Cholesterol Crystals Activate the Lectin Complement Pathway via Ficolin-2 and Mannose-Binding Lectin: Implications for the Progression of Atherosclerosis.

Cholesterol crystals (CC) play an essential role in the formation of atherosclerotic plaques. CC activate the classical and the alternative complement pathways, but the role of the lectin pathway is unknown. We hypothesized that the pattern recognition molecules (PRMs) from the lectin pathway bind CC and function as an upstream innate inflammatory signal in the pathophysiology of atherosclerosis. We investigated the binding of the PRMs mannose-binding lectin (MBL), ficolin-1, ficolin-2, and ficolin-3, the associated serine proteases, and complement activation products to CC in vitro using recombinant proteins, specific inhibitors, as well as deficient and normal sera. Additionally, we examined the deposition of ficolin-2 and MBL in human carotid plaques by immunohistochemistry and fluorescence microscopy. The results showed that the lectin pathway was activated on CC by binding of ficolin-2 and MBL in vitro, resulting in activation and deposition of complement activation products. MBL bound to CC in a calcium-dependent manner whereas ficolin-2 binding was calcium-independent. No binding was observed for ficolin-1 or ficolin-3. MBL and ficolin-2 were present in human carotid plaques, and binding of MBL to CC was confirmed in vivo by immunohistochemistry, showing localization of MBL around CC clefts. Moreover, we demonstrated that IgM, but not IgG, bound to CC in vitro and that C1q binding was facilitated by IgM. In conclusion, our study demonstrates that PRMs from the lectin pathway recognize CC and provides evidence for an important role for this pathway in the inflammatory response induced by CC in the pathophysiology of atherosclerosis.

Human mannose-binding lectin inhibitor prevents Shiga toxin-induced renal injury.

Hemolytic uremic syndrome caused by Shiga toxin-producing Escherichia coli (STEC HUS) is a worldwide endemic problem, and its pathophysiology is not fully elucidated. Here we tested whether the mannose-binding lectin (MBL2), an initiating factor of lectin complement pathway activation, plays a crucial role in STEC HUS. Using novel human MBL2-expressing mice (MBL2 KI) that lack murine Mbls (MBL2(+/+)Mbl1(-/-)Mbl2(-/-)), a novel STEC HUS model consisted of an intraperitoneal injection with Shiga toxin-2 (Stx-2) with or without anti-MBL2 antibody (3F8, intraperitoneal). Stx-2 induced weight loss, anemia, and thrombocytopenia and increased serum creatinine, free serum hemoglobin, and cystatin C levels, but a significantly decreased glomerular filtration rate compared with control/sham mice. Immunohistochemical staining revealed renal C3d deposition and fibrin deposition in glomeruli in Stx-2-injected mice. Treatment with 3F8 completely inhibited serum MBL2 levels and significantly attenuated Stx-2 induced-renal injury, free serum hemoglobin levels, renal C3d, and fibrin deposition and preserved the glomerular filtration rate. Thus, MBL2 inhibition significantly protected against complement activation and renal injury induced by Stx-2. This novel mouse model can be used to study the role of complement, particularly lectin pathway-mediated complement activation, in Stx-2-induced renal injury.

Human mannose-binding lectin inhibitor prevents myocardial injury and arterial thrombogenesis in a novel animal model.

Myocardial infarction and coagulation disorders are leading causes of disability and death in the world. An important role of the lectin complement pathway in myocardial infarction and coagulation has been demonstrated in mice genetically deficient in lectin complement pathway proteins. However, these studies are limited to comparisons between wild-type and deficient mice and lack the ability to examine reversal/inhibition of injury after disease establishment. We developed a novel mouse that expresses functional human mannose-binding lectin (MBL) 2 under the control of Mbl1 promoter. Serum MBL2 concentrations averaged approximately 3 µg/mL in MBL2(+/+)Mbl1(-/-)Mbl2(-/-) [MBL2 knock in (KI)] mice. Serum MBL2 level in MBL2 KI mice significantly increased after 7 (8 µg/mL) or 14 (9 µg/mL) days of hyperglycemia compared to normoglycemic mice (P < 0.001). Monoclonal antibody 3F8 inhibited C3 deposition on mannan-coated plates in MBL2 KI, but not wild-type, mice. Myocardial ischemia/reperfusion in MBL2 KI mice revealed that 3F8 preserved cardiac function and decreased infarct size and fibrin deposition in a time-dependent manner. Furthermore, 3F8 prevented ferric chloride-induced occlusive arterial thrombogenesis in vivo. MBL2 KI mice represent a novel animal model that can be used to study the lectin complement pathway in acute and chronic models of human disease. Furthermore, these novel mice demonstrate the therapeutic window for MBL2 inhibition for effective treatment of disease and its complications.

