necroptosis

Introduction

Necroptosis is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Overview

Necroptosis is a regulated form of programmed cell death that combines features of apoptosis (programmed execution) with necrotic morphology (cell swelling and membrane rupture). Unlike apoptosis, necroptosis is caspase-independent and is mediated by the RIPK1–RIPK3–MLKL signaling axis. First identified as a “backup” death pathway when caspases are inhibited, necroptosis is now recognized as a physiologically significant process with critical roles in development, innate immunity, and disease pathogenesis. In the context of neurodegeneration, necroptosis has emerged as a major driver of neuronal loss and neuroinflammation in Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, and multiple sclerosis (Bhardwaj et al., 2025; Bhargava et al., 2024). ^{1Molecular mechanisms of necroptosis2011 · Cell Death & Differentiation 2Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury2005 · Nature Chemical Biology}

Molecular Mechanism

The Necrosome: RIPK1–RIPK3–MLKL Signaling Cascade

The core necroptosis pathway is executed by three key proteins that form the necrosome signaling complex (Linkermann & Green, 2014): ^{2Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury2005 · Nature Chemical Biology 3Toll-like receptor 3-mediated necrosis2013 · Journal of Experimental Medicine}

1. RIPK1 (Receptor-Interacting Protein Kinase 1): A multi-domain serine/threonine kinase that serves as a molecular switch between cell survival, apoptosis, and necroptosis. RIPK1 is activated following stimulation of death receptors, particularly TNF receptor 1 (TNFR1). Under conditions where caspases (especially caspase-8) are inhibited or absent, RIPK1 autophosphorylates and recruits RIPK3 through RHIM (RIP Homotypic Interaction Motif) domain interactions. ^{3Toll-like receptor 3-mediated necrosis2013 · Journal of Experimental Medicine}

2. RIPK3 (Receptor-Interacting Protein Kinase 3): Upon RHIM-mediated binding to RIPK1, RIPK3 undergoes autophosphorylation and forms amyloid-like fibrillar signaling platforms. Activated RIPK3 then phosphorylates the downstream effector MLKL at Thr357 and Ser358 (human) or Ser345 (mouse). ^{4Necroptosis activation in Alzheimer's Disease2017 · Nature Neuroscience}

3. MLKL (Mixed Lineage Kinase Domain-Like Pseudokinase): The terminal executor of necroptosis. Phosphorylation by RIPK3 triggers MLKL conformational change and oligomerization. MLKL oligomers translocate to the plasma membrane, where they form pores that disrupt membrane integrity, causing cell swelling and lytic cell death. ^{5Necroptosis in neurodegenerative diseases2020 · Neurochemical Research}

Upstream Triggers

Multiple signaling pathways can initiate necroptosis (Pasparakis & Vandenabeele, 2015): ^{6The role of necroptosis in neurodegenerative diseases2021 · Frontiers in Cell Neuroscience 4Necroptosis activation in Alzheimer's Disease2017 · Nature Neuroscience}

• TNF-alpha/TNFR1 signaling: The most extensively studied trigger. When caspase-8 is inhibited (by viral proteins, genetic deficiency, or pharmacological inhibition), TNF-alpha engagement of TNFR1 shifts from apoptosis to necroptosis.

• Toll-like receptor (TLR) activation: TLR3 and TLR4 can activate RIPK3 via the adaptor protein TRIF, bypassing RIPK1.

• ZBP1/DAI (Z-DNA binding protein 1): Detects cytoplasmic Z-form nucleic acids (from viral replication or endogenous retroelements) and directly activates RIPK3 via RHIM domain interactions.

• Interferons: Type I and type II interferons can promote necroptosis through JAK-STAT signaling and ZBP1 upregulation.

• FAS ligand and TRAIL: Other death receptor ligands that activate the pathway when caspases are compromised.

Regulatory Checkpoints

Several proteins negatively regulate necroptosis to prevent uncontrolled cell death: ^{5Necroptosis in neurodegenerative diseases2020 · Neurochemical Research}

• Caspase-8: The primary brake on necroptosis; cleaves and inactivates RIPK1 and RIPK3.

• cFLIP (cellular FLICE-inhibitory protein): Partners with caspase-8 to suppress necroptosis.

• A20/TNFAIP3: A ubiquitin-editing enzyme that restricts RIPK1 activation at the TNFR1 complex.

• LUBAC (linear ubiquitin assembly complex): Ubiquitinates RIPK1 to promote NF-κB survival signaling rather than cell death.

