Epithelial invasion by Escherichia coli bearing Dr fimbriae is controlled by nitric oxide-regulated expression of CD55

A shear stress micromodel of urinary tract infection by the Escherichia coli producing Dr adhesin

In this study, we established a dynamic micromodel of urinary tract infection to analyze the impact of UT-segment-specific urinary outflow on the persistence of E. coli colonization. We found that the adherence of Dr+ E. coli to bladder T24 transitional cells and type IV collagen is maximal at lowest shear stress and is reduced by any increase in flow velocity. The analyzed adherence was effective in the whole spectrum of physiological shear stress and was almost irreversible over the entire range of generated shear force. Once Dr+ E. coli bound to host cells or collagen, they did not detach even in the presence of elevated shear stress or of chloramphenicol, a competitive inhibitor of binding. Investigating the role of epithelial surface architecture, we showed that the presence of budding cells–a model microarchitectural obstacle–promotes colonization of the urinary tract by E. coli. We report a previously undescribed phenomenon of epithelial cell “rolling-shedding” colonization, in which the detached epithelial cells reattach to the underlying cell line through a layer of adherent Dr+ E. coli. This rolling-shedding colonization progressed continuously due to “refilling” induced by the flow-perturbing obstacle. The shear stress of fluid containing free-floating bacteria fueled the rolling, while providing an uninterrupted supply of new bacteria to be trapped by the rolling cell. The progressive rolling allows for transfer of briefly attached bacteria onto the underlying monolayer in a repeating cascading event.

Uropathogenic E. coli (UPEC) equipped with Dr fimbriae are associated with recurrent and chronic urinary tract infections (UTIs). The fimbriae assembled by the chaperone-usher pathway provide strong host-specific adherence which is, however, strongly modulated by the dynamically changing urine flow in the urinary tract (UT). In this paper, we use a dynamic in vitro micro-model of UTI to analyze the UT segment-specific impact of urinary outflow on the persistence and spread of Dr+ E. coli during host colonization. We conclude that the adhesive envelope formed by Dr fimbriae promotes strong and irreversible multivalent adherence of Dr+ E. coli to host receptors under flow conditions. We also observed that budding host cells–a model of any form of epithelial roughness, including carcinogenesis or physical injuries–facilitate the adherence of bacteria at flow conditions typically found in the UT, and our numerical simulations provided a mechanistic explanation for this effect. Finally, we combined the results to propose a rolling-shedding-refilling colonization model that shows how the wash off of detached colonized host cells may provoke a massive spread of UPEC. Our findings shed new light on UTI development and may be instrumental in the development of novel therapeutics.

Nanodiamonds facilitate killing of intracellular uropathogenic E. coli in an in vitro model of urinary tract infection pathogenesis

About 25–44% of women will experience at least one episode of recurrent UTI and the causative agent in over 70% of UTI cases is uropathogenic Escherichia coli (UPEC). UPEC cause recurrent UTI by evading the bladder’s innate immune system through internalization into the bladder epithelium where antibiotics cannot reach or be effective. Thus, it is important to develop novel therapeutics to eliminate these intracellular pathogens. Nanodiamonds (NDs) are biocompatible nanomaterials that serve as promising candidates for targeted therapeutic applications. The objective of the current study was to investigate if 6 or 25 nm NDs can kill extracellular and intracellular UPEC in infected bladder cells. We utilized the human bladder epithelial cell line, T24, and an invasive strain of UPEC that causes recurrent UTI. We found that acid-purified 6 nm NDs displayed greater antibacterial properties towards UPEC than 25 nm NDs (11.5% vs 94.2% CFU/mL at 100 μg/mL of 6 and 25 nm, respectively; P<0.001). Furthermore, 6 nm NDs were better than 25 nm NDs in reducing the number of UPEC internalized in T24 bladder cells (46.1% vs 81.1% CFU/mL at 100 μg/mL of 6 and 25 nm, respectively; P<0.01). Our studies demonstrate that 6 nm NDs interacted with T24 bladder cells in a dose-dependent manner and were internalized in 2 hours through an actin-dependent mechanism. Finally, internalization of NDs was required for reducing the number of intracellular UPEC in T24 bladder cells. These findings suggest that 6 nm NDs are promising candidates to treat recurrent UTIs.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

PI3K/Akt pathway restricts epithelial adhesion of Dr + Escherichia coli by down-regulating the expression of decay accelerating factor

