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Biomedical subjects

H Semb

Publications and source records attributed to H Semb.

At least 19 recordsLinked to original sources
PubMed2001

Dorsal pancreas agenesis in N-cadherin- deficient mice.

Members of the cadherin family of cell adhesion molecules are thought to be crucial regulators of tissue patterning and organogenesis. During pancreatic ontogeny N-cadherin is initially expressed in the pancreatic mesenchyme and later in pancreatic endoderm. Analysis of N-cadherin-deficient mice revealed that these mice suffer from selective agenesis of the dorsal pancreas. Further analysis demonstrated that the mechanism for the lack of a dorsal pancreas involves an essential function of N-cadherin as a survival factor in the dorsal pancreatic mesenchyme.

Animals↗
PubMed1999

Neural cell adhesion molecule (N-CAM) is required for cell type segregation and normal ultrastructure in pancreatic islets.

Classical cell dissociation/reaggregation experiments with embryonic tissue and cultured cells have established that cellular cohesiveness, mediated by cell adhesion molecules, is important in determining the organization of cells within tissue and organs. We have employed N-CAM-deficient mice to determine whether N-CAM plays a functional role in the proper segregation of cells during the development of islets of Langerhans. In N-CAM-deficient mice the normal localization of glucagon-producing alpha cells in the periphery of pancreatic islets is lost, resulting in a more randomized cell distribution. In contrast to the expected reduction of cell-cell adhesion in N-CAM-deficient mice, a significant increase in the clustering of cadherins, F-actin, and cell-cell junctions is observed suggesting enhanced cadherin-mediated adhesion in the absence of proper N-CAM function. These data together with the polarized distribution of islet cell nuclei and Na+/K+-ATPase indicate that islet cell polarity is also affected. Finally, degranulation of beta cells suggests that N-CAM is required for normal turnover of insulin-containing secretory granules. Taken together, our results confirm in vivo the hypothesis that a cell adhesion molecule, in this case N-CAM, is required for cell type segregation during organogenesis. Possible mechanisms underlying this phenomenon may include changes in cadherin-mediated adhesion and cell polarity.

Animals↗
PubMed1999

Odor identification in normal aging and early Alzheimer's disease: effects of retrieval support.

Odor sensitivity and identification were examined in normal aging and early Alzheimer's disease (AD). The aims were to investigate AD as associated with lower odor sensitivity, odor identification as a function of retrieval support, and the relationship between global cognitive functioning (Mini-Mental State Exam [MMSE]; M. F. Folstein, S. E. Folstein, & P. R. McHugh, 1975) and olfactory performance. Results indicated intact odor sensitivity but deficient odor identification in AD. Both groups benefited from cues in identification, and the size of the gains was equally large in AD patients and controls. The finding of no selective benefit from retrieval support in AD suggests that a degradation of olfactory knowledge contributes to the odor identification deficits in these patients. MMSE and identification were positively related, whereas MMSE and olfactory sensitivity were unrelated. These findings suggest that the AD-related olfactory impairment stems from lesions in cortical rather than peripheral structures.

Aged↗
PubMed1999

Reduced expression of neural cell adhesion molecule induces metastatic dissemination of pancreatic beta tumor cells.

As in the development of many human cancers, in a transgenic mouse model of beta-cell carcinogenesis (Rip1Tag2), expression of neural cell adhesion molecule (NCAM) changes from the 120-kDa isoform in normal tissue to the 140/180-kDa isoforms in tumors. NCAM-deficient RiplTag2 mice, generated by crossing Rip1Tag2 mice with NCAM knockout mice, develop metastases, a tumor stage that is not seen in normal Rip1Tag2 mice. In contrast, overexpression of NCAM 120 in NCAM-deficient Rip1Tag2 mice prevents tumor metastasis. The results indicate that the loss of NCAM-mediated cell adhesion is one rate-limiting step in the actual metastatic dissemination of beta tumor cells.

Animals↗
PubMed1998

A causal role for E-cadherin in the transition from adenoma to carcinoma.

