IntroductionHereditary angioedema (HAE) develops in individuals who are heterozygous for deficiency or dysfunction of C1 inhibitor (C1INH). This disease is characterized by recurrent episodes of angioedema involving the skin or the oropharyngeal, laryngeal, or gastrointestinal mucosa. Prior to the use of attenuated androgens such as danazol and stanazolol as chronic therapy for HAE, as many as one-third of patients died from asphyxiation secondary to laryngeal edema.C1INH belongs to the serpin family of serine protease inhibitors. It is the only inhibitor of C1r and C1s, the classical complement pathway proteases (1). It also regulates kinin generation via inactivation of factors XIIa and plasma kallikrein, and intrinsic coagulation via inactivation of factor XIa (2-6). In HAE, the low levels of active C1INH in plasma lead to unregulated activation of the complement and contact cascades and the development of angioedema with its associated complications. Complement system activation results in decreased levels of C4 and C2, while contact system activation results in cleavage of high molecular weight kininogen.In the past several years a great deal has been learned about the structure, genetics, mechanism of action, and inhibitory spectrum of C1INH. However, the pathophysiology of the increased vascular permeability of HAE has remained controversial for over 30 years. It is believed that angioedema results from uncontrolled activation of either the classical complement pathway with generation of a vasoactive peptide (C2 kinin) released from C2, and/or from contact system activation with release of bradykinin from high-molecular-weight kininogen (7-11). Although the majority of the available data support a role for bradykinin, the critical question is whether bradykinin alone could account for the symptoms of patients with HAE, or other mediators are also involved.To investigate the role of C1INH in vivo, and to determine whether bradykinin is involved in the induction of vascular permeability in edema formation, we obtained mice in which the C1INH gene was targeted for disruption in murine embryonic stem cells using gene trapping (12). Neither homozygous nor heterozygous C1INH-deficient mice had an obvious phenotype. However, when compared with wild-type littermates, these animals clearly had increased vascular permeability that could be reversed by treatment with human C1INH, with an inhibitor of contact system activation (DX88), or with a bradykinin type 2 receptor (Bk2R) antagonist (Hoe140). Inhibition of bradykinin inactivation with captopril enhanced vascular permeability in C1INH-deficient mice, but mice doubly deficient in both C1INH and the Bk2R did not demonstrate increased vascular permeability. Heterozygosity for C1 inhibitor (C1INH) deficiency results in hereditary angioedema. Disruption of the C1INH gene by gene trapping enabled the generation of homozygous-and heterozygous-deficient mice. Methods C1INH gene targeting. Mice in which theMating of heterozygous-deficient mice resulted in the expected 1:...

Entamoeba histolytica is a protozoan parasite that causes colitis and liver abscesses. Several Entamoeba species and strains with differing levels of virulence have been identified. E. histolytica HM-1:IMSS is a virulent strain, E. histolytica Rahman is a nonvirulent strain, and Entamoeba dispar is a nonvirulent species. We used an E. histolytica DNA microarray consisting of 2,110 genes to assess the transcriptional differences between these species/strains with the goal of identifying genes whose expression correlated with a virulence phenotype. We found 415 genes expressed at lower levels in E. dispar and 32 genes with lower expression in E. histolytica Rahman than in E. histolytica HM-1:IMSS. Overall, 29 genes had decreased expression in both the nonvirulent species/strains than the virulent E. histolytica HM-1:IMSS. Interestingly, a number of genes with potential roles in stress response and virulence had decreased expression in either one or both nonvirulent Entamoeba species/strains. These included genes encoding Fe hydrogenase (9.m00419), peroxiredoxin (176.m00112), type A flavoprotein (6.m00467), lysozyme (6.m00454), sphingomyelinase C (29.m00231), and a hypothetical protein with homology to both a Plasmodium sporozoite threonine-asparagine-rich protein (STARP) and a streptococcal hemagglutinin (238.m00054). The function of these genes in Entamoeba and their specific roles in parasite virulence need to be determined. We also found that a number of the non-long-terminal-repeat retrotransposons (EhLINEs and EhSINEs), which have been shown to modulate gene expression and genomic evolution, had lower expression in the nonvirulent species/strains than in E. histolytica HM-1:IMSS. Our results, identifying expression profiles and patterns indicative of a virulence phenotype, may be useful in characterizing the transcriptional framework of virulence.