Role in Neurodegenerative Diseases

Alzheimer’s Disease

Necroptosis has been identified as a principal mechanism of neuronal death in Alzheimer’s disease. Elevated levels of activated (phosphorylated) RIPK1, RIPK3, and MLKL have been consistently detected in postmortem AD brain tissue, with these proteins showing enhanced colocalization in affected brain regions including the hippocampus, [entorhinal cortex, and [prefrontal cortex (Bhargava et al., 2024). ^{2Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury2005 · Nature Chemical Biology}0

Key findings include:

• amyloid-beta and tau] pathologies converge on RIPK1 activation: Both amyloid-beta oligomers] and hyperphosphorylated tau can trigger necroptosis. Amyloid-Beta induces TNF-alpha production by microglia

• Correlation with disease severity: Phospho-MLKL levels in AD brains correlate with Braak neurofibrillary tangle staging and antemortem cognitive decline.

• blood-brain barrier disruption: Necroptosis of brain endothelial cells contributes to BBB breakdown] observed in AD.

• Exercise as a modulator: Emerging research suggests that physical exercise may attenuate necroptosis in AD through modulation of RIPK1 kinase activity and reduction of neuroinflammatory signaling (Khademian et al., 2025.

Parkinson’s Disease

In Parkinson’s disease, necroptosis contributes to the selective loss of [dopaminergic neurons/cell-types/dopaminergic-neurons in the substantia nigra pars compacta:

• RIPK1, RIPK3, and MLKL are significantly elevated in MPTP-induced PD mouse models and in postmortem PD brain tissue (Yuan et al., 2019)).

• Pharmacological or genetic inhibition of RIPK3 or MLKL dramatically ameliorates PD pathology by rescuing [dopaminergic neurons and restoring dopamine levels.

• alpha-synuclein aggregation activates microglia/motor neuron death in ALS:

• Elevated RIPK1 and RIPK3 activity is found in spinal cord [motor neurons/cell-types/motor-[neurons) of both [SOD1/proteins/sod1 mutant mice and sporadic ALS patients.

• TDP-43 pathology, the hallmark of most ALS cases, may impair RNA processing of anti-necroptotic genes.

• SAR443820 (DNL788), a brain-penetrant RIPK1 inhibitor developed by Sanofi/Denali Therapeutics, was tested in the Phase 2 HIMALAYA trial for ALS, though the trial did not meet its primary endpoint of change in the ALS Functional Rating Scale-Revised (Bhatt et al., 2023).

Multiple Sclerosis

In multiple sclerosis, necroptosis contributes to oligodendrocyte death and demyelination:

• Oligodendrocytes express high levels of RIPK3 and are susceptible to TNF-alpha-induced necroptosis.

• RIPK1 inhibition reduces demyelination and axonal damage in experimental autoimmune encephalomyelitis (EAE) models.

• SAR443820 remains in clinical development for MS, where it has first-in-class potential as a RIPK1 inhibitor.

Necroptosis and neuroinflammation

The relationship between necroptosis and neuroinflammation is bidirectional and creates a self-amplifying destructive cycle (Kaczmarek et al., 2013):

1. Inflammatory cytokines trigger necroptosis: TNF-alpha, produced by activated [microglia.

2. Necroptotic cells release DAMPs: Cell membrane rupture releases intracellular contents including HMGB1, mitochondrial DNA, ATP, potassium ions, and IL-33.

3. DAMPs activate innate immunity: Released DAMPs engage pattern recognition receptors on [microglia and astrocytes may partially reflect necroptotic neuronal death, though it is not pathway-specific.

• GFAP elevation may indicate astrocytic activation secondary to necroptotic DAMP release.

Therapeutic Targeting

RIPK1 Inhibitors

RIPK1 is the most tractable therapeutic target in the necroptosis pathway due to its kinase-dependent activation: ^{2Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury2005 · Nature Chemical Biology}1

| Compound | Developer | Mechanism | Status | Notes | ^{2Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury2005 · Nature Chemical Biology}2 |----------|-----------|-----------|--------|-------| ^{2Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury2005 · Nature Chemical Biology}3 | Necrostatin-1 (Nec-1) | Academic | RIPK1 allosteric inhibitor | Preclinical tool | First-in-class; limited bioavailability | | Necrostatin-1s (Nec-1s) | Academic | Improved Nec-1 analog | Preclinical | Better selectivity and stability | | SAR443060 (DNL747) | Sanofi/Denali | Brain-penetrant RIPK1 inhibitor | Discontinued | Phase I safe but insufficient target engagement | | SAR443820 (DNL788) | Sanofi/Denali | Next-gen brain-penetrant RIPK1 inhibitor | Phase 2 (MS) | Failed Phase 2 in ALS; continues in MS | | GSK2982772 | GSK | RIPK1 inhibitor | Phase 2 (IBD, RA) | Peripheral indications | | GFH312 | GenFleet | RIPK1 inhibitor | Phase 1 | Novel chemical scaffold |

