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pH-regulated mechanisms account for pigment-type differences in epidermal barrier function.
Roshan Gunathilake1, Nanna Y Schurer, Brenda A Shoo
1Department of Dermatology, Veteran Affairs Medical Center, University of California San Francisco, San Francisco, California 94121, USA. gunathilake@att.net
The Journal of Investigative Dermatology
|January 30, 2009
Summary
Skin pigment type significantly impacts epidermal barrier function. Darker skin (types IV-V) exhibits superior stratum corneum (SC) integrity and faster barrier recovery compared to lighter skin (types I-II), driven by pH differences.
Area of Science:
- Dermatology
- Skin Biology
- Epidermal Physiology
Background:
- Skin pigmentation, categorized by the Fitzpatrick scale, varies globally.
- Epidermal function, including stratum corneum (SC) integrity and barrier homeostasis, is crucial for skin health.
- The relationship between skin pigment type and specific epidermal functions remains incompletely understood.
Purpose of the Study:
- To investigate the influence of skin pigment type on epidermal function, specifically stratum corneum (SC) pH, permeability barrier homeostasis, and SC integrity.
- To compare these functions between individuals with lighter skin (pigment type I-II) and darker skin (pigment type IV-V).
Main Methods:
- Studied stratum corneum (SC) pH, permeability barrier homeostasis, and SC integrity in populations with pigment type I-II versus IV-V skin.
- Assessed transepidermal water loss (TEWL) changes with sequential tape strippings to evaluate SC integrity.
- Measured epidermal lipid content, lamellar body production, serine protease activity, and cathepsin-D activity.
- Examined melanocyte dendrite acidity and melanosome transfer to the SC.
Main Results:
- Subjects with pigment type IV-V skin exhibited lower SC surface pH (approx. 0.5 U), enhanced SC integrity, and more rapid barrier recovery than type I-II subjects.
- Enhanced barrier function in type IV-V skin was linked to increased epidermal lipid content, lamellar body production, and reduced acidity.
- Compromised SC integrity in type I-II skin correlated with increased serine protease activity and accelerated desmoglein-1 (DSG-1)/corneodesmosome degradation.
- Type IV-V skin showed persistent DSG-1-positive corneodesmosomes, with cathepsin-D activity preventing increased SC thickness.
- Adjusting the pH of type I-II SC to type IV-V levels improved epidermal function.
- Melanocytes in type IV-V skin had more acidic dendrites and transferred more melanosomes to the SC, potentially contributing to lower SC pH.
Conclusions:
- Significant differences in epidermal structure and function exist between skin pigment types, primarily driven by pH variations.
- Lower SC pH in darker skin types (IV-V) enhances epidermal barrier function and integrity.
- Higher SC pH in lighter skin types (I-II) is associated with compromised barrier function due to increased protease activity.
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