Biomedical subjects
Publications and source records attributed to P Walter.
Hereditary haemorrhagic telangiectasis (HHT) has long been viewed as a rare disease which is not usually associated with high morbidity and mortality. We report three patients with HHT who developed cerebral abscesses secondary to pulmonary arteriovenous malformations (PAVM).
BACKGROUND: We report on the case of a 23-year-old female who presented with ocular signs of progressive outer retinal necrosis (PORN) syndrome and who failed to respond to acyclovir, ganciclovir, foscarnet and oral sorivudine. METHODS: The patient was treated with the antiviral drugs acyclovir, ganciclovir, foscarnet and oral sorivudine. RESULTS: The patient failed to respond to a combination of antiviral drugs. Unfortunately, progression of the retintis occurred, which led to blindness. CONCLUSION: Despite new drugs, the prognosis of PORN is poor and recurrence is common.
OBJECTIVES: Microembolic signals (high-intensity transient signals, HITS) detected by means of transcranial Doppler sonography (TCD) may be relevant for intraoperative strokes in carotid endarterectomy (CEA). MATERIAL AND METHODS: An intraoperative HITS detection study was performed on 77 patients (63 men, 14 women, mean age+/-SD, 64+/-8 years) with a total of 81 CEAs. Using the Scandinavian Stroke Scale the patients were clinically examined by a neurologist preoperatively and postoperatively within 6 h. A deterioration of the Scandinavian Stroke Scale was considered an intraoperative stroke if persisting longer than 24 h. Cranial computed tomography (CT scan) was performed preoperatively and 3 to 5 days postoperatively. By means of TCD total HITS count and mean blood velocity changes, for shunting, were recorded sufficiently in the middle cerebral artery in 79 CEAs. RESULTS: HITS were significantly more frequent in symptomatic [n = 53; HITS: median, 15 (range 1-159)] than in asymptomatic stenoses [n = 26; HITS: 6.5 (0-41); P < 0.001]. An intraoperative stroke in the hemisphere ipsilateral to the operation occurred in eight of the 81 CEAs. On postoperative CT scans, five of the eight strokes showed new corresponding territorial infarctions. In the three strokes without new CT lesions, the mean blood velocity changes after clamping indicated normal cerebral perfusion. Total HITS count was significantly higher in procedures with intraoperative strokes [n = 8; HITS: 33 (11-159)] than in the uncomplicated [n = 71; HITS: 10 (0-62); P = 0.002]. No stroke occurred in 37 CEAs with 10 or less HITS, but eight in 42 CEAs with 11 or more HITS [P = 0.006; relative risk 1.23 (95% confidence interval: 1.06 to 1.43)]. CONCLUSION: Microembolism seems clinically relevant in carotid endarterectomy. Asymptomatic patients may run a lower risk of intraoperative embolization.
Cells respond to an accumulation of unfolded proteins in the endoplasmic reticulum (ER) by increasing transcription of genes encoding ER resident proteins. The information is transmitted from the ER lumen to the nucleus by an intracellular signaling pathway called the unfolded protein response (UPR). Recent work has shown that this signaling pathway utilizes several novel mechanisms, including translational attenuation and a regulated mRNA splicing step. In this review we aim to integrate these recent advances with current knowledge about maintenance of ER composition and abundance.
