Induction of the Blood/Brain‐Barrier‐Associated Enzyme Alkaline Phosphatase in Endothelial Cells from Cerebral Capillaries is Mediated Via cAMP

Abstract

The mammalian bloodhain barrier is located at the endothelial cells of the cerebral capillaries. Alkaline phosphatase is associated to a very large extent with these cells and has been established as a marker enzyme for a differentiated bloodhain barrier phenotype in vivo and in vitro. Nevertheless cultured brain capillary endothelial cells (BCEC) lose this marker enzyme because of a cessation of de novo synthesis. Since astrocytes have been shown to possess the capability to re-induce the enzymic activity of alkaline phosphatase in BCEC in vitro we were interested in the second messengers involved in the signal-transduction mechanism of this induction in BCEC. For this reason we treated cultured porcine BCEC with a water-soluble and membrane-permeable analogue of CAMP, 8-(4-~hlorophenylthio)-cAMP (CIPhS-CAMP) in the absence of astrocytes. By means of enzymic activity assays we were able to show that within three days the activity of alkaline phosphatase increased up to sixfold compared with the controls. The total activity of alkaline phosphatase in ClPhS-CAMP-treated BCEC was comparable to that of freshly isolated cells. Addition of cycloheximide inhibited the alkaline phosphatase activity increase. We conclude that cAMP is one of the second messengers involved in the induction of alkaline phosphatase activity in BCEC in vitro.

The Evolving Concept of the Blood Brain Barrier (BBB): From a Single Static Barrier to a Heterogeneous and Dynamic Relay Center

“…Subsequent studies showed that astrocyte-derived signaling to CECs leading to increased expression of tight-junctions was mediated by, e.g., transforming growth factor beta (TGFβ), Sonic hedgehog and Wnt signaling (Siddharthan et al, 2007; Alvarez et al, 2011; Wang et al, 2018; Benz et al, 2019). Moreover, astrocytes regulate expression of alkaline phosphatase and Na-ATPase on CECs via cAMP and IL6, suggesting astrocytes regulate ionic homeostasis (Beuckmann et al, 1995; Sun et al, 1997).…”

Tissue-Nonspecific Alkaline Phosphatase in Central Nervous System Health and Disease: A Focus on Brain Microvascular Endothelial Cells

“…The molecular mechanisms underlying TNAP function in the brain have been studied more thoroughly in neurons compared to BMECs. For an in-depth discussion of TNAP function in neurons, the reader is directed towards these excellent reviews [ 53 , 115 , 116 ]. A study from Deracinois et al was the first to show that inhibition of TNAP using a pan-AP inhibitor (levamisole) in bovine capillary endothelial cells (BCECs) increased cellular barrier permeability to Lucifer Yellow (Pe LY ) [ 74 ].…”

“…Several molecules such as retinol, cyclic AMP (cAMP), glucocorticoids, transforming growth factor-beta (TGF-β), interleukin-6 (IL-6), and basic fibroblast growth factor (bFGF) are known to modulate TNAP activity [ 33 ]. While retinol, cyclic cAMP, glucocorticoids, IL-6, and bFGF have been shown in previous studies to increase TNAP activity [ 115 , 116 , 121 , 122 ], TGF-β has been shown to suppress TNAP activity in brain ECs [ 122 ]. This non-exhaustive list of molecules highlights their potential importance in regulating TNAP function in brain ECs; however, the mechanisms through which these molecules modulate TNAP activity remain to be elucidated.…”

Clinical and Genetic Aspects of Epilepsy

“…While most blood-brain barrier enzymes have been detected at the mRNA level, protein expression and activity of only few enzymes have been demonstrated. These include gamma-glutamyl transpeptidase (Beuckmann et al, 1995), alkaline phosphatase (Beuckmann et al, 1995), aromatic L-amino acid decarboxylase (Betz et al, 1980;Matter & Balda, 2003b), the phase I metabolising enzymes CYP1A1 (Filbrandt et al, 2004), CYP1B1 (Filbrandt et al, 2004), CYP3A4 (Ghosh et al, 2010;Ghosh et al, 2011), andCyp4x1 (Al-Anizy et al, 2006), NADPH-CYP P450 reductase (Chat et al, 1998;Ghersi-Egea et al, 1988;Minn et al, 1991;Ravindranath et al, 1990), epoxide hydrolase (Ghersi-Egea et al, 1988;Minn et al, 1991), and the phase II enzymes, 1-naphthol-UDP-glucuronosyltransferase (Ghersi-Egea et al, 1988) and GSTμ (Shang et al, 2008), and GSTπ (Bauer et al, 2008;Shang et al, 2008). The presence of these enzymes in the brain microvasculature indicates the existence of a metabolic barrier.…”