Biology subjects

Ahn, M.

Publications and source records attributed to Ahn, M..

5 recordsLinked to original sources

bioRxiv2024

DOC2b enrichment mitigates proinflammatory cytokine-induced CXCL10 expression by attenuating IKKβ and STAT-1 signaling in human islets

IntroductionType 1 diabetic human islet {beta}-cells are deficient in double C 2 like domain beta (DOC2b) protein. Further, DOC2b protects against cytokine-induced pancreatic islet {beta}-cell stress and apoptosis. However, the mechanisms underpinning the protective effects of DOC2b remain unknown. MethodsBiochemical studies, qPCR, proteomics, and immuno-confocal microscopy were conducted to determine the underlying protective mechanisms of DOC2b in {beta}-cells. DOC2b- enriched or-depleted primary islets (human and mouse) and {beta}-cell lines challenged with or without proinflammatory cytokines, global DOC2b heterozygous knockout mice subjected to multiple-low-dose-streptozotocin (MLD-STZ), were used for these studies. ResultsA significant elevation of stress-induced CXCL10 mRNA was observed in DOC2b- depleted {beta}-cells and primary mouse islets. Further, DOC2b enrichment markedly attenuated cytokine-induced CXCL10 levels in primary non-diabetic human islets and {beta}-cells. DOC2b enrichment also reduced total-NF-{kappa}B p65 protein levels in human islets challenged with T1D mimicking proinflammatory cytokines. IKK{beta}, NF-{kappa}B p65, and STAT-1 are capable of associating with DOC2b in cytokine-challenged {beta}-cells. DOC2b enrichment in cytokine-stressed human islets and {beta}-cells corresponded with a significant reduction in activated and total IKK{beta} protein levels. Total I{kappa}B{beta} protein was increased in DOC2b-enriched human islets subjected to acute cytokine challenge. Cytokine-induced activated and total STAT-1 protein and mRNA levels were markedly reduced in DOC2b-enriched human islets. Intriguingly, DOC2b also prevents ER-stress-IKK{beta} and STAT-1 crosstalk in the rat INS1-832/13 {beta}-cell line. ConclusionThe mechanisms underpinning the protective effects of DOC2b involve attenuation of IKK{beta}-NF-{kappa}B p65 and STAT-1 signaling, and reduced CXCL10 expression. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=179 HEIGHT=200 SRC="FIGDIR/small/629540v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1b9d0acorg.highwire.dtl.DTLVardef@32db73org.highwire.dtl.DTLVardef@e5645aorg.highwire.dtl.DTLVardef@1f7619_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2024

Amyloid forming human lysozyme intermediates are stabilised by non-native amide-π interactions

Mutational variants of human lysozyme cause a rare but fatal hereditary form of systemic amyloidosis by populating an intermediate state that self-assembles into amyloid fibrils. Despite its significance in lysozyme amyloidosis, the intermediate state has been recalcitrant to detailed structural investigation as it is only transiently and sparsely populated. Here, we investigated the intermediate state of a mutational variant of human lysozyme (I59T) using CEST and CPMG RD NMR at low pH. 15N CEST profiles probed the thermal unfolding of the native state into the denatured ensemble and revealed an additional state distinct from the two major states. Global fitting of 15N CEST and CPMG data provided kinetic and thermodynamic parameters for the exchange between all three states, characterising the intermediate state populated at 0.6%. 1H CEST data also confirmed the presence of the intermediate state displaying unusually high or low 1HN chemical shifts. To further investigate the structural details of the intermediate state we used molecular dynamics (MD) simulations, which recapitulated the experimentally observed folding pathway and free energy landscape. A high-energy intermediate state with a locally disordered {beta}-domain and C-helix was observed, revealing non-native hydrogen bonding and amide-{pi} interactions. These interactions account for the anomalous 1H chemical shifts and likely stabilise the transient intermediate state structure. Together, our NMR and MD data provide the first direct structural information on the intermediate state, offering insights into targeting lysozyme amyloidosis.

