Adult hippocampal neurogenesis (AHN) supports learning, memory, and emotional regulation, and is regulated by intrinsic and extrinsic factors. Dopamine influences neurogenesis in animal models, but its direct effects on human hippocampal progenitors and receptor-specific mechanisms remain unclear. This study examined the dose-dependent effects of dopamine on proliferation, differentiation, and survival of human hippocampal progenitor cells (HPC0A07/03) in vitro, and assessed dopamine D4 receptor (DRD4) involvement. Cells were treated with dopamine (1-150 µM) under proliferation and differentiation conditions, with DRD4 modulated via selective agonist, antagonist, or combined treatment. Proliferation (Ki67), stemness (SOX2, Nestin), neuronal differentiation (DCX, MAP2), apoptosis (CC3), total cell counts, and morphology (cytoplasmic area) were assessed using immunocytochemistry, alongside targeted gene expression analysis of cellular stress- and neurogenesis-related pathways. Treatment with supraphysiological dopamine concentration (150 µM) significantly reduced cell counts during differentiation and decreased SOX2 expression during proliferation, suggesting impaired survival and reduced stemness. Complementary transcriptional changes supported a stress-associated cellular response at high dopamine concentrations. Elevated dopamine (150 µM) also increased cytoplasmic area in immature DCX+ neurons during the differentiation phase, suggesting altered morphological maturation. Moderate dopamine concentration (30 µM) showed a trend toward increased proliferation and higher cell counts. No significant changes occurred for other markers or following DRD4 modulation. These findings indicate that dopamine's effects on human hippocampal progenitors are dose-dependent: supraphysiological levels may compromise survival and progenitor identity, potentially via stress-related mechanisms, whereas moderate levels may support neurogenic processes. Understanding this dose-dependent balance has implications for neurological and psychiatric disorders involving dopaminergic dysregulation.

The existence and functional significance of immature neurons in the adult human brain, particularly in the context of neurodegenerative disorders, remain an open question. Although rodent studies have highlighted active roles for adult-born immature neurons in the hippocampus both under healthy conditions and in Alzheimer’s disease (AD), evidence from the human brain is limited and lacks detailed molecular characterization. To address this gap, we performed single-nucleus RNA sequencing in aged healthy, AD, and dementia-resilient human hippocampus samples to probe immature neuronal signatures and gene expression alterations associated with AD pathology and resilience. By applying an integrated experimental and computational pipeline, we identified persistent populations of immature neurons across all donor groups, with transcriptional profiles reflecting “juvenile” cellular functions, which are compromised in AD. Our findings suggest that the presence of these immature neuronal populations per se may actively contribute to maintaining homeostasis within the aged human hippocampus and to cognitive resilience in AD.

Adult hippocampal neurogenesis is essential for learning, memory, and mood regulation, and its disruption is implicated in ageing, neurodegeneration, and mood disorders. However, the mechanisms linking inflammation to adult hippocampal neurogenesis impairment remain unclear. Here, we identify chronic tumour necrosis factor-alpha signalling as a key driver of neurogenic dysregulation via a previously unrecognised type I interferon autocrine/paracrine loop in human hippocampal progenitor cells. Using a female-derived human in vitro neurogenesis model, single-cell RNA sequencing, and functional T cell migration assays, we show that tumour necrosis factor-alpha induces a robust type I interferon response in hippocampal progenitor cells, promoting chemokine-mediated and CXC motif chemokine receptor 3-dependent T cell recruitment and suppressing neurogenesis. This inflammatory signalling cascade drives a fate switch in hippocampal progenitor cells from a neurogenic trajectory towards an immune-defensive phenotype, with critical implications for infectious and inflammatory disease pathogenesis. These findings uncover a key inflammatory checkpoint regulating human adult hippocampal neurogenesis and highlight potential therapeutic targets to restore neurogenesis in chronic inflammatory states.

The 38 currently registered clinical trials with the keyword “adult neurogenesis” indicate growing interest in new neurons as a target for intervention. Today, we have strong evidence that adult neurogenesis is involved in hippocampal function and can contribute to brain functions in health and disease. Neurogenesis research can now ask new questions, such as (1) the identity of stem cells and their input integration for initiating neurogenesis, (2) the nature of the neurogenic niche and neurogenesis without stem cell activity, (3) the complex functionality beyond the hippocampus, and (4) evolutionary and computational theory, including neurogenic neural networks for artificial intelligence.

