Ganglioside GD3 is required for neurogenesis and long-term maintenance of neural stem cells in the postnatal mouse brain

MeHg Suppressed Neuronal Potency of Hippocampal NSCs Contributing to the Puberal Spatial Memory Deficits

Hippocampal neurogenesis-related structural damage, particularly that leading to defective adult cognitive function, is considered an important risk factor for neurodegenerative and psychiatric diseases. Normal differentiation of neurons and glial cells during development is crucial in neurogenesis, which is particularly sensitive to the environmental toxicant methylmercury (MeHg). However, the exact effects of MeHg on hippocampal neural stem cell (hNSC) differentiation during puberty remain unknown. This study investigates whether MeHg exposure induces changes in hippocampal neurogenesis and whether these changes underlie cognitive defects in puberty. A rat model of methylmercury chloride (MeHgCl) exposure (0.4 mg/kg/day, PND 5-PND 33, 28 days) was established, and the Morris water maze was used to assess cognitive function. Primary hNSCs from hippocampal tissues of E16-day Sprague-Dawley rats were purified, identified, and cloned. hNSC proliferation and differentiation and the growth and morphology of newly generated neurons were observed by MTT and immunofluorescence assays. MeHg exposure induced defects in spatial learning and memory accompanied by a decrease in number of doublecortin (DCX)-positive cells in the dentate gyrus (DG). DCX is a surrogate marker for newly generated neurons. Proliferation and differentiation of hNSCs significantly decreased in the MeHg-treated groups. MeHg attenuated microtubule-associated protein-2 (MAP-2) expression in neurons and enhanced the glial fibrillary acidic protein (GFAP)-positive cell differentiation of hNSCs, thereby inducing degenerative changes in a dose-dependent manner. Moreover, MeHg induced deficits in hippocampus-dependent spatial learning and memory during adolescence as a consequence of decreased generation of DG neurons. Our findings suggested that MeHg exposure could be a potential risk factor for psychiatric and neurodegenerative diseases.

Oral supplementation of 2'-fucosyllactose during lactation improves memory and learning in rats

Human milk oligosaccharides have been proposed to exert beneficial effects on brain development. During the last decades, most of the studies have focused on the evaluation of sialylated structures but recent experiments have also tested fucosylated oligosaccharides, i.e. 2'-fucosyllactose (2'-FL). The present study aimed to determine whether oral 2'-FL has an effect on the development of newborn brain, contributing to enhance cognitive skills later in life. Rat pups received an oral supplementation of 2'-FL (2'-FL group) or water (control group) during the lactation period. Thereafter, animals were maintained on a rodent standard diet. Rats (n=12 rats/group) were evaluated twice, at age 4-6weeks and again at age 1year, using classical behavioral tests. In vivo long-term potentiation (LTP) was also performed at the same ages (n=10 rats/group). Both groups showed similar behavior when the animals were assessed just after weaning (age 4-6weeks), although the 2'-FL group seemed to perform slightly better in Morris Water Maze. At age 1year, 2'-FL rats performed significantly better in the Novel Object Recognition and Y maze paradigms, when compared to controls. In addition, LTP was more intense and longer lasting in the rats supplemented with 2'-FL than in control animals, both in young and adult animals. Oral administration of 2'-FL exclusively during lactation enhanced cognitive abilities, not only in childhood but also in adulthood.

The prebiotics 3'Sialyllactose and 6'Sialyllactose diminish stressor-induced anxiety-like behavior and colonic microbiota alterations: Evidence for effects on the gut-brain axis

There are extensive bidirectional interactions between the gut microbiota and the central nervous system (CNS), and studies demonstrate that stressor exposure significantly alters gut microbiota community structure. We tested whether oligosaccharides naturally found in high levels in human milk, which have been reported to impact brain development and enhance the growth of beneficial commensal microbes, would prevent stressor-induced alterations in gut microbial community composition and attenuate stressor-induced anxiety-like behavior. Mice were fed standard laboratory diet, or laboratory diet containing the human milk oligosaccharides 3'Sialyllactose (3'SL) or 6'Sialyllactose (6'SL) for 2 weeks prior to being exposed to either a social disruption stressor or a non-stressed control condition. Stressor exposure significantly changed the structure of the colonic mucosa-associated microbiota in control mice, as indicated by changes in beta diversity. The stressor resulted in anxiety-like behavior in both the light/dark preference and open field tests in control mice. This effect was associated with a reduction in immature neurons in the dentate gyrus as indicated by doublecortin (DCX) immunostaining. These effects were not evident in mice fed milk oligosaccharides; stressor exposure did not significantly change microbial community structure in mice fed 3'SL or 6'SL. In addition, 3'SL and 6'SL helped maintain normal behavior on tests of anxiety-like behavior and normal numbers of DCX+ immature neurons. These studies indicate that milk oligosaccharides support normal microbial communities and behavioral responses during stressor exposure, potentially through effects on the gut microbiota-brain axis.

Ganglioside-Dependent Neural Stem Cell Proliferation in Alzheimer's Disease Model Mice

The aggregation and formation of amyloid plaques by amyloid β-peptides (Aβs) is believed to be one of the pathological hallmarks of Alzheimer's disease (AD). Intriguingly, Aβs have also been shown to possess proliferative effects on neural stem cells (NSCs). Many essential cellular processes in NSCs, such as fate determination and proliferation, are heavily influenced by cell surface glycoconjugates, including gangliosides. It has recently been shown that Aβ1-42 alters several key glycosyltransferases and glycosidases. To further define the effects of Aβs and to clarify the potential mechanisms of action of those peptides on NSCs, NSCs were cultured from embryonic brains of the double-transgenic mouse model of AD [B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J] coexpressing mutants of amyloid precursor protein (APPswe) and presenilin1 (PSEN1dE9). We found that Aβs not only promoted cell proliferation but also altered expression of several key glycogenes for glycoconjugate metabolism, such as sialyltransferases II and III (ST-II & -III) in AD NSCs. In addition, we found upregulation of epidermal growth factor receptor and Notch1 intracellular domain. Moreover, the increased expression of ST-II and -III coincided with the elevated levels of c-series gangliosides (A2B5+ antigens) in AD NSCs. Further, we revealed that epidermal growth factor signaling and gangliosides are necessary components on Aβ-stimulated NSC proliferation. Our present study has thus provided a novel mechanism for the upregulation of c-series ganglioside expression and increases in several NSC markers to account for the proliferative effect of Aβs on NSCs in AD mouse brain. These observations support the potential beneficial effects of Aβs and gangliosides in promoting neurogenesis in AD brain.

The role of gangliosides in neurodevelopment

Gangliosides are important components of neuronal cell membranes and it is widely accepted that they play a critical role in neuronal and brain development. They are functionally involved in neurotransmission and are thought to support the formation and stabilization of functional synapses and neural circuits required as the structural basis of memory and learning. Available evidence, as reviewed herein, suggests that dietary gangliosides may impact positively on cognitive functions, particularly in the early postnatal period when the brain is still growing. Further, new evidence suggests that the mechanism of action may be through an effect on the neuroplasticity of the brain, mediated through enhanced synaptic plasticity in the hippocampus and nigro-striatal dopaminergic pathway.