Piezo1-mediated regulation of smooth muscle cell volume in response to enhanced extracellular matrix rigidity

BACKGROUND AND PURPOSE

Decreased aortic compliance is a precursor to numerous cardiovascular diseases. Compliance is regulated by the rigidity of the aortic wall and the vascular smooth muscle cells (VSMCs). Extracellular matrix stiffening, observed during ageing, reduces compliance. In response to increased rigidity, VSMCs generate enhanced contractile forces that result in VSMC stiffening and a further reduction in compliance. Mechanisms driving VSMC response to matrix rigidity remain poorly defined.

EXPERIMENTAL APPROACH

Human aortic-VSMCs were seeded onto polyacrylamide hydrogels whose rigidity mimicked either healthy (12 kPa) or aged/diseased (72 kPa) aortae. VSMCs were treated with pharmacological agents prior to agonist stimulation to identify regulators of VSMC volume regulation.

KEY RESULTS

On pliable matrices, VSMCs contracted and decreased in cell area. Meanwhile, on rigid matrices VSMCs displayed a hypertrophic-like response, increasing in area and volume. Piezo1 activation stimulated increased VSMC volume by promoting calcium ion influx and subsequent activation of PKC and aquaporin-1. Pharmacological blockade of this pathway prevented the enhanced VSMC volume response on rigid matrices whilst maintaining contractility on pliable matrices. Importantly, both piezo1 and aquaporin-1 gene expression were up-regulated during VSMC phenotypic modulation in atherosclerosis and after carotid ligation.

CONCLUSIONS AND IMPLICATIONS

In response to extracellular matrix rigidity, VSMC volume is increased by a piezo1/PKC/aquaporin-1 mediated pathway. Pharmacological targeting of this pathway specifically blocks the matrix rigidity enhanced VSMC volume response, leaving VSMC contractility on healthy mimicking matrices intact. Importantly, upregulation of both piezo1 and aquaporin-1 gene expression is observed in disease relevant VSMC phenotypes.

Variability of Inverted Repeats in All Available Genomes of Bacteria

Noncanonical secondary structures in nucleic acids have been studied intensively in recent years. Important biological roles of cruciform structures formed by inverted repeats (IRs) have been demonstrated in diverse organisms, including humans. Using Palindrome analyser, we analyzed IRs in all accessible bacterial genome sequences to determine their frequencies, lengths, and localizations. IR sequences were identified in all species, but their frequencies differed significantly across various evolutionary groups. We detected 242,373,717 IRs in all 1,565 bacterial genomes. The highest mean IR frequency was detected in the Tenericutes (61.89 IRs/kbp) and the lowest mean frequency was found in the Alphaproteobacteria (27.08 IRs/kbp). IRs were abundant near genes and around regulatory, tRNA, transfer-messenger RNA (tmRNA), and rRNA regions, pointing to the importance of IRs in such basic cellular processes as genome maintenance, DNA replication, and transcription. Moreover, we found that organisms with high IR frequencies were more likely to be endosymbiotic, antibiotic producing, or pathogenic. On the other hand, those with low IR frequencies were far more likely to be thermophilic. This first comprehensive analysis of IRs in all available bacterial genomes demonstrates their genomic ubiquity, nonrandom distribution, and enrichment in genomic regulatory regions. IMPORTANCE Our manuscript reports for the first time a complete analysis of inverted repeats in all fully sequenced bacterial genomes. Thanks to the availability of unique computational resources, we were able to statistically evaluate the presence and localization of these important regulatory sequences in bacterial genomes. This work revealed a strong abundance of these sequences in regulatory regions and provides researchers with a valuable tool for their manipulation.

