Biomedical subjects

P Westermark

Publications and source records attributed to P Westermark.

At least 109 records · Page 6Linked to original sources

PubMed1991

Islet amyloid polypeptide and insulin expression are controlled differently in primary and transformed islet cells.

The pancreatic beta-cell is a major site of islet amyloid polypeptide (IAPP) biosynthesis, and the peptide is coreleased with insulin. We have analyzed the expression of IAPP (mRNA and protein) in various cell types in normal and transformed murine islet cell cultures by Northern blot analyses and immunocytochemistry. IAPP is primarily coexpressed with insulin in the beta-cell of GH-promoted primary rat islet cell cultures. Additionally, a small population of non-beta-cells exhibited a prominent IAPP expression, and double staining experiments showed colocalization with glucagon or somatostatin in some of these cells. IAPP mRNA was confined to the beta-cell phenotype when analyzing the phenotypically stable in vivo tumor lines, MSL-G2-IN (insulinoma) and MSL-G-AN (glucagonoma), and the transgenic mouse islet cell lines, beta-Tc and alpha-Tc. However, IAPP and insulin expression were completely uncoupled in unstable heterogeneous clones such as NHI-6F. This clone is composed of primarily glucagon-producing cells in vitro, but insulin gene expression becomes dominant after passage in vivo. Interestingly, IAPP was hyperexpressed with glucagon under in vitro conditions in this clone. We conclude that the tissue specificity of expressions of IAPP and insulin are controlled differently, and that coexpression of IAPP with hormones different from insulin may be a marker for pluripotent transformed rat islet cell clones, which are able to activate insulin gene transcription during passage in vivo.

Amyloid↗

PubMed1991

Islet amyloid polypeptide and insulin secretion from isolated perfused pancreas of fed, fasted, glucose-treated, and dexamethasone-treated rats.

Rats from four experimental treatment groups, including fed controls, 24- to 30-h fasted, dexamethasone-treated, and intraperitoneal glucose-treated, were used to assess the effects of these treatments on the immunohistochemically detectable islet amyloid polypeptide (IAPP) content in the pancreatic islets. Isolated perfused pancreases from additional animals in these groups were used to assess insulin and IAPP secretion and relative amounts of these hormones secreted into the perfusate under low-glucose (2.75 mM) and high-glucose (16.7 mM) conditions. Insulin and IAPP concentrations in the perfusate were measured by radioimmunoassays. Titration of immunohistochemical staining revealed the highest levels of IAPP in the dexamethasone- and glucose-treated groups, followed by the fed controls; the least amount was observed in the fasted group. In the perfusion experiments, the dexamethasone-treated group had significantly higher IAPP secretion than did all of the other groups under stimulation with 16.7 mM glucose. In addition, both dexamethasone treatment and glucose treatment increased the relative amount of IAPP to insulin secretion during 16.7 mM glucose stimulation in comparison with fed controls and fasted groups. Fasting tended to have the opposite effect and significantly decreased the relative amount of IAPP to insulin secreted under stimulation with 16.7 mM glucose. In all groups, IAPP and insulin secretion were generally parallel, which is consistent with their colocalization in the beta-cell secretory vesicle and co-release after glucose stimulation. However, significant differences in the insulin-IAPP ratios between experimental groups is consistent with the hypothesis that production of IAPP and insulin are regulated differently in the beta-cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid↗

PubMed1991

Newly identified pancreatic protein islet amyloid polypeptide. What is its relationship to diabetes?

