27 June 2008

How to repair mitochondria?

Transport RNAs (tRNAs) provide the delivery of amino acids for the synthesis of protein molecules in ribosomes. Defects or the absence of tRNAs encoded by mitochondrial genes lead to a violation of the synthesis of proteins that make up mitochondria – cellular organelles that carry out energy synthesis, which leads to a violation of the energy balance of the cell.

It is believed that tRNA defects underlie approximately 60% of diseases associated with mitochondrial dysfunction, including diabetes, deafness and a number of neurological disorders that develop depending on which type of cells are affected.

Mitochondria are covered with their own membrane, which makes it much more difficult to study them.

(The figure shows an electronic micrograph of a single mitochondria, which shows how the structure of its protein matrix and inner membrane is organized.)

According to the results of earlier studies, in lower organisms, such as protozoa, yeast and plants, tRNA can be imported into mitochondria from the cytoplasm of the cell. However, scientists at Ohio State University, working under the leadership of Dr. Juan Alfonzo, demonstrated the existence of this mechanism in mammals, first on rat liver cells, and subsequently on human cells. According to the authors, it was very unexpected to discover such a primitive mechanism characteristic of the simplest organisms in human cells.

The authors believe that this discovery expands the therapeutic possibilities of introducing normal tRNAs into defective mitochondria of patients in order to correct violations. However, they emphasize that to date they have only been able to identify the existence of tRNA imports, and the mechanisms of this process are still unknown.

Previously, experts who believed that the import of mitochondrial tRNAs in mammalian cells was impossible, cherished plans to test the possibility of using mechanisms characteristic of protozoan and yeast cells to manipulate important processes in human cells. However, it turned out that the task is to study the mechanisms and proteins involved in the import of tRNA in human cells.

One of the molecules important for this process has already been identified is adenosine–5-triphosphate (ATP), a compound that plays an important role in the energy transport of the cell. The authors demonstrated the role of ATP in the import of tRNA on the cells of a patient with a rare hereditary form of epilepsy – MERRF syndrome (myoclonus epilepsy, the phenomenon of torn red fibers). This disease is caused by a mutation of mitochondrial DNA, leading to a severe decrease in the ability of mitochondria to synthesize ATP, which, in turn, disrupts the import of tRNA into the mitochondria of patients.

The introduction of ATP into the mitochondria of the cells of such patients restores the normal process of importing tRNA from the cytoplasm into the mitochondria. The authors emphasize that cells of a specific patient were used in the experiment, which is an argument in favor of continuing work in this direction, since the technique, if it is brought to clinical use, will not require the introduction of foreign substances obtained from other organisms.

Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of ScienceDaily


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