Complement inhibition prevents oncolytic vaccinia virus neutralization in immune humans and cynomolgus macaques.

Oncolytic viruses (OVs) have shown promising clinical activity when administered by direct intratumoral injection. However, natural barriers in the blood, including antibodies and complement, are likely to limit the ability to repeatedly administer OVs by the intravenous route. We demonstrate here that for a prototype of the clinical vaccinia virus based product Pexa-Vec, the neutralizing activity of antibodies elicited by smallpox vaccination, as well as the anamnestic response in hyperimmune virus treated cancer patients, is strictly dependent on the activation of complement. In immunized rats, complement depletion stabilized vaccinia virus in the blood and led to improved delivery to tumors. Complement depletion also enhanced tumor infection when virus was directly injected into tumors in immunized animals. The feasibility and safety of using a complement inhibitor, CP40, in combination with vaccinia virus was tested in cynomolgus macaques. CP40 pretreatment elicited an average 10-fold increase in infectious titer in the blood early after the infusion and prolonged the time during which infectious virus was detectable in the blood of animals with preexisting immunity. Capitalizing on the complement dependence of antivaccinia antibody with adjunct complement inhibitors may increase the infectious dose of oncolytic vaccinia virus delivered to tumors in virus in immune hosts.

The alternative complement pathway regulates pathological angiogenesis in the retina.

A defining feature in proliferative retinopathies is the formation of pathological neovessels. In these diseases, the balance between neovessel formation and regression determines blindness, making the modulation of neovessel growth highly desirable. The role of the immune system in these retinopathies is of increasing interest, but it is not completely understood. We investigated the role of the alternative complement pathway during the formation and resolution of aberrant neovascularization. We used alternative complement pathway-deficient (Fb(-/-)) mice and age- and strain-matched control mice to assess neovessel development and regression in an oxygen-induced retinopathy (OIR) mouse model. In the control mice, we found increased transcription of Fb after OIR treatment. In the Fb(-/-) mice, we prepared retinal flatmounts and identified an increased number of neovessels, peaking at postnatal day 17 (P17; P=0.001). Subjecting human umbilical vein endothelial cells (HUVECs) to low oxygen, mimicking a characteristic of neovessels, decreased the expression of the complement inhibitor Cd55. Finally, using laser capture microdissection (LCM) to isolate the neovessels after OIR, we found decreased expression of Cd55 (P=0.005). Together, our data implicate the alternative complement pathway in facilitating neovessel clearance by down-regulating the complement inhibitor Cd55 specifically on neovessels, allowing for their targeted removal while leaving the established vasculature intact.-Sweigard, J. H., Yanai, R., Gaissert, P., Saint-Geniez, M., Kataoka, K., Thanos, A., Stahl, G. L., Lambris, J. D., Connor, K. M. The alternative complement pathway regulates pathological angiogenesis in the retina.

Roles of adipocytes and fibroblasts in activation of the alternative pathway of complement in inflammatory arthritis in mice.

