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Biomedical subjects

S J Hultgren

Publications and source records attributed to S J Hultgren.

At least 19 recordsLinked to original sources
PubMed2001

Structural basis of the interaction of the pyelonephritic E. coli adhesin to its human kidney receptor.

PapG is the adhesin at the tip of the P pilus that mediates attachment of uropathogenic Escherichia coli to the uroepithelium of the human kidney. The human specific allele of PapG binds to globoside (GbO4), which consists of the tetrasaccharide GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc linked to ceramide. Here, we present the crystal structures of a binary complex of the PapG receptor binding domain bound to GbO4 as well as the unbound form of the adhesin. The biological importance of each of the residues involved in binding was investigated by site-directed mutagenesis. These studies provide a molecular snapshot of a host-pathogen interaction that determines the tropism of uropathogenic E. coli for the human kidney and is critical to the pathogenesis of pyelonephritis.

Adhesins, Escherichia coli↗
PubMed2001

Cpx signaling pathway monitors biogenesis and affects assembly and expression of P pili.

P pili are important virulence factors in uropathogenic Escherichia coli. The Cpx two-component signal transduction system controls a stress response and is activated by misfolded proteins in the periplasm. We have discovered new functions for the Cpx pathway, indicating that it may play a critical role in pathogenesis. P pili are assembled via the chaperone/usher pathway. Subunits that go 'OFF-pathway' during pilus biogenesis generate a signal. This signal is derived from the misfolding and aggregation of subunits that failed to come into contact with the chaperone in the periplasm. In response, Cpx not only controls the stress response, but also controls genes necessary for pilus biogenesis, and is involved in regulating the phase variation of pap expression and, potentially, the expression of a panoply of other virulence factors. This study demonstrates how the prototypic chaperone/usher pathway is intricately linked and dependent upon a signal transduction system.

Bacterial Proteins↗
PubMed2001

Bacterial invasion augments epithelial cytokine responses to Escherichia coli through a lipopolysaccharide-dependent mechanism.

One mechanism of initiating innate host defenses against uropathogenic Escherichia coli (UPEC) is the production of cytokines by bladder epithelial cells; however, the means by which these cells recognize bacterial pathogens is poorly understood. Type 1 pili, expressed by the majority of UPEC, have been shown to have a critical role in inducing the expression of IL-6 in bladder epithelial cells after exposure to E. coli. In this study, we demonstrate that type 1 pili are not sufficient to activate IL-6 production by bladder epithelial cells. Instead, it was shown that bacterial invasion mediated by type 1 pili augments bladder epithelial responses to E. coli via an LPS-dependent mechanism, leading to the production of IL-6. RNA transcripts for the LPSR Toll-like receptor 4 (TLR4) was detected in cultured bladder epithelial cells. The in vivo role of TLR4 was assessed using C3H/HeJ mice, which express a dominant negative form of TLR4. After infection with UPEC, C3H/HeJ mice have large foci of intracellular bacteria that persist within the bladder epithelium in the absence of any notable inflammatory response. These results indicate that LPS is required for bacterial invasion to enhance host responses to E. coli within the bladder.

Adhesins, Bacterial↗
PubMed2001

Dynamic interactions between host and pathogen during acute urinary tract infections.

Urinary tract infections (UTIs) have traditionally been viewed as acute and often self-limiting infections caused predominantly by noninvasive Escherichia coli. However, this concept has been challenged by recent findings demonstrating that an acute bladder infection results from a complex series of host-pathogen interactions that can lead to bacterial invasion and persistence and that ultimately can determine the course of the infectious disease. The ability of E. coli to gain a foothold in the bladder is greatly facilitated by type 1 pilus-mediated attachment to and invasion of bladder epithelial cells. Invasion allows uropathogenic strains of E. coli to exploit the intracellular environment by replicating within these epithelial cells while evading a multitude of host defenses. An intracellular location also provides them a safe haven from many common antibiotic therapies. However, attachment and invasion also activates a cascade of innate host defenses, leading to the death and exfoliation of bladder cells and the production of inflammatory mediators. The ability of uropathogenic E. coli to flux out of cells and colonize surrounding cells provides them a mechanism to subvert these defense mechanisms and persist in the bladder epithelium for weeks following the acute infection. The persistence of E. coli in bladder tissue may be relevant to more chronic diseases of the urinary tract such as recurrent UTIs and interstitial cystitis.

Animals↗
PubMed2001

The impact of glaucoma on the quality of life of patients in Norway. I. Results from a self-administered questionnaire.

