The Role Of Autophagy In Ciliogenesis And Its Underlying Mechanism

Cilium is an important organelle in eukaryotic cells. According to the motion characteristics of cilia, it can be divided into two types, one is called motile cilia that each cell has plenty of cilia swing in the same direction regularly, the other one is called non-motile cilia, such as a primary cilium.There is only one primary cilium per cell. Primary cilium plays pivotal roles in external signals sensing and signal transduction. Primary cilia once thought to be evolutionary relic. In recent years, studies have shown that primary cilium plays an important role in the development and normal physiological activity of tissues and organs in the human body, and its function abnormalities can cause a variety of serious genetic diseases, collectively called ciliopathy. Ciliogenesis is strictly regulated, but the molecular mechanism remains unclear. Autophagy is a cellular catabolic process that contributes to homeostasis and react to the external environmental stimulation, and its abnormalities are often closely related to many diseases, such as neurodegenerative diseases, cancer, aging, type II diabetes. Plenty of studies have shown that autophagy induction and ciliogenesis occurs simultaneously under serum starvation, but researchs about the fuctional relation between the autophagy and ciliogenesis is rare, and the molecular mechanism is still not clear.In this study, we find that blocking of induced autophagy under serum starvation can significantly impaire ciliogenesis. Autophagy can significantly promotes ciliogenesis with rapamycin (mTOR inhibitor) treatment under normal culture condition. Inhibiting basal level autophagy have no significant effect on ciliogenesis. Those data suggest that induced autophagy can significantly promotes ciliogenesis. In order to further testify our results, we find Atg5 (Autophagy protein 5) knockout MEF cells, which is autophagy-deficient, have no significant differences in ciliogenesis under normal culture conditions, compared with wild-type MEF cells, but have significant differences under starvation conditions. Those results suggest that induced autophagy is closely related to primary ciliogenesis, but its inherent molecular mechanism remains unclear.Studies have shown that CP110 (centriolar coiled coil protein 110kDa) must disappear from the mother centrioles in the initial stage of primary ciliogenesis. Our research show inhibition of serum-starvation induced autophagy cause CP110 from the mother centriole unable to disappear, but not in the inhibition of proteasome-dependent ubiquitin degradation pathway. These results suggest the exist of autophagy which degrade CP110 on the mother centrioles. Furthermore, we find that a great quantity of LC3, Microtubule-associated protein 1A/1B-light chain 3,were recruited to centrosome under serum starvation, and this recruitment is decreased significantly after inhibition of autophagic degradation. Basal body is generated at the initial stage of ciliogenesis from mothor centriole where cilium grows. We also find that LC3 positioned at the base of primary cilia. Moreover, knockdown of autophagy-related protein p62 inhibit ciliogenesis. All these data suggest that serum-starvation induced autophagy promote ciliogenesis by the degradation of CP110 from mother centriole. Our study will help us further understand the role of autophagy in ciliogenesis, and it may provides a new way for the future treatment of cilia related diseases through autophagy.