Hallmarks and Biomarkers of Skin Senescence: An Updated Review of Skin Senotherapeutics

Nicotinamide N-Methyltransferase (NNMT): A New Hope for Treating Aging and Age-Related Conditions

The complex process of aging leads to a gradual deterioration in the function of cells, tissues, and the entire organism, thereby increasing the risk of disease and death. Nicotinamide N-methyltransferase (NNMT) has attracted attention as a potential target for combating aging and its related pathologies. Studies have shown that NNMT activity increases over time, which is closely associated with the onset and progression of age-related diseases. NNMT uses S-adenosylmethionine (SAM) as a methyl donor to facilitate the methylation of nicotinamide (NAM), converting NAM into S-adenosyl-L-homocysteine (SAH) and methylnicotinamide (MNA). This enzymatic action depletes NAM, a precursor of nicotinamide adenine dinucleotide (NAD+), and generates SAH, a precursor of homocysteine (Hcy). The reduction in the NAD+ levels and the increase in the Hcy levels are considered important factors in the aging process and age-related diseases. The efficacy of RNA interference (RNAi) therapies and small-molecule inhibitors targeting NNMT demonstrates the potential of NNMT as a therapeutic target. Despite these advances, the exact mechanisms by which NNMT influences aging and age-related diseases remain unclear, and there is a lack of clinical trials involving NNMT inhibitors and RNAi drugs. Therefore, more in-depth research is needed to elucidate the precise functions of NNMT in aging and promote the development of targeted pharmaceutical interventions. This paper aims to explore the specific role of NNMT in aging, and to evaluate its potential as a therapeutic target.

Topical Minoxidil Rejuvenates Hair Follicles from Men with Androgenetic Alopecia in Vivo

Abstract is missing (Short communication)

Aging of Superficial Musculoaponeurotic System of the Face-Novel Biomarkers and Micro-CT Relevance of Facial Anti-Gravity Support

The soft superficial tissues of the face are against gravity through an intricate network of ligaments and ligamentous attachments. The aim of this investigation is to delineate the relationship between the muscular, fibrous, and vascular components of the superficial musculoaponeurotic system of the face (SMAS) at the level of its periosteal fixation areas from advanced radiological and novel biomarkers' perspectives. These areas represent key points underlying skin aging and the longevity of restorative surgery results. Methods: This study was carried out on 37 surgical specimens, excised from patients admitted for surgery. On the excised specimens, we used special immunohistochemical techniques, such as markers for collagen type III, angiogenesis, vascular endothelium (I-CAM2) and muscle fibers (MYH2). We performed a micro-CT evaluation of these 37 specimens. Results: The results of this study showed different radiologic and IHC characteristics of the means of periosteal fixation of the SMAS. Evidence of morphohistological and radiological peculiarities of the retaining ligaments highlights new data for future functional studies of these structures. Our research must be continued with larger groups of subjects and through detailed methodological studies of vascular microperfusion and could represent an important new step in biotissue engineering and the customization of surgical techniques involving the sub-SMAS layers.

Dietary supplementation with α-ionone alleviates chronic UVB exposure-induced skin photoaging in mice

Photoaging is widely regarded as the most significant contributor to skin aging damage. It is triggered by prolonged exposure to ultraviolet (UV) light and typically manifests as dryness and the formation of wrinkles. Nutritional intervention is a viable strategy for preventing and treating skin photoaging. In previous studies, we demonstrated that α-ionone had ameliorating effects on photoaging in both epidermal keratinocytes and dermal fibroblasts. Here, we investigated the potential anti-photoaging effects of dietary α-ionone using a UVB-irradiated male C57BL/6N mouse model. Our findings provided compelling evidence that dietary α-ionone alleviates wrinkle formation, skin dryness, and epidermal thickening in chronic UVB-exposed mice. α-Ionone accumulated in mouse skin after 14 weeks of dietary intake of α-ionone. α-Ionone increased collagen density and boosted the expression of collagen genes, while attenuating the UVB-induced increase of matrix metalloproteinase genes in the skin tissues. Furthermore, α-ionone suppressed the expression of senescence-associated secretory phenotypes and reduced the expression of the senescence marker p21 and DNA damage marker p53 in the skin of UVB-irradiated mice. Transcriptome sequencing results showed that α-ionone modifies gene expression profiles of skin. Multiple pathway enrichment analyses on both the differential genes and the entire genes revealed that α-ionone significantly affects multiple physiological processes and signaling pathways associated with skin health and diseases, of which the p53 signaling pathway may be the key signaling pathway. Taken together, our findings reveal that dietary α-ionone intervention holds promise in reducing the risks of skin photoaging, offering a potential strategy to address skin aging concerns.

