Eccrine Sweat Glands are Major Contributors to Reepithelialization of Human Wounds

Abstract

Eccrine sweat glands are skin-associated epithelial structures (appendages) that are unique to some primates including humans and are absent in the skin of most laboratory animals including rodents, rabbits, and pigs. On the basis of the known importance of other skin appendages (hair follicles, apocrine glands, and sebaceous glands) for wound repair in model animals, the present study was designed to assess the role of eccrine glands in the repair of wounded human skin. Partial-thickness wounds were generated on healthy human forearms, and epidermal repair was studied in skin biopsy samples obtained at precise times during the first week after wounding. Wound reepithelialization was assessed using immunohistochemistry and computer-assisted 3-dimensional reconstruction of in vivo wounded skin samples. Our data demonstrate a key role for eccrine sweat glands in reconstituting the epidermis after wounding in humans. More specifically, i) eccrine sweat glands generate keratinocyte outgrowths that ultimately form new epidermis; ii) eccrine sweat glands are the most abundant appendages in human skin, outnumbering hair follicles by a factor close to 3; and iii) the rate of expansion of keratinocyte outgrowths from eccrine sweat glands parallels the rate of reepithelialization. This novel appreciation of the unique importance of eccrine sweat glands for epidermal repair may be exploited to improve our approaches to understanding and treating human wounds. Eccrine sweat glands are skin-associated epithelial structures (appendages) that are unique to some primates including humans and are absent in the skin of most laboratory animals including rodents, rabbits, and pigs. On the basis of the known importance of other skin appendages (hair follicles, apocrine glands, and sebaceous glands) for wound repair in model animals, the present study was designed to assess the role of eccrine glands in the repair of wounded human skin. Partial-thickness wounds were generated on healthy human forearms, and epidermal repair was studied in skin biopsy samples obtained at precise times during the first week after wounding. Wound reepithelialization was assessed using immunohistochemistry and computer-assisted 3-dimensional reconstruction of in vivo wounded skin samples. Our data demonstrate a key role for eccrine sweat glands in reconstituting the epidermis after wounding in humans. More specifically, i) eccrine sweat glands generate keratinocyte outgrowths that ultimately form new epidermis; ii) eccrine sweat glands are the most abundant appendages in human skin, outnumbering hair follicles by a factor close to 3; and iii) the rate of expansion of keratinocyte outgrowths from eccrine sweat glands parallels the rate of reepithelialization. This novel appreciation of the unique importance of eccrine sweat glands for epidermal repair may be exploited to improve our approaches to understanding and treating human wounds. Skin injuries are a part of everyday life, and efficient wound repair is vital to restore the protective barrier function of the skin. Defects associated with cutaneous wound repair represent a tremendous burden for patients and health systems and are estimated to cost several billion dollars a year in the United States alone.1Sen C.K. Gordillo G.M. Roy S. Kirsner R. Lambert L. Hunt T.K. Gottrup F. Gurtner G.C. Longaker M.T. Human skin wounds: a major and snowballing threat to public health and the economy.Wound Repair Regen. 2009; 17: 763-771Crossref PubMed Scopus (2023) Google Scholar Despite important progress in understanding the healing process in animal models, many questions remain regarding the basic principles of cutaneous wound repair in humans. Understanding the basic mechanisms of epithelial repair in human skin after wounding is a necessary first step in the design of therapeutic strategies with the objective of restoring burdening wound-healing defects. In rodents, elegant studies have consistently demonstrated that keratinocytes within pilosebaceous units (consisting of hair follicles and associated sebaceous glands) and at the wound edge proliferate and migrate to the center of the wound to repair the epidermis after wounding.2Ito M. Liu Y. Yang Z. Nguyen J. Liang F. Morris R.J. Cotsarelis G. Stem cells in the hair follicle bulge contribute to wound repair but not to homeostasis of the epidermis.Nat Med. 2005; 11: 1351-1354Crossref PubMed Scopus (1015) Google Scholar, 3Singer A.J. Clark R.A. Cutaneous wound healing.N Engl J Med. 1999; 341: 738-746Crossref PubMed Scopus (4740) Google Scholar, 4Taylor G. Lehrer M.S. Jensen P.J. Sun T.T. Lavker R.M. Involvement of follicular stem cells in forming not only the follicle but also the epidermis.Cell. 2000; 102: 451-461Abstract Full Text Full Text PDF PubMed Scopus (950) Google Scholar, 5Levy V. Lindon C. Zheng Y. Harfe B.D. Morgan B.A. Epidermal stem cells arise from the hair follicle after wounding.FASEB J. 2007; 21: 1358-1366Crossref PubMed Scopus (321) Google Scholar, 6Gurtner G.C. Werner S. Barrandon Y. Longaker M.T. Wound repair and regeneration.Nature. 