Background. Macrophages support skin wound healing by switching their function from pro- inflammatory to anti-inflammatory and tissue remodeling ones. This mechanism is deranged in pathological states including chronic ulcers and skin cancer. However, the mechanisms underlying the functional change of tissue macrophages in health and disease are undefined in vivo due to the lack of suitable animal models, thus posing a formidable hurdle towards the development of therapies aiming at reorienting macrophage functions. Hypothesis. We hypothesize a central role of functional reprogramming of individual macrophages from pro- to non-inflammatory functions, as opposed to expansion and contraction of macrophage populations with invariable function, in governing skin wound healing. We also hypothesize that alteration of macrophage functions, possibly in concert with their impaired migration within the skin, underlies the pathophysiology of diabetic ulcers and melanoma.
Aims. In Aim 1 we will develop strategies to map the functional fate of pro-inflammatory macrophages (PRImap mice), and use them to quantify the contribution of macrophage reprogramming to the generation of reparative and anti-inflammatory macrophages during wound healing.
Aim 2 is dedicated to understand how macrophage function and reprogramming correlates with their motility and location within the skin, and how these aspects may be uncoupled in diabetic ulcers and melanoma. Experimental Design. We will quantify pro-inflammatory macrophage reprogramming to restorative or anti-inflammatory functions by wounding healthy or diabetic mice or injecting melanomas in PRImap mice, using FACS and histological analysis. The motility of pro-inflammatory and reprogrammed macrophages in health and disease will be studied through intravital microscopy. Expected results. We expect to identify which mechanism among macrophage reprogramming, local proliferation of anti-inflammatory macrophages or recruitment of anti-inflammatory monocytes is the driving force of the macrophage functional switch that supports skin wound healing. We will further establish whether pro-inflammatory or reprogrammed macrophages display altered migration in diabetic ulcers and melanoma, contributing to their pathophysiology. Impact. Our study will contribute to the areas of basic immunology and immunotherapy by defining the extent of macrophage reprogramming, and whether it is the main mechanism underlying macrophage functional and migratory changes in physiologic and pathologic contexts. In the long term, PRImap mice will be valuable to identify the molecular determinants of macrophage reprogramming, thus paving the way to the manipulation of macrophage functions for therapeutic purposes.

Public Health Relevance

Manipulation of macrophage function holds the promise of being a valuable strategy to treat diseases including chronic skin wounds and cancer, yet the mechanisms underlying macrophage functional switch in vivo are understudied. We propose to generate experimental systems allowing to map the fate of pro-inflammatory macrophages and to use them to study whether or not macrophage functional switch is a consequence of reprogramming during wound healing and in several pathologic states of the skin. By defining the mechanisms by which macrophages change function in vivo, our investigation will pave the way for the rational manipulation of macrophage function for therapeutic purposes.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Exploratory/Developmental Grants (R21)
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Arthritis, Connective Tissue and Skin Study Section (ACTS)
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Belkin, Alexey
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University of California Irvine
Schools of Medicine
United States
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