Biology subjects

Berggren, P.-O.

Publications and source records attributed to Berggren, P.-O..

6 recordsLinked to original sources

bioRxiv2023

Diet-induced obesity results in endothelial cell desensitization to VEGF-A and permanent islet vascular dysfunction

BackgroundPancreatic islet microvasculature is essential for optimal islet function and glucose homeostasis. However, islet vessel pathogenesis and its role in the manifestation of metabolic disorders remain understudied. Here we depict a time-resolved decline of intra-islet endothelial cell sensitivity to vascular endothelial cell growth factor A (VEGF-A) in a mouse model of diet-induced obesity. MethodsMice were transplanted with reporter islets in their eyes and put on different diet schemes for 48 weeks. Islet vascular morphology, VEGF-A signaling activity in islet endothelial cells and vessel function were longitudinally monitored by in vivo imaging, while the metabolic implication of islet vessel alterations was measured by glucose tolerance tests and insulin secretion assays. ResultsIn parallel with substantial islet vasculature remodeling, diminished VEGF-A response in islet endothelial cells emerged after 12 weeks of western diet feeding. This led to vessel barrier dysfunction and hemodynamic dysregulation, which delayed transportation of secreted insulin into the blood. Islet vessels also exhibited a remarkable metabolic memory long after the removal of western diet. Neither islet endothelial cell VEGF-A sensitivity nor the vascular damage elicited by 24 weeks of western diet feeding was restored by switching to control diet for another 24 weeks. As a result, these refed mice still exhibited mild but significant impairment in glucose clearance, despite a complete normalization of body weight and insulin sensitivity. While plasma levels of soluble VEGF receptor 1 - the natural VEGF-A trap - were similar in all diet groups, increased activity of atypical protein kinase C (aPKC) was observed under both western diet and recovery conditions, which inhibited VEGF receptor 2 (VEGFR2) internalization and dampened VEGF-A triggered signal transduction in vivo and in human endothelial cells cultured under diet-mimicking conditions. ConclusionsLong-term western diet feeding causes irreversible VEGF-A desensitization in islet endothelial cells and islet vessel dysfunction which undermines glucose homeostasis.

physiology↗

bioRxiv2022

An MR-based brain template and atlas for optical projection tomography and light sheet fluorescence microscopy

Optical projection tomography (OPT) and light sheet fluorescence microscopy (LSFM) are high-resolution optical imaging techniques operating in the mm-cm range, ideally suited for ex vivo 3D whole mouse brain imaging. Although these techniques exhibit high sensitivity and specificity for antibody-labeled targets, the provided anatomical information remains limited. To allow anatomical mapping of fluorescent signal in whole brain, we developed a novel magnetic resonance (MR) - based template with its associated tissue priors and atlas labels, specifically designed for brains subjected to tissue processing protocols required for 3D optical imaging. We investigated the effect of tissue pre-processing and clearing on brain size and morphology and developed optimized templates for BABB/Murrays clear (OCUM) and DBE/iDISCO (iOCUM) cleared brains. By creating optical-(i)OCUM fusion images using our mapping procedure, we localized dopamine transporter and translocator protein expression and tracer innervation from the eye to the lateral geniculate nucleus of thalamus and superior colliculus. These fusion images allowed for precise anatomical identification of fluorescent signal in discrete brain areas. As such, these templates enable applications in a broad range of research areas integrating optical 3D brain imaging by providing an MR template for cleared brains.

neuroscience↗

bioRxiv2021

Destabilization of β-cell FIT2 by saturated fatty acids contribute to ER stress and diabetes

Western type diets are linked to obesity and diabetes partly because of their high saturated fatty acid (SFA) content. We found that SFAs, but not unsaturated fatty acids (USFAs), reduced the number of lipid droplets (LDs) within pancreatic {beta}-cells. Mechanistically, SFAs but not USFAs disabled LD biogenesis by inducing palmitoylation and subsequent ERAD-C mediated degradation of LD formation protein, Fat storage-Inducing Transmembrane protein 2 (FIT2). Targeted ablation of FIT2 reduced {beta}-cell LD numbers, lowered {beta}-cell ATP levels, reduced Ca2+ signaling, downregulated {beta}-cell transcription factors (RNA sequencing analysis), and exacerbated diet-induced diabetes in mice. Subsequent mass spectrometry studies revealed increased C16:0 ceramide accumulation in islets of mice lacking {beta}-cell FIT2 under lipotoxic conditions. Inhibition of ceramide synthases ameliorated the enhanced ER stress. Overexpression of FIT2 increased number of intracellular LDs and rescued SFA-induced ER-stress and apoptosis thereby highlighting the protective role of FIT2 and LDs against {beta}-cell lipotoxicity and diet-induced diabetes.

biochemistry↗

bioRxiv2019

Islet vascularization is regulated by primary endothelial cilia via VEGF-A dependent signaling

