Argonaute-2 protects the neurovascular unit from damage caused by systemic inflammation

Background The brain vasculature plays a pivotal role in the inflammatory process by modulating the interaction between blood cells and the neurovascular unit. Argonaute-2 (Ago2) has been suggested as essential for endothelial survival but its role in the brain vasculature or in the endothelial–glial crosstalk has not been addressed. Thus, our aim was to clarify the significance of Ago2 in the inflammatory responses elicited by these cell types. Methods Mouse primary cultures of brain endothelial cells, astrocytes and microglia were used to evaluate cellular responses to the modulation of Ago2. Exposure of microglia to endothelial cell-conditioned media was used to assess the potential for in vivo studies. Adult mice were injected intraperitoneally with lipopolysaccharide (LPS) (2 mg/kg) followed by three daily intraperitoneal injections of Ago2 (0.4 nM) to assess markers of endothelial disruption, glial reactivity and neuronal function. Results Herein, we demonstrated that LPS activation disturbed the integrity of adherens junctions and downregulated Ago2 in primary brain endothelial cells. Exogenous treatment recovered intracellular Ago2 above control levels and recuperated vascular endothelial-cadherin expression, while downregulating LPS-induced nitric oxide release. Primary astrocytes did not show a significant change in Ago2 levels or response to the modulation of the Ago2 system, although endogenous Ago2 was shown to be critical in the maintenance of tumor necrosis factor-α basal levels. LPS-activated primary microglia overexpressed Ago2, and Ago2 silencing contained the inflammatory response to some extent, preventing interleukin-6 and nitric oxide release. Moreover, the secretome of Ago2-modulated brain endothelial cells had a protective effect over microglia. The intraperitoneal injection of LPS impaired blood–brain barrier and neuronal function, while triggering inflammation, and the subsequent systemic administration of Ago2 reduced or normalized endothelial, glial and neuronal markers of LPS damage. This outcome likely resulted from the direct action of Ago2 over the brain endothelium, which reestablished glial and neuronal function. Conclusions Ago2 could be regarded as a putative therapeutic agent, or target, in the recuperation of the neurovascular unit in inflammatory conditions.

Pyocyanin pigment from Pseudomonas aeruginosa modulates innate immune defenses in macrophages

Background: Pseudomonas aeruginosa is a well-known opportunistic pathogen. The gram-negative bacillus, commonly associated with hospital-acquired infections, utilizes the host’s impaired immune responses to establish infection. Of its many virulence factors, pyocyanin is essential for P. aeruginosa to establish its full infectivity. Macrophages act as sentinels of the innate immune system, as well as play other roles in homeostasis, tissue remodeling, and bridging between the innate and adaptive immune systems. Aim: This study aimed to investigate the effects of pyocyanin on macrophage innate immune defenses by assessing the function of macrophages treated with pyocyanin and TLR ligands. Phagocytosis of opsonized zymosan, LPS-induced nitric oxide release and cytokine release were used as measures of functional responses. Results: This study found that pyocyanin inhibited phagocytosis-induced ROS release in a dose-dependent manner and reduced nitric oxide release from macrophages induced with P. aeruginosa LPS. In addition, pyocyanin modulated cytokines and chemokines release from macrophages exposed to P. aeruginosa LPS in a dose-dependent manner. Pyocyanin significantly enhanced IL-1β release as well as several chemokines. Therefore, pyocyanin facilitates Pseudomonas aeruginosa to persevere in the immunocompromised host through modulating macrophage’s innate immune defenses. Conclusion: Pyocyanin inhibits macrophage functional defense responses to facilitate Pseudomonas aeruginosa infection.