Transcriptional and functional diversity of human macrophage repolarization.

BACKGROUND: Macrophage plasticity allows cells to adopt different phenotypes, a property with important implications in disorders such as cystic fibrosis (CF) and asthma. OBJECTIVE: We sought to examine the transcriptional and functional significance of macrophage repolarization from an M1 to an M2 phenotype and assess the role of a common human genetic disorder (CF) and a prototypical allergic disease (asthma) in this transformation. METHODS: Monocyte-derived macrophages were collected from healthy subjects and patients with CF and polarized to an M2 state by using IL-4, IL-10, glucocorticoids, apoptotic PMNs, or azithromycin. We performed transcriptional profiling and pathway analysis for each stimulus. We assessed the ability of M2-repolarized macrophages to respond to LPS rechallenge and clear apoptotic neutrophils and used murine models to determine conserved functional responses to IL-4 and IL-10. We investigated whether M2 signatures were associated with alveolar macrophage phenotypes in asthmatic patients. RESULTS: We found that macrophages exhibit highly diverse responses to distinct M2-polarizing stimuli. Specifically, IL-10 activated proinflammatory pathways and abrogated LPS tolerance, allowing rapid restoration of LPS responsiveness. In contrast, IL-4 enhanced LPS tolerance, dampening proinflammatory responses after repeat LPS challenge. A common theme observed across all M2 stimuli was suppression of interferon-associated pathways. We found that CF macrophages had intact reparative and transcriptional responses, suggesting that macrophage contributions to CF-related lung disease are primarily shaped by their environment. Finally, we leveraged in vitro-derived signatures to show that allergen provocation induces distinct M2 state transcriptional patterns in alveolar macrophages. CONCLUSION: Our findings highlight the diversity of macrophage polarization, attribute functional consequences to different M2 stimuli, and provide a framework to phenotype macrophages in disease states.

MEK1/2 Inhibition Promotes Macrophage Reparative Properties.

Macrophages have important functional roles in regulating the timely promotion and resolution of inflammation. Although many of the intracellular signaling pathways involved in the proinflammatory responses of macrophages are well characterized, the components that regulate macrophage reparative properties are less well understood. We identified the MEK1/2 pathway as a key regulator of macrophage reparative properties. Pharmacological inhibition of the MEK1/2 pathway by a MEK1/2 inhibitor (MEKi) significantly increased expression of IL-4/IL-13 (M2)-responsive genes in murine bone marrow-derived and alveolar macrophages. Deletion of the MEK1 gene using LysMCre+/+Mek1fl/fl macrophages as an alternate approach yielded similar results. MEKi enhanced STAT6 phosphorylation, and MEKi-induced changes in M2 polarization were dependent on STAT6. In addition, MEKi treatment significantly increased murine and human macrophage efferocytosis of apoptotic cells, independent of macrophage polarization and STAT6. These phenotypes were associated with increased gene and protein expression of Mertk, Tyro3, and Abca1, three proteins that promote macrophage efferocytosis. We also studied the effects of MEKi on in vivo macrophage efferocytosis and polarization. MEKi-treated mice had increased efferocytosis of apoptotic polymorphonuclear leukocytes instilled into the peritoneum. Furthermore, administration of MEKi after LPS-induced lung injury led to improved recovery of weight, fewer neutrophils in the alveolar compartment, and greater macrophage M2 polarization. Collectively, these results show that MEK1/2 inhibition is capable of promoting the reparative properties of murine and human macrophages. These studies suggest that the MEK1/2 pathway may be a therapeutic target to promote the resolution of inflammation via modulation of macrophage functions.

Stromelysin-2 (MMP10) Moderates Inflammation by Controlling Macrophage Activation.

