Paul B. McCray

Human beta-defensin-1: an antimicrobial peptide of urogenital tissues.

Antimicrobial peptides are widely distributed mediators of innate host defense in animals and plants. A 36 amino acid antimicrobial peptide belonging to the defensin family, and named human beta-defensin-1 (HBD-1), was purified recently from hemodialysate fluid, but its tissue sources were not identified. By Northern blotting, we found the highest concentrations of HBD-1 mRNA in the kidney and the female reproductive tract. In situ hybridization localized the HBD-1 mRNA in the epithelial layers of the loops of Henle, distal tubules, and the collecting ducts of the kidney and the epithelial layers of the vagina, ectocervix, endocervix, uterus, and fallopian tubes in the female reproductive tract. Using a novel technique designed to detect cationic peptides in urine, we recovered several forms of HBD-1 ranging in length from 36 to 47 amino acid (aa) residues and differing from each other by amino terminal truncation. The total concentration of HBD-1 forms in voided urine was estimated at 10-100 microg/liter, with individual variations in the total amount of HBD-1 peptides and the relative proportion of HBD-1 forms. Multiple forms of HBD-1 (size 36-47 aa) were also found in the blood plasma, bound to carrier macromolecules that released the peptide under acid conditions, and in vaginal mucosal secretions (39, 40, and 44 aa). By immunostaining, HBD-1 was located in the kidney within the lumen of the loops of Henle, but no intracellular storage sites were identified in renal or female reproductive tissues. Recombinant HBD-1 forms (36, 39, and 42 aa) and natural HBD-1 forms were antimicrobial to laboratory and clinical strains of Escherichia coli at micromolar concentrations. HBD-1 activity was not changed appreciably by low pH, but was inhibited by high salt conditions. Some of the HBD-1 peptides retained their activity against E. coli in unconcentrated (low conductance) urine, and the 36 aa form was microbicidal even in normal (high conductance) urine. Production of HBD-1 in the urogenital tract could contribute to local antimicrobial defense.

Disruption of the CFTR Gene Produces a Model of Cystic Fibrosis in Newborn Pigs

Almost two decades after CFTR was identified as the gene responsible for cystic fibrosis (CF), we still lack answers to many questions about the pathogenesis of the disease, and it remains incurable. Mice with a disrupted CFTR gene have greatly facilitated CF studies, but the mutant mice do not develop the characteristic manifestations of human CF, including abnormalities of the pancreas, lung, intestine, liver, and other organs. Because pigs share many anatomical and physiological features with humans, we generated pigs with a targeted disruption of both CFTR alleles. Newborn pigs lacking CFTR exhibited defective chloride transport and developed meconium ileus, exocrine pancreatic destruction, and focal biliary cirrhosis, replicating abnormalities seen in newborn humans with CF. The pig model may provide opportunities to address persistent questions about CF pathogenesis and accelerate discovery of strategies for prevention and treatment.

Current prospects for RNA interference-based therapies

RNA interference (RNAi) is a powerful approach for reducing expression of endogenously expressed proteins. It is widely used for biological applications and is being harnessed to silence mRNAs encoding pathogenic proteins for therapy. Various methods — including delivering RNA oligonucleotides and expressing RNAi triggers from viral vectors — have been developed for successful RNAi in cell culture and in vivo. Recently, RNAi-based gene silencing approaches have been demonstrated in humans, and ongoing clinical trials hold promise for treating fatal disorders or providing alternatives to traditional small molecule therapies. Here we describe the broad range of approaches to achieve targeted gene silencing for therapy, discuss important considerations when developing RNAi triggers for use in humans, and review the current status of clinical trials.

Discovery of five conserved β-defensin gene clusters using a computational search strategy

The innate immune system includes antimicrobial peptides that protect multicellular organisms from a diverse spectrum of microorganisms. β-Defensins comprise one important family of mammalian antimicrobial peptides. The annotation of the human genome fails to reveal the expected diversity, and a recent query of the draft sequence with the blast search engine found only one new β-defensin gene (DEFB3). To define better the β-defensin gene family, we adopted a genomics approach that uses hmmer, a computational search tool based on hidden Markov models, in combination with blast. This strategy identified 28 new human and 43 new mouse β-defensin genes in five syntenic chromosomal regions. Within each syntenic cluster, the gene sequences and organization were similar, suggesting each cluster pair arose from a common ancestor and was retained because of conserved functions. Preliminary analysis indicates that at least 26 of the predicted genes are transcribed. These results demonstrate the value of a genomewide search strategy to identify genes with conserved structural motifs. Discovery of these genes represents a new starting point for exploring the role of β-defensins in innate immunity.