The complement system is involved in mediation of joint damage in rheumatoid arthritis, with evidence suggesting activation of both the classical and alternative pathway (AP). The AP is both necessary and sufficient to mediate collagen Ab-induced arthritis, an experimental animal model of immune complex-induced joint disease. The AP in mice is dependent on MASP-1/3 cleavage of pro-factor D (pro-FD) into mature factor D (FD). The objectives of the current study were to determine the cells synthesizing MASP-1/3 and pro-FD in synovial tissue. Collagen Ab-induced arthritis was studied in wild-type C57BL/6 mice, and the localization of mRNA and protein for FD and MASP-1/3 in synovial adipose tissue (SAT) and fibroblast-like synoviocytes (FLS) was determined using various techniques, including laser capture microdissection. SAT was the sole source of mRNA for pro-FD. Cultured differentiated 3T3 adipocytes, a surrogate for SAT, produced pro-FD but no mature FD. FLS were the main source of MASP-1/3 mRNA and protein. Using cartilage microparticles (CMPs) coated with anti-collagen mAb and serum from MASP-1/3(-/-) mice as a source of factor B, pro-FD in 3T3 supernatants was cleaved into mature FD by MASP-1/3 in FLS supernatants. The mature FD was eluted from the CMP, and was not present in the supernatants from the incubation with CMP, indicating that cleavage of pro-FD into mature FD by MASP-1 occurred on the CMP. These results demonstrate that pathogenic activation of the AP can occur in the joint through immune complexes adherent to cartilage and the local production of necessary AP proteins by adipocytes and FLS.

The lectin pathway of complement activation is a critical component of the innate immune response to pneumococcal infection.

The complement system plays a key role in host defense against pneumococcal infection. Three different pathways, the classical, alternative and lectin pathways, mediate complement activation. While there is limited information available on the roles of the classical and the alternative activation pathways of complement in fighting streptococcal infection, little is known about the role of the lectin pathway, mainly due to the lack of appropriate experimental models of lectin pathway deficiency. We have recently established a mouse strain deficient of the lectin pathway effector enzyme mannan-binding lectin associated serine protease-2 (MASP-2) and shown that this mouse strain is unable to form the lectin pathway specific C3 and C5 convertases. Here we report that MASP-2 deficient mice (which can still activate complement via the classical pathway and the alternative pathway) are highly susceptible to pneumococcal infection and fail to opsonize Streptococcus pneumoniae in the none-immune host. This defect in complement opsonisation severely compromises pathogen clearance in the lectin pathway deficient host. Using sera from mice and humans with defined complement deficiencies, we demonstrate that mouse ficolin A, human L-ficolin, and collectin 11 in both species, but not mannan-binding lectin (MBL), are the pattern recognition molecules that drive lectin pathway activation on the surface of S. pneumoniae. We further show that pneumococcal opsonisation via the lectin pathway can proceed in the absence of C4. This study corroborates the essential function of MASP-2 in the lectin pathway and highlights the importance of MBL-independent lectin pathway activation in the host defense against pneumococci.

The role of properdin in zymosan- and Escherichia coli-induced complement activation.

Properdin is well known as an enhancer of the alternative complement amplification loop when C3 is activated, whereas its role as a recognition molecule of exogenous pathogen-associated molecular patterns and initiator of complement activation is less understood. We therefore studied the role of properdin in activation of complement in normal human serum by zymosan and various Escherichia coli strains. In ELISA, microtiter plates coated with zymosan induced efficient complement activation with deposition of C4b and terminal complement complex on the solid phase. Virtually no deposition of C4b or terminal complement complex was observed with mannose-binding lectin (MBL)-deficient serum. Reconstitution with purified MBL showed distinct activation in both readouts. In ELISA, normal human serum-induced deposition of properdin by zymosan was abolished by the C3-inhibiting peptide compstatin. Flow cytometry was used to further explore whether properdin acts as an initial recognition molecule reacting directly with zymosan and three E. coli strains. Experiments reported by other authors were made with EGTA Mg²âº buffer, permitting autoactivation of C3. We found inhibition by compstatin on these substrates, indicating that properdin deposition depended on initial C3b deposition followed by properdin in a second step. Properdin released from human polymorphonuclear cells stimulated with PMA did not bind to zymosan or E. coli, but when incubated in properdin-depleted serum this form of properdin bound efficiently to both substrates in a strictly C3-dependent manner, as the binding was abolished by compstatin. Collectively, these data indicate that properdin in serum as well as polymorphonuclear-released properdin is unable to bind and initiate direct alternative pathway activation on these substrates.

Mannose-binding lectin-associated serine protease-1 is a significant contributor to coagulation in a murine model of occlusive thrombosis.