PURPOSE: To evaluate the feelings and experiences of patients living with glaucoma. METHODS: A questionnaire was delivered to patients willing to take part, at a regular visit to their ophthalmologist, for filling in anonymously at home. A total of 589 questionnaires were returned. RESULTS: More than 80% reported negative emotions on learning that they had glaucoma, one-third were afraid of going blind. Half the patients had no visual problem at all, 14% complained of poor or very poor vision. This proportion increased with age. One-fourth of the patients on topical medication experienced adverse effects of moderate or high degree. About half the patients being treated with laser or surgery felt their situation had improved afterwards. Nine-tenths of the individuals were satisfied with the information and care given, although their knowledge about glaucoma was rather incomplete. One-fifth missed information, mainly on causes, treatment and prognosis of the disease. The younger patients were more anxious and inquiring, reported more side effects and were less satisfied than the older patients. The women were in general more dissatisfied than the men. CONCLUSION: Giving a patient a diagnosis of glaucoma influences his quality of life negatively. Only half of our patients experienced any visual difficulties, whereas one-fourth reported adverse reactions due to the therapy. Most of the patients were very satisfied with the information and care given. Ophthalmologists in private practice are quite central in the management and care of the glaucoma patients in a medical setting like ours.

Adult↗
PubMed2001

The impact of glaucoma on the quality of life of patients in Norway. II. Patient response correlated to objective data.

PURPOSE: To elucidate the relationship between the visual difficulties reported by patients treated for glaucoma and their objective functional damage, and to evaluate the reliability of the patient responses. METHODS: Questionnaires concerning quality of life filled in at home by 589 patients treated for chronic open angle glaucoma were correlated to corresponding questionnaires returned from their ophthalmologists. RESULTS: Few of our patients had a visual field damage judged to be of functional significance. There was a weak to moderate association between both visual field defects and decreased visual acuity and self-reported visual difficulties. A high proportion of the patients had normal binocular visual field and a stable disease, raising the suspicion that some of them were treated for ocular hypertension. The agreement between the responses from the patients and the ophthalmologists concerning the topical treatment was good, regarding treatment duration and other diseases of the patients the agreement was moderate. CONCLUSION: The association between subjective visual disability and presence of visual field defects was weak to moderate in our patients treated for glaucoma, and this association was further weakened by adjusting for visual acuity. Some patients might be treated unnecessarily, and a favourable prognosis might be given to most of them. The reliability of the patients in general was good.

Adult↗
PubMed2001

Establishment of a persistent Escherichia coli reservoir during the acute phase of a bladder infection.

The vast majority of urinary tract infections are caused by strains of uropathogenic Escherichia coli that encode filamentous adhesive organelles called type 1 pili. These structures mediate both bacterial attachment to and invasion of bladder epithelial cells. However, the mechanism by which type 1 pilus-mediated bacterial invasion contributes to the pathogenesis of a urinary tract infection is unknown. Here we show that type 1-piliated uropathogens can invade the superficial epithelial cells that line the lumenal surface of the bladder and subsequently replicate, forming massive foci of intracellular E. coli termed bacterial factories. In response to infection, superficial bladder cells exfoliate and are removed with the flow of urine. To avoid clearance by exfoliation, intracellular uropathogens can reemerge and eventually establish a persistent, quiescent bacterial reservoir within the bladder mucosa that may serve as a source for recurrent acute infections. These observations suggest that urinary tract infections are more chronic and invasive than generally assumed.

Acute Disease↗
PubMed2000

Role of intestinal surfactant-like particles as a potential reservoir of uropathogenic Escherichia coli.

The binding of uropathogenic Escherichia coli is mediated at the tips of pili by the PapG adhesin, which recognizes the Galalpha(1-4)Gal disaccharide on the uroepithelial surface. These receptors have been identified unequivocally in the human and murine urinary tracts but not in intestinal epithelium, yet uropathogenic E. coli strains are commonly found in normal colonic microflora. The gastrointestinal tract from duodenum to rectum elaborates a phospholipid-rich membrane particle with surfactant-like properties. In these studies, we report that purified murine particles contain a receptor recognized by the class I PapG adhesin because: (1) PapD-PapG complexes and class I pili bound to surfactant-like particles in a solid-phase assay, whereas binding was not detected in microvillous membranes derived from the same tissues, (2) purified PapD-PapG complex bound to a glycolipid receptor detectable in lipid extracts from the particles, and (3) soluble Galalpha(1-4)Gal inhibited the adhesin by 72% from binding to surfactant-like particles. The Galalpha(1-4)Gal receptor present in the intestinal surfactant-like particle which overlies the intestinal mucosa could provide one means to establish an intestinal habitat for uropathogenic E. coli.

Adhesins, Escherichia coli↗
PubMed2000

Cell biology. Bacterial spelunkers.

Bacteria that are engulfed by phagocytic cells of the immune system are usually destroyed once inside the host cell but not always. Why is it that sometimes engulfed bacteria survive and thrive quite happily inside the host cell? As Mulvey and Hultgren explain in their Perspective, the answer may lie in small indentations in the host cell plasma membrane called caveolae that direct certain signal transduction pathways inside the host cell (Shin et al.). If bacteria adhere to regions of the host cell surface that is rich in caveolae, they are better able to survive once inside the cell.

