The secret lives, and deaths, of neurons

Neurons can be cultured in one compartment of a microfluidic chamber (right side) and extend their axons through very small grooves into a separate compartment (left side). Using this technology, study co-author Corey L. Cusack and colleagues were able to separate and study the distinct pathways that mediate whole-cell degeneration versus axon-specific degeneration in neurons. Credit: Deshmukh Lab, UNC School of Medicine

As the human body fine-tunes its neurological wiring, nerve cells often must fix a faulty connection by amputating an axon—the "business end" of the neuron that sends electrical impulses to tissues or other neurons. It is a dance with death, however, because the molecular poison the neuron deploys to sever an axon could, if uncontained, kill the entire cell.

Researchers from the University of North Carolina School of Medicine have uncovered some surprising insights about the process of axon , or "pruning," in a study published May 21 in the journal Nature Communications. Axon pruning has mystified scientists curious to know how a neuron can unleash a self -destruct mechanism within its axon, but keep it from spreading to the rest of the cell. The researchers' findings could offer clues about the processes underlying some neurological disorders.

"Aberrant axon pruning is thought to underlie some of the causes for , such as and autism," said Mohanish Deshmukh, PhD, professor of and physiology at UNC and the study's senior author. "This study sheds light on some of the mechanisms by which neurons are able to regulate axon pruning."

Axon pruning is part of normal development and plays a key role in . Another important process, apoptosis—the purposeful death of an entire cell—is also crucial because it allows the body to cull broken or incorrectly placed neurons. But both processes have been linked with disease when improperly regulated.

The research team placed mouse neurons in special devices called microfluidic chambers that allowed the researchers to independently manipulate the environments surrounding the axon and cell body to induce axon pruning or apoptosis.

They found that although the nerve cell uses the same poison—a group of molecules known as Caspases—whether it intends to kill the whole cell or just the axon, it deploys the Caspases in a different way depending on the context.

"People had assumed that the mechanism was the same regardless of whether the context was axon pruning or apoptosis, but we found that it's actually quite distinct," said Deshmukh. "The neuron essentially uses the same components for both cases, but tweaks them in a very elegant way so the neuron knows whether it needs to undergo apoptosis or axon pruning."

In apoptosis, the neuron deploys the deadly Caspases using an activator known as Apaf-1. In the case of axon pruning, Apaf-1 was simply not involved, despite the presence of Caspases. "This is really going to take the field by surprise," said Deshmukh. "There's very little precedent of Caspases being activated without Apaf-1. We just didn't know they could be activated through a different mechanism."

In addition, the team discovered that neurons employ other molecules as safety brakes to keep the "kill" signal contained to the axon alone. "Having this brake keeps that signal from spreading to the rest of the body," said Deshmukh. "Remarkably, just removing one brake makes the more vulnerable."

Deshmukh said the findings offer a glimpse into how reconfigure themselves during development and beyond. Enhancing our understanding of these basic processes could help illuminate what has gone wrong in the case of some neurological disorders.

Related Stories

A fly mutation suggests a new route for tackling ALS

Apr 08, 2013

A team of researchers, led by Marc Freeman, PhD, an early career scientist with the Howard Hughes Medical Institute and associate professor of neurobiology at the University of Massachusetts Medical School have discovered ...

Tiny worm sheds light on giant mystery about neurons

Apr 30, 2013

Scientists have identified a gene that keeps our nerve fibers from clogging up. Researchers in Ken Miller's laboratory at the Oklahoma Medical Research Foundation (OMRF) found that the unc-16 gene of the roundworm Caenorhabditis el ...

What makes an axon an axon?

Nov 10, 2008

Inside every axon is a dendrite waiting to get out. Hedstrom et al. converted mature axons into dendrites by banishing a protein crucial for neuron development. The results suggest that this transformation could occur after ...

Stay-at-home transcription factor prevents neurodegeneration

Oct 29, 2012

A study in The Journal of Cell Biology shows how a transcription factor called STAT3 remains in the axon of nerve cells to help prevent neurodegeneration. The findings could pave the way for future drug therapies to slow ...

Boundary stops molecule right where it needs to be

May 24, 2012

A molecule responsible for the proper formation of a key portion of the nervous system finds its way to the proper place not because it is actively recruited, but instead because it can't go anywhere else.

Recommended for you

Emotional adjustment following traumatic brain injury

13 hours ago

Life after a traumatic brain injury resulting from a car accident, a bad fall or a neurodegenerative disease changes a person forever. But the injury doesn't solely affect the survivor – the lives of their spouse or partner ...

New ALS associated gene identified using innovative strategy

Oct 22, 2014

Using an innovative exome sequencing strategy, a team of international scientists led by John Landers, PhD, at the University of Massachusetts Medical School has shown that TUBA4A, the gene encoding the Tubulin Alpha 4A protein, ...

User comments