Bleeding disorders and thrombotic complications constitute a major cause of death and disability worldwide. Although it is known that the complement and coagulation systems interact, no studies have investigated the specific role or mechanisms of lectin-mediated coagulation in vivo. FeCl(3) treatment resulted in intra-arterial occlusive thrombogenesis within 10 min in wild-type (WT) and C2/factor B-null mice. In contrast, mannose-binding lectin (MBL)-null and MBL-associated serine protease (MASP)-1/-3 knockout (KO) mice had significantly decreased FeCl(3)-induced thrombogenesis. Reconstitution with recombinant human (rh) MBL restored FeCl(3)-induced thrombogenesis in MBL-null mice to levels comparable to WT mice, suggesting a significant role of the MBL/MASP complex for in vivo coagulation. Additionally, whole blood aggregation demonstrated increased MBL/MASP complex-dependent platelet aggregation. In vitro, MBL/MASP complexes were captured on mannan-coated plates, and cleavage of a chromogenic thrombin substrate (S2238) was measured. We observed no significant differences in S2238 cleavage between WT, C2/factor B-null, MBL-A(-/-), or MBL-C(-/-) sera; however, MBL-null or MASP-1/-3 KO mouse sera demonstrated significantly decreased S2238 cleavage. rhMBL alone failed to cleave S2238, but cleavage was restored when rMASP-1 was added to either MASP-1/-3 KO sera or rhMBL. Taken together, these findings indicate that MBL/MASP complexes, and specifically MASP-1, play a key role in thrombus formation in vitro and in vivo.

The alternative complement pathway propagates inflammation and injury in murine ischemic stroke.

There is mounting evidence indicating an important role for complement in the pathogenesis of cerebral ischemia-reperfusion injury, or ischemic stroke. The role of the alternative complement pathway in ischemic stroke has not been investigated, and there is conflicting data on the role of the terminal pathway. In this study, we show that compared with wild-type mice, mice deficient in the alternative pathway protein factor B or mice treated with the alternative pathway inhibitor CR2-fH have improved outcomes after 60-min middle cerebral artery occlusion and 24-h reperfusion. Factor B-deficient or CR2-fH-treated mice were protected in terms of improved neurologic function and reduced cerebral infarct, demyelination, P-selectin expression, neutrophil infiltration, and microthrombi formation. Mice deficient in both the classical and lectin pathways (C1q/MBL deficient) were also protected from cerebral ischemia-reperfusion injury, and there was no detectable C3d deposition in the ipsilateral brain of these mice. These data demonstrate that the alternative pathway is not alone sufficient to initiate complement activation and indicate that the alternative pathway propagates cerebral injury via amplification of the cascade. Deficiency of C6, a component of the terminal cytolytic membrane attack complex, had no effect on outcome after ischemic stroke, indicating that the membrane attack complex is not involved in mediating injury in this model. We additionally show that the protective effect of factor B deficiency and CR2-fH treatment is sustained in the subacute stage of infarct development, adding to the clinical relevance of these findings.

Role of C3a receptors, C5a receptors, and complement protein C6 deficiency in collagen antibody-induced arthritis in mice.

The complement system, especially the alternative pathway, plays essential roles in the induction of injury in collagen Ab-induced arthritis (CAIA) in mice. The goal of the current study was to directly compare the roles of receptors for C3a and C5a, as well as the membrane attack complex, as effector mechanisms in the pathogenesis of CAIA. Clinical disease activity in C3aR(-/-), C5aR(-/-), and C6-deficient (C6-def) mice was decreased by 52, 94, and 65%, respectively, as compared with wild-type mice. Decreases in histopathologic injury as well as in IgG and C3 deposition paralleled the clinical disease activity. A decrease in the percentage of synovial neutrophils was observed in C3aR(-/-), C5aR(-/-), and C6-def mice, and a decrease in macrophages was observed in C3aR(-/-) and C5aR(-/-), but not in C6-def, mice. Synovial mRNA obtained by laser capture microdissection exhibited a decrease in TNF-α in C5aR(-/-) mice and in IL-1ß in both C5aR(-/-) and C6-def mice, whereas C3aR(-/-) mice demonstrated no change in either cytokine. Our findings show that absent C3aR-, C5aR-, or membrane attack complex-initiated effector mechanisms each decrease susceptibility to CAIA, with clinical effects most pronounced in C5aR-deficient mice. Although the absence of C3aR, C5aR, or C6 led to differential deficiencies in effector mechanisms, decreased proximal joint IgG and C3 deposition was common to all three genotypes in comparison with wild-type mice. These data suggest the existence of positive-feedback amplification pathways downstream of all three effectors that promote additional IgG deposition and C3 activation in the joint.