Development of malignant tumours is in part characterized by the ability of a tumour cell to overcome cell-cell adhesion and to invade surrounding tissue. E-cadherin is the main adhesion molecule of epithelia, and it has been implicated in carcinogenesis because it is frequently lost in human epithelial cancers. Re-establishing the functional cadherin complex in tumour cell lines results in a reversion from an invasive to a benign epithelial phenotype. However, it remained unresolved whether the loss of E-cadherin-mediated cell adhesion was a cause or a consequence of tumour progression in vivo. Here we report that the loss of E-cadherin expression coincides with the transition from well differentiated adenoma to invasive carcinoma in a transgenic mouse model of pancreatic beta-cell carcinogenesis (Rip1Tag2). Intercrossing Rip1Tag2 mice with transgenic mice that maintain E-cadherin expression in beta-tumour cells results in arrest of tumour development at the adenoma stage, whereas expression of a dominant-negative form of E-cadherin induces early invasion and metastasis. The results demonstrate that loss of E-cadherin-mediated cell adhesion is one rate-limiting step in the progression from adenoma to carcinoma.

Adenoma, Islet Cell↗
PubMed1997

A potential role of R-cadherin in striated muscle formation.

We have examined the murine embryonic expression pattern of the cell adhesion molecule R-cadherin in muscle, kidney, thymus, and lung. In developing muscle, R-cadherin was first seen at 10.5-11.5 days postcoitum in the somitic myotome. Consistently, we found R-cadherin expressed at the highest levels in the myotome, early skeletal muscle, and smooth muscle (both vascular and visceral), while very low levels of R-cadherin were detected in the heart. The expression pattern and subcellular localization of R-cadherin in developing skeletal muscle indicate a possible role in myoblast cell-cell interactions during both primary and secondary myogenesis. In the developing kidney, R-cadherin was first detected at 10.5 days postcoitum in the mesonephric epithelial tubule cells. In the metanephric kidney, it was specifically expressed in the pretubular aggregates, comma- and S-shaped bodies, proximal tubules, and collecting ducts. Thus, in the kidney, R-cadherin was associated with the mesenchymal-epithelial transition. R-cadherin was also found in other developing epithelia, for example in the thymic epithelial cells. In the lung, R-cadherin was expressed at the highest levels in the smooth muscle surrounding the lung epithelial tubules. To test whether R-cadherin can direct formation of tissues, we constitutively expressed R-cadherin in E-cadherin-/- ES cells and examined histogenesis in teratomas derived from these cells. R-cadherin exclusively rescued formation of striated muscle and epithelia in the teratomas. R-cadherin's ability to form epithelia in vivo was substantiated by its ability to rescue formation of cystic embryoid bodies in vitro. By comparing our data with the previously reported embryonic expression patterns and histogenetic activities of E- and N-cadherin, we suggest that R-cadherin plays an important role in the formation of striated muscle and possibly also of epithelia.

Animals↗
PubMed1997

Effects of divalent cations on M-cadherin expression and distribution during primary rat myogenesis in vitro.

In the process of myogenesis, cadherins are thought to be involved in the initial cell-cell recognition and possible initiation of myoblast fusion to form multinucleated myotubes. Of the cadherins, M-cadherin, but not N-cadherin, is down-regulated upon inhibition of myogenesis, suggesting that M-cadherin may be a key receptor involved in myogenesis. M-cadherin binds in a calcium-dependent manner, and depletion of divalent cations inhibits myoblast fusion. We analyzed the regulation of M-cadherin protein and mRNA levels in primary rat myogenic cultures in the presence and absence of divalent cations. In untreated cultures M-cadherin was localized to various myogenic cell-cell contacts. M-cadherin protein and mRNA levels showed a peak at day 2 after the initiation of growth. When divalent cations were removed from the cell culture medium, myoblast fusion was inhibited and immunocytochemical analysis revealed a failure of M-cadherin to localize to cell-cell contacts. Analysis of M-cadherin protein and mRNA in fusion-inhibited cultures still revealed a peak at day 2. However, by day 3, M-cadherin protein levels in the fusion-inhibited cultures were reduced in both the detergent-soluble and -insoluble fractions in comparison with the untreated cultures. Interestingly, beta-catenin, a protein associated with cadherins, was frequently observed at intercellular contacts in the fusion-inhibited cultures. We could also show that the intracellular levels of beta-catenin protein remained constant regardless of the presence or absence of divalent cations. In summary, the dynamic regulation of M-cadherin in muscle-fusion-related events is an indication of the importance of M-cadherin for myoblast fusion and myogenic differentiation.

