Immunoproteasome Inhibition Alters Hippocampal Plasticity: Insights from ONX-0914 (PR-957) Administration

Study Background and Research Question

Proteasomes, central to intracellular protein degradation, exist in multiple forms, including standard (constitutive) and non-constitutive (immunoproteasome and intermediate) variants. The immunoproteasome, characterized by the presence of inducible β subunits such as LMP7 (β5i), is upregulated in immune cells and during cellular stress, and is increasingly recognized for roles beyond immunity, including in the brain. However, the specific contribution of non-constitutive proteasomes to central nervous system (CNS) function—especially in synaptic plasticity and learning—remains poorly understood. The reference study by Maltsev et al. (2023) addresses this gap by investigating how chronic inhibition of the immunoproteasome with ONX-0914 (PR-957), a highly selective LMP7 inhibitor, modulates hippocampal long-term potentiation (LTP), a cellular correlate of learning and memory (paper).

Key Innovation from the Reference Study

The central innovation in this work is the chronic, selective targeting of the immunoproteasome in vivo to dissect its role in hippocampal synaptic function. While prior studies have used broad-spectrum proteasome inhibitors, this study leverages the specificity of ONX-0914 (PR-957) to isolate the effects of non-constitutive proteasome inhibition from those of the canonical proteasome system (paper). This approach enables the identification of distinct contributions of the immunoproteasome to different forms of LTP and associated gene expression profiles in the brain.

Methods and Experimental Design Insights

Maltsev et al. implemented a chronic administration protocol in mice, delivering ONX-0914 systemically to achieve sustained immunoproteasome inhibition. Hippocampal slices were then prepared for electrophysiological recordings. Two standard protocols were used to induce LTP:

• Theta-burst stimulation (TBS): Mimics endogenous firing patterns associated with learning.
• Tetanic stimulation: Delivers a high-frequency train of stimuli, a classic method for LTP induction.

Field-excitatory postsynaptic potentials (fEPSPs) were measured to quantify LTP magnitude. Additionally, hippocampal tissue was analyzed for changes in gene expression related to synaptic plasticity and glutamatergic signaling, providing molecular context for the electrophysiological findings.

Protocol Parameters

• assay | chronic ONX-0914 administration | 10 mg/kg, i.p., daily for 7 days | enables sustained immunoproteasome inhibition in vivo | source: paper
• assay | LTP induction (TBS) | 5 bursts of 4 pulses at 100 Hz, 200 ms interburst | models physiological forms of learning-related plasticity | source: paper
• assay | LTP induction (tetanic) | 100 Hz, 1 s | classical LTP model, sensitive to proteasome function | source: paper
• workflow | gene expression analysis | qPCR of synaptic plasticity and glutamate signaling genes | establishes molecular correlates of electrophysiological changes | workflow_recommendation

Core Findings and Why They Matter

The major discovery of the study is the protocol-specific effect of immunoproteasome inhibition on LTP:

• TBS-induced LTP was unaffected by chronic ONX-0914 treatment, indicating that this physiological form of plasticity is resilient to immunoproteasome blockade.
• Tetanic-induced LTP was significantly impaired, as evidenced by reduced fEPSP slopes in hippocampal slices from ONX-0914-treated animals compared to controls (paper).

Gene expression analysis revealed that ONX-0914 administration led to differential regulation of genes involved in synaptic signaling, glutamatergic transmission, and plasticity. These molecular changes are consistent with the observed electrophysiological deficits and implicate immunoproteasomes in the fine-tuning of synaptic adaptation mechanisms. These findings are significant for several reasons:

1. They demonstrate that non-constitutive proteasomes, while less abundant in the CNS, have specific and non-redundant roles in certain forms of synaptic plasticity.
2. This work provides a mechanistic framework for understanding how altered immunoproteasome function—whether due to genetic, inflammatory, or pharmacological factors—could contribute to cognitive dysfunction or resilience.

Comparison with Existing Internal Articles

Several internal resources reinforce and expand upon these findings:

• The article Immunoproteasome Inhibition Alters Hippocampal Synaptic Plasticity outlines the selective impairment of tetanus-induced LTP by ONX-0914, echoing the reference study’s core results and emphasizing the nuanced, context-dependent effects of immunoproteasome inhibition on neural plasticity.
• ONX-0914 (PR-957): Selective Immunoproteasome LMP7 Inhibitor highlights the molecule's robust specificity and validated protocols for immune modulation, providing practical guidance for researchers aiming to translate these findings into autoimmune and neuroinflammation models.
• ONX-0914: Selective Immunoproteasome Inhibitor for Autoim... further contextualizes ONX-0914 as a tool for dissecting cytokine production blockade and immune signaling in diverse disease models, bridging CNS-focused and immunological research domains.

These resources collectively illustrate the molecule’s versatility in both neurobiological and immunological settings, supporting its use in next-generation research on neuroimmune interactions, arthritis research, and diabetes research.

Limitations and Transferability

While the study provides compelling evidence for the involvement of immunoproteasomes in hippocampal LTP, several caveats warrant consideration:

• The chronic administration model may not fully recapitulate acute or disease-driven immune modulation in the brain.
• Findings are currently limited to murine hippocampus and may not directly extrapolate to other CNS regions or to human physiology without further validation.
• The gene expression analysis, while informative, is correlative and does not establish causality between specific downstream targets and the LTP phenotype.

Nonetheless, these insights pave the way for targeted studies into the role of immunoproteasome inhibition in neurodegenerative and neuroinflammatory disorders, as well as in translational models of cognitive dysfunction.

Research Support Resources

Researchers seeking to replicate or extend these findings can utilize ONX-0914 (PR-957) (SKU A4011), a well-characterized immunoproteasome inhibitor with high selectivity for the LMP7 subunit (IC50 ~10 nM; source: product_spec). The compound’s ability to modulate cytokine production and synaptic gene expression makes it suitable for workflows investigating immunoproteasome inhibition in autoimmune disease, neuroinflammation, or synaptic plasticity. For practical guidance on dosing, solubility, and storage, APExBIO provides comprehensive product documentation. As always, ONX-0914 is supplied for research use only and is not intended for diagnostic or therapeutic applications.