Inverted repeats in the monkeypox virus genome are hot spots for mutation

The current monkeypox virus (MPXV) strain differs from the strain arising in 2018 by 50+ single nucleotide polymorphisms (SNPs) and is mutating much faster than expected. The cytidine deaminase apolipoprotein B messenger RNA editing enzyme, catalytic subunit B (APOBEC3) was hypothesized to be driving this increased mutation. APOBEC has recently been identified to preferentially mutate cruciform DNA secondary structures formed by inverted repeats (IRs). IRs were recently identified as hot spots for mutation in severe acute respiratory syndrome coronavirus 2, and we aimed to identify whether IRs were also hot spots for mutation within MPXV genomes. We found that MPXV genomes were replete with IR sequences. Of the 50+ SNPs identified in the 2022 outbreak strain, 63.9% of these were found to have arisen within IR regions in the 2018 reference strain (MT903344.1). Notably, IR sequences found in the 2018 reference strain were significantly lost over time, with an average of 32.5% of these sequences being conserved in the 2022 MPXV genomes. This evidence was highly indicative that mutations were arising within IRs. This data provides further support to the hypothesis that APOBEC may be driving MPXV mutation and highlights the necessity for greater surveillance of IRs of MPXV genomes to detect new mutations.

Conservation and over-representation of G-quadruplex sequences in regulatory regions of mitochondrial DNA across distinct taxonomic sub-groups

G-quadruplexes have important regulatory roles in the nuclear genome but their distribution and potential roles in mitochondrial DNA (mtDNA) are poorly understood. We analysed 11883 mtDNA sequences from 18 taxonomic sub-groups and identified their frequency and location within mtDNA. Large differences in both the frequency and number of putative quadruplex-forming sequences (PQS) were observed amongst all the organisms and PQS frequency was negatively correlated with an increase in evolutionary age. PQS were over-represented in the 3'UTRs, D-loops, replication origins, and stem loops, indicating regulatory roles for quadruplexes in mtDNA. Variations of the G-quadruplex-forming sequence in the conserved sequence block II (CSBII) region of the human D-loop were conserved amongst other mammals, amphibians, birds, reptiles, and fishes. This D-loop PQS was conserved in the duplicated control regions of some birds and reptiles, indicating its importance to mitochondrial function. The guanine tracts in these PQS also displayed significant length heterogeneity and the length of these guanine tracts were generally longest in bird mtDNA. This information provides further insights into how G4s may contribute to the regulation and function of mtDNA and acts as a database of information for future studies investigating mitochondrial G4s in organisms other than humans.

Bis(N-picolinamido)cobalt(II) Complexes Display Antifungal Activity toward Candida albicans and Aspergillus fumigatus

This report highlights the synthesis and characterization of ten new bis(N-picolinamido)cobalt(II) complexes of the type [(L)2 CoX2 ]0/2+ , whereby L=N-picolinamide ligand and X=diisothiocyanato (-NCS), dichlorido (-Cl) or diaqua (-OH2 ) ligands. Single crystal X-ray (SC-XRD) analysis for nine of the structures are reported and confirm the picolinamide ligand is bound to the Co(II) center through a neutral N,O binding mode. With the addition of powder X-ray diffraction (PXRD), we have confirmed the cis and trans ligand arrangements of each complex. All complexes were screened against several fungal species and show increased antifungal activity. Notably, these complexes had significant activity against strains of Candida albicans and Aspergillus fumigatus, with several compounds exhibiting growth inhibition of >80 %, and onecompound inhibiting Aspergillus fumigatus hyphal growth by >90 %. Conversely, no antifungal activity was exhibited toward Cryptococcus neoformans and no cytotoxicity towards mammalian cell lines.

Analysis of putative quadruplex-forming sequences in fungal genomes: novel antifungal targets?

Fungal infections cause >1 million deaths annually and the emergence of antifungal resistance has prompted the exploration for novel antifungal targets. Quadruplexes are four-stranded nucleic acid secondary structures, which can regulate processes such as transcription, translation, replication and recombination. They are also found in genes linked to virulence in microbes, and ligands that bind to quadruplexes can eliminate drug-resistant pathogens. Using a computational approach, we quantified putative quadruplex-forming sequences (PQS) in 1359 genomes across the fungal kingdom and explored their presence in genes related to virulence, drug resistance and biological processes associated with pathogenicity in Aspergillus fumigatus. Here we present the largest analysis of PQS in fungi and identify significant heterogeneity of these sequences throughout phyla, genera and species. PQS were genetically conserved in Aspergillus spp. and frequently pathogenic species appeared to contain fewer PQS than their lesser/non-pathogenic counterparts. GO-term analysis identified that PQS-containing genes were involved in processes linked with virulence such as zinc ion binding, the biosynthesis of secondary metabolites and regulation of transcription in A. fumigatus. Although the genome frequency of PQS was lower in A. fumigatus, PQS could be found enriched in genes involved in virulence, and genes upregulated during germination and hypoxia. Moreover, PQS were found in genes involved in drug resistance. Quadruplexes could have important roles within fungal biology and virulence, but their roles require further elucidation.