Several members of the matrix metalloproteinase (MMP) family control a range of immune processes, such as leukocyte influx and chemokine activity. Stromelysin-2 (MMP10) is expressed by macrophages in numerous tissues after injury; however, little is known of its function. In this study, we report that MMP10 is expressed by macrophages in human lungs from patients with cystic fibrosis and induced in mouse macrophages in response to Pseudomonas aeruginosa infection both in vivo and by isolated resident alveolar and bone marrow-derived macrophages (BMDM). Our data indicates that macrophage MMP10 serves a beneficial function in response to acute infection. Whereas wild-type mice survived infection with minimal morbidity, 50% of Mmp10(-/-) mice died and all showed sustained weight loss (morbidity). Although bacterial clearance and neutrophil influx did not differ between genotypes, macrophage numbers were ∼3-fold greater in infected Mmp10(-/-) lungs than in wild-types. Adoptive transfer of wild-type BMDM normalized infection-induced morbidity in Mmp10(-/-) recipients to wild-type levels, demonstrating that the protective effect of MMP10 was due to its production by macrophages. Both in vivo and in cultured alveolar macrophages and BMDM, expression of several M1 macrophage markers was elevated, whereas M2 markers were reduced in Mmp10(-/-) tissue and cells. Global gene expression analysis revealed that infection-mediated transcriptional changes persisted in Mmp10(-/-) BMDM long after they were downregulated in wild-type cells. These results indicate that MMP10 serves a beneficial role in response to acute infection by moderating the proinflammatory response of resident and infiltrating macrophages.

MMP-10 Regulates Collagenolytic Activity of Alternatively Activated Resident Macrophages.

Matrix metalloproteinase-10 (MMP-10) is expressed by macrophages and epithelium in response to injury, but its functions in wound repair are unknown. We observed increased collagen deposition and skin stiffness in Mmp10(-/-) wounds, with no difference in collagen expression or reepithelialization. Increased collagen deposition in Mmp10(-/-) wounds was accompanied by less collagenolytic activity and reduced expression of specific metallocollagenases, particularly MMP-8 and MMP-13, where MMP-13 was the key collagenase. Ablation and adoptive transfer approaches and cell-based models demonstrated that the MMP-10-dependent collagenolytic activity was a product of alternatively activated (M2) resident macrophages. These data demonstrate a critical role for macrophage MMP-10 in controlling the tissue remodeling activity of macrophages and moderating scar formation during wound repair.

Amphiphilic polymer-coated CdSe/ZnS quantum dots induce pro-inflammatory cytokine expression in mouse lung epithelial cells and macrophages.

Quantum dots (Qdots) are semiconductor nanoparticles with size-tunable fluorescence capabilities with diverse applications. Qdots typically contain cadmium or other heavy metals, hence raising concerns of their potential toxicity, especially in occupational settings where inhalation of nanomaterials may increase the risk of lung disease. Accordingly, we assessed the effects of tri-n-octylphosphine oxide, poly(maleic anhydride-alt-1-tetradecene) (TOPO-PMAT) coated CdSe/ZnS Qdots on mouse lung epithelial cells and macrophages. Mouse tracheal epithelial cells (MTEC), grown as organotypic cultures, bone marrow-derived macrophages (BMDM), and primary alveolar macrophages (AM) were derived from C57BL/6J or A/J mice and treated with TOPO-PMAT CdSe/ZnS Qdots (10-160 nM) for up to 24 h. Cadmium analysis showed that Qdots remained in the apical compartment of MTEC cultures, whereas they were avidly internalized by AM and BMDM, which did not differ between strains. In MTEC, Qdots selectively induced expression (mRNA and protein) of neutrophil chemokines CXCL1 and CXCL2 but only low to no detectable levels of other factors assessed. In contrast, 4 h exposure to Qdots markedly increased expression of CXCL1, IL6, IL12, and other pro-inflammatory factors in BMDM. Higher inflammatory response was seen in C57BL/6J than in A/J BMDM. Similar expression responses were observed in AM, although overall levels were less robust than in BMDM. MTEC from A/J mice were more sensitive to Qdot pro-inflammatory effects while macrophages from C57BL/6J mice were more sensitive. These findings suggest that patterns of Qdot-induced pulmonary inflammation are likely to be cell-type specific and genetic background dependent.