Animals↗
PubMed1996

Cadherins regulate aggregation of pancreatic beta-cells in vivo.

It is thought that the cadherin protein family of cell adhesion molecules regulates morphogenetic events in multicellular organisms. In this study we have investigated the importance of beta-cell cadherins for cell-cell interactions mediating the organization of endocrine cells into pancreatic islets of Langerhans. To interfere with endogenous cadherin activity in beta-cells during pancreatic development, we overexpressed a dominant negative mutant of mouse E-cadherin, lacking nearly all extracellular amino acids, in pancreatic beta-cells in transgenic mice. Expression of the truncated E-cadherin receptor displaced both E- and N-cadherin from pancreatic beta-cells. As a result, the initial clustering of beta-cells, which normally begins at 13.5-14.5 days postcoitum, was perturbed. Consequently, the clustering of endocrine cells into islets, which normally begins at 17.5-18 days postcoitum, was abrogated. Instead, transgenic beta-cells were found dispersed in the tissue as individual cells, while alpha-cells selectively aggregated into islet-like clusters devoid of beta-cells. Furthermore, expression of truncated E-cadherin in beta-cells resulted in an accumulation of beta-catenin in the cytoplasm. Thus, we have for the first time shown in vivo that cadherins regulate adhesive properties of beta-cells which are essential for the aggregation of endocrine cells into islets.

Animals↗
PubMed1995

Mouse R-cadherin: expression during the organogenesis of pancreas and gastrointestinal tract.

Members of the cadherin protein family of cell adhesion molecules are thought to regulate many morphogenetic events during the development of multicellular organisms. We are interested in which cell-cell interactions cadherins regulate during pancreas morphogenesis. Expression and function of E-cadherin in the pancreas have previously been characterized. Recently, R-cadherin cDNA was isolated and the expression patterns of R- and N-cadherin cDNA was isolated and the expression patterns of R- and N-cadherin mRNAs in the pancreas have been described. In the present study, we have investigated the expression of R-cadherin in the pancreas and gastrointestinal tract using specific anti-R-cadherin antibodies. During early stages of pancreas development (E10.5) R-cadherin is expressed in most hormone-producing cells in addition to in primitive duct-like cells. Later, at E18.5, when islets start to form, R-cadherin is not expressed in intraislet endocrine cells, but is instead found in intraductule endocrine and exocrine cells. In adult islets of Langerhans R-cadherin is absent from endocrine cells, but is present in ductule-like cells. Furthermore, the molecule is expressed in exocrine cells: apically and basolaterally on epithelial duct and ductule cells and apically on acinar cells. Interestingly, there appears to be a correlation between the downregulation of R-cadherin expression in intraductule endocrine cells and the migration out of the duct epithelium to form islets. In the gastrointestinal tract R-cadherin is expressed in the pit region of gastric glands and in absorptive cells of the small intestine. The subcellular localization in these tissues is on both the apical and basolateral surfaces. The potential function of R-cadherin, in particular its role in pancreas development, is discussed.

Animals↗
PubMed1992

Renal function not impaired by hip arthroplasty. A prospective study of 26 patients.

To evaluate the importance of various changes during major surgery, 26 patients, electively chosen for total hip replacement (THR), were investigated for renal function preoperatively and postoperatively. In most of the patients, surgery was performed ad modum Charnley (n 25), and anesthesia was given mainly by continuous administration of bupivacaine or mepivacaine through an epidural catheter. Postoperatively, there was an improvement in glomerular filtration rate (GFR) and a reduction in renal concentrating ability (RCA), but no change in diurnal albumin excretion. No correlation was found between the change in GFR and, e.g., the degree of peroperative hypotension, bleeding, transfusions, or volume of infusions. There was a correlation between the impairment of RCA and the lowering of serum albumin concentration. In 3 patients the GFR was slightly impaired. The risk of contracting severe, acute renal failure seems low in THR performed on patients with reduced or normal kidney function.

Acute Kidney Injury↗
PubMed1990

Hyperlipoproteinemia type I in a patient with active lipoprotein lipase in adipose tissue and indications of defective transport of the enzyme.

