Aging & Gerontology

Senescence, from the Latin word senex, meaning “growing old,” is a process characterized by a flat and large cellular morphology, an irreversible proliferative arrest, and a differential expression of genes, including upregulation of cell-cycle–negative modulators. Replicative senescence was first described by Hayflick and Moorhead in 1961.

Senescence is defined as the period when synthetic (anabolic) biochemical process gives way to a degradative (catabolic) process. In general, it is the phenomenon of aging. It is the gradual deterioration of functional characteristics. It is the inevitable fate of all multicellular organisms with germ-soma separation, but it can be delayed. The pattern of Senescence can be,

• Cellular Senescence,
• Tissue Senescence,
• Organ Senescence,
• Organism or Whole plant Senescence

In biology, senescence is a process by which a cell ages and permanently stops dividing but does not die. Over time, large numbers of old (or senescent) cells can build up in tissues throughout the body. These cells remain active and can release harmful substances that may cause inflammation and damage to nearby healthy cells. The phenomena of senescence and the diseases of aging are much more common today than they were a century ago.

Cellular senescence is a dynamic multistep process activated in response to various forms of external stimuli, damage and stress. Senescence is characterized by cell cycle arrest, changes in cellular metabolism, chromatin re-organization (senescence associated heterochromatin foci; SAHF) and induction of a proinflammatory secretome (senescence associated secretory phenotype; SASP). These actions are meant to limit tissue damage, restore homeostasis and mitigate preneoplastic cell growth. While aspects of cellular senescence are beneficial in life as a mean to preserve organ and tissue homeostasis, accumulation of senescent cells can also be detrimental.