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A Nonconventional Look at Ionic Fluxes in the Skin: Lessons From Genetically Modified Mice

Marjorie Guitard, Celine Leyvraz and Edith Hummler

Départment de Pharmacologie et de Toxicologie, Université de Lausanne, CH-1005 Lausanne, Switzerland

	Abstract

 
The mammalian, highly amiloride-sensitive epithelial sodium channel (ENaC) is member of the degenerin/ENaC superfamily of ion channels known to be implicated in sodium homeostasis, mechanosensation, and mechanoperception. A novel role for ENaC implicated in differentiation processes in skin reshapes our current view of this ancient transmembrane channel protein.

	Introduction

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
The highly amiloride-sensitive epithelial sodium channel (ENaC) is a membrane constituent of many salt-reabsorbing epithelia that facilitates Na⁺ movement across the tight epithelia that line the distal nephron, the distal colon, the ducts of salivary and sweat glands, and the lung. In these cells, ENaC drives Na⁺ entry apically into the cell, which then is extruded basolaterally from the cell by the Na⁺-K⁺-ATPase (see Ref. 19 for review). Three highly homologous subunits, -, ß-, and -ENaC, are characterized at the molecular level and are encoded by different genes (Scnn1a, Scnn1b, and Scnn1g) localized on chromosomes 6 (Scnn1a; mouse) and 12 (SCNN1A; human) and chromosomes 7 (Scnn1b, Scnn1g; mouse) and 16 (SCNN1B, SCNN1G; human). In vivo and in vitro experiments clearly demonstrate that in the absence of the -subunit, channels made of ß- and -subunits alone do not confer ENaC activity. Expression of each of the -, ß-, and -ENaC subunits is crucial for survival, as shown in gene-targeting experiments. Nevertheless, the clinical phenotype of each single knockout vary. In vivo, the constitutive inactivation of the -subunit of ENaC leads to complete abolishment of ENaC activity. Null mutant neonates develop respiratory distress syndrome (RDS) and die soon after birth, revealing an important role of channel function in lung liquid clearance at birth (11). In contrast to the -ENaC subunit, the ß-subunit is not required for the transition from a liquid-filled to an air-filled lung but seems rather to be crucial for ENaC function in the kidney. The ß-ENaC-deficient mice show normal prenatal development but also die within 40 h, most likely of hyperkalemia. The -ENaC subunit seems to facilitate neonatal lung liquid clearance but is critical for renal sodium and potassium transport in the kidney. We propose that the variation in phenotype is due to complete abolishment of activity of ENaC in -ENaC knockout mice, whereas ß- and -ENaC knockout mice still retain some ENaC activity (estimated at ~15% of total ENaC activity) (2).

In human, mutations in all three ENaC subunits are reported to result in either ENaC hyper- or hypofunction associated with hypertension or salt-wasting syndrome (type 1 pseudohypoaldosteronism; PHA-1) (10). All PHA-1 mutations tested so far in Xenopus oocytes still confer ENaC activity. More recent investigations demonstrate that patients with systemic pseudohypoaldosteronism fail to absorb liquid from airway surface; the result is an increased volume of liquid in the airways. Immaturity of the liquid absorptive transport system in the very premature infant may be an important factor in the pathogenesis of RDS. In a mouse model with altered ENaC activity, diminished basal Na⁺ transport presents a predisposing factor for edema formation (18). Interestingly, increased morbidity and mortality in human male patients with RDS indicates an organ immaturity other than in the lung. The ontogeny of the epidermal permeability barrier and lung occurs quite in parallel, and hormones like, for example, glucocorticoids and thyroids accelerate maturation. Sex steroid hormones exert opposite effects on lung maturation and on cutaneous barrier formation, with estrogens accelerating and androgens inhibiting. Two published reports (1, 8) describe macroscopic skin lesions like dermatitis in PHA-1 patients carrying ENaC mutations, although the skin phenotype is not further analyzed. Thus it is still unknown whether dysfunction of ENaC expression in skin contributes to and/or is indeed causative for defined skin diseases.

