Human stem cell-derived retinal epithelial cells activate complement via collectin 11 in response to stress

Giorgia Fanelli,Peter Garred,Steven H Sacks,Conrad A Farrar,Anai Gonzalez-Cordero,Milan Fernando,Magdalena Kloc,Arifa Naeem,Qi Peng,Peter J Gardner,Robin R Ali

doi:10.1038/s41598-017-15212-z

Abstract

Age-related macular degeneration (AMD) is a major cause of blindness and is associated with complement dysregulation. The disease is a potential target for stem cell therapy but success is likely to be limited by the inflammatory response. We investigated the innate immune properties of human induced-pluripotent stem cell (iPSC)-derived RPE cells, particularly with regard to the complement pathway. We focused on collectin-11 (CL-11), a pattern recognition molecule that can trigger complement activation in renal epithelial tissue. We found evidence of constitutive and hypoxia-induced expression of CL-11 in iPS-RPE cells, and in the extracellular fluid. Complement activation on the cell surface occurred in conjunction with CL-11 binding. CL-11 has been shown to activate inflammatory responses through recognition of L-fucose, which we confirmed by showing that fucosidase-treated cells, largely, failed to activate complement. The presence of CL-11 in healthy murine and human retinal tissues confirmed the biological relevance of CL-11. Our data describe a new trigger mechanism of complement activation that could be important in disease pathogenesis and therapeutic interventions.

Highlights

The retinal pigment epithelium (RPE) consists of a monolayer of cells situated between the photoreceptor cells and the choroid and plays a critical role in the visual cycle, maintaining the health of photoreceptor cells by providing nutrients, growth factors and by continually phagocytosing photoreceptor outer segment discs
While transplantation of pluripotent stem cell derived-RPE cells is a promising approach to treat visual disorders, a number of factors may impede success and these include the immune response against the transplanted cells and in particular the potential impact of hypoxia in the local environment during cell preparation or in the retinal niche
In this study we present evidence that the complement pattern recognition molecule CL-11 is broadly expressed in the human eye and in RPE cells generated from human skin fibroblasts

Summary

Introduction

The retinal pigment epithelium (RPE) consists of a monolayer of cells situated between the photoreceptor cells and the choroid and plays a critical role in the visual cycle, maintaining the health of photoreceptor cells by providing nutrients, growth factors and by continually phagocytosing photoreceptor outer segment discs. As HIF pathways are linked to inflammation[6] it is possible that some of the chronic dysregulation of local para-inflammatory responses in the eye associated with AMD7–9 may be driven by RPE hypoxic stress resulting in the aberrant activation of complement on host cells. A number of studies have demonstrated preservation of visual function following the transplantation of stem cell–derived RPE into animal models of retinal degeneration[15,16]. The structure and function of CL-11 are similar to MBL regarding the binding to carbohydrates on pathogens and activating MBL-associated serine proteases (MASPs) to initiate the lectin pathway of complement activation[21,24], resulting in the generation of complement activation products including the membrane attack complex (MAC) formation and targeted cell death. A more detailed knowledge of this relationship may provide insights for understanding the potential inflammatory and immune responses of the host environment to stem cell derived-RPE cells following transplantation

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Conclusion