Ischemic brain injury involves interconnected stress responses and regulated death mechanisms whose contributions vary across cells, regions, and time. Apoptosis has extensive mechanistic support, while necroptosis, pyroptosis, ferroptosis, and parthanatos have strengthened the experimental understanding of vascular, inflammatory, lipid, and genotoxic injury. Their relative execution in human stroke remains less certain. Autophagy principally regulates homeostasis and other death pathways. ADCD requires a separate causal demonstration. Shared molecular nodes and emerging PANoptosome evidence provide a basis for testing coordinated intervention, while marker overlap alone does not prove pathway switching or combination efficacy. Cell-specific perturbation, temporal sampling, and clinically relevant functional outcomes are needed to turn this network framework into targeted therapeutic hypotheses.

Figure 1: Apoptotic signaling pathways. Death receptors recruit adaptor and initiator-caspase complexes. Caspase-8 links receptor signaling to mitochondria through BID cleavage. BAX/BAK-mediated mitochondrial outer membrane permeabilization (MOMP) permits cytochrome c release, apoptotic protease-activating factor 1 (Apaf-1)-dependent apoptosome formation, and caspase-9/3/7 activation. B-cell lymphoma 2 (BCL-2)-family proteins and inhibitor-of-apoptosis proteins regulate these steps. Tumor necrosis factor receptor 1 (TNFR1) complex I supports survival and inflammatory signaling, whereas cytosolic death complexes can promote apoptosis or necroptosis. Extensive MOMP commonly supports death commitment, whereas limited MOMP is not necessarily immediately lethal. Apoptosis-inducing factor (AIF)/endonuclease G (EndoG)-associated caspase-independent effects are distinguished from classical caspase-dependent apoptosis. The schematic summarizes general molecular relationships rather than a proven sequence in every ischemic cell. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 2: Necroptotic signaling. TNFR1-associated receptor-interacting protein kinase 1 (RIPK1) signaling can recruit receptor-interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL) when the regulatory context permits necroptosis. Toll/interleukin-1 receptor-domain-containing adaptor-inducing interferon-β (TRIF)-dependent Toll-like receptor signaling provides a RIPK1-independent route to RIPK3. MLKL phosphorylation and membrane injury represent central execution events. Mitochondrial, calcium, and inflammatory signals contribute to contextual amplification rather than universal pathway requirements. Endosomal sorting complexes required for transport III (ESCRT-III)-mediated membrane repair can oppose terminal lysis. Changes in protein expression or cytokine release alone do not establish necroptotic execution. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 3: Regulation of autophagy. Growth-factor and nutrient signals regulate mechanistic target of rapamycin complex 1 (mTORC1), while AMP-activated protein kinase (AMPK) links energy stress to mTORC1 inhibition and unc-51-like kinase 1 (ULK1) activation. Class III phosphatidylinositol 3-kinase (PI3KC3)/Beclin 1 (BECN1)-associated nucleation and autophagy-related (ATG) conjugation systems support microtubule-associated protein 1 light chain 3 (LC3) lipidation and autophagosome formation. Fusion with lysosomes and effective cargo degradation complete autophagic flux. Increased autophagosome abundance may reflect enhanced formation or impaired clearance. The schematic illustrates autophagy regulation rather than evidence of autophagy-dependent cell death. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 4: Pyroptotic signaling pathways. Receptor-associated inflammatory signaling and cyclic GMP-AMP synthase (cGAS)/cyclic GMP-AMP (cGAMP)/stimulator of interferon genes (STING) signaling connect innate immune sensing with nuclear factor κB (NF-κB)-associated priming. Inflammasome-mediated caspase-1 activation promotes cytokine maturation and gasdermin D (GSDMD) cleavage, while gasdermin N-terminal fragments form membrane pores. Cytosolic lipopolysaccharide (LPS) sensing by human caspase-4/5 or murine caspase-11 activates GSDMD. Caspase-3-mediated gasdermin E (GSDME) cleavage represents a distinct route and should not be interpreted as direct cleavage by caspase-4/5/11. The schematic does not establish a universal signaling sequence in ischemic cells. Table 2 summarizes cell-specific findings involving microglia, neurons, astrocytes, and brain endothelial cells, distinguishing execution evidence from association and treating C-X3-C motif chemokine ligand 1 (CX3CL1) and the CHRNA7-FAM7A fusion gene (CHRFAM7A) as modulators8,41,87–94. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 5: Ferroptotic signaling pathways. Iron transport and nuclear receptor coactivator 4 (NCOA4)-associated ferritinophagy influence the labile iron pool. Acyl-coenzyme A synthetase long-chain family member 4 (ACSL4)-dependent lipid remodeling supplies oxidation-sensitive phospholipids. System xc−/glutathione (GSH)/glutathione peroxidase 4 (GPX4), ferroptosis suppressor protein 1 (FSP1)/coenzyme Q (CoQ), dihydroorotate dehydrogenase (DHODH), and GTP cyclohydrolase 1 (GCH1)/tetrahydrobiopterin (BH4) provide complementary antioxidant defenses. Their relative contributions depend on cellular context and are not equally established in ischemic stroke. Phospholipid peroxidation is central to ferroptotic execution, whereas iron accumulation or changes in individual markers are insufficient for pathway identification. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 6: Parthanatos signaling. Excitotoxic and oxidative/nitrosative signals can produce DNA damage and excessive poly(ADP-ribose) polymerase 1 (PARP1) activity. Poly(ADP-ribose) (PAR) accumulation connects nuclear injury with mitochondrial apoptosis-inducing factor (AIF) release and redistribution. AIF recruits macrophage migration inhibitory factor (MIF), whose nuclease activity executes large-scale nuclear DNA cleavage. MIF-mediated cleavage is distinguished from other caspase-independent nuclear mechanisms, including endonuclease G (EndoG)-associated effects. Nicotinamide adenine dinucleotide (NAD+) consumption and bioenergetic impairment contribute to cellular injury but are not specific diagnostic features. Physiological PARP1-dependent DNA repair is distinguished from excessive death-associated PAR signaling. The supported parthanatos execution mechanism is described in the cited literature56,58,59,104. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 7: Interactions among cell death pathways. Shared receptor signaling, organelle dysfunction, oxidative stress, and DNA damage connect multiple regulated cell death pathways. Autophagy is represented as a regulatory process rather than evidence of autophagy-dependent cell death (ADCD). Cross-pathway arrows indicate reported or proposed regulatory interactions and do not establish that every connection operates within the same cell or that all pathways activate simultaneously. PANoptosis requires additional evidence of coordinated death machinery and relevant molecular complex interactions. Multinode therapeutic intervention remains a hypothesis requiring cell- and injury-phase-specific experimental validation. Original schematic created by the authors. Please click here to view a larger version of this figure.