	ENaC expression in skin

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
In mammalian skin, expression of all three ENaC subunits is demonstrated in human keratinocytes, as evidenced by RT-PCR, RNase protection assay, Northern blot, and immunocytochemistry (4, 17, 20). In situ hybridization reveals that ENaC mRNA is expressed throughout adult human epidermis but is absent in 10-wk-old fetal epidermis (17). Patch-clamp recordings on human keratinocytes reveal a sodium channel conductance that is blocked by benzamil, with similar affinity and voltage dependence of the amiloride block as described previously for ENaC (4). Interestingly, expression is increased in more differentiated keratinocytes and is only found in the later stages of fetal epidermal development, suggesting that ENaC-mediated Na⁺ transport may be implicated in the control of keratinocyte differentiation. In human skin, low concentrations of amiloride (10^-8 to 10^-6 M), a specific inhibitor of ENaC, block the formation of cornified envelopes, inhibit the rise in intracellular Ca²⁺ seen as a result of raising extracellular Ca²⁺, and prevent the synthesis and activity of transglutaminase, a Ca²⁺-induced marker of differentiation, presumably by modulations in membrane potential. Further evidence that ENaC is implicated in keratinocyte and epidermal differentiation comes from the analysis of newborn -ENaC knockout mice, which exhibit epidermal thickening, premature lipid secretion in the upper epidermis, and abnormal keratohyalin granules, suggesting that ENaC-mediated sodium fluxes control selective aspects of keratinocyte differentiation (16). These alterations may finally result in epidermal barrier dysfunction.

	Epidermal barrier function

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
The primary function of the epidermis is to form a barrier between an organism and the outside hostile environment designed to advert the invasion of bacteria and other foreign entities while simultaneously preventing the escape of water required for terrestrial life. This role is mainly assumed by the upper layer of the epidermis, called the stratum corneum (Fig. 1). This layer is formed by totally differentiated keratinocytes embedded in a lipid matrix. The stratum corneum is maintained by the constant reproduction of the inner layer of living keratinocytes that migrate upward while undergoing a complex genetic program of terminal differentiation. This includes the formation of desmosomal adherence junctions, the accumulation of specialized keratins that provide mechanical strength to the skin, the accumulation of a complex array of structural proteins, lipids, and enzymes that constitute the cornified envelope, and the synthesis, extrusion, and processing of intercorneocyte lipids. Formation of the cutaneous permeability barrier requires both the secretion of the lipid and the hydrolytic enzyme contents of lamellar bodies and the subsequent postsecretory processing of polar lipids into their nonpolar lipid products. Lamellar body secretion is regulated by changes in extracellular ions, and lipid processing appears to be mediated by a set of hydrolytic, Ca²⁺-dependent enzymes, which produce structural transformations within the stratum corneum interstices, leading to barrier formation.

View larger version (83K): [in this window] [in a new window]   FIGURE 1. Photograph (left) and schematic representation (right) of a 24-h-old newborn mouse skin section showing the architecture of the epidermis, including a single cell layer of stratum basale (basal layer, BL) and several cell layers each of strata spinosum (spinous layer, SL) and granulosum (granular layer, GL), which are covered with stratum corneum (SC). Continuous tight junctions (red, #) were found mainly in the second layer of the stratum granulosum in newborn mice. The extracellular Ca2+ gradient and the increased expression of ENaC subunits in more differentiated cell layers (SL, GL) is indicated.

Until recently, mammalian epidermis that is characterized by multiple layers of less-polarized cells has been considered to be an epithelium with a passive transcutaneous movement of water and ions. But recently, two groups (3, 7) independently reported the presence of tight junctions within the stratum granulosum of the epidermis with typical tight junction morphology and molecular composition, characterized by colocalization of the integral membrane proteins like occludin and claudins (Fig. 1). Interestingly, claudin-1-deficient mice die soon after birth due to severe impairment of the epidermal barrier, demonstrating that tight junctions are crucial for the barrier function of mammalian skin (7). In these mice a subcutaneously injected tracer passes through epidermis, whereas in wild-type mice epidermis tight junctions efficiently prevent its diffusion. This clearly demonstrates that water and ions cannot move transcutaneously through the epidermis but need transporting systems like channels or pumps. Dysfunction of these transporting systems in skin may therefore have severe consequences for normal skin function by altering, for example, differentiation processes in the skin.

