PACAP27 regulates ciliary function in primary cultures of rat brain ependymal cells

High-Speed Video Microscopy of Ependymal Cilia in Brain Organotypic and Cell Culture Models

The wall of the ventricular system within the neuraxis is lined almost entirely by E1 ependymal cells, each of which projects multiple motile cilia from their apical surface into the cerebrospinal fluid (CSF). This specialized layer of E1 cells constitutes the border between the CSF and the brain interstitial fluid (BIF), and by controlling influx and efflux across the CSF to BIF interface, it is increasingly recognized to play an integral role in modulating and maintaining the brain microenvironment. The motile cilia have been shown to be responsive to changes in the CSF microenvironment, and while the physiological role of this mechanism remains incompletely understood, manipulating this control mechanism may influence the brain microenvironment potentially opening a new frontier in therapeutic intervention.In this paper, we describe our techniques for preparing organotypic slices from the murine brain parenchyma and establishing cell cultures of multiciliated ependymal cells from mouse and rat neonatal brain tissue. Our methodology generates a functional readout of ciliary function, specifically high-speed video microscopy (HSVM) enables the quantification of ciliary beat frequency (CBF), and characterization of ciliary beat pattern.

Three types of ependymal cells with intracellular calcium oscillation are characterized by distinct cilia beating properties

Ependymal cells are multiciliated epithelial cells that line the ventricles in the adult brain. Abnormal function or structure of ependymal cilia has been associated with various neurological deficits. For the first time, we report three distinct ependymal cell types, I, II, and III, based on their unique ciliary beating frequency and beating angle. These ependymal cells have specific localizations within the third ventricle of the mouse brain. Furthermore, neither ependymal cell types nor their localizations are altered by aging. Our high-speed fluorescence imaging analysis reveals that these ependymal cells have an intracellular pacing calcium oscillation property. Our study further shows that alcohol can significantly repress the amplitude of calcium oscillation and the frequency of ciliary beating, resulting in an overall decrease in volume replacement by the cilia. Furthermore, the pharmacological agent cilostazol could differentially increase cilia beating frequency in type II, but not in type I or type III, ependymal cells. In summary, we provide the first evidence of three distinct types of ependymal cells with calcium oscillation properties.

Structure and function of the ependymal barrier and diseases associated with ependyma disruption

The neuroepithelium is a germinal epithelium containing progenitor cells that produce almost all of the central nervous system cells, including the ependyma. The neuroepithelium and ependyma constitute barriers containing polarized cells covering the embryonic or mature brain ventricles, respectively; therefore, they separate the cerebrospinal fluid that fills cavities from the developing or mature brain parenchyma. As barriers, the neuroepithelium and ependyma play key roles in the central nervous system development processes and physiology. These roles depend on mechanisms related to cell polarity, sensory primary cilia, motile cilia, tight junctions, adherens junctions and gap junctions, machinery for endocytosis and molecule secretion, and water channels. Here, the role of both barriers related to the development of diseases, such as neural tube defects, ciliary dyskinesia, and hydrocephalus, is reviewed.

A simple method to obtain pure cultures of multiciliated ependymal cells from adult rodents

Ependymal cells form an epithelium lining the ventricular cavities of the vertebrate brain. Numerous methods to obtain primary culture ependymal cells have been developed. Most of them use foetal or neonatal rat brain and the few that utilize adult brain hardly achieve purity. Here, we describe a simple and novel method to obtain a pure non-adherent ependymal cell culture from explants of the striatal and septal walls of the lateral ventricles. The combination of a low incubation temperature followed by a gentle enzymatic digestion allows the detachment of most of the ependymal cells from the ventricular wall in a period of 6 h. Along with ependymal cells, a low percentage (less than 6 %) of non-ependymal cells also detaches. However, they do not survive under two restrictive culture conditions: (1) a simple medium (alpha-MEM with glucose) without any supplement; and (2) a low density of 1 cell/µl. This purification method strategy does not require cell labelling with antibodies and cell sorting, which makes it a simpler and cheaper procedure than other methods previously described. After a period of 48 h, only ependymal cells survive such conditions, revealing the remarkable survival capacity of ependymal cells. Ependymal cells can be maintained in culture for up to 7-10 days, with the best survival rates obtained in Neurobasal supplemented with B27 among the tested media. After 7 days in culture, ependymal cells lose most of the cilia and therefore the mobility, while acquiring radial glial cell markers (GFAP, BLBP, GLAST). This interesting fact might indicate a reprogramming of the cell identity.

Blood-brain interfaces and cerebral drug bioavailability

The low cerebral bioavailability of various drugs is a limiting factor in the treatment of neurological diseases. The restricted penetration of active compounds into the brain is the result of the same mechanisms that are central to the maintenance of brain extracellular fluid homeostasis, in particular from the strict control imposed on exchanges across the blood-brain interfaces. Direct drug entry into the brain parenchyma occurs across the cerebral microvessel endothelium that forms the blood-brain barrier. In addition, local drug concentration measurements and cerebral imaging have clearly shown that the choroid plexuses - the main site of the blood-cerebrospinal fluid (CSF) barrier - together with the CSF circulatory system also play a significant role in setting the cerebral bioavailability of drugs and contrast agents. The entry of water-soluble therapeutic compounds into the brain is impeded by the presence of tight junctions that seal the cerebral endothelium and the choroidal epithelium. The cerebral penetration of many of the more lipid-soluble molecules is also restricted by various classes of efflux transporters that are differently distributed among both blood-brain interfaces, and comprise either multidrug resistance proteins of the ATP-binding cassette superfamily or transporters belonging to several solute carrier families. Expression of these transporters is regulated in various pathophysiological situations, such as epilepsy and inflammation, with pharmacological consequences that have yet to be clearly elucidated. As for brain tumour treatments, their efficacy may be affected not only by the intrinsic resistance of tumour cells, but also by endothelial efflux transporters which exert an even greater impact than the integrity of the endothelial tight junctions. Relevant to paediatric neurological treatments, both blood-brain interfaces are known to develop a tight phenotype very early on in postnatal development, but the developmental profile of efflux transporters still needs to be assessed in greater detail. Finally, the exact role of the ependyma and pia-glia limitans in controlling drug exchanges between brain parenchyma and CSF deserves further attention to allow more precise predictions of cerebral drug disposition and therapeutic efficacy.

High-speed digital imaging of ependymal cilia in the murine brain

The development and health of mammals requires proper ciliary motility. Ciliated epithelia are found in the airways, the uterus and Fallopian tubes, the efferent ducts of the testes, and the ventricular system of the brain. A technique is described for the motion analysis of ependymal cilia in the murine brain. Vibratome sections of the brain are imaged by differential interference contrast microscopy and recorded by high-speed digital imaging. Side views of individual cilia are traced to establish their bending pattern. Tracking of individual cilia recorded in top view allows determination of bend planarity and beat direction. Ciliary beat frequency is determined from line scans of image sequences. The capacity of the epithelium to move fluid and objects is revealed by analyzing the velocity of polystyrene beads added to brain sections. The technique is useful for detailed assessment of how various conditions or mutations affect the fidelity of ciliary motility at the ependyma. The methods are also applicable to other ciliated epithelia, for example, in airways.