Immunolocalization of islet amyloid polypeptide (IAPP) in pancreatic beta cells by means of peroxidase-antiperoxidase (PAP) and protein A-gold techniques.

A novel putative polypeptide hormone identified as islet amyloid polypeptide (IAPP) was recently purified from islet amyloid (IA) of diabetic humans and cats, and also from amyloid of a human insulinoma. Although the function of IAPP is yet unknown, its occurrence in pancreatic endocrine tissue and its partial amino acid sequence identity with calcitonin gene-related peptide (CGRP) suggests an endocrine regulatory effect. In the present investigation, the authors utilized antisera to insulin, glucagon, somatostatin, pancreatic polypeptide, synthetic human CGRP, and a synthetic human IAPP (7-17) undecapeptide to immunohistochemically (PAP technique) document the presence of IAPP immunoreactive cells in the islets of the cat, dog, mouse, and rat, but not in the islets of the horse or calf. In serial sections of islets from these species it was shown that IAPP immunoreactivity occurred in insulin-reactive beta cells. This observation was confirmed immunocytochemically in cat islets by means of protein A-gold probes. With protein A-gold labeling techniques, IAPP immunoreactivity was localized to the outer lucent compartment of the beta cell secretory granule, whereas insulin immunoreactivity was associated with the electron-dense core. These findings provide strong evidence that IAPP or an IAPP precursor is synthesized by beta cells and is stored in beta cell granules for subsequent co-secretion with insulin. The conservation of IAPP in humans and multiple animal species and the localization of IAPP to pancreatic beta cells provide further evidence that IAPP has an important endocrine regulatory function. The propensity of IAPP to polymerize and form IA fibrils in diabetes associated with aging may indicate that IAPP is in some way also linked to the development of Type 2 diabetes.     

Islet amyloid polypeptide in insulinoma and in the islets of the pancreas of non-diabetic and diabetic subjects

Summary Amyloid deposition is a common pathological feature in insulinoma and in the islets of the pancreas in type-2 diabetic patients. The present immunohisto-chemical study revealed that normal B-cells, insulinoma, and amyloid deposits in insulinoma and diabetic pancreatic islets were commonly immunoreactive with antiserum to C-terminal synthetic tetradecapeptide of human islet amyloid polypeptide (IAPP) (24–37). Amyloid fibrils in insulinoma were also positive to IAPP by immunoelectron microscopy. A high level of IAPP was detected in the plasma and tissue of a insulinoma patient by radioimmunoassay suggesting that amyloid deposition in insulinoma is due to overproduction of IAPP. Amyloid deposits immunoreactive to IAPP were also seen in all diabetic pancreatic islets, but in no non-diabetic islets. There was much amyloid deposition in the islets of severe diabetics, whose B-cells demonstrated decreased immunoreactivities for IAPP and insulin. The IAPP content of the pancreas was 649.0 and 847.7 pg/mg wet weight in each of two diabetic patients, and 1034.6 and 1447.7 pg/mg wet weight in two non-diabetic patients. The present study revealed that IAPP is a bioactive peptide secreted from islet B-cells and are amyloidogenic peptide concerned in diabetogenensis and/or the progression of type-2 diabetes mellitus.     

Amyloidosis of pancreatic islets in primary amyloidosis (AL type)

Seven cases of primary amyloidosis (AL-type) were studied immunocytochemically for the possible involvement of pancreatic islets. The two cases with extensive organ involvement by AL-amyloidosis revealed amyloid deposits in pancreatic islets by routine HE and Congo red staining, which were positive for amyloid p and amyloid a, but were only focally positive for light chains kappa and lambda. Positive staining for amyloid p and amyloid a was also noted in the scattered pancreatic acinar tissues, and this positive staining was not specifically located in pancreatic islets as seen in type 2 diabetes mellitus. It is concluded that amyloid deposits in pancreatic islets occur in systemic AL-amyloidosis by a different mechanism from type 2 diabetes. Islet amyloidosis in AL-amyloidosis appears to deposit via circulation, depositing in both pancreatic islets and acinar tissue through blood vessels. In type 2 diabetes, beta islet cells die by cytotoxic effects of smaller amylin (islet amyloid polypeptide, IAPP) aggregates, and the interstitial space created by the necrotic beta cells is replaced by larger IAPP aggregates, to form complex, polymerized islet amyloid. In AL-amyloidosis, the amount of amyloid and light chain deposits in pancreatic islets is much less than that of the other organs and appears to have no connection to type 2 diabetes because the patients did not present diabetes or hyperglycemia. However, considerable islet amyloidosis can be seen in severe AL-type amyloidosis.     

