Jenna L. Cash

Background: Delayed wound healing in advanced age is associated with prolonged inflammation, but the mechanisms that impair inflammatory resolution in this context remain poorly defined. Neutrophils are essential for early repair, but their persis tence is predicted to disrupt resolution and delay healing. Results: Here we show that aged mice exhibit impaired wound closure accompanied by a sustained neutrophil infiltrate from days 7–14 post-injury, long after neutrophils have resolved in young wounds. In aged skin, macrophage abundance and neutrophil–macrophage interactions were reduced, consistent with reduced macrophage-mediated clearance. Instead, neutrophils preferentially localised to perivascular regions, consistent with ongoing recruitment. Transcriptomic profiling demonstrated that young wounds transitioned from inflammatory to reparative programs, whereas aged wounds retained inflammatory signatures, including enrichment for neu trophil chemotaxis and LPS-response pathways. Notably, neutrophil chemoattractants Ccl3, Cxcl2 and Cxcl3 remained elevated in aged wounds. In human chronic ulcers, these transcripts were enriched in myeloid populations, particularly macrophages; concordantly, aged mouse wounds contained more CCL3-positive cells, the majority of which were macrophages. Targeted blockade of CCL3 beginning at day 4 post-injury, after the initial inflammatory response, reduced neutrophil accumulation, accelerated wound closure, and rescued key features of age-impaired healing. Conclusion: Together, these findings identify persistent CCL3 expression as a contributor to sustained neutrophil recruitment and impaired repair in advanced age. Therapeutically targeting this pathway offers a strategy to restore timely resolution and improve healing outcomes.

Delayed wound healing in advanced age is associated with prolonged inflammation, but the mechanisms that impair inflammatory resolution in this context remain poorly defined. Neutrophils are essential for early repair, but their persistence is predicted to disrupt resolution and delay healing. Here we show that aged mice exhibit impaired wound closure accompanied by sustained neutrophil infiltration from days 7 to 14 post injury, long after neutrophils have resolved in young wounds. In aged skin, macrophage abundance and neutrophil:macrophage interactions were reduced, consistent with reduced macrophage mediated clearance. Instead, neutrophils preferentially localised to perivascular regions, consistent with ongoing recruitment. Transcriptomic profiling demonstrated that young wounds transitioned from inflammatory to reparative programs, whereas aged wounds retained inflammatory signatures, including enrichment for neutrophil chemotaxis and LPS response pathways. Notably, Ccl3, Cxcl2 and Cxcl3 remained elevated in aged wounds. Analysis of human chronic ulcers identified macrophages as a major source of these transcripts, and aged mouse wounds possessed more CCL3+ macrophages than in young. Targeted blockade of CCL3 beginning at day 4 post-injury reduced neutrophil accumulation, accelerated wound closure, and rescued key features of age-impaired healing, when administered after the initial inflammatory phase. Together, these findings identify persistent CCL3 expression as a contributor to sustained neutrophil recruitment and impaired repair in advanced age. Therapeutically targeting this pathway offers a strategy to restore timely resolution and improve healing outcomes.

Chronic wounds (CWs) represent a major clinical challenge, characterized by persistent inflammation and failed repair. While proresolving pathways are known to regulate inflammatory responses, their potential dysfunction in CWs remains unexplored. Here, we identify dysregulation of the pro-opiomelanocortin-melanocortin 1 receptor (POMC–MC1R) axis as a common feature across pressure ulcers, venous ulcers, and diabetic ulcers. Using MC1Re/e mice lacking functional MC1R, we demonstrate impaired wound healing marked by delayed reepithelialization and increased neutrophil extracellular traps—pathological features observed in human CWs. To investigate MC1R’s therapeutic potential, we developed a new murine CW model that replicates human pathology, presenting as nonhealing, exudate-rich ulcers. Topical application of the MC1R-selective agonist BMS-470539 restored healing by reducing exudate production, stimulating vascularization, and enabling reepithelialization. The critical role of MC1R was further evidenced by MC1Re/e mice, which developed more severe ulcers with excessive exudate and NETosis. In acute wound studies, we found that topical MC1R agonist enhanced wound bed perfusion and lymphatic drainage through increased angiogenesis and lymphangiogenesis and reduced scarring by modulating fibroblast phenotype. Together, these findings establish the MC1R/POMC axis as a fundamental regulator of skin repair and identify promising therapeutic strategies to drive healing.

Summary: Snakebite claims 138,000 lives a year with an additional 400,000 patients left permanently disabled or disfigured1. Morbidity following envenoming includes the development of chronic wounds around the bite site. The understanding of the underlying pathophysiology of chronic snakebite wounds has been severely limited by the historical reliance on a preclinical model that only captures acute local envenoming pathology. Through the application of three medically important snake venoms (Echis ocellatus, Bothrops atrox and Naja nigricollis) to a recently developed preclinical model of chronic wounds, we have been able to characterise key features of venom wounds. We have been able to show that venom wounds share consistencies with non-venom induced preclinical wounds, and also display unique characteristics such as extracellular matrix degradation and eosinophilic infiltrate. This model will not only serve to increase our understanding the underlying pathophysiology of venom wounds, but will also provide a platform for exploring therapeutic interventions to reduce or resolve snakebite wounds.

