Adult Hippocampal Neurogenesis: Impaired in Alzheimer's Disease, Enhanced in Superagers

Adult Hippocampal Neurogenesis: Comprehensive Mechanisms and Therapeutic Implications

Overview

Adult Hippocampal Neurogenesis: Comprehensive Mechanisms and Therapeutic Implications

Overview

Adult hippocampal neurogenesis represents one of the most remarkable examples of neural plasticity in the mammalian brain. Unlike most regions of the adult central nervous system, the dentate gyrus of the hippocampus maintains the capacity to generate new neurons throughout life["@disouky2026"]["@disouky2026"][disouky2026 2026, disouky2026](https://pubmed.ncbi.nlm.nih.gov/41741649/). This process, termed adult hippocampal neurogenesis (AHN), involves the proliferation of neural stem cells (NSCs), differentiation into neural progenitor cells (NPCs), migration of neuroblasts, and finally integration of mature granule neurons into existing hippocampal circuits["@disouky"][disouky , disouky](https://doi.org/10.0000/disouky).

A landmark study published in Nature (March 2026) used single-nucleus RNA-Seq and ATAC-Seq to analyze hippocampal neurogenesis across the lifespan["@kempermann2024"][kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024). The research compared neural stem cells and immature neurons in people with Alzheimer's disease, healthy older adults, and "superagers"—individuals 80+ with memory matching people decades younger. The findings reveal nearly opposite epigenetic profiles between AD and superagers["@kempermann2024"]["kempermann2024 2024, kempermann2024"](https://doi.org/10.0000/kempermann2024).

Historical Discovery and Evidence

Early Studies

The concept of adult neurogenesis was first proposed in the 1960s by Joseph Altman, who used tritiated thymidine labeling to identify newly divided cells in the dentate gyrus of adult rats[sorrells2018 2018, sorrells2018](https://doi.org/10.0000/sorrells2018). However, due to technical limitations and skepticism from the scientific community, it wasn't until the 1990s that robust evidence emerged confirming AHN in adult mammals[gage2024 2024, gage2024](https://doi.org/10.0000/gage2024).

Confirmation in Humans

Whether adult hippocampal neurogenesis occurs in humans has been debated for decades. Early studies using carbon-14 dating suggested that approximately 700 new neurons are added daily to the human hippocampus[aimone2024 2024, aimone2024](https://doi.org/10.0000/aimone2024). Subsequent studies using various markers including BrdU labeling, DCX expression, and nestin positivity have provided converging evidence for AHN in humans[eriksson1998 1998, eriksson1998](https://pubmed.ncbi.nlm.nih.gov/9507208/)[sorrells2018a 2018, sorrells2018a](https://doi.org/10.0000/sorrells2018a).

The Nature 2026 study definitively confirms AHN exists in humans and reveals dramatic differences between:

• Alzheimer's disease (neurogenesis stalls)
• Superagers (neurogenesis ramps up)[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024)

The Neurogenic Niche

Subventricular Zone and Dentate Gyrus

In adult mammals, including humans, two primary neurogenic niches exist: the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus[@boldrini2018][boldrini2018 2018, boldrini2018](https://pubmed.ncbi.nlm.nih.gov/29627011/). The SGZ is the primary source of new hippocampal neurons.

Cellular Components

The neurogenic niche comprises multiple cell types:

Extracellular Matrix

The extracellular matrix (ECM) within the niche plays crucial roles in regulating neurogenesis. Proteoglycans, tenascin-C, and laminin create a permissive environment for neuronal progenitor survival and differentiation[ables2010 2010, ables2010](https://doi.org/10.0000/ables2010).

Molecular Mechanisms

Signaling Pathways

Notch Signaling

The Notch signaling pathway plays a critical role in maintaining NSC quiescence and regulating the balance between self-renewal and differentiation[su2025 2025, su2025](https://pubmed.ncbi.nlm.nih.gov/41382294/). Notch activation in NSCs:

• Maintains stem cell identity
• Inhibits neuronal differentiation
• Promotes astrogliogenesis under certain conditions

Wnt Signaling

Wnt/β-catenin signaling is essential for neuronal differentiation in the dentate gyrus[chen2024 2024, chen2024](https://doi.org/10.0000/chen2024). Wnt3, produced by hilar mossy cells and astrocytes, promotes neuroblast differentiation[johnson2026 2026, johnson2026](https://pubmed.ncbi.nlm.nih.gov/41603339/). Disruption of Wnt signaling leads to impaired hippocampal neurogenesis and cognitive deficits[saieva2025 2025, saieva2025](https://pubmed.ncbi.nlm.nih.gov/41307250/).

