Biology subjects

Gottschalk, B.

Publications and source records attributed to Gottschalk, B..

5 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

Interaction of the mitochondrial calcium/proton exchanger TMBIM5 with MICU1

Ion transport within mitochondria influences their structure, energy production, and cell death regulation. TMBIM5, a conserved calcium/proton exchanger in the inner mitochondrial membrane, contributes to mitochondrial structure, ATP synthesis, and apoptosis regulation. The relationship of TMBIM5 with the mitochondrial calcium uniporter complex formed by MCU, MICU1-3, and EMRE remains undefined. We generated Tmbim5-deficient Drosophila that exhibit disrupted cristae architecture, premature mitochondrial permeability transition pore opening, reduced calcium uptake, and mitochondrial swelling - resulting in impaired mobility and shortened lifespan. Crossing these with flies lacking mitochondrial calcium uniporter complex proteins was generally detrimental, but partial MICU1 depletion ameliorated the Tmbim5-deficiency phenotype. In human cells, MICU1 rescues morphological defects in TMBIM5-knockout mitochondria, while TMBIM5 overexpression exacerbates size reduction in MICU1-knockout mitochondria. Both proteins demonstrated opposing effects on submitochondrial localization and coexisted in the same macromolecular complex. Our findings establish a functional interplay between TMBIM5 and MICU1 in maintaining mitochondrial integrity, with implications for understanding calcium homeostasis mechanisms.

cell biology↗

bioRxiv2025

Development of a Genetically Encoded Live-Cell Iron Mapping System

Any disturbances in cellular iron regulation can lead to dysfunctions and various diseases. However, our current understanding of iron dynamics in living cells is hampered by the lack of high-resolution iron reporter systems capable of monitoring the iron status of individual cells dynamically. To address this challenge, we have developed the Live-Cell Iron Mapping System (LIMS), which consists of two distinct genetically encoded fluorescent iron reporter systems: the rFeRepS and IronFist. The rFeRepS (ratiometric Iron Reporter Systems) code for two genetically encoded constructs that translate the iron status of individual cells into a ratiometric fluorescent signal. The ratio signal reflects the cellular iron status, based on endogenous iron-responsive proteins. A high rFeRepS ratio indicates ferritin-based cellular iron storage, while a low ratio implies transferrin receptor (TfR)-based active cellular iron uptake. The IronFist (Iron Fluorescent Indicators based on Stability and Translation) is derived from the hemerythrin-like domain (Hr) of the F-box and leucine-rich protein 5 (FXBL5), which undergoes a structural rearrangement upon binding to ferrous iron, preventing its ubiquitination and subsequent degradation. In the IronFist design, we fused either the blue or green fluorescent protein (FP) variant, mTagBFP2 or mNeonGreen, to the C-terminus of Hr and co-expressed mCherry via a ribosomal skipping sequence as a reference protein for normalization. Thus, IronFist dynamically translates fluctuations of the labile iron pool into a ratiometric fluorescent signal. We demonstrated the functionality of both iron reporter systems by treating cells with different iron formulations including iron carbohydrate nanoparticles. Our results show clear cell-to-cell variations in the response to high iron treatments.

biochemistry↗

bioRxiv2023

Visualizing interactions of VDAC1 in live cells using a tetracysteine tag

The voltage-dependent anion channel 1 (VDAC1) is a crucial gatekeeper in the outer mitochondrial membrane, controlling metabolic and energy homeostasis. The available methodological approaches fell short of accurate visualization of VDAC1 in living cells. To permit precise VDAC1 imaging, we used the tetracysteine (TC)-tag approach and visualized VDAC1 dynamics in living cells. TC-tagged VDAC1 had a cluster-like distribution on mitochondria. The majority of VDAC1-clusters were localized at endoplasmic reticulum (ER)-mitochondria contact sites. Notably, VDAC1 colocalized with BCL-2 Antagonist/Killer (BAK)-clusters upon apoptotic stimulation. Additionally, VDAC1 was found at mitochondrial fission sites, likely promoting mitochondrial fragmentation. These findings highlight the suitability of the TC-tag for live-cell imaging of VDAC1, shedding light on the roles of VDAC1 in multiple cellular processes.

cell biology↗

bioRxiv2023

Hexokinase 1 forms rings that constrict mitochondria during energy stress

Metabolic enzymes can adapt during energy stress, but the precise mechanisms and consequences of these adaptations remain understudied. Here, we discovered that hexokinase 1 (HK1), a key glycolytic enzyme, clusters into ring-like structures around mitochondria during energy stress. These HK1-rings constrict mitochondria at contact sites with the endoplasmic reticulum (ER) and prevent mitochondrial fission by displacing the dynamin-related protein 1 (Drp1) from mitochondrial constriction sites. Mechanistically, we identified that the lack of ATP and glucose-6-phosphate (G6P) promotes the clustering of HK1. Moreover, we found several mutations that are critical for the formation of HK1-rings. Utilizing these mutations, we could show that HK1-rings keep mitochondria connected and rewire cellular metabolism during energy stress. Our findings highlight that HK1 is a robust energy stress sensor that regulates the shape, connectivity and metabolic activity of mitochondria. Thus, the formation of HK1-rings may affect mitochondrial function in energy stress-related pathologies.

cell biology↗