Tuft cells (TCs) act as crucial airway sentinels that detect bacterial metabolites and initiate immune responses, yet the underlying mechanisms remain poorly understood. Here, we identify tracheal TCs as the initial source of leukotrienes (LTs), released during bacterial infection. Tracheal TCs discriminate pathogenic from commensal bacteria by sensing extracellular ATP (eATP) released by pathogens, including Pseudomonas aeruginosa and Rodentibacter pneumotropicus, within 4 h of infection, through the transient receptor potential cation channel subfamily M member 5 (Trpm5). This induces the LT release, including LTB4, and promotes rapid recruitment of neutrophils and macrophages to the trachea and alveolar spaces. Trpm5-/- mice failed to detect bacterial eATP, exhibited neutrophil sequestration in the spleen, and became colonized following R. pneumotropicus infection, while Trpm5+/+ mice efficiently cleared the pathogen. These findings uncover a critical TC-dependent sensing mechanism in pneumonia, establishing TCs as both ATP sensors and triggers of acute innate immune responses.

Small extracellular vesicles (sEVs) derived from cytotoxic T lymphocytes (CTLs) are emerging as potential mediators of antitumor immunity; however, their subcellular origins and functional properties remain incompletely defined. In this study, we investigated the intracellular routes and cytotoxic potential of CTL-derived exosomes. Using correlative light and electron microscopy, we discovered that CTL-derived exosomes originate from both classical multivesicular bodies (MVBs) and the recently identified multi core granules (MCGs). Through total internal reflection fluorescence microscopy, we demonstrated that, in contrast to MVB-derived exosomes, MCG-derived exosomes are released at the immunological synapse in a stimulus-dependent manner. To enable functional characterization, we developed a scalable primary cell culture method for the isolation of high-purity exosomes. Super-resolution microscopy revealed significant heterogeneity in exosome size and tetraspanin composition. Notably, MCG-derived exosomes exhibited fivefold higher cytotoxic activity than MVB-derived exosomes, inducing apoptosis in tumor cells via a caspase 3-dependent mechanism. These findings reveal that CTLs exploit distinct secretory pathways to release heterogeneous exosome populations with differential cytotoxic capacities, offering new insights into CTL-mediated immune responses and providing a basis for the development of novel exosome-based immunotherapies.

Transient Receptor Potential Canonical 4 (TRPC4) channels have been implicated in multiple neurological functions, including anxiety and sociability. TRPC4 variants were also found in patients with autism. However, the contributions of TRPC4 to neurodevelopment remain undefined. Here, we show that neurobehavioral deficits appear early in young TRPC4 knockout (Trpc4-/-) mice immediately after weaning, manifesting as alterations in multiple, limbic-related behaviors, such as nesting, marble burying, burrowing, self-grooming, and social interactions. Hippocampal neurons of Trpc4-/- mice exhibit reduced dendritic arborization both in vivo and in vitro. Mechanistically, we found that TRPC4 expression in dendrites surged at the same time when glutamate exerted its stimulatory effect on dendritic branching. In live-cell imaging assays, glutamate induced the formation of new dendrite branches in both wild-type and Trpc4-/- neurons. However, many of the new and preexisting branches retracted in the mutant neurons. Furthermore, TRPC4 mediated Ca2+ entry in dendrites downstream from metabotropic glutamate receptors, leading to phosphorylation of nonmuscle myosin light chain (MLC) by the Ca2+-dependent myosin light chain kinase (MLCK), which in turn supported integrin activation in dendrite branches. Our findings underscore the essential role of TRPC4 channels in both dendrite morphogenesis and modulation of motivation-related behaviors. The mechanistic underpinning elucidated for the impaired dendritic development and abnormal behaviors in juvenile Trpc4-/- mice provides insights into the understanding of neurodevelopmental disorders, particularly autism spectrum disorder, opening potential avenues for targeted therapeutic interventions against TRPC4.

