Aging-related shift of eccrine sweat glands toward the skin surface due to tangling and rotation of the secretory ducts revealed by digital 3D skin reconstruction

Endocrine Controls of Skin Aging

Skin is the largest organ of the human body and undergoes both intrinsic (chronological) and extrinsic aging. While intrinsic skin aging is driven by genetic and epigenetic factors, extrinsic aging is mediated by external threats such as UV irradiation or fine particular matters, the sum of which is referred to as exposome. The clinical manifestations and biochemical changes are different between intrinsic and extrinsic skin aging, albeit overlapping features exist, eg, increased generation of reactive oxygen species, extracellular matrix degradation, telomere shortening, increased lipid peroxidation, or DNA damage. As skin is a prominent target for many hormones, the molecular and biochemical processes underlying intrinsic and extrinsic skin aging are under tight control of classical neuroendocrine axes. However, skin is also an endocrine organ itself, including the hair follicle, a fully functional neuroendocrine "miniorgan." Here we review pivotal hormones controlling human skin aging focusing on IGF-1, a key fibroblast-derived orchestrator of skin aging, of GH, estrogens, retinoids, and melatonin. The emerging roles of additional endocrine players, ie, α-melanocyte-stimulating hormone, a central player of the hypothalamic-pituitary-adrenal axis; members of the hypothalamic-pituitary-thyroid axis; oxytocin, endocannabinoids, and peroxisome proliferator-activated receptor modulators, are also reviewed. Until now, only a limited number of these hormones, mainly topical retinoids and estrogens, have found their way into clinical practice as anti-skin aging compounds. Further research into the biological properties of endocrine players or its derivatives may offer the development of novel senotherapeutics for the treatment and prevention of skin aging.

Research progress on the role of fascia in skin wound healing

The skin, the human body's largest organ, is perpetually exposed to environmental factors, rendering it vulnerable to potential injuries. Fascia, a vital connective tissue that is extensively distributed throughout the body, fulfils multiple functions, including support, compartmentalization, and force transmission. The role of fascia in skin wound healing has recently attracted considerable attention. In addition to providing mechanical support, fascia significantly contributes to intercellular signalling and tissue repair, establishing itself as a crucial participant in wound healing. This review synthesises the latest advancements in fascia research and its implications for skin wound healing.

A comparative study of passive drug diffusion through human skin via intercellular and sweat duct route: effect of aging

A method of drug delivery that could provide control over medicine reaching the bloodstream for systemic circulation would be of immense importance. This work presents a comparative study of the temporal and spatial variation of drugs diffusing passively through two separate routes of human skin, namely intercellular (ICR) and sweat duct route (SDR). An analysis is carried out for two age groups (young < 40 years and old > 60 years of age). Governing equations based on Fick's law for mass transfer have been solved numerically using an in-house developed code. The code has been validated thoroughly with numerical and experimental work from the literature. Each skin route is modeled into three compartments sandwiched between the donor and receiver compartments. To understand the role of diffusion and partition coefficient on drug permeation, four drugs, namely hydrocortisone, trans-cinnamic acid, caffeine, and benzoic acid, are considered. The drug diffusion rate is found greater through ICR as compared to SDR. Further, the amount of drugs diffusing through both routes increases with age. Desirable drug characteristic is inferred to be a lower value of partition coefficient and a higher value of diffusion coefficient. This study could lead to real-time assessment of drugs reaching the bloodstream and beyond.

