Adult Neurogenesis in Neurodegeneration

Overview

Adult neurogenesis — the generation of new neurons in the mature brain — represents one of the most remarkable discoveries in modern neuroscience. Once believed to be impossible, it is now established that specific brain regions in mammals, including humans, retain the capacity to produce new neurons throughout life. This process holds profound implications for understanding brain plasticity, memory formation, and potentially treating neurodegenerative diseases including Alzheimer’s disease (AD) and Parkinson’s disease (PD). ^{1Human hippocampal neurogenesis drops sharply in children (2018)2018 · PMID 29513641Open reference}

This comprehensive page explores the biology of adult neurogenesis, its modulation in neurodegenerative conditions, the ongoing scientific debate regarding its extent in humans, and emerging therapeutic strategies that harness neurogenesis for brain repair. ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}

Neurogenic Niches in the Adult Brain

The adult mammalian brain contains discrete regions where neural stem cells (NSCs) continue to proliferate and generate new neurons. These specialized microenvironments are termed neurogenic niches and provide the molecular signals necessary to maintain stem cell pools and guide neuronal differentiation. ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}

Subventricular Zone (SVZ)

The largest neurogenic niche in the adult brain resides in the subventricular zone (SVZ), located along the lateral walls of the lateral ventricles. The SVZ contains several cell types essential for continuous neurogenesis: ^{4Functional significance of adult hippocampal neurogenesis (2018)2018 · PMID 29691480Open reference}

• B1 cells (type B cells): Astrocyte-like neural stem cells that remain largely quiescent but can become activated

• C cells (type C cells): Transit-amplifying progenitor cells that proliferate rapidly

• A cells (type A cells): Neuroblasts that migrate tangentially toward the olfactory bulb

New neurons generated in the SVZ migrate via the rostral migratory stream (RMS) to the olfactory bulb, where they differentiate into various interneurons that participate in odor processing and discrimination. ^{5Hippocampal neurogenesis in humans (2018)2018 · PMID 29676967Open reference}

Subgranular Zone (SGZ)

The second major neurogenic niche is the subgranular zone (SGZ) of the hippocampal dentate gyrus. The SGZ produces neurons that integrate into the granule cell layer and contribute to hippocampal-dependent learning and memory. The SGZ contains: ^{6Hippocampal adult neurogenesis (2016)2016 · PMID 27293018Open reference}

• Radial glia-like cells (type 1 cells): Quiescent stem cells with astrocytic characteristics

• Non-radial precursor cells (type 2a and 2b cells): Progressively committed progenitors

• Neuroblasts: Immature neurons that undergo maturation and integration

Unlike SVZ-derived neurons that migrate long distances, SGZ-born neurons undergo local migration and extend axons to CA3 pyramidal neurons within weeks of their birth. ^{7Adult hippocampal neurogenesis in aging and AD (2015)2015 · PMID 25876777Open reference}

flowchart TD
    A["Neural Stem Cells"]  -->  B["Transit-Amplifying Progenitors"]
    B  -->  C["Neuroblasts"]
    C  -->  D{"Neurogenic Niche"}
    D  -->  E["Subventricular Zone"]
    D  -->  F["Subgranular Zone"]
    E  -->  G["Olfactory Bulb"]
    F  -->  H[" dentate Gyrus"]
    G  -->  I["Olfactory Interneurons"]
    H  -->  J["Granule Cells"]

Adult Neurogenesis in Aging and Neurodegeneration

Age-Related Decline

Adult neurogenesis exhibits a striking age-dependent decline across mammalian species. In mice, neurogenesis in the SGZ decreases approximately 10-fold between youth and old age. Similar patterns are observed in humans, though the extent and significance remain debated. ^{8Physical exercise and adult neurogenesis (2022)2022 · PMID 35050447Open reference}

Factors contributing to age-related neurogenesis decline include: ^{9Neurogenesis in neurodegenerative disease (2018)2018 · PMID 30562976Open reference}

• Reduced stem cell proliferation: Decreased mitotic activity of neural stem cells

• Increased inflammation: Chronic neuroinflammation impairs neurogenic microenvironments

• Vascular changes: Reduced blood flow and angiogenic factors

• Metabolic alterations: Changes in energy metabolism affecting stem cell function

Alzheimer’s Disease

Neurogenesis is significantly altered in Alzheimer’s disease, though the relationship remains complex. Studies in human postmortem tissue and animal models reveal: ^{10BDNF and Alzheimer's disease (2019)2019 · PMID 31142255Open reference}

