Biology subjects

Gruber, C. W.

Publications and source records attributed to Gruber, C. W..

3 recordsLinked to original sources

bioRxiv2025

Effects of Arginine Vasopressin on Islet Cells in Pancreatic Tissue Slices: Glucose-Dependent Modulation of IP3 Receptor-Specific Responses

Arginine vasopressin (AVP) is well known for regulating fluid volume, osmotic balance, and vascular tone. Its role in the regulation of pancreatic and {beta} cell function has been reported, yet its effects are not fully understood, particularly regarding its interaction with plasma glucose levels. The osmotic and volume challenges posed by hyper- and hypoglycaemia in diabetes can be a significant complication of effective hormonal regulation of metabolism. In this study, we primarily investigated the effects of AVP and synthetic peptide receptor agonists and antagonists on and {beta} cells in pancreatic tissue slices using live confocal Ca2+ imaging. Our findings demonstrate that AVP exerts glucose-dependent effects on both cell types. At low glucose concentrations, AVP, in combination with physiologically or pharmacologically increased cAMP levels, selectively activated cells without significantly affecting {beta} cells. In contrast, at higher glucose concentrations and pharmacologically elevated cAMP levels, physiological levels of AVP enhanced {beta} cell activity, leading to increased Ca2+ oscillations and insulin release. In both cell types, AVP displayed a bell-shaped concentration dependence, with lower AVP concentrations stimulating hormone release and higher concentrations leading to diminished responses, consistent with inositol trisphosphate receptor (IP3R) activation and inactivation properties. Furthermore, our results indicate that AVP acts primarily through V1b receptors in {beta} cells, with no involvement of V1a, V2 or oxytocin receptors. These findings provide new insights into the modulation of glucose-dependent release of pancreatic hormones by AVP in the context of changed blood osmolality due to hyper- or hypoglycemia in diabetes. Importantly, our results emphasize the potential of targeting AVP signaling pathways as a therapeutic approach in diabetes research, aiming to improve hormone regulation and nutrient homeostasis. HighlightsO_LIHighly spatio-temporally resolved imaging of islet Ca2+ oscillations on pancreatic tissue slices provides an in situ-like model for physiological and pharmacological approaches. C_LIO_LIPhysiological glucose stimulation triggers non-linear {beta} cell collective responses that must be taken into account when interpreting single concentration pharmacological experiments. C_LIO_LIIn a high cAMP context, AVP acts through V1b receptors on islet and {beta} cells, exhibiting a bell-shaped dependence driven by the activation-inactivation properties of IP receptors. C_LIO_LIAVP modulates glucose-dependent effects on and {beta} cells in a physiological concentration range, in the presence of altered blood osmolality or volume due to hyperglycemia, or to the direct effects of hypoglycemia in diabetes. C_LI

physiology↗

bioRxiv2022

Multiplexed neuropeptide mapping in ant brains integrating microtomography and 3D mass spectrometry imaging

Neuropeptides are important regulators of animal physiology and behavior. Hitherto large-scale localization of neuropeptides mainly relied on immunohistochemical methods requiring the availability of antibody panels, while another limiting factor has been the brains opacity for subsequent light or fluorescence microscopy. To address these limitations, we integrated high-resolution mass spectrometry imaging (MSI) with microtomography for a multiplexed mapping of neuropeptides in two evolutionary distant ant species, Atta sexdens and Lasius niger. For analyzing the spatial distribution of chemically diverse peptide molecules across the brain in each species, the acquisition of serial mass spectrometry images was essential. As a result, we have comparatively mapped the 3D distributions of eight conserved neuropeptides throughout the brain micro-anatomy. We demonstrate that integrating the 3D MSI data into high-resolution anatomy models can be critical for studying organs with high plasticity such as brains of social insects. Several peptides, like the tachykinin-related peptides TK1 and TK4, were widely distributed in many brain areas of both ant species, whereas others, for instance myosuppressin was restricted to specific regions only. Also, we detected differences at the species level; many peptides were identified in the optic lobe of L. niger, but only one peptide (ITG-like) was found in this region in A. sexdens. Our approach provides the basis for investigating fundamental neurobiological processes by visualizing the unbiased 3D neurochemistry in its complex anatomic environment. Significance statementUntil recently, the inability to detect entire molecules such as neuropeptides within their spatial biological context and simultaneously link their occurrence to anatomically and physiologically relevant areas has limited our understanding of complex neurochemical processes. This situation has now changed dramatically with the optimization of a new multiplexed imaging method based on mass spectrometry, which enables us to study previously invisible processes at the microscopic scale. With the marriage of mass spectrometry imaging and microtomography, we show that it has become possible to build high-resolution maps of neuropeptides in complex anatomical structures as small as ant brains. These maps, embedded in the 3D neuroanatomy, expand the understanding of the spatial organization of brain chemistry and provide a baseline for neurobiological and neurochemical studies.

biophysics↗

bioRxiv2020

Microtiter plate-based antibody-competition assay to determine binding affinities and plasma/blood stability of CXCR4 ligands

C-X-C chemokine receptor type 4 (CXCR4) is involved in several intractable disease processes, including HIV infection, cancer cell metastasis, leukemia cell progression, rheumatoid arthritis, asthma and pulmonary fibrosis. Thus, CXCR4 represents a promising drug target and several CXCR4 antagonizing agents are in preclinical or clinical development. Important parameters in drug lead evaluation are determination of binding affinities to the receptor and assessment of their stability and activity in plasma or blood of animals and humans. Here, we designed a microtiter plate-based CXCR4 antibody competition assay that enables to measure inhibitory concentrations (IC50 values) and affinity constants (Ki values) of CXCR4 targeting drugs. The assay is based on the observation that most if not all CXCR4 antagonists compete with binding of the fluorescence-tagged CXCR4 antibody 12G5 to the receptor. We demonstrate that this antibody-competition assay allows a convenient and cheap determination of binding affinities of various CXCR4 antagonists in living cells within just 3 hours. Moreover, the assay can be performed in the presence of high concentrations of physiologically relevant body fluids, and thus is a useful readout to evaluate stability (i.e. half-life) of CXCR4 ligands in serum/plasma, and even whole human and mouse blood ex vivo. Thus, this optimized 12G5 antibody competition assay allows a robust and convenient determination and calculation of various important pharmacological parameters of CXCR4 receptor-drug interaction and may not only foster future drug development but also animal welfare by reducing the number of experimental animals.

immunology↗