Biology subjects

Mielenz, D.

Publications and source records attributed to Mielenz, D..

10 recordsLinked to original sources

bioRxiv2026

IgA plasma cells co-secrete monomeric and dimeric IgA

Dimeric immunoglobulin A (dIgA) is generated from IgA monomers (mIgA) via JCHAIN-dependent polymerization. DIgA is transported across epithelial barriers by the poly Ig receptor (PIGR) and confers mucosal protection, while serum contains substantial amounts of IgA monomers. Distinct plasma cell subsets have been proposed to produce either monomeric or dimeric IgA, with bone marrow plasma cells as a primary source of mIgA. Here, we addressed whether IgA plasma cell populations segregate based on mIgA or dIgA production. Flow cytometric analysis of antibody-secreting cells from bone marrow, lymphoid and mucosal tissues revealed universal intracellular JCHAIN expression across isotypes and failed to identify a discrete JCHAIN-negative IgA plasma cell population. To detect polymeric IgA, we generated a recombinant soluble PIGR that selectively bound JCHAIN-containing dIgA in Western blot, ELISA, and flow cytometry. Soluble PIGR binding was detected in all IgA plasma cells irrespective of tissue origin, arguing against a dedicated mIgA-producing plasma cell subset incapable of dIgA formation. Ex vivo cultures and single-cell DropMap secretion assays demonstrated that bone marrow and lamina propria IgA antibody-secreting cells co-secrete mIgA and dIgA. These findings suggest that dIgA assembly and secretion are general properties of IgA plasma cells and disfavor a dedicated mIgA-producing population. HighlightsO_LIAll plasma cells express JCHAIN protein C_LIO_LIRecombinant poly Ig receptor detects dimeric IgA in all IgA plasma cells C_LIO_LIBone marrow plasma cells secrete dimeric IgA C_LIO_LIIgA plasma cells co-secrete mono- and dimeric IgA C_LI

immunology↗

bioRxiv2025

Swiprosin-1/EFhd2 promotes mitochondrial spare capacity in response to immobilized antigen in B cells via microtubule stabilization

B cells can recognize soluble and membrane bound antigens, enabling them to initiate and execute versatile immune responses. This study examines Swiprosin-1/EFhd2 (EFhd2) in regulating mitochondrial function and organization in B cells during B cell receptor (BCR) activation and immune synapse formation. Using EFhd2 knockout (KO) and wild-type (WT) murine B cells, we assessed mitochondrial abundance, membrane potential, and respiratory capacity using soluble anti-IgM and anti-CD40/IL-4 stimulation. EFhd2KO B cells exhibit more functional mitochondria and mitochondrial spare capacity selectively in activated but not in resting cells. This phenotype changed absolutely upon BCR synapse formation: While activated WT B cells enhance basal mitochondrial respiration, ATP production and maximal respiration, with large increments of spare capacity, EFhd2KO B cells fail completely to do so. Actin depolymerization and microtubule destabilization impair functional mitochondrial upregulation in WT but not in EFhd2KO B cells, while microtubule stabilization restores full spare capacity in EFhd2KO B cells at the BCR synapse. Live-cell imaging reveals that EFhd2KO B cells fail to organize mitochondria, microtubules, and BCRs symmetrically. Super-resolution 3D imaging shows that WT B cells condense mitochondria at the synapse, whereas EFhd2KO B cells display dispersed, unorganized mitochondria and BCR clusters. EFhd2 re-expression restores mitochondrial polarization in EFhd2KO B cells, confirming its role in coordinating mitochondrial positioning. These findings highlight EFhd2 as a key integrator of cytoskeletal and mitochondrial functions for optimal B cell responses to membrane bound antigens. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=174 HEIGHT=200 SRC="FIGDIR/small/637645v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1844c37org.highwire.dtl.DTLVardef@a7b9eaorg.highwire.dtl.DTLVardef@19ec265org.highwire.dtl.DTLVardef@1eca7fb_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2025

Glycolytic flux sustains human Th1 identity and effector function via STAT1 glycosylation