	Ionic fluxes in keratinocyte differentiation

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
That ions may be important regulators in keratinocyte differentiation is demonstrated by the presence of a calcium gradient within the epidermis, with higher quantities of Ca²⁺ in the upper than in the lower epidermis. Studied by using ion-capture cytochemistry and electron and proton probe X-ray microanalysis, the epidermis in the intact skin displays a Ca²⁺ gradient, with low levels of Ca²⁺ in the basal and lower spinous layers, followed by an increase in extracellular and intracellular Ca²⁺ that peaks in the stratum granulosum. Thus increase of extracellular calcium may serve as a primary trigger for keratinocyte differentiation. Moreover, following acetone disruption of the barrier, this Ca²⁺ gradient is lost, and the decrease in Ca²⁺ levels in the outer epidermis is associated with enhanced lamellar body secretion and lipid synthesis, important components of the repair response. In contrast, if the Ca²⁺ gradient is preserved by the addition of Ca²⁺ to the bath solution, lamellar body secretion, lipid synthesis, and barrier recovery are inhibited. Thereby epidermal calcium regulates the mRNA expression of differentiation-specific markers, like the intermediate filament-associated proteins loricrin, profilaggrin, and involucrin (6). These findings provide direct evidence that acute and sustained fluctuations in epidermal calcium regulate events late in epidermal differentiation that together form the barrier. The passive loss of Ca²⁺ and other electrolytes from the upper epidermis following barrier disruption may signal the repair response. As summarized in Table 1, only recently have mice that are deficient for ion/water channels and transporters been analyzed for their skin phenotype, revealing that indeed ions, like calcium, sodium, and protons, participate in ordered epidermal differentiation. Keratinocytes from mice deficient for the calcium-sensing receptor (CaR) no longer responded to extracellular calcium, and the mice exhibited disordered differentiation. Mice deficient for the sodium channel ENaC show altered expression of the differentiation markers keratin 1, 6, and involucrin as well as premature lipid secretion, which may result in diminished lipid barrier, and mice lacking the NHE3 exchanger exhibit an impaired stratum corneum acidification.

Ionic fluxes seem also to be important in wound repair. Wound healing is a relatively simple but important developmental process that begins with the migration of epithelial cells to cover the wound. There is some indirect evidence that intrinsic fields play a role in promoting the epithelization of wounds. A transepidermal voltage gradient, created by the sodium ion pumps of the epithelium, acts as the driving force for an electrical current that flows through the low-resistance pathway of the wound. When the epidermis’s ability to generate wound currents is impaired by interfering with its Na⁺ transport capacity, epithelization is retarded. Directed migration of keratinocytes is essential for wound healing. This is strongly influenced by the presence of a physiological electric field, and in vitro these cells migrate toward the negative pole of such an electric field (galvanotaxis). Calcium channel blockers like Ni²⁺ and Gd³⁺ can inhibit this galvanotaxis, suggesting that calcium influx through Ca²⁺ channels is required for directed migration of keratinocytes (23). Galvanotaxis may be one of the mechanisms used by keratinocytes to guide wound closure, but the channel(s) involved in those processes is still unknown.

