The advancement of human retinal pigment epithelial cell (hRPE) replacement therapy is partly dependent on optimization of cell culture, cell preservation, and storage medium. This study was undertaken to search for a suitable storage temperature and storage medium for hRPE. hRPE monolayer sheets were cultured under standard conditions at 37°C and then randomized for storage at six temperatures (4, 16, 20, 24, 28, and 37°C) for 7 days. After revealing a suitable storage temperature, hRPE sheets were subsequently stored with and without the silk protein sericin added to the storage medium. Live/dead assay, light microscopy, pH, and phenotypic expression of various proteins were used to assess cell cultures stored at different temperatures. After 7 days of storage, hRPE morphology was best preserved at 4°C. Addition of sericin to the storage medium maintained the characteristic morphology of the preserved cells, and improved pigmentation and levels of pigmentation-related proteins in the cultured hRPE sheets following a 7-day storage period at 4°C.

Epidermal hydration is maintained primarily by natural moisturising factors (NMF), of which free amino acids (AA) are major constituents that are generated by filaggrin degradation. To identify dietary sources that may improve skin dryness of atopic dermatitis (AD), we investigated dietary effects of silk proteins, sericin and fibroin, on epidermal levels of hydration, filaggrins and free AA, as well as PPARγ, peptidylarginine deiminase-3 (PAD3) and caspase-14 proteins involved in filaggrin expression and degradation processes. NC/Nga mice, an animal model of AD, were fed a control diet (group CA: atopic control) or diets with 1 % sericin (group S) or fibroin (group F) for 10 weeks. In group S, epidermal levels of hydration, total filaggrins and total free AA, as well as PPARγ, PAD3 and caspase-14, which were reduced in group CA, were increased to higher or similar levels of a normal control group of BALB/c mice (group C). Furthermore, profilaggrin, a precursor with multiple filaggrin repeats, and three repeat intermediates were increased, while two repeat intermediates and filaggrin were decreased in parallel with increased levels of glutamate and serine, major AA of NMF in group S. Despite increased levels of total filaggrins, total free AA, PPARγ and PAD3, epidermal levels of hydration, glutamate, serine and caspase-14 were not increased, but other minor AA of NMF were highly detected in group F. Dietary sericin improves epidermal hydration in parallel with enhancing profilaggrin expression and degradation into free AA that is coupled with elevated levels of PPARγ, PAD3 and caspase-14 proteins.