Biology subjects

Duennwald, M. L.

Publications and source records attributed to Duennwald, M. L..

6 recordsLinked to original sources

bioRxiv2026

TPR Domains Drive the Functional Phase Separation of HOP and its Regulation by Hsp90 and Hsp70

HOP is a cochaperone that facilitates client transfer between two major chaperones, Hsp90 and Hsp70. Emerging evidence, however, suggests that HOP plays additional roles in coordinating complex proteostasis networks. Upon exposure to proteostatic stress, HOP rapidly sequesters soluble misfolded proteins into cytoplasmic foci in a Hsp90 independent manner, thereby facilitating their clearance through the ubiquitin proteasome system. We demonstrate here that stress-dependent HOP foci are biomolecular condensates formed by liquid-liquid phase separation. Purified HOP forms protein droplets that closely resemble the foci observed in cells. Our biophysical analyses show that the phase separation of HOP is driven by electrostatic interactions between its tandem TPR domains, with a critical role of its TPR2A domain. Of note, Hsp90 and Hsp70 regulate the extent of HOP phase separation, with Hsp70 driving HOP droplet formation and Hsp90 reversing it. Finally, we find that the Y354E phosphomimetic variant of HOP impairs phase separation and sensitizes cells to acute misfolding stress, suggesting a key role of HOP condensation in mitigating protein misfolding stress. Our work thus identifies a new mechanism by which HOP phase separation mitigates protein misfolding stress in eukaryotic cells and is regulated by Hsp70 and Hsp90.

biochemistry↗

bioRxiv2026

Cannabidiol confers neuroprotection against 6-OHDA toxicity by rescuing Nrf2 proteostasis and preserving mitochondrial integrity

Oxidative stress and the progressive degeneration of dopaminergic neurons are key features of Parkinsons disease (PD). The intrinsically disordered structure of the transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2), which coordinates the main cellular antioxidant response of the body, makes it highly susceptible to misfolding and aggregation under severe oxidative stress, compromising cellular survival. Cannabidiol (CBD) has potent neuroprotective properties, but its exact molecular mechanism within the dopaminergic redox environment remains unclear. In this study, we investigated the protective effects of CBD against 6-hydroxydopamine (6-OHDA)-induced toxicity in both undifferentiated and mature, post-mitotic differentiated SH-SY5Y cells. We found that CBD confers robust Nrf2-dependent neuroprotection against 6-OHDA. Importantly, we uncover a previously unexplored mechanism of neuroprotection by which CBD actively prevents the stress-induced sequestration of Nrf2 into insoluble cytoplasmic inclusions under oxidative stress. We find that CBD keeps Nrf2 in a soluble, functional state, increases Ser40 phosphorylation, restores nuclear localization, and drives the robust transcriptional upregulation of antioxidant enzymes. This targeted activation of Nrf2 effectively reduces intracellular ROS, significantly attenuates mitochondrial fragmentation, and decreases aberrant mitophagic activity. Overall, our results show that rather than merely scavenging reactive oxygen species, CBD directly increases Nrf2 activity during oxidative stress, enabling a sustained cytoprotective response. We thus identify CBD as a highly specific, targeted molecule with a high potential for neuroprotective therapy in PD.

cell biology↗

bioRxiv2026

Mitochondrial respiration modulates Hsf1 activation and the heat shock response.

Cells employ a bevy of transcriptional and post-translational stress responses to tolerate the burden of misfolded proteins induced by stress. In particular, the heat shock response facilitates the upregulation of molecular chaperones and protein remodeling factors that mediate proteostasis in response to accumulated misfolded proteins in the nucleus and cytosol. However, in response to stress neurons struggle to induce a canonical heat shock response, highlighting our poor understanding of how neurons maintain proteostasis. Specifically, the ability of post-mitotic respiring cells to regulate the heat shock response in comparison to their rapidly dividing, predominantly glycolytic counterparts has been under-studied. In this study, we employ yeast models that are easily manipulated to generate energy via glycolysis or mitochondrial respiration by changing the carbon source in the media. Using this model, we demonstrate that Hsf1 activity, the heat shock response and proteostasis are impaired in respiring cells. Interestingly, our data show that reduced Hsf1 activity regulates viability of respiring cells, with respiring cells poorly tolerating constitutively activated Hsf1. Finally, we describe alternative post-translational programming of the molecular chaperones Hsp70 and Hsp104 that plausibly enables respiring cells to mediate proteostasis despite a dampened heat shock response. Our findings offer new insights into possible proteostatic strategies employed by cells in different metabolic conditions.