In vitro approaches to assessing the toxicity of quantum dots.

Advances in nanotechnology have produced a new class of fluorescent nanoparticles known as quantum dots (Qdots). Compared with organic dyes and fluorescent proteins, Qdots offer several unique advantages in terms of spectral range, brightness, and photostability. Relative to other imaging modalities, optical imaging with Qdots is highly sensitive, quantitative, and capable of multiplexing. Thus, Qdots are being developed for a wide range of applications, including biomedical imaging. Qdot production has also emerged in a number of industrial applications, such as optoelectronic devices and photovoltaic cells. This widespread development and use of Qdots has outpaced research progress on their potential cytotoxicity, engendering major concerns surrounding occupational, environmental, and diagnostic exposures. Given the extensive physicochemical heterogeneity of Qdots (size, charge, chemical composition, solubility, etc.), high-throughput in vitro cytotoxicity assays represent a feasible means of determining effects of multiple variables and can inform design of lower-throughput in vivo cytotoxicity studies. Here, we describe the application of two commonly used assays, lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), for detection of Qdot-induced cytotoxicity.

A disintegrin and metalloproteinase 17 regulates TNF and TNFR1 levels in inflammation and liver regeneration in mice.

A disintegrin and metalloproteinase 17 (ADAM17), or tumor necrosis factor (TNF)-α-converting enzyme, is a key metalloproteinase and physiological convertase for a number of putative targets that play critical roles in cytokine and growth factor signaling. These interdependent pathways are essential components of the signaling network that links liver function with the compensatory growth that occurs during liver regeneration following 2/3 partial hepatectomy (PH) or chemically induced hepatotoxicity. Despite identification of many soluble factors needed for efficient liver regeneration, very little is known about how such ligands are regulated in the liver. To directly study the role of ADAM17 in the liver, we employed two cell-specific ADAM17 knockout (KO) mouse models. Using lipopolysaccharide (LPS) as a robust stimulus for TNF release, we found attenuated levels of circulating TNF in myeloid-specific ADAM17 KO mice (ADAM17 m-KO) and, unexpectedly, in mice with hepatocyte-specific ADAM17 deletion (ADAM17 h-KO), indicating that ADAM17 expression in both cell types plays a role in TNF shedding. After 2/3 PH, induction of TNF, TNFR1, and amphiregulin (AR) was significantly attenuated in ADAM17 h-KO mice, implicating ADAM17 as the primary sheddase for these factors in the liver. Surprisingly, the extent and timing of hepatocyte proliferation were not affected after PH or carbon tetrachloride injection in ADAM17 h-KO or ADAM17 m-KO mice. We conclude that ADAM17 regulates TNF, TNFR1, and AR in the liver, and its expression in both hepatocytes and myeloid cells is important for TNF regulation after LPS injury or 2/3 PH, but is not required for liver regeneration.

Sustained Glutathione Deficiency Interferes with the Liver Response to TNF-α and Liver Regeneration after Partial Hepatectomy in Mice.

Glutathione (GSH) is a critical intracellular antioxidant that is active in free radical scavenging and as a reducing equivalent in biological reactions. Recent studies have suggested that GSH can affect cellular function at the level of gene transcription as well, in particular by affecting NF-κB activation. Additionally, increased or decreased GSH levels in vitro have been tied to increased or decreased hepatocyte proliferation, respectively. Here, we investigated the effect of GSH on the liver's response to TNF-α injection and 2/3 partial hepatectomy (PH), using mice deficient for the modifier subunit of glutamate-cysteine ligase (GCLM), the rate-limiting enzyme in de novo GSH synthesis. We demonstrate that Gclm-/- mice have a delay in IκBα degradation after TNF-α injection, resulting in delayed NF-κB nuclear translocation. These mice display profound deficiencies in GSH levels both before and during regeneration, and after PH, Gclm-/- mice have an overall delay in cell cycle progression, with slower DNA synthesis, mitosis, and expression of cell cycle proteins. Moreover, there is a delay in expression of downstream targets of NF-κB in the regenerating liver in Gclm-/- mice. These data suggest that GSH may play a role in hepatic NF-κB activation in vivo, which is necessary for accurate timing of liver regeneration.

