Biology subjects

Panagiotou, S.

Publications and source records attributed to Panagiotou, S..

7 recordsLinked to original sources

bioRxiv2026

Mitochondria-insulin granule crosstalk controls the early stages of granule maturation

Insulin secretion from pancreatic {beta}-cells is a tightly controlled process where hormone synthesis, granule formation and release are regulated in order to maintain whole body glucose homeostasis. Failure to produce or release insulin results in hyperglycemia that may develop into diabetes. Insulin-containing granules exist in different pools that have different propensity for release, yet what determined the fate of a granule after initial formation is not clear. In this study we aimed to identify key steps in the early life of an insulin granule that directs it towards release. Using two different methods for time-dependent labeling, we found that insulin granules shortly after budding from the trans-Golgi network associate with mitochondria. This organelle interaction involves the voltage-dependent anion channel (VDAC) and the vesicular nucleotide transporter (VNUT). Reduced VNUT expression prevented the recruitment of VDAC to insulin granules and redirected granules towards autophagy-dependent lysosomal degradation, resulting in reduced insulin content and impaired insulin secretion. These results show the requirement of granule-mitochondria crosstalk for normal progression through the early stages of the secretory pathway.

cell biology↗

bioRxiv2023

The NeuroML ecosystem for standardized multi-scale modeling in neuroscience

Data-driven models of neurons and circuits are important for understanding how the properties of membrane conductances, synapses, dendrites and the anatomical connectivity between neurons generate the complex dynamical behaviors of brain circuits in health and disease. However, the inherent complexity of these biological processes make the construction and reuse of biologically detailed models challenging. A wide range of tools have been developed to aid their construction and simulation, but differences in design and internal representation act as technical barriers to those who wish to use data-driven models in their research workflows. NeuroML, a model description language for computational neuroscience, was developed to address this fragmentation in modeling tools. Since its inception, NeuroML has evolved into a mature community standard that encompasses a wide range of model types and approaches in computational neuroscience. It has enabled the development of a large ecosystem of interoperable open source software tools for the creation, visualization, validation and simulation of data-driven models. Here, we describe how the NeuroML ecosystem can be incorporated into research workflows to simplify the construction, testing and analysis of standardized models of neural systems, and supports the FAIR (Findability, Accessibility, Interoperability, and Reusability) principles, thus promoting open, transparent and reproducible science.

neuroscience↗

bioRxiv2023

OSBP-mediated PI(4)P-cholesterol exchange at endoplasmic reticulum-secretory granule contact sites controls insulin secretion

Insulin secretion is the process whereby insulin-containing granules fuse with the plasma membrane of pancreatic {beta}-cells. Exocytosis is preceded by cargo loading and granule biogenesis at the Golgi, followed by maturation and transport of the secretory granules; processes that require modification of both the protein and lipid composition of the granules. Here, we show that insulin-containing secretory granules form physical contacts with the endoplasmic reticulum. The lipid exchange protein OSBP dynamically redistributes to ER-SG contacts in a process regulated by Ca2+ and cytosolic pH, and contributes to cholesterol loading of the granules. This process depends on granular PI(4)P and ER-localized VAPs, and is positively regulated by granular PI4-kinases and negatively regulated by granule-localized Sac2. Loss of Sac2 results in excess accumulation of cholesterol on insulin granules that is normalized when OSBP expression is reduced, and both acute inhibition and siRNA-mediated knockdown of OSBP suppresses glucose-stimulated insulin secretion without affecting insulin production or intracellular Ca2+ signaling. In conclusion, we show that lipid exchange at ER-granule contact sites is involved in the exocytic process, and propose that these contacts act as reaction centers with multimodal functions during insulin granule maturation.

cell biology↗

bioRxiv2021

Streptococcus pneumoniae rapidly translocates from the nasopharynx through the cribriform plate to invade and inflame the dura

