Small Extracellular Vesicle Signaling and Mitochondrial Transfer Reprograms T Helper Cell Function in Human Asthma.

RATIONALE: Asthma is a chronic inflammatory disease of the airways that involves crosstalk between myeloid-derived regulatory cells (MDRCs) and CD4+ T cells. Although small extracellular vesicles (sEVs) are known to mediate cell-cell communication, the role of sEV signaling via mitochondria in perpetuating asthmatic airway inflammation is unknown. OBJECTIVES: We investigated the effects of MDRC-derived exosomes on dysregulated T cell responses in asthmatics. METHODS: Small extracellular vesicles isolated from bronchoalveolar lavage fluid or airway MDRCs of mild to moderate asthmatics or healthy controls were co-cultured with autologous peripheral and airway CD4+ T lymphocytes. sEV internalization, sEV-mediated transfer of mitochondria targeted GFP to T cells, sEV mitochondrial signaling, and subsequent activation, proliferation and polarization of CD4+ T lymphocytes to Th1, Th2 and Th17 subsets were assessed. MEASUREMENTS AND MAIN RESULTS: Airway MDRC-derived sEVs from asthmatics mediated T cell receptor engagement and transfer of mitochondria that induced antigen-specific activation and polarization into Th17 and Th2 cells, drivers of chronic airway inflammation in asthma. CD4+ T cells internalized sEVs containing mitochondria predominantly by membrane fusion, and blocking mitochondrial oxidant signaling in MDRC-derived exosomes mitigated T cell activation. Reactive oxygen species-mediated signaling that elicited T cell activation in asthmatics was sEV-dependent. A Drp1-dependent mitochondrial fission in pro-inflammatory MDRCs promoted mitochondrial packaging within sEVs, which then co-localized with the polarized actin cytoskeleton and mitochondrial networks in the organized immune synapse of recipient T cells. CONCLUSIONS: Our studies indicate a previously unrecognized role for mitochondrial fission and exosomal mitochondrial transfer in dysregulated T cell activation and Th cell differentiation in asthma which could constitute a novel therapeutic target.

ZKSCAN3 in severe bacterial lung infection and sepsis-induced immunosuppression.

The mortality rates among patients who initially survive sepsis are, in part, associated with a high risk of secondary lung infections and respiratory failure. Given that phagolysosomes are important for intracellular killing of pathogenic microbes, we investigated how severe lung infections associated with post-sepsis immunosuppression affect phagolysosome biogenesis. In mice with P. aeruginosa-induced pneumonia, we found a depletion of both phagosomes and lysosomes, as evidenced by decreased amounts of microtubule associated protein light chain 3-II (LC3-II) and lysosomal-associated membrane protein (LAMP1). We also found a loss of transcription factor E3 (TFE3) and transcription factor EB (TFEB), which are important activators for transcription of genes encoding autophagy and lysosomal proteins. These events were associated with increased expression of ZKSCAN3, a repressor for transcription of genes encoding autophagy and lysosomal proteins. Zkscan3-/- mice had increased expression of genes involved in the autophagy-lysosomal pathway along with enhanced killing of P. aeruginosa in the lungs, as compared to wild-type mice. These findings highlight the involvement of ZKSCAN3 in response to severe lung infection, including susceptibility to secondary bacterial infections due to immunosuppression.

AMPK activates Parkin independent autophagy and improves post sepsis immune defense against secondary bacterial lung infections.

Metabolic and bioenergetic plasticity of immune cells is essential for optimal responses to bacterial infections. AMPK and Parkin ubiquitin ligase are known to regulate mitochondrial quality control mitophagy that prevents unwanted inflammatory responses. However, it is not known if this evolutionarily conserved mechanism has been coopted by the host immune defense to eradicate bacterial pathogens and influence post-sepsis immunosuppression. Parkin, AMPK levels, and the effects of AMPK activators were investigated in human leukocytes from sepsis survivors as well as wild type and Park2-/- murine macrophages. In vivo, the impact of AMPK and Parkin was determined in mice subjected to polymicrobial intra-abdominal sepsis and secondary lung bacterial infections. Mice were treated with metformin during established immunosuppression. We showed that bacteria and mitochondria share mechanisms of autophagic killing/clearance triggered by sentinel events that involve depolarization of mitochondria and recruitment of Parkin in macrophages. Parkin-deficient mice/macrophages fail to form phagolysosomes and kill bacteria. This impairment of host defense is seen in the context of sepsis-induced immunosuppression with decreased levels of Parkin. AMPK activators, including metformin, stimulate Parkin-independent autophagy and bacterial killing in leukocytes from post-shock patients and in lungs of sepsis-immunosuppressed mice. Our results support a dual role of Parkin and AMPK in the clearance of dysfunctional mitochondria and killing of pathogenic bacteria, and explain the immunosuppressive phenotype associated Parkin and AMPK deficiency. AMPK activation appeared to be a crucial therapeutic target for the macrophage immunosuppressive phenotype and to reduce severity of secondary bacterial lung infections and respiratory failure.

