Suppression of leptin signaling reduces polyglucosan inclusions and seizure susceptibility in a mouse model for Lafora disease.

Lafora disease (LD) represents a fatal form of neurodegenerative disorder characterized by the presence of abnormally large number of polyglucosan bodies-called the Lafora bodies-in neurons and other tissues of the affected patients. The disease is caused by defects in the EPM2A gene coding for a protein phosphatase (laforin) or the NHLRC1 gene coding for an ubiquitin ligase (malin). Studies have shown that inhibition of glycogen synthesis in the brain could prevent the formation of Lafora bodies in the neurons and reduce seizure susceptibility in laforin-deficient mouse, an established animal model for LD. Since increased glucose uptake is thought to underlie increased glycogen in LD, and since the adipocyte hormone leptin is known to positively regulate the glucose uptake in neurons, we reasoned that blocking leptin signaling might reduce the neuronal glucose uptake and ameliorate the LD pathology. We demonstrate here that mice that were deficient for both laforin and leptin receptor showed a reduction in the glycogen level, Lafora bodies and gliosis in the brain, and displayed reduced susceptibility to induced seizures as compared to animals that were deficient only for laforin. Thus, blocking leptin signaling could be a one of the effective therapeutic strategies in LD.

Curcumin-derivatives as fluorescence-electrochemical dual probe for ultrasensitive detections of picric acid in aqueous media.

We are reporting the two curcumin derivatives, ferrocenyl curcumin (Fc-cur) and 4-nitro-benzylidene curcumin (NBC), as a probe through dual modalities, i.e., fluorescence and electrochemical methods, for the detection of nitro-analytes, such as picric acid (PA). The probes exhibited aggregation-induced enhanced emission (AIEE), and the addition of picric acid (PA) demonstrated good and specific fluorimetric identification of PA in the aggregated state. By using density functional theory (DFT), the mechanism of picric acid's (PA) interactions with the probes was further investigated. DFT studies shows evidence of charge transfer from curcumin derivatives probe to picric acid resulting into the formation of an adduct. The reduction of trinitrophenol (PA) to 2, 4, 6-trinitrosophenol was investigated utilizing a probe-modified glassy carbon electrode (GCE) with a good detection limit of 9.63 ± 0.001 pM and 41.01 ± 0.002 pM, respectively, for Fc-cur@GCE and NBC@GCE, taking into account the redox behavior of the probe. The applicability of the designed sensor has been utilized for real-time application in the estimation of picric acid in several water samples collected from the different source.

TREM2 and APOE do not modulate phagocytic clearance of dying cells in the live mammalian brain.

TREM2 and APOE are two major risk factors for Alzheimer's disease (AD) that have been proposed to play crucial roles in microglia pathophysiology by affecting their ability to phagocytose cellular debris or aggregated proteins. In this study, we investigated for the first time the impact of TREM2 and APOE on the removal of dying neurons in the live brain by implementing a targeted photochemical method for programmed cell death induction combined with high-resolution two-photon imaging. Our findings showed that the deletion of either TREM2 or APOE did not affect the dynamics of microglia engagement with dying neurons or their efficiency in phagocytosing corpses. Interestingly, while microglia that encapsulate amyloid deposits were capable of phagocytosing dying cells without disengaging from plaques or moving their cell bodies; in the absence of TREM2, microglia cell bodies were observed to readily migrate towards dying cells, further disengaging from plaques. Our data suggest that TREM2 and APOE variants are unlikely to increase risk of AD through impaired corpse phagocytosis.

Increase in brain glycogen levels ameliorates Huntington's disease phenotype and rescues neurodegeneration in Drosophila.

Under normal physiological conditions, the mammalian brain contains very little glycogen, most of which is stored in astrocytes. However, the aging brain and the subareas of the brain in patients with neurodegenerative disorders tend to accumulate glycogen, the cause and significance of which remain largely unexplored. Using cellular models, we have recently demonstrated a neuroprotective role for neuronal glycogen and glycogen synthase in the context of Huntington's disease. To gain insight into the role of brain glycogen in regulating proteotoxicity, we utilized a Drosophila model of Huntington's disease, in which glycogen synthase is either knocked down or expressed ectopically. Enhancing glycogen synthesis in the brains of flies with Huntington's disease decreased mutant Huntingtin aggregation and reduced oxidative stress by activating auto-lysosomal functions. Further, overexpression of glycogen synthase in the brain rescues photoreceptor degeneration, improves locomotor deficits and increases fitness traits in this Huntington's disease model. We, thus, provide in vivo evidence for the neuroprotective functions of glycogen synthase and glycogen in neurodegenerative conditions, and their role in the neuronal autophagy process.