2008; 453: 314-321Crossref PubMed Scopus (3991) Google Scholar In pigs, the sweat apparatus also participates in reepithelialization of skin wounds.7Miller S.J. Burke E.M. Rader M.D. Coulombe P.A. Lavker R.M. Re-epithelialization of porcine skin by the sweat apparatus.J Invest Dermatol. 1998; 110: 13-19Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar Extrapolation of these processes to human skin, however, remains difficult for 2 main reasons. First, hair follicles in humans are of the lowest range of density among mammals, and the healing ability of individual skin sites does not correlate with their respective hair follicle density. Indeed, hairless areas of the human body such as the palms and soles have no inherent healing defects. Second, in pigs, the sweat apparatus is composed of apocrine glands,8Montagna W. Yun J.S. The skin of the domestic pig.J Invest Dermatol. 1964; 42: 11-21Abstract Full Text PDF PubMed Scopus (2) Google Scholar which in humans are restricted to the axillae and rectogenital areas.9Montagna W. Some particularities of human skin and the skin of nonhuman primates.G Ital Dermatol Venereol. 1984; 119: 1-4PubMed Google Scholar In contrast, in humans, the skin sweat apparatus is composed of several million eccrine glands distributed throughout the body. Body eccrine sweat glands are present only in humans and Catarrhini primates and are absent in the skin of all other primates and mammals except for footpads and the volar surface of prehensile tails, where they respond to peculiar stimuli to increase grip.9Montagna W. Some particularities of human skin and the skin of nonhuman primates.G Ital Dermatol Venereol. 1984; 119: 1-4PubMed Google Scholar Apocrine and eccrine glands are fully distinct and differ in their histologic features (1 versus 2 types of secretory epithelial cells), the content of their secretion (oily versus watery), their development,10Marples M.J. The Ecology of the Human Skin. Charles C Thomas Publisher Ltd., Springfield, IL1965Google Scholar and their function and regulation.11Montagna W. The Structure and Function of Skin. Academic Press, New York1956Google Scholar, 12Dobson R.L. Formisano V. Lobitz W.C. Brophy D. Some histochemical observations on the human eccrine sweat glands. III: the effect of profuse sweating.J Invest Dermatol. 1958; 31 (discussion 158–159): 147-158Abstract Full Text PDF PubMed Scopus (13) Google Scholar Most importantly, apocrine glands are associated with pilosebaceous units and discharge in the canal of hair follicles, whereas eccrine glands are solitary and discharge on the skin surface. In general, adult human skin contains more and denser eccrine sweat glands than pilosebaceous units (the head being an exception)13Szabo G. The regional anatomy of the human integument with special reference to the distribution of hair follicles, sweat glands and melanocytes.Phil Trans R Soc Lond B. 1967; 252: 447-485Crossref Google Scholar and few and specially localized apocrine glands.9Montagna W. Some particularities of human skin and the skin of nonhuman primates.G Ital Dermatol Venereol. 1984; 119: 1-4PubMed Google Scholar Considering the physiologic distinctions of the skin of laboratory mammals and humans, we sought to examine the importance of human skin-associated epithelial structures (appendages) during the process of partial-thickness wound closure in humans in vivo. Partial-thickness wounds such as those triggered by a second-degree burn,14Hettiaratchy S. Dziewulski P. ABC of burns: pathophysiology and types of burns.BMJ. 2004; 328 ([published correction appears in BMJ 2004, 329:148]): 1427-1429Crossref PubMed Scopus (222) Google Scholar deep abrasion, or stage II pressure ulcers15Doughty D. Ramundo J. Bonham P. Beitz J. Erwin-Toth P. Anderson R. Rolstad B.S. Issues and challenges in staging of pressure ulcers.J Wound Ostomy Continence Nurs. 2006; 33 (quiz 131–132): 125-130Crossref PubMed Scopus (29) Google Scholar are often left open in humans, as opposed to full-thickness wounds, which are typically closed surgically using stitches or other means. In the present study, partial-thickness wounds were generated on the forearm skin of healthy human individuals with a carbon dioxide (CO2) laser. CO2 lasers produce a beam of infrared radiation that is absorbed by water within the skin, resulting in localized production of heat and tissue vaporization.16Sinclair R.J. Sinclair P.J. Carbon Dioxide laser in the treatment of cutaneous disorders.Australas J Dermatol. 