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PURPOSE: Adjuvant intravitreal daunomycin is frequently used for the management of proliferative vitreoretinopathy (PVR). In this study the authors examined whether daunomycin could induce multidrug resistance (MDR), mediated by the mdr-1 gene product P-glycoprotein, in the cells responsible for reproliferation in vivo and in human retinal pigment epithelial (RPE) cells in vitro. METHODS: Expression of P-glycoprotein was examined by immunohistochemistry in surgically removed epiretinal membranes. The cellular source of P-glycoprotein was examined by colabeling for cytokeratin, glial fibrillary acidic protein, and the macrophage marker EBM-11. P-glycoprotein expression by cultured RPE cells was assessed by reverse transcription-polymerase chain reaction and immunoblot analysis. Daunomycin toxicity was quantified by crystal violet assay. RESULTS: P-glycoprotein expression was detected in 10 of 10 patients pre-exposed to intravitreal daunomycin. In contrast, epiretinal membranes from only 2 of 13 patients never exposed to daunomycin showed faint P-glycoprotein expression. P-glycoprotein expression was strong within 8 months after daunomycin treatment and faded thereafter. Colocalization studies demonstrated predominant expression of P-glycoprotein by RPE cells. Pre-exposure of cultured human RPE cells to subtoxic concentrations of daunomycin induced resistance to daunomycin that was sensitive to the MDR inhibitor, verapamil. Induction of the MDR phenotype in RPE cells by daunomycin was associated with a minor increase in the mdr-1 mRNA level but a prominent increase in P-glycoprotein expression, thus suggesting a primarily translational mechanism of MDR development in human RPE cells. CONCLUSIONS: Intravitreal daunomycin induced P-glycoprotein expression in PVR. Reproliferation in daunomycin-pretreated patients probably necessitates cotreatment with daunomycin and inhibitors of multidrug resistance such as verapamil or administration of antiproliferative drugs such as 5-fluorouracil, which act in a MDR-independent fashion.
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BACKGROUND: The unfolded protein response (UPR) is an intracellular signaling pathway that is activated by the accumulation of unfolded proteins in the endoplasmic reticulum (ER). The UPR results in an increase in transcription of ER-resident proteins that facilitate protein folding in the ER. A key regulatory step in UPR activation is the regulated splicing of HAC1 mRNA, which encodes Hac1p, a transcription factor dedicated to this pathway. Hac1p can be detected only when the spliced form of HAC1 mRNA (termed HAC1i mRNA, for induced) is produced; this was surprising because the unspliced HAC1u mRNA (HAC1u for uninduced) is equally stable in cells. RESULTS: We show that in contrast to most other unspliced pre-mRNAs, the HAC1u mRNA is transported from the nucleus into the cytosol. Although HAC1u mRNA is associated with polyribosomes, no detectable Hac1pu is produced unless the intron is removed, indicating that the presence of the intron prevents mRNA translation. When it is produced, Hac1pu has a stability similar to that of Hac1pi, the form of the Hac1p that is produced from the spliced mRNA and that differs from Hac1pu by a short carboxy-terminal tail sequence. Hac1pu, however, is differently modified and less active in activating transcription. Interestingly, when transplanted into the 3' untranslated region of a completely unrelated mRNA, the HAC1 intron is sufficient to attenuate translation of the preceding open reading frame. CONCLUSIONS: We have shown that the HAC1 mRNA intron is both necessary and sufficient to prevent complete translation of polyribosome-associated mRNAs. To our knowledge, this identifies a new way by which translation of a mRNA can be attenuated.
The endoplasmic reticulum (ER) communicates with the nucleus through the unfolded protein response (UPR), which senses accumulation of unfolded proteins in the ER lumen and leads to increased transcription of genes encoding ER-resident chaperones. As a key regulatory step in this signaling pathway, the mRNA encoding the UPR-specific transcription factor Hac1p becomes spliced by a unique mechanism that requires tRNA ligase but not the spliceosome. Splicing is initiated upon activation of Ire1p, a transmembrane kinase that lies in the ER and/or inner nuclear membrane. We show that Ire1p is a bifunctional enzyme: in addition to being a kinase, it is a site-specific endoribonuclease that cleaves HAC1 mRNA specifically at both splice junctions. The addition of purified tRNA ligase completes splicing; we therefore have reconstituted HAC1 mRNA splicing in vitro from purified components.
The Ffh-4.5S ribonucleoprotein particle (RNP) and FtsY from Escherichia coli are homologous to essential components of the mammalian signal recognition particle (SRP) and SRP receptor, respectively. The ability of these E. coli components to function in a bona fide co-translational targeting pathway remains unclear. Here we demonstrate that the Ffh-4.5S RNP and FtsY can efficiently replace their mammalian counterparts in targeting nascent secretory proteins to microsomal membranes in vitro. Targeting in the heterologous system requires a hydrophobic signal sequence, utilizes GTP and, moreover, occurs co-translationally. Unlike mammalian SRP, however, the Ffh-4.5S RNP is unable to arrest translational elongation, which results in a narrow time window for the ribosome nascent chain to interact productively with the membrane-bound translocation machinery. The highly negatively charged N-terminal domain of FtsY, which is a conserved feature among prokaryotic SRP receptor homologs, is important for translocation and acts to localize the protein to the membrane. Our data illustrate the extreme functional conservation between prokaryotic and eukaryotic SRP and SRP receptors and suggest that the basic mechanism of co-translational protein targeting is conserved between bacteria and mammals.
