Biology subjects

Kalkum, M.

Publications and source records attributed to Kalkum, M..

5 recordsLinked to original sources

bioRxiv2025

De Novo Hepatic Pyrimidine Synthesis Regulates Systemic Energy Homeostasis

Fasting blood uridine is increased in obesity and type 2 diabetes (T2D), but the significance of hepatic uridine biosynthesis to the etiology of both remains elusive. We found that de novo pyrimidine synthesis in the liver is reduced by fasting and diet-induced obesity, while suppression of hepatic pyrimidine synthesis promotes obesity and insulin resistance. The metabolic sequalae of hepatic pyrimidine synthesis suppression, however, is not associated with altered plasma uridine concentration. Instead, it is associated with an increased hepatic glucose production and a decreased hepatic insulin clearance, two key functions of hepatocytes in regulating systemic energy homeostasis. We found that enhanced gluconeogenesis is the primary reason for increased hepatic glucose production. Moreover, uridine, which was maintained stable in the circulation by adipose tissue and the liver, preferentially shut down pyrimidine synthesis in hepatocytes but not adipocytes at blood concentrations that occur with fasting. Remarkably, uridine, at fasting levels, increases gluconeogenesis further in hepatocytes when de novo pyrimidine synthesis is suppressed, indicating a synergistical action of uridine and its biosynthesis pathway in promoting hepatic glucose production, a mechanism highly relevant to the pathophysiology of insulin resistance in obesity. Theologically, maintenance of blood uridine within the narrow range protects mammals from high-rate spontaneous tumorigenesis. Since obesity promotes an increase in blood uridine from adipocytes, suppressing uridine synthesis in hepatocytes becomes a critical response to lower spontaneous tumorigenesis. Pyrimidine synthesis suppression in hepatocytes, however, promotes gluconeogenesis and ultimately triggers obesity and T2D. These findings suggest a new paradigm for the etiology of metabolic deterioration in diet-induced obesity, in which perturbations in uridine promotes obesity and T2D.

pathology↗

bioRxiv2025

Proinflammatory circulating extracellular vesicles from type 1 diabetes patients contribute to beta cell cytotoxicity and disease pathogenicity

In Type 1 diabetes (T1D), {beta}-cell loss and autoimmunity initiate years before disease diagnosis. However, the mechanisms remain unknown. Here, we investigated the role and mechanisms of circulating extracellular vesicles (cEVs) on T1D pathogenesis and {beta}-cell cytotoxicity. We used cEVs isolated from healthy donors (HD), T1D, multiple autoantibody-positive (AAb+), pre- and post-islet transplantation T1D subjects, NOD-T1D mice, and T1D PBMCs. Patient T1D-cEVs significantly induced apoptosis in vitro in human {beta}-cells but not -cells compared to HD-cEVs. cEVs from AAb+ subjects and pre-diabetic mice were cytotoxic, demonstrating that cEV-induced {beta}-cell cytotoxicity precedes T1D onset and diagnosis. cEV reduction in prediabetic NOD-T1D mice improved {beta}-cell health implying cEV contribution to T1D development. Proteomic analysis of patient T1D-cEVs found several proinflammatory proteins, including interferon gamma, which induced {beta}-cell cytotoxicity. Our data using cEVs from pre- and post-islet transplant and PBMC-EVs from T1D patients implicated immune cells as a potential cellular source of cytotoxic cEVs in T1D. Collectively, our data using T1D patient samples coupled with studies in mice demonstrate that cEVs contribute to {beta}-cell cytotoxicity and to the progression of T1D pathogenicity. Our study is one of the first to demonstrate a functional role of the proinflammatory cEV protein cargo on glucose homeostasis, {beta}-cell health, and insulitis. Our studies on T1D-cEVs may lead to discovery of novel biomarkers and therapeutic targets for T1D.

cell biology↗

bioRxiv2025

The reticulocyte restriction: invasion ligand RBP1a of Plasmodium vivax targets human TfR1, prohibitin-2, and basigin

