Senile lentigo or age spots are hyperpigmented macules of skin that commonly develop following long-term exposure to ultraviolet radiation. This condition is caused by accumulation of large numbers of melanosomes (melanin granules) produced by melanocytes within neighboring keratinocytes. However, there is still no consensus regarding the melanosome transfer mechanism in senile lentigo. To date, most pathohistological studies of skin have been two-dimensional and do not provide detailed data on the complex interactions of the melanocyte-keratinocyte network involved in melanosome transfer. We performed a three-dimensional reconstruction of the epidermal microstructure in senile lentigo using three different microscopic modalities to visualize the topological melanocyte-keratinocyte relationship and melanosome distribution. Confocal laser microscopy images showed that melanocyte dendritic processes are more frequently branched and elongated in senile lentigo skin than in normal skin. Serial transmission electron micrographs showed that dendritic processes extend into intercellular spaces between keratinocytes. Focused ion beam-scanning electron micrographs showed that dendritic processes in senile lentigo encircle adjacent keratinocytes and accumulate large numbers of melanosomes. Moreover, melanosomes transferred to keratinocytes are present not only in the supranuclear area but throughout the perinuclear area except on the basal side. The use of these different microscopic methods helped to elucidate the three-dimensional morphology and topology of melanocytes and keratinocytes in senile lentigo. We show that the localization of melanosomes in dendritic processes to the region encircling recipient keratinocytes contributes to efficient melanosome transfer in senile lentigo.

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老年雀斑黑色素细胞和角质形成细胞三维结构分析

老年斑或老年斑是皮肤的色素沉着斑，通常在长期暴露于紫外线辐射后形成。这种情况是由邻近角质形成细胞内的黑色素细胞产生的大量黑色素体（黑色素颗粒）积聚引起的。然而，关于老年斑的黑素体转移机制仍未达成共识。迄今为止，大多数皮肤病理组织学研究都是二维的，并没有提供有关黑素体转移中涉及的黑素细胞-角质形成细胞网络复杂相互作用的详细数据。我们使用三种不同的显微方式对老年雀斑的表皮微观结构进行了三维重建，以可视化拓扑黑素细胞-角质形成细胞关系和黑素体分布。共聚焦激光显微镜图像显示，与正常皮肤相比，老年斑皮肤中的黑色素细胞树突状突起更频繁地分支和伸长。连续透射电子显微照片显示树突状突起延伸到角质形成细胞之间的细胞间隙中。聚焦离子束扫描电子显微照片显示，老年雀斑的树突状突起环绕相邻的角质形成细胞并积累大量黑素体。此外，转移到角质形成细胞的黑素体不仅存在于核上区，而且存在于除基底侧之外的整个核周区。使用这些不同的显微方法有助于阐明老年斑中黑色素细胞和角质形成细胞的三维形态和拓扑结构。