The cAMP Pathway Amplifies Early MyD88-Dependent and Type I Interferon-Independent LPS-Induced Interleukin-10 Expression in Mouse Macrophages.

Interleukin-10 (IL-10) is a key anti-inflammatory cytokine, secreted by macrophages and other immune cells to attenuate inflammation. Autocrine type I interferons (IFNs) largely mediate the delayed expression of IL-10 by LPS-stimulated macrophages. We have previously shown that IL-10 is synergistically expressed in macrophages following a costimulus of a TLR agonist and cAMP. We now show that the cAMP pathway directly upregulates IL-10 transcription and plays an important permissive and synergistic role in early, but not late, LPS-stimulated IL-10 mRNA and protein expression in mouse macrophages and in a mouse septic shock model. Our results suggest that the loss of synergism is not due to desensitization of the cAMP inducing signal, and it is not mediated by a positive crosstalk between the cAMP and type I IFN pathways. First, cAMP elevation in LPS-treated cells decreased the secretion of type I IFN. Second, autocrine/paracrine type I IFNs induce IL-10 promoter reporter activity only additively, but not synergistically, with the cAMP pathway. IL-10 promoter reporter activity was synergistically induced by cAMP elevation in macrophages stimulated by an agonist of either TLR4, TLR2/6, or TLR7, receptors which signal via MyD88, but not by an agonist of TLR3 which signals independently of MyD88. Moreover, MyD88 knockout largely reduced the synergistic IL-10 expression, indicating that MyD88 is required for the synergism displayed by LPS with cAMP. This report delineates the temporal regulation of early cAMP-accelerated vs. late type I IFN-dependent IL-10 transcription in LPS-stimulated murine macrophages that can limit inflammation at its onset.

The bacterial quorum-sensing signal molecule N-3-oxo-dodecanoyl-L-homoserine lactone reciprocally modulates pro- and anti-inflammatory cytokines in activated macrophages.

The bacterial molecule N-3-oxo-dodecanoyl-l-homoserine lactone (C12) has critical roles in both interbacterial communication and interkingdom signaling. The ability of C12 to downregulate production of the key proinflammatory cytokine TNF-α in stimulated macrophages was suggested to contribute to the establishment of chronic infections by opportunistic Gram-negative bacteria, such as Pseudomonas aeruginosa. We show that, in contrast to TNF-α suppression, C12 amplifies production of the major anti-inflammatory cytokine IL-10 in LPS-stimulated murine RAW264.7 macrophages, as well as peritoneal macrophages. Furthermore, C12 increased IL-10 mRNA levels and IL-10 promoter reporter activity in LPS-stimulated RAW264.7 macrophages, indicating that C12 modulates IL-10 expression at the transcriptional level. Finally, C12 substantially potentiated LPS-stimulated NF-κB DNA-binding levels and prolonged p38 MAPK phosphorylation in RAW264.7 macrophages, suggesting that increased transcriptional activity of NF-κB and/or p38-activated transcription factors serves to upregulate IL-10 production in macrophages exposed to both LPS and C12. These findings reveal another part of the complex array of host transitions through which opportunistic bacteria downregulate immune responses to flourish and establish a chronic infection.

Exclusive Temporal Stimulation of IL-10 Expression in LPS-Stimulated Mouse Macrophages by cAMP Inducers and Type I Interferons.

Expression of the key anti-inflammatory cytokine IL-10 in lipopolysaccharide (LPS)-stimulated macrophages is mediated by a delayed autocrine/paracrine loop of type I interferons (IFN) to ensure timely attenuation of inflammation. We have previously shown that cAMP synergizes with early IL-10 expression by LPS, but is unable to amplify the late type I IFN-dependent activity. We now examined the mechanism of this synergistic transcription in mouse macrophages at the promoter level, and explored the crosstalk between type I IFN signaling and cAMP, using the ß-adrenergic receptor agonist, isoproterenol, as a cAMP inducer. We show that silencing of the type I IFN receptor enables isoproterenol to synergize with LPS also at the late phase, implying that autocrine type I IFN activity hinders synergistic augmentation of LPS-stimulated IL-10 expression by cAMP at the late phase. Furthermore, IL-10 expression in LPS-stimulated macrophages is exclusively stimulated by either IFNα or isoproterenol. We identified a set of two proximate and inter-dependent cAMP response element (CRE) sites that cooperatively regulate early IL-10 transcription in response to isoproterenol-stimulated CREB and that further synergize with a constitutive Sp1 site. At the late phase, up-regulation of Sp1 activity by LPS-stimulated type I IFN is correlated with loss of function of the CRE sites, suggesting a mechanism for the loss of synergism when LPS-stimulated macrophages switch to type I IFN-dependent IL-10 expression. This report delineates the molecular mechanism of cAMP-accelerated IL-10 transcription in LPS-stimulated murine macrophages that can limit inflammation at its onset.

