Scientists attempt to identify key genes to control vital functions
November 06, 2013
By Karina Toledo, London
Agência FAPESP – Several of an organism’s vital functions are controlled by the autonomic nervous system, including the heartbeat, arterial pressure and the hydromineral balance (the relationship between water volume and sodium levels). However, for the majority of people, this control becomes impaired with age, increasing the risk of problems such as dehydration, hypertension and several other cardiovascular diseases.
Investigating how advancing age and certain habits – including sedentarism and excessive salt consumption – affect gene expression in certain regions of the brain responsible for autonomic balance is the objective of two projects being conducted by Brazilian and British researchers under an agreement between FAPESP and Research Councils in the United Kingdom.
The preliminary results of these projects were presented on September 26 during FAPESP Week London. FAPESP held the symposium in the U.K. with the support of the British Council and the Royal Society.
David Murphy, a researcher at the University of Bristol and coordinator of the British group in the two projects, described the goal: “If we manage to identify a gene that is activated by exercise in the region of brain we are interested in, for example, we can manipulate this gene in animals to increase its expression and verify whether it produces the same effect as exercise in controlling arterial pressure. We are obviously still on the basic research level, but in the future we can identify the potential targets for development of new medicine.”
In Brazil, Universidade de São Paulo Professor Lisete Compagno Michelini coordinated a Thematic Project focused on investigating the physiological mechanisms responsible for the development of hypertension and verifying whether physical exercise can protect against this autonomic deficit in old age.
“Before the project began, Murphy’s group had identified seven genes related to cardiovascular homeostasis in rats. In the experiments conducted at USP, we had observed that moderate physical activity improves the autonomic balance in hypertensive rats, reduces the cardiac frequency and arterial pressure and modifies gene expression in the same areas that Murphy studied,” explained Michelini.
Using as a model a line of rats with a propensity for developing hypertension as they age, the USP group, in partnership with the British group, decided to study gene expression in a region of the hypothalamus known as the paraventricular core in several phases of the animal’s life. The scientists are also analyzing genes from the solitary tract nucleus and the rostroventrolateral medulla region.
The proposal is to study four groups of rodents: sedentary normotensive and hypertensive and active normotensive and hypertensive. The animals will be subjected to an hour a day of moderate physical activity.
“We intend to monitor these four groups from one month old – when all animals still have normal blood pressure – up to one year and two months of age, which would be the equivalent of 60 or 70 years old in humans”, Michelini said.
Also in Brazil, José Antunes Rodrigues, professor at the Universidade de São Paulo School of Medicine Ribeirão Preto (FMRP-USP), coordinates a Thematic Project that seeks to clarify the neuroendocrine mechanisms that control thirst, appetite for salt and the homeostasis of body fluids.
According to Antunes, salt regulation in an organism depends on the presence of specialized receptors capable of detecting variations in plasma osmolality (the concentration of ions such as sodium, chloride, proteins, bicarbonate, glucose and other substances in the blood) and blood volume.
This information is sent to the central nervous system, which determines the behavioral response, such as greater ingestion of water or sodium, or neuroendocrine and renal responses, such as an increase in water and sodium excretion. Poor functioning of this system could have serious effects, for example, prevent a person from feeling thirsty when he should, increasing the risk of dehydration.
“In the 1960s,” Rodrigues explained, “we had already observed that certain types of lesions in the paraventricular nucleus reduce sodium ingestion and the lesions on the amygdaloid nuclei cause an increase in consumption.”
Recent studies have described the existence of two genes in the hypothalamus – Giot1 and Rasd1 – that are involved in regulation of the control of sodium ingestion in healthy rats. Apparently,stronger expression of Giot1 results in the inhibition of sodium ingestion, whereas Rasd1 increases consumption.
“So we decided to form a partnership to attempt to correlate physiological events that follow an alteration in sodium and water ingestion or excretion with specific alterations in genes in the hypothalamus region,” explained Antunes.
In one of the experiments, the researchers fed pregnant rats a sodium-rich diet throughout gestation and lactation. They observed changes in the standard ingestion of sodium and water in the rats’ offspring.
Antunes said, “We evaluated the physiological and genetic changes that these animals presented at an adult age, both at rest as well as in conditions of hydric restriction or saline overload.”
With broad expertise in the field of physiology, the Brazilian groups work with animal models to identify which parts of an organism are involved in autonomic control. The British group is responsible for the analysis of the so-called transcriptome, i.e., discovering which genes are being expressed at what level and in which regions of the body, and how environmental stimuli affect gene transcription.
“After identifying the genes in these parts of the brain that we know to be crucial for homeostatic regulation, we used bioinformatic tools capable of very complex mathematic processing to map the network of genetic interaction and identify key genes, as well as hub genes, which are those with a greater number of connections with other genes,” explained Murphy.
The objectives, he added, are to identify new targets that can be manipulated in animals and to observe the physiological consequences of these changes.
Antunes stressed that the international partnership has been very important, not only because the work of one group complements that of the other but also because it has made possible the training of post-doctoral students.
Murphy agrees: “I have a laboratory full of Brazilians, and there is an exchange of abilities. We are learning integrative physiology, and other Brazilian post-docs are studying not only transcriptomics but also bioinformatics, and learning to make tools to manipulate in vivo gene expression. Establishing this capacity in São Paulo will be very important”.
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