malin are both required for the polyglucosan body disruption. Consistently, targeted deletion of laforin in brain cells from Epm2a knockout mice increases polyubiquitinated proteins. Knockdown of Epm2a or Nhlrc1 in neuronal Neuro2a cells shows that they cooperate to allow cells to resist ER stress and apoptosis. These results reveal that a functional laforin-malin complex plays a critical role in disrupting Lafora bodies and relieving ER stress, implying that a causative pathogenic mechanism underlies their deficiency in Lafora disease.     

Activation of serum/glucocorticoid-induced kinase 1 (SGK1) underlies increased glycogen levels,mTOR activation,and autophagy defects in Lafora disease

Lafora disease (LD), a fatal genetic form of myoclonic epilepsy, is characterized by abnormally high levels of cellular glycogen and its accumulation as Lafora bodies in affected tissues. Therefore the two defective proteins in LD—laforin phosphatase and malin ubiquitin ligase—are believed to be involved in glycogen metabolism. We earlier demonstrated that laforin and malin negatively regulate cellular glucose uptake by preventing plasma membrane targeting of glucose transporters. We show here that loss of laforin results in activation of serum/glucocorticoid-induced kinase 1 (SGK1) in cellular and animals models and that inhibition of SGK1 in laforin-deficient cells reduces the level of plasma membrane-bound glucose transporter, glucose uptake, and the consequent glycogen accumulation. We also provide evidence to suggest that mammalian target of rapamycin (mTOR) activates SGK1 kinase in laforin-deficient cells. The mTOR activation appears to be a glucose-dependent event, and overexpression of dominant-negative SGK1 suppresses mTOR activation, suggesting the existence of a feedforward loop between SGK1 and mTOR. Our findings indicate that inhibition of SGK1 activity could be an effective therapeutic approach to suppress glycogen accumulation, inhibit mTOR activity, and rescue autophagy defects in LD.     

Ubiquitin conjugating enzyme E2-N and sequestosome-1 (p62) are components of the ubiquitination process mediated by the malin–laforin E3-ubiquitin ligase complex

Lafora disease (LD, OMIM254780, ORPHA501) is a rare neurodegenerative form of epilepsy related to mutations in two proteins: laforin, a dual specificity phosphatase, and malin, an E3-ubiquitin ligase. Both proteins form a functional complex, where laforin recruits specific substrates to be ubiquitinated by malin. However, little is known about the mechanism driving malin–laforin mediated ubiquitination of its substrates. In this work we present evidence indicating that the malin–laforin complex interacts physically and functionally with the ubiquitin conjugating enzyme E2-N (UBE2N). This binding determines the topology of the chains that the complex is able to promote in the corresponding substrates (mainly K63-linked polyubiquitin chains). In addition, we demonstrate that the malin–laforin complex interacts with the selective autophagy adaptor sequestosome-1 (p62). Binding of p62 to the malin–laforin complex allows its recognition by LC3, a component of the autophagosomal membrane. In addition, p62 enhances the ubiquitinating activity of the malin–laforin E3-ubiquitin ligase complex. These data enrich our knowledge on the mechanism of action of the malin–laforin complex as an E3-ubiquitin ligase and reinforces the role of this complex in targeting substrates toward the autophagy pathway.     

Increased Endoplasmic Reticulum Stress and Decreased Proteasomal Function in Lafora Disease Models Lacking the Phosphatase Laforin

Background

Lafora progressive myoclonus epilepsy (Lafora disease; LD) is a fatal autosomal recessive neurodegenerative disorder caused by loss-of-function mutations in either the EPM2A gene, encoding the dual specificity phosphatase laforin, or the EPM2B gene, encoding the E3-ubiquitin ligase malin. Previously, we and others have shown that both proteins form a functional complex that regulates glycogen synthesis by a novel mechanism involving ubiquitination and proteasomal degradation of at least two proteins, glycogen synthase and R5/PTG. Since laforin and malin localized at the endoplasmic reticulum (ER) and their regulatory role likely extend to other proteins unrelated to glycogen metabolism, we postulated that their absence may also affect the ER-unfolded protein response pathway.

