Biology subjects

Koyuncu, S.

Publications and source records attributed to Koyuncu, S..

4 recordsLinked to original sources

bioRxiv2025

Anle138b ameliorates pathological phenotypes in mouse and cellular models of Huntington's disease

Huntingtons disease (HD) is a debilitating hereditary movement disorder caused by a CAG repeat expansion in the huntingtin gene. HD is characterized by deposition of mutant huntingtin (mHTT) aggregates, and by severe neurodegeneration of the basal ganglia and neocortex. No cure is currently available, and new treatment options are urgently needed. Here, we show that the oligomer modifying molecule anle138b (INN: emrusolmin) improves multiple disease phenotypes in cell culture and in two mouse models of HD. Application of anle138b reduced mHTT aggregate formation and ameliorated neurotoxicity in primary neurons. Oral administration of anle138b delayed deposition of mHTT inclusions, reduced brain atrophy, mitigated neuroinflammation, improved motor function and extended life span in HD mice. Downregulation of striatal markers and synapse loss in striatal spiny projection neurons were also partially rescued. No adverse effects of anle138b were observed in wildtype animals. Moreover, anle138b markedly decreased mHTT aggregation in human neural precursor cells differentiated from HD patient-derived induced pluripotent stem cells (iPSCs). Altogether these results illustrate the potential of anle138b as a disease-modifying treatment for HD.

neuroscience↗

bioRxiv2023

Extensive remodeling of the ubiquitination landscape during aging in C. elegans

In previous work, we investigated ubiquitination changes during aging in C. elegans. We identified 2,163 peptides undergoing age-related ubiquitination changes in wild-type animals, corresponding to 1,050 proteins. While many lysine sites had increased ubiquitination with age, a larger number exhibited decreased ubiquitination. Longevity pathways, such as reduced insulin signaling and dietary restriction, prevented ubiquitination changes. Treatment with a broad-spectrum inhibitor of deubiquitinating enzymes (DUBs) or knockdown of specific DUBs ameliorated ubiquitination loss in old worms. Moreover, we identified proteins that accumulate with aging due to reduced ubiquitination and subsequent proteasomal degradation. Our conclusions were supported by multiple approaches, including ubiquitin and total proteomics, western blot, and ubiquitin-less mutations. Concerns were raised by a laboratory regarding the possibility of our protocol omitting insoluble proteins due to a centrifugation step after protein extraction and solubilization. To address these concerns, we have focused on proteins previously reported to become insoluble with aging in C. elegans. Our proteomics experiments successfully detected and quantified all these proteins in old worms. In many cases, the proteins that become insoluble with aging did not change or even increased at the total levels. However, they often exhibited ubiquitination changes, primarily a loss of ubiquitination. Independent work combining analysis of conformational changes with our datasets demonstrated that 92% of the age-dependent metastable proteins exhibit differential ubiquitination during aging. In addition, we performed experiments to confirm that the buffers used for proteomics and western blot efficiently solubilize most of the proteome. Importantly, the analysis of total homogenates combining clear lysates and the remaining debris after protein extraction also revealed decreased ubiquitination during aging, whereas DUB inhibitor treatment (4 h) in old worms restored ubiquitination levels. These data further support our previous conclusions regarding extensive ubiquitination changes during aging in C. elegans.

cell biology↗

bioRxiv2023

Neuroprotective effects of hepatoma-derived growth factor in models of Huntington's disease

Huntingtons disease (HD) is a movement disorder caused by a mutation in the Huntingtin gene, that leads to severe neurodegeneration and inevitable death of the patients. Molecular mechanisms of HD are still not sufficiently understood, and no cure is currently available. Here, we demonstrate neuroprotective effects of hepatoma-derived growth factor (HDGF) in cellular and mouse models of HD. We show that HDGF expression levels in neuronal cell types inversely correlate with cellular vulnerability to HD. Moreover, lack of endogenous HDGF shortened lifespan and worsened rotarod performance of R6/2 HD model mice. AAV-mediated delivery of HDGF into the brain reduced mutant Huntingtin inclusion body load, but had no significant effect on motor behavior or lifespan. Interestingly, both nuclear and cytoplasmic versions of HDGF were equally efficient in rescuing mutant Huntingtin toxicity in cell culture models of HD. Moreover, extracellular application of a recombinant HDGF protein improved viability of mutant Huntingtin-expressing primary neurons and reduced mutant Huntingtin aggregation in neural progenitor cells differentiated from human patient-derived induced pluripotent stem cells (iPSCs). Our findings provide new insights into the pathomechanisms of HD and suggest neuroprotective potential of HDGF in neurodegeneration.

neuroscience↗

bioRxiv2022

Chloroplast protein import determines plant proteostasis and retrograde signaling

Proteins containing polyglutamine (polyQ) repeats are prone to aggregation and can lead to distinct human pathologies. For instance, Huntingtons disease is caused by an abnormal expansion of the polyQ stretch (> Q35) of Huntingtin (HTT) protein. However, plants express hundreds of proteins containing polyQ regions, but no pathologies arising from these factors have been reported to date. Here, we ask how plants maintain the proteostasis of polyQ-containing proteins, which are intrinsically enriched in the plant proteomes. To this end, we overexpressed an aggregation-prone fragment of human HTT (Q69) in plant cells. In contrast to invertebrate and mammalian transgenic models, we find that Arabidopsis thaliana plants suppress Q69 aggregation. This elevated proteostasis ability is mediated through the import and degradation of Q69 in chloroplasts. Conversely, inhibition of chloroplast protein import either genetically or pharmacologically reduces the capacity of plant cells to prevent Q69 aggregation. We find that Q69 interacts with the chloroplast stromal processing peptidase (SPP). Notably, expression of synthetic Arabidopsis SPP is sufficient to suppress aggregation of polyQ-expanded HTT in human cells. Beyond ectopically expressed Q69-HTT, endogenous polyQ-containing proteins also aggregate in Arabidopsis upon inhibition of chloroplast import. Among them, the plastid casein kinase 2 (pCK2), which contains a polyQ region next to the chloroplast targeting sequence motif, can also be localized into the nucleus. Upon inhibition of chloroplast import, pCK2 accumulates at higher levels in the nucleus and forms diamond-shaped amyloid-like fibrils surrounding the chloroplasts. These results indicate that the differential conformation and redistribution of pCK2 to the nucleus depends on chloroplast import efficiency, providing a role of polyQ repeats in chloroplast to nucleus communication (i.e. retrograde signaling). Together, our findings establish chloroplast protein import and proteases as determinants of polyQ proteostasis, with important implications for plant biology that can also lead to therapeutic approaches for human diseases that involve protein aggregation.

plant biology↗