Fluoxetine exerts anti-proliferative effect in human epidermal keratinocytes

We have recently shown that fluoxetine (FX) suppressed polyinosinic-polycytidylic acid-induced inflammatory response and endothelin release in human epidermal keratinocytes, via the indirect inhibition of the phosphoinositide 3-kinase (PI3K)-pathway. Because PI3K-signaling is a positive regulator of the proliferation, in the current, highly focused follow-up study, we assessed the effects of FX (14 µM) on the proliferation and differentiation of human epidermal keratinocytes. We found that FX exerted anti-proliferative actions in 2D cultures (HaCaT and primary human epidermal keratinocytes [NHEKs]; 48- and 72-h; CyQUANT-assay) as well as in 3D reconstructed epidermal equivalents (48-h; Ki-67 immunohistochemistry). Importantly, FX did not influence epidermal thickness (hematoxylin-eosin staining), and it did not have a major impact on the differentiation-associated alteration of the gene expression pattern (24-h treatments; RNA-Seq). Moreover, neither keratin (K)-1, nor K10 expression was altered by FX in NHEKs (RT-qPCR) or in 3D epidermal equivalents (semi-quantitative immunohistomorphometry). FX did not influence differentiation-induced up-regulation of occludin (RT-qPCR; NHEKs), and did not alter differentiation-associated barrier forming capacity of epidermal keratinocytes (electrical impedance; Lucifer Yellow penetration assay). Our data indicate that, besides the previously reported combined anti-inflammatory and putative anti-pruritic effects, FX may also suppress proliferation of human epidermal keratinocytes without impairing their differentiation and barrier-forming capacity.