Basal Sodium-Dependent Vitamin C Transporter 2 polarization in choroid plexus explant cells in normal or scorbutic conditions

Ascorbic acid and its transporter SVCT2, affect radial glia cells differentiation in postnatal stages

Radial glia (RG) cells generate neurons and glial cells that make up the cerebral cortex. Both in rodents and humans, these stem cells remain for a specific time after birth, named late radial glia (lRG). The knowledge of lRG and molecules that may be involved in their differentiation is based on very limited data. We analyzed whether ascorbic acid (AA) and its transporter SVCT2, are involved in lRG cells differentiation. We demonstrated that lRG cells are highly present between the first and fourth postnatal days. Anatomical characterization of lRG cells, revealed that lRG cells maintained their bipolar morphology and stem-like character. When lRG cells were labeled with adenovirus-eGFP at 1 postnatal day, we detected that some cells display an obvious migratory neuronal phenotype, suggesting that lRG cells continue generating neurons postnatally. Moreover, we demonstrated that SVCT2 was apically polarized in lRG cells. In vitro studies using the transgenic mice SVCT2+/- and SVCT2tg (SVCT2-overexpressing mouse), showed that decreased SVCT2 levels led to accelerated differentiation into astrocytes, whereas both AA treatment and elevated SVCT2 expression maintain the lRG cells in an undifferentiated state. In vivo overexpression of SVCT2 in lRG cells generated cells with a rounded morphology that were migratory and positive for proliferation and neuronal markers. We also examined mediators that can be involved in AA/SVCT2-modulated signaling pathways, determining that GSK3-β through AKT, mTORC2, and PDK1 is active in brains with high levels of SVCT2/AA. Our data provide new insights into the role of AA and SVCT2 in late RG cells.

Ascorbate and its transporter SVCT2: The dynamic duo's integrated roles in CNS neurobiology and pathophysiology

Ascorbate is a small antioxidant molecule essential for the proper development and function of the brain. Ascorbate is transported into the brain and between brain cells via the Sodium vitamin C co-transporter 2 (SVCT2). This review provides an in-depth analysis of ascorbate's physiology, including how ascorbate is absorbed from food into the CNS, emphasizing cellular mechanisms of ascorbate recycling and release in different CNS compartments. Additionally, the review delves into the various functions of ascorbate in the CNS, including its impact on epigenetic modulation, synaptic plasticity, and neurotransmission. It also emphasizes ascorbate's role on neuromodulation and its involvement in neurodevelopmental processes and disorders. Furthermore, it analyzes the relationship between the duo ascorbate/SVCT2 in neuroinflammation, particularly its effects on microglial activation, cytokine release, and oxidative stress responses, highlighting its association with neurodegenerative diseases, such as Alzheimer's disease (AD). Overall, this review emphasizes the crucial role of the dynamic duo ascorbate/SVCT2 in CNS physiology and pathology and the need for further research to fully comprehend its significance in a neurobiological context and its potential therapeutic applications.

Role of vitamin C and SVCT2 in neurogenesis

Different studies have established the fundamental role of vitamin C in proliferation, differentiation, and neurogenesis in embryonic and adult brains, as well as in in vitro cell models. To fulfill these functions, the cells of the nervous system regulate the expression and sorting of sodium-dependent vitamin C transporter 2 (SVCT2), as well as the recycling of vitamin C between ascorbic acid (AA) and dehydroascorbic acid (DHA) via a bystander effect. SVCT2 is a transporter preferentially expressed in neurons and in neural precursor cells. In developmental stages, it is concentrated in the apical region of the radial glia, and in adult life, it is expressed preferentially in motor neurons of the cerebral cortex, starting on postnatal day 1. In neurogenic niches, SVCT2 is preferentially expressed in precursors with intermediate proliferation, where a scorbutic condition reduces neuronal differentiation. Vitamin C is a potent epigenetic regulator in stem cells; thus, it can induce the demethylation of DNA and histone H3K27m3 in the promoter region of genes involved in neurogenesis and differentiation, an effect mediated by Tet1 and Jmjd3 demethylases, respectively. In parallel, it has been shown that vitamin C induces the expression of stem cell-specific microRNA, including the Dlk1-Dio3 imprinting region and miR-143, which promotes stem cell self-renewal and suppresses de novo expression of the methyltransferase gene Dnmt3a. The epigenetic action of vitamin C has also been evaluated during gene reprogramming of human fibroblasts to induced pluripotent cells, where it has been shown that vitamin C substantially improves the efficiency and quality of reprogrammed cells. Thus, for a proper effect of vitamin C on neurogenesis and differentiation, its function as an enzymatic cofactor, modulator of gene expression and antioxidant is essential, as is proper recycling from DHA to AA by various supporting cells in the CNS.