Insights into the Structure-Activity Relationship of Glycosides as Positive Allosteric Modulators Acting on P2X7 Receptors

P2X7 is an important ligand-gated ion channel expressed in multiple immune cell populations. This study aimed to investigate the chemical requirements of triterpenoid glycosides within a new binding pocket to characterize the structure-activity relationship. A set of glycosides were screened for positive modulator activity at human P2X7 using a YO-PRO-1 dye uptake assay in HEK-293 cells stably expressing the wild-type human P2X7 variant (HEK-hP2X7 cells). The highest positive modulator activity was with ginsenoside–compound K (CK), containing a monosaccharide (glucose) attached at carbon-20. Ginsenoside-20(S)-Rg3, containing a disaccharide group (glucose-glucose) at carbon-3, displayed positive modulator activity with a reduced EC₅₀ for ATP and increased maximal response at human P2X7. The epimer 20(R)-Rg3 was inactive. A similar stereo-specific pattern was observed for 20(S)-Rh2. Ginsenoside-F1, highly similar to ginsenoside-CK but containing a single additional hydroxyl group, was also inactive at P2X7. Computational docking suggests hydrophobic residues in the pocket are involved in steric discrimination between triterpenoids, whereas the position and identity of the carbohydrate group are important for positive modulator activity at human P2X7. Ginsenosides containing monosaccharide attachments perform better than di- or trisaccharide glycosides. Additional modifications to the triterpenoid scaffold at carbon-6 are not tolerated. Gypenosides from plant sources other than Panax ginseng (gypenoside XVII, gypenoside XLIX, stevenleaf) can also act as positive allosteric modulators of P2X7. We also investigated the effect of positive allosteric modulators on endogenous P2X7 in THP-1 monocytes and confirmed our findings in a calcium response assay. A cell viability assay showed potentiation of ATP-induced cell death with ginsenoside-CK in THP-1 and HEK-hP2X7 cells.

To Inhibit or Enhance? Is There a Benefit to Positive Allosteric Modulation of P2X Receptors?

The family of ligand-gated ion channels known as P2X receptors were discovered several decades ago. Since the cloning of the seven P2X receptors (P2X1-P2X7), a huge research effort has elucidated their roles in regulating a range of physiological and pathophysiological processes. Transgenic animals have been influential in understanding which P2X receptors could be new therapeutic targets for disease. Furthermore, understanding how inherited mutations can increase susceptibility to disorders and diseases has advanced this knowledge base. There has been an emphasis on the discovery and development of pharmacological tools to help dissect the individual roles of P2X receptors and the pharmaceutical industry has been involved in pushing forward clinical development of several lead compounds. During the discovery phase, a number of positive allosteric modulators have been described for P2X receptors and these have been useful in assigning physiological roles to receptors. This review will consider the major physiological roles of P2X1-P2X7 and discuss whether enhancement of P2X receptor activity would offer any therapeutic benefit. We will review what is known about identified compounds acting as positive allosteric modulators and the recent identification of drug binding pockets for such modulators.

Positive allosteric modulation of P2X7 promotes apoptotic cell death over lytic cell death responses in macrophages

P2X7 is an ATP-gated ion channel that is highly expressed by leukocytes, such as macrophages. Here, P2X7 has been demonstrated to be involved in the regulation of various cell death pathways; including apoptosis, pyroptosis, necrosis, and autophagy. However, cell death induction via P2X7 is complex and is reliant upon the nature of the stimulus, the duration of the stimulus, and the cell type investigated. Previous reports state that high extracellular ATP concentrations promote osmotic lysis, but whether positive allosteric modulation of P2X7 in the presence of lower concentrations of ATP condemns cells to the same fate is unknown. In this study, we compared cell death induced by high ATP concentrations, to cell death induced by compound K, a recently identified and potent positive allosteric modulator of P2X7. Based on our observations, we propose that high ATP concentrations induce early cell swelling, loss of mitochondrial membrane potential, plasma membrane rupture, and LDH release. Conversely, positive allosteric modulation of P2X7 primarily promotes an intrinsic apoptosis pathway. This was characterised by an increase in mitochondrial Ca²⁺, accelerated production of mitochondrial ROS, loss of mitochondrial membrane permeability in a Bax-dependent manner, the potential involvement of caspase-1, and caspase-3, and significantly accelerated kinetics of caspase-3 activation. This study highlights the ability of positive allosteric modulators to calibrate P2X7-dependent cell death pathways and may have important implications in modulating the antimicrobial immune response and in the resolution of inflammation.