Endogenous and natural complement inhibitor attenuates myocardial injury and arterial thrombogenesis.

BACKGROUND: Coagulation disorders and reperfusion of ischemic myocardium are major causes of morbidity and mortality. Lectin pathway initiation complexes are composed of multimolecular carbohydrate recognition subcomponents and 3 lectin pathway-specific serine proteases. We have recently shown that the lectin pathway-specific carbohydrate recognition subcomponent mannose-binding lectin plays an essential role in the pathophysiology of thrombosis and ischemia/reperfusion injury. Thus, we hypothesized that the endogenous mannose-binding lectin (MBL)/ficolin-associated protein-1 (MAP-1) that inhibits complement activation in vitro also could be an in vivo regulator by attenuating myocardial schema/reperfusion injury and thrombogenesis when used at pharmacological doses in wild-type mice. METHODS AND RESULTS: In 2 mouse models, MAP-1 preserves cardiac function, decreases infarct size, decreases C3 deposition, inhibits MBL deposition, and prevents thrombogenesis. Furthermore, we demonstrate that MAP-1 displaces MBL/ficolin-associated serine protease (MASP)-1, MASP-2, and MASP-3 from the MBL complex. CONCLUSIONS: Our results suggest that the natural, endogenous inhibitor MAP-1 effectively inhibits lectin pathway activation in vivo. MAP-1 at pharmacological doses represents a novel therapeutic approach for human diseases involving the lectin pathway and its associated MASPs.

Targeting mannose-binding lectin confers long-lasting protection with a surprisingly wide therapeutic window in cerebral ischemia.

BACKGROUND: The involvement of the complement system in brain injury has been scarcely investigated. Here, we document the pivotal role of mannose-binding lectin (MBL), one of the recognition molecules of the lectin complement pathway, in brain ischemic injury. METHODS AND RESULTS: Focal cerebral ischemia was induced in mice (by permanent or transient middle cerebral artery occlusion) and rats (by 3-vessel occlusion). We first observed that MBL is deposited on ischemic vessels up to 48 hours after injury and that functional MBL/MBL-associated serine protease 2 complexes are increased. Next, we demonstrated that (1) MBL(-/-) mice are protected from both transient and permanent ischemic injury; (2) Polyman2, the newly synthesized mannosylated molecule selected for its binding to MBL, improves neurological deficits and infarct volume when given up to 24 hours after ischemia in mice; (3) anti-MBL-A antibody improves neurological deficits and infarct volume when given up to 18 hours after ischemia, as assessed after 28 days in rats. CONCLUSIONS: Our data show an important role for MBL in the pathogenesis of brain ischemic injury and provide a strong support to the concept that MBL inhibition may be a relevant therapeutic target in humans, one with a wide therapeutic window of application.

Absence of mannose-binding lectin prevents hyperglycemic cardiovascular complications.

Diabetes, stress, pharmaceuticals, surgery, and physical trauma can lead to hyperglycemic conditions. A consistent relationship has been found between chronic inflammation and the cardiovascular complications of hyperglycemia. We hypothesized that cardiomyopathy and vasculopathy resulting from acute hyperglycemia are dependent on mannose-binding lectin (MBL) and lectin complement pathway activation. Hyperglycemia was induced in wild-type (WT) C57BL/6 and MBL-null mice after streptozotocin administration. Echocardiographic data and tissue samples were collected after 4, 7, or 14 days of acute hyperglycemia. Hyperglycemic WT mice demonstrated dilated cardiomyopathy with significantly increased short and long axis area measurements during systole and diastole compared to hyperglycemic MBL-null mice. The EC(50) for acetylcholine-induced relaxation of mesenteric arterioles in WT mice after 4 days of hyperglycemia demonstrated a significant loss of nitric oxide-mediated relaxation compared to normoglycemic WT or hyperglycemic MBL-null mice. Myocardial histochemistry and Western blot analysis revealed a significant influx of macrophages, altered morphology, and increased elastin and collagen deposition in hyperglycemic WT hearts compared to MBL-null hearts. Serum transforming growth factor-ß1 levels were significantly lower in hyperglycemic MBL-null compared to WT mice, suggesting decreased profibrotic signaling. Together, these data suggest that MBL and the lectin complement pathway play a significant role in vascular dysfunction and cardiomyopathy after acute hyperglycemia.

