nerve growth factor
Meaning of nerve growth factor: A survival signal made by the tissue rather than by the nerve, which is how the body matches nerve supply to what needs supplying.
Definition of nerve growth factor
Nerve growth factor is a protein that keeps certain nerve cells alive and guides their fibers toward the tissue they supply. It is made by the target tissue itself, so a nerve ending must reach that tissue and take the protein up in order to survive. Nerve cells sensing pain and temperature, and those of the sympathetic nervous system, depend on it most.
Why is a survival signal useful?
An embryo makes far more nerve cells than it will keep. Each target tissue releases a limited quantity of nerve growth factor, and only the fibers that arrive and capture enough of it survive, while the rest die off. This competition matches the number of nerve cells to the size of the tissue they serve, with no plan encoded in advance. The captured protein is carried backward along the fiber to the cell body, where it switches on the genes that keep the cell alive.
Which cells depend on it?
| Cell type | What it does | Effect of losing the signal |
|---|---|---|
| Small sensory neurons | Carry pain, temperature and itch | Insensitivity to pain |
| Sympathetic neurons | Control sweating, blood vessels and heart rate | Poor control of temperature and pressure |
| Basal forebrain neurons | Supply acetylcholine to the cortex | Interest in memory disorders, though no treatment is established |
An inherited fault in the receptor for this protein causes a rare condition in which a child does not feel pain and cannot sweat, which shows how directly the signal maps onto those two functions.
What is its role in pain?
In an adult the protein does more than support survival. Injured and inflamed tissue releases it, and it makes nearby pain sensing endings more excitable, so a smaller stimulus produces a larger signal. That is a useful protective response after an injury and an unhelpful one in long lasting joint disease. Antibodies designed to mop the protein up have been tested for osteoarthritis pain and do reduce it, but a pattern of rapidly progressive joint damage in some participants has complicated their development.
How does it relate to other growth factors?
It was the first growth factor ever identified, and finding it opened up the whole field. It heads a family called the neurotrophins, which includes brain derived neurotrophic factor and others, each supporting a different set of nerve cells. Members of the family share a structure and act through related receptors, so the same signal can support survival through one receptor and trigger cell death through another, depending on which receptor a cell carries.
Also known as
Used in a sentence
Nerve growth factor levels were measured in the joint fluid alongside markers of inflammation.
Good to know
Nerve growth factor is released by injured and inflamed tissue and makes pain sensing endings more excitable, which is why blocking it reduces pain and also why its effects are not confined to one tissue.