Ficolins and the Recognition of Pathogenic Microorganisms: An Overview of the Innate Immune Response and Contribution of Single Nucleotide Polymorphisms

Ficolins are innate pattern recognition receptors (PRR) and play integral roles within the innate immune response to numerous pathogens throughout the circulation, as well as within organs. Pathogens are primarily removed by direct opsonisation following the recognition of cell surface carbohydrates and other immunostimulatory molecules or via the activation of the lectin complement pathway, which results in the deposition of C3b and the recruitment of phagocytes. In recent years, there have been a number of studies implicating ficolins in the recognition and removal of numerous bacterial, viral, fungal, and parasitic pathogens. Moreover, there has been expanding evidence highlighting that mutations within these key immune proteins, or the possession of particular haplotypes, enhance susceptibility to colonization by pathogens and dysfunctional immune responses. This review will therefore encompass previous knowledge on the role of ficolins in the recognition of bacterial and viral pathogens, while acknowledging the recent advances in the immune response to fungal and parasitic infections. Additionally, we will explore the various genetic susceptibility factors that predispose individuals to infection.

Recognition of DHN-melanin by a C-type lectin receptor is required for immunity to Aspergillus

Our resistance to infection is critically dependent upon the ability of pattern recognition receptors to recognise microbial invasion and induce protective immune responses. One such family of receptors are the C-type lectins, which play central roles in antifungal immunity1. These receptors activate key effector mechanisms upon recognition of conserved fungal cell wall carbohydrates. However, several other immunologically active fungal ligands have been described, including melanin2,3, whose mechanisms of recognition remain largely undefined. Here we identify a C-type lectin receptor, Melanin sensing C-type Lectin receptor (MelLec), that plays an essential role in antifungal immunity through recognition of the naphthalene-diol unit of 1,8-dihydroxynaphthalene (DHN)-melanin. MelLec recognises melanin in conidial spores of Aspergillus fumigatus, as well as other DHN-melanised fungi and is ubiquitously expressed by CD31⁺ endothelial cells in mice. MelLec is also expressed by a sub-population of these cells in mice that co-express EpCAM and which were detected only in the lung and liver. In mouse models, MelLec was required for protection against disseminated infection with A. fumigatus. In humans, MelLec is also expressed by myeloid cells, and we identified a single nucleotide polymorphism of this receptor that negatively affected myeloid inflammatory responses and significantly increased susceptibility of stem-cell transplant recipients to disseminated Aspergillus infections. Thus MelLec is a receptor recognising an immunologically active component commonly found on fungi and plays an essential role in protective antifungal immunity in both mice and humans.

Serum opsonin ficolin-A enhances host-fungal interactions and modulates cytokine expression from human monocyte-derived macrophages and neutrophils following Aspergillus fumigatus challenge

Invasive aspergillosis is a devastating invasive fungal disease associated with a high mortality rate in the immunocompromised, such as leukaemia patients, transplant patients and those with HIV/AIDS. The rodent serum orthologue of human L-ficolin, ficolin-A, can bind to and opsonize Aspergillus fumigatus, the pathogen that causes invasive aspergillosis, and may participate in fungal defence. Using human monocyte-derived macrophages and neutrophils isolated from healthy donors, we investigated conidial association and fungal viability by flow cytometry and microscopy. Additionally, cytokine production was measured via cytometric bead arrays. Ficolin-A opsonization was observed to significantly enhance association of conidia, while also inhibiting hyphal growth and contributing to increased fungal killing following incubation with monocyte-derived macrophages and neutrophils. Additionally, ficolin-A opsonization was capable of manifesting a decrease in IL-8, IL-1β, IL-6, IL-10 and TNF-α production from MDM and IL-1β, IL-6 and TNF-α from neutrophils 24 h post-infection. In conclusion, rodent ficolin-A is functionally comparable to human L-ficolin and is capable of modulating the innate immune response to A. fumigatus, down-regulating cytokine production and could play an important role in airway immunity.