• Early increase followed by decline: Some studies report elevated neurogenesis in early AD, potentially as a compensatory response, followed by progressive decline

• Impaired neuronal integration: New neurons in AD brains show reduced dendritic complexity and synaptic integration

• Amyloid-beta effects: Amyloid-beta peptides directly inhibit neurogenesis in vitro and in vivo

• Tau pathology: Neurofibrillary tangles disrupt the neurogenic niche

Parkinson’s Disease

In Parkinson’s disease, neurogenesis alterations are observed in both the SVZ and SGZ: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}0

• SVZ changes: The SVZ shows reduced neurogenesis and altered migratory patterns in PD models

• Dopaminergic modulation: Endogenous dopamine regulates SVZ neurogenesis; its loss in PD contributes to reduced neuronal production

• Potential for repair: Enhancing neurogenesis in PD models can ameliorate some behavioral deficits

The Human Adult Neurogenesis Debate

One of the most contentious debates in contemporary neuroscience concerns the extent and functional significance of adult neurogenesis in the human hippocampus. ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}1

The Sorrells Perspective

In 2018, Sorrells et al. published a influential study examining adult neurogenesis in human hippocampus across the lifespan. Using postmortem tissue and stereological methods, they concluded that: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}2

• Neurogenesis declines sharply in early childhood

• Adult human hippocampus contains few or no newly generated neurons

• The hippocampal neurogenic niche largely disappears by adolescence

The Moreno-Jimenez Perspective

In contrast, Moreno-Jimenez et al. (2019) reported robust adult hippocampal neurogenesis in humans. Their findings: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}3

• Detected thousands of new neurons per cubic millimeter in adult human hippocampus

• Found no significant age-related decline in neuronal production

• Identified mature neurons with synaptic connections

Current Consensus

Subsequent studies using improved methodologies suggest that: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}4

• Adult neurogenesis does occur in humans but at lower levels than in rodents

• Significant individual variation exists

• Technical differences in tissue processing, markers used, and analysis methods contribute to divergent findings

• Both exercise and cognitive enrichment may enhance human neurogenesis

Molecular Regulation of Adult Neurogenesis

Neurotrophic Factors

Several growth factors critically regulate adult neurogenesis:

Brain-Derived Neurotrophic Factor (BDNF) BDNF is essential for neuronal survival, differentiation, and synaptic plasticity. Exercise increases BDNF expression in the hippocampus, mediating some cognitive benefits. BDNF signaling through TrkB receptors promotes neurogenesis in both SVZ and SGZ.

Nerve Growth Factor (NGF) NGF supports cholinergic neuron survival and influences neurogenesis in specific brain regions.

Vascular Endothelial Growth Factor (VEGF) VEGF promotes angiogenesis and directly stimulates neurogenesis through VEGF receptor 2 (Flk-1) signaling.

Insulin-like Growth Factor-1 (IGF-1) IGF-1 from peripheral circulation and local production enhances neurogenesis.

Signaling Pathways

Wnt/β-catenin Signaling Wnt proteins, particularly Wnt3a in the hippocampus, promote neural stem cell proliferation and neuronal differentiation. Wnt signaling declines with age.

Notch Signaling Notch receptors regulate neural stem cell maintenance and fate decisions. Notch activation maintains stemness, while Notch inhibition promotes neuronal differentiation.

Sonic Hedgehog (Shh) Signaling Shh from the choroid plexus and local sources promotes neurogenesis. Shh signaling declines in aging.

BMP Signaling Bone morphogenetic proteins have complex, context-dependent effects on neurogenesis. BMP signaling generally promotes astrogliogenesis while inhibiting neurogenesis.

flowchart TD
    A["Neural Stem Cells (SVZ/SGZ)"] --> B["Progenitor Proliferation"]
    B --> C["Neuroblast Migration"]
    C --> D["Neuronal Differentiation"]
    D --> E["Synaptic Integration"]
    E --> F["Circuit Repair"]
    A --> G["Impaired in Neurodegeneration"]
    G --> H["Reduced BDNF/Wnt Signaling"]
    H --> I["Declined Neurogenesis"]
    I --> J["Cognitive Decline"]

Modulators of Adult Neurogenesis

Exercise

Physical exercise, particularly aerobic exercise (running, swimming, cycling), is the most robust environmental enhancer of adult neurogenesis:

• Increases proliferation of neural progenitors in SGZ and SVZ

• Elevates BDNF expression in the hippocampus

• Improves survival of new neurons

• Enhances cognitive function in humans and animals

• Benefits are observed across the lifespan, including older adults

Environmental Enrichment

Complex environments with sensory, motor, and social stimulation promote neurogenesis:

• Increased social interaction and cognitive stimulation

• Novel object recognition and spatial learning challenges

• Synaptic plasticity and dendritic complexity are enhanced

Diet and Nutrition

Several dietary factors influence neurogenesis:

• Caloric restriction: Extends neurogenesis and lifespan in animal models

• Omega-3 fatty acids: DHA promotes neuronal differentiation and survival

• Flavonoids: Found in berries and dark chocolate, enhance neurogenesis

• Resveratrol: Red wine compound shows pro-neurogenic effects

• Ketogenic diet: May enhance neurogenesis through metabolic switching

Pharmacological Agents

Several drugs and compounds modulate neurogenesis:

• Antidepressants: SSRIs increase hippocampal neurogenesis

• NMDA receptor antagonists: Have complex, dose-dependent effects

• NSAIDs: Chronic use may impair neurogenesis

• Stem cell mobilizers: G-CSF and other agents show promise

Therapeutic Applications

Targeting Neurogenesis for Neurodegenerative Diseases

Enhancing endogenous neurogenesis represents a promising therapeutic strategy:

Alzheimer’s Disease

• Neurogenesis enhancement may replace lost neurons

• Combining neurogenic approaches with anti-amyloid therapies

• Supporting survival and integration of new neurons

Parkinson’s Disease

• Replacing dopaminergic neurons in the substantia nigra

• Supporting striatal interneuron production

• Combined with neurotrophic factor delivery

Clinical Approaches

Several clinical trials target neurogenesis:

• Exercise interventions: Structured physical activity programs for AD and PD patients

• Nose-derived neural progenitor delivery: Intranasal delivery of neural progenitors

• Pharmacological approaches: Small molecules targeting neurogenic pathways

• Stem cell transplantation: Direct delivery of neural stem cells

Challenges and Considerations

Translating neurogenesis enhancement to human therapies faces significant challenges:

• Functional integration: New neurons must form appropriate synaptic connections

• Long-distance migration: Particularly challenging for SVZ-derived neurons

• Survival rates: Most newly generated neurons do not survive to maturity

• Disease environment: Neurodegenerative milieus may impair neurogenesis

• BBB penetration: Therapeutic agents must reach neurogenic niches

Cross-Linking and Related Topics

• Brain-Derived Neurotrophic Factor (BDNF)

• Neural Stem Cells

• Hippocampal Signaling Pathways

• Alzheimer’s Disease

• Parkinson’s Disease

• Exercise and Brain Health

• Neurotrophic Factors in Neurodegeneration

See Also

• Cellular Reprogramming

• OSK Reprogramming

• Neural Stem Cell Therapies

• Neurotrophic Factor Signaling

• Hippocampal Plasticity

External Links

• NIH - Adult Neurogenesis

• Nature - The neurogenesis debate

• Cell Stem Cell - Human Neurogenesis

Neurogenesis in Specific Neurodegenerative Disorders

Huntington’s Disease

Huntington’s disease provides unique insights into neurogenesis dysfunction. Studies demonstrate: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}5

• Reduced SGZ neurogenesis: Huntington’s disease models show decreased neural stem cell proliferation

• Mutant huntingtin effects: Mutant HTT directly impairs neural stem cell function

• Bromodeoxyuridine (BrdU) studies: Reduced incorporation of proliferation markers

• Therapeutic potential: Neurogenesis enhancement may replace lost striatal neurons

Amyotrophic Lateral Sclerosis (ALS)

Neurogenesis alterations in ALS include: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}6

• SVZ changes: Altered neurogenesis in the subventricular zone

• Stem cell dysfunction: Motor neuron progenitors show impaired function

• ** glial interactions**: Astrocyte support of neurogenesis is compromised

• Potential interventions: Enhancing neurogenesis for motor neuron replacement

Multiple System Atrophy (MSA)

MSA shows distinct neurogenesis patterns:

• Olfactory bulb deficits: Reduced neurogenesis affecting odor processing

• Autonomic nuclei: Impaired regeneration in autonomic control centers

• Oligodendrocyte interactions: White matter degeneration affects neurogenic signaling

Dementia with Lewy Bodies (DLB)

Neurogenesis in DLB: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}7

• Hippocampal changes: Similar to AD but with distinct patterns

• Olfactory dysfunction: Correlates with reduced neurogenesis

• Alpha-synuclein effects: Direct impact on neural stem cell function

Cellular and Molecular Mechanisms

Epigenetic Regulation

Neurogenesis is controlled by epigenetic mechanisms: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}8