Tracheal tuft cells shape immune responses in the airways. While some of these effects have been attributed to differential release of either acetylcholine, leukotriene C4 and/or interleukin-25 depending on the activating stimuli, tuft cell-dependent mechanisms underlying the recruitment and activation of immune cells are incompletely understood. Here we show that Pseudomonas aeruginosa infection activates mouse tuft cells, which release ATP via pannexin 1 channels. Taste signaling through the Trpm5 channel is essential for bacterial tuft cell activation and ATP release. We demonstrate that activated tuft cells recruit dendritic cells to the trachea and lung. ATP released by tuft cells initiates dendritic cell activation, phagocytosis and migration. Tuft cell stimulation also involves an adaptive immune response through recruitment of IL-17A secreting T helper cells. Collectively, the results provide a molecular framework defining tuft cell dependent regulation of both innate and adaptive immune responses in the airways to combat bacterial infection.

The Ca2+-selective transient receptor potential vanilloid 6 (TRPV6) channel plays a fundamental role in the female and male murine reproductive system. We have previously shown that TRPV6 is essential for male fertility, and necessary for a proper placental Ca2+ transport, embryonic bone development and calcification, as well as for extracellular matrix formation in the placental labyrinth. Here, we show that lack of functional TRPV6 results in impaired fecundity in female mice with increased latency to first pregnancy, longer interpregnancy intervals and fewer and smaller litters. In mouse endometrium the TRPV6 protein is expressed in epithelial cells (MEECs). Using patch clamp recording and Ca2+ imaging, we show TRPV6-dependent whole-cell currents and that TRPV6 contributes to cytoplasmic Ca2+ signaling in MEECs. MEECs lacking functional TRPV6 Ca2+ channels reveal a significantly reduced frequency of spontaneous cytosolic Ca2+ oscillations, shown in isolated cells and in situ in whole mount uterus preparations. Our results reveal a previously unknown physiological role for TRPV6 in the regulation of endometrial Ca2+ homeostasis and its impact on female fecundity in mice, providing a molecular and cellular framework for further investigation of reproductive disorders, such as those associated with defective Ca2+ regulation in women.

Flower, a highly conserved protein, crucial for endocytosis and cellular fitness, has been implicated in cytotoxic T lymphocyte (CTL) killing efficiency through its role in cytotoxic granule (CG) endocytosis at the immune synapse (IS). This study explores the molecular cues that govern Flower-mediated CG endocytosis by analyzing uptake of Synaptobrevin2, a protein specific to CG in mouse CTL. Using immunogold electron microscopy and total internal fluorescence microscopy, we found that Flower translocates in a stimulus-dependent manner from small vesicles to the IS, thereby ensuring specificity in CG membrane protein recycling. Using confocal live-cell imaging, we assessed the ability of a range of naturally occurring mouse, human and Drosophila isoforms to rescue defective endocytosis in Flower KO CTLs. This analysis demonstrated that the N-terminal portion of the protein, encompassing amino acids 1-106 in mice, is the minimal domain necessary for Synaptobrevin2 endocytosis. Additionally, we identified two pivotal sites through site-specific mutation: a putative AP2-binding site, and a tyrosine at position 104 in mouse Flower. These findings provide insights into Flower's specific functional domain essential for CG endocytosis, which is a key process in mediating T cell serial killing required for the effective fight against cancer.

The analysis of highly toxic proteins such as abrin and ricin is challenging but comprehensive analytical methods are essential for their unambiguous identification after ingestion. This study pursued three primary aims at detecting abrin and ricin in human biosamples while ensuring that laboratory staff remain protected from direct exposure to these toxic proteins. First, two polyclonal antibodies (pAB) against specific peptides of abrin-A and ricin should be produced. Thereby, antibody epitope mapping was performed, which proved that both pAB recognize specifically their target peptide. Second, an affinity column chromatography-based assay was developed, and finally, the generated pAB should be tested using two different approaches (A and B) for their application in mass spectrometry (MS)-based bioanalytical workflows. Approach A used blood and urine samples submitted to the author’s laboratory after suspected ricin intake. Samples were prepared for nanoLC-MS analysis using affinity column chromatography, gel electrophoresis, and overnight trypsin digestion. Analysis resulted in the confirmation of ricin presence in both plasma and urine. Approach B included the enrichment of an abrin-A-peptide and ricin-peptide using affinity column chromatography directly followed by LC-Orbitrap MS with a detection limit of at least 5 ng/mL in plasma and validation according to international recommendations. Since approach B is much more time-efficient and can be applied throughout laboratories due to the less equipment required, this strategy deserves further focus, especially in a clinical setting.

