日本研究皮膚科学会 第41回年次学術大会・総会 モーニングセミナー３Epidermis: Sophisticated Information Processing System
- 開催日時 ：
- 会場 ：
- 仙台国際センター Ｂ会場 ２Ｆ 橘
- 主催 ：
- 第41回日本研究皮膚科学会 第41回年次学術大会・総会
- 共催 ：
- 株式会社 資生堂
Epidermis: Sophisticated Information Processing System
傳田光洋（株式会社資生堂グローバルイノベーションセンター主幹研究員 兼 ＪＳＴ ＣＲＥＳＴ研究者）
For a long time, it was considered that the main role of epidermal keratinocytes is to construct the water-impermeable layer, stratum corneum, at the surface of skin. However, recent findings have dramatically changed this image of epidermal keratinocytes, placing them at the forefront of sensory and information processing systems.
As regards sensory systems, human epidermal keratinocytes express a broad range of receptors. For example, multiple thermo-activated receptors, called the transient receptor potential protein (TRP) superfamily, are functionally expressed. Among them, TRPV1 is a polymodal detector of pain-producing heat (>43℃), as well as chemicals, such as capsaicin and protons. TRPV3 and TRPV4 are both activated by high temperature (around 30℃), while TRPM8 and TRPA1 are activated by low temperature (＜17～22℃). A recent study indicated that stimulation of TRPV1 in keratinocytes is sufficient to evoke acute nociception-related responses. In addition, keratinocytes are excited (their intracellular calcium ion concentration is elevated) by many other kinds of mechanical and chemical stimuli. They respond to visible light (400-750 nm) and express rhodopsin-like and opsin-like proteins similar to those found in the retina, and they also respond to sound in the frequency range of 10-30 kHz.
As regards information processing, cultured human keratinocytes exhibit a variety of electro-chemical spatial-temporal patterns similar to those that appear during information processing in the brain. It has been suggested that information derived from tactile stimulation of the skin is processed in the skin. In addition, we have shown that multiple neurotransmitter receptors involved in information processing in the brain are also functionally expressed in keratinocytes. Thus, various kinds of environmental information might be processed by epidermal keratinocytes.
Finally, we have demonstrated that neurotransmitters or hormones that can influence whole-body physiology and psychological state are generated in and released from epidermal keratinocytes. For example, keratinocytes generate and secrete oxytocin, which is involved in behavior, memory and social bonding. Oxytocin produced in epidermal keratinocytes might influence mental state. Epidermal keratinocytes also generate cortisol under conditions of low humidity. Thus, environmental dryness might induce increased cortisol secretion in epidermis of diseased skin characterized by epidermal barrier dysfunction (e.g. in patients with psoriasis or atopic dermatitis) potentially influencing mental state and systemic physiology.
All these findings are consistent with the idea that epidermal keratinocytes serve as an active interface between the body and the environment, sensing a variety of environmental factors, processing the information obtained, and contributing to the regulation of whole-body physiology and psychological condition.