Pancreatic ß-Cell Identity Change through the Lens of Single-Cell Omics Research.

The main hallmark in the development of both type 1 and type 2 diabetes is a decline in functional ß-cell mass. This decline is predominantly attributed to ß-cell death, although recent findings suggest that the loss of ß-cell identity may also contribute to ß-cell dysfunction. This phenomenon is characterized by a reduced expression of key markers associated with ß-cell identity. This review delves into the insights gained from single-cell omics research specifically focused on ß-cell identity. It highlights how single-cell omics based studies have uncovered an unexpected level of heterogeneity among ß-cells and have facilitated the identification of distinct ß-cell subpopulations through the discovery of cell surface markers, transcriptional regulators, the upregulation of stress-related genes, and alterations in chromatin activity. Furthermore, specific subsets of ß-cells have been identified in diabetes, such as displaying an immature, dedifferentiated gene signature, expressing significantly lower insulin mRNA levels, and expressing increased ß-cell precursor markers. Additionally, single-cell omics has increased insight into the detrimental effects of diabetes-associated conditions, including endoplasmic reticulum stress, oxidative stress, and inflammation, on ß-cell identity. Lastly, this review outlines the factors that may influence the identification of ß-cell subpopulations when designing and performing a single-cell omics experiment.

Single-Cell Transcriptomics Links Loss of Human Pancreatic ß-Cell Identity to ER Stress.

The maintenance of pancreatic islet architecture is crucial for proper ß-cell function. We previously reported that disruption of human islet integrity could result in altered ß-cell identity. Here we combine ß-cell lineage tracing and single-cell transcriptomics to investigate the mechanisms underlying this process in primary human islet cells. Using drug-induced ER stress and cytoskeleton modification models, we demonstrate that altering the islet structure triggers an unfolding protein response that causes the downregulation of ß-cell maturity genes. Collectively, our findings illustrate the close relationship between endoplasmic reticulum homeostasis and ß-cell phenotype, and strengthen the concept of altered ß-cell identity as a mechanism underlying the loss of functional ß-cell mass.

Oxidative Stress Leads to ß-Cell Dysfunction Through Loss of ß-Cell Identity.

Pancreatic ß-cell failure is a critical event in the onset of both main types of diabetes mellitus but underlying mechanisms are not fully understood. ß-cells have low anti-oxidant capacity, making them more susceptible to oxidative stress. In type 1 diabetes (T1D), reactive oxygen species (ROS) are associated with pro-inflammatory conditions at the onset of the disease. Here, we investigated the effects of hydrogen peroxide-induced oxidative stress on human ß-cells. We show that primary human ß-cell function is decreased. This reduced function is associated with an ER stress response and the shuttling of FOXO1 to the nucleus. Furthermore, oxidative stress leads to loss of ß-cell maturity genes MAFA and PDX1, and to a concomitant increase in progenitor marker expression of SOX9 and HES1. Overall, we propose that oxidative stress-induced ß-cell failure may result from partial dedifferentiation. Targeting antioxidant mechanisms may preserve functional ß-cell mass in early stages of development of T1D.

Differential Kinetics of Aspergillus nidulans and Aspergillus fumigatus Phagocytosis.

Invasive aspergillosis mainly occurs in immunocompromised patients and is commonly caused by Aspergillus fumigatus, while A.nidulans is rarely the causative agent. However, in chronic granulomatous disease (CGD) patients, A. nidulans is a frequent cause of invasive aspergillosis and is associated with higher mortality. Immune recognition of A. nidulans was compared to A. fumigatus to offer an insight into why A. nidulans infections are prevalent in CGD. Live cell imaging with J774A.1 macrophage-like cells and LC3-GFP-mCherry bone marrow-derived macrophages (BMDMs) revealed that phagocytosis of A. nidulans was slower compared to A. fumigatus. This difference could be attributed to slower migration of J774A.1 cells and a lower percentage of migrating BMDMs. In addition, delayed phagosome acidification and LC3-associated phagocytosis was observed with A. nidulans. Cytokine and oxidative burst measurements in human peripheral blood mononuclear cells revealed a lower oxidative burst upon challenge with A. nidulans. In contrast, A. nidulans induced significantly higher concentrations of cytokines. Collectively, our data demonstrate that A. nidulans is phagocytosed and processed at a slower rate compared to A. fumigatus, resulting in reduced fungal killing and increased germination of conidia. This slower rate of A. nidulans clearance may be permissive for overgrowth within certain immune settings.

IL-37 protects against obesity-induced inflammation and insulin resistance.

Cytokines of the IL-1 family are important modulators of obesity-induced inflammation and the development of systemic insulin resistance. Here we show that IL-1 family member IL-37, recently characterized as an anti-inflammatory cytokine, ameliorates obesity-induced inflammation and insulin resistance. Mice transgenic for human IL-37 (IL-37tg) exhibit reduced numbers of adipose tissue macrophages, increased circulating levels of adiponectin and preserved glucose tolerance and insulin sensitivity after 16 weeks of HFD. In vitro treatment of adipocytes with recombinant IL-37 reduces adipogenesis and activates AMPK signalling. In humans, elevated steady-state IL-37 adipose tissue mRNA levels are positively correlated with insulin sensitivity and a lower inflammatory status of the adipose tissue. These findings reveal IL-37 as an important anti-inflammatory modulator during obesity-induced inflammation and insulin resistance in both mice and humans, and suggest that IL-37 is a potential target for the treatment of obesity-induced insulin resistance and type 2 diabetes.

Plasma from septic shock patients induces loss of muscle protein.

INTRODUCTION: ICU-acquired muscle weakness commonly occurs in patients with septic shock and is associated with poor outcome. Although atrophy is known to be involved, it is unclear whether ligands in plasma from these patients are responsible for initiating degradation of muscle proteins. The aim of the present study was to investigate if plasma from septic shock patients induces skeletal muscle atrophy and to examine the time course of plasma-induced muscle atrophy during ICU stay. METHODS: Plasma was derived from septic shock patients within 24 hours after hospital admission (n = 21) and healthy controls (n = 12). From nine patients with septic shock plasma was additionally derived at two, five and seven days after ICU admission. These plasma samples were added to skeletal myotubes, cultured from murine myoblasts. After incubation for 24 hours, myotubes were harvested and analyzed on myosin content, mRNA expression of E3-ligase and Nuclear Factor Kappa B (NFκB) activity. Plasma samples were analyzed on cytokine concentrations. RESULTS: Myosin content was approximately 25% lower in myotubes exposed to plasma from septic shock patients than in myotubes exposed to plasma from controls (P < 0.01). Furthermore, patient plasma increased expression of E3-ligases Muscle RING Finger protein-1 (MuRF-1) and Muscle Atrophy F-box protein (MAFbx) (P < 0.01), enhanced NFκB activity (P < 0.05) and elevated levels of ubiquitinated myosin in myotubes. Myosin loss was significantly associated with elevated plasma levels of interleukin (IL)-6 in septic shock patients (P < 0.001). Addition of antiIL-6 to septic shock plasma diminished the loss of myosin in exposed myotubes by approximately 25% (P < 0.05). Patient plasma obtained later during ICU stay did not significantly reduce myosin content compared to controls. CONCLUSIONS: Plasma from patients with septic shock induces loss of myosin and activates key regulators of proteolysis in skeletal myotubes. IL-6 is an important player in sepsis-induced muscle atrophy in this model. The potential to induce atrophy is strongest in plasma obtained during the early phase of human sepsis.