Reduced Airway Surface pH Impairs Bacterial Killing in the Porcine Cystic Fibrosis Lung

Cystic fibrosis (CF) is a life-shortening disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Although bacterial lung infection and the resulting inflammation cause most of the morbidity and mortality, how the loss of CFTR function first disrupts airway host defence has remained uncertain. To investigate the abnormalities that impair elimination when a bacterium lands on the pristine surface of a newborn CF airway, we interrogated the viability of individual bacteria immobilized on solid grids and placed onto the airway surface. As a model, we studied CF pigs, which spontaneously develop hallmark features of CF lung disease. At birth, their lungs lack infection and inflammation, but have a reduced ability to eradicate bacteria. Here we show that in newborn wild-type pigs, the thin layer of airway surface liquid (ASL) rapidly kills bacteria in vivo, when removed from the lung and in primary epithelial cultures. Lack of CFTR reduces bacterial killing. We found that the ASL pH was more acidic in CF pigs, and reducing pH inhibited the antimicrobial activity of ASL. Reducing ASL pH diminished bacterial killing in wild-type pigs, and, conversely, increasing ASL pH rescued killing in CF pigs. These results directly link the initial host defence defect to the loss of CFTR, an anion channel that facilitates HCO3− transport. Without CFTR, airway epithelial HCO3− secretion is defective, the ASL pH falls and inhibits antimicrobial function, and thereby impairs the killing of bacteria that enter the newborn lung. These findings suggest that increasing ASL pH might prevent the initial infection in patients with CF, and that assaying bacterial killing could report on the benefit of therapeutic interventions.

Cystic fibrosis pigs develop lung disease and exhibit defective bacterial eradication at birth.

The lungs of just-born piglets with cystic fibrosis fail to efficiently eliminate bacteria, suggesting that lung problems in cystic fibrosis patients may be secondary to impaired antibacterial defense mechanisms. A Matter of Life and Breath The CafePress and Zazzle Web sites and most yoga-wear boutiques sport an array of teeshirts, bumper stickers, and water bottles prepared to offer simple advice to those living a harried life: “Just breathe.” Not so simple for a cystic fibrosis (CF) patient. Very early on, physicians recognized that difficulty breathing was the most ominous of the mosaic of symptoms that characterize this syndrome. Indeed, lung disease is the main cause of death in cystic fibrosis patients, but the lack of an animal model that mirrors the CF lung pathology seen in people has slowed translational cystic fibrosis research. Now, Stoltz et al. report findings in cystic fibrosis pigs that survive long enough to develop human-like lung disease. At the heart of this recessive genetic disease is the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride-ion channel. CF-causing mutations in the CFTR gene give rise to an aberrant channel that is defective in its ability to transport ions and water across cell membranes, resulting in a dizzying array of defects in the pancreas, intestines, reproductive system, liver, and lungs. It has been hypothesized that the impaired channel causes cells that line body cavities and passageways to become coated with thick mucus. In such an environment, bacteria thrive, leading to the chronic infections characteristic of this disease. However, the precise mechanisms by which CFTR mutations manifest as the complex phenotypes that constitute CF remain unclear, particularly with respect to the inflamed and infected airways of the CF lung. Despite substantial research efforts, scientists have been unable to achieve two crucial goals,to mold an animal model that mimics human CF lung disease and to pinpoint the trigger of CF lung pathology in pristine airways. Stoltz et al. tackled both of these obstacles by producing genetically modified CF pigs and analyzing their airways from birth to 6 months of age. Their studies revealed a spontaneously arising human-like lung disease that developed over time and had the CF hallmarks: multibacterial infections, inflammation, and mucus buildup. Although the lungs of the newborn CF piglets were not yet inflamed, they were less likely to be sterile and less able to eliminate bacteria that had been introduced into their lungs, relative to wild-type animals. Together, these findings suggest that bacterial infiltration spurs the pattern of lung inflammation and pathogenesis associated with CF. Having a clearer conception of CF lung disease can help clinicians devise preventive treatments that can be initiated early in the lives of CF patients. Such interventions may let CF suffers live and breath more fully. Lung disease causes most of the morbidity and mortality in cystic fibrosis (CF). Understanding the pathogenesis of this disease has been hindered, however, by the lack of an animal model with characteristic features of CF. To overcome this problem, we recently generated pigs with mutated CFTR genes. We now report that, within months of birth, CF pigs spontaneously developed hallmark features of CF lung disease, including airway inflammation, remodeling, mucus accumulation, and infection. Their lungs contained multiple bacterial species, suggesting that the lungs of CF pigs have a host defense defect against a wide spectrum of bacteria. In humans, the temporal and causal relations between inflammation and infection have remained uncertain. To investigate these processes, we studied newborn pigs. Their lungs showed no inflammation but were less often sterile than controls. Moreover, after introduction of bacteria into their lungs, pigs with CF failed to eradicate bacteria as effectively as wild-type pigs. These results suggest that impaired bacterial elimination is the pathogenic event that initiates a cascade of inflammation and pathology in CF lungs. Our finding that pigs with CF have a host defense defect against bacteria within hours of birth provides an opportunity to further investigate CF pathogenesis and to test therapeutic and preventive strategies that could be deployed before secondary consequences develop.