TREM2: Modulator of Lipid Metabolism in Microglia.

Lipid-processing mechanisms during demyelination are poorly understood. In this issue of Neuron,Nugent et al. (2020) show by cell-specific lipidomics that Trem2 deficiency leads to cholesterol ester (CE) overload in microglia. This is mediated by misregulation of lipid metabolism genes and is rescued by modulating CE synthesis or efflux.

Astrocytes and microglia play orchestrated roles and respect phagocytic territories during neuronal corpse removal in vivo.

Cell death is prevalent throughout life; however, the coordinated interactions and roles of phagocytes during corpse removal in the live brain are poorly understood. We developed photochemical and viral methodologies to induce death in single cells and combined this with intravital optical imaging. This approach allowed us to track multicellular phagocytic interactions with precise spatiotemporal resolution. Astrocytes and microglia engaged with dying neurons in an orchestrated and synchronized fashion. Each glial cell played specialized roles: Astrocyte processes rapidly polarized and engulfed numerous small dendritic apoptotic bodies, while microglia migrated and engulfed the soma and apical dendrites. The relative involvement and phagocytic specialization of each glial cell was plastic and controlled by the receptor tyrosine kinase Mertk. In aging, there was a marked delay in apoptotic cell removal. Thus, a precisely orchestrated response and cross-talk between glial cells during corpse removal may be critical for maintaining brain homeostasis.

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.

Glycogen synthase protects neurons from cytotoxicity of mutant huntingtin by enhancing the autophagy flux.

Healthy neurons do not store glycogen while they do possess the machinery for the glycogen synthesis albeit at an inactive state. Neurons in the degenerating brain, however, are known to accumulate glycogen, although its significance was not well understood. Emerging reports present contrasting views on neuronal glycogen synthesis; a few reports demonstrate a neurotoxic effect of glycogen while a few others suggest glycogen to be neuroprotective. Thus, the specific role of glycogen and glycogen synthase in neuronal physiology is largely unexplored. Using cellular and animal models of Huntington's disease, we show here that the overexpression of cytotoxic mutant huntingtin protein induces glycogen synthesis in the neurons by activating glycogen synthase and the overexpressed glycogen synthase protected neurons from the cytotoxicity of the mutant huntingtin. Exposure of neuronal cells to proteasomal blockade and oxidative stress also activate glycogen synthase to induce glycogen synthesis and to protect against stress-induced neuronal death. We show that the glycogen synthase plays an essential and inductive role in the neuronal autophagic flux, and helps in clearing the cytotoxic huntingtin aggregate. We also show that the increased neuronal glycogen inhibits the aggregation of mutant huntingtin, and thus could directly contribute to its clearance. Finally, we demonstrate that excessive autophagy flux is the molecular basis of cell death caused by the activation of glycogen synthase in unstressed neurons. Taken together, our results thus provide a novel function for glycogen synthase in proteolytic processes and offer insight into the role of glycogen synthase and glycogen in both survival and death of the neurons.

Loss of malin, but not laforin, results in compromised autophagic flux and proteasomal dysfunction in cells exposed to heat shock.

Heat stress to a cell leads to the activation of heat shock response, which is required for the management of misfolded and unfolded proteins. Macroautophagy and proteasome-mediated degradation are the two cellular processes that degrade polyubiquitinated, misfolded proteins. Contrasting pieces of evidence exist on the effect of heat stress on the activation of the above-mentioned degradative pathways. Laforin phosphatase and malin E3 ubiquitin ligase, the two proteins defective in Lafora neurodegenerative disorder, are involved in cellular stress response pathways and are required for the activation of heat shock transcription factor - the heat shock factor 1 (HSF1) - and, consequently, for cellular protection under heat shock. While the role of laforin and malin in the proteolytic pathways is well established, their role in cellular recovery from heat shock was not explored. To address this, we investigated autophagic flux, proteasomal activity, and the level of polyubiquitinated proteins in Neuro2a cells partially silenced for laforin or malin protein and exposed to heat shock. We found that heat shock was able to induce autophagic flux, proteasomal activity and reduce the polyubiquitinated proteins load in the laforin-silenced cells but not in the malin-deficient cells. Loss of malin leads to reduced proteasomal activity in the heat-shocked cells. Taken together, our results suggest a distinct mode of action for laforin and malin in the heat shock-induced proteolytic processes.