Targeting IKK2 by pharmacological inhibitor AS602868 prevents excitotoxic injury to neurons and oligodendrocytes

NF-κB Pathway and Its Inhibitors: A Promising Frontier in the Management of Alzheimer's Disease

The nuclear factor kappa B (NF-κB) pathway has emerged as a pivotal player in the pathogenesis of various diseases, including neurodegenerative illnesses like Alzheimer's disease (AD). The involvement of the NF-κB pathway in immune system responses, inflammation, oxidative stress, and neuronal survival highlights its significance in AD progression. We discuss the advantages of NF-κB pathway inhibition, including the potential to mitigate neuroinflammation, modulate amyloid beta (Aβ) production, and promote neuronal survival. However, we also acknowledge the limitations and challenges associated with this approach. Balancing the fine line between dampening inflammation and preserving physiological immune responses is critical to avoid unintended consequences. This review combines current knowledge on the NF-κB pathway's intricate involvement in AD pathogenesis, emphasizing its potential as a therapeutic target. By evaluating both advantages and limitations, we provide a holistic view of the feasibility and challenges of NF-κB pathway modulation in AD treatment. As the quest for effective AD therapies continues, an in-depth understanding of the NF-κB pathway's multifaceted roles will guide the development of targeted interventions with the potential to improve AD management.

The Pivotal Role of NF-kB in the Pathogenesis and Therapeutics of Alzheimer’s Disease

Alzheimer’s Disease (AD) is the most common neurodegenerative disease worldwide, with a high prevalence that is expected to double every 20 years. Besides the formation of Aβ plaques and neurofibrillary tangles, neuroinflammation is one the major phenotypes that worsens AD progression. Indeed, the nuclear factor-κB (NF-κB) is a well-established inflammatory transcription factor that fuels neurodegeneration. Thus, in this review, we provide an overview of the NF-κB role in the pathogenesis of AD, including its interaction with various molecular factors in AD mice models, neurons, and glial cells. Some of these cell types and molecules include reactive microglia and astrocytes, β-secretase, APOE, glutamate, miRNA, and tau protein, among others. Due to the multifactorial nature of AD development and the failure of many drugs designed to dampen AD progression, the pursuit of novel targets for AD therapeutics, including the NF-κB signaling pathway, is rising. Herein, we provide a synopsis of the drug development landscape for AD treatment, offering the perspective that NF-κB inhibitors may generate widespread interest in AD research in the future. Ultimately, the additional investigation of compounds and small molecules that target NF-κB signaling and the complete understanding of NF-κB mechanistic activation in different cell types will broaden and provide more therapeutic options for AD patients.

Amelioration of LPS-induced inflammation response in microglia by AMPK activation

Adenosine 5′-monophosphate-activated protein kinase (AMPK) is a key regulator of cellular energy homeostasis via modulating metabolism of glucose, lipid, and protein. In addition to energy modulation, AMPK has been demonstrated to associate with several important cellular events including inflammation. The results showed that ENERGI-F704 identified from bamboo shoot extract was nontoxic in concentrations up to 80 μM and dose-dependently induced phosphorylation of AMPK (Thr-172) in microglia BV2 cells. Our findings also showed that the treatment of BV2 with ENERGI-F704 ameliorated the LPS-induced elevation of IL-6 and TNF-α production. In addition, ENERGI-F704 reduced increased production of nitric oxide (NO) and prostaglandin E2 (PGE2) via downregulating the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2), respectively. Moreover, ENERGI-F704 decreased activated nuclear translocation and protein level of NF-κB. Inhibition of AMPK with compound C restored decreased NF-κB translocation by ENERGI-F704. In conclusion, ENERGI-F704 exerts inhibitory activity on LPS-induced inflammation through manipulating AMPK signaling and exhibits a potential therapeutic agent for neuroinflammatory disease.

Sustained, neuron-specific IKK/NF-κB activation generates a selective neuroinflammatory response promoting local neurodegeneration with aging

Background

Increasing evidence indicates that neuroinflammation is a critical factor contributing to the progression of various neurodegenerative diseases. The IKK/NF-κB signalling system is a central regulator of inflammation, but it also affects neuronal survival and differentiation. A complex interplay between different CNS resident cells and infiltrating immune cells, which produce and respond to various inflammatory mediators, determines whether neuroinflammation is beneficial or detrimental. The IKK/NF-κB system is involved in both production of and responses to these mediators, although the precise contribution depends on the cell type as well as the cellular context, and is only partially understood. Here we investigated the specific contribution of neuronal IKK/NF-κB signalling on the regulation of neuroinflammatory processes and its consequences. To address this issue, we established and analysed a conditional gain-of-function mouse model that expresses a constitutively active allele of IKK2 in principal forebrain neurons (IKK2^nCA). Proinflammatory gene and growth factor expression, histopathology, microgliosis, astrogliosis, immune cell infiltration and spatial learning were assessed at different timepoints after persistent canonical IKK2/NF-κB activation.

