A polymorphism that modulates responses to exertion
CGP/DICYT Polymorphism is the existence of various alleles of the same gene. It refers to variations in the sequence of a given DNA fragment among individuals of a population and, if they affect the coding or regulatory sequences and cause major alterations in the protein structure or in the regulation of its expression, may produce different phenotypes. In recent years, it has become clear that genetic polymorphisms may have a great importance regarding the individual response to physical exercise. The Instituto de Biomedicina de la Universidad de León (Ibiomed), and institute for biomedicine, is working on this research area.
In this regard, there is a mitochondrial enzyme called superoxide dismutase (Mn-SOD) that protects mitochondria from an oxidative damage caused by free radicals, unstable and highly reactive compounds. A recent study by researchers from Ibiomed and the Universidade Federal de Santa Maria (Brazil), that is going to be published soon in Clinical Biochemistry, has analyzed the influence of Mn-SOD polymorphism on the response to acute exertion, that is, an environmental stimulus inducing the development of oxidative stress if there is no adequate response by antioxidant defense.
As DiCYT was told by Dr. Javier Gonzalez Gallego, Ibiomed director and one of the coordinators of the study, in this enzyme, “a single nucleotide polymorphism (SNP) has been described with genetic variations affecting codon 16, producing changes in the secondary structure of the protein”. This polymorphism has been associated with pathologies such as breast cancer and prostate cancer, or cardiovascular risk factors.
This study, that was part of the thesis by Dr. Guillerme Bresciani, was conducted with 60 young individuals who do not carry out physical activity on a regular basis. After genotyping the patients, they developed a stress test to 75% of maximum volume of oxygen in blood that human body can transport and metabolize to exhaustion (VO2 mx). The test was performed with a cycloergometer with electromagnetic brakes, a bicycle especially designed to measure stress.
The study of allele frequency in peripheral blood mononuclear cells proved that, according to the researchers, “25% of the patients carried AA alleles, 33% carried VV alleles and 42% carried AV alleles”. Individuals with AA alleles had increased levels of mRNA, protein and enzyme activity, compared to baseline levels, as a response to stress. By contrast, in VV genotype, mRNA levels were not changed by exertion, but there was a decrease in protein thiol content, a type of chemical compound.
The comparison of different genotypes proved that the protein content of Mn-SOD after stress was higher in genotype AA; “there is a dose-dependent effect in allele A on the activity of the enzyme”.
As Dr. Gonlalez Gallego stated, even if more studies must be done to analyze whether other environmental influences, such as antioxidant intake, may have an impact on the differential response of Mn-SOD polymorphism, these findings “confirm that it plays an important role in oxidative stress modulation triggered by intense exercise and may affect biochemical and clinical variables related to chronic disease risk”.