Islet amyloid polypeptide (IAPP) or amylin is a newly identified 37-amino acid COOH-terminal-amidated polypeptide that is the major protein constituent of amyloid deposits in insulinomas and amyloid deposits in pancreatic islets of non-insulin-dependent (type II) diabetic humans and adult diabetic cats. IAPP is stored with insulin in beta-cell secretory vesicles and is cosecreted with insulin in response to glucose and several secretagogues. IAPP has been demonstrated in normal pancreatic islets of many species, but IAPP-derived amyloid develops commonly in the islets of only a few species (e.g., humans and cats), especially in association with age-related diabetes. IAPP from the human and cat inherently contains a short amyloidogenic sequence that is not present in species that do not form islet amyloid. Studies in animals indicate that an aberration in the synthesis or processing of IAPP, leading to a local increase in concentration of IAPP in the islet, is also required to facilitate the conversion of IAPP to amyloid. The formation of islet amyloid may contribute to the development of type II diabetes by causing disruption of islet cells and by replacement of islets. It has also been proposed that an abnormality of IAPP homeostasis underlies the pathogenesis of type II diabetes. A significant causal relationship between IAPP and type II diabetes is based on reports that IAPP inhibits glucose-stimulated insulin release by beta-cells and that IAPP inhibits insulin-stimulated rates of glycogen synthesis and glucose uptake by skeletal muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid↗

PubMed1991

Islet amyloid polypeptide in proliferating pancreatic B cells during development, hyperplasia, and neoplasia in humans and mice.

The occurrence of islet amyloid polypeptide (IAPP) immunoreactivity was investigated in fetal pancreas, islet cell hyperplasia, and tumors in humans and mice. Transgenic mice heritably developing endocrine tumors of the pancreas (AVP/SV40, Rip 1 Tag2/Rip2PyST1 and Glu2-Tag strains) were used as murine models of islet cells proliferative disease. In the mouse, IAPP immunoreactivity was found in B cells at embryonic day 12 (E12), paralleling the onset of insulin immunoreactivity. In hyperplastic/dysplastic islets and in B-cell tumors of transgenic mice (n = 16), IAPP immunoreactivity was localized consistently to insulin-immunoreactive cells. Ultrastructural single- and double-immunogold labeling of transgenic mice B-cell tumors (n = 3) showed insulin and IAPP to be colocalized in beta granules. In human fetuses, IAPP immunoreactivity was found in insulin-immunoreactive B cells, but at a later gestational age than the onset of insulin immunoreactivity. In pancreatic specimens of infantile/neonatal persistent hyperinsulinemic hypoglycemia (11 cases) and in pancreatic endocrine tumors (21 cases, 10 of which were functioning insulinomas), IAPP immunoreactivity was found consistently in insulin-immunoreactive B cells. Congo-red-positive amyloid deposits present in tumors also were IAPP immunoreactive. Ultrastructural single and double immunogold labeling of infantile/neonatal persistent hyperinsulinemic hypoglycemia cases (n = 3) and functioning insulinomas (n = 2) showed IAPP and insulin to be colocalized in beta granules. In addition, IAPP immunoreactivity was observed in amyloidlike fibrils. These findings indicate that IAPP is a constitutive component of B cells. Possible relationships between IAPP and insulin expression and interspecies differences are suggested and discussed.

Adenoma, Islet Cell↗

PubMed1990

Islet amyloid polypeptide (IAPP) does not inhibit glucose-stimulated insulin secretion from isolated perfused rat pancreas.

Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in the secretory vesicles of beta cells. Several lines of evidence suggested that IAPP might affect glucose-stimulated insulin secretion and, therefore, might play a role in the development of impaired insulin secretion which is typical of type 2 diabetes. In this study, the effects of human IAPP (amide) on glucose-stimulated insulin secretion was evaluated in the isolated perfused rat pancreas. IAPP in concentrations from 5 x 10(-12) to 10(-7) M had no significant effects on insulin secretion. IAPP, therefore, does not appear to be a significant modulator of glucose-stimulated insulin secretion at concentrations that are physiologically relevant.

Amyloid↗

PubMed1990

The human islet amyloid polypeptide (IAPP) gene. Organization, chromosomal localization and functional identification of a promoter region.

