Primary Cilia Length is Critical to Cellular Mechanotransduction

Abstract

Mechanotransduction is an essential cellular function in a variety of tissues including bone, kidney, and endothelia. The primary cilium is a single immotile organelle protruding from the surface of these cells, and has repeatedly been demonstrated as a critical mechanotransducer in these cell types. When the primary cilium is impaired, these cells have an abrogated response to mechanical stimulation. Here, we demonstrate a method to enhance cellular mechanotransduction, by increasing primary cilia length. To elongate primary cilia, we treated MLO-Y4 osteocytes with fenoldopam, lithium chloride, or vehicle control for 16 hours. We then subjected these cells to oscillatory fluid flow for 1 hour at 1 Hz and 1 Pa wall shear stress. Immediately following flow, cells were lysed, and mRNA expression was analyzed. Cells with longer cilia displayed increased expression of osteogenic markers cyclooxygenase-2 and osteopontin, compared to vehicle control, suggesting that these cells are more mechanosensitive. To discern the role of fenoldopam on cilia length from other cellular processes, we treated cells with IFT88 siRNA_IFT88 is critical for primary cilia formation_which resulted shorter cilia and an abrogated response to fluid flow. Fenoldopam was able to restore cilia length in cells with impaired cilia formation, and rescued flow-induced osteogenic signaling. Together, these data suggest that cells with longer cilia are more mechanosensitive, and that cellular mechanotransduction can easily be modulated by pharmacologically lengthening primary cilia. Primary cilia-mediated mechanotransduction is a critical function in an array of cell types, and numerous diseases, such as polycystic kidney disease and Bardet-Biedl Syndrome, are characterized by impaired cilia function. This work suggests a potential therapeutic strategy to combat such conditions.