1991; 32: 165-171Crossref PubMed Scopus (12) Google Scholar We have previously reported that CO2 laser wounding triggers a typical repair reaction with inflammatory, proliferative, and remodeling phases.17Orringer J.S. Kang S. Johnson T.M. Karimipour D.J. Hamilton T. Hammerberg C. Voorhees J.J. Fisher G.J. Connective tissue remodeling induced by carbon dioxide laser resurfacing of photodamaged human skin.Arch Dermatol. 2004; 140: 1326-1332Crossref PubMed Scopus (159) Google Scholar, 18Rittié L. Perbal B. Castellot Jr., J.J. Orringer J.S. Voorhees J.J. Fisher G.J. Spatial-temporal modulation of CCN proteins during wound healing in human skin in vivo.J Cell Commun Signal. 2011; 5: 69-80Crossref PubMed Scopus (35) Google Scholar Herein we report the key previously undocumented role of eccrine sweat glands in epidermal reepithelialization after partial-thickness wounding in humans. The present study was approved by the Institutional Review Board of the University of Michigan, according to the Declaration of Helsinki protocols, and each human subject provided written informed consent before entering the study. Human subject recruitment, CO2 laser treatments, and biopsy preparation were performed as previously described.18Rittié L. Perbal B. Castellot Jr., J.J. Orringer J.S. Voorhees J.J. Fisher G.J. Spatial-temporal modulation of CCN proteins during wound healing in human skin in vivo.J Cell Commun Signal. 2011; 5: 69-80Crossref PubMed Scopus (35) Google Scholar In brief, after administration of 1% lidocaine local anesthesia, partial-thickness wounds were generated on the volar surface of the forearm using 2 passes of a CO2 laser (Ultrapulse; Coherent, Inc., Santa Clara, CA) set at 300 mJ and 60 W and with computer of partial-thickness wounds were on the edge of the the the of the studies the was first using a using a and Inc., or before CO2 laser The CO2 wounds were with water and with a biopsy samples were from the center or the edge of the wound at times after administration of 1% lidocaine local Skin samples were in Ltd., in and at were and to including for forearm reconstruction and to and for studies and to and were performed on skin as previously L. Kang S. Voorhees J.J. Fisher G.J. hair follicle stem in and human 2009; PubMed Scopus Google Scholar was obtained by II and from Inc., and and and J. of human 33 to J. 1998; 17: PubMed Scopus Google Scholar from University of were using a and using Inc., or as a using a Inc., provided by the and of Cell and University of skin or to for biopsy were and and were obtained as and In some was performed a to the of the 3-dimensional reconstruction for biopsy samples are provided in and of areas within skin in main were generated according to In brief, computer-assisted of structures were generated using by a for 2005; PubMed Scopus Google Scholar was performed with and using the and were generated using were to using at were performed on reconstruction using and are as observations of wounded skin samples as the CO2 laser the epidermis and The of tissue was throughout the and was among individuals not wound closure was within after CO2 laser we on the first week after wounding to study the role of skin appendages during wound reepithelialization in human skin. In forearm skin, a of keratinocytes in the lowest of the epidermis and in hair follicle are proliferative, as by of of T. J. The from the known and the Cell 2000; PubMed Scopus Google In few cells are for in eccrine glands of skin with a report that is only in eccrine sweat glands of human Jr., W.C. W. of the human eccrine sweat to center of the epidermal sweat Invest Dermatol. Full Text PDF PubMed Scopus Google Scholar In contrast, at after most of the of the eccrine the wound was for was restricted to and no cells were for after wounding were consistently in each sweat of a wounded skin and in all individuals to their in eccrine glands are difficult to study in a histologic to examine eccrine sweat glands after we computer-assisted of the in we to an eccrine the demonstrated that after all of the cells of eccrine the wound were for In the set of wounded skin biopsy the pilosebaceous units also at after wounding was in the cells of the hair follicle and in the of the sebaceous glands. these that partial-thickness wounding triggers a in eccrine and the of pilosebaceous units in human skin in vivo. In