The signal-recognition particle (SRP) and its receptor (SR) function in the co-translational targeting of nascent protein-ribosome complexes to the membrane translocation apparatus. The SRP protein subunit (termed Ffh in bacteria) that recognizes the signal sequence of nascent polypeptides is a GTPase, as is the SR-alpha subunit (termed FtsY). Ffh and FtsY interact directly, each stimulating the GTP hydrolysis activity of the other. The sequence of Ffh suggests three domains: an amino-terminal N domain of unknown function, a central GTPase G domain, and a methionine-rich M domain that binds both SRP RNA and signal peptides. Sequence conservation suggests that structurally similar N and G domains are present in FtsY. Here we report the structure of the nucleotide-free form of the NG fragment of Ffh. Consistent with a role for apo Ffh in protein targeting, the side chains of the empty active-site pocket form a tight network of interactions which may stabilize the nucleotide-free protein. The structural relationship between the two domains suggests that the N domain senses or controls the nucleotide occupancy of the GTPase domain. A structural subdomain unique to these evolutionarily conserved GTPases constitutes them as a distinct subfamily in the GTPase superfamily.
BACKGROUND: Birt-Hogg-Dubé's syndrome is a rare skin disease characterized by multiple trichofibromas of the skin and polyps of the intestine. Ophthalmologic manifestations associated with the syndrome have not been reported in detail. CASE REPORTS AND METHODS: Two siblings suffering from Birt-Hogg-Dubé syndrome were examined clinically. Electrooculography and electroretinography were performed according to international standards. Color fundus photographs were taken as well as fluorescein angiograms. The two patients showed multiple perifollicular fibromas and trichodiscomas of the skin of the head. Funduscopy and fluorescein angiography revealed a flecked chorioretinopathy in one patient with progressive constriction of visual fields and severely reduced electroretinographic responses. Ophthalmoscopy in his sister showed peripheral pigmentary changes with only minor functional abnormalities. CONCLUSION: These findings suggest that Birt-Hogg-Dubé syndrome may be associated with a progressive flecked chorioretinopathy with constricted visual fields and that patients with the syndrome should undergo ophthalmological examination.
In a patient with uveitis who had been treated with Nd:YAG laser capsulotomy after cataract surgery, several episodes of acute hypotonia occurred which were associated with changes in clinical tests of the eye and of visual function. Immunosuppressive and immunomodulating treatment appeared to reverse the changes in intraocular pressure and normalise the test results. The significance of these observations is discussed.
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BACKGROUND: Vitrectomy serves as an important treatment modality in uveitis, removing inflamed vitreous body and eliminating secondary complications. The aim of our retrospective study was to evaluate the value of vitrectomy in the treatment of complications in uveitis. PATIENTS AND METHOD: We included 50 eyes of 50 patients suffering from chronic uveitis, which underwent vitrectomy surgery during the period of 1990 to 1993. The study only included patients who had vitrectomy for uveitis for the first time. Indications leading to surgery were density of optic media, retinal detachment, cyclitic or preretinal membranes. The mean follow-up was 455 (range 48-1420) days. RESULTS: Vitrectomy was performed at a mean delay of 452 days after initial presentation. The mean visual acuity at the time of surgery was 0.05. The best visual acuity postoperatively was measured at a mean time of 118 days after vitrectomy. Overall, at the last control, eyes with preoperative retinal detachment presented a much worse final functional result (visual acuity of 0.02) than eyes without detachment (visual acuity of 0.5). Ten eyes resulted in hypotonia after surgery (7 eyes with persisting hypotonia). Most frequent complications in the postoperative course were macular pucker (11 eyes), secondary glaucoma (10 eyes), macular edema (6 eyes) and retinal detachment (6 eyes). Fifty percent of all complications occurred within the first 3 months following surgery. CONCLUSION: Vitrectomy leads to a permanent increase in visual acuity through the treatment of complications, on the condition that a stable retinal situation was present preoperatively.
