Tohoku J. Exp. Med., 2020 November, 252(3)

Bone Morphogenetic Proteins Inhibit Ciliogenesis of Ependymal Cells in Vitro

KOTARO HIRAOKA,¹ HITOSHI INADA,^2,3 KAZUHIKO YANAI⁴ and NORIKO OSUMI²

¹Division of Cyclotron Nuclear Medicine, Cyclotron and Radioisotope Center, Tohoku University, Sendai, Miyagi, Japan
²Department of Developmental Neuroscience, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
³Laboratory of Health and Sports Science, Division of Biomedical Engineering for Health and Welfare, Tohoku University Graduate School of Biomedical Engineering, Sendai, Miyagi, Japan
⁴Department of Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Ependymal cells have an essential role in regulating the dynamics of the cerebrospinal fluid flow by the movement of their multiple cilia. Impaired generation or function of cilia could cause hydrocephalus due to the disordered dynamics of the cerebrospinal fluid flow. However, molecular bases regulating differentiation of the ependymal cells and their ciliogenesis have not been fully elucidated. We report here that bone morphogenetic proteins (BMPs), growth factors orchestrating tissue architecture throughout the body, inhibit ciliogenesis during ependymal cell differentiation in primary cell culture. Previous in vitro study has reported that ectopic expression of Smad6 and Smad7 promotes differentiation of embryonic stem cells into multi-ciliated ependymal-like cells. Since Smad6 and Smad7 have been known as the intracellular inhibitory factors of the BMP signaling pathway, the activation of the pathway could cause a deficit in ciliogenesis of ependymal cells. To examine whether activation of the pathway affects ciliogenesis, we investigated the effects of two BMPs, BMP2 and BMP4, on the ependymal differentiation of the primary cultured cells prepared from the neonatal mouse brain. Supplementation of BMP2 or BMP4 in culture media significantly reduced the number of cells with multiple cilia among the total cells, while most of the cells expressed FoxJ1, a master regulator of ciliogenesis. Activation of the pathway was confirmed by the phosphorylation of intracellular Smad1/5/8, downstream factors of the BMP receptors. These in vitro results suggest that inhibition of the BMP signaling pathway might be essential for ciliogenesis during the ependymal cell differentiation in vivo.

Keywords —— bone morphogenetic proteins; ciliogenesis; differentiation; ependymal cells; primary cell culture

© 2020 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2020 252, 199-208.

Correspondence: Hitoshi Inada, Ph.D., Department of Developmental Neuroscience, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan.

e-mail: hinada@med.tohoku.ac.jp