Resolvins resolve to heal mucosal wounds

Resolvin T-series reduce neutrophil extracellular traps

The newly identified 13-series (T-series) resolvins (RvTs) regulate phagocyte functions and accelerate resolution of infectious inflammation. Because severe acute respiratory syndrome coronavirus 2 elicits uncontrolled inflammation involving neutrophil extracellular traps (NETs), we tested whether stereochemically defined RvTs regulate NET formation. Using microfluidic devices capturing NETs in phorbol 12-myristate 13-acetate-stimulated human whole blood, the RvTs (RvT1-RvT4; 2.5 nM each) potently reduced NETs. With interleukin-1β-stimulated human neutrophils, each RvT dose and time dependently decreased NETosis, conveying ∼50% potencies at 10 nM, compared with a known NETosis inhibitor (10 μM). In a murine Staphylococcus aureus infection, RvTs (50 ng each) limited neutrophil infiltration, bacterial titers, and NETs. In addition, each RvT enhanced NET uptake by human macrophages; RvT2 was the most potent of the four RvTs, giving a >50% increase in NET-phagocytosis. As part of the intracellular signaling mechanism, RvT2 increased cyclic adenosine monophosphate and phospho-AMP-activated protein kinase (AMPK) within human macrophages, and RvT2-stimulated NET uptake was abolished by protein kinase A and AMPK inhibition. RvT2 also stimulated NET clearance by mouse macrophages in vivo. Together, these results provide evidence for novel pro-resolving functions of RvTs, namely reducing NETosis and enhancing macrophage NET clearance via a cyclic adenosine monophosphate-protein kinase A-AMPK axis. Thus, RvTs open opportunities for regulating NET-mediated collateral tissue damage during infection as well as monitoring NETs.

E-series resolvin metabolome, biosynthesis and critical role of stereochemistry of specialized pro-resolving mediators (SPMs) in inflammation-resolution: Preparing SPMs for long COVID-19, human clinical trials, and targeted precision nutrition

The COVID-19 pandemic has raised international awareness of the importance of rigorous scientific evidence and the havoc caused by uncontrolled excessive inflammation. Here we consider the evidence on whether the specialized pro-resolving mediators (SPMs) are ready to meet this challenge as well as targeted metabololipidomics of the resolution-inflammation metabolomes. Specific stereochemical mechanisms in the biosynthesis of SPMs from omega-3 essential fatty acids give rise to unique local-acting lipid mediators. SPMs possess stereochemically defined potent bioactive structures that are high-affinity ligands for cognate G protein-coupled surface receptors that evoke the cellular responses required for efficient resolution of acute inflammation. The SPMs biosynthesized from the major omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are coined Resolvins (resolution phase interaction products; E series and D-series), Protectins and Maresins (macrophage mediators in resolving inflammation). Their biosynthesis and stereochemical assignments are established and confirmed (>1,441 resolvin publications in PubMed.gov) as well as their functional roles on innate immune cells and adaptive immune cells (both lymphocyte T-cell subsets and B-cells). The resolution of a protective acute inflammatory response is governed mainly by phagocytes that actively clear apoptotic cells, debris, blood clots and pathogens. These resolution phase functions of the acute inflammatory response are enhanced by SPMs, which together prepare the inflammatory loci for homeostasis and stimulate tissue regeneration via activating stem cells and the biosynthesis of novel cys-SPMs (e.g. MCTRs, PCTRs and RCTRs). These cys-SPMs also activate regeneration, are organ protective and stimulate resolution of local inflammation. Herein, we review the biosynthesis and functions of the E-series resolvins, namely resolvin E1 (the first n-3 resolvin identified), resolvin E2, resolvin E3 and resolvin E4 biosynthesized from their precursor eicosapentaenoic acid (EPA), and the critical role of total organic synthesis in confirming SPM complete stereochemistry, establishing their potent functions in resolution of inflammation, and novel structures. The physical properties of each biologically derived SPM, i.e., ultra-violet (UV) absorbance, chromatographic behavior, and tandem mass spectrometry (MS2) fragmentation, were matched to SPMs biosynthesized and prepared by stereospecific total organic synthesis. We briefly review this approach, also used with the endogenous D-series resolvins, protectins and maresins confirming their potent functions in resolution of inflammation, that paves the way for their rigorous evaluation in human tissues and clinical trials. The assignment of complete stereochemistry for each of the E and D series Resolvins, Protectins and Maresins was a critical and required step that enabled human clinical studies as in SPM profiling in COVID-19 infections and experimental animal disease models that also opened the promise of resolution physiology, resolution pharmacology and targeted precision nutrition as new areas for monitoring health and disease mechanisms.

