Properly Selected Skin Cancer Treatments Are Very Effective

Abstract

The lower amounts of Ki-67 staining when p16INK4A expression is high suggests that downregulation of proliferation is occurring. This decrease is likely a consequence of its increased inhibitory effects on CDK4/6 and the retinoblastoma pathway, resulting in cell cycle arrest (Ortega et al., 2002) and increased senescence (Alcorta et al., 1996). Unexpectedly, we observed that the level of endogenous p16INK4A expression appeared higher in the p16INK4A overexpression model. We speculate that the presence of recombinant p16INK4A protein might indirectly upregulate endogenous p16INK4A protein through various detrimental factors excreted from an increased number of senescent cells. On the basis of these observations, we decided to explore the biological consequences of silencing p16INK4A in the aged donor LSE model. Here, we saw a dramatic improvement in the morphology of the aged donor LSE, which now resembled that of a much younger donor (Figure 2c and d). A striking difference between these LSEs and the atrophic, non–silenced controls was the substantial increase of Ki-67positive cells in the p16INK4A-silenced cultures with a consequent normalization of terminal differentiation, as detected by the restoration of filaggrin, loricrin, and caspase expression. This was repeated in at least three other aged donor models with similar results. In accordance with the conditional knockout model of Baker et al. (2011), in which senescent p16INK4A-expressing cells were selectively eliminated, and as evidenced by this model’s morphology and biomarkers, our results indicate that the atrophic phenotype can be significantly improved in vitro by selectively silencing the expression of p16INK4A. Collectively, these results further substantiate p16INK4A as a major regulator of aging in the epidermis, thus lending strong support for furthering our knowledge on the function and appearance of aged skin. For human cells obtained from donors, the Declaration of Helsinki protocols were followed; donors gave written, informed consent; and the Stony Brook University IRB approved of the study.