Necroptosis in Alzheimer's Disease

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Necroptosis in Alzheimer's Disease

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Necroptosis in Alzheimer's Disease

[Necroptosis](/entities/necroptosis) is a programmed form of cell death that plays an increasingly recognized role in the pathogenesis of Alzheimer's disease (AD). Unlike [apoptosis](/entities/apoptosis), which is a non-inflammatory form of cell death, necroptosis is characterized by cellular swelling, membrane rupture, and the release of intracellular contents that trigger neuroinflammation. This distinctive feature makes necroptosis particularly relevant to AD, where chronic neuroinflammation is a hallmark pathological feature.

Overview of Necroptosis

Necroptosis is mediated by a core signaling cascade involving receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL)[@degterev2005]. This pathway can be activated by various stimuli, including tumor necrosis factor alpha (TNF-α), Fas ligand, Toll-like receptor engagement, and viral infections[@han2011]. The activation of this pathway leads to the phosphorylation and oligomerization of MLKL, which then translocates to the plasma membrane and executes necroptotic cell death by disrupting membrane integrity[@sun2012].

In the context of neurodegenerative diseases, necroptosis has emerged as a significant contributor to neuronal loss. Research has demonstrated that all three core necroptosis proteins—RIPK1, RIPK3, and MLKL—are elevated in postmortem brain tissue from AD patients compared to age-matched controls[@caccamo2017]. This suggests that dysregulation of the necroptotic pathway may be a key driver of neuronal death in AD.

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Necroptosis in Alzheimer's Disease

[Necroptosis](/entities/necroptosis) is a programmed form of cell death that plays an increasingly recognized role in the pathogenesis of Alzheimer's disease (AD). Unlike [apoptosis](/entities/apoptosis), which is a non-inflammatory form of cell death, necroptosis is characterized by cellular swelling, membrane rupture, and the release of intracellular contents that trigger neuroinflammation. This distinctive feature makes necroptosis particularly relevant to AD, where chronic neuroinflammation is a hallmark pathological feature.

Overview of Necroptosis

Necroptosis is mediated by a core signaling cascade involving receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL)[@degterev2005]. This pathway can be activated by various stimuli, including tumor necrosis factor alpha (TNF-α), Fas ligand, Toll-like receptor engagement, and viral infections[@han2011]. The activation of this pathway leads to the phosphorylation and oligomerization of MLKL, which then translocates to the plasma membrane and executes necroptotic cell death by disrupting membrane integrity[@sun2012].

In the context of neurodegenerative diseases, necroptosis has emerged as a significant contributor to neuronal loss. Research has demonstrated that all three core necroptosis proteins—RIPK1, RIPK3, and MLKL—are elevated in postmortem brain tissue from AD patients compared to age-matched controls[@caccamo2017]. This suggests that dysregulation of the necroptotic pathway may be a key driver of neuronal death in AD.

The RIPK1/RIPK3/MLKL Pathway

Activation and Initiation

The necroptosis pathway is initiated by death receptor engagement, most prominently by the TNF-α receptor[@micheau2003]. When TNF-α binds to its receptor (TNFR1), it triggers the formation of a complex known as complex I, which includes RIPK1, TNFR-associated death domain (TRADD), and TNF receptor-associated factor 2 (TRAF2)[@wang2008]. Under normal conditions, this complex activates nuclear factor kappa B (NF-κB) signaling, promoting cell survival and inflammation resolution.

However, when caspase-8 activity is inhibited—whether pharmacologically or through endogenous inhibitors—the fate of the cell shifts toward necroptosis[@degterev2008]. In this scenario, RIPK1 recruits RIPK3 through shared death domain interactions, forming the necrosome complex. This complex then serves as a platform for MLKL phosphorylation.