the of our we that epidermal outgrowths first at after pilosebaceous units and to at the surface of wounded skin reepithelialization the new epidermis and appendages in wounded human skin, skin to of skin were for epithelial and using computer-assisted of in The epithelial of and epidermal cells was The pilosebaceous eccrine sweat glands, and new epidermis structures was respective as previously G. The regional anatomy of the human integument with special reference to the distribution of hair follicles, sweat glands and melanocytes.Phil Trans R Soc Lond B. 1967; 252: 447-485Crossref Google Scholar 2 or pilosebaceous units are often in human skin, whereas eccrine sweat glands are solitary and distributed in Eccrine sweat glands were from pilosebaceous units on the basis of their the of associated sebaceous glands, and the of the by the and secretory in the deep of the in for In epithelial outgrowths were at the surface of the wounded the and were localized within a of outgrowths were first hair follicle at after wounding that of keratinocytes also were each eccrine sweat at after wounding in the reepithelialization outgrowths they with each reconstituting the new epidermis also in of epidermal from that the rate of reepithelialization was and that epidermal by these that the in appendages at after wounding is by the of keratinocyte outgrowths each epidermal outgrowths to epidermis in wounded human skin. We eccrine sweat glands and pilosebaceous units full-thickness biopsy of forearm skin to and data that eccrine glands pilosebaceous units at a of which is typical of human skin except for and of G. The regional anatomy of the human integument with special reference to the distribution of hair follicles, sweat glands and melanocytes.Phil Trans R Soc Lond B. 1967; 252: 447-485Crossref Google Scholar, of and sweat glands on the of a PubMed Scopus Google Scholar We the of keratinocyte outgrowths each from using at and after wounding. these of keratinocyte outgrowths is and of outgrowths is of these that the rate of expansion of eccrine outgrowths was to the reepithelialization which is the of pilosebaceous and eccrine cells that the of eccrine sweat glands throughout the reepithelialization process and was to that of pilosebaceous We also the of on the new hair follicle and of sweat in we that keratinocyte outgrowths are distinct in their and with each other in the these that keratinocyte outgrowths of their with each Our also that eccrine sweat glands pilosebaceous units by a factor close to and to keratinocyte outgrowths with a rate of expansion to that of reepithelialization. The important role of eccrine glands in reepithelialization of forearm skin to that skin of hair such as on palms and soles on eccrine glands for reepithelialization after wounding. we performed a of in which were wounded on the edge of the after biopsy samples were to the wound and the skin. We that each eccrine to keratinocyte outgrowths the eccrine for also demonstrate that eccrine glands are in reepithelialization of skin, as we in skin. The present study was to examine the importance of skin appendages during the process of partial-thickness wound closure in human skin in vivo. This of wound healing is important the unique of human skin, hair follicles and associated sebaceous glands, of hair apocrine sweat glands except in the axillae and and in eccrine sweat glands. This is in with the skin of most laboratory animals that are to study wound healing and that not have eccrine sweat glands in their body skin. our demonstrate that i) eccrine sweat glands and pilosebaceous units contribute to the reepithelialization of human wounds by keratinocyte outgrowths that ultimately form new epidermis; ii) keratinocyte outgrowths at a rate they from sweat glands or pilosebaceous and iii) eccrine sweat glands pilosebaceous units by a factor close to these that eccrine sweat glands are major to reepithelialization of human skin wounds. have to eccrine sweat glands. in footpads in mammals, prehensile in some or palms and soles in primates including humans, eccrine glands produce sweat to and glands have role in M.J. The Ecology of the Human Skin. Charles C Thomas Publisher Ltd., Springfield, IL1965Google Scholar In humans are unique in their on several million body eccrine sweat glands to their heat sweat glands in the body skin of nonhuman primates not respond to heat W. Yun J.S. The skin of the domestic pig.J Invest Dermatol. 