New research highlights how nerves – whether harmed by disease or traumatic injury – start to die, a discovery that unveils novel targets for developing drugs to slow or halt peripheral neuropathies and devastating neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis (ALS).
Peripheral neuropathy damages nerves in the body’s extremities and can cause unrelenting pain, stinging, burning, itching and sensitivity to touch. The condition is commonly associated with diabetes or develops as a side effect of chemotherapy.
Nerve cells talk to each other by transmitting signals along communication cables called axons. Such signals underlie vital activities, such as thinking and memory, movement and language. As part of the study, the researchers showed they could prevent axons from dying, a finding that suggests therapies could be developed to counteract the withering away of nerve axons.
The research, by scientists at Washington University School of Medicine in St. Louis, is reported online April 23 in the journal Science.
“We have uncovered new details that let us piece together a major pathway involved in axon degeneration,” said senior author Jeffrey Milbrandt, MD, PhD, the James S. McDonnell Professor and head of the Department of Genetics. “This is an important step forward and helps to identify new therapeutic targets. That we were able to block axon degeneration in the lab also gives us hope that drugs could be developed to treat patients suffering from a variety of neurological conditions.”
A common thread among many neurological disorders and traumatic nerve injuries is the degeneration of axons, which interrupts nerve signaling and prevents nerves from communicating with one another. Axon degeneration is thought to be an initiating event in many of these disorders. In fact, an unhealthy axon is known to trigger its own death, and researchers are keenly interested in understanding how this happens.
Working in cell cultures, fruit flies and mice, Milbrandt and co-author Aaron DiAntonio, MD, PhD, the Alan A. and Edith L. Wolff Professor of Developmental Biology, and their colleagues showed that a protein already known to be involved in axon degeneration, acts like a switch to trigger axon degeneration after an injury.
Moreover, they found that this protein, once unleashed, causes a rapid decline in the energy supply within axons. Within minutes after the protein – called SARM1 – is activated in neurons, a massive loss of nicotinamide adenine dinucleotide (NAD), a chemical central to a cell’s energy production, occurs within the axon.