molecular biology↗

bioRxiv2025

Deciphering the circular RNAs landscape in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the progressive loss of motor neurons, with most cases lacking a clear genetic basis. Emerging evidence highlights the involvement of non-coding RNAs, particularly circular RNAs (circRNAs), in disease onset and progression. In this study, we investigated circRNAs implicated in ALS and related motor neuron diseases (MNDs). First, we conducted a systematic review to identify ALS-associated circRNAs, followed by in silico analyses of 15 selected candidates. Our results revealed that hsa_circ_0000099, hsa_circ_0001017, hsa_circ_004846, and hsa_circ_0034880 regulate a high number of ALS-related genes through miRNA sponging. Pathway enrichment analysis indicated that hsa_circ_0000099 is particularly involved in unfolded protein response, oxidative stress, cell cycle regulation, and apoptosis. Protein-RNA interaction analysis further showed that ALS-related circRNAs can sponge 20 RNA-binding proteins, with FMR1, ELAVL1, EIF4A3, and SRSF1 exhibiting the highest number of interactions. Additionally, molecular docking analysis demonstrated that FUS mutations significantly alter its binding affinity to hsa_circ_0000567 and hsa_circ_0060762. RNA-seq data from ALS patients confirmed significant alterations in the expression of host genes of ALS-related circRNAs and hub proteins across affected tissues, including the spinal cord and multiple brain regions. Collectively, these findings support circRNAs as active contributors to ALS pathogenesis. In particular, the host gene of hsa_circ_0000099, which is expressed in the spinal cord and hippocampus, emerges as a potential biomarker for tissue-specific impairment in ALS. Moreover, its regulatory role in key ALS-related cellular pathways underscores its promise as a candidate for biomarker development and therapeutic targeting. Further experimental validation is warranted to confirm its role in ALS pathology. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/677871v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@15d0389org.highwire.dtl.DTLVardef@1934327org.highwire.dtl.DTLVardef@11ddd3aorg.highwire.dtl.DTLVardef@1a74c09_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Adjusting extracellular pH restores proteostasis and extends lifespan in a yeast model of polyglutamine toxicity

Impaired proteostasis is a hallmark of aging and is associated with several neurodegenerative diseases, including Huntingtons Disease (HD) where the polyglutamine (polyQ) expanded Huntingtin aggregates to form insoluble inclusions bodies (IBs) associated with neurotoxicity. Chronological lifespan (CLS) in yeast resembles many aspects of aging of non-dividing cells such as neurons. During chronological aging, acidification of the culture media due accumulation of acetic acid is one of the major cell-extrinsic factors contributing to age-related cell death. Thus, buffering media pH to prevent acidification significantly extends longevity. Here, we found that cells expressing pathogenic polyQ expansion proteins display increased sensitivity to acetic acid and shortened CLS. Buffering media pH promotes both polyQ aggregation into IBs and promotes longevity. We also found that growth at alkaline pH induces the activation of heat shock response (HSR) in young cells. Such hormetic HSR activation subsequently allowed aged cells to mount a proper HSR in response to stresses such as heat shock or polyQ misfolding, leading to lifespan extension. Our study thus provides new insight into how pH can promote proteotoxic stress resistance and longevity by modulating the HSR.

cell biology↗

bioRxiv2025

STIP1/HOP Promotes the Formation of Cytotoxic α-Synuclein Oligomers

The accumulation of alpha-synuclein (a-Syn) as toxic oligomers, and subsequently in Lewy bodies, is a pathological hallmark of Parkinsons disease (PD) and other synucleinopathies. Molecular chaperones and co-chaperones are expected to act in concert to maintain physiological activities of proteins, including a-Syn, but in neurodegeneration this process can become mal-adaptive. Transcript levels of Stress inducible phosphoprotein 1 (STIP1), a co-chaperone of Hsp90/Hsp70, are elevated in brain samples from PD patients. In synucleinopathy mouse models, STIP1 has unexpected bidirectional effects on a-Syn, with overexpression of STIP1 aggravating a-Syn toxicity, whereas knockdown of STIP1 improves toxicity and behavioural phenotypes. However, it is unclear how STIP1 enhances the toxicity of a-Syn. Here we unravel the mechanisms by which the direct interaction between STIP1/HOP and a-Syn regulates the neurotoxicity of a-Syn. Specifically, two binding motifs in the C-terminus of a-Syn directly interact with the TPR2A domain of STIP1/HOP in a dynamic manner, competing for a shared interface on TPR2A. Binding of STIP1/HOP to a-Syn attenuates the formation of a-Syn fibrils while promoting the accumulation of high molecular weight amorphous a-Syn species. Samples of a-Syn aggregated in the presence of STIP1/HOP contain significantly more A11-positive oligomeric species and cause a greater reduction in cell viability than a-Syn aggregated in the absence of STIP1/HOP in neuronal cells. Our results provide a mechanism by which the direct interaction between STIP1/HOP and the C-terminus of a-Syn promotes the formation of cytotoxic, non-amyloidogenic, high molecular weight a-Syn species. Our model offers an explanation for the unexpected pathological link between STIP1 and a-Syn toxicity, thus opening new therapeutic avenues for the treatment of synucleinopathies.

biochemistry↗