Results

In contrast to other cell types and organ systems, chronic IKK2/NF-κB signalling in forebrain neurons of adult IKK2^nCA animals did not cause a full-blown inflammatory response including infiltration of immune cells. Instead, we found a selective inflammatory response in the dentate gyrus characterized by astrogliosis, microgliosis and Tnf-α upregulation. Furthermore, downregulation of the neurotrophic factor Bdnf correlated with a selective and progressive atrophy of the dentate gyrus and a decline in hippocampus-dependent spatial learning. Neuronal degeneration was associated with increased Fluoro-jade staining, but lacked activation of apoptosis. Remarkably, neuronal loss could be partially reversed when chronic IKK2/NF-κB signalling was turned off and Bdnf expression was restored.

Conclusion

Our results demonstrate that persistent IKK2/NF-κB signalling in forebrain neurons does not induce overall neuroinflammation, but elicits a selective inflammatory response in the dentate gyrus accompanied by decreased neuronal survival and impaired learning and memory. Our findings further suggest that chronic activation of neuronal IKK2/NF-κB signalling, possibly as a consequence of neuroinflammatory conditions, is able to induce apoptosis-independent neurodegeneration via paracrine suppression of Bdnf synthesis.

Inhibitor kappa B kinase beta dependent cytokine upregulation in nociceptive neurons contributes to nociceptive hypersensitivity after sciatic nerve injury

Inhibitor kappa B kinase (IKK)-mediated nuclear factor-kappa B (NF-κB) activation is a major pathway for transcriptional control of various pro-inflammatory factors. We here assessed whether activation of this pathway specifically in primary nociceptive neurons of the dorsal root ganglia (DRG) contributes to the development of nociceptive hypersensitivity. Mice carrying a cre-loxP-mediated deletion of inhibitor kappa B kinase beta (IKKβ) in DRG neurons were protected from nerve injury-evoked allodynia and hyperalgesia. This effect was mimicked by systemic treatment with an IKKβ inhibitor but was not observed upon specific inhibition of IKKβ in the spinal cord, suggesting a specific role of IKKβ in the peripheral neurons. The deletion of IKKβ in DRG neurons did not affect constitutive neuronal NF-κB activity, but reduced nerve injury-evoked NF-κB stimulation in the DRG and was associated with reduced upregulation of interleukin-16, monocyte chemoattractant protein-1/chemokine (CC motif) ligand 2 (MCP-1/CCL2), and tumor necrosis factor alpha (TNFα) in the DRG. These cytokines evoked a rapid rise of intracellular calcium in subsets of primary DRG neurons. The results suggest that IKKβ-mediated NF-κB stimulation in injured primary sensory neurons promotes cytokine and chemokine production and contributes thereby to the development of chronic pain.

PERSPECTIVE

Inhibitors of IKK that do not pass the blood-brain barrier and act only in the periphery might be useful for reduction of the pro-inflammatory response in peripheral DRG neurons and reduce thereby nerve injury-evoked pain without affecting neuroprotective effects of NF-κB in the central nervous system.

Vinpocetine inhibits oligodendroglial precursor cell differentiation

BACKGROUND

In multiple sclerosis during periods of remission a limited degree of myelin repair can be observed mediated by oligodendroglial precursor cells. Phosphodiesterase inhibitors act as anti-inflammatory agents and might hold promise for future multiple sclerosis treatment.

AIMS

To investigate whether phosphodiesterase inhibitors could also influence myelin repair.

METHODS

We stimulated primary oligodendroglial precursor cells with cilostazol, rolipram and vinpocetine and assessed their effects on repair related cellular processes.

RESULTS

We found that vinpocetine exerted a strong negative effect on myelin expression while cilostazol and rolipram did not show such effects. In addition, vinpocetine decreased morphological complexities suggesting an overall negative impact on oligodendroglial cell maturation. We provide evidence that this is not mediated via a blockade of phosphodiesterase-1 but rather by inhibition of IĸB kinase.

CONCLUSION

These findings suggest that vinpocetine via IĸB inhibition exerts a strong negative impact on oligodendroglial cell maturation and may therefore provide the rationale to restrict its application during periods of remission in multiple sclerosis patients. This is of particular interest since vinpocetine is widely used as a health supplement thought to act as a cognitive and memory enhancer for healthy people and patients with neurological or muscle diseases.

NF-κB and epigenetic mechanisms as integrative regulators of brain resilience to anoxic stress

Brain cells display an amazing ability to respond to several different types of environmental stimuli and integrate this response physiologically. Some of these responses can outlive the original stimulus by days, weeks or even longer. Long-lasting changes in both physiological and pathological conditions occurring in response to external stimuli are almost always mediated by changes in gene expression. To effect these changes, cells have developed an impressive repertoire of signaling systems designed to modulate the activity of numerous transcription factors and epigenetic mechanisms affecting the chromatin structure. Since its initial characterization in the nervous system, NF-κB has shown to respond to multiple signals and elicit pleiotropic activities suggesting that it may play a pivotal role in integration of different types of information within the brain. Ample evidence demonstrates that NF-κB factors are engaged in and necessary for neuronal development and synaptic plasticity, but they also regulate brain response to environmental noxae. By focusing on the complexity of NF-κB transcriptional activity in neuronal cell death, it emerged that the composition of NF-κB active dimers finely tunes the neuronal vulnerability to brain ischemia. Even though we are only beginning to understand the contribution of distinct NF-κB family members to the regulation of gene transcription in the brain, an additional level of regulation of NF-κB activity has emerged as operated by the epigenetic mechanisms modulating histone acetylation. We will discuss NF-κB and epigenetic mechanisms as integrative regulators of brain resilience to anoxic stress and useful drug targets for restoration of brain function. This article is part of a Special Issue entitled: Brain Integration.