To gain insight into the process of mitochondrial transmission in yeast, we directly labeled mitochondrial proteins and mitochondrial DNA (mtDNA) and observed their fate after the fusion of two cells. To this end, mitochondrial proteins in haploid cells of opposite mating type were labeled with different fluorescent dyes and observed by fluorescence microscopy after mating of the cells. Parental mitochondrial protein markers rapidly redistributed and colocalized throughout zygotes, indicating that during mating, parental mitochondria fuse and their protein contents intermix, consistent with results previously obtained with a single parentally derived protein marker. Analysis of the three-dimensional structure and dynamics of mitochondria in living cells with wide-field fluorescence microscopy indicated that mitochondria form a single dynamic network, whose continuity is maintained by a balanced frequency of fission and fusion events. Thus, the complete mixing of mitochondrial proteins can be explained by the formation of one continuous mitochondrial compartment after mating. In marked contrast to the mixing of parental mitochondrial proteins after fusion, mtDNA (labeled with the thymidine analogue 5-bromodeoxyuridine) remained distinctly localized to one half of the zygotic cell. This observation provides a direct explanation for the genetically observed nonrandom patterns of mtDNA transmission. We propose that anchoring of mtDNA within the organelle is linked to an active segregation mechanism that ensures accurate inheritance of mtDNA along with the organelle.
The endoplasmic reticulum (ER) is a multifunctional organelle responsible for production of both lumenal and membrane components of secretory pathway compartments. Secretory proteins are folded, processed, and sorted in the ER lumen and lipid synthesis occurs on the ER membrane itself. In the yeast Saccharomyces cerevisiae, synthesis of ER components is highly regulated: the ER-resident proteins by the unfolded protein response and membrane lipid synthesis by the inositol response. We demonstrate that these two responses are intimately linked, forming different branches of the same pathway. Furthermore, we present evidence indicating that this coordinate regulation plays a role in ER biogenesis.
OBJECTIVES: Helicobacter pylori infection is associated with an exaggeration of gastrin release following meals or bombesin stimulation attributed to a defect of somatostatin secretion of antral D-cells. Nevertheless, these modifications of gastric physiology do not explain the increase of gastric acid secretion which is only observed in duodenal ulcer patients. The inhibitory effect of somatostatin secretion of fundic D-cells on parietal cells is well known. The aim of our prospective study was to compare the number of fundic D-cells and likewise the number of antral G-cells and D-cells between patients with duodenal ulcer and healthy subjects with and without H. pylori infection. METHODS: The numbers of D-cells and G-cells were compared between 19 infected patients with duodenal ulcer and 20 healthy subjects, 10 with and 10 without H. pylori infection. Fundic mucosal biopsy specimens were examined using immunohistochemical techniques specific for the presence of somatostatin, antral mucosal biopsy specimens for the presence of gastrin and somatostatin. RESULTS: The number of G-cells was significantly lower (P = 0.0012) in duodenal ulcer patients by comparison with infected subjects and controls. The number of antral D-cells was significantly less (P < 0.0001) in duodenal ulcer patients (mean of 10 random fields = 0.45 +/- 0.04) than in either asymptomatic infected patients (0.65 +/- 0.07) or uninfected controls (0.88 +/- 0.10). The number of fundic D-cells was significantly lower (P < 0.0001) in duodenal ulcer patients (mean = 0.20 +/- 0.03) than in either asymptomatic infected subjects (0.29 +/- 0.05) or controls (0.73 +/- 0.09); here the difference between the two groups of infected subjects was not significant. Multivariate analysis showed that the presence of H. pylori infection of the fundic mucosa did not influence the number of fundic D-cells. CONCLUSION: Changes in the number of fundic and antral D-cells induced by H. pylori infection did not explain abnormalities of gastric acid secretion usually observed in duodenal ulcer patients; it is suggested that pre-existing abnormalities in the regulation of parietal cell or increase of parietal cell mass are involved.