Accumulation of senescent cells is one of the root causes of aging. Based on the comparatively few measures established in old tissues, the proportion of cells that are senescent does not rise to more than a few percent of all cells even in very old individuals. That few percent is enough to wreak havok, however. Senescent cells actively secrete a mix of signals that promote chronic inflammation, destructively remodel tissue structure, and change the behavior of surrounding cells for the worse. They are harmful enough to be a significant direct contribution to many age-related diseases. Data exists for their baleful influence to produce osteoarthritis, fibrosis of the lung and other organs, and many other conditions.
Given all of this, there is considerable enthusiasm for the development of means to selectively destroy these cells: small molecule senolytic drugs, immunotherapies, and suicide gene therapies are all under development, the first now in human trials. Interestingly, despite some years of this active development, the ability to accurately and usefully measure the count and life span of senescent cells in tissue has lagged behind. There are methods that work well enough in animal studies,
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