Parkin and Pink, Genes that Signal the Appearance of Parkinson’s
May. 10 de 2012
By: Hermann Sáenz, Unimedios
urs when the neurons that produce dopamine are slowly destroyed. Without this important neurotransmitter hormone, brain cells cannot appropriately send messages, leading to loss of muscular function, which worsens over time.
Between 5% and 10% of cases are hereditary; the rest occur sporadically. There is speculation that constant contact with herbicides, pesticides or similar products could cause this disorder. In Colombia, some 75,000 people suffer from it and a large percentage of those diagnosed are above the age of 65.
Why are 90% to 95% of reported cases sporadic? What genes are involved? Gonzalo Arboleda, coordinator of the Cellular Death Group at the Genetic Institute of the Universidad Nacional de Colombia, is working to decipher this enigma.
“We are particularly interested in two genes associated with Parkinson’s, Parkin and Pink1, which undergo mutations in the inherited form and have the particularity of leading to the disease in people under the age of 20”, he says.
The main pathological characteristic is damage to the dopaminergic neurons that constitute the so-called black substance, located in the nucleus of a part of the brain known as the mesencephalon. These cells to a great extent control body movements.
The accumulation of a protein within these neurons known as Lewy Bodies has been detected, whose manifestation begins in the mesencephalon and which, later on, affects other areas of this vital organ such as the limbic and cortical zones.
With the passage of time problems of movement and cognitive type symptoms such as memory loss appear. The UN neurologist affirms that in very advanced stages the genes show peculiar clinical characteristics. “Brains with these mutations do not have Lewy Bodies, but do show degeneration of the black substance, in other words, destruction of the dopaminergic neurons”.
It is known that there is a mutation of these two genes that gives rise to the disease and that the death of these neurons occurs in the inherited types, but the genetic cause in the sporadic cases is unknown.
“We have cultivated mouse neurons; it is an interesting model because they are dopaminergics that express very particular markers that have their prolongation and potentials for action, which is why we want to find out why they die”, according to Arboleda.
In the Genetics Laboratory at the Universidad Nacional they remove the Parkin and Pink1 genes to observe what happens with the neuron. “We have found that these two genes are involved in the dynamic and natural protection of the mitochondria, the organelle of the cell that provides much of its energy.”
“If the cell lacks the ability to ensure that the mitochondria are in a certain place, it will not have sufficient energy to carry out its tasks. At the same time, if the organelle fails to degrade when it must do so, this leads to chaos that can cause premature cellular death and reach damaging levels. That is what interests us: to see how neurons survive when the gene is extracted and how these processes can or cannot regulate the genes”, explains María José Contreras, a doctoral student in biomedical sciences and member of the research team.
They have also investigated what happens if, instead of taking them out, more are applied. “We have found a toxin of environmental origin that has been associated with one type of Parkinson's. It is a lipid called ceramide; we have observed that if the gene is over–expressed, the neurons are more resistant to the toxin and do not die”, says Arboleda.
If the genes mutate they lose their function; that is why, thinking about a possible therapy for Parkinson's, the ideal would be to increase the function of those genes given that they protect the neuron and mitochondria.
Contreras clarifies that all human beings have the Parkin and Pink1 genes, the difference being that people with hereditary Parkinson's have the mutation, which prevents them from fulfilling this function correctly and generates the disease.
It is not known what happens in the sporadic cases. Studies have shown that exposure to herbicides and similar substances are risk factors; in general, animal models use these substances in the experiments.
“We are working with rats that are injected with the toxins and a model is generated in which the problem appears; it is a practice which is just now getting underway at the UN. There are also transgenic models, in other words, with mutations in some of these genes that also generate motor problems, but these experiments are carried out with Drosophila flies.”
Although the experts recognize that we are far from achieving a cure for Parkinson's, this research helps to decipher the mysteries of this complicated disease step–by–step.