Fate decisions of T helper (Th) cells are tightly linked to their metabolic states, but precise mechanistic links remain unknown, especially in humans. Using in vitro stimulation in combination with gene editing we studied how metabolic regulation shapes human Th1 cell identity and effector function. Differentiated Th1 cells displayed elevated STAT1 phosphorylation at Tyr701 and Ser727 as well as heightened T-bet and IFN{gamma} expression, which were dampened by CRISPR/Cas9-mediated STAT1 deletion. Metabolic profiling revealed enhanced glycolytic activity in Th1 in comparison to Act.T cells, evidenced by increased extracellular acidification rate, ATP production via glycolysis, glucose uptake, lactate secretion and NADH abundance. SCENITH analysis demonstrated elevated glycolysis-dependent anabolic activity of Th1 cells. Inhibition of glycolysis reduced IFN{gamma} production and STAT1 phosphorylation independent of JAK1/2 activity, STAT1 abundance or SHP-2 activity, implicating glycolysis directly in sustaining STAT1-mediated Th1 functionality. Mechanistically, O-Glycosylation, facilitated by O-Glycosyltransferase, emerged as pivotal in modulating STAT1 activity, as evident through immunoprecipitation and Western blot analysis. Pharmaceutical O-Glycosyltransferase inhibition prevented Th1 differentiation as well as STAT1 O-glycosylation. CRISPR/Cas9 mediated mutation of the O-glycosylation sites Ser499 and Thr510 sites diminished STAT1 Ser727 phosphorylation and IFN{gamma} synthesis. Together, this study highlights glycolysis as key regulator of human Th1 cell identity and effector function, with STAT1 O-Glycosylation selectively maintaining Th1 effector capacity. This mechanism could be explored to safeguard Th1 cells in antiviral immunity and autoimmunity. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/636644v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1ee58aeorg.highwire.dtl.DTLVardef@1001af6org.highwire.dtl.DTLVardef@1ea2ed7org.highwire.dtl.DTLVardef@1a943fc_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2024

Systematic mapping of MCU-mediated mitochondrial calcium signaling networks

The Mitochondrial Ca2+ Uniporter Channel (MCUC) allows calcium entry into the mitochondrial matrix to regulate energy metabolism but also cell death. Although, several MCUC components have been identified, the molecular basis of mitochondrial Ca2+ signaling networks and their remodeling upon changes in uniporter activity have not been systematically assessed. Using an unbiased and quantitative proteomic approach, we map the MCUC interactome in HEK293 cells under physiological conditions and upon chronic loss or gain of mitochondrial Ca2+ uptake. Besides all previously known subunits of the uniporter, we identify 89 high-confidence interactors linking MCUC to several mitochondrial complexes and pathways, half of which are currently linked to metabolic, neurological, and immunological diseases. As a proof-of-concept, we validate EFHD1 as a binding partner of MCU, EMRE and MCUB with a MICU1-dependent inhibitory effect on Ca2+ uptake. To investigate compensatory mechanisms and functional consequences of mitochondrial Ca2+ dyshomeostasis, we systematically survey the MCU interactome upon silencing of EMRE, MCUB, MICU1 or MICU2. We observe profound changes in the MCU interconnectivity, whereby downregulation of EMRE reduces the number of MCU interactors of over 10-fold, while silencing of MCUB leads to a wider functional network linking MCU to mitochondrial stress response pathways and cell death. Altogether our study provides a comprehensive map of MCUC protein-protein interactions and a rich, high-confidence resource that can be explored to gain insights into the players and mechanisms involved in calcium signal transduction cascades and their relevance in human diseases.

cell biology↗

bioRxiv2022

Quantitative proteomics and lipidomics of TFG-deficient B cells provide insights into mechanisms of autophagic flux and plasma cell biology