Islet amyloid, islet-amyloid polypeptide, and diabetes mellitus

Islet-amyloid deposits, which are a common feature of Type II diabetes mellitus, are derived from the polymerization of a putative hormone identified as IAPP. IAPP is synthesized by normal islet beta cells and probably is cosecreted with insulin. Although the physiologic function of IAPP and its role in the pathogenesis of Type II diabetes mellitus are just beginning to be unraveled, IAPP may play an important part in the development of this most common form of diabetes mellitus by opposing the action of insulin in peripheral tissues. The polymerization of IAPP to form extracellular islet-amyloid deposits may further contribute to the development of Type II diabetes mellitus by destroying islet cells and by disrupting the passage of glucose and hormones to and from them. Substantial evidence indicates that the propensity of IAPP to polymerize and form extracellular amyloid deposits in only certain species (e.g., humans, cats, and raccoons) is directly associated with an intrinsically amyloidogenic part of the molecule--i.e., positions 20 through 29 of IAPP. The inherent amyloidogenicity of IAPP in these species may be further facilitated by increased beta-cell production of IAPP, leading to a high local concentration that predisposes to polymerization. The latter possibility is supported by studies demonstrating that IAPP production by islet beta cells is increased in normoglycemic cats with impaired glucose tolerance. Although increased production of IAPP may initially cause insulin resistance, prolonged overproduction of IAPP may ultimately impair insulin secretion by leading to the progressive deposition of insoluble islet amyloid, a finding apparent in most subjects with overt diabetes. If, as these studies suggest, increased IAPP production is linked to the development of Type II diabetes mellitus, further studies must address the genetic and nongenetic factors that influence this important biologic change in humans and some animal species.     

Islet amyloid polypeptide, islet amyloid, and diabetes mellitus

Islet amyloid polypeptide (IAPP, or amylin) is one of the major secretory products of β-cells of the pancreatic islets of Langerhans. It is a regulatory peptide with putative function both locally in the islets, where it inhibits insulin and glucagon secretion, and at distant targets. It has binding sites in the brain, possibly contributing also to satiety regulation and inhibits gastric emptying. Effects on several other organs have also been described. IAPP was discovered through its ability to aggregate into pancreatic islet amyloid deposits, which are seen particularly in association with type 2 diabetes in humans and with diabetes in a few other mammalian species, especially monkeys and cats. Aggregated IAPP has cytotoxic properties and is believed to be of critical importance for the loss of β-cells in type 2 diabetes and also in pancreatic islets transplanted into individuals with type 1 diabetes. This review deals both with physiological aspects of IAPP and with the pathophysiological role of aggregated forms of IAPP, including mechanisms whereby human IAPP forms toxic aggregates and amyloid fibrils.     

Human islet amyloid polypeptide expression in COS-1 cells. A model of intracellular amyloidogenesis.

Non-insulin-dependent diabetes mellitus is characterized by concurrent loss of beta-cells and deposition of islet amyloid derived from islet amyloid polypeptide (IAPP). We have previously demonstrated that IAPP-derived amyloid forms intracellularly in humans with chronic excess insulin expression (eg, insulinoma and insulin receptor antibody-induced insulin resistance). To determine whether overexpression of IAPP results in intracellular amyloid in mammalian cells, we transfected COS cells with vectors expressing amyloidogenic human IAPP or non-amyloidogenic rat IAPP. Transfected COS-1 cells secreted comparable amounts of human IAPP and rat IAPP (2.1 to 2.8 nmol/L/48 hours). After 96 hours, 90% of cells expressing human IAPP contained amyloid fibrils and were degenerating or dead, whereas cells transfected with rat IAPP lacked amyloid and were viable. Thus, overexpression of human IAPP can result in intracellular amyloid formation that is associated with cell death, suggesting that intracellular amyloid may play a role in beta-cell loss in non-insulin-dependent diabetes mellitus.     

Islet amyloid in type 2 human diabetes mellitus and adult diabetic cats contains a novel putative polypeptide hormone.

