Origin of periodic acid-Schiff-reactive glycoprotein in human eccrine sweat

The challenges and promise of sweat sensing

The potential of monitoring biomarkers in sweat for health-related applications has spurred rapid growth in the field of wearable sweat sensors over the past decade. Some of the key challenges have been addressed, including measuring sweat-secretion rate and collecting sufficient sample volumes for real-time, continuous molecular analysis without intense exercise. However, except for assessment of cystic fibrosis and regional nerve function, the ability to accurately measure analytes of interest and their physiological relevance to health metrics remain to be determined. Although sweat is not a crystal ball into every aspect of human health, we expect sweat measurements to continue making inroads into niche applications involving active sweating, such as hydration monitoring for athletes and physical laborers and later for medical and casual health monitoring of relevant drugs and hormones.

Eccrine Sweat Gland and Its Regeneration: Current Status and Future Directions

Eccrine sweat glands (ESGs) play an important role in temperature regulation by secreting sweat. Insufficiency or dysfunction of ESGs in a hot environment or during exercise can lead to hyperthermia, heat exhaustion, heatstroke, and even death, but the ability of ESGs to repair and regenerate themselves is very weak and limited. Repairing the damaged ESGs and regenerating the lost or dysfunctional ESGs poses a challenge for dermatologists and bum surgeons. To promote and accelerate research on the repair and regeneration of ESGs, we summarized the development, structure and function of ESGs, and current strategies to repair and regenerate ESGs based on stem cells, scaffolds, and possible signaling pathways involved.

Sweat gland regeneration: Current strategies and future opportunities

For patients with extensive skin defects, loss of sweat glands (SwGs) greatly decreases their quality of life. Indeed, difficulties in thermoregulation, ion reabsorption, and maintaining fluid balance might render them susceptible to hyperthermia, heatstroke, or even death. Despite extensive studies on the stem cell biology of the skin in recent years, in-situ regeneration of SwGs with both structural and functional fidelity is still challenging because of the limited regenerative capacity and cell fate control of resident progenitors. To overcome these challenges, one must consider both the intrinsic factors relevant to genetic and epigenetic regulation and cues from the cellular microenvironment. Here, we describe recent progress in molecular biology, developmental pathways, and cellular evolution associated with SwGdevelopment and maturation. This is followed by a summary of the current strategies used for cell-fate modulation, transmembrane drug delivery, and scaffold design associated with SwGregeneration. Finally, we offer perspectives for creating more sophisticated systems to accelerate patients' innate healing capacity and developing engineered skin constructs to treat or replace damaged tissues structurally and functionally.

Defining Key Genes Regulating Morphogenesis of Apocrine Sweat Gland in Sheepskin

The apocrine sweat gland is a unique skin appendage in humans compared to mouse and chicken models. The absence of apocrine sweat glands in chicken and murine skin largely restrains further understanding of the complexity of human skin biology and skin diseases, like hircismus. Sheep may serve as an additional system for skin appendage investigation owing to the distributions and histological similarities between the apocrine sweat glands of sheep trunk skin and human armpit skin. To understand the molecular mechanisms underlying morphogenesis of apocrine sweat glands in sheepskin, transcriptome analyses were conducted to reveal 1631 differentially expressed genes that were mainly enriched in three functional groups (cellular component, molecular function and biological process), particularly in gland, epithelial, hair follicle and skin development. There were 7 Gene Ontology (GO) terms enriched in epithelial cell migration and morphogenesis of branching epithelium that were potentially correlated with the wool follicle peg elongation. An additional 5 GO terms were enriched in gland morphogenesis (20 genes), gland development (42 genes), salivary gland morphogenesis and development (8 genes), branching involved in salivary gland morphogenesis (6 genes) and mammary gland epithelial cell differentiation (4 genes). The enriched gland-related genes and two Kyoto Encyclopedia of Genes and Genomes pathway genes (WNT and TGF-β) were potentially involved in the induction of apocrine sweat glands. Genes named BMPR1A, BMP7, SMAD4, TGFB3, WIF1, and WNT10B were selected to validate transcript expression by qRT-PCR. Immunohistochemistry was performed to localize markers for hair follicle (SOX2), skin fibroblast (PDGFRB), stem cells (SOX9) and BMP signaling (SMAD5) in sheepskin. SOX2 and PDGFRB were absent in apocrine sweat glands. SOX9 and SMAD5 were both observed in precursor cells of apocrine sweat glands and later in gland ducts. These results combined with the upregulation of BMP signaling genes indicate that apocrine sweat glands were originated from outer root sheath of primary wool follicle and positively regulated by BMP signaling. This report established the primary network regulating early development of apocrine sweat glands in sheepskin and will facilitate the further understanding of histology and pathology of apocrine sweat glands in human and companion animal skin.

