Biology subjects

Birner-Gruenberger, R.

Publications and source records attributed to Birner-Gruenberger, R..

6 recordsLinked to original sources

bioRxiv2025

Presenilin-1 controls glucose metabolism and identity of pancreatic beta cells

AbstractPresenilin 1 is an endoplasmic reticulum protein, most known for its role in pathogenesis of familial Alzheimers Disease (AD). Presenilin 1 has been attributed roles in intracellular calcium homeostasis in the brain, as well as in the pancreatic beta cells, where it has been shown to be fundamental for glucose-induced insulin secretion. Functional similarity of presenilin 1 in regulation of intracellular calcium homeostasis in the brain and pancreas prompted us to investigate a prevalent assumption that associates AD and diabetes mellitus. By examining pancreatic islets from AD model mice, we have found deficits in initial phase of glucose-induced calcium signaling and insulin secretion. Furthermore, these transgenic mice showed a tendency towards reduced expression of mature beta cell markers, which was even more pronounced in islets and beta cell lines with a transient knock down of presenilin 1. We demonstrate here that presenilin 1 controls beta cell glycolysis by regulating sub-cellular calcium homeostasis and, in doing so, contributes to preservation of beta cell identity.

cell biology↗

bioRxiv2025

In vivo activation of the dia BGC allows consolidation of the biosynthetic pathways of diaporthin, dichlorodiaporthin, diaporthinic acid, and diaporthinol

Fungal secondary metabolites exhibit remarkable chemical diversity and biological activity, making them valuable sources of bioactive compounds. A group of polyketides, with a similar core structure, have been isolated previously from different fungi - the phytotoxins diaporthin and orthosporin, the mediocre antimicrobial dichlorodiaporthin, as well as diaporthinol and diaporthinic acid. Previous studies in Aspergillus oryzae suggest that diaporthin and orthosporin originate from a different biosynthetic gene cluster than dichlorodiaporthin, while the biosynthetic routes for diaporthinic acid and diaporthinol have not yet been identified. In this study, we successfully activated the dia biosynthetic gene cluster in Trichoderma reesei via transcription factor overexpression, leading to the identification of diaporthinic acid as the primary metabolite. Structural elucidation using NMR confirmed its identity, while bioactivity assays revealed no significant antimicrobial effects. Further, diaporthin, orthosporin, dichlorodiaporthin, and diaporthinol, as well as an isomer of alternariol were attributed to the same cluster. Gene deletion experiments demonstrated that Dia1, Dia4, and Dia5 are essential for diaporthinic acid biosynthesis, with Dia4 likely catalyzing the oxidation of dichlorodiaporthin yielding diaporthinic acid. Dia2 and Dia3 were found to be dispensable, challenging previous in vitro findings for the biosynthesis of dichlorodiaporthin. These findings provide new insights into the biosynthetic network of the dia BGC, expanding our understanding of natural product biosynthesis in filamentous fungi.

biochemistry↗

bioRxiv2024

Discovery of a novel antifungal compound, ilicicolin K, through genetic activation of the ilicicolin biosynthetic pathway in Trichoderma reesei

In the quest to discover novel antifungal agents and new antifungal production processes, we investigated the biosynthetic gene cluster (BGC) for ilicicolin H in the fungus Trichoderma reesei. While the BGC is silent under standard cultivation conditions, we achieved to activate it by over-expressing its transcription factor TriliR. Successful BGC activation was confirmed by RT-qPCR, proteomic and metabolomic analyses. Metabolomic profiling upon BGC expression revealed high-yield production of the supposed main product ilicicolin H. To elucidate the functionality of this BGC, we employed a combination of overexpression and deletions of individual biosynthetic gene cluster constituents. Deletion of triliA, encoding for the core polyketide synthase TriliA, completely ceased product formation, as expected. In contrast to previous heterologous expression experiments, we could demonstrate that the epimerase TriliE is necessary for the formation of ilicicolin H in the native host. While we hardly observed any of the previously reported side- or shunt products associated with heterologous ilicicolin H expression, we discovered a novel member of the ilicicolin family using a metabolomic molecular networking approach. This new compound, which we termed ilicicolin K, is expressed in substantial amounts in the genetically engineered Trichoderma reesei, enabling us to elucidate its structure by NMR. The structure of ilicicolin K is similar to that of ilicicolin H but differs by an additional hydroxylation and an intramolecular etherification of the hydroxyl group at the pyridone towards the tyrosine moiety of the molecule. Initial tests of ilicicolin K showed antifungal activity against Saccharomyces cerevisiae and Aspergillus nidulans with a similar minimum inhibitory concentration as ilicicolin H.