Using genetically engineered mice and cell lines derived from genetically engineered mice we show that depletion of ER delimited Ca 2+ stores activates heteromeric Ca 2+ entry (SOCE) channels formed obligatorily, but not exclusively by Orai1 molecules. Comparison of Orai-dependent Ca 2+ entries revealed Orai1 to be dominant when compared to Orai2 and Orai3. Unexpectedly, we found that store-depletion-activated Ca 2+ entry does not depend obligatorily on functionally intact TRPC molecules, as SOCE monitored with the Fura2 Ca 2+ reporter dye is unaffected in cells in which all seven TRPC coding genes have been structurally and functionally inactivated. Unexpectedly as well, we found that TRPC-independent Gq-coupled receptor-operated Ca 2+ entry (ROCE) also depends on Orai1. Biophysical measurements of Ca 2+ release activated Ca 2+ currents (Icrac) are likewise unaffected by ablation of all seven TRPC genes. We refer to mice and cells carrying the seven-fold disruption of TRPC genes as TRPC heptaKO mice and cells. TRPC heptaKO mice are fertile allowing the creation of a new homozygous inbred strain.

Regulated exocytosis is initiated by increased Ca2+ concentrations in close spatial proximity to secretory granules, which is effectively prevented when the cell is at rest. Here we showed that exocytosis of zymogen granules in acinar cells was driven by Ca2+ directly released from acidic Ca2+ stores including secretory granules through NAADP-activated two-pore channels (TPCs). We identified OCaR1 (encoded by Tmem63a) as an organellar Ca2+ regulator protein integral to the membrane of secretory granules that controlled Ca2+ release via inhibition of TPC1 and TPC2 currents. Deletion of OCaR1 led to extensive Ca2+ release from NAADP-responsive granules under basal conditions as well as upon stimulation of GPCR receptors. Moreover, OCaR1 deletion exacerbated the disease phenotype in murine models of severe and chronic pancreatitis. Our findings showed OCaR1 as a gatekeeper of Ca2+ release that endows NAADP-sensitive secretory granules with an autoregulatory mechanism preventing uncontrolled exocytosis and pancreatic tissue damage.

AbstractThe identification of targetomes remains a challenge given the pleiotropic effect of miRNAs, the limited effects of miRNAs on individual targets, and the sheer number of estimated miRNA–target gene interactions (MTIs), which is around 44,571,700. Currently, targetome identification for single miRNAs relies on computational evidence and functional studies covering smaller numbers of targets. To ensure that the targetome analysis could be experimentally verified by functional assays, we employed a systematic approach and explored the targetomes of four miRNAs (miR-129-5p, miR-129-1-3p, miR-133b, and miR-873-5p) by analyzing 410 predicted target genes, both of which were previously associated with Parkinson’s disease (PD). After performing 13,536 transfections, we validated 442 of the 705 putative MTIs (62,7%) through dual luciferase reporter assays. These analyses increased the number of validated MTIs by at least 2.1-fold for miR-133b and by a maximum of 24.3-fold for miR-873-5p. Our study contributes to the experimental capture of miRNA targetomes by addressing i) the ratio of experimentally verified MTIs to predicted MTIs, ii) the sizes of disease-related miRNA targetomes, and iii) the density of MTI networks. A web service to support the analyses on the MTI level is available online (https://ccb-web.cs.uni-saarland.de/utr-seremato), and all the data have been added to the miRATBase database (https://ccb-web.cs.uni-saarland.de/miratbase).

The continuous emergence of new psychoactive substances (NPS) attracted a great deal of attention within recent years. Lately, the two hallucinogenic NPS 1cP-LSD and 4-AcO-DET have appeared on the global market. Knowledge about their metabolism to identify potential metabolic targets for analysis and their cytotoxic properties is lacking. The aim of this work was thus to study their in vitro and in vivo metabolism in pooled human liver S9 fraction (pHLS9) and in zebrafish larvae (ZL) by means of liquid chromatography-high-resolution tandem mass spectrometry. Monooxygenases involved in the initial metabolic steps were elucidated using recombinant human isozymes. Investigations on their cytotoxicity were performed on the human hepatoma cell line HepG2 using a multiparametric, fluorescence-based high-content screening assay. This included measurement of CYP-enzyme mediated effects by means of the unspecific CYP inhibitor 1-aminbenzotriazole (ABT). Several phase I metabolites of both compounds and two phase II metabolites of 4-AcO-DET were produced in vitro and in vivo. After microinjection of 1cP-LSD into the caudal vein of ZL, three out of seven metabolites formed in pHLS9 were also detected in ZL. Twelve 4-AcO-DET metabolites were identified in ZL after exposure via immersion bath and five of them were found in pHLS9 incubations. Notably, unique metabolites of 4-AcO-DET were only produced by ZL, whereas 1cP-LSD specific metabolites were found both in ZL and in pHLS9. No toxic effects were observed for 1cP-LSD and 4-AcO-DET in HepG2 cells, however, two parameters were altered in incubations containing 4-AcO-DET together with ABT compared with incubations without ABT but in concentrations far above expected in vivo concentration. Further investigations should be done with other hepatic cell lines expressing higher levels of CYP enzymes.

