Exposure to sunlight, mainly UVA, leads to typical changes in the features of the skin known as photoaging. UVA irradiation induces the expression of proteases that are responsible for the degradation of the extracellular matrix proteins to results in photoaging; it also downregulates the expression of proteins that are needed for the skin structure. Since, it is known that cells in the neighborhood of irradiated cells, but not directly exposed to it, often manifest responses like their irradiated counterparts, it is important to evaluate if these bystander cells too, can contribute to photoaging. UVA induced cell cycle arrest has been associated with photoaging, from flow cytometry analysis we found that there was an induction of cell cycle arrest at the G₁/S phase in the UVA-bystander cells. The expression of some key photoaging marker genes likes, matrix metalloproteinases (MMP-1, MMP-3, MMP-9), cyclooxygenase-2 (COX-2), collagen1 and elastin were assessed from qRT-PCR. Up-regulation of MMP-1 and COX-2, downregulation of collagen1 and elastin, along with suppression below normal expression for MMP-3 and MMP-9 was observed in the UVA-bystander A375 cells. Our findings suggest that UVA-bystander cells may contribute to the process of photoaging.

暴露于阳光（主要是 UVA）会导致皮肤特征发生典型变化，称为光老化。UVA 照射诱导蛋白酶的表达，这些蛋白酶负责降解细胞外基质蛋白，从而导致光老化；它还下调皮肤结构所需蛋白质的表达。由于已知受辐照细胞附近的细胞（但不直接暴露于其中）通常会表现出与其受辐照对应物一样的反应，因此评估这些旁观者细胞是否也会导致光老化很重要。UVA 诱导的细胞周期停滞与光老化有关，从流式细胞术分析我们发现在 G _{1处诱导细胞周期停滞}UVA-旁观者细胞中的 /S 期。通过 qRT-PCR 评估了一些关键的光老化标记基因如基质金属蛋白酶 (MMP-1、MMP-3、MMP-9)、环氧合酶-2 (COX-2)、胶原蛋白1 和弹性蛋白的表达。在 UVA 旁观者 A375 细胞中观察到 MMP-1 和 COX-2 的上调、collagen1 和弹性蛋白的下调以及 MMP-3 和 MMP-9 低于正常表达的抑制。我们的研究结果表明，UVA 旁观者细胞可能有助于光老化过程。