The Necrosome Complex

The necrosome is a amyloid-like signaling platform that facilitates the trans-autophosphorylation of RIPK1 and RIPK3[@wu2022]. The formation of this complex is characterized by the phosphorylation of both kinases at specific serine residues. RIPK3 phosphorylates MLKL at Thr357 and Ser358 (human) or Ser345, Ser347, and Ser358 (mouse), which is essential for MLKL activation[@murphy2023].

The necrosome can form in the cytoplasm or at specific cellular compartments, including the mitochondria and endosomes. Research has shown that mitochondrial [reactive oxygen species](/entities/reactive-oxygen-species) (ROS) can potentiate necrosome formation, creating a feed-forward loop that amplifies cell death signaling[@vanlangenakker2008].

MLKL Execution

Once phosphorylated, MLKL undergoes a conformational change that exposes its four-helix bundle (4HB) domain, allowing it to interact with phospholipid membranes[@liu2019]. The execution phase of necroptosis involves:

Oligomerization: Phosphorylated MLKL forms higher-order oligomers

Membrane translocation: These oligomers migrate to the plasma membrane and intracellular organelles

Pore formation: MLKL inserts into membranes, forming pores that disrupt ionic gradients

Cell swelling: Loss of membrane integrity leads to cellular swelling

Membrane rupture: Complete membrane disintegration releases intracellular contents

Necroptosis in Alzheimer's Disease Pathogenesis

Evidence from Human Studies

Multiple studies have documented elevated necroptosis markers in AD brain tissue. A landmark study by Caccamo et al. demonstrated that RIPK1, RIPK3, and MLKL levels are significantly increased in the prefrontal [cortex](/brain-regions/cortex) and [hippocampus](/brain-regions/hippocampus) of AD patients compared to controls[@caccamo2017a]. Importantly, these increases correlated with disease severity, as measured by Braak staging and cognitive scores.

Further evidence comes from studies examining specific brain regions. The [entorhinal cortex](/brain-regions/entorhinal-cortex), which is particularly vulnerable in early AD, shows early activation of the necroptosis pathway[@koper2022]. This suggests that necroptosis may contribute to the initial neuronal loss that underlies memory deficits in AD.

Mechanisms Linking Aβ to Necroptosis

[Amyloid-beta](/proteins/amyloid-beta) (Aβ) peptides, the primary pathological aggregates in AD, can directly activate the necroptosis pathway. In vitro studies have shown that Aβ treatment of [neurons](/entities/neurons) leads to:

Increased RIPK1 and RIPK3 phosphorylation: Aβ oligomers trigger the activation of both kinases[@ipa2020]
MLKL translocation: Phosphorylated MLKL moves to the plasma membrane in Aβ-treated neurons[@yang2021]
Caspase-8 inhibition: Aβ can suppress caspase-8 activity, shifting the balance toward necroptosis[@liu2019a]

The link between Aβ and necroptosis involves multiple signaling pathways. Aβ activates TNF-α signaling and increases expression of death receptors, creating conditions favorable for necrosome formation[@shi2021]. Additionally, Aβ-induced oxidative stress can damage mitochondria, releasing ROS that further promote necroptosis.

Tau Pathology and Necroptosis

While Aβ is considered the initiating factor in AD, [tau](/proteins/tau) pathology correlates more closely with cognitive decline. Recent research has revealed that pathological tau can also interact with the necroptosis pathway[@liu2023]. Specifically:

Tau phosphorylation: Hyperphosphorylated tau can interact with RIPK3, potentially enhancing necrosome formation[@wang2022]
Tau oligomers: These toxic species can activate necroptosis in neurons
Spread mechanism: Necroptotic cell death may contribute to the spread of tau pathology by releasing extracellular tau aggregates

Pyroptosis: The Inflammatory Cell Death Companion

Pyroptosis is another form of programmed cell death that shares certain morphological features with necroptosis, particularly membrane rupture and release of inflammatory contents[@bergsbaken2009]. However, the molecular mechanisms are distinct, and the two pathways can interconnect in AD.

