Examining interactions of animal cells with chloroplasts and their light-induced responses in in vitro cell culture systems

Abstract

Chloroplasts are organelles that convert light energy into chemical energy in plants. The potential to integrate chloroplasts into animal cells presents an exciting frontier in synthetic biology, allowing for photo-controllable biochemical processes within these cells. However, the lack of well-established in vitro experimental systems to study chloroplast-animal cell interactions remains a significant challenge. This study investigates the behavior of human cervical cancer HeLa cells and mouse macrophage-like J774.1 cells, along with the light-induced responses of these cells, when introduced into culture media containing spinach-derived chloroplasts. Additionally, we examine isolated cells from Elysia marginata, a sacoglossan sea slug known for its unique ability to acquire and retain functional chloroplasts through a process known as kleptoplasty. Our results show that HeLa cells primarily adhere to chloroplasts with minimal intracellular uptake, while J774.1 cells actively engulf them. Co-incubation with chloroplasts increases the rate of cell death upon light irradiation. In contrast, naturally chloroplast-containing cells from E. marginata exhibit minimal light-induced damage. Excessive reactive oxygen species (ROS) production is observed in HeLa and J774.1 cells co-incubated with chloroplasts under light exposure, suggesting that photoinduced ROS generation contributes to cytotoxicity. These findings highlight three different patterns of interactions between animal cells and chloroplasts and underscore the importance of considering ROS generation induced by light exposure when analyzing chloroplast-animal cell interactions in vitro experimental systems.