The entry routes and translocation mechanisms of bacterial pathogens into the central nervous system remain obscure. We report here that Streptococcus pneumoniae (Sp) or polystyrene microspheres, applied to the nose of a mouse, appeared in the meninges of the dorsal cortex within minutes. Recovery of viable bacteria from dissected tissue and fluorescence microscopy showed that up to at least 72h, Sp and microspheres were predominantly in the outer of the two meninges, the pachymeninx. No Sp were found in blood or cerebrospinal fluid. Evidence that this was not an artifact of the method of administration is that in mice infected by horizontal transmission, Sp were also predominantly in the meninges and absent from blood. Intravital imaging through the skull, and flow cytometry showed recruitment and activation of LysM+ cells in the dorsal pachymeninx at 5h and 10h following intranasal infection. Imaging of the cribriform plate suggested that both Sp and microspheres entered through its foramina via an inward flow of fluid connecting the nose to the pachymeninx. Our findings bring further insight into the invasion mechanisms of bacterial pathogens such as Sp into the central nervous system, but are also pertinent to the delivery of drugs to the brain, and the entry of air-borne particles into the cranium.

microbiology↗

bioRxiv2021

The endoplasmic reticulum-plasma membrane tethering protein TMEM24 is a regulator of cellular Ca2+ homeostasis

Endoplasmic reticulum (ER) - plasma membrane (PM) contacts are sites of lipid exchange and Ca2+ transport, and both lipid transport proteins and Ca2+ channels specifically accumulate at these locations. In pancreatic {beta}-cells, both lipid- and Ca2+ signaling are essential for insulin secretion. The recently characterized lipid transfer protein TMEM24 dynamically localize to ER-PM contact sites and provide phosphatidylinositol, a precursor of PI(4)P and PI(4,5)P2, to the plasma membrane. {beta}-cells lacking TMEM24 exhibit markedly suppressed glucose-induced Ca2+ oscillations and insulin secretion but the underlying mechanism is not known. We now show that TMEM24 only weakly interact with the PM, and dissociates in response to both diacylglycerol and nanomolar elevations of cytosolic Ca2+. Release of TMEM24 into the bulk ER membrane also enables direct interactions with mitochondria, and we report that loss of TMEM24 results in excessive accumulation of Ca2+ in both the ER and mitochondria and in impaired mitochondria function.

cell biology↗

bioRxiv2019

Combined mRNA and protein single cell analysis in a dynamic cellular system using SPARC

Combined measurements of mRNA and protein expression in single cells enables in-depth analysis of cellular states. We present single-cell protein and RNA co-profiling (SPARC), an approach to simultaneously measure global mRNA and large sets of intracellular protein in individual cells. Using SPARC, we show that mRNA expression fails to accurately reflect protein abundance at the time of measurement in human embryonic stem cells, although the direction of changes of mRNA and protein expression are in agreement during cellular differentiation. Moreover, protein levels of transcription factors better predict their downstream effects than do the corresponding transcripts. We further show that changes of the balance between protein and mRNA expression levels can be applied to infer expression kinetic trajectories, revealing future states of individual cells. Finally, we highlight that mRNA expression may be more varied among cells than levels of the corresponding proteins. Overall, our results demonstrate that mRNA and protein measurements in single cells provide different and complementary information regarding cell states. Accordingly, SPARC can offer valuable insights in gene expression programs of single cells.

cell biology↗

bioRxiv2019

Streptolysin production and activity is central to in vivo pathotype and disease outcome in GAS infections

Streptococcus pyogenes (GAS) is among the most diverse of all human pathogens, responsible for a range of clinical manifestations, from mild superficial infections such as pharyngitis to serious invasive infections such as necrotising fasciitis and sepsis. The drivers of these different disease phenotypes are not known. The GAS cholesterol-dependent cytolysin, streptolysin O (SLO), has well established cell and tissue destructive activity. We investigated the role of SLO in determining disease outcome in vivo, by using two different clinical lineages; the recently emerged hypervirulent outbreak emm type 32.2 strains, which result in sepsis, and the emm type 1.0 strains which cause septic arthritis. Using clinically relevant in vivo mouse models of sepsis and a novel septic arthritis model, we demonstrated that the amount and activity of SLO is vital in determining the pathotype of infection. The emm32.2 strain produced large quantities of highly haemolytic SLO that resulted in rapid development of sepsis. By contrast, the lower levels and haemolytic activity of emm1.0 SLO led to translocation of bacteria to joints. Importantly, sepsis associated strains that were attenuated by deletion or inhibition of SLO also translocated to the joint, confirming the key role of SLO in determining infection niche. Our findings demonstrate that SLO is key to in vivo pathotype and disease outcome. Careful consideration should be given to novel therapy or vaccination strategies that target SLO. Whilst neutralising SLO activity may reduce severe invasive disease, it has the potential to promote chronic inflammatory conditions such as septic arthritis.

microbiology↗