Human Hippocampal Neurogenesis Research Articles

Ketamine Prevents Inflammation-Induced Reduction of Human Hippocampal Neurogenesis via Inhibiting the Production of Neurotoxic Metabolites of the Kynurenine Pathway.

Understanding the precise mechanisms of ketamine is crucial for replicating its rapid antidepressant effects without inducing psychomimetic changes. Here, we explore whether the antidepressant-like effects of ketamine enantiomers are underscored by protection against cytokine-induced reductions in hippocampal neurogenesis and activation of the neurotoxic kynurenine pathway in our well-established in vitro model of depression in a dish. We used the fetal hippocampal progenitor cell line (HPC0A07/03C) to investigate ketamine's impact on cytokine-induced reductions in neurogenesis in vitro. Cells were treated with interleukin- 1beta (IL-1b) (10ng/mL) or IL-6 (50 pg/mL), alone or in combination with ketamine enantiomers arketamine (R-ketamine, 400nM) or esketamine (S-ketamine, 400nM) or antidepressants sertraline (1mM) or venlafaxine (1mM). Resembling the effect of antidepressants, both ketamine enantiomers prevented IL-1b- and IL-6-induced reduction in neurogenesis and increase in apoptosis. This was mediated by inhibition of IL-1b-induced production of IL-2 and IL-13 by R-ketamine and of IL-1b-induced tumor necrosis factor-alpha by S-ketamine. Likewise, R-ketamine inhibited IL-6-induced production of IL-13, whereas S-ketamine inhibited IL-6-induced IL-1b and IL-8. Moreover, both R- and S-ketamine prevented IL-1b-induced increases in indoleamine 2,3-dioxygenase expression as well as kynurenine production, which in turn was shown to mediate the detrimental effects of IL-1b on neurogenesis and apoptosis. In contrast, neither R- nor S-ketamine prevented IL-6-induced kynurenine pathway activation. Results suggest that R- and S-ketamine have pro-neurogenic and anti-inflammatory properties; however, this is mediated by inhibition of the kynurenine pathway only in the context of IL-1b. Overall, this study enhances our understanding of the mechanisms underlying ketamine's antidepressant effects in the context of different inflammatory phenotypes, ultimately leading to the development of more effective, personalized therapeutic approaches for patients suffering from depression.

A roadmap to human hippocampal neurogenesis in adulthood, aging and AD.

In the rodent, hippocampal neurogenesis plays critical roles in learning and memory1,2, is tightly regulated by inhibitory neurons3-7 and contributes to memory dysfunction in Alzheimer's disease (AD) mouse models8-10. In contrast, the mechanisms regulating neurogenesis in the adult human hippocampus, the dynamic shifts in the transcriptomic and epigenomic profiles in aging and AD and putative niche interactions within the cellular environment, remain largely unknown. Using single nuclei multi-omics of postmortem human hippocampi we map the molecular mechanisms of hippocampal neurogenesis across aging, cognitive decline, and AD neuropathology. Transcriptomic and epigenetic profiling of neural stem cells (NSCs), neuroblasts and immature neurons suggests that the earliest shift in the characteristics of neurogenesis takes place in NSCs in aging. Cognitive impairment was associated with changes in neuroblast profile. In AD, there was a widespread cessation of the transcription machinery in immature neurons, with robust downregulation of genes regulating ribosomal and mitochondrial function. Further, there was substantial loss of parvalbumin+ inhibitory neurons in the hippocampus in aging. The number of the rest of inhibitory neurons were reduced as a function of age and diagnosis. Notably, a similar system-level effect was observed between immature and inhibitory neurons in the transition from aging to AD, manifested by common molecular pathways that were ultimately lost in AD. The numbers of neuroblasts, immature and GABAergic neurons inversely correlated with extent of neuropathology. Using CellChat and NeuronChat, we inferred the ligands and receptors by which neurogenic cells communicate with their cellular environment. Loss of synaptic adhesion molecules and neurotransmitters, either sent or received by neurogenic cells, was observed in AD. Together, this study delineates the molecular mechanisms and dynamics of human neurogenesis, functional association with inhibitory neurons and a mechanism of hippocampal hyperexcitability in AD.

Mapping human adult hippocampal neurogenesis with single-cell transcriptomics: Reconciling controversy or fueling the debate?