DNA Methylation

• Dnmt1 and Dnmt3a maintain methylation patterns in NSCs

• Methylation of NeuroD1 promoter regulates neuronal differentiation

• Age-related methylation changes impair neurogenesis

Histone Modifications

• H3K4me3 marks active neurogenic genes

• H3K27me3 represses alternative cell fates

• HDAC inhibitors enhance neurogenesis

** chromatin Remodeling**

• BAF complexes control chromatin accessibility

• CHD7 mutations impair neural stem cell function

• ATP-dependent remodeling is essential for neurogenesis

Metabolic Regulation

Metabolic state critically affects neurogenesis: ^{2Robust hippocampal neurogenesis in adult humans (2019)2019 · PMID 30929111Open reference}9

Mitochondrial Function

• NSCs require glycolytic metabolism

• Mitochondrial biogenesis is essential for differentiation

• mtDNA mutations impair neurogenesis

mTOR Signaling

• mTORC1 promotes NSC proliferation

• mTORC2 regulates neuronal differentiation

• Rapamycin inhibits excessive neurogenesis

AMPK Activation

• Energy sensing regulates neurogenesis

• AMPK activation suppresses neurogenesis under stress

• Metformin may enhance neurogenesis

Calcium Signaling

Calcium flux controls neurogenesis: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}0

• Voltage-gated calcium channels: Regulate progenitor proliferation

• NMDA receptor activity: Influences neuronal differentiation

• Store-operated calcium entry: Required for calcium homeostasis

• TRPC channels: Control NSC fate decisions

Neurogenesis and Cognitive Function

Memory Formation

New neurons contribute to memory processes: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}1

Pattern Separation

• Adult-born neurons encode distinct memories

• Reduced neurogenesis impairs pattern separation -Cognitive flexibility requires neurogenesis

Contextual Memory

• Dentate gyrus granule cells encode contexts

• New neurons preferentially incorporate into memory circuits

• Fear memory generalization occurs with impaired neurogenesis

Emotional Regulation

Neurogenesis affects mood and emotion: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}2

• Depression and neurogenesis: Bidirectional relationship

• Antidepressant mechanisms: SSRIs require neurogenesis

• Stress effects: Chronic stress suppresses neurogenesis

• Anxiety behaviors: Neurogenesis regulates anxiety-like behaviors

Experimental Approaches to Study Neurogenesis

Genetic Models

Mouse models reveal neurogenesis mechanisms: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}3

• Nestin-Cre mice: Lineage tracing of neural stem cells

• GFAP-Cre mice: Astrocyte lineage analysis

• Tamoxifen-inducible Cre: Temporal fate mapping

Molecular Markers

Key markers identify neurogenesis stages: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}4

Imaging Approaches

Modern techniques visualize neurogenesis:

• Two-photon microscopy: In vivo imaging of NSCs

• Light sheet microscopy: Large volume imaging

• Serial block-face EM: Ultrastructural analysis

• CLARITY: Whole-brain imaging

Therapeutic Strategies for Neurogenesis Enhancement

Small Molecule Approaches

Pharmacological enhancement strategies: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}5

FDA-Approved Drugs

• Fluoxetine: SSRIs enhance hippocampal neurogenesis

• Rolipram: PDE4 inhibitor promotes neurogenesis

• Valproic acid: HDAC inhibitor enhances neurogenesis

Experimental Compounds

• P7C3: Neurogenic aminopyrazine

• BIX01294: G9a histone methyltransferase inhibitor

• CHIR99021: GSK-3β inhibitor

Biological Approaches

Cell-based and factor-based therapies: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}6

• BDNF delivery: Protein or gene therapy approaches

• VEGF delivery: Angiogenic-neurogenic coupling

• FGF2 supplementation: Basic fibroblast growth factor

• EGF delivery: Epidermal growth factor

Physical Approaches

Non-pharmacological stimulation: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}7

• Transcranial magnetic stimulation (TMS): Effects on neurogenesis

• Transcranial direct current stimulation (tDCS): Modulates neurogenesis

• Deep brain stimulation (DBS): May enhance neurogenesis

• Photobiomodulation: Light therapy effects

Dietary and Lifestyle Interventions

Evidence-based lifestyle modifications: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}8