Sweat gland progenitors in development, homeostasis, and wound repair

The human body is covered with several million sweat glands. These tiny coiled tubular skin appendages produce the sweat that is our primary source of cooling and hydration of the skin. Numerous studies have been published on their morphology and physiology. Until recently, however, little was known about how glandular skin maintains homeostasis and repairs itself after tissue injury. Here, we provide a brief overview of sweat gland biology, including newly identified reservoirs of stem cells in glandular skin and their activation in response to different types of injuries. Finally, we discuss how the genetics and biology of glandular skin has advanced our knowledge of human disorders associated with altered sweat gland activity.

Forkhead transcription factor FoxA1 regulates sweat secretion through Bestrophin 2 anion channel and Na-K-Cl cotransporter 1

Body temperature is maintained in a narrow range in mammals, primarily controlled by sweating. In humans, the dynamic thermoregulatory organ, comprised of 2-4 million sweat glands distributed over the body, can secrete up to 4 L of sweat per day, thereby making it possible to withstand high temperatures and endure prolonged physical stress (e.g., long-distance running). The genetic basis for sweat gland function, however, is largely unknown. We find that the forkhead transcription factor, FoxA1, is required to generate mouse sweating capacity. Despite continued sweat gland morphogenesis, ablation of FoxA1 in mice results in absolute anihidrosis (lack of sweating). This inability to sweat is accompanied by down-regulation of the Na-K-Cl cotransporter 1 (Nkcc1) and the Ca(2+)-activated anion channel Bestrophin 2 (Best2), as well as glycoprotein accumulation in gland lumens and ducts. Furthermore, Best2-deficient mice display comparable anhidrosis and glycoprotein accumulation. These findings link earlier observations that both sodium/potassium/chloride exchange and Ca(2+) are required for sweat production. FoxA1 is inferred to regulate two corresponding features of sweat secretion. One feature, via Best2, catalyzes a bicarbonate gradient that could help to drive calcium-associated ionic transport; the other, requiring Nkcc1, facilitates monovalent ion exchange into sweat. These mechanistic components can be pharmaceutical targets to defend against hyperthermia and alleviate defective thermoregulation in the elderly, and may provide a model relevant to more complex secretory processes.

Idiopathic acquired generalized anhidrosis due to occlusion of proximal coiled ducts

Idiopathic acquired generalized anhidrosis is a very rare disease of unknown pathogenesis. We report a 25-year-old man with acquired generalized anhidrosis due to occlusion of the coiled ducts. He did not have sweat secretion over the entire surface of the body, including the palms and soles. Sweat-inducing stimuli provoked tingling pain on the skin. Pilocarpine iontophoresis on the forearm did not induce sweat secretion. Neurological examination did not reveal any abnormality in the central or peripheral nervous system. Skin biopsy showed that the coiled ducts were occluded by an amorphous eosinophilic substance. This amorphous eosinophilic substance was positive with periodic acid-Schiff (PAS) staining and was resistant to digestion by diastase. Electron microscopy demonstrated that the coiled ducts were completely occluded by an amorphous substance. The substance occluding the coiled ducts contained fibrous structures. These findings suggested that the acquired generalized anhidrosis in this patient was caused by occlusion of the coiled ducts by a PAS-positive substance probably derived from dark cell granules.

