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Neurodegenerative diseases are a group of heterogeneous diseases characterized by a gradual, progressive and selective decrease in nervous system functions. The etiology of these pathologies remains unknown; however, mitochondrial function has been proposed as a common factor that could be involved in the establishment of these diseases, owing to the high energy requirement neurons have in order to carry out their physiological functions. Mitochondria are extremely dynamic organelles that can change their morphology and function in response to different physiological stimuli and, for this reason, mitochondrial dynamics have started being studied as one of cell survival main regulators. This event comprises different processes, such as the generation of new mitochondria and their elimination when they are no longer functional, as well as mitochondrial fusion and fission processes and the traffic of these organelles within the cellular environment. All these processes are highly regulated, and their main purpose is optimal functionality of mitochondria and cellular homeostasis., (Copyright: © 2019 SecretarÍa de Salud.)

Cellular senescence is defined as the physiological program of terminal growth arrest; in mammals it is an important tumor-suppressor mechanism since it stops premalignant cell proliferation. However, senescence also contributes to the decline associated to aging and the development of several diseases. This is explained by the fact that senescent cells secrete diverse molecules, which compromise the cellular microenvironment, and altogether are referred as senescent-associated secretory phenotype (SASP). The SASP is composed by cytokines, chemokines, growth factors, proteases, etc., whose function is to maintain the antiproliferative state and promote senescent cell clearance by the immune system. Nevertheless, over time, and particularly during old age, SASP might stimulate proliferation and premalignant cell transformation. The multifunctional roles of SASP would depend on the cell type and their physiological nature. Therefore, relying on the biological context, SASP could be beneficial and participate in the repair and regeneration processes, or detrimental and induce degenerative pathologies and cancer.

Living organisms have always had to cope with harsh environmental conditions and in order to survive, they have developed complex mechanisms to deal with them. These responses have been assembled in a concept called hormesis, which has been identified as an evolutionarily conserved process in which a low dose of a stressful stimulus activates an adaptive response that increases the resistance of the cell or organism to higher stress level. The main hormetic agents identified so far are irradiation, heat, heavy metals, antibiotics, ethanol, pro-oxidants, exercise and food restriction. The hormetic response involves the expression of genes that encode cytoprotective proteins such as chaperones like heat-shock proteins, antioxidant enzymes and growth factors. In this review we will discuss the hormetic response mainly during an oxidative challenge, and its relationship with senescence and aging, and some related diseases such as diabetes and neurodegeneration.