The autophagy-flux-promoting protein TFG (Trk-fused gene) is up-regulated during B cell differentiation into plasma cells and supports survival of CH12 B cells. We hypothesized that quantitative proteomics analysis of CH12tfgKO B cells with intact or blocked autophagy-lysosome flux (via NH4Cl) will identify mechanisms of TFG-dependent autophagy, plasma cell biology and B cell survival. Analysis of CH12WT B cells in the presence of NH4Cl will identify proteins whose presence is continuously regulated by lysosomes independent of TFG. We determined hundreds of proteins to be controlled by TFG and/or NH4Cl. Notably, NH4Cl treatment alone increased the abundance of a cluster of cytosolic and mitochondrial translational proteins while it also reduced a number of proteins. Within the B cell relevant protein pool, BCL10 was reduced, while JCHAIN was increased in CH12tfgKO B cells. Furthermore, TFG regulated the abundance of transcription factors, such as JUNB, metabolic enzymes, such as the short-chain fatty acid activating enzyme ACOT9 or the glycolytic enzyme ALDOC. Gene ontology enrichment analysis revealed that TFG-regulated proteins localized to mitochondria and membrane-bounded organelles. Due to these findings we performed shotgun lipidomics of glycerophospholipids, uncovering that a particular phosphatidylethanolamine (PE) species, 32:0 PE, which lipidates LC3 most efficiently, was less abundant while phosphatidylglycerol (PG) was more abundant in CH12tfgKO B cells. In line with the role of PG as precursor for Cardiolipin (CL), the CL content was higher in CH12tfgKO B cells and addition of PG liposomes to B cells increased the amount of CL. We propose a role for TFG in B cell activation and plasma cell biology via regulation of proteins involved in germinal center and plasma cell development, such as BCL10 or JCHAIN, as well as in lipid homeostasis, mitochondria and metabolism.

immunology↗

bioRxiv2022

The microRNA processing subunit DGCR8 is required for a T cell-dependent germinal center response

We have previously shown that the microRNA (miRNA) processor complex consisting of the RNAse Drosha and the DiGeorge Critical Region (DGCR) 8 protein is essential for central B cell maturation. To determine whether miRNA processing is required to initiate T cell-mediated antibody responses, we deleted DGCR8 in maturing B-2 cells by crossing a mouse with loxP-flanked DGCR8 alleles with a CD23-Cre mouse. As expected, non-immunized mice showed reduced numbers of mature B-2 cells and IgG-secreting cells and diminished serum IgG titers. In accordance, germinal centers and antigen-specific IgG-secreting cells were absent in mice immunized with T cell-dependent antigens. Therefore, DGCR8 is required to mount an efficient T cell-dependent antibody response. However, DGCR8 deletion in B-1 cells was incomplete, which explains relatively unaffected B-1 cell numbers and adequate IgM and IgA titers in DGCR8-knock out mice and suggests that this mouse model could be used to analyze B-1 responses in the absence of functional B-2 cells.

immunology↗

bioRxiv2021

A pair of non-competing neutralizing human monoclonal antibodies protecting from disease in a SARS-CoV-2 infection model

TRIANNI mice carry an entire set of human immunoglobulin V region gene segments and are a powerful tool to rapidly generate human monoclonal antibodies. After immunizing these mice against the spike protein of SARS-CoV-2, we identified 29 hybridoma antibodies that reacted with the SARS-CoV-2 spike protein. Nine antibodies neutralized SARS-CoV-2 infection at IC50 values in the subnanomolar range. ELISA-binding studies and DNA sequence analyses revealed one cluster of clonally related neutralizing antibodies that target the receptor-binding domain and compete with the cellular receptor hACE2. A second cluster of neutralizing antibodies binds to the N-terminal domain of the spike protein without competing with the binding of hACE2 or cluster 1 antibodies. SARS-CoV-2 mutants selected for resistance to an antibody from one cluster are still neutralized by an antibody from the other cluster. Antibodies from both clusters markedly reduced viral spread in mice transgenic for human ACE2 and protected the animals from SARS-CoV-2 induced weight loss. Thus, we report two clusters of potent non-competing SARS-CoV-2 neutralizing antibodies providing potential candidates for therapy and prophylaxis of COVID-19. The study further supports the use of transgenic animals with human immunoglobulin gene repertoires in pandemic preparedness initiatives.