Structure and function of human sweat glands studied with histochemistry and cytochemistry

The basic structure and the physiological function of human sweat glands were reviewed. Histochemical and cytochemical techniques greatly contributed the elucidation of the ionic mechanism of sweat secretion. X-ray microanalysis using freeze-dried cryosections clarified the level of Na, K, and Cl in each secretory cell of the human sweat gland. Enzyme cytochemistry, immunohistochemistry and autoradiography elucidated the localization of Na,K-ATPase. These data supported the idea that human eccrine sweat is produced by the model of N-K-2Cl cotransport. Cationic colloidal gold localizes anionic sites on histological sections. Human eccrine and apocrine sweat glands showed completely different localization and enzyme sensitivity of anionic sites studied with cationic gold. Human sweat glands have many immunohistochemical markers. Some of them are specific to apocrine sweat glands, although many of them stain both eccrine and apocrine sweat glands. Histochemical techniques, especially immunohistochemistry using a confocal laser scanning microscope and in situ hybridization, will further clarify the relationship of the structure and function in human sweat glands.

Nonneoplastic disorders of the eccrine glands

Eccrine glands are uniquely susceptible to a variety of pathologic processes. Alteration in the rate of sweat secretion manifests as hypohidrosis and hyperhidrosis. Obstruction of the eccrine duct leads to miliaria. The excretion of drugs into eccrine sweat may be a contributory factor in neutrophilic eccrine hidradenitis (NEH), syringosquamous metaplasia (SSM), coma bulla, and erythema multiforme (EM). Alterations in the electrolyte composition of eccrine sweat can be observed in several systemic diseases, most notably cystic fibrosis. This article summarizes current knowledge of eccrine gland pathophysiology.

Cystic fibrosis affects specific cell type in sweat gland secretory coil

The sweat gland has three distinct cell types: a myoepithelial (ME) cell, a beta-adrenergic-insensitive (beta-I) cell, and a beta-adrenergic-sensitive (beta-S) cell. Using intracellular microelectrodes, we sought to functionally identify the specific cell type(s) affected in cystic fibrosis (CF). We found that in CF secretory coils 1) the ME calls are unaffected, as indicated by normal cell membrane potentials and spontaneous and cholinergically induced depolarizing potentials, 2) the beta-I cells showed normal physiological properties, including a relatively smaller cell membrane potential (approx -25 mV) and a Ba(2+)-inhibitable cholinergic response, and, in contrast, 3) the beta-S cell is abnormal, as shown by the lack of a beta-adrenergically activated cystic fibrosis transmembrane conductance regulator (CFTR) Cl- conductance (GCl). Lack of CFTR GCl in this cell type does not affect either the magnitude of cell membrane potential (approx -56 mV) or the relative cell membrane GCl or the cholinergic response, as compared with that of normal beta-S cells. We conclude that, of the three cell types in secretory coil, only the beta-S cell is specifically affected in the CF secretory tissue of the human sweat gland.

The role of extracellular polysaccharide substance produced by Staphylococcus epidermidis in miliaria

BACKGROUND

Previous studies have indicated that cutaneous bacteria, particularly coagulase-negative staphylococci, play a role in the pathogenesis of miliaria. An accumulation of periodic acid-Schiff (PAS)-positive material has been described as blocking the sweat duct in miliaria. Furthermore, a PAS-positive extracellular polysaccharide substance (EPS) has been identified as a product of some strains of Staphylococcus epidermidis.

OBJECTIVE

We evaluated the relative ability of various species of coagulase-negative staphylococci to induce miliaria with particular reference to the potential role of EPS.

METHODS

We inoculated various strains of coagulase-negative staphylococci on the volar forearms of subjects under an occlusive dressing coupled with thermal stimulation. Ability to induce miliaria as well as microbiologic, histologic, and immunostaining features were evaluated.

RESULTS

Miliaria was induced only with strains of S. epidermidis; other species including S. haemolyticus, S. hominis, S. cohnii, S. saprophyticus, and S. simulans were not capable of inducing miliaria. Moreover, only S. epidermidis strains capable of producing EPS were capable of inducing miliaria.

CONCLUSION

Our data indicate that EPS is the PAS-positive material that obstructs the delivery of sweat to the skin surface in miliaria and therefore demonstrate that the EPS produced by S. epidermidis plays a central role in the pathogenesis of miliaria. Furthermore, in a survey of staphylococcal flora isolated from 68 subjects, EPS-producing strains were found to be common.