We report the isolation and characterization of the human gene encoding islet amyloid polypeptide (IAPP). Previously characterized cDNA sequences correspond to three exons of which the first is noncoding. A functional promoter region was identified in the 5' flanking DNA; however, this was farther upstream than expected. Northern blot analysis of human insulinoma RNA revealed three IAPP mRNAs of sizes 1.2, 1.8 and 2.1 kb, in agreement with three polyadenylation signals present in the 3' end of the gene. In situ hybridization to metaphase chromosomes resulted in two distinct peaks on chromosome 12, at 12p12-p13 and 12q13-q14. Southern blot analysis of genomic DNA suggested a single IAPP locus but also indicated the presence of additional homologous sequences in human genomic DNA.

Amino Acid Sequence↗

PubMed1990

Canine IAPP cDNA sequence provides important clues regarding diabetogenesis and amyloidogenesis in type 2 diabetes.

Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in beta cell granules. IAPP may have a significant role in the development of Type 2 diabetes mellitus due to its propensity to form islet cell-disrupting amyloid deposits, and by opposing the action of insulin in peripheral tissues. Most evidence to-date suggests that an intrinsic structural motif of IAPP is linked to the amyloidogenicity of IAPP, and that this motif occurs only in those species (e.g., humans and cats) that also develop age-associated or Type 2 diabetes We utilized polymerase chain reaction methodology in this study to obtain the IAPP nucleotide and protein sequences of the dog, a species not known to develop islet amyloid. We show that dog IAPP contains the same putative amyloidogenic sequence (GAILS) at residues 24-28 as human and cat IAPP, and that although dogs do not develop islet amyloid they do develop IAPP-derived amyloid in association with neoplastic beta cells (i.e., insulinomas). These results provide strong evidence that the amyloidogenicity of IAPP is linked to at least two prerequisites: a species-specific amyloidogenic structural motif, and aberrations in the synthesis (or processing) of IAPP which leads to increased concentration of IAPP in the local milieau.

Amino Acid Sequence↗

PubMed1990

Amino acid sequence from degu islet amyloid-derived insulin shows unique sequence characteristics.

The main protein of enriched and purified amyloid from Octodon degus pancreatic islets was identified as insulin. The material was reduced and alkylated and the A- and the B-chain were separated by reversed phase chromatography and subjected to Edman degradation and amino acid analysis. It was shown that the A-chain contains two additional C-terminal amino acid residues (i.e. a total of 23 residues) and that the B-chain has a deletion in the C-terminal part (i.e. a total of 29 residues). The obtained sequence follows: A-chain: GIVDQCCNNICTFNQLQNYCNVP B-chain: YSSQHLCGSNLVEALYMTCGRSGFYRPHD.

Amino Acid Sequence↗

PubMed1990

The putative hormone islet amyloid polypeptide (IAPP) induces impaired glucose tolerance in cats.

Islet amyloid polypeptide (IAPP) has been implicated by in vitro studies as an inhibitor of insulin-stimulated glucose utilization by skeletal muscle cells and also as an inhibitor of insulin-stimulated insulin secretion by beta cells. Increased expression and production of IAPP by beta cells, as has been suggested to occur in cats with impaired glucose tolerance, could thus contribute substantially to the development of the insulin resistance and impaired insulin release which are the hallmarks of Type 2 diabetes mellitus. The effects of IAPP with respect to glucose metabolism in living animals, however, have not been previously reported. In the present in vivo study we show that synthetic amidated IAPP induced impaired glucose tolerance in each of the 3 cats studied, with dramatic impairment (increases in glucose to T1/2 values of 124% and 234%) in 2 of the 3 cats. Impaired insulin responses were also evident in the 2 cats with the most dramatic states of glucose intolerance. These results provide the most direct evidence to-date that IAPP may have an important role in the development of Type 2 diabetes mellitus.

Amyloid↗

PubMed1990

Characterization of intracellular amyloid fibrils in the human choroid plexus epithelial cells.