Methodology/Principal Findings

Here, we demonstrate that siRNA silencing of laforin in Hek293 and SH-SY5Y cells increases their sensitivity to agents triggering ER-stress, which correlates with impairment of the ubiquitin-proteasomal pathway and increased apoptosis. Consistent with these findings, analysis of tissue samples from a LD patient lacking laforin, and from a laforin knockout (Epm2a-/-) mouse model of LD, demonstrates constitutive high expression levels of ER-stress markers BIP/Grp78, CHOP and PDI, among others.

Conclusions/Significance

We demonstrate that, in addition to regulating glycogen synthesis, laforin and malin play a role protecting cells from ER-stress, likely contributing to the elimination of unfolded proteins. These data suggest that proteasomal dysfunction and ER-stress play an important role in the pathogenesis of LD, which may offer novel therapeutic approaches for this fatal neurodegenerative disorder.     

Laforin–Malin Complex Degrades Polyglucosan Bodies in Concert with Glycogen Debranching Enzyme and Brain Isoform Glycogen Phosphorylase

In Lafora disease (LD), the deficiency of either EPM2A or NHLRC1, the genes encoding the phosphatase laforin and E3 ligase, respectively, causes massive accumulation of less-branched glycogen inclusions, known as Lafora bodies, also called polyglucosan bodies (PBs), in several types of cells including neurons. The biochemical mechanism underlying the PB accumulation, however, remains undefined. We recently demonstrated that laforin is a phosphatase of muscle glycogen synthase (GS1) in PBs, and that laforin recruits malin, together reducing PBs. We show here that accomplishment of PB degradation requires a protein assembly consisting of at least four key enzymes: laforin and malin in a complex, and the glycogenolytic enzymes, glycogen debranching enzyme 1 (AGL1) and brain isoform glycogen phosphorylase (GPBB). Once GS1-synthesized polyglucosan accumulates into PBs, laforin recruits malin to the PBs where laforin dephosphorylates, and malin degrades the GS1 in concert with GPBB and AGL1, resulting in a breakdown of polyglucosan. Without fountional laforin–malin complex assembled on PBs, GPBB and AGL1 together are unable to efficiently breakdown polyglucosan. All these events take place on PBs and in cytoplasm. Deficiency of each of the four enzymes causes PB accumulation in the cytoplasm of affected cells. Demonstration of the molecular mechanisms underlying PB degradation lays a substantial biochemical foundation that may lead to understanding how PB metabolizes and why mutations of either EPM2A or NHLRC1 in humans cause LD. Mutations in AGL1 or GPBB may cause diseases related to PB accumulation.     

Impaired autophagy in Lafora disease

Lafora disease (LD) is a progressive, lethal, autosomal recessive, neurodegenerative disorder that manifests with myoclonus epilepsy. LD is characterized by the presence of intracellular inclusion bodies called Lafora bodies (LB), in brain, spinal cord and other tissues. More than 50 percent of LD is caused by mutations in EPM2A that encodes laforin. Here we review our recent findings that revealed that laforin regulates autophagy. We consider how autophagy compromise may predispose to LB formation and neurodegeneration in LD, and discuss future investigations suggested by our data.Key words: autophagy, glycogen metabolism, Lafora disease, laforin, malin, neurodegeneration     

Lafora disease: from genotype to phenotype

The progressive myoclonic epilepsy of Lafora or Lafora disease (LD) is a neurodegenerative disorder characterized by recurrent seizures and cognitive deficits. With typical onset in the late childhood or early adolescence, the patients show progressive worsening of the disease symptoms, leading to death in about 10 years. It is an autosomal recessive disorder caused by the loss-of-function mutations in the EPM2A gene, coding for a protein phosphatase (laforin) or the NHLRC1 gene coding for an E3 ubiquitin ligase (malin). LD is characterized by the presence of abnormally branched water insoluble glycogen inclusions known as Lafora bodies in the neurons and other tissues, suggesting a role for laforin and malin in glycogen metabolic pathways. Mouse models of LD, developed by targeted disruption of the Epm2a or Nhlrc1 gene, recapitulated most of the symptoms and pathological features as seen in humans, and have offered insight into the pathomechanisms. Besides the formation of Lafora bodies in the neurons in the presymptomatic stage, the animal models have also demonstrated perturbations in the proteolytic pathways, such as ubiquitin-proteasome system and autophagy, and inflammatory response. This review attempts to provide a comprehensive coverage on the genetic defects leading to the LD in humans, on the functional properties of the laforin and malin proteins, and on how defects in any one of these two proteins result in a clinically similar phenotype. We also discuss the disease pathologies as revealed by the studies on the animal models and, finally, on the progress with therapeutic attempts albeit in the animal models.     