The notion of exploiting the regenerative potential of the human brain in physiological aging or neurological diseases represents a particularly attractive alternative to conventional strategies for enhancing or restoring brain function. However, a major first question to address is whether the human brain does possess the ability to regenerate. The existence of human adult hippocampal neurogenesis (AHN) has been at the center of a fierce scientific debate for many years. The advent of single-cell transcriptomic technologies was initially viewed as a panacea to resolving this controversy. However, recent single-cell RNA sequencing studies in the human hippocampus yielded conflicting results. Here, we critically discuss and re-analyze previously published AHN-related single-cell transcriptomic datasets. We argue that, although promising, the single-cell transcriptomic profiling of AHN in the human brain can be confounded by methodological, conceptual, and biological factors that need to be consistently addressed across studies and openly discussed within the scientific community.

Special properties of adult neurogenesis in the human hippocampus: Implications for its clinical applications.

Special properties of adult neurogenesis in the human hippocampus: Implications for its clinical applications.

In vitro characterization on the role of APOE polymorphism in human hippocampal neurogenesis.

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.

Omega-3-derived endocannabinoids prevent pro-inflammatory cytokine-induced decreases in human hippocampal neurogenesis and astrogliogenesis, and increase in apoptosis

Omega-3-derived endocannabinoids prevent pro-inflammatory cytokine-induced decreases in human hippocampal neurogenesis and astrogliogenesis, and increase in apoptosis

Neurogenesis is disrupted in human hippocampal progenitor cells upon exposure to serum samples from hospitalized COVID-19 patients with neurological symptoms

Coronavirus disease 2019 (COVID-19), represents an enormous new threat to our healthcare system and particularly to the health of older adults. Although the respiratory symptoms of COVID-19 are well recognized, the neurological manifestations, and their underlying cellular and molecular mechanisms, have not been extensively studied yet. Our study is the first one to test the direct effect of serum from hospitalised COVID-19 patients on human hippocampal neurogenesis using a unique in vitro experimental assay with human hippocampal progenitor cells (HPC0A07/03 C). We identify the different molecular pathways activated by serum from COVID-19 patients with and without neurological symptoms (i.e., delirium), and their effects on neuronal proliferation, neurogenesis, and apoptosis. We collected serum sample twice, at time of hospital admission and approximately 5 days after hospitalization. We found that treatment with serum samples from COVID-19 patients with delirium (n = 18) decreased cell proliferation and neurogenesis, and increases apoptosis, when compared with serum samples of sex- and age-matched COVID-19 patients without delirium (n = 18). This effect was due to a higher concentration of interleukin 6 (IL6) in serum samples of patients with delirium (mean ± SD: 229.9 ± 79.1 pg/ml, vs. 32.5 ± 9.5 pg/ml in patients without delirium). Indeed, treatment of cells with an antibody against IL6 prevented the decreased cell proliferation and neurogenesis and the increased apoptosis. Moreover, increased concentration of IL6 in serum samples from delirium patients stimulated the hippocampal cells to produce IL12 and IL13, and treatment with an antibody against IL12 or IL13 also prevented the decreased cell proliferation and neurogenesis, and the increased apoptosis. Interestingly, treatment with the compounds commonly administered to acute COVID-19 patients (the Janus kinase inhibitors, baricitinib, ruxolitinib and tofacitinib) were able to restore normal cell viability, proliferation and neurogenesis by targeting the effects of IL12 and IL13. Overall, our results show that serum from COVID-19 patients with delirium can negatively affect hippocampal-dependent neurogenic processes, and that this effect is mediated by IL6-induced production of the downstream inflammatory cytokines IL12 and IL13, which are ultimately responsible for the detrimental cellular outcomes.

Human adult hippocampal neurogenesis is back, again?

Human adult hippocampal neurogenesis is back, again?

Comment on "Impact of neurodegenerative diseases on human adult hippocampal neurogenesis".

Terreros-Roncal et al. investigated the impacts of human neurodegeneration on immunostainings assumed to be associated with neurogenesis. However, the study provides no evidence that putative proliferating cells are linked to neurogenesis, that multipolar nestin+ astrocytes are progenitors, or that mature-looking doublecortin+ neurons are adult-born. Their histology-marker expression differs from what is observed in species where adult hippocampal neurogenesis is well documented.

Response to Comment on "Impact of neurodegenerative diseases on human adult hippocampal neurogenesis".

Alvarez-Buylla and colleagues provide an alternative interpretation of some of the data included in our manuscript and question whether well-validated markers of adult hippocampal neurogenesis (AHN) are related to this phenomenon in our study. In Terreros-Roncal et al., reconstruction of the main stages of human AHN revealed its enhanced vulnerability to neurodegeneration. Here, we clarify ambiguities raised by these authors.