Toll-like receptor 4 and myeloid differentiation factor 88 provide mechanistic insights into the cause and effects of interleukin-6 activation in mouse liver regeneration.

UNLABELLED: Partial hepatectomy (PH) consistently results in an early increase of circulating interleukin-6 (IL-6), which is thought to play a major role in liver regeneration. Activation of this cytokine after PH requires the adaptor protein, MyD88, but the specific MyD88-related receptors involved remain unidentified. It is also unknown whether the magnitude of IL-6 elevation determines the extent of subsequent hepatocyte proliferation. Here, we uncovered artifacts in the assessment of circulating IL-6 levels when using cardiac puncture in mice after PH. By using retro-orbital bleed sampling, we show that the circulating levels of IL-6 after PH were not directly correlated with the extent of hepatocyte DNA synthesis in individual mice. The IL-6 increase after PH was attenuated in all lipopolysaccharide-hyporesponsive mouse strains studied (e.g., C3H/HeJ, Tlr4 null, Cd14 null, Tlr2,4,9 null, and Tlr2,4-Caspase1 null) and was severely abrogated in Myd88 null mice. Despite attenuated IL-6 levels, Tlr4 null mice showed normal signaling downstream of IL-6 and normal hepatocyte proliferation. In contrast, Myd88 null mice showed severe impairments in signal transducer and activator of transcription 3 phosphorylation and Socs3 induction, but had enhanced and prolonged extracellular signal-related kinase 1 and 2 phosphorylation in the first 6 hours after PH. Unexpectedly, these changes were associated with accelerated initiation of hepatocyte proliferation, as assessed by hepatocyte bromodeoxyuridine incorporation, phospho-histone H3 immunostaining, and cyclin E and A protein expression. CONCLUSION: TLR-4 signaling contributes to IL-6 activation after PH, but the Tlr4-independent component appears sufficient for ensuring intact signaling downstream of IL-6. The lack of correlation between IL-6 levels and hepatocyte proliferation after PH, and the accelerated start of hepatocyte proliferation in Myd88 null mice despite abrogated cytokine activation, may highlight relevant antiproliferative effects of IL-6 signaling, possibly via Socs3, in the regulation of liver regeneration.

Attenuated progression of diet-induced steatohepatitis in glutathione-deficient mice.

In nonalcoholic fatty liver disease (NAFLD), depletion of hepatic antioxidants may contribute to the progression of steatosis to nonalcoholic steatohepatitis (NASH) by increasing oxidative stress that produces lipid peroxidation, inflammation, and fibrosis. We investigated whether depletion of glutathione (GSH) increases NASH-associated hepatic pathology in mice fed a diet deficient in methionine and choline (MCD diet). Wild-type (wt) mice and genetically GSH-deficient mice lacking the modifier subunit of glutamate cysteine ligase (Gclm null mice), the rate-limiting enzyme for de novo synthesis of GSH, were fed the MCD diet, a methionine/choline-sufficient diet, or standard chow for 21 days. We assessed NASH-associated hepatic pathology, including steatosis, fibrosis, inflammation, and hepatocyte ballooning, and used the NAFLD Scoring System to evaluate the extent of changes. We measured triglyceride levels, determined the level of lipid peroxidation products, and measured by qPCR the expression of mRNAs for several proteins associated with lipid metabolism, oxidative stress, and fibrosis. MCD-fed GSH-deficient Gclm null mice were to a large extent protected from MCD diet-induced excessive fat accumulation, hepatocyte injury, inflammation, and fibrosis. Compared with wt animals, MCD-fed Gclm null mice had much lower levels of F2-isoprostanes, lower expression of acyl-CoA oxidase, carnitine palmitoyltransferase 1a, uncoupling protein-2, stearoyl-coenzyme A desaturase-1, transforming growth factor-ß, and plasminogen activator inhibitor-1 mRNAs, and higher activity of catalase, indicative of low oxidative stress, inhibition of triglyceride synthesis, and lower expression of profibrotic proteins. Global gene analysis of hepatic RNA showed that compared with wt mice, the livers of Gclm null mice have a high capacity to metabolize endogenous and exogenous compounds, have lower levels of lipogenic proteins, and increased antioxidant activity. Thus, metabolic adaptations resulting from severe GSH deficiency seem to protect against the development of steatohepatitis.

