On Inflammation in Mouse Longevity Mutants

Chronic inflammation is a bad thing, walking hand in hand with the frailties and degenerations of aging. Rising inflammation contributes to a very broad range of fatal age-related conditions, and the progressive decline of the immune system itself causes ever greater chronic inflammation, even as it fails to protect the body from pathogens and errant cells. Further, visceral fat tissue is a potent source of inflammation, and this is one of the mechanisms thought to link excess fat with lowered life expectancy and greater risk of age-related disease.

There is plenty in the Fight Aging! archives on the subject of inflammation and its role in aging. To pick a handful of examples:

Some of the best known genetically engineered mutant mice with extended longevity are those in which growth hormone and its receptor are suppressed. They are small, need careful husbanding because they don't generate enough body heat to survive well on their own, and live 60-70% longer than ordinary members of their species. As noted in the following review paper, reduced inflammation has some role to play in this extended healthy life span:

Growth hormone, inflammation and aging:

The last 200 years of industrial development along with the progress in medicine and in various public health measures had significant effect on human life expectancy by doubling the average longevity from 35-40 to 75-80. There is evidence that this great increase of the lifespan during industrial development is largely due to decreased exposure to chronic inflammation throughout life. There is strong evidence that exposure of an individual to past infections and the levels of chronic inflammation increase the risk of heart attack, stroke and even cancer.

Centenarians represent exceptional longevity in human populations and it is already known that many of these individuals are escaping from major common diseases such as cancer, diabetes etc. There is ongoing interest in investigating the mechanisms that allow these individuals to reach this exceptional longevity. There are several animal mutants used to study longevity with hope to determine the mechanism of extended lifespan and more importantly protection from age related diseases. In our laboratory we use animals with disruption of growth hormone (GH) signaling which greatly extend longevity.

Mutant animals characterized by extended longevity provide valuable tools to study the mechanisms of aging. Growth hormone and insulin-like growth factor-1 (IGF-1) constitute one of the well-established pathways involved in the regulation of aging and lifespan. Ames and Snell dwarf mice characterized by GH deficiency as well as growth hormone receptor/growth hormone binding protein knockout (GHRKO) mice characterized by GH resistance live significantly longer than genetically normal animals.

During normal aging of rodents and humans there is increased insulin resistance, disruption of metabolic activities and decline of the function of the immune system. All of these age related processes promote inflammatory activity, causing long term tissue damage and systemic chronic inflammation. However, studies of long living mutants and calorie restricted animals show decreased pro-inflammatory activity with increased levels of anti-inflammatory adipokines such as adiponectin. At the same time, these animals have improved insulin signaling and carbohydrate homeostasis that relate to alterations in the secretory profile of adipose tissue including increased production and release of anti-inflammatory adipokines.

This suggests that reduced inflammation promoting healthy metabolism may represent one of the major mechanisms of extended longevity in long-lived mutant mice and likely also in the human.


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