IKKβ in AD: Distinguishing Kinase Functions from NF-κB-Dependent Transcription

The literature on IKKβ in AD appears contradictory because IKKβ activity is often treated as equivalent to canonical NF-κB transcription. Although IKKβ is a major upstream activator of NF-κB, it also regulates autophagy, proteostasis, receptor signaling, and cell-death pathways through mechanisms that are not necessarily mediated by RelA/p65-dependent transcription. Consequently, beneficial or detrimental effects of manipulating IKKβ should not automatically be attributed to NF-κB transcription.

Several acute studies illustrate potentially beneficial functions of IKKβ. In Aβ1–42-exposed mice and HT22 cells, DJ−1 promoted IKKβ activity through von Hippel–Lindau protein (VHL), increased autophagic activity, and reduced phosphorylated tau, whereas suppression of DJ−1 or IKKβ worsened tau-related abnormalities (Chen et al., 2021b). Similarly, bidirectional manipulation of IKKβ in Aβ-treated SH-SY5Y cells and APP/PS1 mice showed that IKKβ activation enhanced autophagy and reduced RIPK1-associated necroptosis, whereas IKKβ silencing produced the opposite effects and increased Aβ accumulation (Wang et al., 2022b). These studies support beneficial IKKβ-dependent effects on proteostasis and cell survival under acute experimental conditions, but neither established that a specific NF-κB dimer or κB-regulated transcriptional program mediated the protection.

The relationship changes in chronic disease models. Schnöder et al. conditionally deleted Ikbkb specifically in neurons of APP- and P301S tau-transgenic mice. Neuronal IKKβ deficiency reduced BACE1 expression and β-secretase activity, cerebral Aβ, phosphorylated tau, apoptosis, and inflammatory abnormalities, while also increasing markers of autophagy (Schnöder et al., 2023). Synaptic preservation and cognitive improvement were evident in the APP model, although cognitive rescue was less apparent in the tau model. These findings show that the relationship between IKKβ and autophagy is context dependent: increasing IKKβ can support autophagy during acute Aβ stress, whereas deleting persistent neuronal IKKβ during chronic amyloid or tau pathology can also improve autophagic markers while reducing disease burden. Thus, IKKβ cannot be assigned a fixed pro- or anti-autophagic role independent of disease state and duration.

Other experimental systems broadly support a detrimental effect of prolonged NF-κB signaling. In Drosophila expressing human Aβ42, genetic reduction of Toll–NF-κB signaling attenuated neurodegeneration, whereas increased signaling worsened the phenotype (Tan et al., 2008b). Similarly, loss of protein arginine methyltransferase 5 (PRMT5) increased E2F1, NF-κB, and GSK3β signaling and promoted neuronal injury in APP-Swedish cells and Aβ-expressing Caenorhabditis elegans; inhibition of NF-κB or GSK3β reduced cell death (Quan et al., 2015). These studies support a pathogenic role for prolonged stress-associated NF-κB signaling, although their simplified organisms and cellular models limit direct extrapolation to the human brain.

Pharmacological inhibition provides additional whole-brain evidence. Rangasamy et al. used a NEMO-binding domain peptide to preferentially inhibit inducible IKK/NF-κB activation in 5xFAD mice. Repeated intranasal treatment reduced hippocampal NF-κB activity, microglial activation, inflammatory gene expression, Aβ burden, tau-related abnormalities, neuronal apoptosis, and memory impairment (Rangasamy et al., 2015b). Because the intervention affected multiple brain cell types, it cannot identify the specific cellular or NF-κB complex responsible for the improvement, but it supports a detrimental role for excessive inducible IKK/NF-κB signaling.

The strongest evidence for a defined pathogenic IKKβ–NF-κB program comes from microglial tau studies. In PS19 tauopathy mice, microglia-specific IKKβ activation increased NF-κB-dependent transcription, tau seeding, and anatomical spread, whereas microglial Ikbkb deletion reduced tau propagation, improved chaperone-mediated autophagy, normalized disease-associated microglial states, and improved learning and memory (Wang et al., 2022a). Pharmacological inhibition of IKKβ similarly reduced release of seeding-competent tau from microglia. Notably, NF-κB inhibition increased tau retained within neuronal inclusions while reducing extracellular seeding and anatomical spread, showing that intracellular aggregate burden and propagation are distinct pathological outcomes.

Human postmortem studies provide complementary disease relevance but weaker causal evidence. Activated NF-κB and increased IκB have been detected in regions containing neurofibrillary pathology (Hattori et al., 2001), while phosphorylated p65 has been localized to granulovacuolar degeneration and tau-positive neurites (Yamaguchi et al., 2019b). A nuclear TDP−43–p65 complex was also particularly prominent in a small subset of individuals with MCI and episodic-memory impairment (Ohta et al., 2014). These findings demonstrate that altered NF-κB regulation accompanies tau-associated pathology in human brain tissue, but they cannot determine whether NF-κB activation preceded, followed, or became sequestered within degenerating structures.

Therapeutic studies targeting broader inflammatory networks are consistent with this pattern. Combined inhibition of NF-κB and the NLRP3 inflammasome reduced inflammatory cytokines and glial activation and improved cognitive and tau-related outcomes in aged wild-type and rTg4510 tauopathy mice (Wahl et al., 2024). Because both pathways were targeted simultaneously, however, the specific contribution of NF-κB inhibition cannot be isolated.

Taken together, the apparent contradiction in the IKKβ literature largely disappears when kinase activity is distinguished from NF-κB-dependent transcription. Under acute stress, IKKβ can support autophagy, proteostasis, and survival through mechanisms that may not require a defined canonical NF-κB transcriptional program. In contrast, chronic neuronal IKKβ activity promotes amyloidogenic and tau-related pathology, while microglial IKKβ–NF-κB signaling can directly facilitate the processing and propagation of seeding-competent tau. Autophagy therefore should not be regarded as a fixed downstream consequence of IKKβ activity; its direction depends on cell type, disease duration, upstream stimulus, and the relative contribution of transcriptional and non-transcriptional IKKβ functions. These distinctions are important therapeutically. Broad IKKβ inhibition could suppress pathological RelA-dependent inflammatory or amyloidogenic signaling while simultaneously interfering with beneficial IKKβ-dependent functions in proteostasis and cell survival. A more precise strategy would therefore target the disease-associated receptor, NF-κB dimer, transcriptional cofactor, post-translational modification, or downstream effector responsible for the pathological program. Studies that manipulate IKKβ without demonstrating dimer-specific activation, κB-site dependence, target-gene involvement, or downstream rescue should therefore be interpreted primarily as evidence about IKKβ biology rather than as definitive evidence that canonical NF-κB transcription is protective or harmful.