Adhesins, Bacterial↗
PubMed2000

Snapshots of usher-mediated protein secretion and ordered pilus assembly.

Type 1 pilus biogenesis was used as a paradigm to investigate ordered macromolecular assembly at the outer cell membrane. The ability of Gram-negative bacteria to secrete proteins across their outer membrane and to assemble adhesive macromolecular structures on their surface is a defining event in pathogenesis. We elucidated genetic, biochemical, and biophysical requirements for assembly of functional type 1 pili. We discovered that the minor pilus protein FimG plays a critical role in nucleating the formation of the adhesive tip fibrillum. Genetic methods were used to trap pilus subunits during their translocation through the outer membrane usher protein, providing data on the structural interactions that occur between subunit components during type 1 pilus formation. Electron microscopic and biochemical analyses of these stepwise assembly intermediates demonstrated that translocation of pilus subunits occurs linearly through the usher's central channel, with formation of the pilus helix occurring extracellularly. Specialized pilin subunits play unique roles both in this multimerization and in the final ultrastructure of the adhesive pilus.

Animals↗
PubMed2000

Bad bugs and beleaguered bladders: interplay between uropathogenic Escherichia coli and innate host defenses.

Strains of uropathogenic Escherichia coli (UPEC) are the causative agents in the vast majority of all urinary tract infections. Upon entering the urinary tract, UPEC strains face a formidable array of host defenses, including the flow of urine and a panoply of antimicrobial factors. To gain an initial foothold within the bladder, most UPEC strains encode filamentous surface adhesive organelles called type 1 pili that can mediate bacterial attachment to, and invasion of, bladder epithelial cells. Invasion provides UPEC with a protective environment in which bacteria can either replicate or persist in a quiescent state. Infection with type 1-piliated E. coli can trigger a number of host responses, including cytokine production, inflammation, and the exfoliation of infected bladder epithelial cells. Despite numerous host defenses and even antibiotic treatments that can effectively sterilize the urine, recent studies demonstrate that uropathogens can persist within the bladder tissue. These bacteria may serve as a reservoir for recurrent infections, a common problem affecting millions each year.

Animals↗
PubMed2000

Stereoselective synthesis of optically active beta-lactams, potential inhibitors of pilus assembly in pathogenic bacteria.

[reaction: see text] Optically active beta-lactams 3 are obtained in excellent yields (up to 93%) and with complete stereoselectivity from Meldrum's acid derivatives 1 and Delta(2)-thiazolines 2. A selective reduction to aldehydes 5 (R = Ar or CH(2)Ar) was then accomplished by using DIBAL-H. This rigid framework, with stereochemistry different than that of penicillin, is designed to be a suitable scaffold for the development of compounds inhibiting pilus formation in uropathogenic Escherichia coli.

Anti-Bacterial Agents↗
PubMed2000

PapD-like chaperones provide the missing information for folding of pilin proteins.

A fundamental question in molecular biology is how proteins fold into domains that can serve as assembly modules for building up large macromolecular structures. The biogenesis of pili on the surface of Gram-negative bacteria requires the orchestration of a complex process that includes protein synthesis, folding via small chaperones, secretion, and assembly. The results presented here support the hypothesis that pilus subunit folding and biogenesis proceed via mechanisms termed donor strand complementation and donor strand exchange. Here we show that the steric information necessary for pilus subunit folding is not contained in one polypeptide sequence. Rather, the missing information is transiently donated by a strand of a small chaperone to allow folding. Providing the missing information for folding, via a 13-amino acid peptide extension to the C-terminal end of a pilus subunit, resulted in the production of a protein that no longer required the chaperone to fold. This mechanism of small periplasmic chaperone function described here deviates from classical hsp60 chaperone-assisted folding.

Adhesins, Bacterial↗
PubMed2000

Type 1 pilus-mediated bacterial invasion of bladder epithelial cells.

Most strains of uropathogenic Escherichia coli (UPEC) encode filamentous adhesive organelles called type 1 pili. We have determined that the type 1 pilus adhesin, FimH, mediates not only bacterial adherence, but also invasion of human bladder epithelial cells. In contrast, adherence mediated by another pilus adhesin, PapG, did not initiate bacterial internalization. FimH-mediated invasion required localized host actin reorganization, phosphoinositide 3-kinase (PI 3-kinase) activation and host protein tyrosine phosphorylation, but not activation of Src-family tyrosine kinases. Phosphorylation of focal adhesin kinase (FAK) at Tyr397 and the formation of complexes between FAK and PI 3-kinase and between alpha-actinin and vinculin were found to correlate with type 1 pilus-mediated bacterial invasion. Inhibitors that prevented bacterial invasion also blocked the formation of these complexes. Our results demonstrate that UPEC strains are not strictly extracellular pathogens and that the type 1 pilus adhesin FimH can directly trigger host cell signaling cascades that lead to bacterial internalization.

Actins↗