Heterozygosity for C1 inhibitor (C1INH) deficiency results in hereditary angioedema. Disruption of the C1INH gene by gene trapping enabled the generation of homozygous- and heterozygous-deficient mice. Mating of heterozygous-deficient mice resulted in the expected 1:2:1 ratio of wild-type, heterozygous, and homozygous-deficient offspring. C1INH-deficient mice showed no obvious phenotypic abnormality. However, following injection with Evans blue dye, both homozygous and heterozygous C1INH-deficient mice revealed increased vascular permeability in comparison with wild-type littermates. This increased vascular permeability was reversed by treatment with intravenous human C1INH, with a Kunitz domain plasma kallikrein inhibitor (DX88), and with a bradykinin type 2 receptor (Bk2R) antagonist (Hoe140). In addition, treatment of the C1INH-deficient mice with an angiotensin-converting enzyme inhibitor (captopril) increased the vascular permeability. Mice with deficiency of both C1INH and Bk2R demonstrated diminished vascular permeability in comparison with C1INH-deficient, Bk2R-sufficient mice. These data support the hypothesis that angioedema is mediated by bradykinin via Bk2R.

Entamoeba histolytica is a leading cause of parasitic death globally. However, the molecular framework regulating pathogenesis is poorly understood. We have previously used expression profiling to identify Entamoeba genes whose expressions were strictly associated with virulent strains (R. C. MacFarlane and U. Singh, Infect. Immun. 74:340-351, 2006). One gene, which we have named EhSTIRP (Entamoeba histolytica serine-, threonine-, and isoleucine-rich protein), was exclusively expressed in virulent but not in nonvirulent Entamoeba strains. EhSTIRP is predicted to be a transmembrane protein and is encoded by a multigene family. In order to characterize its function in amebic biology, we used a double-stranded RNA-based approach and were able to selectively down-regulate expression of this gene family. Upon EhSTIRP down-regulation, we were able to ascribe cytotoxic and adhesive properties to the protein family using lactate dehydrogenase release and Chinese hamster ovary cell adhesion assays. EhSTIRP thus likely represents a novel determinant of virulence in Entamoeba histolytica. This work validates the fact that genes expressed exclusively in virulent strains may represent virulence determinants and highlights the need for further functional analyses of other genes with similar expression profiles.Entamoeba histolytica is a protozoan parasite that causes significant morbidity and mortality in the developing world (48). The life cycle is composed of two stages: the transmissible cyst that is released in the feces of infected humans, and the motile trophozoite, which resides in the large bowel. The infection begins when cysts are ingested, usually through contaminated food or water. Excystation occurs in the small bowel, and the motile trophozoites eventually colonize the large bowel.The majority of individuals with E. histolytica infection remain asymptomatic; however, in some cases the parasites penetrate the colon wall causing dysentery and colitis and occasionally disseminate hematogenously to cause liver abscesses. The potential reasons for why so many individuals remain asymptomatic include differences in host immunity and gut microflora as well as genetic differences between Entamoeba isolates. The molecular processes that underlie the progression from gut commensal to pathogen are not completely understood (46). Invasion begins when the parasite attaches to host cells via the galactose/N-acetylgalactosamine (Gal/GalNAc)-inhibitable lectin. This binding event is followed by rapid cell death, which has been characterized as having both necrotic and apoptotic features (9, 44). Additional molecules important in amebic pathogenesis include the cysteine proteinases, papain family proteases that have been proven to be important in virulence. Parasites genetically engineered to produce low levels of cysteine proteinase activity showed significantly less gut inflammation and were unable to form liver abscesses in animal models of amebic disease (4, 5, 51). The amoebapores, pore-forming peptides, insert into the memb...

