Amyotrophic lateral sclerosis (ALS) is a debilitating neuromuscular disease for which there is no cure. The one substantive characteristic known about this disorder is that the sporadic form of the disease, which is also the more common form, is tied to mutations in the SOD1 gene. Thus far, more than 150 mutations have been documented in this gene, all of which lead to generally similar symptoms: muscle weakness, muscle wasting and eventual death. Research in Dr. Serge Przedborski's laboratory at Columbia University, and in other labs, has shown that it is the astrocyte that contains the mutated SOD1 that kills motor neurons (MNs) in the spinal cord. Further research in the Przedborski lab has shown that these mutated astrocytes produce a substance toxic to MNs which is also released into the surrounding culture medium that remains toxic even after the astrocytes are removed.
Dr. Przedborksi, recipient of an FY07 ALSRP Therapeutic Development Award, has developed a co-culture system containing MNs and conditioned medium from astrocytes to screen compounds for a therapeutically useful drug for ALS. Candidates that mitigated the toxic effects on MNs in the astrocyte-exposed medium would move forward for more extensive testing.
To validate the screening system, Dr. Przedborski's lab replicated their original findings that mutant SOD1 astrocyte-conditioned medium is toxic to primary spinal MNs and demonstrated that MNs exhibit selective vulnerability to the toxic media compared to other types of neurons. These effects were replicable with embryonic stem cell-derived motor neurons (ES-MNs), a preferable source, as they represent an endless supply of viable cells which make the model system readily expandable.
The initial targeted molecular screen has been fruitful, identifying JNK2/3 inhibitors as protective of MNs. A secondary low-throughput screen confirmed that JNK2/3 inhibitors are effective in protecting MNs. JNK inhibition has already been shown to reduce neuronal death and increase behavioral outcomes in neonatal brain injury. JNK seemed to have a role in apoptosis that could be the potential mode of cell death of the large MNs in ALS.
Bax inhibition via the peptide V5 was also found to protect MNs from the toxic astrocyte medium. When MNs from Bax, Bim, and Bak knockout mice were used with mutant astrocyte-conditioned medium, only Bax knockout primary MNs were unaffected by mutant SOD1 toxicity. Necrostatin-1 also offered protection to MNs, and the lab is now testing the potential benefit of necrostatin-1 use in an in vivo model of ALS, as well as trying to determine the effective levels of necrostatin in the blood, brain, and other tissues in these animals.
Dr. Przedborski's group continues to improve the statistical quality of the screening assay by increasing the signal-to-noise ratio from ~2 to almost 2.6, reflective of a high-quality assay with an excellent statistical power (0.80). The Z'-factor has also improved to 0.3, close to the recommended target of 0.50.Both the screen and the class of drug candidates it has already revealed could have a far-reaching impact towards the development of the first effective treatment for ALS.
2012 Amyotrophic Lateral Sclerosis Research Highlights