The Silk-protein Sericin Induces Rapid Melanization of Cultured Primary Human Retinal Pigment Epithelial Cells by Activating the NF-κB Pathway.

J R Eidet,L Pasovic,S Reppe,O K Olstad,I G Fostad,A Z Khan,D F Chen,T Lyberg,T P Utheim

doi:10.1038/srep22671

Abstract

Restoration of the retinal pigment epithelial (RPE) cells to prevent further loss of vision in patients with age-related macular degeneration represents a promising novel treatment modality. Development of RPE transplants, however, requires up to 3 months of cell differentiation. We explored whether the silk protein sericin can induce maturation of primary human retinal pigment epithelial (hRPE) cells. Microarray analysis demonstrated that sericin up-regulated RPE-associated transcripts (RPE65 and CRALBP). Upstream analysis identified the NF-κB pathway as one of the top sericin-induced regulators. ELISA confirmed that sericin stimulates the main NF-κB pathway. Increased levels of RPE-associated proteins (RPE65 and the pigment melanin) in the sericin-supplemented cultures were confirmed by western blot, spectrophotometry and transmission electron microscopy. Sericin also increased cell density and reduced cell death following serum starvation in culture. Inclusion of NF-κB agonists and antagonists in the culture medium showed that activation of the NF-κB pathway appears to be necessary, but not sufficient, for sericin-induced RPE pigmentation. We conclude that sericin promotes pigmentation of cultured primary hRPE cells by activating the main NF-κB pathway. Sericin’s potential role in culture protocols for rapid differentiation of hRPE cells derived from embryonic or induced pluripotent stem cells should be investigated.

Highlights

Sometimes necessitating a total culture period of up to 3 months[13]
Despite the rare occurrence of infections following the use of fetal bovine serum (FBS), measures taken to avoid both the risk of infections and standardize the culture protocols are most welcomed by regulatory authorities
We explored the potential of using the silk protein sericin as serum-substitute in culture medium to induce maturation of primary human retinal pigment epithelial cells

Summary

Introduction

Sometimes necessitating a total culture period of up to 3 months[13]. Cutting down the time necessary for producing differentiated RPE reduces costs of production and lessens the risk of infection during prolonged cultures. It has been recognized to increase cell proliferation in serum-free media[16], promote antioxidant effects[17], inhibit the melanogenesis enzyme tyrosinase[17], enhance wound healing[18] and support the growth and attachment of fibroblasts[18]. Replacing serum with sericin could dramatically reduce the risk of infections, which for animal derived components may be severe, for the patient, and for the larger community[21]. Despite the rare occurrence of infections following the use of fetal bovine serum (FBS), measures taken to avoid both the risk of infections and standardize the culture protocols are most welcomed by regulatory authorities. We explored the potential of using the silk protein sericin as serum-substitute in culture medium to induce maturation of primary human retinal pigment epithelial cells (hRPE). Our results revealed a surprising effect of sericin on promoting hRPE maturation by activating the NF-κ B pathway

Methods

Results

Conclusion