Distinct different contributions of the alternative and classical complement activation pathway for the innate host response during sepsis.

Complement activation represents a crucial innate defense mechanism to invading microorganisms, but there is an eminent lack of understanding of the separate contribution of the different complement activation pathways to the host response during sepsis. We therefore investigated different innate host immune responses during cecal ligation and puncture (CLP)-induced sepsis in mice lacking either the alternative (fD(-/-)) or classical (C1q(-/-)) complement activation pathway. Both knockout mice strains showed a significantly reduced survival and increased organ dysfunction when compared with control mice. Surprisingly, fD(-/-) mice demonstrated a compensated bacterial clearance capacity as control mice at 6 h post CLP, whereas C1q(-/-) mice were already overwhelmed by bacterial growth at this time point. Interestingly, at 24 h after CLP, fD(-/-) mice failed to clear bacteria in a way comparable to control mice. However, both knockout mice strains showed compromised C3 cleavage during sepsis. Investigating potential causes for this discrepancy, we were able to demonstrate that despite normal bacterial clearance capacity early during the onset of sepsis, fD(-/-) mice displayed increased inflammatory cytokine generation and neutrophil recruitment into lungs and blood when compared with both control- and C1q(-/-) mice, indicating a potential loss of control over these immune responses. Further in vitro experiments revealed a strongly increased Nf-κB activation capacity in isolated neutrophils from fD(-/-) mice, supporting this hypothesis. Our results provide evidence for the new concept that the alternative complement activation pathway exerts a distinctly different contribution to the innate host response during sepsis when compared with the classical pathway.

Identification of a cytochrome P4502E1/Bid/C1q-dependent axis mediating inflammation in adipose tissue after chronic ethanol feeding to mice.

Chronic, heavy alcohol exposure results in inflammation in adipose tissue, insulin resistance, and liver injury. Here we have identified a CYP2E1/Bid/C1q-dependent pathway that is activated in response to chronic ethanol and is required for the development of inflammation in adipose tissue. Ethanol feeding for 25 days to wild-type (C57BL/6J) mice increased expression of multiple markers of adipose tissue inflammation relative to pair-fed controls independent of increased body weight or adipocyte size. Ethanol feeding increased the expression of CYP2E1 in adipocytes, but not stromal vascular cells, in adipose tissue and Cyp2e1(-/-) mice were protected from adipose tissue inflammation in response to ethanol. Ethanol feeding also increased the number of TUNEL-positive nuclei in adipose tissue of wild-type mice but not in Cyp2e1(-/-) or Bid (-/-) mice. Apoptosis contributed to adipose inflammation, as the expression of multiple inflammatory markers was decreased in mice lacking the Bid-dependent apoptotic pathway. The complement protein C1q binds to apoptotic cells, facilitating their clearance and activating complement. Making use of C1q-deficient mice, we found that activation of complement via C1q provided the critical link between CYP2E1/Bid-dependent apoptosis and onset of adipose tissue inflammation in response to chronic ethanol. In summary, chronic ethanol increases CYP2E1 activity in adipose, leading to Bid-mediated apoptosis and activation of complement via C1q, finally resulting in adipose tissue inflammation. Taken together, these data identify a novel mechanism for the development of adipose tissue inflammation that likely contributes to the pathophysiological effects of ethanol.

Genetic ablation or chemical inhibition of phosphatidylcholine transfer protein attenuates diet-induced hepatic glucose production.