Characterization of age-associated gene expression changes in mouse sweat glands

Evaporation of sweat on the skin surface is the major mechanism for dissipating heat in humans. The secretory capacity of sweat glands (SWGs) declines during aging, leading to heat intolerance in the elderly, but the mechanisms responsible for this decline are poorly understood. We investigated the molecular changes accompanying SWG aging in mice, where sweat tests confirmed a significant reduction of active SWGs in old mice relative to young mice. We first identified SWG-enriched mRNAs by comparing the skin transcriptome of Eda mutant Tabby male mice, which lack SWGs, with that of wild-type control mice by RNA-sequencing analysis. This comparison revealed 171 mRNAs enriched in SWGs, including 47 mRNAs encoding 'core secretory' proteins such as transcription factors, ion channels, ion transporters, and trans-synaptic signaling proteins. Among these, 28 SWG-enriched mRNAs showed significantly altered abundance in the aged male footpad skin, and 11 of them, including Foxa1, Best2, Chrm3, and Foxc1 mRNAs, were found in the 'core secretory' category. Consistent with the changes in mRNA expression levels, immunohistology revealed that higher numbers of secretory cells from old SWGs express the transcription factor FOXC1, the protein product of Foxc1 mRNA. In sum, our study identified mRNAs enriched in SWGs, including those that encode core secretory proteins, and altered abundance of these mRNAs and proteins with aging in mouse SWGs.

Wearable sweat chloride sensors: materials, fabrication and their applications

Chloride is a crucial anion required for multiple functions in the human body including maintaining acid-base balance, fluid balance, electrical neutrality and supporting muscles and nerve cells. Low-chloride levels can cause nausea, diarrhoea, etc. Chloride levels are measured in different body fluids such as urine, serum, sweat and saliva. Sweat chloride measurements are used for multiple applications including disease diagnosis, sports monitoring, and geriatric care. For instance, a sweat chloride test is performed for cystic fibrosis screening. Further, sweat also offers continuous non-invasive access to body fluids for real-time monitoring of chloride that could be used for sports and geriatric care. This review focuses on wearable chloride sensors that are used for periodic and continuous chloride monitoring. The multiple sections in the paper discuss the clinical significance of chloride, detection methods, sensor fabrication methods and their application in cystic fibrosis screening, sports and geriatric care. Finally, the last section discusses the limitation of current sensors and future directions for wearable chloride sensors.

Juvenile-onset Skin Fragility with Acral Blistering: A Quiz

Abstract is missing (Quiz)

Effects of skin moisturization on various aspects of touch showing differences with age and skin site

The human body is encompassed by a thin layer of tissue, the skin, which is heterogenous and highly specialized to protect the body and encode interactions with the external world. There is a fundamental scientific drive to understand its function, coupled with the need to preserve skin as we age, which impacts on our physiological and psychological well-being. In the present study, we aimed to define differences in touch perception between age groups and with skin cream application. We investigated touch on the finger, the forearm and cheek in younger (20-28 years, n = 22) and older (65-75 years, n = 22) females. We measured skin hydration, touch detection, finger spatial discrimination, forearm tactile pleasantness together with electrodermal activity, and perceptual ratings about cream use, skin dryness, and cosmetic habits. Glabrous finger skin became drier and touch performance was impaired with age, but these aspects were preserved in hairy skin. Skin moisturization immediately increased hydration levels, but did not significantly change touch perception. We also found that touch appreciation increased with age. We conclude that reduced finger capacity may impact self-evaluation of the skin and that long-term skin care strategies should focus on hydrating the hand to preserve touch capacities.

Intrinsic and extrinsic factors affecting axillary odor variation. A comprehensive review

Humans produce odorous secretions from multiple body sites according to the microbiomic profile of each area and the types of secretory glands present. Because the axilla is an active, odor-producing region that mediates social communication via the sense of smell, this article focuses on the biological mechanisms underlying the creation of axillary odor, as well as the intrinsic and extrinsic factors likely to impact the odor and determine individual differences. The list of intrinsic factors discussed includes sex, age, ethnicity, emotions, and personality, and extrinsic factors include dietary choices, diseases, climate, and hygienic habits. In addition, we also draw attention to gaps in our understanding of each factor, including, for example, topical areas such as the effect of climate on body odor variation. Fundamental challenges and emerging research opportunities are further outlined in the discussion. Finally, we suggest guidelines and best practices based on the factors reviewed herein for preparatory protocols of sweat collection, data analysis, and interpretation.

Morphology and volume of Meibomian glands ex vivo pre and post partial tarsal plate excision, cryotherapy and laser therapy in the dog using microCT

OBJECTIVE

To determine the morphology and volume of Meibomian glands (MG) of dogs with microCT before and after partial tarsal plate excision (PTPE), cryotherapy, and laser therapy.