Cutaneous Redox Senescence

Our current understanding of skin cell senescence involves the role of environmental stressors (UV, O3, cigarette smoke, particulate matter, etc.), lifestyle (diet, exercise, etc.) as well as genetic factors (metabolic changes, hormonal, etc.). The common mechanism of action of these stressors is the disturbance of cellular redox balance characterized by increased free radicals and reactive oxygen species (ROS), and when these overload the intrinsic antioxidant defense system, it can lead to an oxidative stress cellular condition. The main redox mechanisms that activate cellular senescence in the skin involve (1) the oxidative damage of telomeres causing their shortening; (2) the oxidation of proteomes and DNA damage; (3) an a in lysosomal mass through the increased activity of resident enzymes such as senescence-associated β-galactosidase (SA-β-gal) as well as other proteins that are products of lysosomal activity; (4) and the increased expression of SASP, in particular pro-inflammatory cytokines transcriptionally regulated by NF-κB. However, the main targets of ROS on the skin are the proteome (oxi-proteome), followed by telomeres, nucleic acids (DNAs), lipids, proteins, and cytoplasmic organelles. As a result, cell cycle arrest pathways, lipid peroxidation, increased lysosomal content and dysfunctional mitochondria, and SASP synthesis occur. Furthermore, oxidative stress in skin cells increases the activity of p16INK4A and p53 as inhibitors of Rb and CDks, which are important for maintaining the cell cycle. p53 also promotes the inactivation of mTOR-mediated autophagic and apoptotic pathways, leading to senescence. However, these markers alone cannot establish the state of cellular senescence, and multiple analyses are encouraged for confirmation. An updated and more comprehensive approach to investigating skin senescence should include further assays of ox-inflammatory molecular pathways that can consolidate the understanding of cutaneous redox senescence.

Revitalizing Photoaging Skin through Eugenol in UVB-Exposed Hairless Mice: Mechanistic Insights from Integrated Multi-Omics

Chronic ultraviolet (UV) exposure causes photoaging, which is primarily responsible for skin damage. Nutritional intervention is a viable strategy for preventing and treating skin photoaging. Eugenol (EU) presents anti-inflammatory and antioxidant properties, promotes wound healing, and provides contact dermatitis relief. This study explored the ability of EU to mitigate skin photoaging caused by UVB exposure in vitro and in vivo. EU alleviated UVB-induced skin photodamage in skin cells, including oxidative stress damage and extracellular matrix (ECM) decline. Dietary EU alleviated skin photoaging by promoting skin barrier repair, facilitating skin tissue regeneration, and modulating the skin microenvironment in photoaged mice. The transcriptome sequencing results revealed that EU changed the skin gene expression profiles. Subsequent pathway enrichment analyses indicated that EU might reverse the pivotal ECM-receptor interaction and cytokine-cytokine receptor interaction signaling pathways. Furthermore, EU alleviated the intestinal dysbiosis induced by chronic UVB exposure. Spearman analysis results further revealed the close connection between gut microbiota and skin photoaging. Considering the near-inevitable UVB exposure in modern living, the findings showed that the EU effectively reverted skin photoaging, offering a potential strategy for addressing extrinsic skin aging.

Hesperetin activates CISD2 to attenuate senescence in human keratinocytes from an older person and rejuvenates naturally aged skin in mice

BACKGROUND

CDGSH iron-sulfur domain-containing protein 2 (CISD2), a pro-longevity gene, mediates healthspan in mammals. CISD2 is down-regulated during aging. Furthermore, a persistently high level of CISD2 promotes longevity and ameliorates an age-related skin phenotype in transgenic mice. Here we translate the genetic evidence into a pharmaceutical application using a potent CISD2 activator, hesperetin, which enhances CISD2 expression in HEK001 human keratinocytes from an older person. We also treated naturally aged mice in order to study the activator's anti-aging efficacy.

METHODS

We studied the biological effects of hesperetin on aging skin using, firstly, a cell-based platform, namely a HEK001 human keratinocyte cell line established from an older person. Secondly, we used a mouse model, namely old mice at 21-month old. In the latter case, we investigate the anti-aging efficacy of hesperetin on ultraviolet B (UVB)-induced photoaging and naturally aged skin. Furthermore, to identify the underlying mechanisms and potential biological pathways involved in this process we carried out transcriptomic analysis. Finally, CISD2 knockdown HEK001 keratinocytes and Cisd2 knockout mice were used to study the Cisd2-dependent effects of hesperetin on skin aging.

