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Biomedical subjects

J R Thorpe

Publications and source records attributed to J R Thorpe.

13 recordsLinked to original sources
PubMed2001

Utilizing the peptidyl-prolyl cis-trans isomerase pin1 as a probe of its phosphorylated target proteins. Examples of binding to nuclear proteins in a human kidney cell line and to tau in Alzheimer's diseased brain.

The human parvulin Pin1 is a member of the peptidyl-prolyl cis-trans isomerase group of proteins, which modulate the assembly, folding, activity, and transport of essential cellular proteins. Pin1 is a mitotic regulator interacting with a range of proteins that are phosphorylated before cell division. In addition, an involvement of Pin1 in the tau-related neurodegenerative brain disorders has recently been shown. In this context, Pin1 becomes depleted from the nucleus in Alzheimer's disease (AD) neurons when it is redirected to the large amounts of hyperphosphorylated tau associated with the neurofibrillary tangles. This depletion from the nucleus may ultimately contribute to neuron cell death. Recently we have devised a novel methodology in which exogenous Pin1 is used as a TEM probe for its target proteins. Here we extend this methodology to provide further evidence that Pin1 binds at enhanced levels to mitotic nuclear proteins and to hyperphosphorylated tau in AD brain. We suggest that exogenous Pin1 labeling can be used to elucidate the phosphorylation status of its target proteins in general and could specifically provide important insights into the development of tau-related neurodegenerative brain disorders.

Alzheimer Disease↗
PubMed2000

Sticky-end assembly of a designed peptide fiber provides insight into protein fibrillogenesis.

Coiled-coil motifs provide simple systems for studying molecular self-assembly. We designed two 28-residue peptides to assemble into an extended coiled-coil fiber. Complementary interactions in the core and flanking ion-pairs were used to direct staggered heterodimers. These had "sticky-ends" to promote the formation of long fibers. For comparison, we also synthesized a permuted version of one peptide to associate with the other peptide and form canonical heterodimers with "blunt-ends" that could not associate longitudinally. The assembly of both pairs was monitored in solution using circular dichroism spectroscopy. In each case, mixing the peptides led to increased and concentration-dependent circular dichroism signals at 222 nm, consistent with the desired alpha-helical structures. For the designed fiber-producing peptide mixture, we also observed a linear dichroism effect during flow orientation, indicative of the presence of long fibrous structures. X-ray fiber diffraction of partially aligned samples gave patterns indicative of coiled-coil structure. Furthermore, we used electron microscopy to visualize fiber formation directly. Interestingly, the fibers observed were at least several hundred micrometers long and 20 times thicker than expected for the dimeric coiled-coil design. This additional thickness implied lateral association of the designed structures. We propose that complementary features present in repeating structures of the type we describe promote lateral assembly, and that a similar mechanism may underlie fibrillogenesis in certain natural systems.

Amino Acid Motifs↗
PubMed1999

Binding of a putative and a known chaperone protein revealed by immunogold labeling transmission electron microscopy: A suggested use of chaperones as probes for the distribution of their target proteins.

Parvulins are a distinct family within the peptidyl-prolyl cis-trans isomerase group of proteins that catalyse the cis-trans isomerization of proline-containing peptides. The intracellular distribution of a novel human parvulin homologue (hEPVH) has been investigated in a human kidney cell line (HEK 293) by immunogold labeling transmission electron microscopy (TEM). This showed hEPVH to be distributed throughout HEK 293 cells but in highest concentration within mitochondria. Unexpectedly, preabsorption of anti-hEPVH antiserum with recombinant hEPVH exaggerated the observed immunolabel density in a pattern that mirrored that of the endogenous hEPVH. The hEPVH protein itself was then used to label sections, and the specificity of its binding was confirmed with the use of polyclonal and monoclonal antibodies in conjunction with homologous and irrelevant protein controls. The pattern of hEPVH binding also mirrored that of endogenous hEPVH. A known chaperone protein, Pin1, was also found to bind to cells in a pattern mirroring that of the endogenous protein. This lends considerable weight to our hypothesis that hEPVH is binding to its target protein(s) within the cell, reflecting its postulated chaperone function. Finally, we suggest that chaperone proteins in general might be used as TEM probes for their target (or substrate) proteins. (J Histochem Cytochem 47:1633-1640, 1999)

Absorption↗
PubMed1996

Nitric oxide donors decrease the function and survival of human pancreatic islets.

