Entropy Meets Physiology: Should We Translate Aging as Disorder?

Aging is characterized by an alteration of several physiological processes and biological pathways that leads to an increased susceptibility to age-related diseases and death. Normally, multipotential stem/progenitor cells may contribute to tissue homeostasis, and to minimize the age-depending DNA damage. Scientific research has demonstrated that aging induces several complex changes affecting even the mesenchymal stromal/stem cells (MSCs) ability to self-renew, differentiate, and immunomodulate the human tissues, causing further alterations in the local microenvironment. Cellular senescence can thus be considered as an overall response to several damages. Accordingly, aging seems to create the proper conditions to decrease the tissue's metabolic performance, and the cell-to-cell communication, resulting in a progressive tissue destruction; on the other hand, the MSCs functions appear to be severely reduced. This concise review summarizes the main alterations affecting the MSCs during aging, and it also explains the role of inflammation as a key player in age-related syndromes. The hypothesis is to suggest a parallelism between the thermodynamic concept of "entropy" and biological aging, speculating that both can increase within irreversible systems and both lead toward an irreversible disorder; so, the question is: should we translate aging as disorder?