The evidence of the past decades, and particularly the past seven years, strongly supports the idea that the accumulation of senescent cells is a root cause of aging. Cells become senescent in large numbers day in and day out, a normal end of life state for somatic cells that have reached the Hayflick limit. Cells also become senescent as the result of damage, or a toxic environment, and there is ever more of that with advancing age. Near all of these cells are destroyed quite quickly after they enter a senescent state, but enough linger to ensure that a few percent of all cells are senescent in old age. These problem cells secrete a potent mix of signals that induces chronic inflammation, degrades tissue structure, and alters the behavior of normal cells for the worse.
Senescent cells are not the only component of aging, but given enough time senescent cells alone would be able to kill you. Senescent cells are a prominent cause of fibrosis and declining function of organs such as the lungs, kidneys, liver, and heart. They cause arthritis. Ever more immune cells are senescent in later life.
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