Urokinase-type plasminogen activator in human eccrine sweat

The presence of urokinase-type plasminogen activator (uPA) in human eccrine sweat has not been reported previously. Clean sweat was obtained from the upper trunk and arms of subjects which had been painted with white petrolatum to minimize epidermal contamination. Sweat was concentrated x 50 by ultrafiltration, and its PA activity determined by the two-step assay method (conversion of plasminogen to plasmin with the subsequent assay of plasmin activity using the substrate S-2251). PA activity was detectable in nine of 17 subjects by this method, which probably represents an underestimate of the true activity because of possible loss of the enzyme during concentration. Scraped (crude) sweat samples contained less PA activity. Sephacryl S-200 gel chromatography of the PA-positive pooled sweat showed a major peak of PA activity at M(r) 55,000. Gelatin-polyacrylamide enzymography revealed a major PA band at M(r) 55,000 and a minor band at 33,000. Sweat PA activity was 94% inhibited by epidermal PA inhibitor and anti-uPA IgG, but not by anti-tPA IgG. We conclude that the PA activity in sweat is derived from the sweat gland and is most likely of the urokinase type. The physiological significance of sweat uPA remains to be determined.

Etretinate increases carcinoembryonic antigen in palmar scrapings

BACKGROUND

Retinoids can affect epithelial structure and function. Patients who take etretinate can develop stickiness of their palms and soles.

OBJECTIVE

We measured carcinoembryonic antigen, a representative glycoprotein in palmar scrapings, to see whether levels were increased in patients taking etretinate when compared with a variety of controls.

METHODS

Carcinoembryonic antigen was measured by a standard immunoassay in scrapings taken from the palm.

RESULTS

Carcinoembryonic antigen is increased in palmar scrapings in patients taking etretinate.

CONCLUSION

Etretinate usage may affect sweat gland function or possibly adherence of carcinoembryonic antigen to surface keratinocytes. The presence of increased amounts of glycoprotein on the surface of the skin may explain the stickiness often noted by patients taking etretinate.

Electrophysiologically distinct cell types in human sweat gland secretory coil

The human sweat gland secretory coil consists of three histologically distinct cell types: myoepithelial (ME), light (or clear), and dark cells. The electrophysiological properties of all these cells are poorly defined. Employing electrophysiological techniques, we report distinct pharmacological responses of three different cell types from freshly isolated human sweat gland secretory coil. The superficial ME cells are characterized by 1) spontaneous depolarizing spikes (2 to 50 mV), 2) high cell membrane potentials [Vm = -68.6 +/- 3.9 (SE) mV; n = 21], 3) a K(+)-selective cell membrane (slope response = 54.2 +/- 6.7 mV per decade K+ concentration; n = 4), 4) depolarizing responses to cholinergic agonist mecholyl (delta Vm = 29.1 +/- 3.1 mV, n = 21), and 5) insensitivity to beta-adrenergic stimulation (n = 12). Two other types of cells, presumably secretory, were also observed. We arbitrarily labeled these cells as beta-adrenergic sensitive (beta-S) and beta-adrenergic insensitive (beta-I) cells based on their respective sensitivity to isoproterenol (IPR), a beta-adrenomimetic. Properties of the beta-S cells include 1) relatively higher basolateral membrane potentials (Vm = -57.3 +/- 3.1 mV; n = 13), 2) depolarizing responses to IPR (delta Vm = 16.8 +/- 2.6 mV; n = 9) inhibitable by the beta-adrenergic antagonist propranolol, and 3) hyperpolarizing responses to mecholyl (delta Vm = -21.8 +/- 2.0 mV; n = 13). The beta-I cells are characterized by 1) low basolateral membrane potentials (Vm = -23.6 +/- 2.1 mV; n = 16), 2) insensitivity to beta-adrenergic stimulation, and 3) hyperpolarizating responses to mecholyl (delta Vm = -16.1 +/- 2.1 mV; n = 16).

