Diabetes induces stable intrinsic changes to myeloid cells that contribute to chronic inflammation during wound healing in mice

Abstract

SUMMARYAcute inflammation in response to injury is a tightly regulated process by which subsets of leukocytes are recruited to the injured tissue and undergo behavioural changes that are essential for effective tissue repair and regeneration. The diabetic wound environment is characterised by excessive and prolonged inflammation that is linked to poor progression of healing and, in humans, the development of diabetic foot ulcers. However, the underlying mechanisms contributing to excessive inflammation remain poorly understood. Here we show in a murine model that the diabetic environment induces stable intrinsic changes in haematopoietic cells. These changes lead to a hyper-responsive phenotype to both pro-inflammatory and anti-inflammatory stimuli, producing extreme M1 and M2 polarised cells. During early wound healing, myeloid cells in diabetic mice show hyperpolarisation towards both M1 and M2 phenotypes, whereas, at late stages of healing, when non-diabetic macrophages have transitioned to an M2 phenotype, diabetic wound macrophages continue to display an M1 phenotype. Intriguingly, we show that this population predominantly consists of Gr-1+ CD11b+ CD14+ cells that have been previously reported as ‘inflammatory macrophages’ recruited to injured tissue in the early stages of wound healing. Finally, we show that this phenomenon is directly relevant to human diabetic ulcers, for which M2 polarisation predicts healing outcome. Thus, treatments focused at targeting this inflammatory cell subset could prove beneficial for pathological tissue repair.

Targeting CD64 mediates elimination of M1 but not M2 macrophages in vitro and in cutaneous inflammation in mice and patient biopsies

“…During chronic inflammation, there is strong evidence for an inappropriate persistence of M1 macrophages, which are directly associated with the development and perpetuation of many chronic inflammatory and autoimmune diseases. 8,35 In rheumatoid arthritis, crosstalk between M1 and Th17 cells is implicated in severity and chronicity of the disease and targeting either population is proposed as a potent therapeutic strategy for autoimmune disease. 36 Human CD64 is the high-affinity FcgR in humans, and it displays several unique properties such as the ability to bind and rapidly internalize monomeric IgG 37 and constitutive expression restricted to macrophages, monocytes and their progenitors.…”

Diabetes Inhibits Gr-1+ Myeloid Cell Maturation viaCebpaDeregulation

“…Db-derived BM Gr-1 + cells perform poorly in functional assays (7,36) and do not promote angiogenesis in vivo (7). Their altered differentiation capacity is shown both in their skewed colony formation (7) and in their hyperpolarization in response to stimuli (5). Wound resolution requires myeloid cells (40), but the excessive numbers of defective cells found in the db wound are believed to impair healing (41).…”

“…In both humans and mice (3), diabetes impairs the orderly transition from an early, inflammatory phase of repair to a later, prohealing stage, preventing timely healing. Excessive numbers of myeloid cells are found in the wound (2,4), and they display a persistent proinflammatory, M1-like (classical) or M1/M2 (mixed) phenotype, instead of a clear transition to an M2-like (alternative) state (5,6).…”

“…Chronic inflammation perturbs hematopoiesis, possibly via increased myeloid cell turnover at inflammatory sites and a correspondingly elevated demand (12). Stable intrinsic defects induced in myeloid cells by diabetes prior to wound recruitment promote chronic inflammation and impair healing (5). Persistent Ly6C/Gr-1 and diminished F4.80 expression in the db wound suggest that one facet of the aberrant myeloid cell phenotype is persistent immaturity (5,6).…”

“…Stable intrinsic defects induced in myeloid cells by diabetes prior to wound recruitment promote chronic inflammation and impair healing (5). Persistent Ly6C/Gr-1 and diminished F4.80 expression in the db wound suggest that one facet of the aberrant myeloid cell phenotype is persistent immaturity (5,6). It is unknown whether this is prespecified, but peripheral blood myeloid cells from db patients have impaired effector functions, including bacterial killing and phagocytosis, that are characteristic of immaturity (13).…”