Cobalt chloride-simulated hypoxia elongates primary cilia in immortalized human retina pigment epithelial-1 cells

Abstract

Primary cilia are microtubule-based organelles that are involved in sensing micro-environmental cues and regulating cellular homeostasis via triggering signaling cascades. Hypoxia is one of the most common environmental stresses that organ and tissue cells may often encounter during embryogenesis, cell differentiation, infection, inflammation, injury, cerebral and cardiac ischemia, or tumorigenesis. Although hypoxia has been reported to promote or inhibit primary ciliogenesis in different tissues or cultured cell lines, the role of hypoxia in ciliogenesis is controversial and still unclear. Here we investigated the primary cilia change under cobalt chloride (CoCl₂)-simulated hypoxia in immortalized human retina pigment epithelial-1 (hTERT RPE-1) cells. We found CoCl₂ treatment elongated primary cilia in a time- and dose-dependent manner. The prolonged cilia recovered back to near normal length when CoCl₂ was washed out from the cell culture medium. Under CoCl₂-simulated hypoxia, the protein expression levels of HIF-1/2α and acetylated-α-tubulin (cilia marker) were increased, while the protein expression level of Rabaptin-5 is decreased during hypoxia. Taken together, our results suggest that hypoxia may elongate primary cilia by downregulating Rabaptin-5 involved endocytosis. The coordination between endocytosis and ciliogenesis may be utilized by cells to adapt to hypoxia.

Keywords: Cilia length; Cobalt chloride; Endocytosis; Hypoxia; Primary ciliogenesis; Rabaptin-5.