Non-healing wounds in patients with Type 2 Diabetes (T2D) are a major cause of morbidity and mortality and are increasing at an alarming rate. The factors controlling macrophage function and how these cells transition from an inflammatory to a reparative phenotype in wound tissues are not understood; leaving a large deficit in our ability to prevent and treat these wounds. Our laboratory is investigating novel epigenetic changes, induced via post-transitional modifications of histones, as mechanism(s) to regulate the macrophage phenotype during wound healing. We present data that the cytokine environment established in wounds following injury induces the expression of specific epigenetic machinery in macrophages that control gene transcription, and hence, function. Using human cells and our experimental murine model of wound healing, we have identified that interferon-beta (IFN?) induces the expression of SETDB2, an epigenetic-based lysine methyltransferase that is responsible for setting a suppressive histone mark that results in the silencing of inflammatory and metabolic genes. This sequence of events is beneficial in normal wound healing, allowing for the transition from an inflammatory to a reparative macrophage phenotype needed to promote healing. We hypothesize that during the evolution of normal wound healing, IFN?-mediated induction of SETDB2 in wound macrophages represses NFKB-mediated inflammatory and metabolic genes resulting in decreased wound inflammation and enhanced wound repair. We further postulate that this process does not occur in diabetic wounds where SETDB2 is not induced in wound macrophages, resulting in increased inflammation and non-healing wounds. This hypothesis will be investigated via the following specific aims: 1) Elucidate the regulation of NFkB-mediated gene expression by SETDB2 in normal and diabetic wound macrophages; 2) Determine the IFN?-mediated mechanism(s) that upregulate macrophage-specific SETDB2 expression in normal and diabetic wound tissue; and 3) Establish the role of SETDB2-regulated uric acid on normal and diabetic wound macrophage phenotypes during healing.
The relevance of our proposed studies is to demonstrate that the wound cytokine environment directs epigenetic-dependent molecular mechanisms in macrophages which subsequently influences their phenotype and function in wounds. During normal wound healing the cytokine, interferon-beta (IFN?), is expressed at high levels in the tissues; the subsequent binding of this cytokine to its receptor increases the chromatin-modifying enzyme (CME), SETDB2, which acts to repress inflammatory gene transcription in macrophages. In the setting of diabetes, SETDB2 is not induced during wound healing and increased inflammatory macrophages in tissue promote chronic inflammation and non-healing. It is this pathway that may contribute to the poorly understood conundrum whereby diabetic wounds display chronic inflammation and fail to heal. It is this unique sequence of events we will study under the auspices of this application. The success of the studies outlined in this proposal may lead to new therapeutic targets that may decrease morbidity and mortality related to diabetic wounds.
