Iron Metabolism of the Skin: Recycling versus Release

Increased melanin induces aberrant keratinocyte - melanocyte - basal - fibroblast cell communication and fibrogenesis by inducing iron overload and ferroptosis resistance in keloids

BACKGROUND

Keloid is a typical skin fibrotic disease with unclear mechanisms and limited therapeutic options. Fibroblast-induced fibrogenesis is a crucial cause of KD. However, the types of cells involved in fibroblast fibrogenesis in KD and the specific mechanisms are unclear. This study aimed to investigate the role of melanocyte-secreted melanin in promoting fibroblast fibrogenesis and its mechanism and to evaluate the potential therapeutic effect of intervening melanin in treating keloid.

METHODS

The activity of pigmentation-related pathways in KD melanocytes was examined using single-cell RNA-sequence (scRNA-seq) analysis. Masson-Fontana staining or isolated melanin quantification detected the melanin levels and distribution in the skin and cells. Collagen deposition, wounding healing, and proliferation analysis were employed to integratively assess fibroblast fibrogenesis. After melanin treatment, bulk-seq identified fibroblasts' differentially expressed genes (DEGs). The iron levels were detected by Perl's staining or isolated iron quantification. Cell viability, LipidROS, and malondialdehyde assay accessed the ferroptosis levels. The therapeutic potential of ML329 was evaluated in keloid-bearing mice.

RESULTS

We found the enriched skin pigmentation-related pathways in the melanocytes of keloid by single-cell RNA-sequence (scRNA-seq) analysis. We further validated increased melanin levels in keloid patients. Additionally, melanin positively correlated with the Keloid Area and Severity Index in keloid. Furthermore, melanocyte-secreted melanin significantly promoted fibroblast proliferation, migration, and collagen synthesis. Mechanically, melanin increased basal cell permeability and inflammation to facilitate its transfer to the dermis, where it further activated fibroblasts by evoking iron overload and ferroptosis resistance. Consistently, iron overload and ferroptosis resistance were validated in primary fibroblasts and skin tissues of keloid patients. Inhibition of iron overload and ferroptosis resistance effectively diminish melanin-induced fibrogenesis. Interestingly, melanin induced iron overload and ferroptosis resistance in melanocytes in an autocrine manner and further stimulated keratinocytes to take up melanin to deepen skin color by upregulating the F2R-like trypsin receptor 1 (F2RL1). In vivo, the delivery of ML329, a microphthalmia-associated transcription factor (MITF) inhibitor, could suppress melanogenesis and alleviate keloid in human keloid-bearing nude mice. Meanwhile, ML329 decreased the iron content and restored the sensitivities of ferroptosis.

CONCLUSION

Collectively, melanin-lowing strategies may appear as a potential new therapeutic target for keloid.

Metal ion formulations for diabetic wound healing: Mechanisms and therapeutic potential

Metals are vital in human physiology, which not only act as enzyme catalysts in the processes of superoxide dismutase and glucose phosphorylation, but also affect the redox process, osmotic adjustment, metabolism and neural signals. However, metal imbalances can lead to diseases such as diabetes, which is marked by chronic hyperglycemia and affects wound healing. The hyperglycemic milieu of diabetes impairs wound healing, posing significant challenges to patient quality of life. Wound healing encompasses a complex cascade of hemostasis, inflammation, proliferation, and remodeling phases, which are susceptible to disruption in hyperglycemic conditions. In recent decades, metals have emerged as critical facilitators of wound repair by enhancing antimicrobial properties (e.g., iron and silver), providing angiogenic stimulation (copper), promoting antioxidant activity and growth factor synthesis (zinc), and supporting wound closure (calcium and magnesium). Consequently, research has pivoted towards the development of metal ion-based therapeutics, including innovative formulations such as nano-hydrogels, nano-microneedle dressings, and microneedle patches. Prepared by combining macromolecular materials such as chitosan, hyaluronic acid and sodium alginate with metals, aiming at improving the management of diabetic wounds. This review delineates the roles of key metals in human physiology and evaluates the application of metal ions in diabetic wound management strategies.

Skin Aging and the Upcoming Role of Ferroptosis in Geroscience

The skin is considered the most important organ system in mammals, and as the population ages, it is important to consider skin aging and anti-aging therapeutic strategies. Exposure of the skin to various insults induces significant changes throughout our lives, differentiating the skin of a young adult from that of an older adult. These changes are caused by a combination of intrinsic and extrinsic aging. We report the interactions between skin aging and its metabolism, showing that the network is due to several factors. For example, iron is an important nutrient for humans, but its level increases with aging, inducing deleterious effects on cellular functions. Recently, it was discovered that ferroptosis, or iron-dependent cell death, is linked to aging and skin diseases. The pursuit of new molecular targets for ferroptosis has recently attracted attention. Prevention of ferroptosis is an effective therapeutic strategy for the treatment of diseases, especially in old age. However, the pathological and biological mechanisms underlying ferroptosis are still not fully understood, especially in skin diseases such as melanoma and autoimmune diseases. Only a few basic studies on regulated cell death exist, and the challenge is to turn the studies into clinical applications.

Zinc, Copper, and Iron in Selected Skin Diseases

Trace elements are essential for maintaining the body's homeostasis, and their special role has been demonstrated in skin physiology. Among the most important trace elements are zinc, copper, and iron. A deficiency or excess of trace elements can be associated with an increased risk of skin diseases, so increasing their supplementation or limiting intake can be helpful in dermatological treatment. In addition, determinations of their levels in various types of biological material can be useful as additional tests in dermatological treatment. This paper describes the role of these elements in skin physiology and summarizes data on zinc, copper, and iron in the course of selected, following skin diseases: psoriasis, pemphigus vulgaris, atopic dermatitis, acne vulgaris and seborrheic dermatitis. In addition, this work identifies the potential of trace elements as auxiliary tests in dermatology. According to preliminary studies, abnormal levels of zinc, copper, and iron are observed in many skin diseases and their determinations in serum or hair can be used as auxiliary and prognostic tests in the course of various dermatoses. However, since data for some conditions are conflicting, clearly defining the potential of trace elements as auxiliary tests or elements requiring restriction/supplement requires further research.