The urogenital microbial infection in pregnancy is an important cause of maternal and neonatal morbidity and mortality. Uropathogenic Escherichia coli strains which express Dr fimbriae (Dr+) are associated with unique gestational virulence and they utilize cell surface decay accelerating factor (DAF or CD55) as one of the cellular receptor before invading the epithelial cells. Previous studies in our laboratory established that nitric oxide reduces the rate of E. coli invasion by delocalizing the DAF protein from cell surface lipid rafts and down-regulating its expression. The phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) cell signal pathway plays an important role in host-microbe interaction because many bacteria including E. coli activate this pathway in order to establish infection. In the present study, we showed that the PI3K/Akt pathway negatively regulated the expression of DAF on the epithelial cell surface and thus inhibited the adhesion of Dr(+) E. coli to epithelial cells. Initially, using two human cell lines Ishikawa and HeLa which differ in constitutive activity of PI3K/Akt, we showed that DAF levels were associated with the PI3K/Akt pathway. We then showed that the DAF gene expression was up-regulated and the Dr(+) E. coli adhesion increased after the suppression of PI3K/Akt pathway in Ishikawa cells using inhibitor LY294002, and a plasmid which allowed the expression of PI3K/Akt regulatory protein PTEN. The down-regulation of PTEN protein using PTEN-specific siRNA activated the PI3K/Akt pathway, down-regulated the DAF, and decreased the adhesion of Dr(+) E. coli. We conclude that the PI3K/Akt pathway regulated the DAF expression in a nitric oxide independent manner.

Nitric oxide induces segregation of decay accelerating factor (DAF or CD55) from the membrane lipid-rafts and its internalization in human endometrial cells

Recent studies suggest that DAF (decay accelerating factor), a complement regulatory protein, present in lipid rafts, is utilized by Dr fimbriated Escherichia coli for their binding and internalization. Previous studies in our laboratory have shown that NO (nitric oxide) can reduce the invasion of Dr(+) E. coli and the severity of uterine infection in pregnant rats. Also, the expression level of DAF both at the mRNA and protein levels has been shown to be reduced by NO. Therefore NO mediated down-regulation of DAF appears to be an important factor in reducing the susceptibility to E. coli infection. However, it is unclear if NO can actually modulate the membrane association of DAF and therefore initial bacterial binding to cells. We found that NO induces the delocalization of DAF from the G(M1)-rich lipid rafts. Using biochemical and cell biological approaches in a uterine epithelial cell model (Ishikawa cells), DAF accumulates in caveolae upon exposure to NO. Interaction of DAF with the caveolar protein, caveolin1, leads to their internalization by endosomes. NO-induced delocalization of DAF from the lipid raft and its accumulation in caveolae are mediated through a cGMP (cyclic guanosine monophosphate) pathway. The acute localized synthesis of NO and its influence on DAF localization may represent an important unrecognized phenomenon of host defence against Dr(+) E. coli bacteria, as well as many disease conditions that involve complement system.

Role of transcription factor Sp1 and RNA binding protein HuR in the downregulation of Dr+ Escherichia coli receptor protein decay accelerating factor (DAF or CD55) by nitric oxide

We previously reported that nitric oxide (NO) reduces the rate of bacteremia and maternal mortality in pregnant rats with uterine infection by Escherichia coli expressing the Dr Fimbria (Dr(+) ). The epithelial invasion of Dr(+) E. coli is dependent on the expression level of its cellular receptor decay accelerating factor (DAF). NO reduces the rate of bacteremia by downregulating the expression of DAF. In this study, we elucidated the role of transcription factor Sp1 and RNA binding protein HuR in the downregulation of human DAF by NO. We generated a series of deletion mutant constructs of DAF gene 5'-untranslated region and mapped the NO-response region upstream to the core promoter region of the DAF gene. One of the several Sp1 binding sites in the DAF 5'-untranslated region was located within the NO-response region. The binding of Sp1 to this site was inhibited by NO. Furthermore, NO also promoted the degradation of DAF mRNA. The 3'-untranslated region of DAF harbors an AU-rich element and this element destabilized the mRNA transcript. NO promoted the rapid degradation of DAF mRNA by inhibiting the binding of mRNA stabilizing protein HuR to this AU-rich region. The inhibition of binding of HuR to the AU-rich region was due to the S-nitrosylation of one or more cysteine residues by NO. Thus, these data reveal the molecular mediators of transcriptional and post-transcriptional regulation of DAF by NO with implications in pathophysiology related to DAF.

Maternal/fetal mortality and fetal growth restriction: role of nitric oxide and virulence factors in intrauterine infection in rats

OBJECTIVE

The mechanism of infection-related deaths of pregnant rats and intrauterine growth restriction are not understood. We assessed whether nitric oxide (NO) has differential effects on infection with Escherichia coli Dr/Afa mutants that lack either AfaE or AfaD invasins.

STUDY DESIGN

Sprague-Dawley rats were infected intrauterinally with the clinical strain of E coli AfaE(+)D(+) or 1 of its isogenic mutants in the presence or absence of the NO synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Maternal/fetal mortality rates, fetoplacental weight, and infection rates were evaluated.

RESULTS

Maternal and/or fetal death was associated with the presence of at least 1 virulence factor (AfaE(+)D(+)>AfaE(+)D(-)>AfaE(-)D(+)) and was increased by L-NAME treatment. The fetal and placental weights were lower than controls and were further reduced by L-NAME treatment.