Structural and functional aspects of the hippocampus have been shown to be sensitive to the aging process, resulting in deficits in hippocampal-dependent cognition. Similarly, adult hippocampal neurogenesis (AHN), described as the generation of new neurons from neural stem cells in the hippocampus, has shown to be negatively affected by aging throughout life. Extensive research has highlighted the role of physical exercise (PE) in positively regulating hippocampal-dependent cognition and AHN. Here, by critically reviewing preclinical and clinical studies, we discuss the significance of PE in reversing age-associated changes of the hippocampus via modulation of AHN. We indicate that PE-induced changes operate on two main levels. On the first level, PE can potentially cause structural modifications of the hippocampus, and on the second level, it regulates the molecular and cellular pathways involved. These changes result in the vascular remodelling of the neurogenic niche, as well as the secretion of neurotrophic and antioxidant factors, which can in turn activate quiescent neural stem cells, while restoring their proliferation capacity and boosting their survival - features which are negatively impacted during aging. Understanding these mechanisms will allow us to identify new targets to tackle cognitive aging and improve quality of life.

Background: Identifying compounds with neuroprotective properties that target the neurogenic process will have a considerable impact on dementia prevention. Methods: This is a secondary analysis of a 24-week randomised, double-blind, placebo-controlled anthocyanin supplementation trial in 181 participants. Using blood-derived serum collected during this trial, we treated hippocampal progenitor cells and analysed the ensuing cellular changes in the context of the participant’s clinical and blood-based biomarker data. Results: We show that anthocyanin supplementation impacts hippocampal progenitor cells and that this can impact hippocampal-dependent cognition. We also show for the first time that blood-based dementia biomarkers correlate with human in vitro neurogenesis markers. Conclusions: Our data demonstrates moderator effects of BMI and ApoE4 carrier status and supports the need for more individualised trials. Further studies are warranted to explore the mechanism of action of anthocyanins and the use of blood-based biomarkers for clinical trial enrichment, trial individualization, and therapy development. Trial registration: NCT03419039; date first registered: 15/01/2018.

Selenium has been shown to be a key regulatory element in the health, survival and proliferation of neural stem and progenitor cells, with various studies underlining its anti-aging properties. However, most of this knowledge is derived from rodent models, leaving its effects on human hippocampal progenitor cells unclear. In this study, we utilized a human hippocampal progenitor cell (HPC) line to examine the effects of varying concentrations of sodium selenite, an inorganic form of selenium (0 µM, 0.1 µM, 0.23 µM, 0.5 µM, and 1.0 µM), on the proliferation, apoptosis, and progenitor integrity of these cells. To do this, HPCs were exposed to these concentrations for 48 h, followed by immunocytochemistry to quantify, cell number (DAPI-positive cells), proliferation (KI67-positve cells), apoptosis (CC3-positve cells), and progenitor integrity (SOX2- and Nestin-positive cells). While our results indicated no significant effects of selenium concentrations on proliferation or apoptosis, we demonstrated that absence of selenium (0 μM) in the culture media significantly reduced both cell number and percentage of Nestin-positive cells, but only when compared to the condition with the highest selenium concentration (1.0 μM). Our findings underscore the role of selenium in regulating the survival and integrity of human HPCs. Lastly, we emphasize the need for further research to uncover the mechanisms underlying these observed changes.