PROCEDURE

MicroCT scans were made of 12 upper lids (ULs) and lower lids (LLs) of 12 dogs. After undergoing PTPE, 10 ULs and LLs were scanned again, and one UL and one LL was scanned after laser therapy and one UL and one LL after cryotherapy.

RESULTS

The length of the area containing MGs did not change pre- and post-PTPE, and cryo- or laser therapy. The mean number of MGs in the ULs and LLs was 30.50 and 29.42, respectively, and did not change during the procedures. The average length of one individual MG was 2.60 mm. The mean volume of MGs in the 10 ULs and LLs pre-PTPE was 21.45 and 17.2 mm³ , respectively, and 12.84 and 11.25 mm³ in the UL and LL after PTPE, respectively. The mean volume of MGs decreased from 29.78 mm³ precryotherapy to 28.91 mm³ post-treatment and in the lower eyelid from 22.87 to 22.4 mm³ after cryotherapy. The mean volume of MGs in the UL and LL before laser therapy was 8.95 and 6.78 mm³ , respectively, and after 9.25 and 6.38 mm³ , respectively.

CONCLUSION

MicroCT is a valuable tool to determine the morphology and the volume of MGs and to demonstrate changes that occur after PTPE, laser-, and cryotherapy. There is no need for additional preparation, such as staining, of the specimen prior to scanning.

Perieccrine Coil Elastosis: An Unusual and Previously Unrecognized Aging-Related Phenomenon

ABSTRACT

Elastic fibers are present as a thin line around the normal secretory coil of eccrine and apocrine glands, although they are virtually imperceptible with hematoxylin-eosin staining. Skin aging is a consequence of intrinsic and extrinsic factors, and glycation and ultraviolet irradiation are involved in this process favoring elastosis. We report an unusual and prominent perieccrine elastosis on the left temple in the vicinity of a basal cell carcinoma in a 78-year old man with type 2 diabetes, dyslipidemia, and hypertension. Very thick multilamellar and tortuous elastic fibers surrounded the eccrine coils. This increased amount of elastic fibers was confirmed by orcein staining as well as amyloid-P and lysozyme immunostaining. Perieccrine coil elastosis is a very unusual phenomenon that to the best of our knowledge has not been reported. Similar to dermal actinic elastosis, the presence of perieccrine coil elastosis in a skin cancer microenvironment might hypothetically promote tumor growth because of the release of elastin-derived peptides.

Fat infiltration into dermal layer induces aged facial appearance by decreasing dermal elasticity

BACKGROUND

Facial morphology changes with aging, producing an aged appearance, but the mechanisms involved are not fully established. We recently showed that subcutaneous fat infiltrates into the dermal layer with aging, but it is not yet clear whether and how this drastic change of the dermal layer influences facial appearance.

PURPOSE

We aimed to establish the role of fat infiltration in producing an aged facial appearance and to clarify the mechanism involved.

METHODS

We analyzed the severity of fat infiltration in cheek skin of 30 middle-aged female volunteers by means of ultrasonography. Severity of the nasolabial fold, an established age-related morphology, was evaluated based on our photographic grading criteria as a measure of aged appearance. Skin elasticity was measured with a Cutometer.

RESULTS

Fat infiltration to the dermal layer was detected at the cheek skin noninvasively by means of ultrasonography. Fat infiltration severity, measured as the minimum depth of the fat inside the dermal layer from the skin surface, was positively correlated with the magnitude of the nasolabial fold. Further, fat infiltration severity was significantly negatively correlated with dermal elasticity.

CONCLUSIONS

Our results suggest that fat infiltration into the dermal layer is a critical factor inducing aged appearance of the face. The infiltrated fat decreases the dermal elasticity, which exacerbates nasolabial folds, namely producing an aged facial appearance.

Quantitative characterization of 3D structure of vellus hair arrector pili muscles by micro CT

BACKGROUND

Vellus hair is the fine, wispy hair found over most of the body surface, and the arrector pili muscles (hair muscle) serve to raise these hairs. Hair muscles are also critical for skin regeneration, contributing to the maintenance of stem cells in epidermis and hair follicles. However, little is known about their fundamental properties, especially their structure, because of the limitations of conventional two-dimensional histological analysis.

