Neurofilaments: what they are, components and characteristics

Neurofilaments are a type of 7 nanometer thick intermediate filaments present in the cytoplasm of neurons. They are involved in the maintenance of neuronal structure and in axonal transport.

Sometimes, biological structures keep many more secrets than we initially believe. In the world of nature, knowledge is practically infinite, since it covers layers and morphological layers until reach the most basic compounds of any living being, amino acids and the chemical elements that make them up. How far do we want to go in this search for knowledge?

On the one hand, we have the neurons with their delimited sections (axon, dendrites and soma), the communication between them through the synapses, the neurotransmitters and their effects on the brain. All these topics have already been extensively covered, but we can still dig deeper. In this opportunity, we take the opportunity to show you everything you need to know about neurofilaments.

• Related article: "What are the parts of the neuron?"

Neurofilaments: the neural skeleton

It is incredible to know that the skeleton of living beings is made up of cells, but that cells also need their own "skeletal structure" to maintain their shape and functionality. That is to say, we find complex organization even in the most basic functional unit that life gives us.

Since we cannot address the role of neurofilaments without first understanding the structural organization of a cell, we are going to dwell for a moment on the cytoskeleton and its function.

About the cytoskeleton

The cytoskeleton is defined as a three-dimensional lattice of proteins that provides internal support in cells, but which is also involved in the transport of compounds, organization and cell division. Making an analog with the observable macroscopic world, this complex network would act like the beams of a building, but also like the elevator and the stairs. Incredible true?

The cytoskeleton is composed of three main compounds:

• Microfilaments: composed of two chains of actin, a globular protein. They maintain the shape of the cell.
• Intermediate filaments: composed of a more heterogeneous family of proteins, they provide stability to cell organelles due to their strong links.
• Microtubules: formed by alba and beta tubulin, they are responsible for the movement of substances within the cell and its division.

It should be noted that the structure and dynamics of the cytoskeleton depend on the way in which the cell is related to the exterior (that is, the extracellular matrix) and the stresses of tension, rigidity and compression that it experiences throughout its life. development. We are facing a dynamic and by no means rigid framework, which adapts exquisitely to the process that the cell is undergoing at any given time. Now, how are neurofilaments related to all of the above?

Navigating in the cytoplasm

The answer to the previous question is simple, since these structures that concern us today are nothing more than intermediate filaments of the specific cytoskeleton of neurons.

Like all other cells, neurons have a skeleton of both structural and transporter function. This protein framework is made up of three components, very similar to those that we have described with previously, since they are the microtubules (or neurotubules), neurofilaments (intermediate filaments) and microfilaments. Before getting lost in the morphology of these structures, let's define the functions of the neuronal cytoskeleton:

• Mediate the movement of organelles between different areas of the neuronal body.
• Fix the location of certain components (such as membrane chemical receptors) in the right places so that they can function.
• Determine the three-dimensional shape of the neuron.

As we can see, Without this protein framework, neurons (and therefore human thought) could not exist as we know them. Today. To understand the structure of a neurofilament we have to extensively dissect its morphology down to a basal level. Go for it.

First we must know the most basal “brick” of the structure, cytokeratin. This is an essential fibrous protein in the intermediate filaments of epithelial cells, as well as nails, hair and feathers of animals. The association of a set of these proteins in a linear fashion gives rise to a monomer, and two of these chains wound around each other, to a dimer.

In turn, two coiled dimers give rise to a thicker structure, the tetrameric complex (tetra-four, as it is made up of a total of four monomers). The union of several tetrameric complexes forms a protofilament, and two joined protofilaments, a protofibril. Finally, three coiled protofibrils give rise to the sought-after neurofilament.

So, to understand the structure of this intermediate filament we have to imagine a series of chains winding around each other. on themselves to give an "analogous" structure (over the incredible distances) to the double helix of DNA for all known. Every time more and more interconnected chains are added between them, increasing the complexity of the structure and the thickness of it. As with electrical wiring, the more chains and windings, the greater the mechanical resistance of the final framework.

These neurofilaments, with a dizzying structural complexity, are distributed in the cytoplasm of the neuron and bridge the neurotubules and connect the cell membrane, mitochondria and polyribosomes. It should be noted that they are the most abundant components of the cytoskeleton, since they represent the internal structural support of the neuron.

• You may be interested in: "Cytoskeleton of the neuron: parts and functions"

Practical cases

Not everything is reduced to a microscopic world, since the composition of the cytoskeleton, surprising as it may seem, conditions the responses of living beings to the environment and the efficiency of their nerve transmissions.

For example, studies have investigated the abundance of neural intermediate filaments in mammalian rodents after brain lesions and subsequent exposure to low-intensity laser and ultrasound therapies for the purpose of therapy. Nerve damage is correlated with a decrease in neurofilaments within each neuron., since this type of mechanical stress decreases the caliber of the axon and the “health” (for lack of a more complex term) of the cell subjected to trauma.

The results are revealing, since the mice that were subjected to the described therapies increased the number of these filaments at the cellular level. These types of experiments show that Low intensity laser therapies (LBI) can play an essential role in the regeneration of injured nerves after trauma.

Beyond the microscopic world: filaments and Alzheimer's

We go further, because beyond the experimental studies with laboratory rodents, the effect of the composition and number of component filaments of the cytoskeleton in diseases such as alzheimer.

For example, serum neurofilament light (Nfl) concentration is increased in people with familial Alzheimer's before the symptoms of the disease even begin to appear. Therefore, these could act as non-invasive bioindicators of the pathology to control it from the earliest stages. Of course, more information and study are still required to cement this knowledge, but the bases have already been laid.

Summary

As we have been able to observe, the world of neurofilaments is not only reduced to a structural protein framework. We move to nanoscopic scales, but clearly the effects of the abundance of these components essential elements of the neuronal cytoskeleton are expressed at the behavioral and physiological level in living beings. alive.

This puts in evidence the importance of each of the elements that make up our cells. Who was going to tell us that a greater abundance of a specific filament could be an indicator of the early stages of a disease like Alzheimer's?

In the end, each small component is one more piece of the puzzle that gives rise to the sophisticated machine that is the human body. If one of them fails, the effect can reach levels much larger than the few micrometers or nanometers that this structure can occupy in a physical space.

Bibliographic references:

• Chesta, C.A.A. (2006). Isolation and analysis of the degree of phosphorylation of cerebrospinal fluid neurofilaments from patients with spastic paraparesis tropical (Doctoral dissertation, Department of Biochemistry and Molecular Biology, Faculty of Chemical and Pharmaceutical Sciences, University of Chili).
• Matamala, F., Cornejo, R., Paredes, M., Farfán, E., Garrido, O., & Alves, N. (2014). Comparative Analysis of the Number of Neurofilaments in Sciatic Nerves of Rats Subjected to Neuropraxia Treated with Low Intensity Laser and Therapeutic Ultrasound. International Journal of Morphology, 32(1), 369-374.
• Neurofilament, University of Navarra Clinic. Collected on August 30 in https://www.cun.es/diccionario-medico/terminos/neurofilamento
• Neurofilament, Fleni (Neurology, neurosurgery and rehabilitation). Collected on August 30 in https://www.fleni.org.ar/patologias-tratamientos/neurofilamento/
• Weston, P. S. Serum light neurofilament in familial Alzheimer's disease.