H-ficolin binds Aspergillus fumigatus leading to activation of the lectin complement pathway and modulation of lung epithelial immune responses

Aspergillus fumigatus is an opportunistic fungal pathogen that typically infects the lungs of immunocompromised patients leading to a high mortality. H-Ficolin, an innate immune opsonin, is produced by type II alveolar epithelial cells and could participate in lung defences against infections. Here, we used the human type II alveolar epithelial cell line, A549, to determine the involvement of H-ficolin in fungal defence. Additionally, we investigated the presence of H-ficolin in bronchoalveolar lavage fluid from transplant patients during pneumonia. H-Ficolin exhibited demonstrable binding to A. fumigatus conidia via l-fucose, d-mannose and N-acetylglucosamine residues in a calcium- and pH-dependent manner. Moreover, recognition led to lectin complement pathway activation and enhanced fungal association with A549 cells. Following recognition, H-ficolin opsonization manifested an increase in interleukin-8 production from A549 cells, which involved activation of the intracellular signalling pathways mitogen-activated protein kinase MAPK kinase 1/2, p38 MAPK and c-Jun N-terminal kinase. Finally, H-ficolin concentrations were significantly higher in bronchoalveolar lavage fluid of patients with lung infections compared with control subjects (n = 16; P = 0·00726). Receiver operating characteristics curve analysis further highlighted the potential of H-ficolin as a diagnostic marker for lung infection (area under the curve = 0·77; P < 0·0001). Hence, H-ficolin participates in A. fumigatus defence through the activation of the lectin complement pathway, enhanced fungus-host interactions and modulated immune responses.

The serum opsonin L-ficolin is detected in lungs of human transplant recipients following fungal infections and modulates inflammation and killing of Aspergillus fumigatus

BACKGROUND

Invasive aspergillosis (IA) is a life-threatening systemic fungal infection in immunocompromised individuals that is caused by Aspergillus fumigatus. The human serum opsonin, L-ficolin, has been observed to recognize A. fumigatus and could participate in fungal defense.

METHODS

Using lung epithelial cells, primary human monocyte-derived macrophages (MDMs), and neutrophils from healthy donors, we assessed phagocytosis and killing of L-ficolin-opsonized live A. fumigatus conidia by flow cytometry and microscopy. Additionally, cytokines were measured by cytometric bead array, and L-ficolin was measured in bronchoalveolar lavage (BAL) fluid from lung transplant recipients by enzyme-linked immunosorbent assay.

RESULTS

L-ficolin opsonization increased conidial uptake and enhanced killing of A. fumigatus by MDMs and neutrophils. Opsonization was also shown to manifest an increase in interleukin 8 release from A549 lung epithelial cells but decreased interleukin 1β, interleukin 6, interleukin 8, interleukin 10, and tumor necrosis factor α release from MDMs and neutrophils 24 hours after infection. The concentration of L-ficolin in BAL fluid from patients with fungal infection was significantly higher than that for control subjects (P = .00087), and receiving operating characteristic curve analysis highlighted the diagnostic potential of L-ficolin for lung infection (area under the curve, 0.842; P < .0001).

CONCLUSIONS

L-ficolin modulates the immune response to A. fumigatus. Additionally, for the first time, L-ficolin has been demonstrated to be present in human lungs.

Role of ficolin-A and lectin complement pathway in the innate defense against pathogenic Aspergillus species