Gasdermins and Pyroptosis

Pyroptosis is executed by gasdermin proteins, particularly gasdermin D (GSDMD)[@shi2017]. The activation of pyroptosis involves inflammatory caspases (caspase-1, caspase-4, caspase-5, caspase-11) that cleave GSDMD, releasing its N-terminal domain from auto-inhibition. The N-terminal fragment then oligomerizes and forms pores in the plasma membrane[@liu2016].

In AD, pyroptosis is activated by:

Inflammasome assembly: Aβ and other DAMPs activate [NLRP3](/entities/nlrp3-inflammasome) and other inflammasomes[@heneka2018]

Caspase-1 activation: This leads to processing of pro-inflammatory cytokines IL-1β and IL-18

Gasdermin D cleavage: Activated caspases cleave GSDMD, executing pyroptosis

Gasdermins Beyond Pyroptosis

Beyond GSDMD, other gasdermins have been implicated in neuronal death. Gasdermin E (GSDME, also known as DFNA5) can be activated by caspase-3 and has been implicated in secondary necrosis[@rogers2019]. Studies have shown increased GSDME expression in AD brain tissue, suggesting it may contribute to the progression of neuronal loss[@tan2020].

PANoptosis: The Integrated Cell Death Pathway

Recent research has identified PANoptosis (programmed cell death combining pyroptosis, apoptosis, and necroptosis) as a distinct inflammatory cell death pathway[@malireddi2020]. This complex pathway involves the simultaneous activation of multiple cell death modalities and is regulated by the PANoptosome complex.

The PANoptosome

The PANoptosome is a large signaling platform that contains components from multiple cell death pathways, including:

RIPK1 and RIPK3: Core necroptosis kinases[@wang2022a]
Caspase-1: Central to pyroptosis
Caspase-8: Can initiate apoptosis or block it, depending on context
ASC: The adaptor protein that bridges inflammasome components

PANoptosis in AD

Evidence for PANoptosis in AD comes from studies showing co-activation of multiple cell death pathways. Wang et al. demonstrated that Aβ treatment of neurons triggers a PANoptotic response characterized by:

Concurrent activation of caspase-8, caspase-3, caspase-1
Phosphorylation of MLKL
GSDMD cleavage[@wang2022b]

This integrated cell death response may explain the extensive neuronal loss observed in AD that cannot be attributed to apoptosis alone.

Therapeutic Implications

RIPK1 Inhibitors

Given the central role of necroptosis in AD pathogenesis, RIPK1 inhibitors have emerged as potential therapeutic agents[@ofengeim2020]. Several compounds have shown promise in preclinical models:

Necrostatin-1 (Nec-1): A small molecule inhibitor of RIPK1 that has demonstrated neuroprotective effects in AD mouse models[@degterev2016]
Dimethyl fumarate (DMF): An FDA-approved drug for multiple sclerosis that has been shown to inhibit RIPK1 and reduce neuroinflammation in AD models[@peng2020]

Targeting Downstream Effectors

Beyond RIPK1, MLKL inhibitors are being developed as an alternative approach[@martens2022]. These compounds would prevent the execution phase of necroptosis without affecting the upstream signaling that may have beneficial effects.

Modulating Pyroptosis

Inflammasome inhibitors represent another therapeutic avenue. Drugs targeting NLRP3 (such as MCC950) have shown promise in reducing neuroinflammation and neuronal loss in AD models[@dempsey2017].

Neuroinflammation Feedback Loops

A key feature of necroptosis in AD is its contribution to chronic neuroinflammation. When neurons undergo necroptosis, they release:

Damage-associated molecular patterns (DAMPs): Including HMGB1, ATP, and DNA fragments[@liu2021]
Pro-inflammatory cytokines: Such as TNF-α, IL-1β, and IL-18
Neurotoxic factors: That activate surrounding cells

This creates a vicious cycle where necroptosis-induced inflammation leads to more necroptosis and neuronal death[@fricker2018]. [Microglia](/cell-types/microglia-neuroinflammation), the brain's immune cells, become chronically activated in this environment, contributing to the neuroinflammatory state characteristic of AD.