Laforin Prevents Stress-Induced Polyglucosan Body Formation and Lafora Disease Progression in Neurons

Glycogen, the largest cytosolic macromolecule, is soluble because of intricate construction generating perfect hydrophilic-surfaced spheres. Little is known about neuronal glycogen function and metabolism, though progress is accruing through the neurodegenerative epilepsy Lafora disease (LD) proteins laforin and malin. Neurons in LD exhibit Lafora bodies (LBs), large accumulations of malconstructed insoluble glycogen (polyglucosans). We demonstrated that the laforin–malin complex reduces LBs and protects neuronal cells against endoplasmic reticulum stress-induced apoptosis. We now show that stress induces polyglucosan formation in normal neurons in culture and in the brain. This is mediated by increased glucose-6-phosphate allosterically hyperactivating muscle glycogen synthase (GS1) and is followed by activation of the glycogen digesting enzyme glycogen phosphorylase. In the absence of laforin, stress-induced polyglucosans are undigested and accumulate into massive LBs, and in laforin-deficient mice, stress drastically accelerates LB accumulation and LD. The mechanism through which laforin–malin mediates polyglucosan degradation remains unclear but involves GS1 dephosphorylation by laforin. Our work uncovers the presence of rapid polyglucosan metabolism as part of the normal physiology of neuroprotection. We propose that deficiency in the degradative phase of this metabolism, leading to LB accumulation and resultant seizure predisposition and neurodegeneration, underlies LD.     

Conservation of the glucan phosphatase laforin is linked to rates of molecular evolution and the glucan metabolism of the organism

Background  

Lafora disease (LD) is a fatal autosomal recessive neurodegenerative disease. A hallmark of LD is cytoplasmic accumulation of insoluble glucans, called Lafora bodies (LBs). Mutations in the gene encoding the phosphatase laforin account for ~50% of LD cases, and this gene is conserved in all vertebrates. We recently demonstrated that laforin is the founding member of a unique class of phosphatases that dephosphorylate glucans.     

Dimeric Quaternary Structure of Human Laforin

The phosphatase laforin removes phosphate groups from glycogen during biosynthetic activity. Loss-of-function mutations in the gene encoding laforin is the predominant cause of Lafora disease, a fatal form of progressive myoclonic epilepsy. Here, we used hybrid structural methods to determine the molecular architecture of human laforin. We found that laforin adopts a dimeric quaternary structure, topologically similar to the prototypical dual specificity phosphatase VH1. The interface between the laforin carbohydrate-binding module and the dual specificity phosphatase domain generates an intimate substrate-binding crevice that allows for recognition and dephosphorylation of phosphomonoesters of glucose. We identify novel molecular determinants in the laforin active site that help decipher the mechanism of glucan phosphatase activity.     

Malin knockout mice support a primary role of autophagy in the pathogenesis of Lafora disease

Lafora disease (LD), a fatal neurodegenerative disorder characterized by intracellular inclusions called Lafora bodies (LBs), is caused by recessive loss-of-function mutations in the genes encoding either laforin or malin. Previous studies suggested a role of these proteins in regulating glycogen biosynthesis, in glycogen dephosphorylation and in the modulation of intracellular proteolytic systems. However, the contribution of each of these processes to LD pathogenesis is unclear. Here we review our recent finding that dysfunction of autophagy is a common feature of both laforin- and malin-deficient mice, preceding other pathological manifestations. We propose that autophagy plays a primary role in LD pathogenesis and is a potential target for its treatment.