Neurotrophins and Neurotrphic Factors

NEUROTROPHINS – NEUROTROPHIC FACTORS

Neurotrophins or neurotrophic factors are the protein substances, which play an important role in growth and functioning of nervous tissue.

Neurotrophins and Neurotrphic Factors


Source of Secretion

Neurotrophins are secreted by many tissues in the body, particularly muscles, neuroglial cells called astrocytes and neurons.

Functions

Neurotrophins:

1. Facilitate initial growth and development of nerve cells in central and peripheral nervous system

2. Promote survival and repair of the nerve cells

3. Play an important role in the maintenance of nervous tissue and neural transmission.

Recently, it is found that neurotrophins are capable of making the damaged neurons regrow their

processes in vitro and in animal models. This indicates the possibilities of reversing the devastating symptoms of nervous disorders like Parkinson disease and Alzheimer disease. Commercial preparations of neurotrophins are used for the treatment of some neural diseases.

Mode of Action

Neurotrophins act via neurotrophin receptors, which are situated at the nerve terminals and nerve cell body. Neurotrophins bind with receptors and initiate the phosphorylation of tyrosine kinase.

Types

Nerve growth factor (NGF) was the first protein substance identified as neurotrophin. Now, many types

of neurotophic factors are identified.

NERVE GROWTH FACTOR

Nerve growth factor (NGF) is a neurotrophin found in many peripheral tissues.

Chemistry

NGF is a peptide with 118 amino acids. Each molecule of NGF is made up of two α-subunits, two β-subunits and two γ-subunits. Only the β-subunits have nerve growth-stimulating activity.

Functions

1. NGF promotes early growth and development of neurons. Its major action is on sympathetic

and sensory neurons, particularly the neurons concerned with pain. Because of its major action on

sympathetic neurons, it is also called sympathetic NGF. NGF also promotes the growth of cholinergic

neurons in cerebral hemispheres.

2. Commercial preparation of NGF extracted from snake venom and submaxillary glands of male mouse

is used to treat sympathetic neuron diseases.

3. NGF plays an important role in treating many nervous disorders such as Alzheimer disease,

neuron degeneration in aging and neuron regeneration in spinal cord injury.

OTHER NEUROTROPHINS

1. Brain-derived Neurotrophic Growth Factor

Brain-derived neurotrophic growth factor (BDGF) was first discovered in the brain of pig. Now it is found in human brain and human sperm. BDGF promotes the survival of sensory and motor neurons, arising from embryonic neural crest. It also protects the sensory neurons in peripheral nervous system and motor neurons of pyramidal system. It enhances the growth of cholinergic, dopaminergic and optic nerves. It is suggested that BDGF may regulate synaptic transmission. Commercial preparation is used to treat motor

neuron diseases.

2. Ciliary Neurotrophic Factor (CNTF)

CNTF is secreted in peripheral nerves, ocular muscles and cardiac muscle. It protects neurons of ciliary

ganglion and motor neurons.

3. Glial Cell Line-derived Neurotrophic Factor (GNDF)

GDNF is found in neuroglial cells. It has a potent protective action on dopaminergic neurons. It is used

for the treatment of Parkinson disease.

4. Fibroblast Growth Factor (FGF)

FGF was first discovered as growth factor promoting the fibroblastic growth. It is also known to protect the

neurons.

5. Neurotrophin-3 (NT-3)

Neurotrophin-3 (NT-3) acts on γ-motor neurons, sympathetic neurons and neurons from sensory organs.

It also regulates the release of neurotransmitter from neuromuscular junction.

NT-3 is useful for the treatment of motor axonal neuropathy and diabetic neuropathy. Recently, few more substances belonging to the neurotrophin family such as NT-4, NT-5 and leukemiainhibiting

factor are identified. NT-4 and NT-5 act on sympathetic neurons, sensory neurons and motor neurons.

 

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