RationaleAccumulating evidence point to a role for primary cilia in endothelial cell function. Islet vascularization is an important determinant of islet function and glucose homeostasis. We have previously shown that {beta}-cell cilia directly regulate insulin secretion. However, it is unclear whether primary cilia are also implicated in islet vascularization and thus contribute to glucose homeostasis.\n\nObjectiveTo characterize the role of primary cilia in islet vascularization.\n\nMethods and ResultsAt four weeks, Bbs4-/- islets show markedly lower intra-islet capillary density with enlarged diameters. We transplanted islets into the anterior chamber (ACE) of mouse eyes for longitudinal and non-invasive in vivo monitoring of vascular morphology. Bbs4-/- islets exhibited significantly delayed re-vascularization and enlarged vessels during engraftment. Similar vascular phenotypes were observed in two other ciliopathy models. By shifting the relative contributions of host versus donor endothelial cells in islet revascularization, we found that primary cilia on endothelial cells is essential for this process. Electron microscopy analysis further revealed a lack of fenestration in engrafted Bbs4-/- islets, partially impairing vascular permeability and glucose delivery to {beta}-cells. Finally, we identified that Vascular endothelial cell growth factor A (VEGF-A)/VEGF receptor 2 (VEGFR2) signalling is involved in islet vascularization, islet function and vascular fenestration. In vitro silencing of two different ciliary genes in endothelial cells disrupts VEGF-A/ VEGFR2 internalization and phospho-activation of downstream signalling components. Consequently, key features of angiogenesis including proliferation, migration and tube formation are attenuated in BBS4 silenced endothelial cells.\n\nConclusionsEndothelial cell primary cilia regulate islet vascularization and vascular barrier function via VEGF-A/ VEGFR2 signaling pathway. Islet vascularization is impaired in four weeks old Bbs4-/- mice. Long-time monitoring of re-vascularization of WT and Bbs4-/- islets recapitulates the phenotype and demonstrates a role for cilia in islet vascularization and vascular barrier function. VEGF-A/ VEGFR2-dependent signalling is regulated by endothelial primary cilia.

physiology↗

bioRxiv2019

Islet macrophages drive islet remodeling and compensatory hyperinsulinemia in the early diabetes

{beta}-cells respond to peripheral insulin resistance by increasing circulating insulin in early type-2 diabetes (T2D). Islet remodeling supports this compensation but the drivers of this process remain poorly understood. Infiltrating macrophages have been implicated in late stage T2D but relatively little is known on islet resident macrophages, especially in early T2D. We hypothesize that islet resident macrophages contribute to islet vascular remodeling and hyperinsulinemia, the failure of which results in a rapid progression to T2D. Using genetic and diet-induced models of compensatory hyperinsulinemia we show that its depletion significantly compromises islet remodeling in terms of size, vascular density and insulin secretion capacity. Depletion of islet macrophages reduces VEGF-A secretion from both human and mouse islets ex vivo and the impact of reduced VEGF-A functionally translates to delayed re-vascularization upon transplantation in vivo. Hence, we show a new role of islet resident macrophages in the context of early T2D and suggest that there is considerable utility in harnessing islet macrophages to promote islet remodeling and islet insulin secretion capacity.\n\nHighlightsO_LIThe compensatory hyperinsulinemic phase of type-2 diabetes is accompanied with significant pancreatic islet remodeling.\nC_LIO_LIBona fide islet resident macrophages are increased during the diabetic compensation phase by largely in situ proliferation.\nC_LIO_LIAblating macrophages severely compromises the islet remodeling process and exacerbates glycemic control in vivo.\nC_LIO_LIMouse and human islet macrophages contribute VEGF-A to the islet environment.\nC_LIO_LISpecific removal of islet macrophages delays islet vascularization in compensatory hyperinsulinemic mice.\nC_LI

molecular biology↗

bioRxiv2018

Silk assembly integrates cells into a 3D fibrillar network that promotes cell spreading and proliferation

Tissues are built of cells integrated in an extracellular matrix (ECM) which provides a three-dimensional (3D) fibrillar network with specific sites for cell anchorage. By genetic engineering, motifs from the ECM can be functionally fused to recombinant silk proteins. Such a silk protein, FN-silk, which harbours a motif from fibronectin, has the ability to self-assemble into fibrillar networks under physiological-like conditions. Herein we describe a method by which mammalian cells are added to the silk solution before assembly, and thereby get uniformly integrated between the formed fibrils. In the resulting 3D scaffold, the cells proliferate and spread out with tissue-like morphology. Elongated cells containing filamentous actin and defined focal adhesion points confirm proper cell attachment to the FN-silk. The cells remain viable in culture for at least 90 days. The method is also scalable to macro-sized 3D cultures. Silk fibers with integrated cells are both strong and extendable, with mechanical properties similar to that of artery walls. The described method enables both differentiation of stem- or precursor cells in 3D and facile co-culture of several different cell types. We show that inclusion of endothelial cells leads to the formation of vessel-like structures throughout the tissue constructs. Hence, silk-assembly in presence of cells constitutes a viable option for 3D culture of cells integrated in a fibrillary ECM-like network, with potential as base for engineering of functional tissue.

bioengineering↗