Emerging Dynamics of Macrophage Cellular Senescence and Immunosenescence in Governing Organismal Aging and Disease: Concepts and Opportunities

Abstract

An intricate relationship between impaired immune functions and the age-related accumulation of tissue senescent cells (SC) is rapidly emerging. The immune system is unique as it undergoes mutually inclusive and deleterious processes of immunosenescence and cellular senescence with advancing age. While factors inducing immunosenescence and cellular senescence may be shared, however, both these processes are fundamentally different which holistically influence the aging immune system. Immunosenescence is a well-characterized phenomenon, but our understanding and biological impact of cellular senescence in immune cells, especially in the innate immune cells such as macrophages, is only beginning to be understood. Tissue-resident macrophages are long-lived, and while functioning in tissue-specific and niche-specific microenvironments, senescence in macrophages can be directly influenced by senescent host cells which may impact organismal aging. In addition, evidence of age-associated immunometabolic changes as drivers of altered macrophage phenotype and functions such as inflamm-aging is also emerging. The present review describes the emerging impact of cellular senescence vis-à-vis immunosenescence in aging macrophages, its biological relevance with other senescent non-immune cells, and known immunometabolic regulators. Gaps in our present knowledge, as well as strategies aimed at understanding cellular senescence and its therapeutics in the context of macrophages, have been reviewed.