biophysics↗

bioRxiv2024

Distinct basal ganglia decision dynamics under conflict and uncertainty

The basal ganglia (BG) play a key role in decision-making, preventing impulsive actions in some contexts while facilitating fast adaptations in others. The specific contributions of different BG structures to this nuanced behavior remain unclear, particularly under varying situations of noisy and conflicting information that necessitate ongoing adjustments in the balance between speed and accuracy. Theoretical accounts suggest that dynamic regulation of the amount of evidence required to commit to a decision (a dynamic "decision boundary") may be necessary to meet these competing demands. Through the application of novel computational modeling tools in tandem with direct neural recordings from human BG areas, we find that neural dynamics in the theta band manifest as variations in a collapsing decision boundary as a function of conflict and uncertainty. We collected intracranial recordings from patients diagnosed with either Parkinsons disease (n=14) or dystonia (n=3) in the subthalamic nucleus (STN), globus pallidus internus (GPi), and externus (GPe) during their performance of a novel perceptual discrimination task in which we independently manipulated uncertainty and conflict. To formally characterize whether these task and neural components influenced decision dynamics, we leveraged modified diffusion decision models (DDMs). Behavioral choices and response time distributions were best characterized by a modified DDM in which the decision boundary collapsed over time, but where the onset and shape of this collapse varied with conflict. Moreover, theta dynamics in BG structures predicted the onset and shape of this collapse but differentially across task conditions. In STN, theta activity was related to a prolonged decision boundary (indexed by slower collapse and therefore more deliberate choices) during high-conflict situations. Conversely, rapid declines in GPe theta during low conflict conditions were related to rapidly collapsing boundaries and expedited choices, with additional complementary decision bound adjustments during high uncertainty situations. Finally, GPi theta effects were uniform across conditions, with increases in theta prolonging the collapse of decision bounds. Together, these findings provide a nuanced understanding of how our brain thwarts impulsive actions while nonetheless enabling behavioral adaptation amidst noisy and conflicting information.

neuroscience↗

bioRxiv2024

Synthesis and Biological Assessment of Chalcone and Pyrazoline Derivatives as novel inhibitor for ELF3-MED23 Interaction

HER2 overexpression significantly contributes to the aggressive nature and recurrent patterns observed in various solid tumors, notably gastric cancers. Trastuzumab, HER2-targeting monoclonal antibody drug, has shown considerable clinical success, however, readily emerging drug resistance emphasizes the pressing need for improved interventions in HER2-overexpressing cancers. To address this, we proposed targeting the protein-protein interaction (PPI) between ELF3 and MED23 as an alternative therapeutic approach to trastuzumab. In this study, we synthesized a total of 26 compounds consisting of 10 chalcones, 7 pyrazoline acetyl, and 9 pyrazoline propionyl derivatives, and evaluated their biological activity as potential ELF3-MED23 PPI inhibitors. Upon systematic analysis, candidate compound 10 was selected due to its potency in downregulating reporter gene activity of ERBB2 promoter confirmed by SEAP activity and its effect on HER2 protein and mRNA levels. Compound 10 effectively disrupted the binding interface between the ELF3 TAD domain and the 391-582 amino acid region of MED23, resulting in successful inhibition of the ELF3-MED23 PPI. This intervention led to a substantial reduction in HER2 levels and its downstream signals in the HER2-positive gastric cancer cell line. Subsequently, compound 10 induced significant apoptosis and anti-proliferative effects, demonstrating superior in vitro and in vivo anticancer activity overall. We found that the anticancer activity of compound 10 was not only restricted to trastuzumab-sensitive cases, but was also valid for trastuzumab-refractory clones. This suggests its potential as a viable therapeutic option for trastuzumab-resistant gastric cancers. In summary, compound 10 could be a novel alternative therapeutic strategy for HER2-overexpressing cancers, overcoming the limitations of trastuzumab.

pharmacology and toxicology↗

bioRxiv2023

Single-Cell RNA-Seq Analysis Reveals Four Stages of Replicative Senescence in Human Umbilical Vein Endothelial Cells

Cellular senescence is a phenomenon marked by an irreversible growth arrest with altered physiological properties. Many studies have focused on the characteristics of cells that have already entered a senescent state. However, to elucidate the mechanisms of cellular aging, it is essential to investigate the gradual transition of proliferative cells into senescent cells. We assumed that cellular senescence is a complex and multi-step process, and each stage exhibits unique traits. To test this hypothesis, we utilized publicly available single-cell RNA-Seq (scRNA-Seq) data from human umbilical vein endothelial cells (HUVECs) undergoing replicative senescence. We employed Seurat and Monocle 3 to capture the transition from proliferating to senescent states in HUVECs. Four clusters were identified, and each cluster displayed distinct expression patterns of cellular senescence markers and the senescence-associated secretory phenotypes (SASPs). We also employed SCENIC to identify the expression patterns of core transcription factors (TFs) during replicative senescence. While the majority of TFs exhibited a linear trend, HMGB1, FOSL1, SMC3, RAD21, SOX4, and XBP1 showed fluctuating expression patterns during replicative senescence. Furthermore, the expression patterns of these TFs exhibited slight differences in the ionizing radiation (IR) model of senescence. Overall, our study unveils the distinct characteristics of each phase during replicative senescence and identifies expression trends in TFs that may play pivotal roles in this process. These findings highlight the intricate nature of cellular senescence and provide new insights into the process of cellular aging.

bioinformatics↗