1964; 42: 11-21Abstract Full Text PDF PubMed Scopus (2) Google Scholar, Jr., Jr., The of sweat J 1991; PubMed Scopus Google Scholar, W. The skin of nonhuman Scopus Google In humans, eccrine sweat glands also in the of the that the the of skin and with M.J. The Ecology of the Human Skin. Charles C Thomas Publisher Ltd., Springfield, IL1965Google Scholar, R. S. L. M. is generated on the skin surface by of sweat Invest Dermatol. Full Text PDF PubMed Scopus Google Scholar The of the of eccrine sweat glands to epidermal repair after wounding a novel function of human eccrine glands. demonstrated that sweat glands in remain during epidermal L. C. of stem in sweat glands and in homeostasis and wound Full Text Full Text PDF PubMed Scopus Google Scholar are in with our to the sweat glands of the human these observations that the repair function of eccrine glands during function is unique to humans is an that remains to be The of sweat glands of the of eccrine sweat glands in the skin of animals that are in wound-healing In skin, which contains only pilosebaceous apocrine glands,8Montagna W. Yun J.S. The skin of the domestic pig.J Invest Dermatol. 1964; 42: 11-21Abstract Full Text PDF PubMed Scopus (2) Google Scholar reepithelialization in the of pilosebaceous units and epidermal is which that reepithelialization also arise from apocrine S.J. Burke E.M. Rader M.D. Coulombe P.A. Lavker R.M. Re-epithelialization of porcine skin by the sweat apparatus.J Invest Dermatol. 1998; 110: 13-19Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar In humans, eccrine sweat glands after to the epidermal or Jr., W.C. W. of the human eccrine sweat to center of the epidermal sweat Invest Dermatol. Full Text PDF PubMed Scopus Google Scholar, Jr., W.C. Brophy D. of the human eccrine sweat to Invest Dermatol. (discussion Full Text PDF PubMed Scopus Google Scholar or in sites with and the of epithelial the of skin on a study of the healing of sites in J Full Text PDF PubMed Scopus Google Scholar The of a to surface of epithelial cells remain within the wound was by wounds in human a histologic study of healing with epithelial Google Scholar studied human wounds more than More in studies have that eccrine sweat keratinocytes are to and form epidermis in T. L. S. S. C. M. Human eccrine sweat cells a Invest Dermatol. Full Text Full Text PDF PubMed Scopus Google Scholar our the present study is the first to demonstrate a major of eccrine sweat glands in epidermal repair of human skin in vivo. eccrine sweat glands also contribute to epidermal homeostasis in the of wounds is an that be not all eccrine glands are as sweat production in R.L. Formisano V. Lobitz W.C. Brophy D. Some histochemical observations on the human eccrine sweat glands. III: the effect of profuse sweating.J Invest Dermatol. 1958; 31 (discussion 158–159): 147-158Abstract Full Text PDF PubMed Scopus (13) Google Scholar, W. and in of skin, Eccrine sweat glands and eccrine Press, New Scholar, R.L. and individual in the function of the human eccrine sweat Invest Dermatol. Full Text PDF PubMed Scopus Google Scholar our data that each sweat to reepithelialization during wound This important in as opposed to a a wounded be as a of distributed repair that ultimately with each The that to be by keratinocytes is the that 2 eccrine sweat glands, not the wound This is according to body and sweat density and is the on skin, which is of pilosebaceous units but the density of eccrine sweat glands in the human M.J. The Ecology of the Human Skin. Charles C Thomas Publisher Ltd., Springfield, IL1965Google Scholar, G. The regional anatomy of the human integument with special reference to the distribution of hair follicles, sweat glands and melanocytes.Phil Trans R Soc Lond B. 1967; 252: 447-485Crossref Google Scholar, of and sweat glands on the of a PubMed Scopus Google Scholar Our data that human eccrine sweat glands an important of cells of that be on wounding. on human skin on the of cells in the of human eccrine M. Y. The of cells in eccrine Invest Dermatol. 2009; Full Text Full Text PDF PubMed Scopus Google Scholar In cells were distributed in a to that of stem cells in the human and M. Y. The of cells in eccrine Invest Dermatol. 2009; Full Text Full Text PDF PubMed Scopus Google Scholar of cells have in the eccrine glands of the L. C. of stem in sweat glands and in homeostasis and wound Full Text Full Text PDF PubMed Scopus Google Scholar eccrine glands during repair after epidermal in with their human as reported by Lobitz Jr., W.C. W. of the human eccrine sweat to center of the epidermal sweat Invest Dermatol. Full Text PDF PubMed Scopus Google Scholar, Jr., W.C. Brophy D. of the human eccrine sweat to Invest Dermatol. (discussion Full Text PDF PubMed Scopus Google Scholar and in the present the distinct eccrine were to contribute to their and after L. 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