Nitric oxide (NO) has been proposed as a possible mediator of beta-cell damage in human IDDM. This hypothesis is based on in vitro studies with rodent pancreatic islets. In the present study we examined whether human beta-cells are affected by NO. In view of species differences in beta-cell sensitivity to damaging agents, rat islets were investigated in parallel. Isolated islets were exposed for 90 min to different concentrations of three chemically unrelated NO donors, SIN-1, GSNO or RBS. At the end of this incubation, human insulin release was mostly similar in control and NO-treated islets but, 48 h later, islet retrieval, islet DNA and insulin content, and glucose-induced insulin release were markedly lower in islets exposed to NO donors. Rat islets were already inhibited during the initial 90 min; 48 h later their loss in beta-cell function was similar to that in human islets. Nicotinamide or succinic acid monomethyl ester partially protected against SIN-1 induced islet cell loss, but not against the functional inhibition of human pancreatic islets. Exposure of human or rat islets to RBS was associated with significant DNA strand breakage, as judged by the comet assay (single cell gel electrophoresis) and by ultrastructural signs of cell damage. DNA damage was more severe in rat islet cells exposed to similar amounts of RBS. It is concluded that NO donors can damage human pancreatic islets, an effect paralleled by induction of nuclear DNA strand breaks.

Adolescent↗
PubMed1992

A novel methodology for double protein A-gold immunolabeling utilizing the monovalent fragment of protein A.

A method for sequential protein A-gold immunolabeling is described whereby the binding of second gold probe to the first antibody-protein A-gold complex is reduced to acceptably minimal levels. Immunolabeling of thin sections of embedded pituitary tissue was used as a model system. After an initial immunolabeling for prolactin, sections were incubated in normal serum (rabbit) followed by a monovalent fragment of protein A. These latter two incubations reduced artifactual second gold probe label over prolactin-labeled secretory granules to minimal levels (much less than 1 particle per granule) when sections were subsequently immunolabeled with normal serum. The combination of normal serum and protein A fragment incubations saturates IgG and protein A binding sites on the first antibody-gold probe complex. The latter is thereafter unable to bind further IgG (and thus gold probe) because of the monovalent nature of the protein A fragment. It is suggested that this methodology may be extended to multiple immunolabeling procedures for electron microscopy. In addition, when used before single labeling this method may be an effective way to minimize nonspecific IgG binding in cases where the tissue or antibody under study may be a problem.

Animals↗
PubMed1991

Immunocytochemical and morphometric studies of mammotrophs, somatotrophs and somatomammotrophs in sheep pituitary cell cultures.

Alterations occurring when sheep anterior pituitary cells are placed in culture for 4 days were studied using electron microscopy and immunogold labelling. The majority of cells present showed marked morphological changes during culture, with degranulation and development of extensive rough endoplasmic reticulum. The proportions of somatotrophs and mammotrophs, as identified by immunogold labelling, fell during culture. The majority (70%) of somatotrophs showed relatively little degranulation but the remainder were extensively degranulated after 4 days in culture, suggesting two subpopulations of this cell type. Conversely, most (80%) of the mammotrophs showed extensive degranulation after culture, but one-fifth remained heavily granulated, suggesting that mammotrophs too are heterogeneous. The proportion of cells labelling for both GH and prolactin (somatomammotrophs) increased during culture to about 3% of the cells present, compared with less than 0.2% of all cells before culture.

Animals↗
PubMed1990

The occurrence and receptor specificity of endogenous opioid peptides within the pancreas and liver of the rat. Comparison with brain.

Our observations that opioid peptides have direct effects on islet insulin secretion and liver glucose production prompted a search for endogenous opiates and their receptors in these peripheral tissues. Mu-, delta- and kappa-receptor-active opiates were demonstrated in brain, pancreas and liver extracts by displacement studies using selective ligands for the three opiate receptor subtypes [( 3H][D-Ala2,MePhe4,Gly5-ol]enkephalin, [3H][D-Ala2,D-Leu5]enkephalin and [3H]dynorphin respectively). Receptor-active opiates in brain extracts exhibited a stronger preference for delta-opiate-receptor sites than for mu and kappa sites. Pancreatic extract opiates demonstrated a similar activity at mu and delta sites, but substantially less at kappa sites. Liver extracts displayed similar selectivity for all three sites. The affinities of the receptor-active opiates for mu-, delta- and kappa-receptor subtypes displayed a rank order of potency: brain much greater than pancreas greater than liver. Total immunoreactive beta-endorphin and [Met5]enkephalin levels in liver and hepatocytes were greater than those in brain. Immunoreactive [Met5]enkephalin levels in pancreas were similar to, but beta-endorphin levels were substantially higher than, those in brain. Delta and kappa opiate-binding sites of high affinity were identified in crude membrane preparations of islets of Langerhans, but no specific opiate-binding sites could be demonstrated in liver membrane preparations. Immunoreactive dynorphin and beta-endorphin were demonstrated by immunogold labelling in rat pancreatic islet cells. No positive staining of liver sections for opioids was observed. These results suggest that the tissue content of opiate-receptor-active compounds in the pancreas and the liver is very significant and could contribute to the regulation of normal blood glucose levels.

