Inflammaging as the basis of age-associated diseases

Aging is one of the most complex biological phenomena that affects all human physiological systems, including the immune system. Immunosenescence is understood as structural and functional changes in both adaptive and innate immunity systems. The so-called inflammaging(definition) is among manifestations of immune aging. It is an age-related increase in inflammatory mediators and development of an inflammatory phenotype. An important role in development of inflammaging is assigned to chronic stimulation of immune system by exogenous and endogenous danger signals (pathogen-associated molecular pattern, PAMP and damage-associated molecular pattern, DAMP), which include viruses, microbiota of the gastrointestinal tract, free radicals, etc. PAMP and DAMP are recognized by the innate immunity system cells through the pattern recognition receptors (PRR), e.g., Toll-like receptors (TLR), RIG-I-like receptors (RLR), NODlike receptors (NLR), lectin receptors. Stimulation of PRR leads to activation of intracellular signaling and increased expression of pro-inflammatory factors. PAMPs are the most powerful activators of PRR and inflammation triggers; DAMPs can activate the same receptors and signaling pathways, causing the development of a sterile inflammatory response. The NF-kB signaling pathway is considered as a key signaling pathway for inflammaging. NLR stimulation also leads to formation of inflammasome. Its function is to transform the pro-inflammatory cytokines to a biologically active form, which is an important for the formation of a pro-inflammatory phenotype and development of inflammaging. This process is considered an important risk factor for morbidity and mortality among older people. Chronic inflammation underlies pathogenesis of many age-related diseases, such as osteoporosis, atherosclerosis, Alzheimer’s disease, Parkinson’s disease, type 2 diabetes. Various chronic diseases associated with age are directly related to PAMP and DAMP-induced TLR or NLRP3-mediated inflammatory response. Hence, these ligands and their receptors can be suggested as biomarkers and interventional targets for age-related disorders. Despite numerous studies in age-associated pathology, there are only few works on the contribution of innate immunity in healthy aging. It remains unclear whether the inflammatory phenotype is a manifestation of healthy aging, or it is associated with development of age-related pathology. Further study of the mechanisms of inflammatory aging will reveal biomarkers of healthy aging and potential targets for the treatment of age-associated diseases.