Multiple Primary Cilia Modulate the Fluid Transcytosis in Choroid Plexus Epithelium

Abstract

Functional defects in cilia are associated with various human diseases including congenital hydrocephalus. Previous studies suggested that defects in cilia not only disrupt the flow of cerebrospinal fluid (CSF) generated by motile cilia in ependyma lining the brain ventricles, but also cause increased CSF production at the choroid plexus. However, the molecular mechanisms of CSF overproduction by ciliary dysfunction remain elusive. To dissect the molecular mechanisms, choroid plexus epithelial cells (CPECs) were isolated from porcine brain. These cells expressed clusters of primary cilia on the apical surface. Deciliation of CPECs elevated the intracellular cyclic AMP (cAMP) levels and stimulated basolateralto-apical fluid transcytosis, without detrimental effects on other morphological and physiological features. The primary cilia possessed neuropeptide FF (NPFF) receptor 2. In deciliated cells, the responsiveness to NPFF was reduced at nanomolar concentrations. Furthermore, CPECs expressed NPFF precursor along with NPFFR2. An NPFFR antagonist, BIBP3226, increased the fluid transcytosis, suggesting the presence of autocrine NPFF signaling in CPECs for a tonic inhibition of fluid transcytosis. These results suggest that the clusters of primary cilia in CPECs act as a sensitive chemosensor to regulate CSF production.

Structural defects in cilia of the choroid plexus, subfornical organ and ventricular ependyma are associated with ventriculomegaly

“…Compared to the abundant ependymal cilia lining the ventricles, primary cilia on the apical surface of the choroid plexus were rare and occurred in clusters. Examination of cross-sections of 15 month-old wild- type and Bbs6 −/− mouse choroid plexus cilia along the ciliary shaft distal to the transition zone showed occasional clusters of primary cilia with typical derivatives of the 9 + 0 arrangement of microtubule doublets including 8 + 1 axonemes with displacement of one pair of peripheral doublets, and rarely, 7 + 2 axonemes with displacement of 2 pairs of peripheral doublet (Figure 4C, D) in agreement with previous studies [7,9,29,30]. …”

“…In light of the growing body of evidence that choroid plexus primary cilia play an important role in signaling and CSF homeostasis [7-9], we used TEM to examine their ultrastructure in young (P0 and P9) BBS mutant mice as well as in 15 month-old mice when ventriculomegaly had progressed. Seen in cross-section, the choroid plexus epithelium of Bbs1 M390R/M390R mice had multiple intact basal bodies (Figure 4Ac).…”

“…Animal models of hydrocephalus have demonstrated a relationship between cilia defects of the choroid plexus and ependyma and the development of the disorder [[2,5,7-9,25,33,39-41] and references therein]. In this report, we used functional assays and ultrastructural analyses to examine ventriculomegaly in four BBS mutant mouse strains widely used as models of ciliopathies.…”

“…Animal models have implicated damage to or loss of the ependymal layer, reduction in number or loss of its cilia, impaired ependymal cilia motility, dysfunction of the subcommissural organ (SCO), and aqueduct stenosis in the development of hydrocephalus [[2,5]; and references therein]. Further, primary cilia on the apical surface of the choroid plexus epithelium contribute to CSF homeostasis by acting as pressure sensors or as chemosensors that regulate CSF production, osmolarity, or CSF transcytosis from the choroid plexus epithelium into the ventricles via a cilia-based receptor and autonomic system of regulation [6-9]. …”

Motile Cilia and Brain Function: Ependymal Motile Cilia Development, Organization, Function and Their Associated Pathologies

“…Defects in ependymal motile cilia are responsible for only some forms of hydrocephalus. For example, excess CSF production by the choroid plexus also leads to hydrocephalus but is primarily due to chemosensory defects of primary cilia in the choroid plexus cells (Banizs et al 2005 ;Narita et al 2010 ) .…”