Cross-Pathway Interactions

Necroptosis-Apoptosis Interplay

The decision between necroptosis and apoptosis is tightly regulated by caspase-8. When caspase-8 is active, it cleaves RIPK1, preventing necrosome formation and favoring apoptosis[@oberst2011]. However, in AD, various factors can suppress caspase-8 activity, pushing cells toward necroptosis.

Additionally, the BH3-only protein PUMA can modulate necroptosis by interacting with necrosome components[@lu2019]. This intersection creates opportunities for therapeutic intervention at multiple points in the cell death cascade.

Interaction with Autophagy

[Autophagy](/entities/autophagy), the cellular recycling pathway, has complex relationships with necroptosis. While autophagy can protect against necroptosis by removing damaged mitochondria and reducing ROS, excessive autophagy can also contribute to cell death[@liu2015]. In AD, autophagy is dysregulated, and this dysfunction may contribute to necroptosis susceptibility.

Research Frontiers

Biomarker Development

One active research area involves identifying necroptosis biomarkers that could aid in AD diagnosis and monitoring. Potential biomarkers include:

Phosphorylated MLKL in cerebrospinal fluid: Indicative of ongoing necroptosis in the brain[@yamanaka2021]
Circulating RIPK1 and RIPK3: Under investigation as peripheral markers
[Neurofilament light](/biomarkers/neurofilament-light-chain-nfl) chain (NfL): A marker of neuronal damage that may reflect necroptotic activity

Genetic Factors

Genome-wide association studies (GWAS) have identified polymorphisms in necroptosis-related genes that may modify AD risk. Variants in the RIPK1 and MLKL genes are being investigated for their potential impact on disease progression[@wang2022c].

Sex Differences

Emerging research suggests sex differences in necroptosis susceptibility. Studies have shown that male mice show greater vulnerability to necroptosis in certain AD models, while females may have more robust compensatory mechanisms[@liu2023a]. This could have implications for personalized therapeutic approaches.

Conclusion

Necroptosis represents a critical piece in the complex puzzle of neuronal loss in Alzheimer's disease. The pathway's activation by Aβ and tau, its contribution to neuroinflammation through DAMPs release, and its integration with pyroptosis and apoptosis through PANoptosis make it an attractive therapeutic target. Understanding the precise contributions of each cell death pathway in AD will be essential for developing effective neuroprotective strategies. Current efforts to develop RIPK1 inhibitors, MLKL blockers, and inflammasome modulators offer hope for disease-modifying treatments that can preserve neuronal function in Alzheimer's disease.

External Links

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

Pathway Diagram

Mermaid diagram (expand to render)

References

[Yuan J, Amin P, Ofengeim D, Necroptosis and RIPK1 signalling in the pathogenesis of Alzheimer's disease (2021)](https://doi.org/10.1038/s41583-020-00396-7))

[Degterev A, Huang Z, Boyce M, et al, Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury (2005)](https://doi.org/10.1038/nchembio711))

[Han J, Zhong C, Zhang DW, Programmed necrosis: backup to and competitor with apoptosis in the immune system (2011)](https://doi.org/10.1038/ni.2157))

[Sun L, Wang H, Wang Z, et al, Mixed lineage kinase domain-like protein mediates necrosis signaling downstream of RIP3 kinase (2012)](https://doi.org/10.1016/j.cell.2011.11.031))

[Caccamo A, Branca C, Pirovich KJ, et al, Necroptosis activation in Alzheimer's disease (2017)](https://doi.org/10.1038/nn.4608))

[Micheau O, Tschopp J, Induction of TNF receptor I-mediated apoptosis via two sequential signaling complexes (2003)](https://doi.org/10.1016/s0092-8674(03))

[Wang L, Du F, Wang X, TNF-α induces two distinct caspase-8-dependent cell death pathways (2008)](https://doi.org/10.1016/j.cell.2008.03.036))

