Research

Inflammation is a necessary early phase of the healing process. In healthy individuals, monocyte/macrophage immune cells initiate the inflammatory process in the first stages of healing, and then they transition to play a more reparative role. This ability to transition to a reparative phenotype is known as plasticity, and the signaling underlying this process is impaired in diabetes. The signaling problems — more specifically an imbalance between pro- and anti-inflammatory signaling molecules known as cytokines — prevent the switch, resulting in chronic inflammation and wounds that don’t heal.

How this transition takes place at the genetic, molecular and cellular levels has not been well characterized. Our laboratory's work is focused around identifying and clarifying the mechanisms that control monocyte/macrophage plasticity and encourage the chronic inflammatory state we see in diabetic wounds. Our aim is to translate the findings and discoveries in our laboratory to new and better treatments for clinicians to offer their patients in the clinic one day soon.

Our laboratory conducts investigations using human cells and tissues, experimental murine models of wound healing and advanced analytic methods, including sequencing, to perform complex single-cell, genetic, molecular, and metabolomic analyses.

Building upon our earlier findings and discoveries, we continue to delve into the many pathways involved in inflammation and wound healing. Current research strategies and projects include investigations into the mechanisms and epigenetic pathways that regulate immunity, inflammation and metabolism in diabetic wounds and healing. In particular, we are looking at the interferon-beta/SETDB2 axis as well as how epigenetic changes in prostaglandin E2 synthesis alters macrophage function.

In parallel, we have established a new consortium of diabetic foot ulcer clinical research units funded through the NIH to identify and validate potential biomarkers and other predictive indicators of wound healing.

Additionally, we are examining the role of aortic epigenetic enzyme JMJD33 in monocytes/macrophages in aortic aneurism development. Research education is a pillar of our laboratory's work as well. We are training the next cadre of surgeon-scientists in translational medicine by mentoring undergraduate and graduate students, post-doctoral fellows and residents. Dr. Gallagher is part of the graduate program in immunology as well as the vascular surgery T32. She has trained several T32 and F32 fellows as well as K12 recipients and MICHR translational training grants.

Over the years our laboratory has made a number of important discoveries that advance the understanding of disordered diabetic wound healing.

Early work looked at impairments in angiogenesis and vasculogenesis in diabetic wounds and clarified the mechanisms underlying how endothelial progenitor cells (EPCs) in the bone marrow impact wounds expressing the chemokine SDF-1a during hyperbaric oxygen (HBO) therapy and also clarified the role of bone marrow endothelial nitric oxide synthase (eNOS) in mobilizing EPCs during HBO therapy.

We then began to investigate changes in immune cell phenotypes and chronic inflammation. That work led to the discovery that macrophage phenotypes are indeed altered in diabetic wounds. Investigating further, we were the first team to reveal that these changes in phenotype are driven by epigenetic changes, namely in histone methylation, in bone marrow stem cells and peripheral monocytes.

This work also led us to identify the role of a number of the enzymes involved, including chromatin modifying enzymes, the histone demethylase JMJD3, the histone methyltransferases, MLL1 and, importantly, SETDB2 in macrophage plasticity and inflammation in diabetic wounds. Further work led to the discovery that SETDB2 is involved in the uric acid pathways implicated in gout. Targeting this pathway in our experiments with an approved agent led to improved diabetic wound healing in our murine model. The results suggest a potential new therapeutic target to further investigate to improve healing in patients with diabetes.

Our lab has also clarified the role of infiltrating monocytes on wound macrophage phenotype and how recruited monocytes affect inflammation and tissue repair. We were the first to show that Ly6CHi monocyte/macrophages are recruited to the tissue and, from our RNA sequencing data, showed that these have a different inflammatory profile from Ly6CHi cells from non-diabetic animals.

We also were one of the first groups to show involvement of impaired TLR4 (toll-like receptor) and Notch signaling pathways in macrophage phenotype in diabetic wounds. Further, we showed epigenetic changes in signaling were different in diabetes, promoting an inflammatory macrophage phenotype in these wounds. We also found that murine macrophage chemokine receptor CCR2 is a key player in macrophage recruitment, function and inflammation in diabetic wound healing, providing another potential therapeutic target.

Nonhealing diabetic wounds are a significant public health problem, directly impacting costs of care and our patients' quality of life. The fundamental discoveries in our laboratory pointing the field toward new drug targets and therapeutic approaches to treating these wounds. Early work suggests cytokine-targeted immune-based therapies can improve healing in our translational models.

We continue to look at the role of epigenetic enzymes in both normal and diabetic wounds and AAA to help sustain inflammation. We also continue to look at epigenetic changes and stem cells in the bone marrow and their role in monocyte/macrophage function and inflammation. And we are expanding our collaborations to further investigate the interplay of inflammation and metabolites in vascular disease.

Our laboratory maintains several active collaborations to improve our understanding of wound healing in diabetes.