Uncontrolled macrophage activation is now considered to be a critical event in the pathogenesis of chronic inflammatory diseases such as atherosclerosis, multiple sclerosis, and chronic venous leg ulcers. However, it is still unclear which environmental cues induce persistent activation of macrophages in vivo and how macrophage-derived effector molecules maintain chronic inflammation and affect resident fibroblasts essential for tissue homeostasis and repair. We used a complementary approach studying human subjects with chronic venous leg ulcers, a model disease for macrophage-driven chronic inflammation, while establishing a mouse model closely reflecting its pathogenesis. Here, we have shown that iron overloading of macrophages — as was found to occur in human chronic venous leg ulcers and the mouse model — induced a macrophage population in situ with an unrestrained proinflammatory M1 activation state. Via enhanced TNF-α and hydroxyl radical release, this macrophage population perpetuated inflammation and induced a p16INK4a-dependent senescence program in resident fibroblasts, eventually leading to impaired wound healing. This study provides insight into the role of what we believe to be a previously undescribed iron-induced macrophage population in vivo. Targeting this population may hold promise for the development of novel therapies for chronic inflammatory diseases such as chronic venous leg ulcers.
Anca Sindrilaru, Thorsten Peters, Stefan Wieschalka, Corina Baican, Adrian Baican, Henriette Peter, Adelheid Hainzl, Susanne Schatz, Yu Qi, Andrea Schlecht, Johannes M. Weiss, Meinhard Wlaschek, Cord Sunderkötter, Karin Scharffetter-Kochanek
Activation of NF-κB and 5-lipoxygenase–mediated (5-LO–mediated) biosynthesis of the lipid mediator leukotriene B4 (LTB4) are pivotal components of host defense and inflammatory responses. However, the role of LTB4 in mediating innate immune responses elicited by specific TLR ligands and cytokines is unknown. Here we have shown that responses dependent on MyD88 (an adaptor protein that mediates signaling through all of the known TLRs, except TLR3, as well as IL-1β and IL-18) are reduced in mice lacking either 5-LO or the LTB4 receptor BTL1, and that macrophages from these mice are impaired in MyD88-dependent activation of NF-κB. This macrophage defect was associated with lower basal and inducible expression of MyD88 and reflected impaired activation of STAT1 and overexpression of the STAT1 inhibitor SOCS1. Expression of MyD88 and responsiveness to the TLR4 ligand LPS were decreased by Stat1 siRNA silencing in WT macrophages and restored by Socs1 siRNA in 5-LO–deficient macrophages. These results uncover a pivotal role in macrophages for the GPCR BLT1 in regulating activation of NF-κB through Stat1-dependent expression of MyD88.
Carlos H. Serezani, Casey Lewis, Sonia Jancar, Marc Peters-Golden
Granulocytes are pivotal regulators of tissue injury. However, the transcriptional mechanisms that regulate granulopoiesis under inflammatory conditions are poorly understood. Here we show that the transcriptional coregulator B cell leukemia/lymphoma 3 (Bcl3) limits granulopoiesis under emergency (i.e., inflammatory) conditions, but not homeostatic conditions. Treatment of mouse myeloid progenitors with G-CSF — serum concentrations of which rise under inflammatory conditions — rapidly increased Bcl3 transcript accumulation in a STAT3-dependent manner. Bcl3-deficient myeloid progenitors demonstrated an enhanced capacity to proliferate and differentiate into granulocytes following G-CSF stimulation, whereas the accumulation of Bcl3 protein attenuated granulopoiesis in an NF-κB p50–dependent manner. In a clinically relevant model of transplant-mediated lung ischemia reperfusion injury, expression of Bcl3 in recipients inhibited emergency granulopoiesis and limited acute graft damage. These data demonstrate a critical role for Bcl3 in regulating emergency granulopoiesis and suggest that targeting the differentiation of myeloid progenitors may be a therapeutic strategy for preventing inflammatory lung injury.
