The role of ERK5 signalling in macrophage behaviour during wound healing

Over 150 million individuals worldwide are affected by impaired wound healing, which can lead to chronic wound pathologies that often require lower limb amputations. Impaired wound healing is particularly prevalent in two growing demographics: aged and diabetic populations. Impaired wound healing continues to persist due to a lack of viable treatment options, exacerbated by an incomplete understanding of the mechanisms of wound healing. Research in this area has highlighted a significant role of dysregulated immune cells in impaired wound healing. We aimed to investigate the role of a key immune cell in wound healing: macrophages and how a known regulator of macrophages in other contexts, ERK5, influences wound healing, using genetic and therapeutic manipulations targeted at ERK5, both in vitro and in vivo. Genetic in vivo hyperactivation of ERK5 causes a persistent inflammatory profile in wounds, which aligned with similar observations of aberrant ERK5 signalling contributing to inflammation driven cancer progression. In contrast, genetic inactivation caused a brief increase in inflammation followed by an earlier shift to the resolution phase of wound healing as confirmed by flow cytometry and histology. This increase in reparative wound signalling in response to targeting ERK5 was also observed in human systems, using an in vitro keratinocyte model treated with a novel compound that targets and degrades ERK5, called OS1. Furthermore, using OS1 we were able to prime M0 THP-1 macrophages towards a reparative M2-like phenotype. This OS1-mediated pro-healing wound phenotype was recapitulated in vivo, where topical treatment with OS1 (inducing ERK5 loss in the entire wound) increased the rate of wound closure and was associated with an influx of M2-like macrophages and an earlier switch to the resolution phase of wound healing. This work is the first ever evaluation of the in vivo role of ERK5 in wound healing. We discovered that ERK5 signalling drives macrophage polarisation and immune infiltration during wound healing. The findings have the potential to improve diagnosis, stratification and treatment of chronic wounds. This study also provides evidence of the need to deviate from the traditional approach to target ERK5 via kinase inhibitors, since OS1-mediated degradation of ERK5, unlike ERK5 kinase inhibitors, was able to recapitulate the immune phenotypes of ERK5 genetic ablation models. Overall, this work highlights the potential for OS1 to be used to treat patients with impaired wound healing, such as those associated with diabetes.