By protecting against cutaneous inflammation, epidermal pigmentation provided an additional advantage for ancestral humans

Low-concentration imiquimod treatment promotes enhanced skin barrier functions through epidermal melanization reaction regulation

The primary function of the skin is to form a mechanical, permeability, antimicrobial, and ultraviolet radiation barrier, which is essential for maintaining physiological homeostasis. Our previous studies demonstrated that cutaneous pigmentation could promote skin barrier function in addition to providing anti-ultraviolet irradiation defense. The present study aimed to develop a new regimen that enhances skin barrier function by regulating skin pigmentation using low-concentration imiquimod. Results showed that topical application of low-concentration imiquimod effectively induced skin hyperpigmentation in the dorsal skin and external ear of mice without inducing inflammatory cell infiltration. An in vitro study also revealed that low-concentration imiquimod did not induce any cytotoxic effects on melanoma cells but triggered excessive melanin synthesis. In coculture systems, low-concentration imiquimod was noted to increase tyrosinase activity in a broader cellular context, revealing the potential role of neighboring cells in melanin production. The next-generation sequencing result indicated that PKCη and Dnm3 might regulate melanin synthesis and release during imiquimod treatment. Overall, our study presents new insights into the regulation of melanin production by low-concentration imiquimod, both in a mice model and cultured cells. Furthermore, our study highlights the potential benefits of imiquimod in promoting melanin synthesis without causing skin disruptions or inducing inflammation, validating its potential to serve as a method for enhancing skin barrier functions by regulating the epidermal melanization reaction.

Atopic Dermatitis Across Shades of Skin

Atopic dermatitis (AD) is a chronic, heterogeneous inflammatory skin disease that is associated with immense patient burden globally. There is increasing appreciation of disparities among patients identified as having skin of color (SOC), which often refers to patients of non-White race or non-European ancestry, but can broadly include individuals from a number of different racial, ethnic, ancestral, and skin pigmentation groups based on definition. In this narrative review, we discuss key terminology as it relates to AD across shades of skin, including modern definitions of 'race', 'ethnicity', and 'SOC'. We then synthesize the current literature describing disparities in AD prevalence, disease recognition, and burden alongside current data regarding genetic and immunologic findings across SOC populations. In the context of these findings, we highlight key concomitant social determinants of health, including environmental factors, socioeconomic status, and access to care, for which race often serves as a proxy for true biological and genetic differences. Finally, we discuss future efforts to shift to a more inclusive understanding of AD to encompass all shades of skin, to ensure equitable representation of diverse populations in high impact research, and intensify efforts to address the critical upstream factors driving observed disparities.

The pigmentation phenotype of melanocytes affects their response to nitric oxide in vitro

Introduction

It has been shown that nitric oxide (NO) can modulate the immune properties of epidermal melanocytes, and that overexpression of NO in the skin may contribute to inflammation-related pigmentary disorders. Little is known about whether constitutive cell pigmentation affects the sensitivity of melanocytes to NO.

Aim

To compare the effect of NO on melanin synthesis and the expression of key melanogenesis-related genes in normal human melanocytes of various degrees of constitutive pigmentation.

Material and methods

Human epidermal melanocytes derived from lightly and darkly pigmented skin (HEMn-LP and HEMn-DP, respectively) were cultured with or without a NO donor (SPER/NO). Then the total melanin content, the pheomelanin content, the activity and concentration of tyrosinase, and the expressions of TYR and DCT were assessed.

Results

NO released from SPER/NO did not alter the total amount of melanin produced by cultured cells but increased the proportion of pheomelanin, especially in HEMn-DP. Transcriptional activity of the melanogenesis-related genes, in particular DCT, was downregulated in HEMn-DP and upregulated in HEMn-LP cultured with SPER/NO.

Conclusions

NO can promote pheomelanogenesis in human epidermal melanocytes, and the cell response in this respect is associated with the pigmentation phenotype. During exposure to NO, melanocytes from dark skin produce much more pheomelanin than lightly pigmented cells. NO-induced overproduction of pheomelanin in the skin could be one of the factors responsible for the greater propensity to develop severe inflammatory dermatoses in dark-skinned individuals, or even melanoma de novo formation based on local chronic inflammation.

