MYSTERIES OF BRAIN METABOLISM AND LAFORA DISEASE
One of the mysteries of brain metabolism and for that matter Lafora Disease is why normal nerve cells do not store glycogen. Glucose is the main source of energy in the brain as in other cells and glycogen is the main storage for glucose. Hence glycogen is a source for chronic energy and yet glycogen is not present in normal nerve cells. In contrast, in Lafora Disease, a progressive and deadly form of epilepsy, excessive amounts of abnormally branched glycogen accumulate in toxic amounts and kill nerve cells. This suggested that there must be finely-tuned machinery in the brain that prevents glycogen from appearing much less accumulating in normal nerve cells. This mystery is rapidly being solved by expert biochemists in glycogen metabolism and protein phosphatases spurred on by the discoveries of the disease causing genes in Lafora Disease by clinician scientists. This separate group of scientists has worked furiously, independently but harmoniously, in the last 12 years. In spring of 2007, these scientists met for a Workshop in Sarlat, France, stimulating collaborations, speeding up research, triggering a spate of publications and helping set up the stage for treatment protocols in Lafora Disease.
Finding the Disease Causing Gene of Lafora Disease
The modern story of Lafora Disease started in 1995 in the Epilepsy Genetics/Genomics Laboratories at the Epilepsy Center of Excellence of the Greater Los Angeles VA Medical Center and the David Geffen School of Medicine at UCLA. There, the first chromosome locus (6p24) for Lafora Disease was discovered. This led to the eventual identification of EPM2A (Laforin) in 1998 and EPM2B (Malin) in 2003 by the Los Angeles scientists and previous PhD and postdoctoral students who had then branched out into their own independent laboratories in Toronto (Canada), Madrid (Spain) and Kanpur (India). The families being studied by the Lafora Disease researchers then showed that Laforin belonged to a group of enzymes called dual specificity phosphatases that targeted glycogen while Malin was an E3 ubiquitin ligase, an enzyme involved in the cell disposal unit (like the garbage disposal of a kitchen). By 2002, two mice models of lafora disease were made — one where the laforin gene was knocked out in the developing embryo was made by collaboration between Los Angeles and Japanese scientists. Another, where a mutation of laforin was inserted in the developing embryo was prepared by Toronto scientists.
Setting the Stage for Laforin Gene Replacement Treatment
Enter the scientist experts on protein phosphatases and glycogen metabolism. First to help in 2005, was the protein phosphatase lab at UC San Diego which showed that EPM2B/malin actually tagged EPM2A/Laforin with a marker (ubiquitin) and set it on its way to the cell disposal unit. In the ensuing two years, the same group of scientists from UC San Diego and Norwich, UK, together with plant biologists in Austria, discovered the counterpart of Laforin in plant and other organisms and showed that humans and other organisms share the common function of laforin in purging excessive carbohydrates and glycogen and preventing glycogen buildup that is harmful to the plant and organism cells. Next came the experts on glycogen metabolism. In 2007, a consortium of scientists from Madrid, Barcelona and Valencia, confirmed by the same UC San Diego team, showed that a complex of Laforin and Malin acting together suppresses the enzyme machinery that makes glycogen in nerve cells. The same complex of Laforin and Malin also sets up for the cell disposal unit the Laforin docking regions for protein phosphatase-1 and glycogen synthase (enzymes necessary for making glycogen). This way, the Laforin-Malin complex ensures suppression and blockade of glycogen formation in nerve cells as well as elimination of glycogen and its necessary enzymes by the cell disposal unit. When nature places a mutation in either Laforin or Malin, not only is poorly branched glycogen formed in excess but elimination through the cell disposal unit of glycogen and its components and its control systems by the Laforin/Malin complex is also dysfunctional and nerve cells die.
Also in 2007, both UC San Diego scientists and Indiana University scientists independently demonstrated that Laforin could release phosphate from amylopectin, a plant carbohydrate similar to glycogen and actual mammalian glycogen. This is very important because it shows for the first time that glycogen like amylopectin is a substrate of Laforin. If Laforin acts as a glycogen phosphatase in vivo, then the phosphate content in glycogen would be elevated in Lafora Disease. This is what is found in the mice whose Laforin has been knocked out. Glycogen phosphatase assay could, thus, provide a way of monitoring treatment.
Blood Brain Barrier Experts in the Epilepsy Center of Excellence at Los Angeles
As the functions of Laforin and Malin were unraveling, so the mysteries of glycogen metabolism were being demystified. Meanwhile, a team of experts on the blood-brain barrier in Los Angeles started to devise a method to deliver Laforin from the blood through the blood-brain barrier into brain nerve cells of mice with Lafora Disease. If the function of Laforin is to purge glycogen from nerve cells, then delivering Laforin into the brain of Lafora Disease patients would clear the brain of Lafora inclusion bodies. Starting in 2002, these scientists in Los Angeles labored through the details of placing Laforin inside a vehicle that should be harmless to humans, namely, pegylated immunoliposomes. (Placing Laforin inside lipids contrasts to placing the gene inside adenoviruses which have now been suspected to cause death in 2 persons and possible leukemia in 2 children.) By 2006, Laforin delivered by immunoliposomes into brains of mice with Lafora Disease was shown to indeed purge and decrease the load of Lafora inclusion bodies. Now, the timing of delivery, the exact doses, the frequency of delivery, and the interval of delivery of Laforin are being fine-tuned in mice with Lafora Disease. All this information will be important when Laforin is actually delivered to patients with Lafora disease.
Monitoring Results of Laforin Gene Therapy
One other advantage gained from defining glycogen and amylopectin as substrates of Laforin is the deduction that the Lafora inclusion bodies must be made of poorly branched glycogen. This could allow the imaging of Lafora inclusion bodies in patients suffering from the disease using a positron emission labeled chemical that is part of Lafora inclusion bodies. This would be an important project for chemists — to produce a ligand that targets a part of lafora inclusion bodies and that could be imaged on PET scans. This can be another way for monitoring the results of treatment. If Laforin can really purge excessive glycogen like the Lafora inclusion bodies, then we should be able to show the inclusion bodies decrease and even disappear on PET scans that image Lafora bodies.
Where is the Story of Lafora Disease Leading us
This story is taking us to the treatment protocols and studies that need to be developed and developed rapidly if we are to save lives. Besides laboratory work and collaborations with various experts, this involves applications to the Institutional Review Boards to obtain approval for treatment in patients.
Thus, funds are urgently needed to develop a treatment team for Lafora Disease. This treatment team should address the following:
(1) A treatment team dedicated to
- A safety trial of laforin gene therapy in non-human simians
- Laforin human gene therapy and
- Gentamycin treatment
(2) An assay team that monitors gene replacement treatment results
(3) A PET scan team that assays turnover and purging of Lafora bodies during gene replacement treatment
December 28, 2007 – Progressive Myoclonus Epilepsy, Lafora Type
Lafora disease (LD) is characterized by fragmentary, symmetric, or generalized myoclonus and/or generalized tonic-clonic seizures, visual hallucinations (occipital seizures), and progressive neurologic degeneration including cognitive and/or behavioral deterioration, dysarthria, and ataxia beginning in previously healthy adolescents between 12 and 17 years. read more