	Consequences of ENaC deficiency on epidermal differentiation

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
To determine the importance of ENaC function in epidermal differentiation, we analyzed skin from newborn mice in which the -ENaC subunit, and as a consequence the whole channel function, had been deleted. Newborn -ENaC knockout mice demonstrate epithelial hyperplasia, and all suprabasal levels are thickened, suggesting that absence of ENaC function results in defects in epidermal differentiation (16). In addition, the epidermis demonstrates focal abnormalities in epidermal maturation, including a failure of suprabasal cells to flatten progressively as well as nuclear atypia. Electron microscopy reveals additional defects. Keratohyalin granules are decreased in number and premature lipid secretion is noted in the mid-stratum granulosum in -ENaC knockout mice. We therefore conclude that normal lipid secretion requires full channel activity, since -ENaC transgenic rescue mice with ~15% of residual ENaC activity retain this premature lipid secretion (12, 16). Epidermal differentiation is not influenced by a reduction of ENaC activity, as demonstrated in the mouse model for pseudohypoaldosteronism. Only complete abolishment of ENaC function in -ENaC null mutant mice results in altered epidermal differentiation (16).

"Galvanotaxis may be one of the mechanisms used by keratinocytes to guide wound closure, but the channel(s) involved in those processes is still unknown."

	How ENaC may trigger normal differentiation of keratinocytes

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
Increased extracellular calcium may serve as a primary trigger for keratinocyte differentiation. Calcium-responsive cells, like parathyroid cells, express on their surface a low-affinity transmembrane calcium receptor. Binding of calcium and/or other divalent or trivalent cations to this receptor triggers downstream signaling pathways, which include phospholipase C (PLC) activation and increase of intracellular calcium (5). Calcium may enter keratinocytes via the CaR, because keratinocytes from CaR-deficient mice did not respond to extracellular calcium. This suggests that the full-length CaR is required to mediate calcium signaling in keratinocytes (Table 1) (14).

We propose that calcium enters the keratinocyte via the CaR that activates phosphoinositide-specific PLC. This leads to the formation of membrane diacylglycerol and soluble inositol 1,4,5-triphosphate (IP₃). IP₃ diffuses rapidly in the cytosol and binds to the IP₃ receptor, which stimulates the release of Ca²⁺ from internal stores (5). ENaC might be activated by a Ca²⁺-sensitive process, e.g., via MAPK. Sodium entry might depolarize the membrane, thereby allowing Ca²⁺ influx via, for example, voltage-gated calcium channels. Although the Ca²⁺-permeable channels in the granular-layer keratinocytes have not yet been characterized by molecular, electrophysiological, and pharmacological methods, ion substitution experiments suggest that these keratinocytes express T- or L-type voltage-sensitive Ca²⁺ channels (6). Moreover, raised intracellular Ca²⁺ blocks lipid secretion in a manner that is reversible by L-type channel blockers (15).

Thus abolishing Na⁺ influx through the ENaC may hyperpolarize the membrane and decrease Ca²⁺ influx, thereby allowing unregulated lipid secretion. Decreased Ca²⁺ influx also inhibits the posttranslational processing of profilaggrin to filaggrin, which are major constituents of these granules. This might explain the presence of abnormal keratohyalin granules in -ENaC knockout mice.

	Perspectives and conclusion

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 
Ionic fluxes might play an important role in skin differentiation processes, as shown by identification of mutations in two calcium pumps leading to severe skin pathologies (Hailey-Hailey disease and Darier disease). In Hailey-Hailey disease, a mutation in the calcium pump ATP2C1 leads to a skin disease characterized by persistent blisters and erosions of the skin (9). Impaired intercellular adhesion and epidermal blistering occurs in patients with Darier disease, which is caused by mutations in a gene encoding a sarco(endo)plasmic reticulum-Golgi calcium pump (SERCA2) (22). The analysis of ENaC-deficient mice revealed that ENaC expression is required for normal epidermal differentiation, suggesting a novel role of ENaC in skin. Since constitutive inactivation of the -ENaC subunit leads to early postnatal death, functional consequences of ENaC deficiency in adult skin could not be addressed. We have now generated mice exhibiting a conditional ("floxed") allele of the -ENaC gene locus that can be used to induce a tissue-specific knockout of this sodium channel (13, 21). These mice can now be crossed with mice expressing the Cre recombinase in basal keratinocytes either in an inducible or a constitutive manner (e.g., through a keratin 14-driven Cre recombinase). This should lead to inactivation of the ENaC in cells expressing keratin 14, like basal keratinocytes, and consequently to absence of ENaC in all epidermal keratinocytes.

