Neurofilaments: what are they, components and characteristics?

Neurofilaments are much more than the rigid structures that shape neurons.

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

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

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

Neurofilaments: the neuronal skeleton

It is incredible to know that the skeleton of living beings is formed by cells, but that these also need their own "skeletal structure" to maintain their shape and functionality. In other words, we find complex organization even in the most basic functional unit that gives us life..

Since we cannot address the role of neurofilaments without first understanding the structural organization of a cell, let us 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 cellsbut which is also involved in the transport of compounds, cell organization and division. Analogous to the macroscopic observable world, this complex network would act like the beams of a building, but also like the elevator and the staircase.. Incredible, isn't it?

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 bonds.
• 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 relates to the outside (i.e. the extracellular matrix) and the stresses of tension, rigidity and compression that it experiences throughout its development. We are dealing with a dynamic and not at all rigid framework, which adapts exquisitely to the adapts exquisitely to the process that the cell is undergoing at any given time.. Now, how do neurofilaments relate to all of the above?

Navigating in the cytoplasm

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

Just like the rest of the cells, neurons have a skeleton with both structural and transport functions.. This protein framework is composed of three components, very similar to those we have described above, namely microtubules (or neurotubules), neurofilaments (intermediate filaments) and microfilaments. Before getting lost in the morphology of these structures, let us define the functions of the neuronal cytoskeleton:

• Mediate the movement of organelles between different areas of the neuronal body.
• To 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. as we know them today. To understand the structure of a neurofilament we have to dissect its morphology extensively down to a basal level. Let's get down to it.

First we must get to 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 in the nails, hair and feathers of animals. The association of a set of these proteins in linear form gives rise to a monomer, and two of these chains coiled one with the other, to a dimer.

In turn, two rolled dimers give rise to a thicker structure, the tetrameric complex (tetra-four, since it is formed by a total of four monomers). The union of several tetrameric complexes forms a protofilament, and two joined protofilaments form a protofibril. Finally, three coiled protofibrils give rise to the desired neurofilament.

Thus, to understand the structure of this intermediate strand, we have to imagine a series of chains coiling on themselves to give a structure "analogous" (saving the incredible distances) to the double helix of DNA known to all. More and more interconnected more and more interconnected chains are added to each other, increasing the complexity of the structure and its thickness.. As with electrical wiring, the more strands and more windings, the greater the mechanical strength of the final lattice.

These neurofilaments, with a dizzying structural complexity, are distributed in the cytoplasm of the neuron and generate junctional bridges with 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.

Case studies

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

For example, studies have investigated the abundance of neuronal intermediate filaments in rodent mammals following brain injury and subsequent exposure to low-intensity laser and ultrasound therapies for therapeutic purposes. Nerve damage is correlated with a decrease of neurofilaments within each neuron.This type of mechanical stress decreases the axon caliber and the "health" (for lack of a more complex term) of the cell subjected to the 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. This type of experiment shows that low level laser therapies (LBI) can play an that low level laser (LBI) therapies can play an essential role in the regeneration of injured nerves after trauma. after trauma.

Beyond the microscopic world: filaments and Alzheimer's disease

Going beyond experimental studies with laboratory rodents, the effect of the composition and number of filament components of the cytoskeleton on diseases such as Alzheimer's disease has been investigated.

For example, the serum concentration of light neurofilament (Nfl) is increased in individuals with familial Alzheimer's disease before 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 is still required to cement this knowledge, but the foundations have already been laid.

Summary

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

This highlights the importance of the importance of each of the elements that make up our cells.Who would have thought that an increased abundance of a particular filament could be an indicator of the early stages of a disease such as Alzheimer's?

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

Bibliographical references:

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