Sodium channel Nax is a regulator in epithelial sodium homeostasis
Science Translational Medicine • 4 Nov 2015 • Vol 7, Issue 312 • p. 312ra177 • DOI: 10.1126/scitranslmed.aad0286
Rubbing sodium in a wound
The skin serves as a critical barrier to the outside world; however, little is known about how this barrier returns to homeostasis after it is disturbed. Water loss occurs during many skin disorders, resulting in an increase in extracellular sodium concentration. Now, Xu et al. report that the sodium channel Nax functions as a sodium sensor that contributes to epithelial homeostasis. Nax, which is present in multiple epithelial tissues and up-regulated in scars, increases sodium flux and induces the downstream production of mediators of epithelial cell proliferation and inflammation that may lead to scar formation. Indeed, blocking Nax in animal models decreases scarring and atopic dermatitis–like symptoms, suggesting that Nax may contribute to epithelial homeostasis.
Abstract
The mechanisms by which the epidermis responds to disturbances in barrier function and restores homeostasis are unknown. With a perturbation of the epidermal barrier, water is lost, resulting in an increase in extracellular sodium concentration. We demonstrate that the sodium channel Nax functions as a sodium sensor. With increased extracellular sodium, Nax up-regulates prostasin, which results in activation of the sodium channel ENaC, resulting in increased sodium flux and increased downstream mRNA synthesis of inflammatory mediators. Nax is present in multiple epithelial tissues, and up-regulation of its downstream genes is found in hypertrophic scars. In animal models, blocking Nax expression results in improvement in scarring and atopic dermatitis–like symptoms, both of which are pathological conditions characterized by perturbations in barrier function. These findings support an important role for Nax in maintaining epithelial homeostasis.
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Supplementary Material
Summary
Fig. S1. Nax immunostaining in keratinocytes.
Fig. S2. Expression of Nax and ENaC-α in mouse tissues (C57BL/6).
Fig. S3. Nax downstream gene expression in human primary keratinocytes, and knockdown and overexpression of Nax in HaCaT cells.
Fig. S4. The skin equivalent models used in the study.
Fig. S5. Immunofluorescence staining of Nax, prostasin, and ENaC-α.
Fig. S6. Change of the intracellular sodium concentrations in HaCaT cells.
Fig. S7. Expression of Nax, prostasin, and ENaC-α in stratified HaCaT cells.
Fig. S8. Cluster analysis of the protein kinase phosphorylation array.
Fig. S9. mRNA expression in WNK1 or p38α knockdown HaCaT cells treated with external serine protease.
Fig. S10. Activation of dermal fibroblasts was modulated by cocultured keratinocytes.
Fig. S11. Expression of prostasin in Nax-DsiRNA– or sham-DsiRNA–treated wounds was detected with its specific antibody and visualized with a fluorescently labeled secondary antibody.
Fig. S12. Inhibition of the Nax pathway by DsiRNA.
Fig. S13. Involvement of PAR-2 in the Nax pathway.
Fig. S14. Knockdown of Nax in HaCaT cells.
Table S1. Sequence information used for RNAi.
Table S2. Differentially expressed genes in wild-type and Nax knockdown keratinocytes under the stimulation with high sodium concentration.
Table S3. Sequence information for qPCR primers.
Source data
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Science Translational Medicine
Volume 7 | Issue 312
November 2015
November 2015
Copyright
Copyright © 2015, American Association for the Advancement of Science.
Submission history
Received: 15 July 2015
Accepted: 19 September 2015
Acknowledgments
We would like to acknowledge M. M. Tamkun from the Department of Biochemical Sciences at the Colorado State University, College of Veterinary Medicine, for the full-length human Nax clone. We thank E. Friedrich in the laboratory, A. Mustoe from the University of North Carolina, and K. Stallcup from Northwestern University for the critical reading of the manuscript. Funding: This study was supported by internal funding from the Division of Plastic and Reconstructive Surgery, Northwestern University Feinberg School of Medicine, and in part from the Geneva Foundation a grant to D.J.S. from the JPB Foundation. Author contributions: W.X., S.J.H., D.M.P., D.J.S., K.P.L., R.D.G., and T.A.M. designed the research; W.X., S.J.H., A.Z., S.J., P.X., Z.X., M.Z., J.Z., and S.N.-B. performed the research; D.M.P., D.J.S., and K.P.L. contributed new reagents/analyzed data; and W.X., S.J.H., and T.A.M. wrote the paper. Competing interests: The authors declare that they have no competing interests. Data and materials availability: The microarray data are deposited in the NCBI GEO with a serial record GSE65366.
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