Response to Comment on "Impact of neurodegenerative diseases on human adult hippocampal neurogenesis".

Rakic and colleagues challenge the use of extensively validated adult hippocampal neurogenesis (AHN) markers and postulate an alternative interpretation of some of the data included in our study. In Terreros-Roncal et al., reconstruction of the main stages encompassed by human AHN revealed enhanced vulnerability of this phenomenon to neurodegenerative diseases. Here, we clarify points and ambiguities raised by these authors.

Comment on "Impact of neurodegenerative diseases on human adult hippocampal neurogenesis".

Comment on "Impact of neurodegenerative diseases on human adult hippocampal neurogenesis".

Adult human neurogenesis: early studies clarify recent controversies and go further.

Evidence on adult mammalian neurogenesis and scarce studies with human brains led to the idea that adult human neurogenesis occurs in the subgranular zone (SGZ) of the dentate gyrus and in the subventricular zone (SVZ). However, findings published from 2018 rekindled controversies on adult human SGZ neurogenesis. We systematically reviewed studies published during the first decade of characterization of adult human neurogenesis (1994-2004) - when the two-neurogenic-niche concept in humans was consolidated - and compared with further studies. The synthesis of both periods is that adult human neurogenesis occurs in an intensity ranging from practically zero to a level comparable to adult mammalian neurogenesis in general, which is the prevailing conclusion. Nonetheless, Bernier and colleagues showed in 2000 intriguing indications of adult human neurogenesis in a broad area including the limbic system. Likewise, we later showed evidence that limbic and hypothalamic structures surrounding the circumventricular organs form a continuous zone expressing neurogenesis markers encompassing the SGZ and SVZ. The conclusion is that publications from 2018 on adult human neurogenesis did not bring novel findings on location of neurogenic niches. Rather, we expect that the search of neurogenesis beyond the canonical adult mammalian neurogenic niches will confirm our indications that adult human neurogenesis is orchestrated in a broad brain area. We predict that this approach may, for example, clarify that human hippocampal neurogenesis occurs mostly in the CA1-subiculum zone and that the previously identified human rostral migratory stream arising from the SVZ is indeed the column of the fornix expressing neurogenesis markers.

Lithium treatment and human hippocampal neurogenesis

Lithium is a first-line treatment for bipolar disorder, where it acts as a mood-stabilizing agent. Although its precise mechanism remains unclear, neuroimaging studies have shown that lithium accumulates in the hippocampus and that chronic use amongst bipolar disorder patients is associated with larger hippocampal volumes. Here, we tested the chronic effects of low (0.75 mM) and high (2.25 mM) doses of lithium on human hippocampal progenitor cells and used immunocytochemistry to investigate the effects of lithium on cell parameters implicated in neurogenesis. Corresponding RNA-sequencing and gene-set enrichment analyses were used to evaluate whether genes affected by lithium in our model overlap with those regulating the volume of specific layers of the dentate gyrus. We observed that high-dose lithium treatment in human hippocampal progenitors increased the generation of neuroblasts (P ≤ 0.01), neurons (P ≤ 0.01), and glia (P ≤ 0.001), alongside the expression of genes, which regulate the volume of the molecular layer of the dentate gyrus. This study provides empirical support that adult hippocampal neurogenesis and gliogenesis are mechanisms that could contribute to the effects of lithium on human hippocampal volume.

Impact of neurodegenerative diseases on human adult hippocampal neurogenesis.

Disrupted hippocampal performance underlies psychiatric comorbidities and cognitive impairments in patients with neurodegenerative disorders. To understand the contribution of adult hippocampal neurogenesis (AHN) to amyotrophic lateral sclerosis, Huntington’s disease, Parkinson’s disease, dementia with Lewy bodies, and frontotemporal dementia, we studied postmortem human samples. We found that adult-born dentate granule cells showed abnormal morphological development and changes in the expression of differentiation markers. The ratio of quiescent to proliferating hippocampal neural stem cells shifted, and the homeostasis of the neurogenic niche was altered. Aging and neurodegenerative diseases reduced the phagocytic capacity of microglia, triggered astrogliosis, and altered the microvasculature of the dentate gyrus. Thus, enhanced vulnerability of AHN to neurodegeneration might underlie hippocampal dysfunction during physiological and pathological aging in humans.