The sodium channel ENaC controls selective aspects of epidermal differentiation, including synthesis of markers of differentiation, keratohyalin granule formation, and lipid secretion, but it is still an open question whether ENaC is implicated in wound repair processes. Tissue-specific gene targeting of this channel will help to clarify its functional role in skin function.

	Acknowledgments

 
Thanks to Friedrich Beermann for suggestions on the manuscript and to Hanspeter Gaeggeler for help with the photographic work. Thanks also to all members of the laboratory for contributing to the research project.

We apologize for having omitted many citations due to space constraints.

The work originating in the laboratory of E. Hummler was supported by grants from the Swiss National Science Foundation, the Novartis Foundation, and the Roche Foundation.

	References

Top Introduction ENaC expression in skin Epidermal barrier function Ionic fluxes in keratinocyte... Consequences of ENaC deficiency... How ENaC may trigger... Perspectives and conclusion References

 

1. Aberer E, Gebhart W, Mainitz M, Pollak A, Reichel G, and Scheibenreiter S. Die Schweissdrüsen beim Pseudohypoaldosteronism. Hautarzt 38: 484–487, 1987.[Medline]
2. Bonny O and Hummler E. Dysfunction of epithelial sodium transport: from human to mouse. Kidney Int 57: 1313–1318, 2000.[CrossRef][ISI][Medline]
3. Brandner JM, Kief S, Grund C, Rendl M, Houdek P, Kuhn C, Tschachler E, Franke WW, and Moll I. Organization and formation of the tight junction system in human epidermis and cultured keratinocytes. Eur J Cell Biol 81: 253–263, 2002.[CrossRef][ISI][Medline]
4. Brouard M, Casado M, Djelidi S, Barrandon Y, and Farman N. Epithelial sodium channel in human epidermal keratinocytes: expression of its subunits and relation to sodium transport and differentiation. J Cell Sci 112: 3343–3352, 1999.[Abstract]
5. Dotto GP. Signal transduction pathways controlling the switch between keratinocyte growth and differentiation. Crit Rev Oral Biol Med 10: 442–457, 1999.[Abstract/Free Full Text]
6. Elias PM, Ahn SK, Denda M, Brown BE, Crumrine D, Kimutai LK, Kämüves L, Lee SH, and Feingold KR. Modulations in epidermal calcium regulate the expression of differentiation-specific markers. J Invest Dermatol 119: 1128–1136, 2002.[CrossRef][ISI][Medline]
7. Furuse M, Hata M, Furuse K, Yoshida Y, Haratake A, Sugitani Y, Noda T, Kubo A, and Tsukita S. Claudin-based tight junctions are crucial for the mammalian epidermal barrier: a lesson from claudin-1-deficient mice. J Cell Biol 156: 1099–1111, 2002.[Abstract/Free Full Text]
8. Garty B-Z. Chronic Pseudomonas colonization of the skin, ear and eyes in a child with type I pseudohypoaldosteronism. Acta Paediatr 88: 472–473, 1999.[CrossRef][Medline]
9. Hu Z, Bionifas JM, Beech J, Bench G, Shigihara T, Ogawa H, Ikeda S, Mauro T, and Epstein EH. Mutations in ATP2C1 encoding a calcium pump cause Hailey-Hailey disease. Nat Genet 24: 61–65, 2000.[CrossRef][ISI][Medline]
10. Hummler E. Epithelial sodium channel, salt intake and hypertension. Curr Hypertens Rep 5: 11–18, 2003.[ISI][Medline]
11. Hummler E, Barker P, Gatzy J, Beermann F, Verdumo C, Schmidt A, Boucher R, and Rossier BC. Early death due to defective neonatal lung liquid clearance in ENaC-deficient mice. Nat Genet 12: 325–328, 1996.[CrossRef][ISI][Medline]