Transporter-Mediated Drug Delivery

Transmembrane transport of small organic and inorganic molecules is one of the cornerstones of cellular metabolism. Among transmembrane transporters, solute carrier (SLC) proteins form the largest, albeit very diverse, superfamily with over 400 members. It was recognized early on that xenobiotics can directly interact with SLCs and that this interaction can fundamentally determine their efficacy, including bioavailability and intertissue distribution. Apart from the well-established prodrug strategy, the chemical ligation of transporter substrates to nanoparticles of various chemical compositions has recently been used as a means to enhance their targeting and absorption. In this review, we summarize efforts in drug design exploiting interactions with specific SLC transporters to optimize their therapeutic effects. Furthermore, we describe current and future challenges as well as new directions for the advanced development of therapeutics that target SLC transporters.

SVCT2-GLUT1-mediated ascorbic acid transport pathway in rat dental pulp and its effects during wound healing

Ascorbic acid (AA; vitamin C) plays a crucial role in the biosynthesis and secretion of collagen to produce the organic matrix of hard tissues. Nevertheless, the detailed mechanism by which AA induces reparative dentinogenesis is still unknown. This study aimed to investigate the pathway and function of AA during wound healing in a rat pulpotomy model. Sodium-dependent vitamin C transporter (SVCT) 2 and glucose transporter (GLUT) 1 were detected in odontoblasts, endothelial cells, and nerve fibers in normal pulp tissues. SVCT2 and GLUT1 were also expressed in odontoblast-like cells in pulpotomized tissues of Wistar rats, and immunopositive cells of SVCT2 were significantly increased at 5 days after pulpotomy (p < 0.05). By contrast, osteogenic disorder Shionogi (ODS) rats, which cannot generate AA, also expressed SVCT2 and GLUT1 in normal and wound healing conditions. However, in ODS rats, when compared with the AA-addition group, the formation of dentin bridges in the AA-loss group was not evident, a layer of osteopontin was significantly increased beneath the wound surface (p < 0.05), and alpha smooth muscle actin at the odontoblast-like cells observed along this layer was significantly increased (p < 0.05), but not Nestin. Moreover, the amounts of type 1 collagen generated in the reparative dentin and beneath the wound healing site were significantly diminished (p < 0.05). Macrophages expressing CD68 and CD206 increased beneath the wound site. Hence, AA may be involved in odontoblast-like cell differentiation and anti-inflammatory response during dental pulp wound healing. Our results provide new insights into the function of AA through SVCT2 and GLUT1 in reparative dentinogenesis and may help in developing new therapeutic targets for dental pulpal disease.

Salmonella Typhimurium Infection Reduces the Ascorbic Acid Uptake in the Intestine

Salmonella Typhimurium infection of the gastrointestinal tract leads to damage that compromises the integrity of the intestinal epithelium and results in enterocolitis and inflammation. Salmonella infection promotes the expression of inflammasome NLRP3, leading to activation and release of proinflammatory cytokines such as IL-1β, and the infected host often displays altered nutrient levels. To date, the effect of Salmonella infection and proinflammatory cytokine IL-1β on the intestinal uptake of ascorbic acid (AA) is unknown. Our results revealed a marked decrease in the rate of AA uptake in mouse jejunum infected with Salmonella wild type (WT). However, the nonpathogenic mutant (Δ invA Δ spiB) strain did not affect AA uptake. The decrease in AA uptake due to Salmonella WT infection is accompanied by significantly lower expression of mouse (m)SVCT1 protein, mRNA, and hnRNA levels. NLRP3 and IL-1β expression levels were markedly increased in Salmonella-infected mouse jejunum. IL-1β-exposed Caco-2 cells displayed marked inhibition in AA uptake and significantly decreased hSVCT1 expression at both protein and mRNA levels. Furthermore, the activity of the SLC23A1 promoter was significantly inhibited by IL-1β exposure. In addition, GRHPR (a known SVCT1 interactor) protein and mRNA expression levels were significantly reduced in Salmonella-infected mouse jejunum. These results indicate that Salmonella infection inhibits AA absorption in mouse jejunum and IL-1β-exposed Caco-2 cells. The observed inhibitory effect may partially be mediated through transcriptional mechanisms.