In Alzheimer’s disease, microglial phagocytosis is engaged in the pathogenesis as it clears abnormal protein accumulations, debris, and apoptotic cells in the early stages of Alzheimer’s disease, but fuels neuroinflammation and accelerates disease progression in later stages. In vivo parabiosis experiments in aged animals have demonstrated that blood-born factors modulate synaptic plasticity, neurogenesis, and microglial responses. We hypothesize that peripheral factors can modulate microglial function and thereby possibly influence Alzheimer’s disease pathology. The objective of this study is to investigate the effects of Alzheimer’s disease serum on microglial phagocytosis. Here, we use an immortalized human microglial cell line in an in vitro parabiosis assay to investigate the impact of the serum from individuals diagnosed with Alzheimer’s disease ( n = 30) and age-matched controls ( n = 30) (PRODEM study) on microglial phagocytosis. Exposure to Alzheimer’s disease serum increased microglial phagocytic uptake of pH-sensitive fluorescent particles and downregulated expression of the lysosomal master regulator transcription factor EB ( TFEB ) and of ATPase H + transporting lysosomal V1 subunit B2 ( ATP6V1B2 ), a component of the vacuolar ATPase. To identify serum components that may relate to changes in phagocytosis, serum samples of the Three-City Study (3C Study) were used. In the 3C Study, blood samples were collected up to 12 years before the onset of cognitive decline or dementia and their serum metabolome is well-defined. Microglia exposed to the serum of future Alzheimer’s disease patients from the 3C Study displayed an increased phagocytic uptake compared with the serum of matched controls, depending on the presence of the apolipoprotein E ε4 allele in the Alzheimer’s disease patients. Furthermore, microglial phagocytosis correlated inversely with serum levels of the omega-3 fatty acid eicosapentaenoic acid. We confirmed this inverse correlation between eicosapentaenoic acid and phagocytosis in the serum samples of the PRODEM cohort. In addition, in vitro testing of eicosapentaenoic acid on microglial phagocytosis showed a concentration-dependent decrease in phagocytic uptake. In conclusion, following incubation with Alzheimer’s disease blood serum, we observed increased microglial phagocytic uptake and the downregulation of TFEB and ATP6V1B2 , possibly indicating lysosomal dysfunction. Furthermore, microglial phagocytosis was inversely correlated with serum eicosapentaenoic acid levels, suggesting an important role for dietary eicosapentaenoic acid in microglial function.

Adult hippocampal neurogenesis (AHN) is essential for learning, memory, and mood regulation, and its disruption is implicated in ageing, neurodegeneration, and mood disorders. However, the mechanisms linking inflammation to AHN impairment remain unclear. Here, we identify chronic tumour necrosis factor-alpha (TNF-⍺) signalling as a key driver of neurogenic dysregulation via a previously unrecognized type I interferon (IFN) autocrine/paracrine loop in human hippocampal progenitor cells (HPCs). Using a human in vitro neurogenesis model, single-cell RNA sequencing, and functional T cell migration assays, we show that TNF-⍺ induces a robust type I IFN response in HPCs, promoting chemokine and CXCR3-dependent T cell recruitment and suppressing neurogenesis. This inflammatory signalling cascade drives a fate switch in HPCs from a neurogenic trajectory towards an immune-defensive phenotype, with critical implications for infectious and inflammatory disease pathogenesis. These findings uncover a key inflammatory checkpoint regulating human AHN and highlight potential therapeutic targets to restore neurogenesis in chronic inflammatory states. ### Competing Interest Statement The authors have declared no competing interest. Wellcome Trust, 218452/Z/19/Z Medical Research Council, MR/S00484X/1, MR/R015643/1 The Galen and Hilary Weston Foundation

The existence and functional significance of immature neurons in the adult human brain, particularly in the context of neurodegenerative disorders, remain controversial. While rodent studies have highlighted active roles for adult-born immature neurons in the hippocampus under both healthy conditions and in Alzheimer's disease (AD), evidence from the human brain is limited and lacks detailed molecular characterization. To address this gap, we performed single-nucleus RNA sequencing in aged healthy, AD and dementia-resilient human hippocampus to probe immature neuronal signatures and gene expression alterations associated with AD pathology and resilience. Employing a novel experimental and computational pipeline, we identified persistent populations of immature neurons across all donor groups, with transcriptional profiles distinct from both fetal counterparts and adult mature hippocampal neurons. These profiles were associated with 'juvenile' cellular functions, suggesting that the presence of these immature neuronal populations per se may actively contribute to maintaining homeostasis within the aged human hippocampus, a role that may be disrupted in AD. In the resilient brain, immature neurons were involved in transcriptional programs and intercellular interactions associated with anti-inflammatory, neurotrophic, neuroprotective, myelinating, anti-apoptotic and anti-amyloidogenic signaling pathways, suggesting active roles for the immature cells in enhancing cognitive resilience in the presence of AD pathology. Our findings reveal novel, putative physiological roles for immature neurons in the healthy and resilient adult human brain, and offer a resource for probing new strategies with potential functional relevance in AD. ### Competing Interest Statement J.B. and W.M. are employees of F. Hoffmann-La Roche AG. The remaining authors have no conflicts of interest to declare.