Amyloid deposition is a very typical alteration in the islets of Langerhans in human Type 2 (non-insulin-dependent) diabetes mellitus and in feline diabetes mellitus. Amyloid infiltration is also commonly found in insulin-producing pancreatic tumors. It was shown recently that amyloid purified from an insulinoma was composed mainly of a novel polypeptide (insulinoma amyloid polypeptide, IAPP), which had partial identity with the neuropeptide calcitonin gene-related peptide (CGRP). Cat islet amyloid contained a similar polypeptide. This finding is verified in the present study, and it is shown that the cat IAPP differs from the human peptide only in two of the 16 elucidated amino acid residues. The authors now also show by N-terminal amino acid sequence analysis that human islet amyloid is of IAPP origin. Although the significance of IAPP is unknown, its occurrence in pancreatic endocrine tissue and partial identity with a known neuropeptide suggests an endocrine regulatory function.     

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.     

APOLIPOPROTEIN E IS ASSOCIATED WITH ISLET AMYLOID AND OTHER AMYLOIDOSES: IMPLICATIONS FOR ALZHEIMER'S DISEASE

Apolipoprotein E (ApoE) has recently been proposed as an aetiological factor of Alzheimer's disease (AD): ApoE is co-localized to amyloid plaques and neurofibrillary tangles in the brain and binds to Aβ -protein in vitro. An association of ApoE ϵ4 allele with the development of AD has been reported. Islet amyloid is formed from islet amyloid polypeptide (IAPP) in pancreatic islets of 90 per cent of patients with non-insulin-dependent diabetes mellitus (NIDDM) which, like AD, is an age-dependent pathology. The relationship of ApoE to islet amyloid and other amyloidoses is largely unknown. In this study, ApoE was localized by immunocytochemistry on pancreatic specimens from non-diabetic man, monkey, and mouse, and on amyloid-containing human tissues from pancreas, heart, brain, and intestine. All types of amyloid deposits, irrespective of the constituent peptide, site of deposition, or species, showed immunoreactivity for ApoE (ApoE-IR). Quantitative morphometry showed that similar proportions of islet amyloid were labelled for IAPP and ApoE in monkey islets. ApoE-IR was observed in pancreatic islet cells of non-diabetics. These results suggest that the association of ApoE with amyloid is non-specific for AD or to the component peptide of amyloid fibrils. If ApoE promotes amyloid formation, its synthesis in pancreatic islets could be important for the initiation or the development of pancreatic amyloid in NIDDM.     

Role of amylin in the pathogenesis of type II diabetes mellitus

Amylin, a peptide, which was isolated from the islet amyloid of type II diabetics, might play a potential role in the pathogenesis of type II diabetes mellitus. In in vitro and in vivo studies it has been shown that amylin has an effect on insulin secretion as well as on insulin sensitivity. From measurements of plasma amylin levels it is known that amylin is cosecreted with insulin and patients with hyperinsulinemia have also elevated amylin levels. In patients with impaired glucose tolerance and type II diabetes amylin levels are decreased compared to insulin. A secretory defect of amylin and its local accumulation in the islets of type II diabetics might be a cause for the insulin secretory defect in type II diabetes. Additionally, amylin can induce peripheral insulin resistance, which might also be a cause for type II diabetes mellitus. Amylin is a new pancreatic peptide, which might play an important role in the pathogenesis of diabetes mellitus.     

High prevalence of pancreatic islet amyloid in patients with end-stage renal failure on dialysis treatment

Islet amyloid polypeptide (IAPP) is the main proteinaceous component of pancreatic islet amyloid, which is a characteristic feature of type 2 diabetes. The factors responsible for amyloid deposition are unclear. Patients with end-stage renal failure (ESRF) on dialysis treatment have increased insulin resistance which is associated with hypersecretion of beta-cell products. Furthermore, elevated concentrations of circulating IAPP are found in these patients due to reduced renal clearance of IAPP. To determine the prevalence of islet amyloid in this group of patients, pancreas was examined from 23 non-diabetic [aged 62 (29-79) years, median and range] and four type 2 diabetic [aged 67 (56-72) years] patients with ESRF on dialysis treatment. Pancreatic specimens from 30 non-diabetic control subjects [aged 67.5 (56-86) years] and 14 type 2 diabetic subjects without renal disease [aged 69 (48-86) years] were used as control groups. Islet amyloid was present in all type 2 diabetic patients with ESRF and in 12 out of 14 type 2 diabetic control subjects (86 per cent). Amyloid deposits were found in 8 out of 23 non-diabetic patients with ESRF (35 per cent), which was a higher prevalence than that found in non-diabetic control subjects (3 per cent) (P<0.01). This may be related to undiagnosed (pre)diabetes. Elevated secretion rates of IAPP due to insulin resistance and high circulation IAPP concentrations as a result of severely reduced renal clearance of IAPP will cause high pericellular concentrations of IAPP. This condition is likely to enhance amyloid fibril formation in pancreatic islets similar to that observed in type 2 diabetes.     