Intracellular inclusions with staining properties of amyloid are very common in the aging choroid plexus epithelial cells. In many ways these inclusions show similarities with the neurofibrillary tangles, found in cerebral cortical neurons in patients with Alzheimer's dementia. We have now designed a purification method for choroid plexus amyloid and performed a transmission and scanning electron microscopic study. This shows that one form of choroid plexus inclusions, the Biondi ring, is a homogeneous globule covered with a thin layer of amyloid fibrils. Partial immunochemical characterization of the choroid plexus amyloid reveals that it is different from the neurofibrillary tangles although there are similarities.

Aged↗

PubMed1990

The relation of atrial natriuretic factor to isolated atrial amyloid.

Isolated atrial amyloid (IAA) is a very common age-related amyloid form which is seen only in the atria of the heart. Chemical characterization has indicated that the major subunit protein is atrial natriuretic factor (ANF). In this ultrastructural study we show that the fibrils in IAA most frequently are located extracellularly especially along the cell membranes of the myocytes, but that small deposits also seem to be present intracellularly. No obvious relation was noted between the fibrils and the endocrine granules. Antiserum to a low molecular fraction of IAA labeled amyloid fibrils and granules in the same way as a commercial antiserum to ANF, but no other structures in the myocyte. Finally we show that ANF can polymerize to fibrils with an amyloid appearance. The study thus supports the fact that ANF is an important and integrated part in the IAA fibrils.

Absorption↗

PubMed1990

Amyloid inclusions in choroid plexus epithelial cells. A simple autopsy method to rapidly obtain information on the age of an unknown dead person.

Different methods such as X-ray examination of the skeleton and inspection of the teeth have been described for estimation of the age of an unidentified dead person. These methods are more or less exact but the results will not be available until many days after the autopsy. In the present paper, we present a fairly simple method to obtain information on the age of a deceased using amyloid inclusions in the choroid plexus epithelial cells.

Adult↗

PubMed1990

Islet amyloid polypeptide: pinpointing amino acid residues linked to amyloid fibril formation.

Islet amyloid polypeptide (IAPP), a putative polypeptide hormone, is a product of pancreatic beta-cells and the major constituent of the amyloid deposits seen mainly in islets of type 2 diabetic humans and diabetic cats. The connection between IAPP amyloid formation and diabetes is unknown, but a limited segment of the IAPP molecule, positions 20-29, seems responsible for the aggregation to fibrils. Differences in the amino acid sequence of this region probably determine whether or not islet amyloid can develop in a particular species. Amyloid fibril formation can be mimicked in vitro with the aid of synthetic peptides. With this technique we show that peptides corresponding to IAPP positions 20-29 of human and cat, species that develop IAPP-derived islet amyloid, form amyloid-like fibrils in vitro. The corresponding IAPP segment from three rodent species that do not develop IAPP-derived amyloid did not give rise to fibrils. Substitution of the human IAPP-(20-29) decapeptide with one or two amino acid residues from species without islet amyloid generally reduced the capacity to form fibrils. We conclude that the sequence Ala-Ile-Leu-Ser-Ser, corresponding to positions 25-29 of human IAPP, is strongly amyloidogenic and that a proline-for-serine substitution in position 28, as in several rodents, almost completely inhibits formation of amyloid fibrils.

Amino Acid Sequence↗

PubMed1990

Fibril in senile systemic amyloidosis is derived from normal transthyretin.

The amyloid fibril in senile systemic amyloidosis (SSA), like that of familial amyloidotic polyneuropathy, is derived from transthyretin (TTR). SSA, however, is a common disease, affecting to some degree 25% of the population greater than 80 years old. In familial amyloidotic polyneuropathy, the amyloidogenesis has been considered to depend on point mutations leading to TTR variants. We show that the TTR molecule in SSA, on the other hand, has a normal primary structure. Factors other than the primary structure of TTR must therefore be important in the pathogenesis of TTR-derived amyloid.