Figure 8: Cell death in the neurovascular unit. A microvessel, perivascular microglia, astrocytic endfeet, and a neuron illustrate representative mechanisms in the peri-infarct environment. Microglial tumor necrosis factor-α (TNF-α) engages endothelial TNFR1/RIPK1/RIPK3/MLKL signaling in a death-complex-permissive context, with caspase-8-mediated restraint indicated. Membrane injury is depicted locally rather than as a separate outcome panel74. Microglial STING-associated NLR family pyrin domain-containing 3 (NLRP3)/caspase-1/GSDMD signaling and cytokine release are shown at their relevant cellular sites89. Within neurons, mitochondria connect BAX/BAK-dependent permeabilization, cytochrome c/apoptosome/caspase signaling, and AIF redistribution. Nuclear PARP1/PAR signaling recruits the AIF-MIF mechanism, in which MIF executes DNA cleavage58. ACSL4-associated phospholipid remodeling, iron-dependent lipid injury, and GSH/GPX4 antioxidant defense are depicted near membrane lipids97,98. Autophagosomes and lysosomes illustrate completed cargo degradation rather than an assumed autophagy-dependent death program11. Endothelial ferroportin 1 (FPN1)-mediated iron export is represented as transport, with phase-dependent implications for acute injury and recovery107. Arrows indicate signaling or transport, potentially involving intermediate steps, while inhibition bars indicate regulatory restraint. Cell outlines organize representative findings without implying simultaneous activation of all mechanisms. Timing labels are descriptive; model-dependent chronology, core/penumbra distinctions, and evidence gaps are summarized in Table 3. Original schematic created for this review. Please click here to view a larger version of this figure.
Table 1: Evidence for cell death pathway identification. Summary of complementary molecular and functional evidence used to identify regulated cell death pathways. Rescue experiments should be interpreted alongside target engagement and appropriate controls. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and lactate dehydrogenase (LDH) measurements are not pathway-specific8,11,47,59. Abbreviations: MDA = malondialdehyde; 4-HNE = 4-hydroxynonenal. Please click here to download this file.
Table 2: Cell-specific pyroptotic signaling. Summary of pyroptosis-associated signaling in neurons, microglia, astrocytes, and endothelial cells, distinguishing molecular associations from evidence of pathway execution. Arrows indicate supported signaling relationships or execution frameworks but do not imply that every step was demonstrated in every experimental model. Canonical caspase-1/GSDMD, noncanonical human caspase-4/5 or murine caspase-11/GSDMD, and caspase-3/GSDME signaling represent distinct routes8,41. Inflammasome assembly, cytokine maturation, gasdermin cleavage, pore formation, and terminal lysis require separate interpretation. Abbreviations: OGD/R = oxygen-glucose deprivation/reoxygenation; MCAO/R = middle cerebral artery occlusion/reperfusion. Please click here to download this file.
Table 3: Spatial and temporal patterns of cell death. Summary of representative cell-specific mechanisms across ischemic injury, reperfusion, and recovery. The stages are descriptive and may overlap. Evidence remains incomplete for pericytes, oligodendrocytes, aged or comorbid models, and human cell-resolved pathway execution. Abbreviations: I/R = ischemia/reperfusion; Cdh5 = cadherin 5; Fpn1 = ferroportin 1. Please click here to download this file.
Table 4: Therapeutic strategies targeting cell death. Summary of selected experimental interventions, treatment conditions, and molecular or functional evidence relevant to therapeutic interpretation. Findings from genetic knockout experiments establish susceptibility rather than directly deliverable treatments, and preclinical outcomes do not establish clinical efficacy or a generalizable treatment window. Abbreviations: tMCAO = transient middle cerebral artery occlusion; PC12 = rat pheochromocytoma cell line; ERK = extracellular signal-regulated kinase; IgG = immunoglobulin G; NOX2 = NADPH oxidase 2. Please click here to download this file.