Targeting and modulating infarct macrophages with hemin formulated in designed lipid-based particles improves cardiac remodeling and function.

Uncontrolled activation of pro-inflammatory macrophages after myocardial infarction (MI) accelerates adverse left ventricular (LV) remodeling and dysfunction. Hemin, an iron-containing porphyrin, activates heme oxygenase-1 (HO-1), an enzyme with anti-inflammatory and cytoprotective properties. We sought to determine the effects of hemin formulated in a macrophage-targeted lipid-based carrier (denoted HA-LP) on LV remodeling and function after MI. Hemin encapsulation efficiency was ~100% at therapeutic dose levels. In vitro, hemin/HA-LP abolished TNF-α secretion from macrophages, whereas the same doses of free hemin and drug free HA-LP had no effect. Hemin/HA-LP polarized peritoneal and splenic macrophages toward M2 anti-inflammatory phenotype. We next induced MI in mice and allocated them to IV treatment with hemin/HA-LP (10mg/kg), drug free HA-LP, free hemin (10mg/kg) or saline, one day after MI. Active in vivo targeting to infarct macrophages was confirmed with HA-LP doped with PE-rhodamine. LV remodeling and function were assessed by echocardiography before, 7, and 30days after treatment. Significantly, hemin/HA-LP effectively and specifically targets infarct macrophages, switches infarct macrophages toward M2 anti-inflammatory phenotype, improves angiogenesis, reduces scar expansion and improves infarct-related regional function. In conclusion, macrophage-targeted lipid-based drug carriers with hemin switch macrophages into an anti-inflammatory phenotype, and improve infarct healing and repair. Our approach presents a novel strategy to modulate inflammation and improve infarct repair.

Targeting macrophage subsets for infarct repair.

Macrophages are involved in every cardiovascular disease and are an attractive therapeutic target. Macrophage activation is complex and can be either beneficial or deleterious, depending upon its mode of action, its timing, and its duration. An important macrophage characteristic is its plasticity, which enables it to switch from one subset to another. Macrophages, which regulate healing and repair after myocardial infarction, have become a major target for both treatment and diagnosis (theranostic). The aim of the present review is to describe the recent discoveries related to targeting and modulating of macrophage function to improve infarct repair. We will briefly review macrophage polarization, plasticity, heterogeneity, their role in infarct repair, regeneration, and cross talk with mesenchymal cells. Particularly, we will focus on the potential of macrophage targeting in situ by liposomes. The ability to modulate macrophage function could delineate pathways to reactivate the endogenous programs of myocardial regeneration. This will eventually lead to development of small molecules or biologics to enhance the endogenous programs of regeneration and repair.

Hyaluronan-modified and regular multilamellar liposomes provide sub-cellular targeting to macrophages, without eliciting a pro-inflammatory response.

Macrophages, pivotal cells in onset and progression of inflammation, can benefit from sub-cellular drug targeting to the molecular loci of drug action, whether cell membrane or cell interior. Postulating manipulation of liposome size and surface properties can provide sub-cellular targeting, we studied: thermodynamics of liposome-macrophage binding; liposome cellular localizations; liposome safety including pro-inflammatory cytokine production. We aimed at extending the body of knowledge on interactions of regular unilamellar (RL-ULV) and multilamellar (RL-MLV) liposomes with macrophages. We investigated, for the first time, the interactions of hyaluronan (HA) surface-modified liposomes (HA-ULV and HA-MLV) with macrophages, with respect to multiple equilibria binding combined with cellular localization. Macrophages bound all four liposome types, substantially-favoring the two MLV species over the two ULV species, and internalizing only RL-MLV. Three macrophage-internalization inhibitors (2-deoxyglucose, LY294002 and Wortmannin) reduced RL-MLV internalization but not binding affinity nor binding capacity. Both MLV types were not detrimental to cell proliferation, nor did they elicit TNF-α production in resting and in LPS-activated macrophages. Moreover, a 24-hour exposure of LPS-activated macrophages to HA-MLV reduced TNF-α production by 40%, indicating potential for anti-inflammatory activity. In conclusion RL-MLV and HA-MLV are the liposomes of choice for delivering anti-inflammatory drugs to the macrophage surface or its interior, according to the loci of drug action.