Amino Acid Sequence↗

PubMed1990

Islet amyloid polypeptide and calcitonin gene-related peptide immunoreactivity in amyloid and tumor cells of canine pancreatic endocrine tumors.

Seven canine pancreatic endocrine tumors were evaluated immunohistochemically for the presence of islet amyloid polypeptide (IAPP), calcitonin gene-related peptide (CGRP), and several other pancreatic hormones. Four tumors contained cells with IAPP immunoreactivity, and four had cells with CGRP immunoreactivity. IAPP and CGRP immunoreactivities were localized to distinctly different cell populations in three tumors in which both peptides were detected; however, IAPP immunoreactivity consistently was found in cells that also contained insulin immunoreactivity. Amyloid deposits, which were found in three of the seven tumors, showed strong immunoreactivity with antiserum against IAPP and weaker immunoreactivity with antiserum to CGRP. These results indicate that amyloid deposits in canine pancreatic endocrine tumors are likely derived from IAPP, as is amyloid found in human pancreatic endocrine tumors and pancreatic islet amyloid in aged and diabetic persons and cats.

Amyloid↗

PubMed1990

Structure of cat islet amyloid polypeptide and identification of amino acid residues of potential significance for islet amyloid formation.

Cats and humans, unlike most rodent species, develop amyloid in the islets of Langerhans in conjunction with non-insulin-dependent diabetes mellitus. The amyloid consists of a 37-amino acid polypeptide referred to as islet amyloid polypeptide (IAPP). The primary structures of IAPP from human and three rodent species have previously been determined. Sequence divergence was seen in the region corresponding to amino acid residues 20-29, which in human IAPP has been suggested to confer the amyloidogenic properties to the molecule. Using polymerase chain-reaction methodology, we determined the primary sequence of cat IAPP. Amino acid region 20-29 shows specific similarities and differences compared with human and rodent IAPP, respectively. A synthetic cat IAPP20-29 decapeptide formed amyloid fibrils spontaneously in vitro. Comparison between the structure and amyloid fibril-forming activity of various synthetic peptides suggests that the amino acid residues at positions 25-26 in mature IAPP are important for the amyloidogenic properties of the molecule.

Amino Acid Sequence↗

PubMed1990

Age-related accumulation of amyloid inclusions in adrenal cortical cells.

Cytoplasmic fine fibrillar inclusions with properties of amyloid occur as neurofibrillary tangles in the brain and in the aging choroid plexus. In the present study we show that inclusions, similar but not identical to those in the choroid plexus, are common in the adrenal cortex of elderly persons. The inclusions consist of aggregates of parallel fine fibrils, often in contact with lipid droplets and partially limited by a membrane. The inclusions have affinity for Congo red and exhibit a bright green birefringence after this staining. Therefore, the inclusions can be regarded as a form of senile amyloid.

Adrenal Cortex↗

PubMed1990

AA-amyloidosis. Tissue component-specific association of various protein AA subspecies and evidence of a fourth SAA gene product.

Protein AA, the major repetitive protein subunit present in fibrils deposited in AA-amyloidosis, is an N-terminal cleavage product of a 104-amino acid precursor, serum amyloid A (SAA). Protein AA subspecies varying between 45 and 94 amino acids in length have been described. In this study it is shown that the different protein AA subspecies are not evenly distributed in amyloid deposits and that in single patients, certain subspecies of protein AA are deposited in specific tissue component sites. Thus larger protein AA subspecies occur in lower concentration in amyloid in the glomeruli compared to other sites and are especially found in amyloid in vessel walls. Three different SAA forms have been predicted from genomic and complementary DNA studies. The existence of a fourth type has been suspected from amino acid sequence studies of purified SAA. Protein AA derived from this fourth type of SAA is now shown to be present in amyloid fibrils in one of the patients studied in this paper.

Amino Acid Sequence↗