Aspergillus species are saprophytic molds causing life-threatening invasive fungal infections in the immunocompromised host. Innate immune recognition, in particular, the mechanisms of opsonization and complement activation, has been reported to be an integral part of the defense against fungi. We have shown that the complement component ficolin-A significantly binds to Aspergillus conidia and hyphae in a concentration-dependent manner and was inhibited by N-acetylglucosamine and N-acetylgalactosamine. Calcium-independent binding to Aspergillus fumigatus and A. terreus was observed, but binding to A. flavus and A. niger was calcium dependent. Ficolin-A binding to conidia was increased under low-pH conditions, and opsonization led to enhanced binding of conidia to A549 airway epithelial cells. In investigations of the lectin pathway of complement activation, ficolin-A-opsonized conidia did not lead to lectin pathway-specific C4 deposition. In contrast, the collectin mannose binding lectin C (MBL-C) but not MBL-A led to efficient lectin pathway activation on A. fumigatus in the absence of ficolin-A. In addition, ficolin-A opsonization led to a modulation of the proinflammatory cytokine interleukin-8. We conclude that ficolin-A may play an important role in the innate defense against Aspergillus by opsonizing conidia, immobilizing this fungus through enhanced adherence to epithelial cells and modulation of inflammation. However, it appears that other immune pattern recognition molecules, i.e., those of the collectin MBL-C, are involved in the Aspergillus-lectin complement pathway activation rather than ficolin-A.

Opsonizing properties of rat ficolin-A in the defence against Cryptococcus neoformans

Cryptococcus neoformans is a pathogenic fungus causing life threatening infections in humans. The present in vitro study aimed to investigate the opsonizing properties of a well characterized serum ficolin (rat ficolin-A), a member of carbohydrate-recognition molecules of the innate immune system, in the defence against this fungal pathogen. Using flow cytometric analysis we have been able to demonstrate that ficolin-A readily binds to two different acapsular C. neoformans serotypes (representative of the primary infectious form of this fungus) whereas the encapsulated forms are not being recognized. The ficolin-A binding was concentration dependent and inhibited by the acetylated sugars N-acetyleglucosamine and N-acetylegalactosamine but less so by galactose, glucose and mannan. The binding was enhanced at acidic pHs (5.7 and 4.7) compared to physiological pH (7.4) which may indicate that the carbohydrate recognizing fibrinogen-like domains of ficolins undergo conformational changes providing more efficient binding at sites of inflammation where the pH is much lower than normal. We further assessed the biological consequence of the ficolin-A recognition of acapsular C. neoformans by investigating their interaction with lung epithelial cells (type II pneumocytes cell line A549). Flow cytometric analysis demonstrated that ficolin-A opsonized acapsular C. neoformans showed significantly increased adherence to A549 cells when exposed to acidic conditions compared to the unopsonized controls (p=0.04). We conclude that ficolin-A binds acapsular C. neoformans via their carbohydrate recognizing fibrinogen-like domains leading to enhanced uptake by lung epithelial cells in vitro.

Constitutive lysosome exocytosis releases ATP and engages P2Y receptors in human monocytes

Elucidating mechanisms by which Ca(2+) signals are generated by monocytes is important for understanding monocyte function in health and disease. We have investigated mechanisms underlying Ca(2+) signals generated following disruption of lysosomes by exposure to the cathepsin C substrate glycyl-L-phenylalanine-β-napthylamide (GPN). Exposure to 0.2 mM GPN resulted in robust increases in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in the absence of extracellular Ca(2+). The response was antagonised by thapsigargin and evoked capacitative Ca(2+) entry. Dantrolene-sensitive Ca(2+) responses were observed at higher concentrations of GPN (0.4 mM) but not at 0.2 mM. Strikingly, GPN-evoked Ca(2+) responses and β-hexosaminidase secretion were inhibited by the ATPase/ADPase apyrase. Simultaneous measurement of [Ca(2+)](i) and extracellular ATP revealed a concomitant secretion of ATP during GPN-evoked Ca(2+) signalling. Furthermore, the ability of GPN to raise [Ca(2+)](i) was inhibited by P2Y receptor antagonists or by inhibiting vesicular exocytosis with N-ethylmaleimide (NEM). NEM treatment was associated with an inability of GPN to trigger ATP secretion, a drop in baseline [Ca(2+)](i) and reduction in extracellular ATP concentration. Antagonism of purinergic signalling also caused a reduction in baseline [Ca(2+)](i). In summary, these data suggest that P2Y receptor activation contributes significantly to GPN-evoked Ca(2+) signalling, and that constitutive secretion of lysosomal ATP is a major determinant of Ca(2+) homeostasis in monocytes. Lysosomal Ca(2+) stores can communicate with ER Ca(2+) stores either directly through activation of ryanodine receptors, or indirectly through release of ATP and engagement of P2Y receptors.