Biology subjects

Ulfig, A.

Publications and source records attributed to Ulfig, A..

4 recordsLinked to original sources

bioRxiv2026

Loss of KMT2D accelerates hypertrophic chondrocyte differentiation and senescence by increasing mitochondrial ROS production

Longitudinal bone growth occurs through endochondral ossification, which is accompanied by the differentiation of chondrocytes in the growth plate. Disruption in chondrocyte maturation can lead to skeletal growth abnormalities, such as those observed in Kabuki syndrome type 1 (KS1), a genetic disorder caused by heterozygous pathogenic variants in the KMT2D gene. KS1 patients exhibit postnatal growth deficiency, craniofacial hypoplasia, and skeletal deformities, yet the mechanisms underlying these phenotypic manifestations remain poorly understood. Our study investigated the effects of KMT2D deficiency on chondrocyte maturation and identified premature chondrocyte hypertrophy as a key driver of skeletal abnormalities in KS1. We previously observed reduced femur and tibia length in a KS1 mouse model, along with altered growth plate architecture, particularly affecting the heights of the proliferative and hypertrophic zones. Here, we show that KMT2D-deficient chondrocytes exhibit accelerated differentiation and early senescence upon exposure to supraphysiological oxygen levels (20% O2). These pathological changes were linked to increased mitochondrial reactive oxygen species (ROS) production likely caused by deficiencies in electron transport chain function, leading to oxidative stress and premature hypertrophy. Pharmacological ROS neutralization or hypoxic conditions mitigated these effects, restoring normal chondrocyte differentiation and preventing premature ossification. These findings demonstrate that KMT2D loss induces oxidative stress-driven chondrocyte hypertrophy, disrupting the balance of cartilage growth and ossification. Our study provides crucial mechanistic insights into KS1-associated skeletal abnormalities and suggests mitochondrial ROS regulation as a potential therapeutic avenue.

molecular biology↗

bioRxiv2025

A patient derived missense mouse model of Kabuki syndrome 1

Kabuki syndrome (KS) is a rare cause of intellectual disability resulting from heterozygous pathogenic variants in the gene encoding the histone methyltransferase KMT2D. A previously established loss-of-function mouse model of KS exhibits key phenotypic features, and therapeutic trials in this mouse model suggest postnatal malleability of neurological symptoms. However, 15-30% of individuals with KS, carry missense variants. To investigate whether missense variants lead to similar phenotypic presentation in mice, we used CRISPR-Cas9 to introduce the KS patient variant R5230H into C57BL/6NTac. Computational and in vitro testing suggests that the R5230H variant does not impair protein stability or loss of enzyme function of KMT2D. Despite a distinct mechanistic basis, our new mouse model (Kmt2d+/R5230H) recapitulates most phenotypes of our prior loss-of-function model, including growth deficiency, craniofacial anomalies, and IgA deficiency but not altered neurological function. Kmt2d+/R5230Hmice show perinatal lethality and a high frequency of unilateral kidney agenesis, a novel phenotype in KS mouse models. Kmt2d+/R5230H mice provide a unique opportunity to understand the impact of missense variants on KMT2D function and uncover developmental and perinatal abnormalities in KS. Summary statementA novel Kabuki syndrome missense mouse model with intact KMT2D enzymatic function shares most features with prior KS models, except disruption of adult neurogenesis, and exhibits novel unilateral kidney loss.

genetics↗

bioRxiv2023

Comparison of the mechanism of antimicrobial action of the gold(I) compound auranofin in Gram-positive and Gram-negative bacteria

The antirheumatic gold(I) compound auranofin has been suggested to exhibit bactericidal activity by disrupting the thiol homeostasis through direct inhibition of bacterial thioredoxin reductase (TrxB). While highly effective at killing Gram-positive bacteria, it lacks significant activity against Gram-negative species for reasons that largely remain unclear. Here, we aimed to elucidate the molecular mechanisms underlying the low susceptibility of the Gram-negative model organism Escherichia coli to auranofin when compared to the Gram-positive model organism Bacillus subtilis. A change in the proteome of E. coli exposed to auranofin suggested that the effect of this gold compound is a combination of inactivation of thiol-containing enzymes, upregulation of proteins involved in basal metabolism, and the consequent induction of systemic oxidative stress. Susceptibility tests in E. coli mutants lacking the proteins upregulated upon auranofin treatment suggested that none of them are directly involved in E. colis high tolerance to auranofin. To elucidate factors that could make Gram-negative bacteria less susceptible to auranofin, we tested E. coli cells lacking the efflux pump component TolC. These cells were more sensitive to auranofin treatment than the wild type, but not to an extent that would fully explain the observed difference in susceptibility of Gram-positive and Gram-negative organisms. We thus tested if E. colis thioredoxin reductase (TrxB) is inherently less sensitive to auranofin than TrxB from B. subtilis, which was not the case. E. coli cells lacking components of the thioredoxin-system were also only marginally more susceptible to auranofin. However, E. coli strains lacking the low molecular weight thiol glutathione, but not glutathione reductase, showed a high susceptibility to auranofin. Bacterial cells expressing the genetically encoded redox probe roGFP2 allowed us to observe the oxidation of cellular protein thiols in situ. In line with their susceptibility, the kinetics of probe oxidation and the degree of oxidation promoted by auranofin is significantly higher in Gram-positive bacteria when compared to Gram-negative bacteria. Based on our findings, we hypothesize that auranofin leads to a global disturbance in the cellular thiol redox homeostasis in bacteria, but Gram-negative bacteria are inherently more resistant due to the presence of drug export systems and high cellular concentrations of glutathione.

biochemistry↗

bioRxiv2019

N-chlorination mediates protective and immunomodulatory effects of oxidized human plasma proteins

Hypochlorous acid (HOCl), a powerful antimicrobial oxidant, is produced by neutrophils to fight infections. Here we show that N-chlorination, induced by HOCl concentrations encountered at sites of inflammation, converts blood plasma proteins into chaperone-like holdases that protect other proteins from aggregation. This chaperone-like conversion was reversible by antioxidants and was abrogated by prior methylation of basic amino acids. Furthermore, reversible N-chlorination of basic amino acid side chains is the major factor that converts plasma proteins into efficient activators of immune cells. Finally, HOCl-modified serum albumin was found to act as a pro-survival molecule that protects neutrophils from cell death induced by highly immunogenic foreign antigens. We propose that activation and enhanced persistence of neutrophils mediated by HOCl-modified plasma proteins, resulting in the increased and prolonged generation of ROS, including HOCl, constitutes a potentially detrimental positive feedback loop that can only be attenuated through the reversible nature of the modification involved.

biochemistry↗