Vitamin A Transduction Pathways in Human Arachnoid Granulation Tissue and Culture

Abstract

Abstract: : Purpose: Pseudotumor cerebri (PTC) is a disorder that is defined clinically by elevated intracranial pressure (ICP) which may damage the optic nerve and can lead to blindness. The mechanisms of the various forms of PTC are not fully understood and may result from poor outflow of cerebrospinal fluid (CSF). CSF outflow is thought to occur mainly through the arachnoid granulations (AGs) of the brain into the superior sagittal sinus. Aberrations of vitamin A metabolism have been implicated in abnormalities of CSF dynamics. In calves a deficiency in vitamin A is associated with a thickening of the AG's and an increased CSF pressure. In humans, toxicity due to excess vitamin A is a known cause of secondary PTC. Vitamin A and its metabolites are critical to cell growth and differentiation. In order to understand the mechanism of this disease process, we are investigating the vitamin A signal transduction pathways in human AG tissues and in AG cell culture. Methods: Human AG tissue and arachnoid membrane was recovered within 24 hours post–mortem. Tissue samples were flash frozen and homogenized to extract tissue lysates. Cells were grown to confluence in vitro either from AG explants or from enzyme digestion of AG tissue, and lysates were collected from 1–4 passage from primary culture. Western blot measured expression of bound and unbound forms of vitamin A metabolites, receptors, and binding proteins including: α & ß retinoic acid receptors (αRAR, ßRAR (both 60kDa)), cellular retinoic acid binding protein (CRABP) (16kDa), and retinol binding protein (RBP)(21kDa). Results: See Table. Conclusions: Because CSF pressures have been shown to increase with both hypo and hyper vitaminosis A it follows that metabolism of vitamin A might be directly implicated in the etiology of decreased CSF egress in the diseased state. The presence of these vitamin A associated proteins in AG tissues and AG cell cultures helps to support the importance of vitamin A transport in these tissues. Localization of these proteins is under investigation.  

Keywords: retinoids/retinoid binding proteins • receptors: pharmacology/physiology • metabolism