Relationships between deficits in tissue mass and transcriptional programs after partial hepatectomy in mice.

Liver regeneration after two-thirds partial hepatectomy (2/3 PH) results in synchronized proliferation of hepatocytes and rapid restoration of liver mass. Understanding the mechanisms that regulate this process has both biological and clinical importance. Using cDNA microarray analysis, we investigated whether gene activation after 2/3 PH is specifically related to liver growth and hepatocyte proliferation. We generated gene expression profiles at 4, 12, 20, and 30 hours after 2/3 PH and compared them with profiles obtained at the same time points after 1/3 PH, a procedure that causes minimal DNA replication. Surprisingly, a significant number of genes whose expression is altered after 2/3 PH are similarly up- or down-regulated after 1/3 PH, particularly at 4 hours. We identified a number of genes and transcription factors that are more highly expressed ("preferential expression") after 2/3 PH and show that a shift in transcriptional programs in the regenerating liver occurs between 4 and 12 hours after 2/3 PH, a time at which the decision to replicate appears to be made. These results show that the liver responds to PH with massive changes of gene expression, even in the absence of DNA replication. We suggest that the changes in gene expression during the first 4 to 6 hours after 2/3 PH may induce chromatin remodeling and facilitate the binding of new sets of transcription factors required for DNA replication.

Regulation of liver regeneration and hepatocarcinogenesis by suppressor of cytokine signaling 3.

Suppressor of cytokine signaling 3 (SOCS3) down-regulates several signaling pathways in multiple cell types, and previous data suggest that SOCS3 may shut off cytokine activation at the early stages of liver regeneration (Campbell, J.S., L. Prichard, F. Schaper, J. Schmitz, A. Stephenson-Famy, M.E. Rosenfeld, G.M. Argast, P.C. Heinrich, and N. Fausto. 2001.J. Clin. Invest. 107:1285-1292). We developed Socs3 hepatocyte-specific knockout (Socs3 h-KO) mice to directly study the role of SOCS3 during liver regeneration after a two-thirds partial hepatectomy (PH). Socs3 h-KO mice demonstrate marked enhancement of DNA replication and liver weight restoration after PH in comparison with littermate controls. Without SOCS3, signal transducer and activator of transcription 3 (STAT3) phosphorylation is prolonged, and activation of the mitogenic extracellular signal-regulated kinase 1/2 (ERK1/2) is enhanced after PH. In vitro, we show that SOCS3 deficiency enhances hepatocyte proliferation in association with enhanced STAT3 and ERK activation after epidermal growth factor or interleukin 6 stimulation. Microarray analyses show that SOCS3 modulates a distinct set of genes, which fall into diverse physiological categories, after PH. Using a model of chemical-induced carcinogenesis, we found that Socs3 h-KO mice develop hepatocellular carcinoma at an accelerated rate. By acting on cytokines and multiple proliferative pathways, SOCS3 modulates both physiological and neoplastic proliferative processes in the liver and may act as a tumor suppressor.