Molecular biologists win Hughes Institute grants

by Charles Ker
Staff writer

Vanessa Auld and B. Brett Finlay fight disease one molecule at a time.

The UBC scientists have received $275,000 (U.S.) each from the Howard Hughes Medical Institute to further research into the genesis of nerve disorders and bacterial infections -- innovative work combining genetics, biochemistry and molecular and cell biology.

Finlay, a professor in UBC's Biotechnology Laboratory, looks at molecules which aid and abet the passage of disease-causing bacteria in the human body. His focus has been on salmonella and Eschericia coli (E. coli), two bacterial strains which result in typhoid fever, debilitating diarrhea and other gastrointestinal diseases.

E. coli, cause of the "hamburger disease" introduced in 1995, grabbed headlines last summer when almost 10,000 Japanese children were stricken and 11 died. Unpasteurized apple juice was the source of another fatal outbreak last fall in B.C. and the western United States.

However, it is in developing countries where E. coli does the most damage, annually killing one million children. The onset of diarrhea leads to a fatal loss of fluids and eventual dehydration.

E. coli has traditionally been treated through rehydration and antibiotics but Finlay says bacteria are rapidly becoming resistant to current medication.

According the Finlay, more than 96 per cent of all salmonella typhi coming out of India are resistant to multiple antibiotics.

"So if you're coming out of India and get typhoid fever you are basically guaranteed of getting multiple resistant bacteria," he says. "Under those cases there is a 50 per cent fatality rate because they can't be treated."

Apart from preventing infections with new vaccines, Finlay seeks to block the bacterium's ability to operate in the body.

He describes salmonella, one of the leading causes of death among HIV patients, and E. coli as having their own "little tool boxes" to manipulate human cells.

E. coli, for instance, is called an adherent bacteria because it sticks to the surface of human intestinal cells. Once in place, the E. coli secretes special molecules from its tool box into the host cell causing it to build a pedestal upon which the bacterium sits.

"We know a lot of the molecules the bacteria use to build these structures and if we make a mutation in one of those molecules, the pedestals don't get built and people don't get sick," says Finlay, whose lab was one of the first to examine what happens to mammalian host cells when they come in contact with bacteria.

Salmonella, as an intracellular bacteria, infects from the inside of cells. It has a range of sophisticated molecular tools, the first of which tricks human epithelial cells into engulfing it. Epithelial cells line the nose, ears, mouth, stomach and intestinal tract forming a barrier, like Gortex, between the outside and the inside of the body.

Once the bacteria breaks through the epithelial barrier of the intestine, it hitches a ride inside phagocytes (another molecular trick) which are designed to kill foreign particles entering the bloodstream. The phagocytes transport the salmonella to the liver and spleen where the bacteria grow and kill more host cells.

Finlay grows models of epithelial cell barriers in tissue culture to determine how the molecular process works.

"Our home-grown epithelial barriers look very much like what the bacteria would encounter in the human intestine," says Finlay. "They allow us to study how bacteria survive in cells, how they replicate, break out and spread to other tissue."

Finlay's lab is collaborating with several pharmaceutical companies to identify molecular compounds that will block these processes. One project with the local firm INEX seeks to control salmonella and other intracellular parasites by tricking cells into swallowing capsules of existing antibiotics. This technology would enable drugs to work from the inside out.

He is also working with another UBC spin-off company, Terragen Diversity Inc., to develop drugs to treat infections.

Auld, an assistant professor with the Dept. of Zoology, investigates molecular interactions between the brain's two basic cell types: nerve cells (neurons) and glial cells. Breakdowns in these interactions can lead to a variety of neurodegenerative diseases.

Auld's research explores how glial cells and neurons develop together in the peripheral nervous system (PNS), the sensory system existing outside the brain and spinal cord.

There are about 100 billion neurons in the brain and up to 10 times that number of glial cells offering physical and nutritional support.

Auld explains that neurons represent the body's wiring and glia provide the necessary insulation, or glial shealth, for that wiring. When the nervous system is setting up, glia can act as guideposts or highways to make sure nerves go to the right places.

Once the nervous system is established, the glial shealth acts as a both a protectant against short circuits and an air conditioner, cleaning up residual ions or neurotransmittors left over from electrical firings between neurons.

"To serve and protect, that's their role," says Auld, who uses the fruit fly, Drosophila melanogaster, as the model to analyze glial-neuron interactions.

In 1991, Auld discovered gliotactin, a gene specific to glial cells expressed in the fruit fly's embryonic PNS.

Gliotactin mediates the interaction between neurons and glial cells by setting up a barrier or membrane between the blood system and the nervous system. This so-called blood-brain barrier insulates and protects the nerves.

"The gliotactin protein sits in the membrane surface of the glial cell and has a region that sticks outside the cell that is interacting with what we hope is another protein on the neuron," says Auld. "Somehow they signal with each other to form this blood-brain barrier."

Mutations in the gliotactin protein lead to paralysis in fruit flies as the gene plays an essential role in establishing the glial wrapping of the PNS.

Auld will use the Howard Hughes grant to look for mutants or new genes that affect the development of glia and their interactions with the nervous system. The process involves isolating new mutations in Drosophila and looking for defects that involve glia.

"We'll be looking for anything that effects how the glia are positioned, how they migrate, how they wrap the neuron and anything that disrupts this development," she says. "At the molecular level, this would show up in a gene."

In Drosophila melanogaster, the process of finding mutated genes that affect nervous system development is relatively straightforward because the fruit fly has a simple nervous system and small genome. Auld's long-range plans are to use the fruit fly as a springboard to discovering the same genes in vertebrate systems. She says that many genes important to vertebrate development were originally discovered in Drosophila.

For instance, Auld believes that the corresponding protein to gliotactin in vertabrates will have the same biological functions as the Drosophila protein. The eventual cloning of vertebrate gliotactin will play an important role in establishing the connections between neurons and glial cells during the development of the nervous system.

Finlay and Auld are among 20 Canadians named International Research Scholars of the Howard Hughes Medical Institute.