Adherens junction protein nectin-4 is the epithelial receptor for measles virus

Measles virus is an aerosol-transmitted virus that affects more than 10 million children each year and accounts for approximately 120,000 deaths. Although it was long believed to replicate in the respiratory epithelium before disseminating, it was recently shown to infect initially macrophages and dendritic cells of the airways using signalling lymphocytic activation molecule family member 1 (SLAMF1; also called CD150) as a receptor. These cells then cross the respiratory epithelium and transport the infection to lymphatic organs where measles virus replicates vigorously. How and where the virus crosses back into the airways has remained unknown. On the basis of functional analyses of surface proteins preferentially expressed on virus-permissive human epithelial cell lines, here we identify nectin-4 (ref. 8; also called poliovirus-receptor-like-4 (PVRL4)) as a candidate host exit receptor. This adherens junction protein of the immunoglobulin superfamily interacts with the viral attachment protein with high affinity through its membrane-distal domain. Nectin-4 sustains measles virus entry and non-cytopathic lateral spread in well-differentiated primary human airway epithelial sheets infected basolaterally. It is downregulated in infected epithelial cells, including those of macaque tracheae. Although other viruses use receptors to enter hosts or transit through their epithelial barriers, we suggest that measles virus targets nectin-4 to emerge in the airways. Nectin-4 is a cellular marker of several types of cancer, which has implications for ongoing measles-virus-based clinical trials of oncolysis.

Antimicrobial peptides in animals and their role in host defences

Domesticated animals have a large variety of antimicrobial peptides that serve as natural innate barriers limiting microbial infection or, in some instances, act as an integral component in response to inflammation or microbial infection. These peptides differ in size, composition, mechanisms of activity and range of antimicrobial specificities. They are expressed in many tissues, polymorphonuclear leukocytes, macrophages and mucosal epithelial cells. There is a small group of anionic antimicrobial peptides found in ruminants and a much larger group of cationic antimicrobial peptides found in all domesticated animals. The cationic peptides include linear, helical peptides, linear peptides rich in proline and cysteine-stabilized peptides with a beta-sheet and are commonly referred to as cathelicidins and defensins. These peptides are generally broad-spectrum for Gram-positive bacteria, Gram-negative bacteria and fungi (e.g. myeloid antimicrobial peptides, alpha-, beta-defensins, and protegrins) or are specific to one of these groups (e.g. porcine cecropin P1, Bac5, Bac7, PR-39 and prophenin).

Bactericidal Activity of Mammalian Cathelicidin-Derived Peptides

ABSTRACT Endogenous antimicrobial peptides of the cathelicidin family contribute to innate immunity. The emergence of widespread antibiotic resistance in many commonly encountered bacteria requires the search for new bactericidal agents with therapeutic potential. Solid-phase synthesis was employed to prepare linear antimicrobial peptides found in cathelicidins of five mammals: human (FALL39/LL37), rabbit (CAP18), mouse (mCRAMP), rat (rCRAMP), and sheep (SMAP29 and SMAP34). These peptides were tested at ionic strengths of 25 and 175 mM against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus. Each peptide manifested activity against P. aeruginosa irrespective of the NaCl concentration. CAP18 and SMAP29 were the most effective peptides of the group against all test organisms under both low- and high-salt conditions. Select peptides of 15 to 21 residues, modeled on CAP18 (37 residues), retained activity against the gram-negative bacteria and methicillin-sensitive S. aureus, although the bactericidal activity was reduced compared to that of the parent peptide. In accordance with the behavior of the parent molecule, the truncated peptides adopted an α-helical structure in the presence of trifluoroethanol or lipopolysaccharide. The relationship between the bactericidal activity and several physiochemical properties of the cathelicidins was examined. The activities of the full-length peptides correlated positively with a predicted gradient of hydrophobicity along the peptide backbone and with net positive charge; they correlated inversely with relative abundance of anionic residues. The salt-resistant, antimicrobial properties of CAP18 and SMAP29 suggest that these peptides or congeneric structures have potential for the treatment of bacterial infections in normal and immunocompromised persons and individuals with cystic fibrosis.

Discovery of new human β-defensins using a genomics-based approach

Abstract Epithelial β-defensins are broad-spectrum cationic antimicrobial peptides that also act as chemokines for adaptive immune cells. In the human genome, all known defensin genes cluster to a