39.7: 皮肤表皮干细胞的更新

皮肤分为表皮、真皮和皮下组织，即皮肤的最外层、中层和内层。人类表皮层会定期进行更新，旧的、死亡的细胞被新细胞取代。表皮干细胞（EpiSCs）分裂并分化以补充丢失的细胞。为了完成更新过程，一些EpiSCs会不断自我更新。相比之下，少数EpiSCs会分化为过渡增殖细胞，这些细胞随后会形成棘细胞或角细胞，接着是颗粒细胞，并最终变成死亡的角质鳞片，这些鳞片会定期从皮肤上脱落。

为了维持更新过程，应该控制和调节许多因素。 其中包括干细胞和转运扩增或 TA 细胞分裂率、细胞离开基底层和分化所需的时间，以及最后去除老细胞和死亡细胞。 当细胞开始分化时，它们表达不同的角蛋白分子。 基底细胞表达角蛋白标记物K5和K14，棘细胞表达K1和K10，颗粒细胞表达聚丝蛋白原和兜蛋白，而角化细胞表达聚丝蛋白。 在伤口或组织损伤的情况下，上皮角质形成细胞迁移到伤口部位并使该部位重新上皮化。

表皮干细胞通过干细胞表达的β1-整合素附着在基底层。整合素将基底细胞的肌动蛋白纤维与细胞外基质连接起来。除了附着之外，整合素还在信号通路中发挥作用。其他信号通路包括 Wnt、Hedgehog、Notch、BMP 和 EGF，它们是更新和维持表皮细胞所必需的。这些途径中任何一个的突变都可能导致皮肤癌。

表皮是人体最外层的保护层。它通过位于基底层的表皮干细胞或 EpiSCs 的分化不断自我更新。

EpiSCs 表达与底层基底膜结合的整合素。EpiSCs-基底膜相互作用调节 EpiSCs 的增殖和分化。

EpiSCs 自我更新并依次分化形成由棘细胞、颗粒细胞和死亡角化鳞屑组成的多层表皮。

两种模型用于解释 EpiSC 分化。

在分层模型中，EpiSCs 不对称分裂形成增殖子细胞和转运扩增或 TA 细胞。TA 细胞进一步分化为不同的表皮细胞类型。

在随机模型中，每个子细胞将随机保持增殖或形成分化的表皮细胞。

• Epidermis Regeneration - The process of skin renewal done by stem cells in the epidermis layer.
• Transit Amplifying Cells - Differentiate from stem cells, contribute to renewal process of epidermis.
• Keratinized Squames - Dead epidermal cells that are routinely shed off the skin.
• β1-integrins - Protein structures that help stem cells attach to the basal layer.
• Signaling Pathways - Communication channels for cells, including Wnt, Hedgehog, Notch, BMP, and EGF. Crucial for epidermal renewal and maintenance.

• Define Epidermis Regeneration – Explain its relation to skin renewal (e.g., Epidermis regeneration).
• Contrast Stem Cells vs Transit Amplifying Cells – Explain their roles in skin renewal (e.g., stem cell renewal).
• Explore Keratinized Squames – Description of their formation and shedding (e.g., dead keratinized cells).
• Explain the Role of β1-integrins – Their role in maintaining the basal attachment of stem cells.
• Apply the Understanding of Signaling Pathways – Their roles in epidermis maintenance and the links to potential health issues, for instance, skin cancer.

• What is epidermis regeneration and how does it relate to skin renewal?
• How do stem cells and transit amplifying cells contribute to the renewal of the epidermis?
• What are keratinized squames, and how are they routinely shed off?

• Students – Gaining comprehension on epidermis regeneration and how it supports our understanding of skin biology.
• Educators – Provides a clear educational framework on the topic of skin biology and epidermis renewal.
• Researchers – Explore the elements of skin renewal and repair for medical science or dermatology.
• Anyone Interested in Biology – Offers a deeper understanding of the human body, particularly in the area of skin biology and regeneration.