Mechanisms Underlying Impaired Diabetic Wound Healing

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ABSTRACT Persistent unresolved inflammation impairs diabetic wound healing. The function and fate of wound monocyte/macrophages (mϕ) hold the key to the outcome of wound inflammation. This proposal builds on observations originating from live functional wound macrophages (wmϕ) and wound fluid derived from chronic wounds of patients which were then developed further using experimental models. Given current ambiguity in macrophage nomenclature, and proposed misfit of wmϕ with the M1/M2 nomenclature, for this proposal we classify wmϕ based on the pro-inflammatory (mϕinf) or pro-resolution/healing (mϕheal) functional states. We have reported that i) successful wmϕ efferocytosis (Eff) helps resolve inflammation; and ii) Efferocytosis severely impaired (Efflo) in wmϕ of diabetic wounds causing unresolved inflammation, and iii) correction of Efflo with recombinant MFG-E8 (rMFG-E8) in wmϕ of diabetic wounds resolves inflammation and promotes wound healing. Our laboratory was the first to report a critical role of miRNA-21 in the regulation of wound inflammation. We recently reported the framework of a new paradigm proposing that the plasticity of wmϕ at the wound-site is a major determinant of the state of wound inflammation. The current proposal seeks to characterize this paradigm with emphasis on two novel aspects: (i) that miR cargo captured in extracellular vesicles (EVs) at the site of wound inflammation determine the fate of wmϕ and state of inflammation; and (ii) that at the site of diabetic wound inflammation miR is epigenetically silenced (methylated) such that inflammation persists. The following three aims are proposed: Aim 1: Test miR-21 and efferocytosis as critical determinants of monocyte/macrophage fate at the wound-site. §1.1 A unique subset of wmϕ convert from mϕinf  mϕF; miR-21 encapsulated in wound-site extracellular vesicles (EV) are delivered to wmϕ to cause such conversion. §1.2 Another subset of wmϕ undergoes mϕinfmϕheal; this subset plays a critical role in resolution of wound inflammation and healing. Aim 2: Determine how diabetes redirects the fate of wmϕ causing derailment of healing. §2.1 Diabetic conditions cause miR-21 epigenetic silencing in wmϕ (miR-21lo). Such deficit, in combination with impaired efferocytosis (Efflo), stalls wmϕ in mϕinf; §2.2 In diabetic wmϕ, correction of miR-21 and efferocytosis advances diabetic mϕinfmϕheal/mϕF resuming healing. Novel macrophage-targeted lipid nanoparticle (LNPmφ) will correct diabetic miR-21lo. Aim 3: Study live wmϕ and wound-edge tissue biopsies isolated from diabetic wounds of patients testing whether: §3.1 transition of wmϕ to mϕF (or mϕheal) is compromised in poorly controlled diabetics (HbA1c>9) where miR-21 is epigenetically silent; §3.2 correction of miR-21 and efferocytosis advances diabetic wmϕ from mϕinfmϕheal/mϕF.