Animals↗
PubMed1990

Safe and easy eucapercha paste preparation.

This article presents a method that uses an amalgam capsule and an amalgamator to simplify the preparation of eucapercha paste. The pestle, rubbing against the gutta-percha inside the amalgam capsule, generates enough frictional heat to blend the gutta-percha and the eucalyptol. The consistency of the mixture can be adjusted for a variety of clinical situations.

Drug Combinations↗
PubMed1990

Occurrence of rare somatomammotrophs in ovine anterior pituitary tissue studied by immunogold labelling and electron microscopy.

Prolactin and GH are distinct hormones that have been conventionally thought to be produced and secreted by separate cells in the anterior pituitary gland. Recently it has been suggested that some cells (somatomammotrophs) may secrete both hormones. We have examined the occurrence of somatomammotrophs in sheep anterior pituitary tissue using immunogold labelling. Of a number of procedures used, double labelling using first antibodies raised in different species proved the least susceptible to apparent co-localization of hormones due to artifacts. Using this approach it was shown that a large proportion of the cells in the sheep anterior pituitary glands examined were mammotrophs or somatotrophs, showing no significant co-localization of GH and prolactin. Of 1800 cells examined, only two were somatomammotrophs. One of these, from a female animal, contained GH and prolactin in different granules within the same cell. The other, from a male animal, showed co-localization of these two hormones within the same granules.

Animals↗
PubMed1990

Increased sensitivity to insulin-releasing and glucoregulatory effects of dynorphin A1-13 and U 50488h in ob/ob versus lean mice.

The effects of two kappa-opiate agonists, U 50488h and dynorphin A1-13, on plasma insulin and glucose concentrations in vivo and insulin release in vitro were tested in fasted genetically obese (ob/ob) and lean (+/+) mice at 12-15 wk of age. Fasting plasma insulin concentrations in ob/ob and lean mice were 1.22 +/- 0.10 and 0.23 +/- 0.05 nM, and plasma glucose levels were 6.90 +/- 0.84 and 4.70 +/- 0.29 mM, respectively. Administration of U 50488h (1 mg/kg body wt i.p.) to ob/ob mice dramatically raised plasma insulin by 670 and 790 pM at 15 and 30 min. Plasma glucose was raised from 5 min onward to a maximum increment of 4.2 mM above baseline. These effects were blocked by simultaneous administration of naloxone (10 mg/kg). A higher dose of U 50488h (10 mg/kg body wt i.p.) was required to produce significant increases in lean mouse plasma insulin (81 pM at 15 min) and glucose (0.7, 1.1, and 1.7 mM at 5, 15, and 30 min, respectively). Dynorphin (1 mg/kg body wt i.p.) raised plasma insulin in ob/ob mice by 380 and 410 pM at 15 and 30 min and raised plasma glucose by 1.6 mM at 15 min. In lean mice, the same dose of dynorphin had no effect on plasma insulin concentrations but induced a small rise in glucose. In ob/ob mice, the agonist-induced rise in glucose did not cause the insulin response, because insulin levels were not elevated by a glucose challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1982

Localization and properties of ATPase activity in pea stems and wheat coleoptiles.

Microsomal fractions from wheat coleoptiles and pea stems contain a microsomal ATPase activity that requires divalent cations (Ca2+ is more effective than Mg2+) and shows further stimulation by KCl. The effects of added indoleacetic acid were inconclusive. Cytochemical studies on both species showed most pronounced staining for ATPase in the plasmalemma at pH 7.0. However, at pH 5.5, the coleoptile cells showed heaviest staining for ATPase in the endoplasmic reticulum and dictyosomes. The results are discussed with regard to the postulated role of ATPase activity in relation to proton pumping and plant cell elongation.

Adenosine Triphosphatases↗