Chronic Immunoproteasome Inhibition Shapes Synaptic Plasticity and Glutamate Signaling in the Murine Hippocampus

Study Background and Research Question

The ubiquitin–proteasome system (UPS) is central to protein homeostasis. While the canonical (constitutive) proteasome’s role in protein degradation is well characterized, less is known about the functional implications of non-constitutive (immunoproteasome) subunits, particularly in the central nervous system (CNS). Immunoproteasomes, defined by the replacement of standard β subunits with inducible β1i, β2i, and β5i (notably LMP7/β5i), are upregulated during inflammation and in immune cells but are also present in lower levels in neurons, astrocytes, and microglia. Prior studies have suggested that broad-spectrum proteasome inhibition disrupts synaptic plasticity, but the specific contributions of immunoproteasome activity remained unclear (paper).

The central research question addressed by Maltsev et al. (2023) is: How does chronic, selective inhibition of the immunoproteasome affect hippocampal synaptic plasticity—specifically long-term potentiation (LTP)—and glutamate signaling-related gene expression in mice?

Key Innovation from the Reference Study

This work is among the first to systematically examine the consequences of sustained, selective immunoproteasome inhibition in the murine hippocampus using ONX-0914 (PR-957), a potent and specific LMP7/β5i inhibitor. Unlike pan-proteasome inhibitors, ONX-0914 allows researchers to dissect the unique roles of non-constitutive subunits, advancing understanding of immunoproteasome functions in neural contexts (paper).

Methods and Experimental Design Insights

The investigators used a chronic dosing paradigm in mice, administering ONX-0914 systemically and comparing outcomes to both vehicle (DMSO) and untreated controls. Electrophysiological recordings were performed on acute hippocampal slices to assess LTP, a measurable correlate of learning and memory, using two standard induction protocols:

• Theta-burst stimulation (TBS): Mimics physiological neural firing patterns.
• Tetanic stimulation: High-frequency stimulation more sensitive to synaptic modifications.

Field excitatory postsynaptic potentials (fEPSPs) were recorded to quantify synaptic strength. In parallel, the team analyzed hippocampal gene expression profiles, with a focus on genes implicated in synaptic plasticity and glutamatergic neurotransmission (paper).

Protocol Parameters

• assay | ONX-0914 systemic administration | chronic dosing (dose not specified in abstract) | murine hippocampal LTP studies | selective targeting of immunoproteasome | paper
• assay | Electrophysiology (fEPSP) | TBS and tetanic protocols | quantification of synaptic plasticity | allows discrimination between forms of LTP | paper
• workflow_recommendation | ONX-0914 (PR-957) dosing | 5–20 mg/kg (common in rodent studies) | dosing should be titrated based on pilot toxicity/efficacy and tissue penetration studies | see product_spec
• workflow_recommendation | Compound solubility | ≥29.03 mg/mL in DMSO, ≥69 mg/mL in ethanol | ensure proper dissolution to achieve consistent dosing | product_spec

Core Findings and Why They Matter

The study demonstrated that chronic ONX-0914 administration does not affect LTP induced by TBS but significantly reduces fEPSP slopes following tetanic stimulation. This suggests that non-constitutive proteasomes—via LMP7 inhibition—are specifically involved in tetanus-evoked synaptic plasticity, while TBS-induced LTP remains immunoproteasome-independent (paper).

Gene expression analysis revealed that ONX-0914 treatment alters the transcription of multiple genes related to synaptic signaling and glutamatergic synapse function, indicating a molecular basis for the observed physiological changes. Together, these results underscore that immunoproteasome activity modulates not only immune signaling but also neural plasticity and potentially learning processes.

Comparison with Existing Internal Articles

Internal resources such as "ONX-0914 (PR-957): Immunoproteasome LMP7 Inhibitor in Adv..." and "ONX-0914: Selective Immunoproteasome Inhibitor for Autoim..." predominantly focus on immunoproteasome inhibition in autoimmune disease and inflammation models. These articles highlight ONX-0914’s ability to block proinflammatory cytokine production (e.g., >90% inhibition of IL-23 and ~50% inhibition of TNF-α and IL-6 in PBMCs) and attenuate disease in models of arthritis and diabetes (source: product_spec; internal_article).

The present study broadens this perspective by demonstrating ONX-0914’s impact on neural synaptic processes, adding a neurobiological dimension to its established utility in immunology and cytokine production blockade. While internal articles emphasize immune modulation, Maltsev et al. (2023) provide direct evidence for immunoproteasome involvement in neural plasticity—a previously underexplored domain.

Limitations and Transferability

Several limitations warrant consideration. The dosing regimen and its translational relevance to human CNS exposures require further clarification, as do potential off-target effects at higher systemic concentrations. The study's focus on male mice and hippocampal slices limits generalizability across sexes, species, and brain regions. Additionally, while gene expression changes were observed, functional consequences for behavior and cognition were not directly assessed (paper).

Transferability to disease models should be approached cautiously. While the findings suggest that immunoproteasome inhibition may modulate learning and memory, implications for therapeutic strategies in neurodegenerative or neuroinflammatory disorders remain speculative absent further in vivo behavioral data.

Research Support Resources

For researchers aiming to replicate or extend these findings, ONX-0914 (PR-957) (SKU A4011) is commercially available from APExBIO. This compound is validated for selective LMP7 inhibition and can be formulated in DMSO or ethanol for in vivo or in vitro studies (source: product_spec). It is advisable to consult recent workflow recommendations and internal guides (see internal protocols) for assay optimization and dosing strategies. All research use should be aligned with the latest literature and safety guidance.