RESULTS

Four findings are pinpointed. Firstly, in human skin, CISD2 is mainly expressed in proliferating keratinocytes from the epidermal basal layer and, furthermore, CISD2 is down-regulated in the sun-exposed epidermis. Secondly, in HEK001 human keratinocytes from an older person, hesperetin enhances mitochondrial function and protects against reactive oxygen species-induced oxidative stress via increased CISD2 expression; this enhancement is CISD2-dependent. Additionally, hesperetin alleviates UVB-induced damage and suppresses matrix metalloproteinase-1 expression, the latter being a major indicator of UVB-induced damage in keratinocytes. Thirdly, transcriptomic analysis revealed that hesperetin modulates a panel of differentially expressed genes that are associated with mitochondrial function, redox homeostasis, keratinocyte function, and inflammation in order to attenuate senescence. Intriguingly, hesperetin activates two known longevity-associated regulators, namely FOXO3a and FOXM1, in order to suppress the senescence-associated secretory phenotype. Finally, in mouse skin, hesperetin enhances CISD2 expression to ameliorate UVB-induced photoaging and this occurs via a mechanism involving CISD2. Most strikingly, late-life treatment with hesperetin started at 21-month old and lasting for 5 months, is able to retard skin aging and rejuvenate naturally aged skin in mice.

CONCLUSIONS

Our results reveal that a pharmacological elevation of CISD2 expression at a late-life stage using hesperetin treatment is a feasible approach to effectively mitigating both intrinsic and extrinsic skin aging and that hesperetin could act as a functional food or as a skincare product for fighting skin aging.

Potential roles of circulating microRNAs in the healing of type 1 diabetic wounds treated with green tea extract: molecular and biochemical study

Background

Circulating miRNAs have been implicated in various aspects of diabetic wound healing, including inflammation, angiogenesis, and extracellular matrix remodeling. Thus, in alternative herbal medicine strategies, miRNAs will be potential therapeutic molecular targets in nonhealing wounds. These could be valuable elements for understanding the molecular basis of diabetic wound healing and could be used as good elements in bioinformatics.

Objectives

To elucidate the molecular mechanisms of microRNAs in association with apoptosis-inducing genes in controlling skin wound healing in diabetic wounds treated with green tea polyphenols (GTPs).

Methods

Green tea hydro extract (GTE) at doses of100-200 mg/ml was topically applied to the skin tissues of rats with T1DM induced by a single dose of streptozotocin (STZ; 100 mg/kg, in 0.01 M sodium citrate, pH 4.3-4.5) injected intraperitoneally for seven consecutive days to induce T1DM. The rats were treated with green tea for three weeks. A sterile surgical blade was used to inflict a circular wound approximately 2 cm in diameter on the anterior-dorsal side of previously anesthetized rats by a combination of ketamine hydrochloride (50 mg/kg, i.e., body weight) and xylazine hydrochloride. Afterward, the molecular roles of the circulating miRNAs miR-21, miR-23a, miR-146a, and miR-29b and apoptotic genes were determined by quantitative real-time PCR to evaluate Bax, Caspase-3, and Bcl-2 in wound healing. In addition, HPLC analysis was also performed to estimate the active polyphenols (GTPs) present in the hydro extract of green tea leaves.

Results

Wound healing was improved in diabetic skin wounds following treatment with GTE at doses of 100-200 mg/dl for three weeks. The wound parameters contraction, epithelialization, and scar formation significantly improved in a short time (14 days) compared to the longer periods identified in diabetic non-treated rats (20 days) and the standard control (15.5 days). Molecular analyses reported a significant increase in the levels of miR-21, miR-23a, and miR-146a and a decrease in the levels of miR-29b in green tea-treated diabetic rats compared to those in the standard control and STZ-diabetic non-treated rats. In addition, the molecular apoptotic genes Bax and caspase-3 significantly increased, and the BcL-2 gene significantly decreased following treatment with green tea polyphenols.

Conclusions

The data showed that active green tea polyphenols (GTPs) present in GTE significantly improved diabetic wound healing by controlling apoptotic genes and the circulating microRNAs miR-21, miR-23a, miR-146a, and miR-29b, which might be involved in cellular apoptosis and angiogenesis processes. Thus, to establish a future model for the treatment of diabetic wounds, further studies are needed to understand the potential association of these biological parameters with the wound-healing process in diabetic wounds.

Inflammaging and Immunosenescence as Part of Skin Aging-A Narrative Review

Inflammaging and immunosenescence are associated with aging of the human body, but there are key differences between them. Immunosenescence aims to adapt the body systems to aging, while inflammaging is considered a consequence of immunosenescence. There has been much research in the area of immunosenescence and inflammaging recently, yet our understanding of aging and the ability to develop interventions to decrease the harmful effect of aging on the human body is insufficient. This review is focused on immunosenescence and inflammaging processes in the skin. We aimed to identify factors that influence inflammaging, skin aging, and their mechanisms. We discussed the role of triggering factors (e.g., UV radiations, changes in bioavailability of nitric oxide, senescence-associated secretory phenotype factors, and reactive oxygen species) and inhibiting factors that can potentially be used as anti-aging treatments, as well as the idea of geroprotectors and senotherapeutics. We concluded that while knowledge on external factors can help people to improve their health conditions, knowledge on biochemical factors can help researchers to understand inflammaging process and develop interventions to minimize the impact of aging on the human body. Further research is needed to better understand the role of factors that can slow down or accelerate inflammaging.