Why do we age? It’s a question that has fascinated scientists for centuries. As longevity researchers discover more about the aging process, it’s becoming clear that all aging has certain cellular phenomena in common. Called the twelve hallmarks of aging, these phenomena are responsible for everything from the wrinkles we start to see in our 20s to the age-related diseases that plague us in old age.
Recently, research has shown that one of these twelve hallmarks stands above the rest: cellular senescence, a central aging marker that activates a number of the other eleven hallmarks. Cellular senescence is so integral to the aging process that it links both major types of aging: intrinsic and extrinsic aging. Let’s take a closer look at the science behind these discoveries.
Reference Lab
May 10, 2023
01 The difference between extrinsic and intrinsic aging
Determined largely by your genetics, intrinsic aging is the predetermined process that your body will undergo over time based on its innate ability to repair damage. This type of aging is beyond your control–and the reason you might notice similarities in the way your family members age.
While intrinsic aging is out of your hands, extrinsic aging occurs as a result of external and often preventable environmental and lifestyle factors. Common extrinsic agers include UV exposure, smoking cigarettes, and sedentary lifestyles. It’s extrinsic aging we have to thank for the fact that siblings or other close family members sometimes age at very different rates and in very different ways.
02 Is This The Root Cause of Aging?
Determined largely by your genetics, intrinsic aging is the predetermined process that your body will undergo over time based on its innate ability to repair damage. This type of aging is beyond your control–and the reason you might notice similarities in the way your family members age.
While intrinsic aging is out of your hands, extrinsic aging occurs as a result of external and often preventable environmental and lifestyle factors. Common extrinsic agers include UV exposure, smoking cigarettes, and sedentary lifestyles. It’s extrinsic aging we have to thank for the fact that siblings or other close family members sometimes age at very different rates and in very different ways.
03 Both intrinsic & extrinsic factors increase cellular senescence
We know that when the body experiences an extrinsic or intrinsic stimulus, aging occurs. But why? Scientists believe that both extrinsic and intrinsic factors activate cellular senescence, the accumulation of zombie cells at the end of their lifecycle that accelerate aging in the cells around them.
Research has shown that intrinsic factors–like the activation of certain genes–can contribute to the accumulation of senescent cells. Similarly, extrinsic factors like radiation and or cigarette smoke can cause cells to enter senescence.
04Extrinsically induced senescent cells active intrinsic aging
While extrinsic and intrinsic aging are often thought of as separate, it’s clear that they actually intersect. Research has shown that external aging factors actually increase the rate at which we experience intrinsic aging. Scientists believe that cellular senescence may be the factor that links the two together.
Extrinsic aging factors induce early senescence in cells, causing the body to act older than it actually is. With increasing exposure to these factors, the body can no longer keep up with the rate of senescence occurring–leading to an accumulation of senescent cells. These senescent cells secrete a wide range of factors collectively called the senescence-associated secretory phenotype (SASP). This is where the link to intrinsic aging comes into play. SASP itself can actually activate intrinsic aging – inducing inflammation, altering tissue homeostasis and promoting cellular dysfunction. This means that increasing rates of extrinsic aging can actually contribute to increasing rates of intrinsic aging through cellular senescence. When both extrinsic and intrinsic aging increase, we experience earlier onset of age-related diseases. For example, the accumulation of senescent cells in the brain can impair cognitive function and contribute to neurodegenerative diseases such as Alzheimer's.
05The quest to address the root cause of aging
While extrinsic and intrinsic aging are often thought of as separate, it’s clear that they actually intersect. Research has shown that external aging factors actually increase the rate at which we experience intrinsic aging. Scientists believe that cellular senescence may be the factor that links the two together.
06 Key Takeaways
- All aging is either intrinsic, caused by internal factors like genetics, or extrinsic, mediated by external stimuli like UV radiation and toxins.
- By increasing cellular senescence, UV radiation accelerates skin aging and leads to the degradation of collagen and elastin.
- Both extrinsic and intrinsic factors activate cellular senescence, a central hallmark of aging that accelerates aging in neighboring cells.
- Extrinsically induced senescent cells release factors that activate intrinsic aging, creating a connection between intrinsic and extrinsic aging.
- This connection accelerates systemic aging and contributes to the early onset of age-related disease.
- By addressing cellular senescence as the root cause of aging, longevity scientists like those on our team hope to make age-related disease a thing of the past.