Variable phenotypes have been identified for Entamoeba species. Entamoeba histolytica is invasive and causes colitis and liver abscesses but only in ϳ10% of infected individuals; 90% remain asymptomatically colonized. Entamoeba dispar, a closely related species, is avirulent. To determine the extent of genetic diversity among Entamoeba isolates and potential genotype-phenotype correlations, we have developed an E. histolytica genomic DNA microarray and used it to genotype strains of E. histolytica and E. dispar. On the basis of the identification of divergent genetic loci, all strains had unique genetic fingerprints. Comparison of divergent genetic regions allowed us to distinguish between E. histolytica and E. dispar, identify novel genetic regions usable for strain and species typing, and identify a number of genes restricted to virulent strains. Among the four E. histolytica strains, a strain with attenuated virulence was the most divergent and phylogenetically distinct strain, raising the intriguing possibility that genetic subtypes of E. histolytica may be partially responsible for the observed variability in clinical outcomes. This microarray-based genotyping assay can readily be applied to the study of E. histolytica clinical isolates to determine genetic diversity and potential genotypic-phenotypic associations.Entamoeba histolytica causes amebic colitis and liver abscesses. Worldwide, 50 million people have invasive E. histolytica, and 100,000 die each year, making it the second most common cause of parasitic death in humans (71). In Dhaka, Bangladesh, where diarrheal diseases are the leading cause of death in children less than 6 years old, ϳ50% of children have serological evidence of exposure to E. histolytica by age 5 (34, 35). Infected children suffer from significant morbidity with malnourishment and growth delays. A number of interesting epidemiologic trends have been identified for amebic disease. The data, although limited, indicate that a minority (ϳ10%) of individuals who become infected with E. histolytica progress to clinically overt disease; others remain asymptomatically colonized (29). In individuals with invasive disease, occurrence of amebic liver abscess (ALA) is 5 to 50 times less common than diarrhea (65). Geographically variable disease predilections have been observed, and invasive disease predominantly affects men (1, 2, 11, 61).The extent of genetic diversity among E. histolytica clinical isolates is unclear. Studies have analyzed a small number of highly repetitive and polymorphic genetic loci by techniques, such as randomly amplified polymorphic DNA (RAPD), RNA arbitrarily primed PCR, and restriction fragment length polymorphism (RFLP), to conclude that there is significant genetic diversity (7,18,23,31,33,64,72,73). Contradictory data were obtained by two studies; in one study, the lectin gene was sequenced, and in the other study, the intergenic region between the superoxide dismutase gene and the actin 3 gene was analyzed (9, 30). These studies found minimal genetic diversi...

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Previous analysis of a naturally occurring C1 inhibitor P2 mutant (Ala443→Val) indicated a role for P2 in specificity determination. To define this role and that of other reactive center loop residues, a number of different amino acids were introduced at P2, as well as at P6 (Ala439) and P8′/9′ (Gln452Gln453). Ala439→Val is a naturally occurring mutant observed in a patient with hereditary angioedema. Previous data suggested that Gln452Gln453 might be a contact site for C1s. Reactivity of the inhibitors toward target (C1s, C1r, kallikrein, β factor XIIa, and plasmin) and nontarget proteases (α-thrombin and trypsin) were studied. Substitution of P2 with bulky or charged residues resulted in decreased reactivity with all target proteases. Substitution with residues with hydrophobic or polar side chains resulted in decreased reactivity with some proteases, but in unaltered or increased reactivity with others. Second order rate constants for the reaction with C1s were determined for the mutants with activities most similar to the wild-type protein. The three P2 mutants showed reductions in rate from 3.35 × 105 M−1s−1 for the wild type to 1.61, 1.29, and 0.63 × 105 for the Ser, Thr, and Val mutants, respectively. In contrast, the Ala439→Val and the Gln452Gln453→Ala mutants showed little difference in association rates with C1s, in comparison with the wild-type inhibitor. The data confirm the importance of P2 in specificity determination. However, the P6 position appears to be of little, if any, importance. Furthermore, it appears unlikely that Gln452Gln453 comprise a portion of a protease contact site within the inhibitor.

The ability to regulate gene expression in the protozoan parasite Entamoeba histolytica is critical in determining gene function. We previously published that expression of dsRNA specific to E. histolytica serine threonine isoleucine rich protein (EhSTIRP) resulted in reduction of gene expression (MacFarlane, 2007). However, after approximately one year of continuous drug selection, the expression of EhSTIRP reverted to wild-type levels. We confirmed that the parasites (i) contained the appropriate dsRNA plasmid, (ii) were not contaminated with other plasmids, (iii) the drug selectable marker was functional, and (iv) sequenced the dsRNA portion of the construct. This work suggests that in E. histolytica long term cultivation of parasites expressing dsRNA can lead to the loss of dsRNA based silencing through the selection of "RNAi" negative parasites. Thus, users of the dsRNA silencing approach should proceed with caution and regularly confirm gene down regulation. The development and use of constructs for inducible expression of dsRNA may help alleviate this potential problem.