IL-1\u03b2 and HMGB1 are anti-neurogenic to endogenous neural stem cells in the sclerotic epileptic human hippocampus

BackgroundThe dentate gyrus exhibits life-long neurogenesis of granule-cell neurons, supporting hippocampal dependent learning and memory. Both temporal lobe epilepsy patients and animal models frequently have hippocampal-dependent learning and memory difficulties and show evidence of reduced neurogenesis. Animal and human temporal lobe epilepsy studies have also shown strong innate immune system activation, which in animal models reduces hippocampal neurogenesis. We sought to determine if and how neuroinflammation signals reduced neurogenesis in the epileptic human hippocampus and its potential reversibility.MethodsWe isolated endogenous neural stem cells from surgically resected hippocampal tissue in 15 patients with unilateral hippocampal sclerosis. We examined resultant neurogenesis after growing them either as neurospheres in an ideal environment, in 3D cultures which preserved the inflammatory microenvironment and/or in 2D cultures which mimicked it.Results3D human hippocampal cultures largely replicated the cellular composition and inflammatory environment of the epileptic hippocampus. The microenvironment of sclerotic human epileptic hippocampal tissue is strongly anti-neurogenic, with sustained release of the proinflammatory proteins HMGB1 and IL-1β. IL-1β and HMGB1 significantly reduce human hippocampal neurogenesis and blockade of their IL-1R and TLR 2/4 receptors by IL1Ra and Box-A respectively, significantly restores neurogenesis in 2D and 3D culture.ConclusionOur results demonstrate a HMGB1 and IL-1β-mediated environmental anti-neurogenic effect in human TLE, identifying both the IL-1R and TLR 2/4 receptors as potential drug targets for restoring human hippocampal neurogenesis in temporal lobe epilepsy.

Omega-3 polyunsaturated fatty acids protect against inflammation through production of LOX and CYP450 lipid mediators: relevance for major depression and for human hippocampal neurogenesis

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can exert antidepressant, anti-inflammatory and neuroprotective properties, but the exact molecular mechanism underlying their effects is still not fully understood. We conducted both in vitro and clinical investigations to test which EPA or DHA metabolites are involved in these anti-inflammatory, neuroprotective and antidepressant effects. In vitro, we used the human hippocampal progenitor cell line HPC0A07/03C, and pre-treated cells with either EPA or DHA, followed by interleukin 1beta (IL1β), IL6 and interferon-alpha (IFN-α). Both EPA and DHA prevented the reduction in neurogenesis and the increase in apoptosis induced by these cytokines; moreover, these effects were mediated by the lipoxygenase (LOX) and cytochrome P450 (CYP450) EPA/DHA metabolites, 5-hydroxyeicosapentaenoic acid (HEPE), 4-hydroxydocosahexaenoic acid (HDHA), 18-HEPE, 20-HDHA, 17(18)-epoxyeicosatetraenoic acid (EpETE) and 19(20)-epoxydocosapentaenoic acid (EpDPA), detected here for the first time in human hippocampal neurones using mass spectrometry lipidomics of the supernatant. In fact, like EPA/DHA, co-treatment with these metabolites prevented cytokines-induced reduction in neurogenesis and apoptosis. Moreover, co-treatment with 17(18)-EpETE and 19(20)-EpDPA and the soluble epoxide hydroxylase (sEH) inhibitor, TPPU (which prevents their conversion into dihydroxyeicosatetraenoic acid (DiHETE)/ dihydroxydocosapentaenoic acid (DiHDPA) metabolites) further enhanced their neurogenic and anti-apoptotic effects. Interestingly, these findings were replicated in a sample of n = 22 patients with a DSM-IV Major Depressive Disorder, randomly assigned to treatment with either EPA (3.0 g/day) or DHA (1.4 g/day) for 12 weeks, with exactly the same LOX and CYP450 lipid metabolites increased in the plasma of these patients following treatment with their precursor, EPA or DHA, and some evidence that higher levels of these metabolites were correlated with less severe depressive symptoms. Overall, our study provides the first evidence for the relevance of LOX- and CYP450-derived EPA/DHA bioactive lipid metabolites as neuroprotective molecular targets for human hippocampal neurogenesis and depression, and highlights the importance of sEH inhibitors as potential therapeutic strategy for patients suffering from depressive symptoms.

Understanding the Real State of Human Adult Hippocampal Neurogenesis From Studies of Rodents and Non-human Primates.