12. Hummler E, Barker P, Talbot C, Wang Q, Verdumo C, Grubb B, Gatzy J, Burnier M, Horisberger J-D, Beermann F, Boucher R, and Rossier BC. A mouse model for the renal salt-wasting syndrome pseudohypoaldosteronism. Proc Natl Acad Sci 94: 11710–11715, 1997.[Abstract/Free Full Text]
13. Hummler E, Mérillat A-M, Rubera I, Rossier B, and Beermann F. Conditional gene targeting of the Scnn1a (alpha ENaC) gene locus. Genesis 32: 169–172, 2002.[CrossRef][Medline]
14. Komuves L, Oda Y, Tu CL, Chang WH, Ho-Pao CL, Mauro T, and Bikle DD. Epidermal expression of the full-length extracellular calcium-sensing receptor is required for normal keratinocyte differentiation. J Cell Physiol 192: 45–54, 2002.[CrossRef][ISI][Medline]
15. Lee SH, Elias PM, Proksch E, Menon GK, Mao-Quiang MM, and Feingold KR. Calcium and potassium are important regulators of barrier homeostasis in murine epidermis. J Clin Invest 89: 530–538, 1992.[Medline]
16. Mauro T, Guitard M, Oda Y, Crumrine D, Komuves L, Behne M, Rassner U, Elias PM, and Hummler E. The ENaC channel is required for normal epidermal differentiation. J Invest Dermatol 118: 589–594, 2002.[CrossRef][ISI][Medline]
17. Oda Y, Imanzahrei A, Kwong A, Komuves L, Elias PM, Largman C, and Mauro T. Epithelial sodium channel are upregulated during epidermal differentiation. J Invest Dermatol 113: 796–801, 1999.[CrossRef][Medline]
18. Olivier R, Scherrer U, Horisberger J-D, Rossier BC, and Hummler E. Lung Edema Clearance: 20 Years of Progress: Selected Contribution: Limiting Na⁺ transport rate in airway epithelia from -ENaC transgenic mice: a model for pulmonary edema. J Appl Physiol 93: 1881–1887, 2002.[Abstract/Free Full Text]
19. Rossier BC, Pradervand S, Schild L, and Hummler E. Epithelial sodium channel and the control of sodium balance: interaction between genetic and environmental factors. Ann Rev Physiol 64: 877–897, 2002.[CrossRef][ISI][Medline]
20. Roudier-Pujol C, Rochat A, Escoubet B, Eugène E, Barrandon Y, Bonvalet JP, and Farman N. Differential expression of epithelial sodium channel subunit mRNAs in rat skin. J Cell Sci 109: 379–385, 1996.[Abstract]
21. Rubera I, Loffing J, Palmer LG, Frindt G, Fowler-Jaeger N, Carroll T, McMahon A, Hummler E, and Rossier BC. Collecting duct specific gene activation of alphaENaC in the mouse kidney does not impair sodium and potassium balance. J Clin Invest 112: 554–565, 2003.[CrossRef][ISI][Medline]
22. Sakuntabhai A, Ruiz-Perez V, Carter S, Jacobsen N, Burge S, Monk S, Smith M, Munro CS, O’Donovan M, Craddock N, Kucherlapati R, Rees JL, Owen M, Lathrop GM, Monaco AP, Stachan T, and Hovnanian A. Mutations in ARP2A2, encoding a Ca²⁺ pump, cause Darier disease. Nat Genet 21: 271–277, 1999.[CrossRef][ISI][Medline]
23. Trollinger DR, Isseroff RR, and Nuccitelli R. Calcium channel blockers inhibit galvanotaxis in human keratinocytes. J Cell Physiol 193: 1–9, 2002.[CrossRef][ISI][Medline]
24. Warner RR. Corneocytes undergo systematic changes in element concentrations across the human inner stratum corneum. J Invest Dermatol 104: 530–536, 1995.[CrossRef][Medline]

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