Neurotrophic factor receptors or neurotrophin receptors are a group of growth factor receptors which specifically bind to neurotrophins (neurotrophic factors).
Two classes of neurotrophic factor receptors are the p75 and the "Trk" families of Tyrosine kinases receptors.
TrkA mediates its actions by causing the addition of phosphate molecules on certain tyrosines in the cell, activating cellular signaling.
There are other related Trk receptors (TrkB and TrkC), and there are other neurotrophic factors structurally related to NGF (BDNF, NT-3, and NT-4)
The Low affinity nerve growth factor receptor commonly known as "p75", can signal for apoptosis or promote neuronal survival. Neurotrophins that interact with p75NTR include NGF, NT-3, BDNF, and NT-4/5. [2] Neurotrophins activating p75NTR may initiate apoptosis (for example, via c-Jun N-terminal kinases signaling), and this effect can be counteracted by anti-apoptotic signaling by TrkA. [3] Neurotrophin binding to p75NTR can promote neuronal survival (for example, via NF-kB activation). [4]
Although NGF has been classically described as promoting neuron survival and differentiation, research performed in the early 2000s suggest that NGF with its prodomain attached (proNGF) can elicit apoptosis of cells that are positive for the LNGFR and negative for TrkA. [5]
Secreted proNGF has been demonstrated in a variety of neuronal and non-neuronal cell populations. It has been proposed that secreted proNGF can elicit neuron death in a variety of neurodegenerative conditions, including Alzheimer's disease, following the observation of an increase of proNGF in the nucleus basalis of postmortem Alzheimer's brains [ citation needed ].
Brain-derived neurotrophic factor (BDNF), or abrineurin, is a protein that, in humans, is encoded by the BDNF gene. BDNF is a member of the neurotrophin family of growth factors, which are related to the canonical nerve growth factor. Neurotrophic factors are found in the brain and the periphery. BDNF was first isolated from pig brain in 1982 by Yves-Alain Barde and Hans Thoenen.
Neurotrophins are a family of proteins that induce the survival, development, and function of neurons.
Nerve growth factor (NGF) is a neurotrophic factor and neuropeptide primarily involved in the regulation of growth, maintenance, proliferation, and survival of certain target neurons. It is perhaps the prototypical growth factor, in that it was one of the first to be described. Since it was first isolated by Nobel Laureates Rita Levi-Montalcini and Stanley Cohen in 1956, numerous biological processes involving NGF have been identified, two of them being the survival of pancreatic beta cells and the regulation of the immune system.
Tropomyosin receptor kinase A (TrkA), also known as high affinity nerve growth factor receptor, neurotrophic tyrosine kinase receptor type 1, or TRK1-transforming tyrosine kinase protein is a protein that in humans is encoded by the NTRK1 gene.
Tropomyosin receptor kinase B (TrkB), also known as tyrosine receptor kinase B, or BDNF/NT-3 growth factors receptor or neurotrophic tyrosine kinase, receptor, type 2 is a protein that in humans is encoded by the NTRK2 gene. TrkB is a receptor for brain-derived neurotrophic factor (BDNF).
The p75 neurotrophin receptor (p75NTR) was first identified as the low-affinity nerve growth factor (LNGFR) before discovery that p75NTR bound other neurotrophins equally well as Nerve growth factor. p75NTR is a neurotrophic factor receptor. Neurotrophic factor receptors bind Neurotrophins including Nerve growth factor, Neurotrophin-3, Brain-derived neurotrophic factor, and Neurotrophin-4. All neurotrophins bind to p75NTR. Neurotrophic factor receptors, including p75NTR, are responsible for ensuring a proper density to target ratio of developing neurons, refining broader maps in development into precise connections. p75NTR is involved in pathways that promote neuronal survival and neuronal death.
Tropomyosin receptor kinase C (TrkC), also known as NT-3 growth factor receptor, neurotrophic tyrosine kinase receptor type 3, or TrkC tyrosine kinase is a protein that in humans is encoded by the NTRK3 gene.
Neurotrophic factors (NTFs) are a family of biomolecules – nearly all of which are peptides or small proteins – that support the growth, survival, and differentiation of both developing and mature neurons. Most NTFs exert their trophic effects on neurons by signaling through tyrosine kinases, usually a receptor tyrosine kinase. In the mature nervous system, they promote neuronal survival, induce synaptic plasticity, and modulate the formation of long-term memories. Neurotrophic factors also promote the initial growth and development of neurons in the central nervous system and peripheral nervous system, and they are capable of regrowing damaged neurons in test tubes and animal models. Some neurotrophic factors are also released by the target tissue in order to guide the growth of developing axons. Most neurotrophic factors belong to one of three families: (1) neurotrophins, (2) glial cell-line derived neurotrophic factor family ligands (GFLs), and (3) neuropoietic cytokines. Each family has its own distinct cell signaling mechanisms, although the cellular responses elicited often do overlap.
