Biology subjects

Kiefmann, M.

Publications and source records attributed to Kiefmann, M..

3 recordsLinked to original sources

bioRxiv2026

Lipid-mediated regulation of pneumolysin balances vascular injury and bacterial containment during pneumococcal infection

Severe infection with Streptococcus (S.) pneumoniae is a leading cause of acute lung injury, multiorgan failure, and death despite appropriate antibiotic therapy. A major contributor to tissue damage is pneumolysin (PLY), a cholesterol-dependent pore-forming toxin that is released in large amounts during bacterial lysis. Because antibiotic treatment enhances PLY release, understanding the mechanisms that control PLY-induced host injury is critical for the development of strategies that limit tissue damage without impairing antibacterial defense. Using isolated perfused lungs and in situ two-photon imaging, we show that S. pneumoniae induces platelet and leukocyte recruitment, pulmonary edema, perfusion failure, and intravascular bacterial trapping within pulmonary arterioles. These responses required PLY and were associated with endothelial Ca{superscript 2} influx and plasma membrane permeabilization. The oxysterol 25-hydroxycholesterol (25-HC) prevented PLY-dependent Ca{superscript 2} entry, vascular leakage, and perfusion failure by reducing accessible membrane cholesterol through activation of acyl-CoA:cholesterol acyltransferase (ACAT). Unexpectedly, pneumococcal infection suppressed expression of cholesterol-25-hydroxylase (CH25H), the enzyme responsible for 25-HC synthesis, although induction of this pathway would be predicted to protect against toxin-mediated injury. We show that this downregulation results from inhibition of platelet-activating factor (PAF) receptor (PAFR) signaling by pneumococcal phosphocholine-containing cell wall components. Remarkably, both PAF itself and the anti-phosphocholine antibody TEPC directly inhibited PLY pore formation independently of PAFR, while preserving intravascular coagulation and bacterial trapping. Thus, although 25-HC protects against toxin-mediated vascular injury, its suppression may allow coagulation-dependent bacterial containment, with PAF acting as a compensatory antagonist of PLY. These findings identify a lipid-based host defense system in which 25-HC and PAF differentially regulate PLY activity to balance tissue protection with bacterial clearance and suggest new therapeutic approaches to limit the harmful effects of antibiotic-induced PLY release during pneumococcal infection.

immunology↗

bioRxiv2026

A Hierarchical Model of Purinergic Receptor Activation in Bronchial Epithelial Cells

Purinergic signaling coordinates diverse epithelial responses to extracellular nucleotides such as ATP, ADP, and UDP. Although many epithelial cell types co-express multiple P2 receptors, the logic by which these receptors integrate nucleotide signals has remained unclear. Here, using primary human airway epithelial cells as a model, we reveal a hierarchical system in which P2Y2 functions as a central licensing receptor that both enables and constrains downstream activation of P2Y6 and P2Y12. Molecular analysis, calcium assays, and pharmacological profiling show that P2Y6 and P2Y12 exhibit intrinsic activity when co-express to P2Y2 but in turn lose responsiveness to their specific agonists upon upstream activation of P2Y2. This gating mechanism filters background noise by secondary nucleotides and enforces contextual control over downstream signaling. These findings uncover a previously unrecognized principle of purinergic receptor coordination that may apply broadly across epithelial systems, and offer new insight into nucleotide signaling as a therapeutic target.

Cell Biology↗

bioRxiv2026

Cigarette Smoke Extract (CSE) reduces expression of functional TRPV4 channels in primary human bronchial epithelial cells differentiated at an Air Liquid Interface (ALI) in vitro

Primary human bronchial epithelial cells (pHBECs) of the airways of smokers are chronically exposed to cigarette smoke, which may induce chronic obstructive pulmonary disease (COPD) ranked fourth among the most common global causes of death. Using an established protocol for differentiation of pHBECs to a pseudostratified epithelium at an air liquid interface (ALI), we analyzed functional expression of transient receptor potential vanilloid 4 (TRPV4) proteins after application of cigarette smoke extract (CSE), which upregulated seven smoke exposure regulated genes (SERGs). TRPV4 protein expression in the plasma membrane and localization next to the cilia of ciliated cells was reduced, while cell barrier function was not altered after chronic exposure to CSE for 28 days compared to untreated control cells. Accordingly, TRPV4-mediated Ca2+ influx was blocked in pHBECs after CSE exposure. Moreover, Os-9 protein, which after binding mediates protection from degradation of TRPV4 protein by polyubiquitination, was significantly less expressed in pHBECs upon CSE exposure. Most interestingly, overexpression of OS-9 in pHBECs rescued reduced TRPV4 protein levels induced by CSE. Our study identifies a novel molecular mechanism of toxicity by CSE interfering with TRPV4 and OS-9 expression in pHBECs, which may blaze the trail for new therapeutic options in COPD.

cell biology↗