Polarized endocytosis and transcytosis in the hypothalamic tanycytes of the rat

Abstract

Four types of tanycytes can be distinguished in the rat hypothalamus: alpha(1) and alpha(2) tanycytes establish an anatomical link between the ventricular cerebrospinal fluid (CSF) and the arcuate nucleus, whereas beta(1) and beta2 tanycytes establish a link between CSF and portal blood. Endocytosis and transcytosis in these cells have been investigated by (1) immunocytochemistry with antibodies against molecular markers of the endocytotic and transcytotic pathways; (2) the administration of wheat germ agglutinin (WGA) into the ventricular or subarachnoidal CSF and following its internalisation by and its routing through tanycytes. The four populations of tanycytes show marked differences concerning the expression and subcellular location of proteins involved in endocytosis and transcytosis, such as clathrin, caveolin-1, Rab4 and ARF6. Thus, beta1,2 tanycytes express caveolin-1 at the ventricular cell pole and at their terminals contacting the portal capillaries, whereas alpha1,2 tanycytes do not, suggesting that caveolae-dependant endocytosis does not occur in the latter and that, in beta1,2 tanycytes, it may occur at both cell poles. In beta1,2 tanycytes, clathrin is only expressed at the ventricular cell pole indicating that clathrin-dependant endocytosis operates for compounds present in the ventricular CSF and not for those exposed to the terminals. This agrees with the property of beta1,2 tanycytes of internalising WGA through the ventricular cell pole but not through the terminals. The subcellular distribution in beta1,2 tanycytes of WGA and of the proteins clathrin and Rab4 indicates that part of the internalised WGA follows the degradative pathway and part is sorted to a transcytotic pathway and that the transcytotic and the secretory pathways might intersect.

Localization of Angiopoietin-1 and Tie2 Immunoreactivity in Rodent Ependyma and Adjacent Blood Vessels Suggests Functional Relationships

“…The observation that tanycytes endocytose substances from the CSF and transport them down their basal processes supports this hypothesis (Peruzzo et al 2004).…”

Astrocytes in the arcuate nucleus and median eminence that take up a fluorescent dye from the circulation express leptin receptors and neuropeptide Y Y1 receptors

“…This has led to a debate about how the diffusion of substances from the median eminence could be restricted. In a series of studies addressing this question it was found that horseradish peroxidase (HRP) injected into either the cisterna magna or the third ventricle, quickly entered the perivascular spaces around the portal vessels in the external zone of the median eminence but no diffusion into the SEZ was observed (Peruzzo et al, 2004). The organisation of the b-tanycytes and the distribution of HRP suggested that the b1-tanycytes limit the dorsal diffusion in the median eminence and that the b2-tanycytes limit the D) or AgRP-immunoreactivity (red in E) did not take up OHSt (blue).…”

Acute injection of ASP in the third ventricle inhibits food intake and locomotor activity in rats

“…New data is emerging, suggesting an active role of tanycytes, cells lining the third ventricle, in controlling the movement of blood-borne molecules to the CSF and also from the CSF to the arcuate nucleus (28,38). It is tempting to speculate that chronically increased plasma ASP may lead to increased central ASP (as with insulin and leptin), and if so, this could induce a similar state of ASP resistance, as is demonstrated with insulin resistance and leptin resistance.…”