In Vitro Models of the Blood–Cerebrospinal Fluid Barrier and Their Applications in the Development and Research of (Neuro)Pharmaceuticals

The pharmaceutical research sector has been facing the challenge of neurotherapeutics development and its inherited high-risk and high-failure-rate nature for decades. This hurdle is partly attributable to the presence of brain barriers, considered both as obstacles and opportunities for the entry of drug substances. The blood–cerebrospinal fluid (CSF) barrier (BCSFB), an under-studied brain barrier site compared to the blood–brain barrier (BBB), can be considered a potential therapeutic target to improve the delivery of CNS therapeutics and provide brain protection measures. Therefore, leveraging robust and authentic in vitro models of the BCSFB can diminish the time and effort spent on unproductive or redundant development activities by a preliminary assessment of the desired physiochemical behavior of an agent toward this barrier. To this end, the current review summarizes the efforts and progresses made to this research area with a notable focus on the attribution of these models and applied techniques to the pharmaceutical sector and the development of neuropharmacological therapeutics and diagnostics. A survey of available in vitro models, with their advantages and limitations and cell lines in hand will be provided, followed by highlighting the potential applications of such models in the (neuro)therapeutics discovery and development pipelines.

Identification of an exporter that regulates vitamin C supply from blood to the brain

Vitamin C (VC) distribution in our body requires VC transporters. However, mammalian VC exporters are yet to be identified. Herein, to unravel this long-standing mystery, we focused on the pathways whereby VC moves from blood to the brain, which should require a VC entrance and exit system composed of an importer and a latent exporter. Via cell-based transport analyses of VC efflux and using knockout mice generated via the CRISPR-Cas9 system, we identified GLUT12/SLC2A12 as a physiologically important VC efflux protein expressed in the choroid plexus; Glut12/Slc2a12 knockout halved the cerebral VC levels, markedly increased VC accumulation in the choroid plexus, and reduced the cerebrospinal fluid VC levels. These findings facilitate our understanding of VC regulation and the physiological impact of VC in our body.

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A long-standing mystery in vitamin C handling in mammalians was uncovered

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GLUT12 was identified as a physiologically important vitamin C efflux protein—VCEP

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GLUT12 is expressed in the choroid plexus and acts as a vitamin C exporter

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Glut12 knockout halved the cerebral vitamin C levels in mice

Histone deacetylase inhibitors regulate vitamin C transporter functional expression in intestinal epithelial cells

Intestinal absorption of vitamin C in humans is mediated via the sodium-dependent vitamin C transporters (hSVCT1 and hSVCT2). hSVCT1 and hSVCT2 are localized at the apical and basolateral membranes, respectively, of polarized intestinal epithelia. Studies have identified low plasma levels of vitamin C and decreased expression of hSVCT1 in patients with several inflammatory conditions including inflammatory bowel disease (IBD). Investigating the underlying mechanisms responsible for regulating hSVCT1 expression are critical for understanding vitamin C homeostasis, particularly in conditions where suboptimal vitamin C levels detrimentally affect human health. Previous research has shown that hSVCT1 expression is regulated at the transcriptional level, however, little is known about epigenetic regulatory pathways that modulate hSVCT1 expression in the intestine. In this study, we found that hSVCT1 expression and function were significantly decreased in intestinal epithelial cells by the histone deacetylase inhibitors (HDACi), valproic acid (VPA), and sodium butyrate (NaB). Further, expression of transcription factor HNF1α, which is critical for SLC23A1 promoter activity, was significantly down regulated in VPA-treated cells. Chromatin immunoprecipitation (ChIP) assays showed significantly increased enrichment of tetra-acetylated histone H3 and H4 within the SLC23A1 promoter following VPA treatment. In addition, knockdown of HDAC isoforms two, and three significantly decreased hSVCT1 functional expression. Following VPA administration to mice, functional expression of SVCT1 in the jejunum was significantly decreased. Collectively, these in vitro and in vivo studies demonstrate epigenetic regulation of SVCT1 expression in intestinal epithelia partly mediated through HDAC isoforms two and three.