Daniel Kreisel, Seiichiro Sugimoto, Jeremy Tietjens, Jihong Zhu, Sumiharu Yamamoto, Alexander S. Krupnick, Ruaidhri J. Carmody, Andrew E. Gelman
Chong Chen, Yu Liu, Yang Liu, Pan Zheng
The alternative pathway (AP) of complement activation is constitutively active and must be regulated by host proteins to prevent autologous tissue injury. Dysfunction of AP regulatory proteins has been linked to several human inflammatory disorders. Properdin is a positive regulator of AP complement activation that has been shown to extend the half-life of cell surface–bound C3 convertase C3bBb; it may also initiate AP complement activation. Here, we demonstrate a critical role for properdin in autologous tissue injury mediated by AP complement activation. We identified myeloid lineage cells as the principal source of plasma properdin by generating mice with global and tissue-specific knockout of Cfp (which encodes properdin) and by generating BM chimeric mice. Properdin deficiency rescued mice from AP complement–mediated embryonic lethality caused by deficiency of the membrane complement regulator Crry and markedly reduced disease severity in the K/BxN model of arthritis. Ab neutralization of properdin in WT mice similarly ameliorated arthritis development, whereas reconstitution of properdin-null mice with exogenous properdin restored arthritis sensitivity. These data implicate systemic properdin as a key contributor to AP complement–mediated injury and support its therapeutic targeting in complement-dependent human diseases.
Yuko Kimura, Lin Zhou, Takashi Miwa, Wen-Chao Song
Hepcidin is a peptide hormone that regulates iron homeostasis and acts as an antimicrobial peptide. It is expressed and secreted by a variety of cell types in response to iron loading and inflammation. Hepcidin mediates iron homeostasis by binding to the iron exporter ferroportin, inducing its internalization and degradation via activation of the protein kinase Jak2 and the subsequent phosphorylation of ferroportin. Here we have shown that hepcidin-activated Jak2 also phosphorylates the transcription factor Stat3, resulting in a transcriptional response. Hepcidin treatment of ferroportin-expressing mouse macrophages showed changes in mRNA expression levels of a wide variety of genes. The changes in transcript levels for half of these genes were a direct effect of hepcidin, as shown by cycloheximide insensitivity, and dependent on the presence of Stat3. Hepcidin-mediated transcriptional changes modulated LPS-induced transcription in both cultured macrophages and in vivo mouse models, as demonstrated by suppression of IL-6 and TNF-α transcript and secreted protein. Hepcidin-mediated transcription in mice also suppressed toxicity and morbidity due to single doses of LPS, poly(I:C), and turpentine, which is used to model chronic inflammatory disease. Most notably, we demonstrated that hepcidin pretreatment protected mice from a lethal dose of LPS and that hepcidin-knockout mice could be rescued from LPS toxicity by injection of hepcidin. The results of our study suggest a new function for hepcidin in modulating acute inflammatory responses.
Ivana De Domenico, Tian Y. Zhang, Curry L. Koening, Ryan W. Branch, Nyall London, Eric Lo, Raymond A. Daynes, James P. Kushner, Dean Li, Diane M. Ward, Jerry Kaplan
HSCs are BM-derived, self-renewing multipotent cells that develop into circulating blood cells. They have been implicated in the repair of inflamed parenchymal tissue, but the signals that regulate their trafficking to sites of inflammation are unknown. As monocytes are recruited to sites of inflammation via chemoattractants that activate CCR2 on their surface, we investigated whether HSCs are also recruited to sites of inflammation through CCR2. Initial analysis indicated that in mice, CCR2 was expressed on subsets of HSCs and hematopoietic progenitor cells (HPCs) and that freshly isolated primitive hematopoietic cells (Lin–c-Kit+ cells) responded to CCR2 ligands in vitro. In vivo analysis indicated that after instillation of thioglycollate to cause aseptic inflammation and after administration of acetaminophen to induce liver damage, endogenous HSCs/HPCs were actively recruited to the peritoneum and liver, respectively, in WT but not Ccr2–/– mice. HSCs/HPCs recovered from the peritoneum successfully engrafted into the BM of irradiated primary and secondary recipients, confirming their self renewal and multipotency. Importantly, administration of exogenous WT, but not Ccr2–/–, HSCs/HPCs accelerated resolution of acetaminophen-induced liver damage and triggered the expression of genes characteristic of the macrophage M2 or repair phenotype. These findings reveal what we believe to be a novel role for CCR2 in the homing of HSCs/HPCs to sites of inflammation and suggest new functions for chemokines in promoting tissue repair and regeneration.
