You may recall from biology classes that most DNA is located in the nucleus, the cell’s command center that dictates cell growth, maturation, division and even cell death. But occasionally, in aging cells that stop growing and dividing (senescent cells), bits of DNA pinch off and accumulate in the cytoplasm. Although this may seem like an innocent act, cytoplasmic DNA actually triggers an inflammatory path that contributes to many diseases linked with aging.
“We are studying the mechanics of “inflammaging,” says Peter Adams, PhD, professor at SBP. “The term refers to the pervasive, chronic inflammation that occurs in aging tissue. Understanding how inflammation occurs in aging tissue opens new avenues to treat a variety of age-related diseases such as rheumatoid arthritis, liver disease, atherosclerosis, muscle wasting (sarcopenia), and even cancer.”
Adams’ most recent study, a collaboration with Shelley Berger, PhD, professor at University of Pennsylvania, studied senescent cells to figure out how cytoplasmic DNA activates inflammation. Senescent cells can be long-lived and accumulate in aged and damaged organs, attracting inflammatory cells that promote tissue damage.
Their new research, published in Nature, is the first to describe how in senescent cells, cytoplasmic DNA fragments activate the cGAS-STING pathway, a component of the immune system that leads to the secretion of pro-inflammatory cytokines.
“Pro-inflammatory cytokines, such as interferon and tumor necrosis factor (TNF) promote inflammation, which can be a good thing when you need it,” explains Adams. “Acute inflammation, for example, is a natural, healthy process that attracts and activates immune cells to heal wounds and fight infections. And in the right circumstances, when our immune system recognizes cancer cells as foreign, these cytokines can activate powerful anti-tumor immune responses.
“But chronic, uncontrolled inflammation is a potentially harmful process. It can lead to the destruction of tissue, and a list of diseases that range from skin conditions like psoriasis to deadly liver cancer. So the inflammatory process must be tightly regulated to avoid excessive tissue damage and spillover to normal tissue—and these risks increase with age.
“Now that we understand how cytoplasmic DNA leads to chronic inflammation in senescent cells—through the cGAS-STING pathway—we have the opportunity to think about therapeutic strategies to intervene to delay or prevent “inflammaging” related diseases.
Related: Cancer biology: Genome jail-break triggers lockdown (Nature Magazine)