Inducible nitric oxide synthase is required for epidermal permeability barrier homeostasis in mice

Abstract

Nitric oxide (NO) regulates a variety of epidermal functions, including epidermal proliferation, differentiation and cutaneous wound healing. However, whether nitric oxide (NO) and its synthetic enzymes regulate epidermal permeability barrier homeostasis is not clear. In the present study, we employed inducible nitric oxide synthase (iNOS) KO mice to explore the role of iNOS in epidermal permeability barrier homeostasis. Our results showed that iNOS mice displayed a comparable levels of basal transepidermal water loss rates, stratum corneum hydration and skin surface pH to their wild‐type mice, but epidermal permeability barrier recovery was significantly delayed both 2 and 4 hours after acute barrier disruption by tape stripping. In parallel, expression levels of mRNA for epidermal differentiation‐related proteins and lipid synthetic enzymes were lower in iNOS KO mice versus wild‐type controls. Topical applications of two structurally unrelated NO donors to iNOS KO mice improved permeability barrier recovery kinetics and upregulated expression levels of mRNA for epidermal differentiation‐related proteins and lipid synthetic enzymes. Together, these results indicate that iNOS and its product regulate epidermal permeability barrier homeostasis in mice.

Role of nitric oxide in regulating epidermal permeability barrier function

“…39,40 However, recent studies by Dang et al demonstrated a need for iNOS in epidermal permeability barrier homeostasis. 22 First, disruption of the epidermal permeability barrier increased expression levels of iNOS mRNA by over onefold in mouse epidermis, consistent with previous findings that barrier disruption increases NO release in the epidermis. 39 While iNOS deficiency delays permeability barrier recovery, topical applications of NO donors largely corrected the permeability barrier F I G U R E 1 Schematic diagram of nitric oxide synthesis abnormality in iNOS knockout mice.…”

“…37 A recent study demonstrated an elevation in iNOS mRNA expression following acute disruption of the epidermal permeability barrier. 22 In addition to enzymatic production of NO, non-enzymatic decomposition of photo-reactive nitrogen oxides can produce NO in the skin. For example, UVA irradiation (40 J/cm 2 ) of either human skin or skin homogenates can increase NO content by ≈90%.…”

“…39 While iNOS deficiency delays permeability barrier recovery, topical applications of NO donors largely corrected the permeability barrier F I G U R E 1 Schematic diagram of nitric oxide synthesis abnormality in iNOS knockout mice. 22 The discrepant results between various studies in iNOS knockout mice likely can be attributed to the differences in methodology. In one study which showed no alterations in barrier recovery in iNOS knockout mice, 40 ears were used to assess barrier recovery.…”

“…Previous studies showed that NO regulates keratinocyte proliferation and differentiation as well as epidermal permeability barrier homeostasis. [20][21][22]…”

Aged and young mice differentially respond to tape‐stripping in epidermal gene expression

“…Barrier disruption was achieved by repeated applications of cellophane tape to both flanks of mouse skin until ≥2-fold increase in transepidermal water loss rates (TEWL), measured with a TM300 probe connected to MPA580 (C&K). 12 Skin samples were collected from mice without tape-stripping and 1 h after tape-stripping. The epidermis was separated from the dermis by heat separation as described previously.…”