The Na⁺‐dependent l‐ascorbic acid transporter SVCT2 expressed in brainstem cells, neurons, and neuroblastoma cells is inhibited by flavonoids

Abstract

Ascorbic acid (AA) is best known for its role as an essential nutrient in humans and other species. As the brain does not synthesize AA, high levels are achieved in this organ by specific uptake mechanisms, which concentrate AA from the bloodstream to the CSF and from the CSF to the intracellular compartment. Two different isoforms of sodium–vitamin C co‐transporters (SVCT1 and SVCT2) have been cloned. Both SVCT proteins mediate high affinity Na+‐dependent l‐AA transport and are necessary for the uptake of vitamin C in many tissues. In the adult brain the expression of SVCT2 was observed in the hippocampus and cortical neurons by in situ hybridization; however, there is no data regarding the expression and distribution of this transporter in the fetal brain. The expression of SVCT2 in embryonal mesencephalic neurons has been shown by RT‐PCR suggesting an important role for vitamin C in dopaminergic neuronal differentiation. We analyze SVCT2 expression in human and rat developing brain by RT‐PCR. Additionally, we study the normal localization of SVCT2 in rat fetal brain by immunohistochemistry and in situ hybridization demonstrating that SVCT2 is highly expressed in the ventricular and subventricular area of the rat brain. SVCT2 expression and function was also confirmed in neurons isolated from brain cortex and cerebellum. The kinetic parameters associated with the transport of AA in cultured neurons and neuroblastoma cell lines were also studied. We demonstrate two different affinity transport components for AA in these cells. Finally, we show the ability of different flavonoids to inhibit AA uptake in normal or immortalized neurons. Our data demonstrates that brain cortex and cerebellar stem cells, neurons and neuroblastoma cells express SVCT2. Dose‐dependent inhibition analysis showed that quercetin inhibited AA transport in cortical neurons and Neuro2a cells.

Typical and atypical stem cells in the brain, vitamin C effect and neuropathology

“…By a variety of methods, Caprile and collaborators demonstrated that SVCT2 is highly expressed in the ventricular and subventricular areas of fetal rat brain. Further functional analysis carried out in immature neurons isolated from either embryonic brain cortex or cerebellum showed that SVCT2 is localized in the cellular membrane and is involved in vitamin C uptake in these cells (Caprile et al, 2009). Similar results have been obtained in Neuro2a and HN33.11 cell lines, demonstrating that SVCT2 is critical for vitamin C transport (Caprile et al, 2009).…”

“…Further functional analysis carried out in immature neurons isolated from either embryonic brain cortex or cerebellum showed that SVCT2 is localized in the cellular membrane and is involved in vitamin C uptake in these cells (Caprile et al, 2009). Similar results have been obtained in Neuro2a and HN33.11 cell lines, demonstrating that SVCT2 is critical for vitamin C transport (Caprile et al, 2009). In line with our hypothesis, SVCT2 has also been implicated in neuronal maturation possibly by regulating the differentiation of embryonic cortical precursors into neurons and astrocytes.…”

“…Therefore, SVCTs are the major homeostatic regulators of vitamin C levels in the central nervous system (CNS; Rice, 2000), actively uptaking its reduced form, L-ascorbate (Caprile et al, 2009;Castro et al, 2001;Garcia et al, 2005). L-ascorbate is transported against its concentration gradient ( Daruwala et al, 1999;Tsukaguchi et al, 1999), and thus the energy required for the transport is supplied by sodium exchange through the Na + /K + -ATPase pump (Castro et al, 2001).…”

Vitamin C Transporter (SVCT2) Distribution in Developing and Adult Brains

“…Similarly, studies addressing the effect of physiological brain concentrations of AA have shown that this nutrient promotes differentiation of embryonic cortical precursors into neurons and astrocytes [19]. Expression and polarization of SVCT2 have been studied during rat and human embryonic development in the cortex at 9 weeks of gestation [20,21]. In lissencephaly, SVCT2 is localized in radial glial cells in the ventricular zone, where it is polarized toward the ventricular cavity, and in subapical and intermediate apical progenitors in the subventricular zone [21].…”

Sodium-Dependent Vitamin C Transporter 2 Deficiency Causes Hypomyelination and Extracellular Matrix Defects in the Peripheral Nervous System

“…In our previous work we demonstrated the expression and transport activity of sodiumdependent vitamin C transporter 2 (SVCT2) in Schwann cell cultures (Gess et al, 2010). SVCT2 is thought to be the main ascorbic acid transport protein in the brain and was shown to be expressed in cultured neurons, neuroblastoma cells, hypothalamic glia cells, and choroid epithelia cells (Angelow et al, 2003;Garcia Mde et al, 2005;Caprile et al, 2009). The SVCT2-null mouse dies of brain hemorrhages and lung failure shortly after birth (Sotiriou et al, 2002).…”