Biology subjects

Gresch, A.

Publications and source records attributed to Gresch, A..

4 recordsLinked to original sources

bioRxiv2024

Rapid fluctuations in histamine associated with intake of nutritive and non-nutritive solutions

The neurotransmitter histamine is involved in control of food intake, yet its dynamics during individual feeding episodes remain unexplored. Therefore, we used the novel genetically-encoded histamine sensor, HisLightG, combined with fiber photometry to measure histamine release in two hypothalamic regions critical for the food-suppressive effects of histamine, the paraventricular nucleus of the hypothalamus (PVH), and the ventromedial hypothalamus (VMH). Male mice were tested under different conditions to assess whether hunger, time of day, or the caloric content of the solution they were given affected histamine fluctuations. We found that histamine levels changed rapidly in response to eating. These histamine fluctuations were influenced by experimental conditions, with slightly smaller responses when the test solution was sucralose (both regions) or during the light cycle (PVH only). Notable regional differences were identified, such that in the PVH histamine rebounded to baseline levels, whereas in the VMH histamine remained lower than baseline for at least 10 seconds after licking ceased. In a separate cohort of male and female mice, enhancing histamine tone via administration of a histamine precursor (L-histidine) reduced the number of licks across multiple sucrose concentrations. Together, these findings indicate that histaminergic activity is modulated rapidly during ingestive episodes, and that understanding these release patterns will give insight into histamines role in appetite suppression.

neuroscience↗

bioRxiv2024

Probing PAC1 receptor activation across species with an engineered sensor

Class-B1 G protein-coupled receptors (GPCRs) are an important family of clinically relevant drug targets that remain difficult to investigate via high-throughput screening and in animal models. Here, we engineered PAClight1P78A, a novel genetically-encoded sensor based on a class-B1 GPCR (the human PAC1 receptor, hmPAC1R) endowed with high dynamic range ({Delta}F/F0 = 1100%), excellent ligand selectivity and rapid activation kinetics ({tau}ON = 1.15 sec). To showcase the utility of this tool for in vitro applications, we thoroughly characterized and compared its expression, brightness and performance between PAClight1P78A transfected and stably-expressing cells. Demonstrating its use in animal models, we show robust expression and fluorescence responses upon exogenous ligand application ex vivo and in vivo in mice, as well as in living zebrafish larvae. Thus, the new GPCR-based sensor can be used for a wide range of applications across the life sciences empowering both basic research and drug development efforts.

neuroscience↗

bioRxiv2023

Resolving spatiotemporal electrical signaling within the islet via CMOS microelectrode arrays

Glucose-stimulated beta-cells synchronize calcium waves across the islet to recruit more beta-cells for insulin secretion. Compared to calcium dynamics, the formation and cell-to-cell propagation of electrical signals within the islet are poorly characterized. To determine factors that influence the propagation of electrical activity across the islet underlying calcium oscillations and beta-cell synchronization, we used high-resolution CMOS multielectrode arrays (MEA) to measure voltage changes associated with the membrane potential of individual cells within intact mouse islets. We measured both fast (milliseconds, spikes) and slow (seconds, waves) voltage changes and analyzed the spatiotemporal voltage dynamics. Treatment of islets from C57BL6 mice with increasing glucose concentrations revealed that single spike activity and wave signal velocity were both glucose-dependent. A repeated glucose stimulus involved a highly active subset of cells in terms of spike activity. When islets were pretreated for 72 hours with glucolipotoxic medium, the wave velocity was significantly reduced. Network analysis confirmed that the synchrony of islet cells was affected due to slower propagating electrical waves and not due to altered spike activity. In summary, this approach provided novel insight regarding the propagation of electrical activity and opens a wide field for further studies on signal transduction in the islet cell network. Article HighlightsThis study presents a new method for characterizing islet spatiotemporal electrical dynamics and subpopulations of beta-cells. We asked whether a high-resolution CMOS-MEA is suited to detect electrical signals on a level close to single cells, and whether we can track the propagation of electrical activity through the islet on a cellular scale. A highly active subpopulation of islet cells was identified by action potential-like spike activity, whereas slower waves were a measure for synchronized electrical activity. Further, propagating waves were slowed by glucolipotoxicity. The technique is a useful tool for exploring the pancreatic islet network in health and disease.

physiology↗

bioRxiv2023

Optical tools for visualizing and controlling human GLP-1 receptor activation with high spatiotemporal resolution

The glucagon-like peptide-1 receptor (GLP1R) is a broadly expressed target of peptide hormones with essential roles in energy and glucose homeostasis, as well as of the blockbuster weight-loss drugs semaglutide and liraglutide. Despite its large clinical relevance, tools to investigate the precise activation dynamics of this receptor with high spatiotemporal resolution are limited. Here we introduce a novel genetically-encoded sensor based on the engineering of a circularly-permuted green fluorescent protein into the human GLP1R, named GLPLight1. We demonstrate that fluorescence signal from GLPLight1 accurately reports the expected receptor conformational activation in response to pharmacological ligands with high sensitivity (max {Delta}F/F0 = 528%) and temporal resolution ({tau}ON = 4.7 sec). We further demonstrated that GLPLight1 shows comparable responses to GLP-1 derivatives as observed for the native receptor. Using GLPLight1, we established an all-optical assay to characterize a novel photocaged GLP-1 derivative (photo-GLP1) and to demonstrate optical control of GLP1R activation. Thus, the new all-optical toolkit introduced here enhances our ability to study GLP1R activation with high spatiotemporal resolution.

biochemistry↗