May 16, 2024
RIKEN
Keio University School of Medicine
An international joint research group—led by Senior Scientist Keitaro Fukuda (part-time lecturer, Department of Dermatology, Keio University School of Medicine) and Team Leader Masayuki Amagai (professor, Department of Dermatology, Keio University School of Medicine) of the Laboratory for Skin Homeostasis, RIKEN Center for Integrative Medical Sciences; Team Leader Atsushi Miyawaki of the Laboratory for Cell Function and Dynamics, RIKEN Center for Brain Science; and full-time lecturer Yoshihiro Ito of the Department of Dermatology, Keio University School of Medicine—has discovered that the stratum corneum, the outermost layer of the skin responsible for the skin barrier function, forms a three-layered structure of stratum corneum pH (potential of hydrogen) to maintain its homeostasis.
The results of this research are expected to contribute to the development of therapeutic strategies for allergic diseases such as atopic dermatitis, which are induced by a decline in skin barrier function.
The international joint research group developed a technique for live imaging of the stratum corneum's pH and resident skin bacteria, and observed the stratum corneum of living mice. They found that the stratum corneum is not merely an accumulation of dead keratinocytes (corneocytes), but differentiates from the bottom up into weakly acidic, acidic, and neutral layers, forming a three-layered pH structure. The pH of the upper layer of the stratum corneum changes in response to the environment and is neutralized by resident skin bacteria under healthy conditions. Staphylococcus aureus, which proliferates during inflammation, was found to invade and multiply at the boundary between the upper and middle layers of the stratum corneum. It was also found that the acidic middle layer of the stratum corneum has a role in defending against bacterial invasion. Furthermore, this three-layered structure of the stratum corneum was found to be suitable for maintaining a constant thickness by activating proteolytic enzymes that exfoliate corneocytes only in the upper layer. Even though corneocytes are dead cells, they form an ingenious mechanism to differentiate and maintain the stratum corneum.
This research was published in the online edition of the scientific journal Nature Communications on May 15.
For the full press release, please see below.