Learning, Neurogenesis, and Effects of Flavonoids on Learning

Flavonoid chrysin activates both TrkB and FGFR1 receptors while upregulates their endogenous ligands such as brain derived neurotrophic factor to promote human neurogenesis

Neurogenesis is the process of generating new neurons from neural stem cells (NSCs) and plays a crucial role in neurological diseases. The process involves a series of steps, including NSC proliferation, migration and differentiation, which are regulated by multiple pathways such as neurotrophic Trk and fibroblast growth factor receptors (FGFR) signalling. Despite the discovery of numerous compounds capable of modulating individual stages of neurogenesis, it remains challenging to identify an agent that can regulate multiple cellular processes of neurogenesis. Here, through screening of bioactive compounds in dietary functional foods, we identified a flavonoid chrysin that not only enhanced the human NSCs proliferation but also facilitated neuronal differentiation and neurite outgrowth. Further mechanistic study revealed the effect of chrysin was attenuated by inhibition of neurotrophic tropomyosin receptor kinase-B (TrkB) receptor. Consistently, chrysin activated TrkB and downstream ERK1/2 and AKT. Intriguingly, we found that the effect of chrysin was also reduced by FGFR1 blockade. Moreover, extended treatment of chrysin enhanced levels of brain-derived neurotrophic factor, as well as FGF1 and FGF8. Finally, chrysin was found to promote neurogenesis in human cerebral organoids by increasing the organoid expansion and folding, which was also mediated by TrkB and FGFR1 signalling. To conclude, our study indicates that activating both TrkB and FGFR1 signalling could be a promising avenue for therapeutic interventions in neurological diseases, and chrysin appears to be a potential candidate for the development of such treatments.

The impact of flavonoids and BDNF on neurogenic process in various physiological/pathological conditions including ischemic insults: a narrative review

OBJECTIVE

Ischemic stroke is the leading cause of mortality and disability worldwide with more than half of survivors living with serious neurological sequelae thus, it has recently attracted considerable attention in the field of medical research. Neurogenesis is the process of formation of new neurons in the brain, including the human brain, from neural stem/progenitor cells [NS/PCs] which reside in neurogenic niches that contain the necessary substances for NS/PC proliferation, differentiation, migration, and maturation into functioning neurons which can integrate into a pre-existing neural network.Neurogenesis can be modulated by many exogenous and endogenous factors, pathological conditions. Both brain-derived neurotrophic factor, and flavonoids can modulate the neurogenic process in physiological conditions and after various pathological conditions including ischemic insults.

AIM

This review aims to discuss neurogenesis after ischemic insults and to determine the role of flavonoids and BDNF on neurogenesis under physiological and pathological conditions with a concentration on ischemic insults to the brain in particular.

METHOD

Relevant articles assessing the impact of flavonoids and BDNF on neurogenic processes in various physiological/pathological conditions including ischemic insults within the timeline of 1965 until 2023 were searched using the PubMed database.

CONCLUSIONS

The selected studies have shown that ischemic insults to the brain induce NS/PC proliferation, differentiation, migration, and maturation into functioning neurons integrating into a pre-existing neural network. Flavonoids and BDNF can modulate neurogenesis in the brain in various physiological/pathological conditions including ischemic insults. In conclusion, flavonoids and BDNF may be involved in post-ischemic brain repair processes through enhancing endogenous neurogenesis.

Nelumbo nucifera leaves extract ameliorated scopolamine-induced cognition impairment via enhanced adult hippocampus neurogenesis

In this presentation, we explored the molecular mechanisms of N. nucifera leaf water extracts (NLWEs) and polyphenol extract (NLPE) on scopolamine-induced cell apoptosis and cognition defects. The administration of NLWE and NLPE did not alter the body weight and serum biomarker rs and significantly ameliorated scopolamine-induced cognition impairment according to Y-maze test analysis. In mice, treatment with scopolamine disrupted normal histoarchitecture in the hippocampus, whereas the administration of NLWE and NLPE reversed the phenomenon. Western blot analysis revealed that scopolamine mitigated the expression of doublecortin (DCX), nestin, and NeuN, and cotreatment with NLWE or NLPE significantly recovered the expression of these proteins. NLWE and NLPE upregulated DCX and NeuN expression in the hippocampus region, as evidenced by immunohistochemical staining analysis of scopolamine-treated mice. NLWE and NLPE obviously elevated brain-derived neurotrophic factor (BDNF) and enhanced its downstream proteins activity. NLWE and NLPE attenuated scopolamine-induced apoptosis by reducing Bax and increased Bcl-2 expression. In addition, scopolamine also triggered apoptosis in human neuroblastoma SH-SY5Y cells whereas co-treatment with NLWE or quercetin-3-glucuronide (Q3G) reversed the phenomenon. NLWE or Q3G enhanced Bcl-2 and reduced Bax expression in the presence of scopolamine in SH-SY5Y cells. NLWE or Q3G recovered the inhibitory effects of scopolamine on neurogenesis and BDNF signals in SH-SY5Y cells. Overall, our results revealed that N. nucifera leaf extracts and Q3G promoted adult hippocampus neurogenesis and prevented apoptosis to mitigate scopolamine-induced cognition dysfunction through the regulation of BDNF signaling pathway.