IAPP as a regulator of glucose homeostasis and pancreatic hormone secretion (review).

IAPP is a 37-amino acid peptide that is predominantly expressed in pancreatic beta cells. Despite co-secretion from islets the relative amounts of IAPP and insulin may vary. Since IAPP was first described as the major peptide constituent of amyloid in the islets of Langerhans of subjects with type 2 diabetes and insulinoma, many studies have been devoted to investigating the role of IAPP in formation of amyloid deposits and in diabetes pathogenesis. However, there is growing evidence for IAPP as an active islet hormone in addition to insulin and glucagon in glucose metabolic control. An inhibitory effect is seen by IAPP on gastric emptying, glycogen synthesis in skeletal muscle, islet insulin and glucagon secretion, whereas a stimulatory effect is seen on hepatic gluconeogenesis.     

A feline model of experimentally induced islet amyloidosis

The study of the pathogenesis of islet amyloidosis and its relationship to the development and progression of type 2 diabetes mellitus has been hampered by the lack of an experimentally inducible animal model. The domestic cat, by virtue of the fact that it is one of the few species that spontaneously develop a form of diabetes mellitus that closely resembles human type 2 diabetes, including the formation of amyloid deposits derived from islet amyloid polypeptide (IAPP), was considered to be an excellent candidate species in which to attempt to develop a nontransgenic animal model for this disease process. To develop the model, 8 healthy domestic cats were given a 50% pancreatectomy, which was followed by treatment with growth hormone and dexamethasone. Once a stable diabetic state was established, cats were randomly assigned to groups treated with either glipizide or insulin at doses appropriate to control hyperglycemia. Cats were maintained on this treatment regimen for 18 months and then euthanized. Based on light microscopic examination of Congo red-stained sections of pancreas, all cats were negative for the presence of islet amyloid at the time of pancreatectomy. At the end of the study all 4 glipizide-treated cats had islet amyloid deposits, whereas only 1 of 4 insulin-treated cats had detectable amyloid. In addition, the glipizide treated cats had threefold higher basal and fivefold higher glucose-stimulated plasma IAPP concentrations than insulin-treated cats, suggesting an association between elevated IAPP secretion and islet amyloidosis. Blood-glycosylated hemoglobin concentrations were not significantly different between the two treatment groups. This study documents for the first time an inducible model of islet amyloidosis in a nontransgenic animal.     

IAPP免疫反应细胞在成年大鼠胃肠胰系统的分布与形态学研究

用免疫组织化学和免疫电镜双标记法研究了胰淀粉样多肽免疫反应细胞在正常大鼠胃肠胰系统的分布、定位和形态特征，并观察了ＩＡＰＰ与胰岛素在胰腺的共存。结果表明，大鼠胰腺和胃道各段均见有ＩＡＰＰ免疫反应细胞。在胰腺，ＩＡＰＰ与胰岛素共存于胰岛的Ｂ细胞内，也共存在散在于外分泌部的胰岛素免疫反应细胞内。胃肠道粘膜内ＩＡＰＰ免疫反应细胞主要存在于上皮和固有膜，它们的数量以胃和十二指肠较多，结肠较少。本研究首次发     

人胰腺导管上皮表达胰岛淀粉样多肽

目的　观察人胰腺导管上皮胰岛淀粉样多肽的分布。　方法　 4例正常成人胰腺组织石蜡切片 ,用免疫组织化学 PAP方法显示 IAPP- IR细胞 ,Mayer苏木素复染。　结果　发现胰腺小叶间导管、小叶内导管、闰管上皮细胞至泡心细胞均呈胰岛淀粉样多肽免疫反应性 ,阳性物质主要分布于核上方及两侧。　结论　本研究证明人胰腺导管上皮细胞表达胰岛淀粉样多肽 ,推测其可能与胰腺的自我保护和胰液中碳酸氢盐的分泌有关     

