About Neuritin / NRN:
Neuritin is a “neurotrophic factor,” a chemical found in biological organisms which promotes the growth of tissues associated with the brain and central nervous system. It’s just one member of a broader family of growth-promoting factors, involved in neurite replication and branching.
Several reviews discuss neuritin’s mechanisms of action in biological systems. However, the precise way it exerts its effect, including how it binds, is not yet fully understood. Researchers believe that neuritin may have both physiological and pathological function in both nerve and non-nerve tissue. Whether it acts through a receptor is not yet known. Neither are researchers sure how downstream signals react after binding. Neuritin’s mechanisms are an active field of scientific enquiry.
As discussed, whether neuritin uses receptors to bind to cells remains an active area of research. The evidence seems to suggest, however, that neuritin may act as a ligand, but there is a lack of published work on the receptors responsible for neuritin signalling.
One possibility is that neuritin binds to the same receptor as insulin-like growth factor, 1R (IGF-1R). The evidence for this comes from studies on cerebellar granule neurons (CGNs). When these neurons are incubated with neuritin, the density of their transient outward potassium currents increases, something similar that happens with the administration of insulin. The presence of insulin-like growth factors in CGNs may indicate that the receptors are structurally similar.
NRN 1 Function
Neuritin is so named for its role in promoting the growth of neurites - projections or outgrowths from neurons. The primary function of neuritin is to protect and regenerate neurons, but it may also play a variety of other roles, some of which are pathological. Neuritin, for instance, may be involved in the development of arterial plaques, tumours, and changes to the immune system. There’s also substantial evidence that neuritin expression is up- and down-regulated in certain forms of cancer, meaning that it could be a modifiable cancer risk.
A growing body of literature has found that neuritin may have a role in promoting neuritogenesis and neuronal regeneration. Researchers have observed that neuritin appears to encourage the growth of new neurons in the hippocampus region of the brains of rats. The addition of neuritin through a virus in a depression model prevented the wasting away of dendrites and dendritic spines often seen in cases of chronic stress. Neuritin, therefore, could play a substantial neuroprotective role.
The human neuritin gene, called CPG15, is on chromosome six. It is highly conserved between humans and mice, with a 97 per cent homology. Biology found a winning formula and stuck with it.
CPG15 has only one paralogue in both the mouse and human genome: CPG15-2. Both appear to share basic biological properties but are expressed differently in different parts of the body. CPG15 is found more represented in the brain and the liver, while CPG15-2 was found most abundantly in the eye and the und brain.
The discovery of CPG15-2 suggested to some researchers that there may be a neuritin-2. However, whether CPG15-2 does indeed code for a different form of neuritin with similar biological properties is not yet known. Further studies need to be conducted.