By Dean A. Haycock

Special To BioWorld Today

It's a case of "a gene for a gene."

Scientists have tested the effect of a gene that counters cell death in mice with symptoms of amyotrophic lateral sclerosis (ALS). The therapeutic crossbreeding delays the onset of the disease but doesn't stop it.

A report in today's issue of Science, "Bcl-2 prolonging life in a transgenic mouse model of familial amyotrophic lateral sclerosis," suggests it is possible to prolong survival in a mouse model of ALS using the product of a proto-oncogene, called Bcl-2, which counters cell death induced by many factors, including free radicals and hypoxia. That work has implications for improved understanding of the pathophysiology and potential treatment of ALS. ALS is the most common motor neuron disease and causes muscle wasting, paralysis and, ultimately, death.

Senior author Serge Przedborski, an assistant professor in the department of neurology at Columbia University, and his co-authors were the ones who, in a sense, crossbred a disease with a treatment. The team took transgenic mice with a mutation in the gene encoding superoxide dismutase type 1 (SOD-1) that produces ALS symptoms and crossbred them with mice that over-express the gene bcl-2. The mice that inherited both the disease gene and the bcl-2 gene outlived mice equipped with the mutated SOD-1 gene. While the presence of Bcl-2 delayed the onset of the disease, it did not alter its duration. All the mice eventually died with ALS-like symptoms.

"Once the disease is initiated it seems to go at its own pace, whether bcl-2 is there or not," Przedborski said. "Bcl-2 seems to delay the moment when the animals come down with the disease and reach the end stage."

The reason the researchers could use this unique approach, Przedborski is quick to point out, is because other scientists carefully laid the groundwork.

"If this is an interesting paper, it is also thanks to a huge amount of work done by other investigators that we are incredibly grateful to," Przedborski said.

Przedborski referred to those who identified in approximately 15 percent of families with familial ALS a mutation of the enzyme SOD-1 that scavenges free-radicals. Then there was the development of a mouse model of ALS that involves the same mutation. And other researchers characterized the Bcl-2 gene product, which is one of a family of proteins that inhibits the lethal effects of more than a half dozen factors in cultured cells. Just as important, a strain of mouse that over-expressed bcl-2 was available.

All of this background work contributed to the unique crossbreeding approach the authors were able to use to compare mice who inherited the disease gene alone to mice who inherited the disease gene plus the bcl-2 gene.

"If you think about it, there are very few or no other cases similar to this and certainly not for neurodegeneration," Przedborski said.

By exploiting these advances in their crossbreeding experiments, the authors were able to show that at the same time the diseased mice lacking bcl-2 were dying, mice with the bcl-2 gene had significantly more cells. These cells also appeared to be healthier based on the expression of fewer markers of cell damage.

Another indication of the healthy status of the remaining cells is their continued production of neurotransmitter and neurotransmitter synthesizing enzymes.

Further study of the surviving cell's condition involving electrophysiological analysis is under way in the lab of co-author Michel Dubois-Dauphin at the Hospital of the University of Geneva, in Switzerland.

"[The published results] strongly suggest that bcl-2 over-expression doesn't seem to render the cells more resistant," Przedborski explained. "Although they are building up the same magnitude of suffering at the end, they seem to reach this stage at a slower rate. This suggests to us that bcl-2 is attenuating the deleterious effect the mutated gene may have on the cell."

The work suggests a useful approach for studying ALS and potential therapies. One avenue of research high on the scientists' priority list is to study more of the biochemical effects induced by the Bcl-2 protein in motor neurons. Bcl-2 is believed to be an "upstream" regulator of cell death.

"The question is: 'What is going on downstream?' A lot of arguments suggest that activation of caspases [cysteine proteases that play a role in apoptosis] may be located more downstream in programmed cell death. If so, what would be the place for prevention therapy?" Przedborski asked.

For such studies, the researchers would not use bcl-2 transgenic animals but animals that either lacked caspases or had been treated with caspase inhibitors to suppress the expression or activation of the enzyme.

The team from Columbia University and the University of Geneva also plans to look for morphologic evidence of apoptosis in the motor neurons affected in ALS. The impetus for this line of investigation is that the proto-oncogene Bcl-2 protects against programmed cell death in general, not just the subtype of programmed cell death known as apoptosis.

They also intend to look for evidence of the involvement of specific genes and specific proteins that play a critical role in programmed cell death.

"If our study has a merit, it might be to show that the model is suitable to test potential therapies," Przedborski concluded. *