Single cell molecular alterations reveal target cells and pathways of conditioned fear memory

OBJECTIVES

Recent evidence indicates that hippocampus is important for conditioned fear memory (CFM). Though few studies consider the roles of various cell types' contribution to such a process, as well as the accompanying transcriptome changes during this process. The purpose of this study was to explore the transcriptional regulatory genes and the targeted cells that are altered by CFM reconsolidation.

METHODS

A fear conditioning experiment was established on adult male C57 mice, after day 3 tone-cued CFM reconsolidation test, hippocampus cells were dissociated. Using single cell RNA sequencing (scRNA-seq) technique, alterations of transcriptional genes expression were detected and cell cluster analysis were performed and compared with those in sham group.

RESULTS

Seven non-neuronal and eight neuronal cell clusters (including four known neurons and four newly identified neuronal subtypes) has been explored. Among them, CA subtype 1 has characteristic gene markers of Ttr and Ptgds, which is speculated to be the outcome of acute stress and promotes the production of CFM. The results of KEGG pathway enrichment indicate the differences in the expression of certain molecular protein functional subunits in long-term potentiation (LTP) pathway between two types of neurons (DG and CA1) and astrocytes, thus providing a new transcriptional perspective for the role of hippocampus in the CFM reconsolidation. More importantly, the correlation between the reconsolidation of CFM and neurodegenerative diseases-linked genes is substantiated by the results from cell-cell interactions and KEGG pathway enrichment. Further analysis shows that the reconsolidation of CFM inhibits the risk-factor genes App and ApoE in Alzheimer's Disease (AD) and activates the protective gene Lrp1.

CONCLUSIONS

This study reports the transcriptional genes expression changes of hippocampal cells driven by CFM, which confirm the involvement of LTP pathway and suggest the possibility of CFM-like behavior in preventing AD. However, the current research is limited to normal C57 mice, and further studies on AD model mice are needed to prove this preliminary conclusion.

Dietary Flavonoids and Adult Neurogenesis: Potential Implications for Brain Aging

Adult neurogenesis deficiency has been proposed to be a common hallmark in different age-related neurodegenerative diseases. The administration of flavonoids is currently reported as a potentially beneficial strategy for preventing brain aging alterations, including adult neurogenesis decline. Flavonoids are a class of plant-derived dietary polyphenols that have drawn attention for their neuroprotective and pro-cognitive effects. Although they undergo extensive metabolism and localize in the brain at low concentrations, flavonoids are now believed to improve cerebral vasculature and interact with signal transduction cascades involved in the regulation of adult neurogenesis. Furthermore, many dietary flavonoids have been shown to reduce oxidative stress and neuroinflammation, improving the neuronal microenvironment where adult neurogenesis occurs. The overall goal of this review is to summarize the evidence supporting the role of flavonoids in modulating adult neurogenesis as well as to highlight how these dietary agents may be promising candidates in restoring healthy brain function during physiological and pathological aging.

TAT-LBD-Ngn2-improved cognitive functions after global cerebral ischemia by enhancing neurogenesis

BACKGROUND

Stroke is the major cause of adult neurocognitive disorders (NCDs), and presents a significant burden on both of the families and society. To improve the cerebral injury, we generated a blood-brain barrier penetrating peptide TAT-LBD-Ngn2, in which Ngn2 (Neurogenin2) is a classical preneural gene that enhances neurogenesis, and neural precursor cells survival and differentiation. We previously demonstrated that it has a short-term protective effect against cerebral ischemia-reperfusion injury. However, it is uncertain if TAT-LBD-Ngn2 could promote neurogenesis to exhibit long-term therapeutic impact.

METHODS AND RESULTS

In present study, TAT-LBD-Ngn2 was administered for 14 or 28 days following bilateral common carotid arteries occlusion (BCCAO). After confirming that TAT-LBD-Ngn2 could cross the brain blood barrier and aggregate in the hippocampus, we conducted open field test, Morris water maze and contextual fear conditioning to examine the long-term effect of TAT-LBD-Ngn2 on cognition. We discovered that TAT-LBD-Ngn2 significantly improved the spatial and contextual learning and memory on both days 14 and 28 after BCCAO, while TAT-LBD-Ngn2 exhibited anxiolytic effect only on day 14, but had no effect on locomotion. Using western blot and immunofluorescence, TAT-LBD-Ngn2 was also shown to promote neurogenesis, as evidenced by increased BrdU⁺ and DCX⁺ neurons in dentate gyrus. Meanwhile, TAT-LBD-Ngn2 elevated the expression of brain derived neurotrophic factor rather than nerve growth factor compared to the control group.

CONCLUSIONS

Our findings revealed that TAT-LBD-Ngn2 could dramatically promote learning and memory in long term by facilitating neurogenesis in the hippocampus after global cerebral ischemia, indicating that TAT-LBD-Ngn2 may be an appealing candidate for treating poststroke NCD.