biochemistry↗

bioRxiv2021

Transcriptomic profiling of atrial fibrillation canine models at disease onset

BackgroundAtrial fibrillation (AF), the most common sustained arrhythmia, is associated with increased morbidity, mortality, and health-care costs. AF develops over many years and is often related to substantial atrial structural and electrophysiological remodeling. AF may lack symptoms at onset and atrial biopsy samples are generally obtained in subjects with advanced disease, so it is difficult to study earlier-stage pathophysiology in humans. MethodsHere, we characterized comprehensively the transcriptomic (miRNAseq and mRNAseq) changes in the left atria of two robust canine AF-models after one week of electrically-maintained AF, without or with ventricular rate-control via atrioventricular node-ablation/ventricular pacing. ResultsOur RNA-sequencing experiments identified thousands of genes that are differentially expressed, including a majority that have never before been implicated in AF. Gene-set enrichment analyses highlighted known (e.g. extracellular matrix structure organization) but also many novel pathways (e.g. muscle structure development, striated muscle cell differentiation) that may play a role in tissue remodeling and/or cellular transdifferentiation. Of interest, we found dysregulation of a cluster of non-coding RNAs, including many microRNAs but also the MEG3 long non-coding RNA orthologue, located in the syntenic region of the imprinted human DLK1-DIO3 locus. Interestingly (in the light of other recent observations), our analysis identified gene-targets of differentially expressed microRNAs at the DLK1-DIO3 locus implicating glutamate signaling in AF pathophysiology. ConclusionsOur results capture molecular events that occur at an early stage of disease development using well-characterized animal models, and may therefore inform future studies that aim to further dissect the causes of AF in humans.

genomics↗

bioRxiv2020

Plasma glutathione status as indicator of pre-analytical centrifugation delay

Prolonged incubation of blood prior to plasma preparation can significantly influence the quality of the resulting data. Different markers for this pre-clinical variability have been proposed over the years but with limited success. In this study we explored the usefulness of glutathione (GSH) status, namely ratio of reduced to oxidized glutathione (GSH/GSSG), as potential marker of plasma preparation delay. For that purpose, blood from 20 healthy volunteers was collected into tubes with a cysteine quencher (N-ethylmaleimide; NEM) for GSH stabilization. Plasma preparation was delayed at room temperature for up to 3 hours and every hour, a plasma sample was prepared and the GSH/GSSG ratio measured. We report that over the course of the investigation, plasma concentrations of both GSH and GSSG increased linearly (R2 = 0.99 and 0.98, respectively). Since GSH increased at a much faster rate compared to GSSG, the GSH/GSSG ratio also increased linearly in a time dependent manner (R2 = 0.99). As GSH is an intracellular antioxidant, we speculated that this might stem from ongoing blood hemolysis, which was confirmed by the time dependent rise in lactate dehydrogenase (LDH) activity in the plasma samples. Moreover, we demonstrate that the addition of the thiol alkylating reagent NEM directly to the blood tubes does not seem to influence downstream analysis of clinical parameters. In conclusion we propose that the glutathione status could be used as an indicator of the centrifugation delay prior to plasma preparation.

pathology↗

bioRxiv2019

Cysteine oxidation triggers amyloid fibril formation of the tumor suppressor p16INK4A

Accumulation of the CDK4/6 inhibitor p16INK4A in response to oncogenic transformation leads to cell cycle arrest and senescence and is therefore frequently lost in cancer. p16INK4A is also known to accumulate under conditions of oxidative stress and thus could potentially be regulated by the reversible oxidation of cysteines (redox signaling). Indeed, oxidation of the single cysteine in p16INK4A in human cells occurs under relatively mild oxidizing conditions and leads to disulfide-dependent dimerization. p16INK4A is an all alpha-helical protein, but here we report that upon cysteine-dependent dimerization, p16INK4A undergoes a dramatic structural rearrangement and forms aggregates that have the typical features of amyloid fibrils, including binding of diagnostic dyes, presence of cross-{beta} sheet structure, and typical dimensions found in electron microscopy. p16INK4A amyloid formation abolishes its function as a CDK4/6 inhibitor. Collectively, these observations mechanistically link the cellular redox state to the inactivation of p16INK4A through the formation of amyloid fibrils.

biochemistry↗