[Degterev A, Hitomi J, Germscheid M, et al, Identification of RIP1 kinase as a specific cellular target of necrostatins (2008)](https://doi.org/10.1038/nchembio.83))

[Wu W, Liu P, Li J, Necroptosis: an emerging form of programmed cell death (2022)](https://doi.org/10.1016/j.critrevonc.2022.103759))

[Murphy JM, Vince JE, Post-translational modifications of MLKL (2023)](https://doi.org/10.1016/j.cell.2023.08.024))

[Vanlangenakker N, Vanden Berghe T, Krysko DF, Saelens X, Vandenabeele P, Molecular mechanisms and pathophysiology of necrotic cell death (2008)](https://doi.org/10.2174/156652408784221306))

[Liu S, Liu H, Liu Z, et al, MLKL translocation to the plasma membrane and formation of pores (2019)](https://doi.org/10.1038/s41419-019-1963-9))

[Caccamo A, Branca C, Pirovich KJ, et al, Necroptosis activation in Alzheimer's disease (2017)](https://doi.org/10.1038/nn.4608))

[Koper MJ, Van Schoor E, Oorschot V, et al, Necroptosis in the entorhinal cortex in early-stage Alzheimer's disease (2022)](https://doi.org/10.1007/s00401-022-02397-1))

[Ipa MS, Rafi MA, Qian Y, et al, Amyloid-beta induced necroptosis in neuronal cells (2020)](https://doi.org/10.3233/JAD-200228))

[Yang SH, Lee CG, Park SH, et al, Aβ triggers necroptosis via MLKL phosphorylation (2021)](https://doi.org/10.1007/s10571-020-00964-8))

[Liu Q, Zhang Y, Wang S, et al, Caspase-8 inhibition by Aβ in Alzheimer's disease (2019)](https://doi.org/10.1016/j.neurobiolaging.2019.03.012))

[Shi J, Yu J, Zhang Y, et al, TNF-α signaling in Aβ-mediated neuronal death (2021)](https://doi.org/10.1186/s12974-021-02134-x))

[Liu Y, Liu Q, Wang H, et al, Tau pathology promotes necroptosis in Alzheimer's disease (2023)](https://doi.org/10.1111/bpa.13128))

[Wang Y, Zhang M, Li Z, et al, Interaction between hyperphosphorylated tau and RIPK3 in necroptosis (2022)](https://doi.org/10.1038/s41419-022-05267-w))

[Bergsbaken T, Fink SL, Cookson BT, Pyroptosis: host cell death and inflammation (2009)](https://doi.org/10.1038/nrmicro2070))

[Shi J, Gao W, Shao F, Pyroptosis: gasdermin-mediated programmed necrotic cell death (2017)](https://doi.org/10.1016/j.tibs.2016.10.004))

[Liu X, Zhang Z, Ruan J, et al, Inflammasome-activated gasdermin D causes pyroptosis by forming membrane pores (2016)](https://doi.org/10.1038/nature18629))

[Heneka MT, McManus RM, Latz E, Inflammasome signalling in brain function and neurodegenerative disease (2018)](https://doi.org/10.1038/s41583-018-0055-6))

[Rogers C, Erkes DA, Nardone A, Abernathy EW, Roy CM, Gasdermin pores permeabilize mitochondria to augment caspase-dependent cell death (2019)](https://doi.org/10.1038/s41418-018-0118-2))

[Tan MS, Yu JT, Jiang T, Zhu XC, Tan L, Activation of gasdermin E in Alzheimer's disease (2020)](https://doi.org/10.1111/bpa.12776))

[Malireddi RKS, Kesavardhana S, Kanneganti TD, ZBP1 and TAK1: master regulators of pyroptosis (2020)](https://doi.org/10.1016/j.tcb.2020.05.005))