Immunohistology of islet amyloid polypeptide in diabetes mellitus: Semi-qantitative studies in a post-mortem series

Summary Immunoreactivity for islet amyloid polypeptide (IAPP) in the islets of Langerhans of non-insulin-dependent diabetic patients and non-diabetic patients of a non-selected post-mortem series was studied with a new polyclonal IAPP antibody. Out of 133 patients examined, 124 exhibited immunoreactivity for IAPP. Immunoreactivity was localized intra- and extracellularly and was limited to the islets of Langerhans. No extracellular immunoreactivity was observed in amyloid-negative cases. Co-localization of insulin and IAPP in the same islet-cells was verified by double staining with monoclonal insulin and polyclonal IAPP antibodies. Of 100 patients with non-insulin-dependent diabetes mellitus (NIDDM) and islet amyloid, 98 exhibited IAPP-positive deposits and 71 exhibited intracellular immunoreactivity. Evaluation of intracellular immunoreactivity and degree of islet amyloid deposition in cases of overt NIDDM revealed an inverse relationship, in that intracellular IAPP immunoreactivity were reduced in patients with developing islet amyloid deposition. Our data are consistent with the hypothesis of primary-cell dysfunction leading to amyloid formation, with subsequent disturbance of-cell homeostasis.Supported by the Johanna and Fritz Buch-Gedächtnisstiftung (Hamburg, FRG)     

Metastasizing islet cell carcinoma of the pancreas in a 10-year-old girl (author's transl)]

A medullary islet cell carcinoma of the pancreas with liver and peritoneal metastases was found at autopsy of a 10-year-old girl. Ultrastructurally, the carcinoma cells showed typical secretion granules resembling prevailingly A1 (D) cell granules in pancreatic islets. Silver impregnation according to Hellerstr?m and Hellman (1960) for demonstration of A1 islet cells was moderately positive in the tumor cells. Therefore, it is suggested that the presented metastasizing islet cell carcinoma may have derived from A1 islet cells.     

糖尿病小鼠胰岛β细胞结构的光镜和电镜研究

目的观察2型糖尿病模型db/db小鼠胰岛β细胞的超微结构、胰岛素表达及数量变化,探讨β细胞的病理改变与2型糖尿病病因的关系。方法分别选取3、5、8月龄尾静脉空腹血糖高于10.1mmol/L,且肥胖的db/db自发性糖尿病小鼠,每组8只,作为糖尿病组;选取相应年龄段尾静脉空腹血糖低于6.0mmol/L,体重正常的db/+m表型正常小鼠,每组8只,作为对照组。于相应年龄段取胰尾,用于透射电镜观察、免疫组织化学观察和图像分析。结果电镜下随病情进展,db/db小鼠胰岛β细胞内的分泌颗粒数量明显减少,有的细胞甚至缺如,致密芯电子密度降低,β细胞可见凋亡的早期改变以及细胞核和细胞器的病理改变,细胞间髓样小体增多。免疫组织化学显示同月龄糖尿病组小鼠胰岛β细胞阳性率和胰岛素蛋白平均光密度值(OD值)低于相应对照组(p<0.05),且随着病程的进展,db/db小鼠胰岛β细胞阳性率和胰岛素表达呈现递减趋势(p<0.05)。结论2型糖尿病β细胞的超微结构遭到破坏,引起β细胞合成分泌胰岛素障碍和数量减少,与2型糖尿病病情的轻重有关,反映了2型糖尿病病程不同阶段的病机特点。     

Evidence for Proteotoxicity in β Cells in Type 2 Diabetes : Toxic Islet Amyloid Polypeptide Oligomers Form Intracellularly in the Secretory Pathway