TAp63 is a transcriptional target of NF-kappaB

The p53 homologue p63 encodes multiple protein isoforms either with (TA) or without (DeltaN) the N-terminal transactivation domain. Accumulating evidence indicates that TAp63 plays an important role in various biological processes, including cell proliferation, differentiation, and apoptosis. However, how TAp63 is regulated remains largely unclear. In this study, we demonstrate that NF-kappaB induces TAp63 gene expression. The responsible elements for NF-kappaB-mediated TAp63 induction are located within the region from -784 to -296 bp in the TAp63 promoter, which contains two NF-kappaB binding sites. Ectopic expression of RelA stimulates TAp63 promoter-driven reporter activity and increases endogenous TAp63 mRNA levels. Inhibition of NF-kappaB by IkappaBalpha super-repressor or with a chemical inhibitor leads to down regulation of TAp63 mRNA expression and activity. In addition, mutations in the critical NF-kappaB-binding sites significantly abolish the effects of NF-kappaB on TAp63. Activation of NF-kappaB by TNFalpha enhances p50/RelA binding to the NF-kappaB binding sites. Furthermore, we show that an Sp1 site adjacent to the NF-kappaB sites plays a role in NF-kappaB-mediated upregulation of TAp63. Taken together, these data reveal that TAp63 is a transcriptional target of NF-kappaB, which may play a role in cell proliferation, differentiation and survival upon NF-kappaB activation by various stimuli.

Unique aspects of transcriptional regulation in neurons--nuances in NFkappaB and Sp1-related factors

The unique physiology and function of neurons create differences in their cellular physiology, including their regulation of gene expression. We began several years ago exploring the relationships between the NFκB transcription factor, neuronal survival, and glutamate receptor activation in telencephalic neurons. These studies led us to conclude that this population of cells is nearly incapable of activating the NFκB that is nonetheless expressed at reasonable levels. A subset of the κB cis elements are instead bound by members of the Sp1 family in neurons. Also surprising was our discovery that Sp1 itself, typically described as ubiquitous, is severely restricted in expression within forebrain neurons; Sp4 seems to be substituted during neuronal differentiation. These findings and their implications for neuronal differentiation – as well as potential dedifferentiation during degenerative processes – are discussed here.

Post-ischemic brain damage: NF-kappaB dimer heterogeneity as a molecular determinant of neuron vulnerability

Nuclear factor-kappaB (NF-kappaB) has been proposed to serve a dual function as a regulator of neuron survival in pathological conditions associated with neurodegeneration. NF-kappaB is a transcription family of factors comprising five different proteins, namely p50, RelA/p65, c-Rel, RelB and p52, which can combine differently to form active dimers in response to external stimuli. Recent research shows that diverse NF-kappaB dimers lead to cell death or cell survival in neurons exposed to ischemic injury. While the p50/p65 dimer participates in the pathogenesis of post-ischemic injury by inducing pro-apoptotic gene expression, c-Rel-containing dimers increase neuron resistance to ischemia by inducing anti-apoptotic gene transcription. We present, in this report, the latest findings and consider the therapeutic potential of targeting different NF-kappaB dimers to limit ischemia-associated neurodegeneration.

NF-kappaB dimers in the regulation of neuronal survival

Nuclear factor-kappaB (NF-kappaB) is a dimeric transcription factor composed of five members, p50, RelA/p65, c-Rel, RelB, and p52 that can diversely combine to form the active transcriptional dimer. NF-kappaB controls the expression of genes that regulate a broad range of biological processes in the central nervous system such as synaptic plasticity, neurogenesis, and differentiation. Although NF-kappaB is essential for neuron survival and its activation may protect neurons against oxidative-stresses or ischemia-induced neurodegeneration, NF-kappaB activation can contribute to inflammatory reactions and apoptotic cell death after brain injury and stroke. It was proposed that the death or survival of neurons might depend on the cell type and the timing of NF-kappaB activation. We here discuss recent evidence suggesting that within the same neuronal cell, activation of diverse NF-kappaB dimers drives opposite effects on neuronal survival. Unbalanced activation of NF-kappaB p50/RelA dimer over c-Rel-containing complexes contributes to cell death secondary to the ischemic insult. While p50/RelA acts as transcriptional inducer of Bcl-2 family proapoptotic Bim and Noxa genes, c-Rel dimers specifically promote transcription of antiapototic Bcl-xL gene. Changes in the nuclear content of c-Rel dimers strongly affect the threshold of neuron vulnerability to ischemic insult and agents, likewise leptin, activating a NF-kappaB/c-Rel-dependent transcription elicit neuroprotection in animal models of brain ischemia.