The innate immune system is involved in tissue maintenance and regeneration. That includes populations of monocytes, circulating innate immune cells in the bloodstream that enter damaged tissue to become macrophages. Monocytes are somewhat easier to catalog and study than is the case for macrophages. The former can be found in a blood sample, while the latter require a tissue sample. Researchers tend to follow the incentives attending the cost and availability of data, and thus we have examples like today's open access paper, in which the authors focus on circulating monocytes in the context of bone fracture.
You might read this paper as a companion piece to a recent investigation of the bad behavior of macrophages in aged bone, and their tendency to do more harm than good following injury. How much of this altered macrophage behavior can be traced back to differences in circulating monocyte populations? No doubt at least some researchers will be looking into this question in the years ahead. Manipulation of innate immune cell state is a growing area of interest for the research community, and while not straightforward, there is the promise of being able to better control tissue maintenance, regeneration, and inflammation.
Monocyte alteration in elderly hip fracture healing: monocyte promising role in bone regeneration
One of the body systems profoundly affected by aging is the skeletal system, giving rise to conditions such as osteoporosis and osteoarthritis that become increasingly prevalent with age. Additionally, there is a notable upswing in the incidence of bone fractures, which is associated with higher rates of morbidity and mortality. Among these fractures, hip fractures (HF) stand out as particularly concerning due to their severe consequences. HF not only leads to chronic pain and disability but also entails a high morbidity risk, an increased susceptibility to major depression, and a loss of autonomy, and often necessitates institutionalization for individuals who were previously independent.
Peripheral blood monocytes, a heterogeneous population comprising approximately 10% of peripheral leukocytes in humans, play a pivotal role in both innate and adaptive immunity. They function as phagocytic cells, eliminating pathogens, and also produce cytokines. Understanding the roles and mechanisms of macrophages, which monocytes can differentiate into, in the context of fractures, may provide valuable insights into predicting the timing of surgery for HF patients and mitigating the immunosuppressive effects that contribute to mortality.
A notable change in older adults is the increased expression of activation, adhesion, and migration markers in circulating monocytes. However, there is a decrease in the expression of co-inhibitory molecules. Recently, research evidence has shown that the migration of specific monocyte subsets to the site of hip fracture plays a crucial role in bone resorption and remodeling, especially concerning age-related factors. In this review, we summarize the current knowledge about uniqueness characteristics of monocytes, and their potential regulation and moderation to enhance the healing process of hip fractures. This breakthrough could significantly contribute to the comprehension of aging process at a fundamental aging mechanism through this initiative would represent a crucial stride for diagnosing and treating age related hip fracture.
View the full article at FightAging
