Biology subjects

Myeku, N.

Publications and source records attributed to Myeku, N..

4 recordsLinked to original sources

bioRxiv2026

Immunoproteasome Deficiency Impairs Microglial Clearance and Worsens Tau and Amyloid Pathology

Immunoproteasome induction is prominent in Alzheimers disease (AD), but whether it protects proteostasis or amplifies neuroinflammation remains unresolved. Here, we generated immunoproteasome-deficient PS19 tauopathy and APP/human tau double-knock-in mice by crossing each disease model with L7M1 mice lacking two immunoproteasome catalytic subunits. Immunoproteasome deficiency increased phospho-tau burden, exacerbated amyloid-{beta} pathology and heightened microglial reactivity without suppressing constitutive 26S proteasome activity. In primary microglia and longitudinal two-photon imaging, immunoproteasome-deficient microglia engaged and engulfed tau aggregate-bearing material but failed to resolve internalized cargo, revealing a post-engulfment degradative checkpoint. Single-nucleus transcriptomics identified a remodeled P2ry12low/Trem2high microglial state with impaired phagolysosomal and mitochondrial programs. Reanalysis of human single-nucleus transcriptomic datasets showed that reduced microglial immunoproteasome expression was associated with cargo-processing gene-program changes similar to those observed in immunoproteasome-deficient mouse microglia. Together, these findings identify immunoproteasome biogenesis as a protective glial stress response that supports microglial aggregate clearance in AD.

neuroscience↗

bioRxiv2025

Early Proteasome Gene Downregulation And Impaired Proteasomes Function Underlie Proteostasis Failure In Alzheimer's Disease

Alzheimers disease (AD) is characterized by the accumulation of pathogenic proteins, notably amyloid-beta and hyperphosphorylated tau, which disrupt neuronal function and contribute to cognitive decline. Although proteotoxic stress is well-established in AD, the role of the ubiquitin-proteasome system (UPS) in maintaining neuronal proteostasis, and how it becomes compromised during disease progression remains incompletely understood. Here we integrated multiple approaches to characterize proteasome function, composition, and regulation in post-mortem human AD brain tissue compared to age-matched controls. These included proteasome kinetic assays, affinity purification of intact 26S proteasomes, in-gel activity assays and proteomics. According to Braak staging, we further interrogated bulk RNA-seq and single-nucleus RNA-seq (sn-RNA-seq) datasets spanning the progression of AD pathology. Finally, we examined Nrf1/NFE2L1 binding and subcellular localization to understand the transcriptional regulation of proteasome genes in AD. We found that proteasome activity is significantly impaired in AD brains, affecting both 26S and 20S complexes. This reduction in proteolytic capacity persisted after proteasome purification, implicating intrinsic defects within the proteasome complex. Proteomic profiling revealed diminished abundances of constitutive proteasome complexes and the co-purification of proteasomes with aggregation-prone substrates (e.g., tau, -synuclein), suggesting proteasome entrapment in pathological aggregates. Transcriptomic analyses showed progressive downregulation of constitutive proteasome subunit genes in individuals along the Braak stage axis, with downregulation apparent even at the earliest Braak stages, in tissue without overt tau aggregation. Neurons were disproportionately affected, whereas non-neuronal cells did not show substantial differences in proteasome-related gene expression, possibly through immunoproteasome induction. Despite elevated NFE2L1 expression, a key transcription factor normally driving proteasome gene transcription, AD brains exhibited impaired Nrf1 nuclear localization, preventing the expected compensatory upregulation of proteasome components. Collectively, our findings suggest that proteasome dysfunction in AD arises early and deepens over the disease course. Intrinsic alterations in proteasome complexes, coupled with early transcriptional downregulation of proteasome subunits and disrupted Nrf1-mediated regulatory pathways, contribute to a vicious cycle of proteotoxic stress and neuronal vulnerability. Restoring proteasome function and enhancing Nrf1-driven transcriptional responses may represent promising therapeutic strategies to preserve proteostasis and mitigate neurodegeneration in AD.

pathology↗

bioRxiv2023

5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy

Accumulation of tau in synapses in Alzheimers disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of pathology through synaptically connected neurons. Synaptic loss correlates with a decline in cognition, providing an opportunity to investigate strategies to target synaptic tau to rescue or prevent cognitive decline. One of the promising synaptic targets is the 5-HT4 receptor present post-synaptically in the brain areas involved in the memory processes. 5-HT4R activation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tauopathy. The goal of this study was to investigate the impact of stimulation of 5-HT4R in tauopathy mice. Our results show that 5-HT4R agonism led to reduced tauopathy and synaptic tau and correlated with increased proteasome activity and improved cognitive functioning in PS19 mice. Thus, stimulation of 5-HT4R offers a promising therapy to rescue synapses from toxic synaptic tau.

neuroscience↗

bioRxiv2020

GPCR-mediated clearance of tau in post-synaptic compartments attenuates tau pathology in vivo

Accumulation of pathological tau in synapses has been identified as an early pathogenic event in Alzheimers disease (AD) and correlates strongly with cognitive decline in patients with AD. Tau is a cytosolic, axonal protein. However, in the disease condition, tau accumulates in post-synaptic compartments and pre-synaptic terminals, either due to missorting within neurons, trans-synaptic transfer between neurons or due to failure of clearance systems in synapses. Using a sub-cellular fractionation assay, we show that progressive deposition of seed competent tau occurs predominantly in post-synaptic compartments in a tau transgenic mouse and in AD patient brain, making these neuronal structures particularly vulnerable to tau toxicity. Tau-mediated post-synaptic toxicity could be further exacerbated by impaired proteasome activity which we detected by measuring the levels of polyubiquitin chains that target proteins to proteasomal degradation. To combat the accumulation of tau and proteasome impairment at the subcellular level, we devised a therapeutic strategy of proteasome-mediated clearance of tau restricted to the post-synaptic compartment. Utilizing the pharmacology of GPCRs, we show that in vivo stimulation of the PAC1R receptor by its ligand can propagate intracellular PKA signaling leading to enhanced synaptic proteasome activity and reduced tau in the post-synaptic compartment. Over time, clearance of post-synaptic tau led to reduced tauopathy and cognitive decline in rTg4510 mice. Together, these results highlight a novel therapeutic strategy of targeting GPCRs that propagate cAMP/PKA signaling as a tool to activate proteolysis restricted to synapses to prevent the accumulation of tau in the early stages of AD.

neuroscience↗