This paper presents a case of typical hyperlipoproteinemia type I in a young woman. Her serum triglycerides varied between 2 and 90 mmol/l and she had substantial amounts of apolipoprotein B-48 in fasting plasma. She had no detectable lipoprotein lipase (LPL) activity in post-heparin plasma (less than 0.2 percent of normal). Southern blot analysis suggested no major defect in her LPL gene and Northern blot analysis of adipose tissue RNA showed normal-sized LPL-mRNA. A 2-h [35S]methionine incorporation experiment with adipose tissue pieces in vitro showed that she produced normal-sized LPL and had LPL catalytic activity in the tissue. The amounts were, however, only 5-10% of control. No detectable LPL radioactivity or catalytic activity was released from patient tissue even in the presence of heparin in the incubations. Immunofluorescent staining of adipose tissue biopsies from the patient showed LPL immunoreactivity only in adipocytes and little or none within the capillaries. Treatment of immunoprecipitated labeled LPL with endoglycosidase H showed that the oligosaccharide chains on her enzyme were of the high-mannose type and not processed as in controls. Taken together the data suggest that the patient synthesizes a relatively normal LPL protein which is core-glycosylated and folded into active enzyme as in normal subjects, but is not effectively transported via the Golgi to the cell surface.

Adipose Tissue↗
PubMed1989

Two different mechanisms are involved in nutritional regulation of lipoprotein lipase in guinea-pig adipose tissue.

Lipoprotein lipase activity in adipose tissue responds rapidly to changes in the physiological state. To study what mechanisms are involved in the regulation, guinea pigs were fasted and the decrease in adipose-tissue lipoprotein lipase activity was compared with the decreases in mRNA and lipase synthesis. The mRNA pattern (three species) did not change. There was a close parallelism between the abundance of lipase mRNA and relative lipase synthesis (immunoprecipitable 35S-labelled lipoprotein lipase as fraction of total [35S]protein after pulse-labelling with [35S]methionine). Total protein synthesis decreased on fasting, compounding the decrease in relative lipase synthesis. Lipoprotein lipase mRNA changed similarly in fat-pads and in isolated adipocytes, whereas lipase activity changed more in the pads, indicating disproportionally large changes in extracellularly located lipase. In old guinea pigs the decreases in lipoprotein lipase activity and lipase synthesis were comparable, but in young animals the change in lipase activity was substantially larger than the change in lipase synthesis. Refeeding of fasted young guinea pigs with glucose resulted in a rapid increase in lipoprotein lipase activity, but there was only a small change in lipase mRNA. Old animals responded slowly to refeeding. The results indicate that in older animals the major mechanism for regulation of adipose lipoprotein lipase activity is a relatively slow change in lipase mRNA, whereas in younger animals an additional, more rapid, regulation is exerted on the transport and turnover of the enzyme.

Adipose Tissue↗
PubMed1989

The relation between glycosylation and activity of guinea pig lipoprotein lipase.

Previous studies have indicated that the processing of oligosaccharide chains is necessary for lipoprotein lipase to become catalytically active and may be involved in the regulation of lipase release. Guinea pig adipocytes and perfused guinea pig hearts were labeled with [35S]methionine, and lipoprotein lipase was immunoprecipitated. Digestion with endo-beta-N-acetylglucosaminidase H (Endo H) showed that the mature enzyme contains one high mannose and two complex oligosaccharide chains. Limited proteolysis indicated where in the molecule the chains are attached. Pulse-chase experiments showed that some lipase molecules were rapidly processed and appeared in the medium within 40 min. Other lipase molecules remained fully Endo H-sensitive for more than 2 h, and this form of the lipase did not appear in the medium. Both forms co-eluted with the sole lipoprotein lipase activity peak from heparin-Sepharose; this indicates that both were dimeric. Separation of the two forms was achieved by lectin chromatography and demonstrated that both were catalytically active. Cells treated with methyl-deoxynojirimycin or with deoxymannojirimycin produced and released active lipoprotein lipase which was fully Endo H-sensitive. These studies demonstrate that the trimming and processing of the oligosaccharide chains is not necessary for lipoprotein lipase to become catalytically active and be secreted, and they suggest that a comparatively large fraction of the lipase molecules is retained in the endoplasmic reticulum. Whether they ever reach the processing apparatus in the Golgi or are degraded is not clear.