Recognition of Melanocytes in Immuno-Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis

Melanocytes produce melanin to protect the skin from UV-B radiation. Notwithstanding, the spectrum of their functions extends far beyond their well-known role as melanin production factories. Melanocytes have been considered as sensory and computational cells. The neurotransmitters, neuropeptides, and other hormones produced by melanocytes make them part of the skin’s well-orchestrated and complex neuroendocrine network, counteracting environmental stressors. Melanocytes can also actively mediate the epidermal immune response. Melanocytes are equipped with ectopic sensory systems similar to the eye and nose and can sense light and odor. The ubiquitous inner circadian rhythm controls the body’s basic physiological processes. Light not only affects skin photoaging, but also regulates inner circadian rhythms and communicates with the local neuroendocrine system. Do melanocytes “see” light and play a unique role in photoentrainment of the local circadian clock system? Why, then, are melanocytes responsible for so many mysterious functions? Do these complex functional devices work to maintain homeostasis locally and throughout the body? In addition, melanocytes have also been shown to be localized in internal sites such as the inner ear, brain, and heart, locations not stimulated by sunlight. Thus, what can the observation of extracutaneous melanocytes tell us about the “secret identity” of melanocytes? While the answers to some of these intriguing questions remain to be discovered, here we summarize and weave a thread around available data to explore the established and potential roles of melanocytes in the biological communication of skin and systemic homeostasis, and elaborate on important open issues and propose ways forward.

Role of nitric oxide in regulating epidermal permeability barrier function

Nitric oxide (NO), a free radical molecule synthesized by nitric oxide synthases (NOS), regulates multiple cellular functions in a variety of cell types. These NOS, including endothelial NOS (eNOS), inducible NOS (iNOS) and neural NOS (nNOS), are expressed in keratinocytes. Expression levels of both iNOS and nNOS decrease with ageing, and insufficient NO has been linked to the development of a number of disorders such as diabetes and hypertension, and to the severity of atherosclerosis. Conversely, excessive NO levels can induce cellular oxidative stress, but physiological levels of NO are required to maintain the normal functioning of cells, including keratinocytes. NO also regulates cutaneous functions, including epidermal permeability barrier homeostasis and wound healing, through its stimulation of keratinocyte proliferation, differentiation and lipid metabolism. Topical applications of a diverse group of agents which generate nitric oxide (called NO donors) such as S-nitroso-N-acetyl-D,L-penicillamine (SNAP) can delay permeability barrier recovery in barrier-disrupted skin, but iNOS is still required for epidermal permeability barrier homeostasis. This review summarizes the regulatory role that NO plays in epidermal permeability barrier functions and the underlying mechanisms involved.

Two Birds One Stone: The Neuroprotective Effect of Antidiabetic Agents on Parkinson Disease-Focus on Sodium-Glucose Cotransporter 2 (SGLT2) Inhibitors

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease affecting more than 1% of the population over 65 years old. The etiology of the disease is unknown and there are only symptomatic managements available with no known disease-modifying treatment. Aging, genes, and environmental factors contribute to PD development and key players involved in the pathophysiology of the disease include oxidative stress, mitochondrial dysfunction, autophagic-lysosomal imbalance, and neuroinflammation. Recent epidemiology studies have shown that type-2 diabetes (T2DM) not only increased the risk for PD, but also is associated with PD clinical severity. A higher rate of insulin resistance has been reported in PD patients and is suggested to be a pathologic driver in this disease. Oral diabetic drugs including sodium-glucose cotransporter 2 (SGLT2) inhibitors, glucagon-like peptide-1 (GLP-1) receptor agonists, and dipeptidyl peptidase-4 (DPP-4) inhibitors have been shown to provide neuroprotective effects in both PD patients and experimental models; additionally, antidiabetic drugs have been demonstrated to lower incidence rates of PD in DM patients. Among these, the most recently developed drugs, SGLT2 inhibitors may provide neuroprotective effects through improving mitochondrial function and antioxidative effects. In this article, we will discuss the involvement of mitochondrial-related oxidative stress in the development of PD and potential benefits provided by antidiabetic agents especially focusing on sglt2 inhibitors.

Both Prevalence and Severity of Pruritus are Associated with Age in Chinese Patients with Skin Diseases

BACKGROUND

Although the characteristics of pruritus in some skin diseases are documented, characteristics of pruritus related to gender-, age-, and skin disorder have not yet been well defined.

OBJECTIVE

To characterize dermatosis-associated pruritus in Chinese patients.

METHODS

A cross-sectional study was carried out in a single center. The intensity of pruritus was evaluated using a 0-10 visual analog scale (VAS). Skin disorders were diagnosed by dermatologists. The prevalence and intensity of pruritus were compared among skin disorders, and between males and females.

RESULTS

Valid questionnaires were obtained from 1,246 female and 864 male patients. Patients with acne, eczematous dermatitis, and urticaria accounted for 18%, 17%, and 14%, respectively. Both the prevalence and severity of pruritus varied greatly with skin disorders (p<0.0001). Patients with either urticaria or eczematous dermatitis displayed a higher prevalence of pruritus (92% and 82%, respectively), while subjects with urticaria exhibited the highest VAS in comparison to those with other skin disorders (p<0.05 to p<0.001 vs the others). Moreover, both the prevalence and severity of pruritus were positively associated with age in both males and females (p<0.0001). Furthermore, 60 out of 77 patients (78%) with topical glucocorticoid-induced dermatitis experienced pruritus, with a VAS of 2.03±0.21. Finally, a lower VAS was found in subjects with oily skin than those with either dry or normal skin.