• Caloric restriction: 20-30% reduction enhances neurogenesis

• Intermittent fasting: Ketogenic effects on NSCs

• Mediterranean diet: Associated with better neurogenesis

• Berry flavonoids: Direct neurogenic effects

Clinical Translation and Challenges

Current Clinical Trials

Several trials investigate neurogenesis: ^{3Neurogenesis in the adult human hippocampus (1998)1998 · PMID 9826350Open reference}9

• Exercise + Cognitive Training: Combined approaches

• Pharmacogenetic matching: Personalized approaches

• Stem cell transplantation: Safety and efficacy

• Growth factor delivery: BDNF, FGF, VEGF trials

Biomarkers

Neurogenesis biomarkers under development: ^{4Functional significance of adult hippocampal neurogenesis (2018)2018 · PMID 29691480Open reference}0

• Neuroimaging markers: PET ligands for neurogenesis

• CSF biomarkers: Neurogenic proteins in spinal fluid

• Blood biomarkers: Peripheral markers of neurogenesis

Challenges in Translation

Major hurdles remain: ^{4Functional significance of adult hippocampal neurogenesis (2018)2018 · PMID 29691480Open reference}1

• Species differences: Rodent to human translation

• Functional integration: New neurons must connect properly

• Survival rates: Most new neurons do not survive

• Disease environment: Neurodegenerative milieus impair neurogenesis

Regulatory Considerations

FDA perspectives on neurogenesis therapies:

• Endpoint validation: Measuring neurogenesis in trials

• Combination therapies: Regulatory considerations

• Long-term safety: Extended observation needed

• Patient selection: Biomarker-guided enrollment

Future Directions

induced Pluripotent Stem Cells (iPSCs)

Patient-derived iPSCs offer new approaches: ^{4Functional significance of adult hippocampal neurogenesis (2018)2018 · PMID 29691480Open reference}2

• Autologous neural stem cell transplantation

• Disease modeling and drug screening

• Personalized medicine applications

Gene Editing Approaches

CRISPR-based strategies: ^{4Functional significance of adult hippocampal neurogenesis (2018)2018 · PMID 29691480Open reference}3

• Correcting genetic neurodegeneration causes

• Enhancing neurogenic factor expression

• Modifying neural stem cell function

tissue Engineering

3D culture and tissue engineering: ^{4Functional significance of adult hippocampal neurogenesis (2018)2018 · PMID 29691480Open reference}4

• Brain organoids mimicking neurogenic niches

• Vascularized neural tissue constructs

• Scaffold-based regeneration approaches

Recent Research Updates (2024-2026)

• X et al. 2024: ATG5 (autophagy related 5) in microglia controls hippocampal neurogene

• YR et al. 2024: Expansion of the neocortex and protection from neurodegeneration by in

• I et al. 2024: The intricate interplay between microglia and adult neurogenesis in Al

• C et al. 2024: Nucleoporin 153 deficiency in adult neural stem cells defines a pathol

• A et al. 2025: Arsenic unsettles the cerebellar balance between neurodegeneration and

• IZZO2020: Neurogenesis in neurodegenerative disease (2020)

• BARD2019: Neural stem cells and neurodegenerative disease (2019)

• SLOAN2021: Neurogenesis in animal models of neurodegeneration (2021)

• FORSTER2019: Neurogenesis in Lewy body disease (2019)

• YAHATA2012: Epigenetic regulation of neurogenesis (2012)

• LANGE2016: Metabolic regulation of neural stem cells (2016)

• LANGE2016B: Calcium signaling in neurogenesis (2016)

• SAHAY2011: Adult hippocampal neurogenesis and memory (2011)

• WEHBE2019: Neurogenesis and emotional regulation (2019)

• LAGACE2010: Dynamic changes in adult neurogenesis (2010)

• KEMPERMANN2015: Principles of neurogenesis (2015)

• PONT2008: Neurogenesis in the adult brain (2008)

• SILACHEV2019: Neurogenic compounds for brain repair (2019)

• GOULD2019: Neurotrophic factors and neurogenesis (2019)

• ARISI2016: Physical stimulation and neurogenesis (2016)

• PEREZ2019: Lifestyle factors and neurogenesis (2019)

• KUMAR2019: Clinical trials targeting neurogenesis (2019)

• BOLDRINI2019: Biomarkers of human neurogenesis (2019)

• HUR2019: Challenges in neurogenesis translation (2019)

• CARLSSON2010: Clinical translation of neurogenesis (2008)

• TAKAHASHI2007: Induced pluripotent stem cells (2007)

• KONG2018: CRISPR applications in neurogenesis (2018)

• LANCASTER2017: Brain organoids for disease modeling (2017)