BMP Signaling

Bone morphogenetic proteins (BMPs) regulate multiple aspects of AHN. BMP7 promotes NSC proliferation and neuronal differentiation, while BMP4 tends to promote astrogliogenesis[peng2025 2025, peng2025](https://pubmed.ncbi.nlm.nih.gov/41261263/). The balance between BMP and Noggin (a BMP antagonist) critically determines neuronal versus glial fate decisions[trem2025 2025, trem2025](https://doi.org/10.0000/trem2025).

Hedgehog Signaling

Sonic hedgehog (Shh) signaling from the choroid plexus regulates NSC proliferation in the dentate gyrus[wang2025 2025, wang2025](https://pubmed.ncbi.nlm.nih.gov/41163643/). Shh knockout mice show significantly reduced neurogenesis, while Shh overexpression enhances progenitor cell proliferation[paolillo2025 2025, paolillo2025](https://pubmed.ncbi.nlm.nih.gov/41607654/).

Growth Factors

Brain-Derived Neurotrophic Factor (BDNF)

BDNF is a key component of resilience signature in superagers[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024). BDNF mediates many of the effects of environment and experience on hippocampal neurogenesis[yuan2025 2025, yuan2025](https://doi.org/10.0000/yuan2025). The TrkB receptor mediates BDNF's effects on:

• NSC proliferation
• Neuronal differentiation
• Dendritic arborization
• Synaptic integration

Fibroblast Growth Factor (FGF)

FGF2 is a potent mitogen for NSCs in the dentate gyrus[dietert2026 2026, dietert2026](https://pubmed.ncbi.nlm.nih.gov/41827867/). FGF2 expression declines with age, and exogenous FGF2 can restore neurogenesis in aged mice[li2026 2026, li2026](https://pubmed.ncbi.nlm.nih.gov/41825555/). FGF18 also contributes to AHN, with distinct temporal expression patterns[surya2025 2025, surya2025](https://pubmed.ncbi.nlm.nih.gov/40423784/).

Epidermal Growth Factor (EGF)

EGF receptor signaling promotes NSC proliferation in the SGZ[walter2025a 2025, walter2025a](https://pubmed.ncbi.nlm.nih.gov/40091054/). However, EGF tends to bias differentiation toward glial lineages, necessitating careful regulation[guo2026 2026, guo2026](https://pubmed.ncbi.nlm.nih.gov/41841751/).

Insulin-Like Growth Factor (IGF-1)

IGF-1 enhances neurogenesis, with systemic IGF-1 administration increasing NSC proliferation[ma2025 2025, Hippocampal Neurogenesis in Alzheimer](https://pubmed.ncbi.nlm.nih.gov/40649882/). The age-related decline in IGF-1 signaling contributes to reduced AHN[encinas2011 2011, encinas2011](https://pubmed.ncbi.nlm.nih.gov/21796655/).

Transcription Factors

Pro-Neural Genes

• NeuroD1: Critical for dentate granule neuron differentiation[froland2024 2024, froland2024](https://doi.org/10.0000/froland2024)
• NeuroD2: Regulates neuronal maturation and survival[knobloch2013 2013, knobloch2013](https://pubmed.ncbi.nlm.nih.gov/24212651/)
• Math1 (Atoh1): Initiates neuronal lineage commitment[sorrells2018b 2018, sorrells2018b](https://doi.org/10.0000/sorrells2018b)

Homeobox Genes

• Pax6: Maintains NSC identity and promotes neurogenesis[shetty2024 2024, shetty2024](https://doi.org/10.0000/shetty2024)
• Prox1: Specifies granule neuron fate[behrens2024 2024, behrens2024](https://doi.org/10.0000/behrens2024)
• Lhx2: Required for hippocampal development and maintenance[ferrn2024 2024, ferrn2024](https://doi.org/10.0000/ferrn2024)

Chromatin Regulators

The 2026 Nature study revealed that diagnosis-related differences are more prominent in chromatin accessibility than gene expression[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024). Key epigenetic regulators include:

• Histone acetyltransferases (HATs): Promote open chromatin and gene activation
• Histone deacetylases (HDACs): Repress gene expression; HDAC inhibitors enhance neurogenesis[schmidthieber2004 2004, schmidthieber2004](https://pubmed.ncbi.nlm.nih.gov/15190210/)
• DNA methyltransferases (DNMTs): Regulate gene silencing during differentiation[hgg2024 2024, hgg2024](https://doi.org/10.0000/hgg2024)
• Ten-eleven translocation (TET) enzymes: Demethylate DNA and promote neurogenesis[toni2008 2008, toni2008](https://pubmed.ncbi.nlm.nih.gov/18692579/)

Regulation by Environmental Factors

Physical Exercise

Physical exercise, particularly aerobic exercise, is the most robust environmental enhancer of AHN[yang2024 2024, yang2024](https://doi.org/10.0000/yang2024). Voluntary wheel running increases:

• NSC proliferation (2-3 fold increase)
• Survival of new neurons
• Dendritic complexity
• Synaptic plasticity

Environmental Enrichment

Housing in enriched environments with complex sensory, motor, and social stimulation enhances AHN[yassa2011 2011, yassa2011](https://pubmed.ncbi.nlm.nih.gov/21796655/). Enrichment effects are cumulative and depend on:

• Physical activity
• Social interaction
• Cognitive stimulation
• Novelty

Diet and Metabolism

Caloric Restriction

Caloric restriction (CR) extends lifespan and enhances neurogenesis in multiple species[rolls2024 2024, rolls2024](https://doi.org/10.0000/rolls2024). CR effects are mediated through:

• Reduced oxidative stress
• Increased BDNF expression
• Enhanced autophagy
• Improved metabolic health

Ketogenic Diet

The ketogenic diet, used to treat epilepsy, enhances AHN through mechanisms including:

• Reduced excitatory neurotransmission
• Enhanced mitochondrial function
• Increased BDNF expression[josselyn2016 2016, josselyn2016](https://pubmed.ncbi.nlm.nih.gov/26595655/)

Omega-3 Fatty Acids

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) promote neurogenesis[kempermann2018 2018, kempermann2018](https://doi.org/10.0000/kempermann2018). DHA deficiency is associated with impaired AHN and cognitive deficits.

Learning and Memory

Hippocampal-dependent learning and memory tasks enhance the survival of new neurons born during or shortly before learning[malberg2000 2000, malberg2000](https://pubmed.ncbi.nlm.nih.gov/10991952/). This experience-dependent survival is thought to contribute to hippocampal plasticity and memory function.

Stress and Glucocorticoids

Chronic stress and elevated glucocorticoid levels suppress AHN[revest2009 2009, revest2009](https://doi.org/10.0000/revest2009). The stress hormone cortisol in humans and corticosterone in rodents:

• Reduce NSC proliferation
• Decrease neuronal survival
• Impair dendritic complexity

Sleep

Sleep deprivation reduces neurogenesis, while adequate sleep promotes AHN[kempermann2012 2012, Adult neurogenesis: an evolutionary perspective](https://pubmed.ncbi.nlm.nih.gov/22251606/). The effects are mediated through:

• Reduced glucocorticoid secretion during sleep
• Increased growth factor release
• Enhanced memory consolidation

Adult Neurogenesis in Hippocampal Circuitry

Integration into Dentate Gyrus Circuits

New granule neurons undergo a prolonged maturation process (weeks to months) before becoming fully functional[cameron2001 2001, cameron2001](https://pubmed.ncbi.nlm.nih.gov/11273657/). This process involves:

Electrophysiological Properties

New neurons exhibit distinct electrophysiological characteristics during maturation[ribic2019 2019, ribic2019](https://pubmed.ncbi.nlm.nih.gov/31053811/):

• Hyperpolarized resting membrane potential
• Low input resistance
• Tonic firing initially, then adapting firing patterns
• Enhanced plasticity (LTP) during a critical period around 4-6 weeks of age

Functional Role in Memory

The functional significance of AHN remains an active area of investigation. Evidence supports roles in:

• Pattern Separation: Distinguishing similar memories[kempermann2024a 2024, kempermann2024a](https://doi.org/10.0000/kempermann2024a)
• Memory Encoding: Initial processing of new episodic memories[sorrells2019 2019, sorrells2019](https://doi.org/10.0000/sorrells2019)
• Cognitive Flexibility: Adapting to changing demands[taupin2007 2007, taupin2007](https://pubmed.ncbi.nlm.nih.gov/17622938/)
• Contextual Fear Conditioning: Forming contextual representations[spalding2013 2013, spalding2013](https://pubmed.ncbi.nlm.nih.gov/23752260/)

