Storage Temperature Alters the Expression of Differentiation-Related Genes in Cultured Oral Keratinocytes

Purpose Storage of cultured human oral keratinocytes (HOK) allows for transportation of cultured transplants to eye clinics worldwide. In a previous study, one-week storage of cultured HOK was found to be superior with regard to viability and morphology at 12 degrees C compared to 4 degrees C and 37 degrees C. To understand more of how storage temperature affects cell phenotype, gene expression of HOK before and after storage at 4 degrees C, 12 degrees C, and 37 degrees C was assessed. Materials and Methods Cultured HOK were stored in HEPES-and sodium bicarbonate-buffered Minimum Essential Medium at 4 degrees C, 12 degrees C, and 37 degrees C for one week. Total RNA was isolated and the gene expression profile was determined using DNA microarrays and analyzed with Partek Genomics Suite software and Ingenuity Pathway Analysis. Differentially expressed genes (fold change > 1.5 and P < 0.05) were identified by one-way ANOVA. Key genes were validated using qPCR. Results Gene expression of cultures stored at 4 degrees C and 12 degrees C clustered close to the unstored control cultures. Cultures stored at 37 degrees C displayed substantial change in gene expression compared to the other groups. In comparison with 12 degrees C, 2,981 genes were differentially expressed at 37 degrees C. In contrast, only 67 genes were differentially expressed between the unstored control and the cells stored at 12 degrees C. The 12 degrees C and 37 degrees C culture groups differed most significantly with regard to the expression of differentiation markers. The Hedgehog signaling pathway was significantly downregulated at 37 degrees C compared to 12 degrees C. Conclusion HOK cultures stored at 37 degrees C showed considerably larger changes in gene expression compared to unstored cells than cultured HOK stored at 4 degrees C and 12 degrees C. The changes observed at 37 degrees C consisted of differentiation of the cells towards a squamous epithelium-specific phenotype. Storing cultured ocular surface transplants at 37 degrees C is therefore not recommended. This is particularly interesting as 37 degrees C is the standard incubation temperature used for cell culture.