UNLABELLED: Phosphatidylcholine transfer protein (PC-TP, synonym StARD2) is a highly specific intracellular lipid binding protein that is enriched in liver. Coding region polymorphisms in both humans and mice appear to confer protection against measures of insulin resistance. The current study was designed to test the hypotheses that Pctp-/- mice are protected against diet-induced increases in hepatic glucose production and that small molecule inhibition of PC-TP recapitulates this phenotype. Pctp-/- and wildtype mice were subjected to high-fat feeding and rates of hepatic glucose production and glucose clearance were quantified by hyperinsulinemic euglycemic clamp studies and pyruvate tolerance tests. These studies revealed that high-fat diet-induced increases in hepatic glucose production were markedly attenuated in Pctp-/- mice. Small molecule inhibitors of PC-TP were synthesized and their potencies, as well as mechanism of inhibition, were characterized in vitro. An optimized inhibitor was administered to high-fat-fed mice and used to explore effects on insulin signaling in cell culture systems. Small molecule inhibitors bound PC-TP, displaced phosphatidylcholines from the lipid binding site, and increased the thermal stability of the protein. Administration of the optimized inhibitor to wildtype mice attenuated hepatic glucose production associated with high-fat feeding, but had no activity in Pctp-/- mice. Indicative of a mechanism for reducing glucose intolerance that is distinct from commonly utilized insulin-sensitizing agents, the inhibitor promoted insulin-independent phosphorylation of key insulin signaling molecules. CONCLUSION: These findings suggest PC-TP inhibition as a novel therapeutic strategy in the management of hepatic insulin resistance.

Mannose-binding lectin binds to amyloid ß protein and modulates inflammation.

Mannose-binding lectin (MBL), a soluble factor of the innate immune system, is a pattern recognition molecule with a number of known ligands, including viruses, bacteria, and molecules from abnormal self tissues. In addition to its role in immunity, MBL also functions in the maintenance of tissue homeostasis. We present evidence here that MBL binds to amyloid ß peptides. MBL binding to other known carbohydrate ligands is calcium-dependent and has been attributed to the carbohydrate-recognition domain, a common feature of other C-type lectins. In contrast, we find that the features of MBL binding to Aß are more similar to the reported binding characteristics of the cysteine-rich domain of the unrelated mannose receptor and therefore may involve the MBL cysteine-rich domain. Differences in MBL ligand binding may contribute to modulation of inflammatory response and may correlate with the function of MBL in processes such as coagulation and tissue homeostasis.

Essential role of complement mannose-binding lectin-associated serine proteases-1/3 in the murine collagen antibody-induced model of inflammatory arthritis.

Gene-targeted mice deficient in the complement mannose-binding lectin-associated serine protease-1 and -3 (MASP1/3(-/-)) express only the zymogen of factor D (pro-factor D [pro-Df]), a necessary component of the alternative pathway (AP). We used the murine collagen Ab-induced arthritis (CAIA) model, in which the AP is unique among complement pathways in being both necessary and sufficient for disease induction, to determine whether MASP-1/3 are required in vivo for the development of tissue injury. Disease activity scores, complement C3 tissue deposition in the joint, and histopathologic injury scores were markedly decreased in MASP1/3(-/-) as compared with wild-type (WT) mice. MASP-1 protein was immunochemically localized to synovial cells of knees of WT mice with arthritis. Pro-Df was present in both synovial cells and chondrocytes of knees of WT and MASP1/3(-/-) mice without arthritis, with increased amounts present in synovial cells of WT mice with CAIA. No conversion of pro-Df to mature Df was detectable in the serum of MASP1/3(-/-) mice during the evolution of CAIA. C3 activation and deposition as well as C5a generation induced in vitro by adherent anti-type II collagen mAbs were absent using sera from MASP1/3(-/-) mice under conditions in which only the AP was active. The addition of human Df fully reconstituted in vitro C3 activation and C5a generation using sera from MASP1/3(-/-) mice. Our studies demonstrate for the first time, to our knowledge, the absolute requirement for the activity of MASP-1 protein in autoimmune-associated inflammatory tissue injury in vivo through activation of the AP of complement by cleavage of pro-Df to mature Df.