Yue Si, Chia-Lin Tsou, Kelsey Croft, Israel F. Charo
Down syndrome critical region gene 1 (DSCR-1) short variant (DSCR-1s) is an inhibitor of calcineurin/NFAT signaling encoded by exons 4–7 of DSCR1. We previously reported that VEGF induces DSCR-1s expression in endothelial cells, which in turn negatively feeds back to attenuate endothelial cell activation. Here, in order to characterize the role of the promoter that drives DSCR-1s expression in mediating inducible expression in vivo and to determine the functional relevance of DSCR-1s in inflammation, we targeted a DNA construct containing 1.7 kb of the human DSCR1s promoter coupled to the lacZ reporter to the hypoxanthine guanine phosphoribosyl transferase (Hprt) locus of mice. We determined that lacZ was uniformly expressed in the endothelium of transgenic embryos but was markedly downregulated postnatally. Systemic administration of VEGF or LPS in adult mice resulted in cyclosporine A–sensitive reactivation of the DSCR1s promoter and endogenous gene expression in a subset of organs, including the heart and brain. The DSCR1s promoter was similarly induced in the endothelium of tumor xenografts. In a mouse model of endotoxemia, DSCR-1s–deficient mice demonstrated increased sepsis mortality, whereas adenovirus-mediated DSCR-1s overexpression protected against LPS-induced lethality. Collectively, these data suggest that the DSCR1s promoter directs vascular bed–specific expression in activated endothelium and that DSCR-1s serves to dampen the host response to infection.
Takashi Minami, Kiichiro Yano, Mai Miura, Mika Kobayashi, Jun-ichi Suehiro, Patrick C. Reid, Takao Hamakubo, Sandra Ryeom, William C. Aird, Tatsuhiko Kodama
Mucosal diseases are often characterized by an inflammatory infiltrate that includes polymorphonuclear leukocytes (PMNs), monocytes, lymphocytes, and platelets. A number of studies have suggested that the interaction of platelets with leukocytes has an essential proinflammatory role. Here, we examined whether platelets migrate across mucosal epithelium, as PMNs are known to do, and whether platelets influence epithelial cell function. Initial studies revealed that human platelets did not efficiently transmigrate across human epithelial cell monolayers. However, in the presence of human PMNs, platelet movement across the epithelium was proportional to the extent of PMN transmigration, and strategies that blocked PMN transmigration diminished platelet movement. Furthermore, platelet-PMN comigration was observed in intestinal tissue derived from human patients with inflammatory bowel disease (IBD). The translocated platelets were found to release large quantities of ATP, which was metabolized to adenosine via a 2-step enzymatic reaction mediated by ecto-nucleotidases, including CD73 and ecto–nucleoside triphosphate diphosphohydrolases (ecto-NTPDases), expressed on the apical membrane of the intestinal epithelial cells. In vitro studies and a mouse model of intestinal inflammation were employed to define a mechanism involving adenosine-mediated induction of electrogenic chloride secretion, with concomitant water movement into the intestinal lumen. These studies demonstrate that ecto-NTPDases are expressed on the apical membrane of epithelial cells and are involved in what we believe to be a previously unappreciated function for platelets in the inflamed intestine, which might promote bacterial clearance under inflammatory conditions.
Thomas Weissmüller, Eric L. Campbell, Peter Rosenberger, Melanie Scully, Paul L. Beck, Glenn T. Furuta, Sean P. Colgan
Inflammation plays a critical role in the development of cardiovascular diseases. Infiltration of leukocytes to sites of injury requires their exit from the blood and migration across basement membrane; this process has been postulated to require remodeling of the ECM. Plasminogen (Plg) is a protease that binds to the ECM and, upon conversion to plasmin, degrades multiple ECM proteins. In addition, plasmin directly activates MMPs. Here, we used Plg–/– mice to investigate the role of Plg in inflammatory leukocyte migration. After induction of peritonitis by thioglycollate injection, we found that Plg–/– mice displayed diminished macrophage trans-ECM migration and decreased MMP-9 activation. Furthermore, injection of the active form of MMP-9 in Plg–/– mice rescued macrophage migration in this model. We used periaortic application of CaCl2 to induce abdominal aortic aneurysm (AAA) and found that Plg–/– mice displayed reduced macrophage infiltration and were protected from aneurysm formation. Administration of active MMP-9 to Plg–/– mice promoted macrophage infiltration and the development of AAA. These data suggest that Plg regulates macrophage migration in inflammation via activation of MMP-9, which, in turn, regulates the ability of the cells to migrate across ECM. Thus, targeting the Plg/MMP-9 pathway may be an attractive approach to regulate inflammatory responses and AAA development.
Yanqing Gong, Erika Hart, Aleksey Shchurin, Jane Hoover-Plow
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