The concept of adult hippocampal neurogenesis (AHN) has been widely accepted, and a large number of studies have been performed in rodents using modern experimental techniques, which have clarified the nature and developmental processes of adult neural stem/progenitor cells, the functions of AHN, such as memory and learning, and its association with neural diseases. However, a fundamental problem is that it remains unclear as to what extent AHN actually occurs in humans. The answer to this is indispensable when physiological and pathological functions of human AHN are deduced from studies of rodent AHN, but there are controversial data on the extent of human AHN. In this review, studies on AHN performed in rodents and humans will be briefly reviewed, followed by a discussion of the studies in non-human primates. Then, how data of rodent and non-human primate AHN should be applied for understanding human AHN will be discussed.

Pro- and anti-inflammatory properties of interleukin (IL6) in vitro: relevance for major depression and for human hippocampal neurogenesis.

BackgroundAlthough the pro-inflammatory cytokine interleukin (IL)6 has been generally regarded as “depressogenic,” recent research has started to question this assumption in light of the fact that this cytokine can also have anti-inflammatory properties. This bimodal action seems to be dependent on its concentration levels and on the concomitant presence of other pro-inflammatory cytokines.MethodsWe exposed a human hippocampal progenitor cell line, HPC0A07/03C, to cytokine levels described in depressed patients (IL6 5 pg/mL with IL1β 10 pg/mL or Macrophage Migration Inhibitory Factor (300 pg/mL) in healthy individuals (IL6 with IL1β, 1 pg/mL or Macrophage Migration Inhibitory Factor 10 pg/mL), as well as to the potentially anti-inflammatory, much higher concentrations of IL6 (50 000 pg/mL).ResultsTreatment with high concentrations of IL6 with IL1β or Macrophage Migration Inhibitory Factor (resembling depressed patients) decreases neurogenesis compared with low concentrations of the same cytokines (healthy individuals) and that this is mediated via production of, respectively, IL8 and IL1β in cell supernatant. Instead, treatment with very high, anti-inflammatory concentration of IL6 (50 000 pg/mL) together with high IL1β or Macrophage Migration Inhibitory Factor prevents decrease in neurogenesis and reduces both IL8 and IL1β. When high concentrations of both IL1β and Macrophage Migration Inhibitory Factor were used in co-treatment, as a model of treatment-resistant depression, we also demonstrated a reduction in neurogenesis and that this is mediated via a decrease in IL4; moreover, co-treatment with high IL1β and Macrophage Migration Inhibitory Factor and the very high concentration of IL6 prevented the reduction in neurogenesis and increased IL4.ConclusionsOur results demonstrate that IL6 can exert both pro- and anti-inflammatory (potentially antidepressant) properties, depending on its concentrations and combinations with other inflammatory cytokines.

The role of omega-3 fatty acids in preventing glucocorticoid-induced reduction in human hippocampal neurogenesis and increase in apoptosis

Glucocorticoids have been suggested to be involved in several neuropsychiatric disorders, including depression. One of the possible mechanisms through which glucocorticoids contribute to the development of the depressive symptomatology is via regulation of distinct neurogenic mechanisms in the brain. A preventive or protective approach for these patients might be the use of omega-3 polyunsaturated fatty acids (n-3 PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are known for they neuroprotective properties. We used the human hippocampal progenitor cell line HPC0A07/03C and pre-treated cells with either EPA or DHA, followed by treatment with the glucocorticoid cortisol either alone, or in co-treatment with the same n-3 PUFA during subsequent 3 days of proliferation and 7 days of differentiation. During proliferation, both EPA and DHA were able to prevent cortisol-induced reduction in proliferation and increase in apoptosis, when used in pre-treatment, and both pre- and co-treatment. During differentiation, EPA was able to prevent cortisol-induced reduction in neurogenesis and increase in apoptosis, when used in pre-treatment, and both pre- and co-treatment only during the proliferation stage; however, DHA required continuous treatment also during the differentiation stage to prevent cortisol-induced reduction in neurogenesis. Using transcriptomic analyses, we showed that both EPA and DHA regulated pathways involved in oxidative stress and immune response [e.g., nuclear factor (erythroid-derived 2)-like 2 (Nrf2), Signal transducer and activator of transcription 3 (STAT3), Interferon (IFN) and Interleukin (IL)-1 signaling], whereas DHA also regulated pathways involved in cell development and neuronal formation [e.g., cAMP-response element binding protein (CREB) signaling]. We provide the first evidence for treatment with both EPA and DHA to prevent cortisol-induced reduction in human hippocampal neurogenesis, and identify novel molecular mechanisms underlying these effects.