OBJECTIVES

We aimed to quantitatively characterize the structure of vellus hair muscles by establishing a method to visualize the 3D structure of hair muscle.

METHODS

We observed young female abdominal skin specimens by means of X-ray micro CT and identified hair muscles in each cross-sectional CT image. We then digitally reconstructed the 3D structure of the hair muscles on computer (digital-3D skin), and numerically evaluated their structural parameters.

RESULTS

Vellus hair muscles were clearly distinguished from the surrounding dermal layer in X-ray micro CT images and were digitally reconstructed in 3D from those images for quantification of the structural parameters. The mean value of number of divisions of vellus hair muscles was 1.6, mean depth was 943.6 μm from the skin surface, mean angle to the skin surface was 28.8 degrees, and mean length was 1657.9 μm. These values showed relatively little variation among subjects. The mean muscle volume was approximately 20 million μm³ but showed greater variability than the other parameters.

CONCLUSION

Digital-3D skin technology is a powerful approach to understand the tiny but complex 3D structure of vellus hair muscles. The fundamental nature of vellus hair muscles was characterized in terms of their 3D structural parameters, including number of divisions, angle to the skin surface, depth, and volume.

Infiltration of subcutaneous adipose layer into the dermal layer with aging

BACKGROUND

The elasticity of the dermal layer decreases with aging, leading to ulcer formation and wrinkling, but the mechanism of this change is not fully understood, because it is difficult to access the complex three-dimensional (3D) internal structure of the dermis.

OBJECTIVE

To clarify age-dependent changes in the overall 3D structure of the dermal layer by means of 3D analysis technology.

METHODS

We observed sun-protected human skin by means of X-ray micro CT, identified the layers of the skin, and reconstructed the 3D structure on computer. Age-dependent structural changes of the dermal layer were evaluated by statistical comparison of young and aged skin.

RESULTS

Histological observations suggested the presence of two types of ectopic fat deposits, namely infiltrated subcutaneous fat and isolated fat, in the lower region of the reticular dermal layer in aged skin. To elucidate their nature, we observed skin specimens by X-ray microCT. The epidermis, dermal layer, and subcutaneous adipose layer were well differentiated on CT images, and 3D skin was digitally reconstructed on computer. This method clearly showed that the isolated fat observed histologically was in fact connected to the subcutaneous fat, namely all ectopic fat is connected to the subcutaneous adipose layer. Statistical analysis showed that the severity of fat infiltration into dermal layer is significantly increased in aged skin compared with young skin.

CONCLUSION

Our findings indicate that subcutaneous fat infiltrates into the dermal layer of aged skin. Our 3D analysis approach is advantageous to understand changes of complex internal skin structures with aging.

Aging-related shift of eccrine sweat glands toward the skin surface due to tangling and rotation of the secretory ducts revealed by digital 3D skin reconstruction

Background

Sweat gland function deteriorates with aging, leading to loss of heat tolerance. However, it is unclear whether and how the structure of sweat glands changes during aging, because the 3D structure is complex and inaccessible.

Methods

To clarify age‐dependent changes in sweat glands, we developed a method for 3D structure analysis of sweat glands by means of X‐ray micro‐CT observation of human skin specimens followed by 3D digital reconstruction on computer (digital 3D skin).

Results

Comparison of eccrine sweat glands of abdominal skin from young and old subjects showed that the density and volume of sweat glands do not change with aging. In contrast, the depth of the secretory coil from the skin surface is decreased in the aged group. Surprisingly, the secretory ducts appear tortuous or meandering though their length is unchanged. The secretory coils are located at the dermal‐adipose layer boundary in both groups, but the thickness of the dermal layer decreases with aging, and the depth of the coils is correlated with the dermal thickness.

Conclusion

Our results suggest that sweat glands twist and rotate with aging to maintain the position of the coil at the dermal‐adipose boundary, causing an overall shift toward the skin surface.