Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl) homoserine lactone induces calcium signaling-dependent crosstalk between autophagy and apoptosis in human macrophages

The role of AbaI quorum sensing molecule synthase in host cell inflammation induced by Acinetobacter baumannii and its effect on zebrafish infection model

Acinetobacter baumannii is currently one of the most important opportunistic pathogens causing severe nosocomial infections worldwide. Quorum Sensing (QS) system is a widespread mechanism in bacteria to coordinate group behavior by sensing the density of bacterial populations and affect eukaryotic host cell. In Acinetobacter baumannii, AbaI protein is used as QS molecule synthetase to synthesize N- acyl homoserine lactones (AHLs). Currently, QS has made great progress in the study of drug resistance, but there is still a lack of complete understanding of its damage to host cells after adhesion and invasion. Thus, in this study, we examined the effects of abaI mutant (ΔabaI) on the functions of adhesion and invasion, cell viability, inflammation, apoptosis in A. baumannii infected A549 cells, to evaluate the effects of ΔabaI in a zebrafish model. We found the group infected with ΔabaI increased cell viability, reduced adhesion and invasion, cell injury, inflammatory cytokine production and apoptosis. By RNA-Seq, we explored the possibility that abaI stimulated A549 cells inflammation by A. baumannii infection via TLR4/MAPK signaling pathway. In addition, the ΔabaI significantly reduced pathogenicity and recruitment to neutrophils in zebrafish. These observations suggest that abaI plays a major role in A. baumannii infection.

Fibroinase plays a vital role in silk gland degeneration by regulating autophagy and apoptosis in the silkworm, Bombyx mori

The silkworm is an incredibly valuable insect that produces silk through its silk gland. Within this organ, Fibroinase has been identified and named due to its ability to fibroin degradation. The expression of Fibroinase in the silk gland significantly increases during the larval-pupal stage, which might be associated with the degeneration of the silk gland. In this study, Fibroinase was overexpressed and knocked down specifically both in the middle and posterior silk glands, respectively, using transgenic technology. The investigation of silk gland development in these transgenic silkworms showed that Fibroinase plays a direct role in accelerating silk gland degeneration. The staining analyses performed in the silk glands of transgenic silkworms suggest that Fibroinase is involved in the processes of autophagy and apoptosis during silk gland degeneration. Further experiments demonstrated that Fibroinase, acting as a lysosomal regulator, negatively regulates autophagy via the mTOR (mechanistic target of rapamycin) pathway. Moreover, during apoptosis, Fibroinase could activate Caspase3 by increasing the activity of BmCaspase1, ultimately accelerating the apoptosis process. These findings enhance our understanding of the physiological role of Fibroinase in promoting silk gland degeneration, which plays a role in breaking down proteins in the silk gland and coordinating the regulation of autophagy and apoptosis.

Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone mediates Ca+2 dysregulation, mitochondrial dysfunction, and apoptosis in human peripheral blood lymphocytes

N-(3-oxododecanoyl)-l-homoserine lactone is a Pseudomonas aeruginosa secreted quorum-sensing molecule that mediates the secretion of virulence factors, biofilm formation and plays a pivotal role in proliferation and persistence in the host. Apart from regulating quorum-sensing, the autoinducer signal molecule N-(3-oxododecanoyl)-l-homoserine lactone (3O-C12-HSL or C12) of a LasI-LasR circuit exhibits immunomodulatory effects and induces apoptosis in various host cells. However, the precise pathophysiological impact of C12 on human peripheral blood lymphocytes and its involvement in mitochondrial dysfunction remained largely elusive. In this study, the results suggest that C12 (100 μM) induces upregulation of cytosolic and mitochondrial Ca+2 levels and triggers mitochondrial dysfunction through the generation of mitochondrial ROS (mROS), disruption of mitochondrial transmembrane potential (ΔΨm), and opening of the mitochondrial permeability transition pore (mPTP). Additionally, it was observed that C12 induces phosphatidylserine (PS) exposure and promotes apoptosis in human peripheral blood lymphocytes. However, apoptosis plays a critical role in the homeostasis and development of lymphocytes, whereas enhanced apoptosis can cause immunodeficiency through cell loss. These findings suggest that C12 exerts a detrimental effect on lymphocytes by mediating mitochondrial dysfunction and enhancing apoptosis, which might further impair the effective mounting of immune responses during Pseudomonas aeruginosa-associated infections.

Pseudomonas quinolone signal induces organelle stress and dysregulates inflammation in human macrophages

Pseudomonas quinolone signal (PQS) is a quorum-sensing molecule associated with Pseudomonas aeruginosa that regulates quorum sensing, extracellular vesicle biogenesis, iron acquisition, and the secretion of virulence factors. PQS has been shown to have immunomodulatory effects on the host. It induces oxidative stress, modulates cytokine levels, and activates regulated cell death in the host. In this study, we investigated the effects of PQS (10 μM) on host organelle dynamics and dysfunction in human macrophages at the interphase of endoplasmic reticulum (ER), mitochondria, and lysosome. This study showed that PQS increases cytosolic Ca⁺² levels and elevates ER stress, as evidenced by increased expression of BiP and activation of the PERK-CHOP axis of unfolded protein response (UPR). Moreover, PQS also negatively affects mitochondria by disrupting mitochondrial membrane potential and increasing mitochondrial ROS generation (mROS). Additionally, PQS stimulation decreased the number of acridine orange-positive lysosomes, indicating lysosomal destabilization. Furthermore, PQS-induced lysosomal destabilization also induces overexpression of the lysosomal stress-responsive gene TFEB. Besides organelle dysfunction, PQS dysregulates inflammation-related genes by upregulating NLRC4, TMS1, and Caspase 1 while downregulating NLRP3 and IL-1β. Also, PQS increases gene expression of pro-inflammatory cytokines (IL-6, TNF-α, and IFN-γ). In conclusion, our findings suggest that PQS negatively affects human macrophages by interfering with organelle function and dysregulating inflammatory response. Consequently, this study provides crucial insight into PQS-driven macrophage dysfunction and may contribute to a better understanding of Pseudomonas aeruginosa-associated infections.