immunology↗

bioRxiv2021

Metabolic breakdown of non-small cell lung cancers by mitochondrial HSPD1 targeting

The identification of novel targets is of paramount importance to develop more effective drugs and improve the treatment of non-small cell lung cancer (NSCLC), the leading cause of cancer-related deaths worldwide. Since cells alter their metabolic rewiring during tumorigenesis and along cancer progression, targeting key metabolic players and metabolism-associated proteins represents a valuable approach with a high therapeutic potential. Metabolic fitness relies on the functionality of heat shock proteins (HSPs), molecular chaperones that facilitate the correct folding of metabolism enzymes and their assembly in macromolecular structures. Here, we show HSPD1 (HSP60) as a survival gene ubiquitously expressed in NSCLC and associated with poor patients prognosis. HSPD1 knockdown or its chemical disruption by the small molecule KHS101 induces a drastic breakdown of oxidative phosphorylation, and suppresses cell proliferation both in vitro and in vivo. By combining drug profiling with transcriptomics and through a whole-genome CRISPR/Cas9 screen, we demonstrate that HSPD1-targeted anti-cancer effects are dependent on OXPHOS and validated molecular determinants of KHS101 sensitivity, in particular, the creatine-transporter SLC6A8 and the subunit of the cytochrome c oxidase complex COX5B. These results highlight mitochondrial metabolism as an attractive target and HSPD1 as a potential theranostic marker for developing therapies to combat NCSLC. SignificanceHSPD1 elimination or disruption interferes with NSCLC metabolic activity causing a strong OXPHOS-dependent energetic breakdown, which the cancer cells fail to overcome, highlighting HSPD1 as a potential theranostic marker for improving lung cancer therapy.

cancer biology↗

bioRxiv2021

Mitochondrial function is essential for humoral immunity by controlling flux of the TCA cycle, phosphatidic acid and mTOR activity in B cells

The function of mitochondrial respiration during B cell fate decisions and differentiation remains equivocal. This study reveals that selection for mitochondrial fitness occurs during B cell activation and is essential for subsequent plasma cell differentiation. By expressing a mutated mitochondrial helicase in transitional B cells, we depleted mitochondrial DNA during B cell maturation, resulting in reduced oxidative phosphorylation. Although no changes in follicular B cell development were evident, germinal centers, class switch recombination to IgG, plasma cell generation and humoral immunity were diminished. Defective oxidative phosphorylation led to aberrant flux of the tricarboxylic acid cycle and lowered the amount of saturated phosphatidic acid. Consequently, MTOR activity and BLIMP-1 induction were curtailed whereas HIF1, glycolysis and AMPK activity were amplified. Exogenous phosphatidic acid increased mTOR activity in activated B cells. Hence, mitochondrial function is required and selected for in activated B cells for the successful generation of functional plasma cells.

immunology↗

bioRxiv2019

The Trk fused gene-product (Tfg) is part of a 600-700kDa CARMA1 complex

B cell receptor (BCR) mediated activation of nuclear factor {kappa}B (NF-{kappa}B) is key to humoral immunity. CARMA1 (CARD11) is essential for BCR mediated NF-{kappa}B activation by interacting with Bcl10 and MALT1. Besides these two main players, few interaction partners of the CARMA1 complex are known. Here we identified new interaction partners of CARMA1. We generated two rabbit antisera against mouse CARMA1 to immunopurify endogenous CARMA1 from lysates of mouse B cells. Nik-binding protein (NIBP), Ras-GAP SH3 binding protein 2 (G3BP1) and Trk-fused gene (Tfg) were identified by peptide mass fingerprinting in immunopurified CARMA1 complexes. The interaction of Tfg and CARMA1 was confirmed by co-immunoprecipitation and Blue native polyacrylamide gel electrophoresis using the anti CARMA1 and newly generated anti Tfg antibodies. This analysis revealed that CARMA1 formed complexes of 600-1000 kDa. Additionally, Tfg was found in complexes of 500-600 kDa which increased in size to [~]740 kDa upon overexpresssion.

biochemistry↗