Efficient clearance of apoptotic cells, named efferocytosis, is a fundamental physiological process for tissue development and homeostasis. The contribution of non-professional phagocytes like fibroblasts to efferocytosis has been established, although the underlying mechanisms are not well understood. We recently demonstrated that horizontal DNA transfer can occur through the uptake of apoptotic human papillomavirus-positive cancer cells by human primary fibroblasts leading to their transformation. The aim of this present study was to analyze the cellular and molecular mechanisms that drive the phagocytic activity of human primary fibroblasts in the context of apoptotic cervical cancer cell removal.

Here we provide evidence that human primary fibroblasts engulf late more efficiently than early apoptotic cells, but their phagocytic ability remains limited compared to professional phagocytes such as human monocyte-derived macrophages. The engulfment occurs in a time-, temperature- and calcium-dependent manner. Remodeling of actin-fibers contributes to the biogenesis of apoptotic cell containing-macroendocytic vacuoles. Both morphological analyses and pharmacological approaches confirmed the involvement of actin driven-phagocytosis and likely macropinocytotic mechanisms in apoptotic target internalization. The uptake of apoptotic cells requires phosphatidylserine recognition, which is mainly mediated by phosphatidylserine-receptor brain-specific angiogenesis inhibitor 1. Confocal microscopy analyses with organelle-specific markers revealed that internalized apoptotic material traffics into late phagolysosomes and specific features of microtubule-associated protein 1 light chain 3-associated phagocytosis were observed.

Our in vitro data show that fibroblasts contribute to apoptotic tumor cell removal by phagocytosis and likely macropinocytotic mechanisms. Efferocytosis by fibroblasts involves phosphatidylserine receptor brain-specific angiogenesis inhibitor 1, which participates in subsequent uptake orchestration via actin cytoskeleton remodeling.

Our results highlight the cellular and molecular mechanisms of fibroblast-mediated clearance of apoptotic tumor cells. Consequences regarding alternative mechanism of carcinogenesis or tumor progression should be addressed. This article is protected by copyright. All rights reserved.