Characterization of a monoclonal antibody against a mucin-type glycoprotein in human sweat

We report the preparation and characterization of an IgG2 monoclonal antibody (MAb), HSMA, prepared against a human pooled sweat extract (HPSE). The major component of HPSE was a mucin-type molecule, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) stained with periodic acid-Schiff (PAS) reagent. By immunoblotting, HSMA revealed a smear in the high molecular weight range, typical of mucins. In enzyme-linked immunosorbent assay (ELISA), HSMA failed to react with HPSE fractions isolated after anionic exchange gel chromatography. Similarly, radio-immunobinding assays demonstrated no reactivity between HSMA and A, B, H, and Lewis blood group-related structures. The immunohistological labeling on normal skin showed that HSMA reacted with the cells of eccrine sweat glands, and to a lesser extent, with sebaceous glands and epidermal cells. Periodate treatment in situ abolished these reactions, thus suggesting the carbohydrate structure of the HSMA-epitope. In indirect immunofluorescence (IF) studies, HSMA also reacted with other exocrine glands, e.g. mammary glands, sublingual glands, mixed sero-mucous glands of the trachea, and in the pancreas. Sparse positive cells were also observed in the testis, kidney, thyroid and digestive tract.

Immunohistochemical identification of interleukin I alpha and beta in human eccrine sweat-gland apparatus

Bouin-fixed paraffin sections or acetone-fixed cryostat sections were labelled with the avidin-biotin complex (ABC) or peroxidase-antiperoxidase (PAP) method using three monoclonal antibodies (MAbs) and two polyclonal antisera to human recombinant interleukin I beta (IL-I beta) and three polyclonal antisera to human recombinant interleukin I alpha (IL-I alpha). In the secretory coil both IL-alpha and beta were detected in the clear, but not in the dark cells. Both luminal and basal cells of the coiled and straight ducts expressed IL-I alpha and beta, the IL-I labelling being more intense in the luminal cells. IL-I was not usually detected in the initial portion of the intraepidermal eccrine sweat duct, whereas intense labelling was seen in the upper part including through the stratum corneum. In skin biopsies of the palm, taken after exercise, there was only faint IL-I labelling of the secretory cells, whereas the luminal cells of the dermal ducts showed intense labelling for both IL-I alpha and beta. In the acrosyringium, exercise did not alter the pattern for IL-I alpha and beta, except that in the palm, some of the antibodies to IL-I beta produced a more intense immunolabelling of the acrosyringeal cells. This study identifies a distinct and similar distribution of the two forms of IL-I throughout the eccrine sweat-gland apparatus and indicates that part of the IL-I epidermal pool originates from the sweat.

Biology of sweat glands and their disorders. I. Normal sweat gland function

The basic mechanisms of sweat gland function and an updated review of some relatively common disorders of sweat secretion, are presented. Although sweat secretion and ductal absorption are basically biophysical and biologic cellular processes, a detailed description of the basic biophysical principles of membrane transport has been avoided to make the discussion more readable. The cited references will, however, help those readers primarily interested in the basic details of sweat gland function. Part I of this article includes a discussion of morphologic characteristics, central and peripheral nervous control of sweat secretion, neurotransmitters, intracellular mediators and stimulus secretion coupling, Na-K-Cl cotransport model for the ionic mechanism of sweat secretion, ingredients of sweat, ductal function, the pathogenesis of abnormal sweat gland function in cystic fibrosis, and the discovery of the apoeccrine sweat gland. Part II, to be published in the May issue of the Journal, reviews reports of all those major disorders of hyperhidrosis and hypohidrosis that have appeared in the literature during the past 10 years. It is hoped that this review will serve as a resource for clinicians who encounter puzzling disorders of sweating in their patients, as well as for investigators who wish to obtain a quick update on sweat gland function.

Dye-coupling compartments in the human eccrine sweat gland

The dye-coupling status of secretory and reabsorptive cells in micro-dissected lengths of human eccrine sweat gland was investigated by means of intracellular microiontophoresis of the fluorescent naphthalimide dye Lucifer yellow CH (Mr 457), which passes through gap junctions. Cells of the reabsorptive duct exhibited complete dye coupling between the apical and basal layers of the epithelium. Conversely, cells of the secretory tubule exhibited selective dye coupling. Of the three cell types present, clear, dark, and myoepithelial, the dark cells were impaled and labeled almost exclusively in the present study. These cells were observed either as single cells or as dye-coupled groups of neighboring dark cells. In no instance were dark cells observed to be dye coupled to clear cells or to myoepithelial cells. Because myoepithelial cells are known to be dye coupled exclusively to neighboring myoepithelial cells, the remaining clear cells must either be uncoupled or show selective dye coupling to neighboring clear cells. The significance of these findings is considered with respect to the regulation and function of the different cell types present in the human eccrine sweat gland.