BACKGROUND:Tight control of cytoplasmic Ca2+ concentration in endothelial cells is essential for the regulation of endothelial barrier function. Here, we investigated the role of Cav beta 3, a subunit of voltage-gated Ca2+ (Cav) channels, in modulating Ca2+ signaling in brain microvascular endothelial cells (BMECs) and how this contributes to the integrity of the blood-brain barrier.METHODS:We investigated the function of Cav beta 3 in BMECs by Ca2+ imaging and Western blot, examined the endothelial barrier function in vitro and the integrity of the blood-brain barrier in vivo, and evaluated disease course after induction of experimental autoimmune encephalomyelitis in mice using Cav beta 3-/- (Cav beta 3-deficient) mice as controls.RESULTS:We identified Cav beta 3 protein in BMECs, but electrophysiological recordings did not reveal significant Cav channel activity. In vivo, blood-brain barrier integrity was reduced in the absence of Cav beta 3. After induction of experimental autoimmune encephalomyelitis, Cav beta 3-/- mice showed earlier disease onset with exacerbated clinical disability and increased T-cell infiltration. In vitro, the transendothelial resistance of Cav beta 3-/- BMEC monolayers was lower than that of wild-type BMEC monolayers, and the organization of the junctional protein ZO-1 (zona occludens-1) was impaired. Thrombin stimulates inositol 1,4,5-trisphosphate-dependent Ca2+ release, which facilitates cell contraction and enhances endothelial barrier permeability via Ca2+-dependent phosphorylation of MLC (myosin light chain). These effects were more pronounced in Cav beta 3-/- than in wild-type BMECs, whereas the differences were abolished in the presence of the MLCK (MLC kinase) inhibitor ML-7. Expression of Cacnb3 cDNA in Cav beta 3-/- BMECs restored the wild-type phenotype. Coimmunoprecipitation and mass spectrometry demonstrated the association of Cav beta 3 with inositol 1,4,5-trisphosphate receptor proteins.CONCLUSIONS:Independent of its function as a subunit of Cav channels, Cav beta 3 interacts with the inositol 1,4,5-trisphosphate receptor and is involved in the tight control of cytoplasmic Ca2+ concentration and Ca2+-dependent MLC phosphorylation in BMECs, and this role of Cav beta 3 in BMECs contributes to blood-brain barrier integrity and attenuates the severity of experimental autoimmune encephalomyelitis disease.

The adrenergic nervous system augments cardiac contraction by increasing the activity of L-type voltage-gated Ca V 1.2 channels. Dysregulation of this process is linked to severe cardiac dysfunctions. The signaling cascade involves activation of β-adrenergic receptors, elevation of cAMP levels, separation of protein kinase A (PKA) regulatory subunit (PKAR) from catalytic subunit (PKAC), and phosphorylation of the inhibitory protein Rad leading to increased Ca 2+ influx. In cardiomyocytes, the core subunit of Ca V 1.2 (α 1C ) exists in two forms: full-length (FL) or proteolytically processed (truncated), lacking the distal C-terminus (dCT). Specificity and efficiency in the cascade are believed to emanate from unique protein-protein interactions, such as anchoring PKA (via PKAR) to α 1C by A-kinase anchoring proteins (AKAPs). However, most AKAPs do not interact with the truncated α 1C , and their role in βAR regulation of cardiac Ca V 1.2 remains unclear. Here we show that PKAC, independently of PKAR or AKAPs, directly interacts with α 1C at two domains in α 1C -CT: the proximal and distal C-terminal regulatory domains (PCRD and DCRD), which also interact with each other. Furthermore, we find that DCRD competes with PCRD and reduces its interaction with PKAC. The physiological consequences of these complex interactions are incompletely understood; our data suggest that they may fine-tune the βAR regulation of Ca V 1.2. We propose that the newly discovered interactions take part in governing colocalization of regulatory proteins within the βAR-Ca V 1.2 multimolecular signaling complexes in cardiomyocytes.

