Transcription Factor Activity Regulating Macrophage Heterogeneity during Skin Wound Healing.

Monocytes and macrophages (Mos/Mϕs) play diverse roles in wound healing by adopting a spectrum of functional phenotypes; however, the regulation of such heterogeneity remains poorly defined. We enhanced our previously published Bayesian inference TF activity model, incorporating both single-cell RNA sequencing and single-cell ATAC sequencing data to infer transcription factor (TF) activity in Mos/Mϕs during skin wound healing. We found that wound Mos/Mϕs clustered into early-stage Mos/Mϕs, late-stage Mϕs, and APCs, and that each cluster showed differential chromatin accessibility and differential predicted TF activity that did not always correlate with mRNA or protein expression. Network analysis revealed two highly connected large communities involving a total of 19 TFs, highlighting TF cooperation in regulating wound Mos/Mϕs. This analysis also revealed a small community populated by NR4A1 and NFKB1, supporting a proinflammatory link between these TFs. Importantly, we validated a proinflammatory role for NR4A1 activity during wound healing, showing that Nr4a1 knockout mice exhibit decreased inflammatory gene expression in early-stage wound Mos/Mϕs, along with delayed wound re-epithelialization and impaired granulation tissue formation. In summary, our study provides insight into TF activity that regulates Mo/Mϕ heterogeneity during wound healing and provides a rational basis for targeting Mo/Mϕ TF networks to alter phenotypes and improve healing.

Liver insulin-like growth factor-1 mediates effects of low-intensity vibration on wound healing in diabetic mice.

Chronic wounds in diabetic patients are associated with significant morbidity and mortality; however, few therapies are available to improve healing of diabetic wounds. Our group previously reported that low-intensity vibration (LIV) could improve angiogenesis and wound healing in diabetic mice. The purpose of this study was to begin to elucidate the mechanisms underlying LIV-enhanced healing. We first demonstrate that LIV-enhanced wound healing in db/db mice is associated with increased IGF1 protein levels in liver, blood, and wounds. The increase in insulin-like growth factor (IGF) 1 protein in wounds is associated with increased Igf1 mRNA expression both in liver and wounds, but the increase in protein levels preceded the increase in mRNA expression in wounds. Since our previous study demonstrated that liver was a primary source of IGF1 in skin wounds, we used inducible ablation of IGF1 in the liver of high-fat diet (HFD)-fed mice to determine whether liver IGF1 mediated the effects of LIV on wound healing. We demonstrate that knockdown of IGF1 in liver blunts LIV-induced improvements in wound healing in HFD-fed mice, particularly increased angiogenesis and granulation tissue formation, and inhibits the resolution of inflammation. This and our previous studies indicate that LIV may promote skin wound healing at least in part via crosstalk between the liver and wound. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Liver is a primary source of insulin-like growth factor-1 in skin wound healing.

Insulin-like growth factor (IGF)-1 plays important role in tissue repair through its ability to stimulate wound cell activity. While IGF-1 is expressed locally by wound cells, liver-derived IGF-1 is also present at high levels in the circulation, and the contributions of local vs circulating IGF-1 to wound levels remain undefined. The hypothesis of this study was that liver is a primary source of IGF-1 during skin wound healing. To test this hypothesis, we utilized a model that allows inducible ablation of IGF-1 specifically in liver of adult mice. We demonstrate that ablation of liver IGF-1 leads to >85% loss of circulating IGF-1 and ~60% decrease in wound IGF-1 during the proliferative phase of healing in both male and female mice. This reduction of liver-derived IGF-1 did not alter local mRNA expression of Igf1 in wounds. Knockdown of liver IGF-1 significantly delayed wound re-epithelialization and reduced granulation tissue formation and collagen deposition. Knockdown of liver IGF-1 also significantly reduced angiogenesis and resulted in persistent macrophage accumulation. In summary, liver is a primary source of IGF-1 in skin wounds and contributes to many aspects of both epithelial and dermal healing.

Parameter-Dependency of Low-Intensity Vibration for Wound Healing in Diabetic Mice.

Chronic wounds in diabetic patients represent an escalating health problem, leading to significant morbidity and mortality. Our group previously reported that whole body low-intensity vibration (LIV) can improve angiogenesis and wound healing in diabetic mice. The purpose of the current study was to determine whether effects of LIV on wound healing are frequency and/or amplitude dependent. Wound healing was assessed in diabetic (db/db) mice exposed to one of four LIV protocols with different combinations of two acceleration magnitudes (0.3 and 0.6 g) and two frequencies (45 and 90 Hz) or in non-vibration sham controls. The low acceleration, low frequency protocol (0.3 g and 45 Hz) was the only one that improved wound healing, increasing angiogenesis and granulation tissue formation, leading to accelerated re-epithelialization and wound closure. Other protocols had little to no impact on healing with some evidence that 0.6 g accelerations negatively affected wound closure. The 0.3 g, 45 Hz protocol also increased levels of insulin-like growth factor-1 and tended to increase levels of vascular endothelial growth factor in wounds, but had no effect on levels of basic fibroblast growth factor or platelet derived growth factor-bb, indicating that this LIV protocol induces specific growth factors during wound healing. Our findings demonstrate parameter-dependent effects of LIV for improving wound healing that can be exploited for future mechanistic and therapeutic studies.