CONCLUSION

These results demonstrate that NO enhanced AfaE- and AfaD-mediated virulence and plays an important role in Dr/Afa(+)E coli gestational tropism.

Preterm labor: CD55 in maternal blood leukocytes

PROBLEM

Intrauterine inflammation is a frequent and significant factor associated with the pathogenesis of preterm labor/birth (PTL/PTB). However, it remains unclear whether the intrauterine inflammatory responses activate the maternal peripheral circulation. We explored the association between PTL/PTB and the 'activation' of the peripheral circulatory system by determining whether CD55 mRNA expression within peripheral WBCs differed between PTL and control patients not in labor.

METHOD OF STUDY

RNA was purified from white blood cells collected from pregnant women with preterm labor (n = 45), and from pregnant (n = 30) control women. CD55 gene expression was evaluated by quantitative PCR.

RESULTS

The mean CD55 mRNA level within the PTL group (0.77 +/- 0.03) was 1.48-fold higher than that observed (0.52 +/- 0.02) within the control group (P < 0.0001); 71% of PTL patients and only 6.7% of control subjects expressed elevated CD55 mRNA. The receiver operating characteristics (with 95% CI) of CD55 as a marker for PTL were as follows: Sensitivity, 69% (53-82%); Specificity, 93% (78-99%); Positive Predictive Value, 94% (80-99%); and Negative Predictive Value, 67% (51-80%). In the patient population that delivered prematurely (before 37 weeks), 81% expressed elevated CD55 mRNA levels with a mean of 0.78 +/- 0.03 and 95% CI of 0.71-0.84. The receiver operating characteristics were as follows: Sensitivity, 73% (54-88%); Specificity, 86% (71-95%); Positive Predictive Value, 81.5% (62-94%); and Negative Predictive Value, 80% (64-91%).

CONCLUSION

Here we report for the first time that CD55 mRNA expression was elevated in the peripheral WBCs of subjects with preterm labor compared with control gestationally-matched pregnant woman and that elevated leukocyte CD55 may be a useful predictor of subsequent PTB.

Nitric oxide: new evidence for novel therapeutic indications

BACKGROUND

Nitric oxide (NO) deficiency is implicated in many pathophysiological processes in mammals. NO is a ubiquitous molecule involved in multiple cellular functions. Uncontrolled or inappropriate production of NO may lead to several disease states including septic shock, rheumatoid and inflammatory arthropathies, and expansion of cerebral damage after stroke. However, to date, there are no therapeutic agents available that can overcome these conditions. Similarly, underproduction of NO by NO synthase or enhanced breakdown of NO also leads to diseases such as hypertension, ischemic conditions, pre-eclampsia, premature delivery, among others. NO donor therapies are indicated in these conditions.

RESULTS

Nitroglycerin and nitrates (NO donors) have been used as therapeutic agents for the past century, particularly to treat vascular disease, and the only significant adverse effects are headaches. NO donors are highly cost-effective and have beneficial effects in multiple body systems. When the body cannot generate NO via NO synthase or due to rapid turnover leading to inadequate amounts of NO available for biological homeostasis, administration of exogenous NO, or prolongation of the actions of endogenous NO, are practical ways to supplement NO.

CONCLUSION

Recipients of such therapy include patients with angina pectoris, coronary artery disease, hypertension, osteoporosis, gastrointestinal motility disorders, pregnancy-related disorders including premature delivery, pre-eclampsia, vulvodynia, and erectile dysfunction in men. Postmenopausal NO deficiency is rectified with hormone replacement therapy, which enhances local production of NO. Declining local NO production secondary to estrogen deficiency in postmenopausal women and perhaps in older men could be one of the reasons for age-related increased incidences of cardiovascular events and sexual dysfunction. Thus, in addition to supplementation of NO compounds in acute situations like alleviating angina and erectile dysfunction, chronic NO therapy is cost-effective in decreasing cardiovascular events, and improving the urogenital system and skeletal health.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

Covert operations of uropathogenic Escherichia coli within the urinary tract

Entry into host cells is required for many bacterial pathogens to effectively disseminate within a host, avoid immune detection and cause disease. In recent years, many ostensibly extracellular bacteria have been shown to act as opportunistic intracellular pathogens. Among these are strains of uropathogenic Escherichia coli (UPEC), the primary causative agents of urinary tract infections (UTIs). UPEC are able to transiently invade, survive and multiply within the host cells and tissues constituting the urinary tract. Invasion of host cells by UPEC is promoted independently by distinct virulence factors, including cytotoxic necrotizing factor, Afa/Dr adhesins, and type 1 pili. Here we review the diverse mechanisms and consequences of host cell invasion by UPEC, focusing also on the impact of these processes on the persistence and recurrence of UTIs.