The transgenic model was created through overexpression of laforin carrying a phosphatase inactivating point mutation (Cys26-6Ser). This dominant-negative model was used to trap the unknown laforin substrate and produce LD pathology. The transgenic LD mouse provided valuable information regarding the laforin protein localization. In brain, this protein localizes to the neuronal soma and dendrites. It was also demonstrated that laforin localizes to the ER, but not to the ribosomes, as initially thought. Importantly, this model allowed the characterization of laforin binding to different polysaccharides, and the preferential binding to polyglucosans over glycogen (33). Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical The knockout model

was created through deletion of the EPM2A exon containing the PTP domain. EPM2A null mice had pathological evidence

of LD as early as 2 months of age. Phenotypically, they had normal growth and development until the age of 4 months, when behavioral changes started to occur. Myoclonic seizures, ataxia and electroencephalographic changes were seen at 9 months. These animals showed a peculiar Inhibitors,research,lifescience,medical neurodegeneration mechanism involving organellar disintegration. In addition, it was observed that neurodegeneration and the onset of LB inclusions occurred prior to any behavioral abnormalities (34). Pathophysiology of LBs To date it is not clear why LBs are formed in the absence of laforin or malin. Evidence to date indicates that both proteins are involved in the metabolism of glycogen. Further supporting this hypothesis is the observation that higher levels of cytosolic glycogen Inhibitors,research,lifescience,medical are correlated with higher levels of laforin, while absence of glycogen is correlated with a 60% reduction of laforin. Mouse models which over-express glycogen synthase and have massive over-accumulation

of glycogen with lafora-like bodies show a 7-fold elevation of muscle laforin (35). Selleck Go6983 However, laforin binds preferentially to the polyglucosans forming the LBs than to glycogen (33). Inhibitors,research,lifescience,medical This observation suggests that polyglucosans do normally form in the cell, likely as a by-product of glycogen metabolism, and laforin’s (and possibly malin’s) proper function is important in preventing the accumulation of the those toxic polyglucosans. Crafting of properly branched and soluble glycogen requires a number of coordinated enzymatic activities. The complex between these enzymes and glycogen has been termed the glycogenosome. A main component of this complex is glycogen synthase (GS), which elongates glycogen strands by adding glucose units. Glycogen branching enzyme (BE) then moves the extended oligosaccharides to branch points, maintaining the globularity and solubility of glycogen. An abnormally high GS to BE ratio results in inadequately branched polysaccharides, namely polyglucosans (36). Laforin may downregulate GS via PTG-PP1 and via GSK3.