Commentary: Triggering Receptor Expressed on Myeloid Cells-1 Inhibitor Targeted to Endothelium Decreases Cell Activation

Triggering Receptors Expressed on Myeloid Cells 1 : Our New Partner in Human Oncology?

Inflammation is recognized as one of the hallmarks of cancer. Indeed, strong evidence indicates that chronic inflammation plays a major role in oncogenesis, promoting genome instability, epigenetic alterations, proliferation and dissemination of cancer cells. Mononuclear phagocytes (MPs) have been identified as key contributors of the inflammatory infiltrate in several solid human neoplasia, promoting angiogenesis and cancer progression. One of the most described amplifiers of MPs pro-inflammatory innate immune response is the triggering receptors expressed on myeloid cells 1 (TREM-1). Growing evidence suggests TREM-1 involvement in oncogenesis through cancer related inflammation and the surrounding tumor microenvironment. In human oncology, high levels of TREM-1 and/or its soluble form have been associated with poorer survival data in several solid malignancies, especially in hepatocellular carcinoma and lung cancer. TREM-1 should be considered as a potential biomarker in human oncology and could be used as a new therapeutic target of interest in human oncology (TREM-1 inhibitors, TREM-1 agonists). More clinical studies are urgently needed to confirm TREM-1 (and TREM family) roles in the prognosis and the treatment of human solid cancers.

TREM-1 Modulation Strategies for Sepsis

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a pattern recognition receptor, which can be upregulated in inflammatory diseases as an amplifier of immune responses. Once activated, TREM-1 induces the production and release of pro-inflammatory cytokines and chemokines, in addition to increasing its own expression and circulating levels of the cleaved soluble extracellular portion of TREM-1 (sTREM-1). This amplification of the inflammatory response by TREM-1 has now been considered as a critical contributor to the dysregulated immune responses in sepsis. Studies have shown that in septic patients there is an elevated expression of TREM-1 on immune cells and increased circulating levels of sTREM-1, associated with increased mortality. As a result, a considerable effort has been made towards identifying endogenous ligands of TREM-1 and developing TREM-1 inhibitory peptides to attenuate the exacerbated inflammatory response in sepsis. TREM-1 modulation has proven a promising strategy for the development of therapeutic agents to treat sepsis. Therefore, this review encompasses the ligands investigated as activators of TREM-1 thus far and highlights the development and efficacy of novel inhibitors for the treatment of sepsis and septic shock.

Design of the lentivirus-driven sustained LR12 delivery system for TREM-1 inhibition for palliating atherosclerosis

Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) has been a potential target in the management of pathophysiology and clinical sequelae of atherosclerosis. LR12 peptide effectively blocks ligand-TREM-1 interaction; however, the short half-life of LR12 is a major hurdle in its translational application in atherosclerosis management warranting new methods for sustained bioavailability in clinical applications. The present study reports a novel method of packing the coding sequence of LR12 in a lentiviral system to ensure a sustained expression and bioavailability for effective TREM-1 inhibition. Lentivirus vector systems (LV-LR12 and LV-SP) for the expression of LR12 peptide and SP (scrambled peptide) were successfully designed, constructed, and tested in vitro in smooth muscle cells (SMCs). Viral amounts obtained were 703.6 ± 145.12 and 609.3 ± 145.93 ng/ml p24 for LV-LR12 and LV-SP, respectively which correspond to ~ 107 IFU/ml for both vectors. Dot blot assay revealed significantly increased expression of LR12-FLAG and SP-FLAG in 125 μg total protein which was doubled in 250 μg protein with respect to un-transduced SMCs suggesting the sustained release of LR12/SP as confirmed by ELISA. Cellular expression of LR12-FLAG and SP-FLAG displayed 8.44-fold and 7.55-fold increase, respectively compared to the control SMCs. The findings demonstrated a promising strategy for packing the LR12 coding sequence in lentiviral vector for TREM-1 inhibition for the management of atherosclerosis and other inflammatory diseases.

Activation of NLRP3 inflammasome up-regulates TREM-1 expression in murine macrophages via HMGB1 and IL-18

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NLRP3 inflammasome inhibition reduces TREM-1 expression in the lungs of mice with ALI.

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Activation of NLRP3 inflammasome up-regulates TREM-1 expression in murine macrophages via HMGB1 and IL-18.

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NLRP3 inflammasome activation induces TREM-1 expression, contributing to the inflammatory network in the lungs of ALI mice.

NOD-, LRR- and pyrin domain-containing 3 (NLRP3) inflammasome and triggering receptor expressed on myeloid cells-1 (TREM-1) are considered critical orchestrators of the inflammatory response in acute lung injury (ALI). However, few assumptions are based on the relationship between them. Here, we investigated the effect of NLRP3 inflammasome activation on the TREM-1 expression in lipopolysaccharide (LPS)-induced ALI and macrophages. We found that inhibition of the NLRP3 inflammasome reduced the TREM-1 expression and pathological lung injury in mice with ALI. Then, primary murine macrophages were used to dissect the underlying mechanistic events of the activation NLRP3 inflammasome involved in the TREM-1 expression. Our results demonstrated that the conditioned medium (CM) from NLRP3 inflammasome-activated-macrophages up-regulated the TREM-1 expression in macrophages, while this effect was reversed by an NLRP3 inflammasome inhibitor MCC950. Furthermore, neutralizing antibodies anti-IL-18 and anti-HMGB1 reduced the TREM-1 expression induced by NLRP3 inflammasome activation. Mechanistically, we found that CM from NLRP3 inflammasome-activated-macrophages increased the level of inhibitor κB kinase protein phosphorylation (p-IκBα) and reactive oxygen species (ROS) content, and promoted IκBα protein degradation in macrophages. While the inhibition of nuclear factor kappa-B (NF-κB) and scavenging ROS eliminated the up-regulation of TREM-1 induced by the NLRP3 inflammasome activation in macrophages. In summary, our study confers NLRP3 inflammasome as a new trigger of TREM-1 signing, which allows additional insight into the pathological of the inflammatory response in ALI.