Enhanced Proliferation of Ly6C+ Monocytes/Macrophages Contributes to Chronic Inflammation in Skin Wounds of Diabetic Mice

Abstract

Diabetic wounds are characterized by persistent accumulation of proinflammatory monocytes (Mo)/macrophages (MΦ) and impaired healing. However, the mechanisms underlying the persistent accumulation of Mo/MΦ remain poorly understood. In this study, we report that Ly6C⁺F4/80^lo/- Mo/MΦ proliferate at higher rates in wounds of diabetic mice compared with nondiabetic mice, leading to greater accumulation of these cells. Unbiased single cell RNA sequencing analysis of combined nondiabetic and diabetic wound Mo/MΦ revealed a cluster, populated primarily by cells from diabetic wounds, for which genes associated with the cell cycle were enriched. In a screen of potential regulators, CCL2 levels were increased in wounds of diabetic mice, and subsequent experiments showed that local CCL2 treatment increased Ly6C⁺F4/80^lo/- Mo/MΦ proliferation. Importantly, adoptive transfer of mixtures of CCR2^-/- and CCR2^+/+ Ly6C^hi Mo indicated that CCL2/CCR2 signaling is required for their proliferation in the wound environment. Together, these data demonstrate a novel role for the CCL2/CCR2 signaling pathway in promoting skin Mo/MΦ proliferation, contributing to persistent accumulation of Mo/MΦ and impaired healing in diabetic mice.