Hypoxia-inducible factor-dependent induction of myeloid-derived netrin-1 attenuates natural killer cell infiltration during endotoxin-induced lung injury

Sepsis and sepsis‐associated lung inflammation significantly contribute to the morbidity and mortality of critical illness. Here, we examined the hypothesis that neuronal guidance proteins could orchestrate inflammatory events during endotoxin‐induced lung injury. Through a targeted array, we identified netrin‐1 as the top upregulated neuronal guidance protein in macrophages treated with lipopolysaccharide (LPS). Furthermore, we found that netrin‐1 is highly enriched in infiltrating myeloid cells, particularly in macrophages during LPS‐induced lung injury. Transcriptional studies implicate hypoxia‐inducible factor HIF‐1α in the transcriptional induction of netrin‐1 during LPS treatment. Subsequently, the deletion of netrin‐1 in the myeloid compartment (Ntn1^loxp/loxp LysM Cre) resulted in exaggerated mortality and lung inflammation. Surprisingly, further studies revealed enhanced natural killer cells (NK cells) infiltration in Ntn1^loxp/loxp LysM Cre mice, and neutralization of NK cell chemoattractant chemokine (C‐C motif) ligand 2 (CCL2) reversed the exaggerated lung inflammation. Together, these studies provide functional insight into myeloid cell‐derived netrin‐1 in controlling lung inflammation through the modulation of CCL2‐dependent infiltration of NK cells.

Cysteinyl-specialized proresolving mediators link resolution of infectious inflammation and tissue regeneration via TRAF3 activation

The recently elucidated proresolving conjugates in tissue regeneration (CTR) maresin-CTR (MCTR), protectin-CTR (PCTR), and resolvin-CTR (RCTR), termed cysteinyl-specialized proresolving mediators (cys-SPMs) each promotes regeneration, controls infection, and accelerates resolution of inflammation. Here, we sought evidence for cys-SPM activation of primordial pathways in planaria (Dugesia japonica) regeneration that might link resolution of inflammation and regeneration. On surgical resection, planaria regeneration was enhanced with MCTR3, PCTR3, or RCTR3 (10 nM), each used for RNA sequencing. The three cys-SPMs shared up-regulation of 175 known transcripts with fold-change > 1.25 and combined false discovery rate (FDR) < 0.002, and 199 canonical pathways (FDR < 0.25), including NF-κB pathways and an ortholog of human TRAF3 (TNFR-associated factor 3). Three separate pathway analyses converged on TRAF3 up-regulation by cys-SPMs. With human macrophages, three cys-SPMs each dose-dependently increased TRAF3 expression in a cAMP-PKA-dependent manner. TRAF3 overexpression in macrophages enhanced Interleukin-10 (IL-10) and phagocytosis of Escherichia coli IL-10 also increased phagocytosis in a dose-dependent manner. Silencing of mouse TRAF3 in vivo significantly reduced IL-10 and macrophage phagocytosis. TRAF3 silencing in vivo also relieved cys-SPMs' actions in limiting polymorphonuclear neutrophil in E. coli exudates. These results identify cys-SPM-regulated pathways in planaria regeneration, uncovering a role for TRAF3/IL-10 in regulating mammalian phagocyte functions in resolution. Cys-SPM activation of TRAF3 signaling is a molecular component of both regeneration and resolution of infectious inflammation.