The islet in type 2 diabetes mellitus (T2DM) is characterized by a deficit in β cells and islet amyloid derived from islet amyloid polypeptide (IAPP), a protein co-expressed with insulin by β cells. It is increasingly appreciated that the toxic form of amyloidogenic proteins is not amyloid but smaller membrane-permeant oligomers. Using an antibody specific for toxic oligomers and cryo-immunogold labeling in human IAPP transgenic mice, human insulinoma and pancreas from humans with and without T2DM, we sought to establish the abundance and sites of formation of IAPP toxic oligomers. We conclude that IAPP toxic oligomers are formed intracellularly within the secretory pathway in T2DM. Most striking, IAPP toxic oligomers appear to disrupt membranes of the secretory pathway, and then when adjacent to mitochondria, disrupt mitochondrial membranes. Toxic oligomer-induced secretory pathway and mitochondrial membrane disruption is a novel mechanism to account for cellular dysfunction and apoptosis in T2DM.Type 2 diabetes (T2DM) is characterized by a progressive deficit in β cell function and mass with increased β cell apoptosis.^1,2 In common with several neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, the loss of β cells in T2DM is associated with accumulation of locally expressed misfolded proteins that share a propensity to form amyloid.³ Islet amyloid in T2DM is composed primarily of a 37-amino acid protein, islet amyloid polypeptide (IAPP).³ IAPP is co-expressed and secreted with insulin by pancreatic β cells, and is thought to play a paracrine inhibitory role in regulation of insulin secretion.^4,5 The property of IAPP to form amyloid fibrils depends on IAPP_20-29. This sequence is closely homologous in humans, nonhuman primates and cats,⁶ all of which spontaneously develop T2DM characterized by a deficit in β cell mass and islet amyloid. In contrast, rodent IAPP (mouse and rat) does not have the propensity to form amyloid fibrils due to proline substitutions in IAPP_20-29 and wild-type mice and rats do not spontaneously develop T2DM.There is accumulating evidence that the toxic form of amyloidogenic protein aggregates is distinct from amyloid fibrils. The latter tend to accumulate extracellularly where they are relatively inert.^3,7 Abnormal non-fibrillar intracellular IAPP aggregates were noted in human insulinoma tissue adjacent to disrupted intracellular membranes.⁸ The impression that IAPP oligomers might act by disruption of cell membranes was supported by the observation that oligomers of IAPP, like Alzheimer β protein (AβP_1-42), can act as nonselective ion channels and disrupt membranes.^7,9 Moreover toxic oligomers formed from different amyloidogenic proteins apparently share a close structure. This was revealed by the finding that antibodies raised against toxic oligomers of AβP_1-42 also bind to those formed from IAPP, synuclein, and prion, in each case neutralizing the toxicity of these oligomers.¹⁰ Availability of this antibody provided an important tool to resolve the question, do toxic oligomers form intra or extracellularly?To test the hypothesis that IAPP oligomers form and act intracellularly requires ultrastructural studies. This presents challenges since the antibody for toxic oligomers loses specificity and sensitivity with many fixation and tissue embedding procedures used for conventional electron microscopy. To overcome this, we used cryo-immunogold labeling by oligomer-specific antibody in islets isolated from human IAPP (hIAPP) transgenic mice. The hypothesis that toxic oligomers form intracellularly was confirmed, with toxic IAPP oligomers present in β cells at all steps of the secretory pathway. These findings were reproduced in IAPP expressing human insulinoma, supporting the concept that IAPP oligomers form in the secretory pathway in humans. Finally, toxic oligomers were also identified intracellularly in β cells in humans with T2DM.     

Intracellular amyloidogenesis by human islet amyloid polypeptide induces apoptosis in COS-1 cells

Human islet amyloid polypeptide (hIAPP) is co-secreted with insulin from pancreatic islet beta cells. This peptide spontaneously aggregates in the form of fibrils, and amyloid deposits are associated with dead or degenerating beta cells, a hallmark of noninsulin-dependent diabetes mellitus. We demonstrated that COS-1 cells transfected with vectors expressing hIAPP exhibited intracellular amyloid deposits that were associated with cell death (O'Brien, Butler, Kreutter, Kane, Eberhardt, Am J Pathol 1995, 147:609-616). To establish the mechanism of cell death, we transfected COS-1 cells with vectors expressing amyloidogenic hIAPP or nonamyloidogenic rat IAPP and mutant hIAPP constructs and assayed them for markers characteristic of apoptosis and necrosis by fluorescence-activated cell sorting analysis. Amyloidogenic hIAPP-transfected COS cells contained up to threefold more apoptotic cells present at 96 hours after transfection compared with the nonamyloidogenic vector controls. The hIAPP-induced apoptosis was negligible at 24 and 48 hours after transfection and was maximal at 96 hours which parallels the time course of amyloidogenesis. Immunohistochemical staining and confocal microscopy showed that hIAPP is localized with distinct clustering in the endoplasmic reticulum and Golgi apparatus with no discernable extracellular staining. These experiments provide direct evidence that intracellular hIAPP amyloid causes cell death by triggering apoptotic pathways.