Transient receptor potential (TRP) cation channels are a diverse family of channels whose members play prominent roles as cellular sensors and effectors. The important role of TRP channels (and mechanosensitive piezo channels) in the complex interaction of our senses with the environment was underlined by the award of the Nobel Prize in Physiology or Medicine to 2 pioneers in this field, David Julius and Ardem Patapoutian. There are many competent and comprehensive reviews on many aspects of the TRP channels, and there is no intention to expand on them. Rather, after an introduction to the nomenclature, the molecular architecture of native TRP channel/protein complexes in vivo will be summarized using TRP channels of the canonical transient receptor potential subfamily as an example. This molecular architecture provides the basis for the signatures of native canonical transient receptor potential currents and their control by endogenous modulators and potential drugs.

Englerin A (EA) is a potent agonist of tetrameric transient receptor potential canonical (TRPC) ion channels containing TRPC4 and TRPC5 subunits. TRPC proteins form cation channels that are activated by plasma membrane receptors. They convert extracellular signals such as angiotensin II into cellular responses, whereupon Na+ and Ca2+ influx and depolarization of the plasma membrane occur. Via depolarization, voltage-gated Ca2+ (CaV) channels can be activated, further increasing Ca2+ influx. We investigated the extent to which EA also affects the functions of CaV channels using the high-voltage-activated L-type Ca2+ channel CaV1.2 and the low-voltage-activated T-type Ca2+ channels CaV3.1, CaV3.2, and CaV3.3. After expression of cDNAs in human embryonic kidney (HEK293) cells, EA inhibited currents through all T-type channels at half-maximal inhibitory concentrations (IC50) of 7.5 to 10.3 μM. In zona glomerulosa cells of the adrenal gland, angiotensin II-induced elevation of cytoplasmic Ca2+ concentration leads to aldosterone release. We identified transcripts of low- and high-voltage-activated CaV channels and of TRPC1 and TRPC5 in the human adrenocortical (HAC15) zona glomerulosa cell line. Although no EA-induced TRPC activity was measurable, Ca2+ channel blockers distinguished T- and L-type Ca2+ currents. EA blocked 60% of the CaV current in HAC15 cells and T- and L-type channels analyzed at -30 mV and 10 mV were inhibited with IC50 values of 2.3 and 2.6 μM, respectively. Although the T-type blocker Z944 reduced basal and angiotensin II-induced 24-hour aldosterone release, EA was not effective. In summary, we show here that EA blocks CaV1.2 and T-type CaV channels at low-micromolar concentrations. SIGNIFICANCE STATEMENT: In this study we showed that englerin A (EA), a potent agonist of tetrameric transient receptor potential canonical (TRPC)4- or TRPC5-containing channels and currently under investigation to treat certain types of cancer, also inhibits the L-type voltage-gated Ca2+ (CaV) channel CaV1.2 and the T-type CaV channels CaV3.1, CaV3.2, and CaV3.3 channels at low micromolar concentrations.

Among the concepts in biology that are widely taken granted is a potentiated cooperative effect of multiple miRNAs on the same target. This strong hypothesis contrasts insufficient experimental evidence. The quantity as well as the quality of required side constraints of cooperative binding remain largely hidden. For miR-21-5p and miR-155-5p, two commonly investigated regulators across diseases, we selected 15 joint target genes. These were chosen to represent various neighboring 3′UTR binding site constellations, partially exceeding the distance rules that have been established for over a decade. We identified different cooperative scenarios with the binding of one miRNA enhancing the binding effects of the other miRNA and vice versa. Using both, reporter assays and whole proteome analyses, we observed these cooperative miRNA effects for genes that bear 3′UTR binding sites at distances greater than the previously defined limits. Astonishingly, the experiments provide even stronger evidence for cooperative miRNA effects than originally postulated. In the light of these findings the definition of targetomes specified for single miRNAs need to be refined by a concept that acknowledges the cooperative effects of miRNAs.