1-Deoxynojirimycin↗
PubMed1988

Tissue-specific regulation of guinea pig lipoprotein lipase; effects of nutritional state and of tumor necrosis factor on mRNA levels in adipose tissue, heart and liver.

Levels of mRNA for lipoprotein lipase (LPL) in guinea pig epididymal adipose tissue, heart and liver were determined by dot blot analysis of total RNA using a cDNA probe complementary to the coding region, and compared to the LPL activity. For adipose tissue we also measured the incorporation of radioactivity into immunoprecipitable LPL after pulse-labeling with [35S]methionine. LPL activity was 93%, LPL mRNA 82% and LPL synthesis 85% lower in epididymal fat pads from animals fasted for 48 h compared to rigorously fed animals. In contrast, neither LPL activity nor LPL mRNA levels differed in heart. A single dose of tumor necrosis factor (TNF) decreased LPL activity and LPL mRNA in fat pads with no effects in heart. In the liver, TNF caused a marked increase in LPL mRNA levels, which are normally very low. Northern-blot analysis confirmed a previous observation that the patterns of mRNA species differ between heart, in which a 3.8-kb mRNA dominates, and adipose tissue, in which the LPL mRNAs of 3.3 and 2.1 kb occur in similar abundance as the 3.8-kb species.

Adipose Tissue↗
PubMed1987

Mechanisms for turnover of lipoprotein lipase in guinea pig adipocytes.

Guinea-pig adipocytes released lipoprotein lipase activity to the medium without depletion of cell-associated lipoprotein lipase activity. Heparin caused immediate release of 20-25% of the lipase activity to the medium, and also enhanced the continued release. After addition of cycloheximide, cell-associated lipoprotein lipase activity decreased rapidly. Release of lipase activity to the medium continued unabated for about 30 min, but there was little release thereafter. The release accounted for only about 25% of the initial lipoprotein lipase activity in the absence and about 50% in the presence of heparin. In pulse-chase experiments with [35S]methionine, labeled lipoprotein lipase appeared in the medium within 40 min, and most of the release occurred during the first h of chase. In a 4-h chase the total (cells + medium) amount of labeled lipase decreased to 34%. Thus, degradation was a main fate of the lipase. Heparin markedly increased the amount of labeled lipase that was released to the medium and decreased the amount that was degraded. Heparin did not change the time-course for the release, and the amount of labeled lipase degraded was proportional to the amount not released to the medium, indicating that the effect of heparin was primarily on release, not on degradation as such. This study demonstrates that adipocytes synthesize lipoprotein lipase in excess of what is being released, and that the excess is rapidly degraded.

Adipose Tissue↗
PubMed1987

Multiple effects of tumor necrosis factor on lipoprotein lipase in vivo.

A single dose of recombinant murine tumor necrosis factor (TNF) suppressed lipoprotein lipase activity in adipose tissue of fed rats, mice, and guinea pigs for 48 h, even though TNF itself is rapidly metabolized in vivo. Immunoprecipitation of [35S]lipoprotein lipase from fat pads pulse-labeled with [35S]methionine showed a decrease in relative synthesis of the enzyme, which correlated to the decrease in activity. There was no decrease in general protein synthesis and no change in distribution of the enzyme between adipocytes and extracellular locations in the tissue. This is in contrast to fasting in which case there is redistribution of the enzyme within the tissue, decrease in general protein synthesis, but no change in relative synthesis of lipoprotein lipase. TNF did not decrease lipoprotein lipase activity in any tissue other than the adipose but increased the activity in several cases, most markedly in the liver. No [35S]methionine was incorporated into lipoprotein lipase by liver slices from normal or TNF-treated animals. Thus, the increased activity can not be ascribed to enhanced hepatic synthesis of the enzyme. There was an increase in lipoprotein lipase activity in plasma, which correlated to the increase in liver. Thus, TNF suppresses lipoprotein lipase synthesis in adipocytes, but not in other tissues, and has some as yet undefined effect on lipoprotein lipase turnover in extrahepatic tissues, which results in increased transport of active lipase through plasma to the liver.

Adipose Tissue↗