Immunoglobulin E (IgE)-mediated food allergies are reported to affect around 3.5% of children and 2.4% of adults, with symptoms varying in range and severity. While being the gold standard for diagnosis, oral food challenges are burdensome, and diagnostic tools based on specific IgE can be flawed. Furthering our understanding of the mechanisms behind food allergy onset, severity and persistence could help reveal immune profiles associated with the disease, to ultimately aid in diagnosis. Alterations to cytokine levels and immune cell ratios have been identified, though further research is needed to fully capture the heterogenous nature of food allergy. Moreover, the existence of such immune alterations also raises the question of potential wider systemic effects. For example, recent research has emphasised the existence and impact of neuro-immune interactions and implicated behavioural and neurological changes associated with food allergy. This review will provide an overview of such food allergy-driven neuro-immune interactions, with the aim of emphasising the importance of furthering our understanding of the immune mechanisms underlying IgE-mediated food allergy.

Hippocampal neurogenesis (HN) occurs throughout the life course and is important for memory and mood. Declining with age, HN plays a pivotal role in cognitive decline (CD), dementia, and late-life depression, such that altered HN could represent a neurobiological susceptibility to these conditions. Pertinently, dietary patterns (e.g., Mediterranean diet) and/or individual nutrients (e.g., vitamin D, omega 3) can modify HN, but also modify risk for CD, dementia, and depression. Therefore, the interaction between diet/nutrition and HN may alter risk trajectories for these ageing-related brain conditions. Using a subsample (n = 371) of the Three-City cohort-where older adults provided information on diet and blood biobanking at baseline and were assessed for CD, dementia, and depressive symptomatology across 12 years-we tested for interactions between food consumption, nutrient intake, and nutritional biomarker concentrations and neurogenesis-centred susceptibility status (defined by baseline readouts of hippocampal progenitor cell integrity, cell death, and differentiation) on CD, Alzheimer's disease (AD), vascular and other dementias (VoD), and depressive symptomatology, using multivariable-adjusted logistic regression models. Increased plasma lycopene concentrations (OR [95% CI] = 1.07 [1.01, 1.14]), higher red meat (OR [95% CI] = 1.10 [1.03, 1.19]), and lower poultry consumption (OR [95% CI] = 0.93 [0.87, 0.99]) were associated with an increased risk for AD in individuals with a neurogenesis-centred susceptibility. Increased vitamin D consumption (OR [95% CI] = 1.05 [1.01, 1.11]) and plasma gamma-tocopherol concentrations (OR [95% CI] = 1.08 [1.01, 1.18]) were associated with increased risk for VoD and depressive symptomatology, respectively, but only in susceptible individuals. This research highlights an important role for diet/nutrition in modifying dementia and depression risk in individuals with a neurogenesis-centred susceptibility.

Stress exposure during the sensitive period of early development has been shown to program the brain and increases the risk to develop cognitive deficits later in life. We have shown earlier that early-life stress (ES) leads to cognitive decline at an adult age, associated with changes in adult hippocampal neurogenesis and neuroinflammation. In particular, ES has been shown to affect neurogenesis rate and the survival of newborn cells later in life as well as microglia, modulating their response to immune or metabolic challenges later in life. Both of these processes possibly contribute to the ES-induced cognitive deficits.Emerging evidence by us and others indicates that early nutritional interventions can protect against these ES-induced effects through nutritional programming. Based on human metabolomics studies, we identified various coffee-related metabolites to be part of a protective molecular signature against cognitive decline in humans. Caffeic and chlorogenic acids are coffee-polyphenols and have been described to have potent anti-oxidant and anti-inflammatory actions. Therefore, we here aimed to test whether supplementing caffeic and chlorogenic acids to the early diet could also protect against ES-induced cognitive deficits.We induced ES via the limited nesting and bedding paradigm in mice from postnatal(P) day 2-9. On P2, mice received a diet to which 0.02% chlorogenic acid (5-O-caffeoylquinic acid) + 0.02% caffeic acid (3’,4’-dihydroxycinnamic acid) were added, or a control diet up until P42. At 4 months of age, all mice were subjected to a behavioral test battery and their brains were stained for markers for microglia and neurogenesis. We found that coffee polyphenols supplemented early in life protected against ES-induced cognitive deficits, potentially this is mediated by the survival of neurons or microglia, but possibly other mechanisms not studied here are mediating the effects. This study provides additional support for the potential of early nutritional interventions and highlights polyphenols as nutrients that can protect against cognitive decline, in particular for vulnerable populations exposed to ES.

