According to the World Health Organization, by 2050 there will be more adults over the age of 65 than children under the age of five. "Aging is a risk factor for metabolic, neurodegenerative diseases and cancer. As we get older, declining functional properties increase vulnerability to disease and death." Diana Lizbeth de la Cruz Ramírez, a postdoctoral researcher in the Department of Physiology and Biophysics at the University of Washington in Seattle, said this while participating in the Complexity and Health Seminar at the UNAM's Center for Complexity Sciences.
According to the American Federation for Aging Research, this represents the greatest risk for cancer, Alzheimer's, heart disease, diabetes, and dementia. Also for infectious diseases, such as COVID-19. It is a process that we all experience. From the biological point of view, it is the consequence of the accumulation of molecular and cellular damage over time, which deteriorates or decreases functional properties.
The doctor in Biomedical Sciences from the Faculty of Medicine of the UNAM recalled that people globally are aging. In 2019, one in 12, or nine percent of the total population, was over 65 years of age. It is estimated that in 2050 one in six, 16 percent, will be in this age range. This sector will become more significant numerically every year; understanding their needs from a clinical and social point of view is key to meeting their requirements, stressed the expert.
In her presentation "How does our sympathetic nervous system age? An approach from the postganglionic neurons", she mentioned that at the cellular level it is established that aging is a multicausal process; that is, more than one variable is involved. It can be determined by genomic instability, dysfunction in protein synthesis, and degradation because neurons cannot censor nutrients, mitochondrial dysfunction, or stem cell depletion. Also when intercellular communication is damaged, the expert explained.
Her current research project seeks to understand the molecular and cellular mechanisms of the aging of the sympathetic nervous system (SNS), "specifically from the peripheral component which are the postganglionic neurons". In this regard, she added: the body's function is decreasing. Homeostasis -the state of equilibrium between the systems needed to survive and function correctly- is regulated through the nervous system, so its study is key to understanding, from a global perspective, how this process occurs.
De la Cruz Ramírez mentioned that the SNS is part of the autonomic nervous system and is mainly related to non-voluntary functions, such as pupil dilation. It is also involved in the activation of the body for stressful situations, with the fight, flight, or "freeze" reactions. It helps to manage the level of stress by modifying our physiological function and adapting us to cope with these stimuli.
It is composed of the brain and medulla, that is, the central nervous system, and a peripheral part: neurons in the ganglia of the sympathetic chain, which innervate directly the so-called white organs, such as the eyes, salivary gland, and heart. This system regulates the secretion of tears and dilates the pupil, as well as accelerates the heart rate and induces vasoconstriction; it inhibits salivation, insulin secretion, and bladder contraction.
Several of these functions are affected as we age: we present dry eye, which hinders vision; reduction in saliva secretion, related to the increase in caries that leads to tooth loss; arrhythmias and hypertension; inflammatory bowel disease, obesity, and diabetes, or urinary incontinence, said the scientist. One of the characteristics of aging is the increase in the activity of the sympathetic system; that is, it is more active as we get older.
De la Cruz Ramírez commented that the SNS has preganglionic neurons in the central nervous system that innervate (reach an organ or part of the body) those found in the ganglia, or postganglionic neurons that, in turn, innervate the target organs. How the postganglionic fiber communicates with the organs is through the secretion of a neurotransmitter called noradrenaline, whose plasma levels increase with age. It is also a fact that their activity increases, those that innervate the heart, kidney, pancreas, etcetera.
Aging is related to the overactivity of the SNS and the hypothesis we have is that it alters the function (electrical properties) of the postganglionic neurons at this stage of life. We are demonstrating for the first time that these are also affected as we get older, she concluded.