Oxidative cross-linking of fibronectin confers protease resistance and inhibits cellular migration.

The oxidation of tyrosine residues to generate o,o'-dityrosine cross-links in extracellular proteins is necessary for the proper function of the extracellular matrix (ECM) in various contexts in invertebrates. Tyrosine oxidation is also required for the biosynthesis of thyroid hormone in vertebrates, and there is evidence for oxidative cross-linking reactions occurring in extracellular proteins secreted by myofibroblasts. The ECM protein fibronectin circulates in the blood as a globular protein that dimerizes through disulfide bridges generated by cysteine oxidation. We found that cellular (fibrillar) fibronectin on the surface of transforming growth factor-ß1 (TGF-ß1)-activated human myofibroblasts underwent multimerization by o,o'-dityrosine cross-linking under reducing conditions that disrupt disulfide bridges, but soluble fibronectin did not. This reaction on tyrosine residues required both the TGF-ß1-dependent production of hydrogen peroxide and the presence of myeloperoxidase (MPO) derived from inflammatory cells, which are active participants in wound healing and fibrogenic processes. Oxidative cross-linking of matrix fibronectin attenuated both epithelial and fibroblast migration and conferred resistance to proteolysis by multiple proteases. The abundance of circulating o,o'-dityrosine-modified fibronectin was increased in a murine model of lung fibrosis and in human subjects with interstitial lung disease compared to that in control healthy subjects. These studies indicate that tyrosine can undergo stable, covalent linkages in fibrillar fibronectin under inflammatory conditions and that this modification affects the migratory behavior of cells on such modified matrices, suggesting that this modification may play a role in both physiologic and pathophysiologic tissue repair.

NOX2 decoy peptides disrupt trauma-mediated neutrophil immunosuppression and protect against lethal peritonitis.

Trauma and sepsis are frequent causes of immunosuppression and risk of secondary bacterial infections and mortality among critically ill patients. Reduced activity of neutrophil NADPH oxidase 2 (NOX2) and impaired bacterial killing are among the major indices of immunosuppression. We hypothesize that NOX2-decoy peptides disrupt the inhibition of neutrophil NOX2 by plasma of patients with severe trauma and immunosuppression, thereby preserving the neutrophil respiratory burst that is a central antimicrobial mechanism. We demonstrate that plasma from trauma/hemorrhage (T/H) patients, but not healthy donors (HD), significantly reduced the activity of neutrophil NOX2 and impaired bacterial killing. The inhibitory action of plasma was associated with an increase in bacterial infections among trauma survivors. High Mobility Group Box 1 (HMGB1) is a mediator of lethality in trauma and sepsis and our mechanistic studies revealed that disulfide and oxidized forms of HMGB1 bind to the gp91phox subunit of NOX2, and thus decrease the neutrophil respiratory burst and bacterial killing. NOX2 decoy Anti-Immunosuppression (Ai) Peptides 1 and 3 effectively disrupted the immunosuppressive action of T/H plasma. HMGB1 selectively binds to Ai-Peptide 3, supporting the possibility for direct interaction between HMGB1 and the third external loop of gp91phox. In vivo, Ai-Peptides improved survival of mice subjected to lethal peritonitis. Taken together, plasma-dependent inhibition of neutrophil NOX2 appeared to be a suitable indicator of immunosuppression in patients with severe trauma. Given that gp91phox decoys protected the neutrophil respiratory burst, selected Ai-Peptides have therapeutic potential to reduce bacterial infections and end-organ injury associated with sepsis/trauma-induced immunosuppression.

SIRT3 diminishes inflammation and mitigates endotoxin-induced acute lung injury.