Cognitive function undergoes a dynamic trajectory across the lifespan, influenced by multifaceted mechanisms encompassing genetics, lifestyle, and environmental factors. This review explores the impact of nutrition, specifically energy and bioactive components, on cognitive health across different life stages. Nutrition plays a pivotal role, influencing cognitive development, brain function, and age-related changes. Understanding these connections offers insights into strategies for extending cognitive healthspan. The review synthesizes evidence highlighting the nuanced effects of nutrition on cognition throughout life. Notably, age-specific energy balance emerges as a crucial factor in maintaining cognitive healthspan. Different life stages exhibit distinct nutritional demands affecting cognitive function. Maternal nutrition impacts prenatal and childhood cognitive development, while heightened glucose demands in adolescence influence long-term cognitive health. Midlife witnesses hormonal changes and decreased brain plasticity, while old age demands strategies addressing chronic lifestyle factors and energy restriction. We conclude that it is crucial to recognize the diverse requirements and biological changes across the lifespan and that deeper mechanistic investigations are vital to tailor nutritional recommendations for optimal cognitive health in all populations across the lifespan.

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases.Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

Adult hippocampal neurogenesis is important for learning and memory and is altered early in Alzheimer's disease. As hippocampal neurogenesis is modulated by the circulatory systemic environment, evaluating a proxy of how hippocampal neurogenesis is affected by the systemic milieu could serve as an early biomarker for Alzheimer's disease progression. Here, we used an in vitro assay to model the impact of systemic environment on hippocampal neurogenesis. A human hippocampal progenitor cell line was treated with longitudinal serum samples from individuals with mild cognitive impairment, who either progressed to Alzheimer's disease or remained cognitively stable. Mild cognitive impairment to Alzheimer's disease progression was characterized most prominently with decreased proliferation, increased cell death and increased neurogenesis. A subset of 'baseline' cellular readouts together with education level were able to predict Alzheimer's disease progression. The assay could provide a powerful platform for early prognosis, monitoring disease progression and further mechanistic studies.

Alzheimer's disease is a complex neurodegenerative disorder leading to a decline in cognitive function and mental health. Recent research has positioned the gut microbiota as an important susceptibility factor in Alzheimer's disease by showing specific alterations in the gut microbiome composition of Alzheimer's patients and in rodent models. However, it is unknown whether gut microbiota alterations are causal in the manifestation of Alzheimer's symptoms. To understand the involvement of Alzheimer's patient gut microbiota in host physiology and behaviour, we transplanted faecal microbiota from Alzheimer's patients and age-matched healthy controls into microbiota-depleted young adult rats. We found impairments in behaviours reliant on adult hippocampal neurogenesis, an essential process for certain memory functions and mood, resulting from Alzheimer's patient transplants. Notably, the severity of impairments correlated with clinical cognitive scores in donor patients. Discrete changes in the rat caecal and hippocampal metabolome were also evident. As hippocampal neurogenesis cannot be measured in living humans but is modulated by the circulatory systemic environment, we assessed the impact of the Alzheimer's systemic environment on proxy neurogenesis readouts. Serum from Alzheimer's patients decreased neurogenesis in human cells in vitro and were associated with cognitive scores and key microbial genera. Our findings reveal for the first time, that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming a causal role of gut microbiota in Alzheimer's disease, and highlight hippocampal neurogenesis as a converging central cellular process regulating systemic circulatory and gut-mediated factors in Alzheimer's.

Hippocampal neurogenesis (HN) is considered an important mechanism underlying lifelong brain plasticity, and alterations in this process have been implicated in early Alzheimer's disease progression. APOE polymorphism is the most common genetic risk factor for late-onset Alzheimer's disease where the ε4 genotype is associated with a significantly earlier disease onset compared to the neutral ε3 allele. Recently, APOE has been shown to play an important role in the regulation of HN. However, the time-dependent impact of its polymorphism in humans remains elusive, partially due to the difficulties of studying human HN in vivo. To bridge this gap of knowledge, we used an in vitro cellular model of human HN and performed a time course characterization on isogenic induced pluripotent stem cells with different genotypes of APOE. We found that APOE itself was more highly expressed in ε4 at the stem cell stage, while the divergence of differential gene expression phenotype between ε4 and ε3 became prominent at the neuronal stage of differentiation. This divergence was not associated with the differential capacity to generate dentate gyrus granule cell-like neurons, as its level was comparable between ε4 and ε3. Transcriptomic profiling across different stages of neurogenesis indicated a clear "maturation of functional neurons" phenotype in ε3 neural progenitors and neurons, while genes differentially expressed only in ε4 neurons suggested potential alterations in "metabolism and mitochondrial function." Taken together, our in vitro investigation suggests that APOE ε4 allele can exert a transcriptome-wide effect at the later stages of HN, without altering the overall level of neurogenesis per se.