Plasmodium vivax is the most widespread malaria species with predominance in Latin America and Southeast Asia. Devising effective controls against P. vivax infections presents unique challenges due to the parasites exclusive invasion of reticulocytes, a transient developmental stage of red blood cells. The ephemeral nature and limited availability of reticulocytes complicate efforts to establish continuous in vitro cultures to study the parasites biology and receptor-ligand interactions. Here, the potential of the erythroid cell lines JK-1 and BEL-A as alternatives to reticulocytes was confirmed through successful parasite invasion, marking the first report of P. vivax entry to BEL-A cells. Furthermore, LC-MS was used to quantitatively compare the membrane proteomes of these cell lines with those of reticulocytes and mature erythrocytes. This analysis revealed significant similarities between the membrane proteomes of JK-1, BEL-A, and reticulocytes. In addition to the known Plasmodium receptors, transferrin receptor protein 1 (TfR1 or CD71), CD98hc, and basigin (BSG), potential receptor candidates involved in the parasites invasion pathway were identified, including prohibitin-2 (PHB2), CAT-1 (SLC7A1), ATB(0) (SLC1A5), CD36, integrin beta-1 (ITGB1), and Metal transporter CNNM3. Proximity labeling using TurboID enabled the identification of specific interactions between PvRBP1a158-650 and TfR1, BSG, and prohibitin-2 in the erythroid cell lines. Notably, this is the first report of prohibitin-2 as a receptor for P. vivax. These findings advance the understanding of P. vivax receptor-ligand interactions and underscore the potential of JK-1 and BEL-A cell lines as alternative models for the study of parasite biology. Author SummaryPlasmodium vivax is a major cause of malaria, particularly in Latin America and Southeast Asia. Unlike other malaria parasites, it infects only immature red blood cells (reticulocytes), which are rare and short-lived, making laboratory studies challenging. No continuous in vitro culture system currently exists for P. vivax, limiting research into its invasion mechanisms. In this study, we evaluated two erythroid cell lines, JK-1 and BEL-A, as potential reticulocyte surrogates. We demonstrate that P. vivax can invade both cell types, including BEL-A cells, which had not previously been tested. Comparative analysis revealed key differences in surface protein expression between these cell lines and reticulocytes, compared to mature red blood cells, identifying seven potential parasite-receptor proteins. We further applied a proximity-based protein tagging approach to identify host-parasite interactions mediated by a specific P. vivax protein ligand, RBP1a. This technique revealed a potential role for prohibitin-2, TfR1, and basigin in mediating P. vivax entry into red blood cells by RBP1a binding. The role of prohibitin-2 as a Plasmodium receptor is a novel Discovery. Our results highlight JK-1 and BEL-A cells as valuable tools for P. vivax research and suggest new avenues for investigating host-pathogen interactions, with implications for malaria treatment and vaccine development.

microbiology↗

bioRxiv2023

Discovery of post-translationally modified self-peptides that promote hypertension

Post translational modifications can enhance immunogenicity of self-proteins. In several conditions including hypertension, systemic lupus, and heart failure, isolevuglandins (IsoLGs) are formed by lipid peroxidation and covalently bond with protein lysine residues. Here we show that the murine class-I major histocompatibility complex (MHC-I) variant H-2Db uniquely presents isoLG modified peptides and developed a computational pipeline that identifies structural features for MHC-I accommodation of such peptides. We identified isoLG-adducted peptides from renal proteins including the sodium glucose transporter 2, Cadherin 16, Kelch Domain containing protein 7A and solute carrier family 23, that are recognized by CD8+ T cells in tissues of hypertensive mice, induce T cell proliferation in vitro, and prime hypertension after adoptive transfer. Finally, we find similar patterns of isoLG-adducted antigen restriction in class-I human leukocyte antigens as in murine analogues. Thus, we have used a combined computational and experimental approach to define likely antigenic peptides in hypertension.

immunology↗

bioRxiv2018

Discovery of a bacterial peptide as a modulator of GLP-1 and metabolic disease

Early work in germ-free rodents highlighted the gut microbiotas importance in metabolic disease, including Type II Diabetes Mellitus (T2DM) and obesity. Glucagon-like peptide-1 (GLP-1) is an incretin secreted by enteroendocrine L-cells lining the gastrointestinal epithelium. GLP-1 has important functions including promoting insulin secretion, insulin sensitivity, and {beta}-cell mass, while inhibiting gastric emptying and appetite. We set out to elucidate how the microbiota can modulate GLP-1 secretion, with the goal to identify microbial strains with GLP-1 stimulatory activity as a metabolic disease therapeutic. Over 1500 human-derived strains were isolated from fecal, breast milk, and colon and intestinal biopsy samples from healthy individuals. In vitro screening for GLP-1 modulation was performed by incubating bacterial cell-free supernatants with NCI H716 human L-cells. Approximately 45 strains capable of increasing GLP-1 levels, measured by ELISA, were discovered. Interestingly, all positive strains were identified as Staphylococcus epidermidis by 16S rRNA sequencing. Non-GLP-1 stimulatory S. epidermidis strains were also identified. Mass spectrometry analysis identified a 3 kDa peptide, termed GLP-1 stimulating peptide (GspA), present in GLP-1 positive but absent in GLP-1 neutral S. epidermidis. Studies in human L-cells and intestinal enteroids demonstrated that GspA alone is sufficient to enhance GLP-1 secretion. When administered in high-fat-fed mice, GspA-producing S. epidermidis significantly reduced markers associated with obesity and T2DM, including adiposity and hyperinsulinemia. Further characterization of GspA suggests a GLP-1 stimulatory action via calcium signaling. The presented results identify a novel host-microbe interaction which may ultimately lead to the development of a microbial peptide-based therapeutic for obesity and T2DM.\n\nImportanceThe human gastrointestinal microbiota has been shown to modulate metabolic disease, including Type II Diabetes Mellitus and obesity, through mechanisms involving gut hormone secretion. We initiated this study to identify bacterial strains that can stimulate one of these hormones, glucagon-like peptide-1. We first identified that some strains of Staphylococcus epidermidis have such stimulatory activity. We then found that these strains could be used in a mouse model of high-fat feeding to reduce markers associated with metabolic disease, including adiposity and elevated insulin levels. We also identified the peptide from S. epidermidis that stimulates glucagon-like peptide-1 and propose a mode of action through calcium signaling. This newly identified microbial-derived peptide and host-microbe interaction provide a promising therapeutic approach against Type II Diabetes Mellitus and obesity.

microbiology↗