Optical coherence tomography-based angiography (OCTA) has attracted attention in clinical applications as a non-invasive and high-resolution imaging modality. Motion artifacts are the most seen artifact in OCTA. Eigen-decomposition (ED) algorithms are popular choices for OCTA reconstruction, but have limitations in the reduction of motion artifacts. The OCTA data do not meet one of the requirements of ED, which is that the data should be normally distributed. To overcome this drawback, we propose an easy-to-deploy development of ED, windowed-ED (wED). wED applies a moving window to the input data, which can contrast the blood-flow signals with significantly reduced motion artifacts. To evaluate our wED algorithm, pre-acquired dorsal wound healing data in a murine model were used. The ideal window size was optimized by fitting the data distribution with the normal distribution. Lastly, the cross-sectional and en face results were compared among several OCTA reconstruction algorithms, Speckle Variance, A-scan ED (aED), B-scan ED, and wED. wED could reduce the background noise intensity by 18% and improve PSNR by 4.6%, compared to the second best-performed algorithm, aED. This study can serve as a guide for utilizing wED to reconstruct OCTA images with an optimized window size.

Cutaneous wound healing typically results in scarring; however, chronic wounds (CWs) represent a global and escalating health burden causing substantial morbidity and mortality. Estimated to cost Medicare up to $96.8 billion pa and with a profound paucity of effective therapeutics, novel interventions to improve healing are urgently needed. In this study, we assess the impact of manipulating the melanocortin 1 receptor (MC1R) on acute wound healing using a selective agonist, BMS-470539 (MC1R-Ag). MC1R agonism resulted in accelerated wound closure and reepithelialisation in wildtype but not MC1Re/e mice, which harbour a non-functional receptor. MC1R-Ag improved wound perfusion and lymphatic drainage by promoting angiogenesis and lymphangiogenesis, reducing local oxidative stress and inflammation with a knock-on effect of reduced scarring. To assess whether manipulating MC1R would be of benefit in pathological healing, we developed a novel murine model of chronic cutaneous wounds. By combining advanced age and locally elevated oxidative stress, factors shown to be present in most human CWs regardless of their category, resultant wounds expand 5-fold into the surrounding tissue, produce exudate and generate slough. Histological comparisons to human CWs demonstrate robust recapitulation of the hallmarks of human disease, including hyperproliferative epidermis, fibrinous exudate and vasculitis. Crucially, our model facilitates the in vivo study of candidate therapies to rescue derailed healing responses. We have identified that abrogation of MC1R signalling, using MC1Re/e mice, exacerbates CWs with enhanced exudate and NETosis. In contrast, topical administration of an MC1R agonist following ulcer debridement rescues the healing response, highlighting MC1R agonism as a candidate therapeutic approach for human CWs. We anticipate that our unique model will become a valuable tool to elucidate mechanisms of ulcer development and persistence.

The skin is the largest organ of the human body and serves essential functions to maintain homeostasis of the body. The epidermal homeostasis can be disrupted by various skin diseases, which often cause morphological changes in the epidermis.^1,2 Epidermal thickness is critically important information in the assessment and treatment planning of a variety of dermatologic conditions. Traditional invasive modality, e.g., biopsy, can cause complications such as bleeding, infection, and scarring.^{3 – 5}

The skin is the largest organ of the human body and provides essential functions to maintain homeostasis of the body. One of the most important roles of the skin is to protect the body against harmful pathogens which exist in the external environment. Any form of injury initiates a rapid response to restore the integrity of the skin and remove potential invading pathogens. The process of tissue repair following injury is a fundamental process of all living organisms and can even be observed in primitive multi-cellular organisms. Despite species and tissue specificity to the tissue repair process, there are four canonical overlapping phases involved in the wound healing process: hemostasis, inflammation, proliferation, and remodeling.¹

Neutrophilic inflammation is central to disease pathogenesis, for example, in chronic obstructive pulmonary disease, yet the mechanisms that retain neutrophils within tissues remain poorly understood. With emerging evidence that axon guidance factors can regulate myeloid recruitment and that neutrophils can regulate expression of a class 3 semaphorin, SEMA3F, we investigated the role of SEMA3F in inflammatory cell retention within inflamed tissues. We observed that neutrophils upregulate SEMA3F in response to proinflammatory mediators and following neutrophil recruitment to the inflamed lung. In both zebrafish tail injury and murine acute lung injury models of neutrophilic inflammation, overexpression of SEMA3F delayed inflammation resolution with slower neutrophil migratory speeds and retention of neutrophils within the tissues. Conversely, constitutive loss of sema3f accelerated egress of neutrophils from the tail injury site in fish, whereas neutrophil-specific deletion of Sema3f in mice resulted in more rapid neutrophil transit through the airways, and significantly reduced time to resolution of the neutrophilic response. Study of filamentous-actin (F-actin) subsequently showed that SEMA3F-mediated retention is associated with F-actin disassembly. In conclusion, SEMA3F signaling actively regulates neutrophil retention within the injured tissues with consequences for neutrophil clearance and inflammation resolution.

Cutaneous wound repair is a complex, dynamic process with the goal of rapidly sealing any breach in the skin’s protective barrier. Myeloid cells compose a significant proportion of the inflammatory cells recruited to a wound site and play important roles in decontaminating the injured tissue of any invading microorganisms. Subsequently, myeloid cells are able to influence many aspects of the healing response, in part through their capacity to release a large array of signaling molecules that allow them to communicate with and regulate the behavior of other wound cells and in turn, be themselves exquisitely regulated by the wound microenvironment. Macrophages, for example, appear to play important, temporally changing roles in the initiation of scarring and subsequently in matrix remodeling to resolve fibrosis. In this way, myeloid cells seem to play both positive (e.g., pathogen killing and matrix remodeling) and negative (e.g., scarring) roles in wound repair. Further research is of course needed to elucidate the precise temporal and spatial myeloid cell phenotypes and behaviors and ultimately to design effective strategies to optimize the beneficial functions of these cells while minimizing their detrimental contributions to improve wound healing in the clinic.