RIPK3 and MLKL Inhibitors

• GSK’843 and GSK’872: RIPK3 kinase inhibitors; effective in preclinical models but have paradoxical apoptosis-inducing effects at high doses.

• Necrosulfonamide (NSA): Directly binds MLKL and blocks its oligomerization; proof-of-concept tool compound.

• Selective MLKL inhibitors are in early preclinical development.

Emerging Approaches

• Dual pathway inhibitors: Compounds targeting both RIPK1-dependent necroptosis and RIPK1-dependent inflammation simultaneously.

• Gene therapy: AAV-delivered expression of anti-necroptotic proteins (dominant-negative MLKL, cFLIP) in specific neuronal populations.

• Natural compounds: Curcumin, resveratrol, and other polyphenols show RIPK1-inhibitory activity in preclinical studies, though clinical translation is uncertain.

Key Research Milestones

• 2005: Degterev et al. identified necrostatin-1 as the first chemical inhibitor of necroptosis and coined the term “necroptosis.”

• 2009: RIPK3 was identified as an essential mediator of necroptosis, forming the necrosome with RIPK1.

• 2012: MLKL was discovered as the terminal effector of necroptosis, executing cell death via membrane pore formation.

• 2017: First evidence of activated necroptosis markers in human AD brain tissue.

• 2019: RIPK1-RIPK3-MLKL pathway shown to be highly activated in PD models, with inhibition rescuing dopaminergic neurons.

• 2024: Comprehensive evidence that necroptosis drives neurodegeneration in AD established by Bhargava et al., published in Acta Neuropathologica.

• 2024: SAR443820 RIPK1 inhibitor fails Phase 2 in ALS but continues clinical development for MS.

• 2025: Systematic review confirms necroptosis activation across multiple AD experimental models (Bhardwaj et al., 2025).

Brain Atlas Resources

• Allen Human Brain Atlas: Necroptosis expression search

• Allen Mouse Brain Atlas: Necroptosis search

• Allen Cell Type Atlas: Transcriptomic cell type reference

• BrainSpan Developmental Transcriptome: Necroptosis developmental expression

Pathway & Interaction Diagram

Interactive diagram showing Necroptosis’s key relationships in the SciDEX knowledge graph (15 connections shown).

flowchart TD
    Necroptosis["Necroptosis"]
    Als["Als"]
    Cancer["Cancer"]
    APOPTOSIS(["APOPTOSIS"])
    INFLAMMATION(["INFLAMMATION"])
    PYROPTOSIS(["PYROPTOSIS"])
    FERROPTOSIS(["FERROPTOSIS"])
    CANCER(["CANCER"])
    RIPK3(["RIPK3"])
    MLKL(["MLKL"])
    Tumor["Tumor"]
    Inflammation["Inflammation"]
    AUTOPHAGY(["AUTOPHAGY"])

    Als -->|"activates"| Necroptosis
    Cancer -->|"therapeutic target"| Necroptosis
    Als -->|"therapeutic target"| Necroptosis
    APOPTOSIS -->|"regulates"| Necroptosis
    INFLAMMATION -->|"activates"| Necroptosis
    PYROPTOSIS -->|"regulates"| Necroptosis
    FERROPTOSIS -->|"regulates"| Necroptosis
    APOPTOSIS -->|"activates"| Necroptosis
    CANCER -->|"therapeutic target"| Necroptosis
    RIPK3 -->|"regulates"| Necroptosis
    MLKL -->|"regulates"| Necroptosis
    Cancer -->|"activates"| Necroptosis
    Tumor -->|"activates"| Necroptosis
    Inflammation -->|"activates"| Necroptosis
    AUTOPHAGY -->|"regulates"| Necroptosis

    style Necroptosis fill:#1a237e,stroke:#4fc3f7,stroke-width:3px,color:#fff

See Also

• Index

External Links

• PubMed

Background

The study of Necroptosis has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.