Acute lung injury (ALI) is characterized by exuberant proinflammatory responses and mitochondrial dysfunction. However, the link between mitochondrial dysfunction and inflammation in ALI is not well understood. In this report, we demonstrate a critical role for the mitochondrial NAD+-dependent deacetylase, sirtuin-3 (SIRT3), in regulating macrophage mitochondrial bioenergetics, ROS formation, and proinflammatory responses. We found that SIRT3 expression was significantly diminished in lungs of mice subjected to LPS-induced ALI. SIRT3-deficient mice (SIRT3-/-) develop more severe ALI compared with wild-type controls (SIRT3+/+). Macrophages obtained from SIRT3-/- mice show significant alterations in mitochondrial bioenergetic and redox homeostasis, in association with a proinflammatory phenotype characterized by NLRP3 inflammasome activation. The SIRT3 activator viniferin restored macrophage bioenergetic function in LPS-treated macrophages. Viniferin also reduced NLRP3 activation and the production of proinflammatory cytokines, effects that were absent in SIRT3-/- macrophages. In-vivo administration of viniferin reduced production of inflammatory mediators TNF-α, MIP-2, IL-6, IL-1ß, and HMGB1, and diminished neutrophil influx and severity of endotoxin-mediated ALI; this protective effect of vinferin was abolished in SIRT3-/- mice. Taken together, our results show that the induction/activation of SIRT3 may serve as a new therapeutic strategy in ALI by modulating cellular bioenergetics, controlling inflammatory responses, and reducing the severity of lung injury.

Author Correction: Metformin reverses established lung fibrosis in a bleomycin model.

In the version of this article originally published, a grant was omitted from the Acknowledgements section. The following sentence should have been included: "R.B.M. was supported by a Department of Veterans Affairs Merit Award (5I01BX003272)." The error has been corrected in the HTML and PDF versions of this article.

Metformin reverses established lung fibrosis in a bleomycin model.

Fibrosis is a pathological result of a dysfunctional repair response to tissue injury and occurs in a number of organs, including the lungs1. Cellular metabolism regulates tissue repair and remodelling responses to injury2-4. AMPK is a critical sensor of cellular bioenergetics and controls the switch from anabolic to catabolic metabolism5. However, the role of AMPK in fibrosis is not well understood. Here, we demonstrate that in humans with idiopathic pulmonary fibrosis (IPF) and in an experimental mouse model of lung fibrosis, AMPK activity is lower in fibrotic regions associated with metabolically active and apoptosis-resistant myofibroblasts. Pharmacological activation of AMPK in myofibroblasts from lungs of humans with IPF display lower fibrotic activity, along with enhanced mitochondrial biogenesis and normalization of sensitivity to apoptosis. In a bleomycin model of lung fibrosis in mice, metformin therapeutically accelerates the resolution of well-established fibrosis in an AMPK-dependent manner. These studies implicate deficient AMPK activation in non-resolving, pathologic fibrotic processes, and support a role for metformin (or other AMPK activators) to reverse established fibrosis by facilitating deactivation and apoptosis of myofibroblasts.

Frontline Science: D1 dopaminergic receptor signaling activates the AMPK-bioenergetic pathway in macrophages and alveolar epithelial cells and reduces endotoxin-induced ALI.

Catecholamines, including ß-adrenergic and dopaminergic neurotransmitters, have an essential role in regulating the "fight or flight" reflex and also affects immune cell proinflammatory action. However, little is known about whether catecholamines prevent dysfunction of metabolic pathways associated with inflammatory organ injury, including development of acute lung injury (ALI). We hypothesize that selected catecholamines may reduce metabolic alterations in LPS-stimulated macrophages and in the lungs of mice subjected to endotoxin-induced ALI, a situation characterized by diminished activity of AMP-activated protein kinase (AMPK). We found that activation of the dopamine 1 receptor (D1R) with fenoldopam, but not stimulation of adrenergic receptors with norepinephrine, resulted in a robust activation of AMPK in peritoneal macrophages, human monocytes, or alveolar epithelial cells (AECs). Such AMPK activation was mediated by a phospholipase C (PLC)-dependent mechanism. Unlike norepinephrine, D1R activation also prevented Thr172-AMPK dephosphorylation and kinase inactivation in LPS-treated macrophages. Furthermore, we show that a culture of AECs with either fenoldopam or the AMPK activator metformin effectively diminished IL-1ß-induced release of adverse paracrine signaling, which promotes the macrophage proinflammatory response. In vivo, fenoldopam reduced the severity of LPS-induced ALI, including development of pulmonary edema, lung permeability, and production of inflammatory cytokines TNF-α, MIP-2, or KC and HMGB1. Fenoldopam also prevented AMPK dephosphorylation in the lungs of LPS-treated mice and prevented loss of mitochondrial complexes NDUFB8 (complex I) and ATP synthase (complex V). Collectively, these results suggest that dopamine is coupled to AMPK activation, which provides a substantial anti-inflammatory and bioenergetic advantage and reduces the severity of endotoxin-induced ALI.