Breaking the barrier: In vitro models to study choroid plexus development

The choroid plexus is central to normal brain function by secreting cerebrospinal fluid and dynamically regulating its composition throughout development and homoeostasis. Much of our current understanding of this region of the brain comes from studies in animal models. These fundamental studies have shed light on choroid plexus mechanisms of secretion, barrier function and homoeostatic regulation. However, how these specific mechanisms are regulated in the human choroid plexus is much less understood, due to ethical and technical limitations. A number of recent breakthroughs have enabled a new range of techniques and tools for functional characterisation of choroid plexus development and physiology. With the advance of new technologies such as in vivo imaging, single-cell transcriptomics and in vitro three-dimensional cultures we are now able to address a number of outstanding questions in choroid plexus biology. Here, we discuss some of these recent breakthroughs and we focus in particular on how in vitro models can be a powerful tool to study human cerebrospinal fluid secretion and barrier function.

Dietary Nutrients and Prevention of Alzheimer's disease

Alzheimer's disease is an irrevocable, progressive brain disorder that gradually destroys memory and cognitive skills. One of the extensively studied method of preventing Alzheimer's disease (AD) disease progression is by providing nutritional diet. Several reports have shown that intake of nutritional elements as huperzine A, ursolic acid, vitamins etc. can directly influence pathogenesis of AD. Surprisingly, occurrence of metabolic disorders due to unhealthy diet has been known to be a major environmental causes for AD. It has been noted that AD disease severity can be controlled by supplementing dietary supplements containing huge amounts of health-promoting ingredients. These elements promote cell health, regeneration, and the anti-aging process that specifically interrupt the pathogenic pathways in AD development. Fortunately, incorporating changes in the nutritional content is inexpensive, easy, acceptable, safe, effective, and in most cases free from major adverse events. Many nutritional phytoconstituents such as flavonoids, alkaloids, and terpenoids are still being evaluated in the hope of identifying a successful therapy for AD. This review discusses the therapeutical potential of several key nutrients that have been researched for treating AD treatment and the method of their neuroprotective intervention.

Human CNS barrier-forming organoids with cerebrospinal fluid production

Cerebrospinal fluid (CSF) is a vital liquid, providing nutrients and signaling molecules and clearing out toxic by-products from the brain. The CSF is produced by the choroid plexus (ChP), a protective epithelial barrier that also prevents free entry of toxic molecules or drugs from the blood. Here, we establish human ChP organoids with a selective barrier and CSF-like fluid secretion in self-contained compartments. We show that this in vitro barrier exhibits the same selectivity to small molecules as the ChP in vivo and that ChP-CSF organoids can predict central nervous system (CNS) permeability of new compounds. The transcriptomic and proteomic signatures of ChP-CSF organoids reveal a high degree of similarity to the ChP in vivo. Finally, the intersection of single-cell transcriptomics and proteomic analysis uncovers key human CSF components produced by previously unidentified specialized epithelial subtypes.

Dehydroascorbic acid, the oxidized form of vitamin C, improves renal histology and function in old mice

Oxidative stress and inflammation are crucial factors that increase with age. In the progression of multiple age-related diseases, antioxidants and bioactive compounds have been recognized as useful antiaging agents. Oxidized or reduced vitamin C exerts different actions on tissues and has different metabolism and uptake. In this study, we analyzed the antiaging effect of vitamin C, both oxidized and reduced forms, in renal aging using laser microdissection, quantitative reverse-transcription polymerase chain reaction, and immunohistochemical analyses. In the kidneys of old SAM mice (10 months of age), a model of accelerated senescence, vitamin C, especially in the oxidized form (dehydroascorbic acid [DHA]) improves renal histology and function. Serum creatinine levels and microalbuminuria also decrease after treatment with a decline in azotemia. In addition, sodium-vitamin C cotransporter isoform 1 levels, which were increased during aging, are normalized. In contrast, the pattern of glucose transporter 1 expression is not affected by aging or vitamin C treatment. We conclude that oxidized and reduced vitamin C are potent antiaging therapies and that DHA reverses the kidney damage observed in senescence-accelerated prone mouse 8 to a greater degree.