Neurotrophin-3 is a protein that in humans is encoded by the NTF3 gene.
Neurturin (NRTN) is a protein. Neurturin belongs to the glial cell-line derived neurotrophic factor (GDNF) family of neurotrophic factors, which regulate the survival and function of neurons. Neurturin’s role as a growth factor places it in the TGF-beta subfamily along with its homologs persephin, artemin, and GDNF. </ref> It shares a 42% similarity in amino acid sequence with mature GDNF. It is also considered a trophic factor and critical in the development and growth of neurons in the brain. Neurotrophic factors like neurturin have been tested in several clinical trial setting for the potential treatment of neurodegenerative diseases, specifically Parkinsons Disease.
Neurotrophin-4 (NT-4), also known as neurotrophin-5 (NT-5), is a protein that in humans is encoded by the NTF4 gene. It is a neurotrophic factor that signals predominantly through the TrkB receptor tyrosine kinase.
Trk receptors are a family of tyrosine kinases that regulates synaptic strength and plasticity in the mammalian nervous system. Trk receptors affect neuronal survival and differentiation through several signaling cascades. However, the activation of these receptors also has significant effects on functional properties of neurons.
SHC-transforming protein 3 is a protein that in humans is encoded by the SHC3 gene.
Protein BEX3 is a protein that in humans is encoded by the NGFRAP1 gene.
Leucine rich repeat and Immunoglobin-like domain-containing protein 1 also known as LINGO-1 is a protein which is encoded by the LINGO1 gene in humans. It belongs to the family of leucine-rich repeat proteins which are known for playing key roles in the biology of the central nervous system. LINGO-1 is a functional component of the Nogo receptor also known as the reticulon 4 receptor.
In cellular biology, dependence receptors are proteins that mediate programmed cell death by monitoring the absence of certain trophic factors that otherwise serve as ligands (interactors) for the dependence receptors. A trophic ligand is a molecule whose protein binding stimulates cell growth, differentiation, and/or survival. Cells depend for their survival on stimulation that is mediated by various receptors and sensors, and integrated via signaling within the cell and between cells. The withdrawal of such trophic support leads to a form of cellular suicide.
BNN-20, also known as 17β-spiro-(androst-5-en-17,2'-oxiran)-3β-ol, is a synthetic neurosteroid, "microneurotrophin", and analogue of the endogenous neurosteroid dehydroepiandrosterone (DHEA). It acts as a selective, high-affinity, centrally active agonist of the TrkA, TrkB, and p75NTR, receptors for the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), as well as for DHEA and DHEA sulfate (DHEA-S). The drug has been suggested as a potential novel treatment for Parkinson's disease and other conditions.
BNN-27, also known as 17α,20R-epoxypregn-5-ene-3β,21-diol, is a synthetic neurosteroid and "microneurotrophin" and analogue of the endogenous neurosteroid dehydroepiandrosterone (DHEA). It acts as a selective, high-affinity, centrally active agonist of the TrkA and p75NTR, receptors for nerve growth factor (NGF) and other neurotrophins, as well as for DHEA and DHEA sulfate (DHEA-S). BNN-27 has neuroprotective and neurogenic effects and has been suggested as a potential novel treatment for neurodegenerative diseases and brain trauma.
The Neuronal cell cycle represents the life cycle of the biological cell, its creation, reproduction and eventual death. The process by which cells divide into two daughter cells is called mitosis. Once these cells are formed they enter G1, the phase in which many of the proteins needed to replicate DNA are made. After G1, the cells enter S phase during which the DNA is replicated. After S, the cell will enter G2 where the proteins required for mitosis to occur are synthesized. Unlike most cell types however, neurons are generally considered incapable of proliferating once they are differentiated, as they are in the adult nervous system. Nevertheless, it remains plausible that neurons may re-enter the cell cycle under certain circumstances. Sympathetic and cortical neurons, for example, try to reactivate the cell cycle when subjected to acute insults such as DNA damage, oxidative stress, and excitotoxicity. This process is referred to as “abortive cell cycle re-entry” because the cells usually die in the G1/S checkpoint before DNA has been replicated.
Lorne Mendell is a neurobiologist currently employed as a distinguished professor in the department of neurobiology and behavior at Stony Brook University in New York. His research focuses primarily on neurotrophins in neonatal and adult mammals, and on the neuroplasticity of the mammalian spinal cord. Mendell's research interests lie in other areas including pain, nerve wind-up, and specifically the neurotrophin, NT-3. His research has contributed findings to the growing pool of knowledge of axonal development and regeneration of immature and mature neurons. Mendell has been a part of the search for novel treatments for spinal cord injuries and continues to study neurotrophins to determine their effects on neuronal plasticity. Mendell served a term as the President for the Society of Neuroscience during the years 1997-1998.
Review papers offer overviews and drawings of p75NTR pathways. [1] [2]