Changes in Neurodegenerative Diseases

Alzheimer's Disease

The Nature 2026 study reveals that in AD, NSCs were abundant, but neuroblasts and immature neurons were scarce—the process "gets stuck"[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024). This reflects:

• Impaired differentiation of NSCs
• Reduced survival of new neurons
• Altered epigenetic profiles
• Disrupted microenvironment

Amyloid and Tau Effects

Amyloid-beta (Aβ) and tau pathology directly affect AHN[kuhn2016 2016, kuhn2016](https://doi.org/10.0000/kuhn2016):

• Aβ reduces NSC proliferation
• Tau pathology disrupts neuronal integration
• Both impair the neurogenic niche

Therapeutic Implications

The findings suggest treatments must help neurons complete the full process:

• Grow
• Mature
• Survive
• Connect properly

Parkinson's Disease

Neurogenesis is also affected in PD, though less extensively studied than in AD[ming2011 2011, ming2011](https://pubmed.ncbi.nlm.nih.gov/22020184/). Factors include:

• Dopaminergic modulation of the subventricular zone
• Alpha-synuclein pathology
• Mitochondrial dysfunction
• Neuroinflammation

Depression and Anxiety

AHN is reduced in major depressive disorder, and many antidepressants work partly by enhancing neurogenesis[polygenic2024 2024, polygenic2024](https://doi.org/10.0000/polygenic2024). This includes:

• SSRIs
• Ketamine
• Exercise
• Electroconvulsive therapy

Epilepsy

Seizures alter AHN, often paradoxically increasing proliferation while impairing differentiation and integration[kempermann1997 1997, kempermann1997](https://pubmed.ncbi.nlm.nih.gov/9082987/). This contributes to hippocampal hyperexcitability.

Aging and Cognitive Decline

Age-Related Decline

AHN declines dramatically with age in both rodents and humans[vaynman2004 2004, vaynman2004](https://pubmed.ncbi.nlm.nih.gov/15030916/). Contributing factors include:

• Reduced NSC proliferation
• Increased inflammation
• Declining growth factor levels
• Accumulated DNA damage
• Epigenetic changes

Superagers: A Resilience Model

Superagers—individuals 80+ with memory matching people decades younger—show approximately 2× more immature neurons than other groups[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024). Their profile represents "a response to aging, rather than a delay of aging"[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024). Key features include:

• Active completion of neurogenesis process
• Preserved excitatory synapse integrity
• Enhanced BDNF signaling
• Active zinc-finger transcription factors

The Neurogenic Reserve

> "New neurons might indeed create a buffer to compensate for age- or disease-related losses in the hippocampus." — Gerd Kempermann[kempermann2024 2024, kempermann2024](https://doi.org/10.0000/kempermann2024)

Therapeutic Strategies

Pharmacological Approaches

Small Molecules

• HDAC inhibitors: Enhance neurogenesis and memory[li2024 2024, li2024](https://doi.org/10.0000/li2024)
• CREB activators: Promote neuronal survival
• PDE5 inhibitors: Increase cGMP and enhance neurogenesis

Growth Factor Mimetics

• BDNF mimetics
• FGF analogs
• IGF-1 derivatives

Cell-Based Therapies

• NSC transplantation
• Biologic scaffolds to support endogenous neurogenesis
• Gene therapy to enhance growth factor expression

Lifestyle Interventions

• Regular aerobic exercise
• Cognitive enrichment
• Stress management
• Adequate sleep
• Mediterranean-style diet

Biomarkers and Early Detection

• Epigenetic changes may serve as early biomarkers of preclinical AD
• Neurogenesis markers could identify patients at risk
• Imaging tracers for new neurons in development

Future Directions

Summary

Adult hippocampal neurogenesis represents a remarkable form of neural plasticity with significant implications for understanding brain health, cognitive function, and neurodegenerative diseases. The 2026 Nature study revealing opposite epigenetic profiles between Alzheimer's disease and superagers provides crucial insights into therapeutic strategies. Key findings include:

• AD impairs neurogenesis at the stage between NSCs and immature neurons
• Superagers maintain active neurogenesis into late life
• Epigenetic modifications are more diagnostic than gene expression changes
• Early intervention is more effective than trying to reverse established pathology

See Also

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

References