CONCLUSION

The prevalence and severity of pruritus vary with skin disorders, skin type, age, and gender in Chinese patients.

Adaptation and co-adaptation of skin pigmentation and vitamin D genes in native Americans

We carried out an exhaustive review regarding human skin color variation and how much it may be related to vitamin D metabolism and other photosensitive molecules. We discuss evolutionary contexts that modulate this variability and hypotheses postulated to explain them; for example, a small amount of melanin in the skin facilitates vitamin D production, making it advantageous to have fair skin in an environment with little radiation incidence. In contrast, more melanin protects folate from degradation in an environment with a high incidence of radiation. Some Native American populations have a skin color at odds with what would be expected for the amount of radiation in the environment in which they live, a finding challenging the so-called "vitamin D-folate hypothesis." Since food is also a source of vitamin D, dietary habits should also be considered. Here we argue that a gene network approach provides tools to explain this phenomenon since it indicates potential alleles co-evolving in a compensatory way. We identified alleles of the vitamin D metabolism and pigmentation pathways segregated together, but in different proportions, in agriculturalists and hunter-gatherers. Finally, we highlight how an evolutionary approach can be useful to understand current topics of medical interest.

Agonism of Gpr40 Protects the Capacities of Epidermal Stem Cells (ESCs) Against Ultraviolet-B (UV-B)

Introduction

Skin damage due to overexposure to ultraviolet B (UV-B) radiation can lead to the development of cancers and reduce the skin's functionality as a vital protective barrier. Epidermal stem cells (ESCs) are pluripotent cells responsible for skin regeneration and healing. Upon exposure to UV-B radiation, ESCs produce excess amounts of reactive oxygen species (ROS) and inflammatory cytokines. However, the functional protection of ESCs is not fully explored. G-protein coupled G protein-coupled receptor 40 (Gpr40) is a free fatty acid receptor that is emerging as a potential treatment target for various diseases. Gpr40 has been found to be expressed in various cell types.

Methods

ESCs were exposed to UV-B at the intensities of 25, 50, and 100 mJ/cm² for 24 h using TL 20 W/12 RS UV lamps. ESCs were treated with UV-B at 50 mJ/cm² in the presence or absence of 25 or 50 µM of the Gpr40 agonist GW9508 for 24 h. The gene expression of the Wnt1 pathway and proinflammatory cytokines were evaluated. To antagonize Gpr40 expression, ESCs were treated with 10 µM GW1100.

Results

Our findings demonstrate that Gpr40 agonism can reduce the production of ROS as well as the expression of interleukins 1β and 8, two key proinflammatory cytokines. We demonstrate that agonism of Gpr40 can rescue the reduction in integrin β1 and Krt19 induced by UV-B exposure, thereby improving the capacities of ESCs to resist UV-B damage. Moreover, we show that the effects of Gpr40 agonism observed in our experiments are mediated through the Wnt/β-catenin canonical signaling pathway, as evidenced by the expression of Wnt1 and cyclin D1.

Conclusion

Our findings present evidence of the role of Gpr40 agonism in mediating the protective capacities of ESCs against insult from UV-B radiation.

Seasonal variations of epidermal biophysical properties in Kunming, China: A self-controlled cohort study

BACKGROUND

Epidermal biophysical properties can be affected by many factors, including body site, age, gender, ethnicity, disease, temperature, humidity, and ultraviolet (UV) radiation. Information about variation of epidermal biophysical properties with seasons is still limited. In the present study, we determined seasonal variation of epidermal biophysical properties of women in Kunming, China.

MATERIALS AND METHODS

A total of 72 women, aged 22.96 ± 2.11 years, were enrolled in this study. Transepidermal water loss rates (TEWL), stratum corneum (SC) hydration, sebum content, melanin index (MI), erythema index (EI), and L*a* values were measured on the right cheek and the right forearm, using a non-invasive skin physiological instrument in the spring, summer, autumn, and winter in Kunming, China.

RESULTS

On the cheek, TEWL, SC hydration, sebum, MI, and L*a* values varied greatly with seasons (P < .05). SC hydration, sebum, MI, and a*value peaked in the summer, but went lowest in winter. In contrast, TEWL and L*value went lowest in summer but peaked in winter. Similarly, SC hydration, MI, and L*value also varied with seasons on the forearm (P < .05). In addition, SC hydration, sebum, MI, EI, and a*value of the cheek were higher than that of the forearm (P < .001), but L*values of the cheek were lower than that of the forearm (P < .001). There were no correlations among TEWL and MI, EI, and L*a*values in any season (P > .05).

CONCLUSIONS

Both epidermal permeability barrier function, sebum, and skin pigment in healthy women vary seasons in Kunming, China.