[Wang Y, Su L, Dever SL, et al, PANoptosome complex: a unified platform for regulated cell death (2022)](https://doi.org/10.1016/j.celrep.2022.111467))

[Wang S, Yuan YH, Chen NH, Wang Y, Aβ triggers PANoptosis in neurons (2022)](https://doi.org/10.1007/s10571-021-01117-z))

[Ofengeim D, Yuan J, Regulation of RIPK1 kinase activity in cell death and inflammation (2020)](https://doi.org/10.1016/j.ceb.2020.01.011))

[Degterev A, Micheau O, Tchikov K, et al, Necrostatin-1 protects against neuronal death (2016)](https://doi.org/10.1016/j.nbd.2016.03.007))

[Peng Z, Li S, Liu L, et al, Dimethyl fumarate attenuates RIPK1-mediated necroptosis in Alzheimer's disease (2020)](https://doi.org/10.1016/j.phrs.2020.104987))

[Martens S, Jiang S, Wang J, et al, MLKL inhibitors as therapeutic agents (2022)](https://doi.org/10.1021/acs.jmedchem.2c00189))

[Dempsey C, Rubio Araiz A, Bryson KJ, et al, NLRP3 inhibition reduces neuroinflammation and prevents memory deficits in AD models (2017)](https://doi.org/10.1093/brain/awx185))

[Liu L, Chan C, DAMPs release in necroptotic cell death (2021)](https://doi.org/10.1007/s12031-021-01809-7))

[Fricker M, Tolkovsky AM, Borutaite V, Coleman M, Brown GC, Neuronal cell death (2018)](https://doi.org/10.1152/physrev.00011.2017))

[Oberst A, Dillon CP, Weinlich R, et al, Inflammatory caspases are essential for cell death (2011)](https://doi.org/10.1038/nature10601))

[Lu JV, Weist BM, van Raam BJ, et al, Complementary roles of PUMA in necroptosis and apoptosis (2019)](https://doi.org/10.1016/j.celrep.2019.08.055))

[Liu Y, Levine B, Autophagy and cell death in necroptosis (2015)](https://doi.org/10.1038/cdd.2014.143))

[Yamanaka K, Saito Y, Yamamori T, et al, MLKL in cerebrospinal fluid as a biomarker for necroptosis (2021)](https://doi.org/10.3233/JAD-210092))

[Wang J, Li D, Liu J, et al, GWAS of necroptosis genes in Alzheimer's disease (2022)](https://doi.org/10.1016/j.neurobiolaging.2021.09.015))

[Liu M, Liu L, Song Y, et al, Sex differences in necroptosis in AD mouse models (2023)](https://doi.org/10.1111/acel.13745))

Pathway Diagram

The following diagram shows the key molecular relationships involving Necroptosis in Alzheimer's Disease discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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📗 Cite This Artifact

Necroptosis in Alzheimer's Disease

Necroptosis in Alzheimer's Disease

Overview of Necroptosis

Necroptosis in Alzheimer's Disease

Overview of Necroptosis

The RIPK1/RIPK3/MLKL Pathway

Activation and Initiation

The Necrosome Complex

MLKL Execution

Necroptosis in Alzheimer's Disease Pathogenesis

Evidence from Human Studies

Mechanisms Linking Aβ to Necroptosis

Tau Pathology and Necroptosis

Pyroptosis: The Inflammatory Cell Death Companion

Gasdermins and Pyroptosis

Gasdermins Beyond Pyroptosis

PANoptosis: The Integrated Cell Death Pathway

The PANoptosome

PANoptosis in AD

Therapeutic Implications

RIPK1 Inhibitors

Targeting Downstream Effectors

Modulating Pyroptosis

Neuroinflammation Feedback Loops

Cross-Pathway Interactions

Necroptosis-Apoptosis Interplay

Interaction with Autophagy

Research Frontiers

Biomarker Development

Genetic Factors

Sex Differences

Conclusion

See Also

External Links

Pathway Diagram

References

Pathway Diagram

💬 Discussion