Type 2 diabetes (T2DM) is characterized by insulin resistance, defective insulin secretion, loss of beta-cell mass with increased beta-cell apoptosis and islet amyloid. The islet amyloid is derived from islet amyloid polypeptide (IAPP, amylin), a protein coexpressed and cosecreted with insulin by pancreatic beta-cells. In common with other amyloidogenic proteins, IAPP has the propensity to form membrane permeant toxic oligomers. Accumulating evidence suggests that these toxic oligomers, rather than the extracellular amyloid form of these proteins, are responsible for loss of neurons in neurodegenerative diseases. In this review we discuss emerging evidence to suggest that formation of intracellular IAPP oligomers may contribute to beta-cell loss in T2DM. The accumulated evidence permits the amyloid hypothesis originally developed for neurodegenerative diseases to be reformulated as the toxic oligomer hypothesis. However, as in neurodegenerative diseases, it remains unclear exactly why amyloidogenic proteins form oligomers in vivo, what their exact structure is, and to what extent these oligomers play a primary or secondary role in the cytotoxicity in what are now often called unfolded protein diseases.

OBJECTIVE-Endoplasmic reticulum (ER) stress-induced apoptosis may be a common cause of cell attrition in diseases characterized by misfolding and oligomerisation of amyloidogenic proteins. The islet in type 2 diabetes is characterized by islet amyloid derived from islet amyloid polypeptide (IAPP) and increased ␤-cell apoptosis. We questioned the following: 1) whether IAPP-induced ␤-cell apoptosis is mediated by ER stress and 2) whether ␤-cells in type 2 diabetes are characterized by ER stress. RESEARCH DESIGN AND METHODS-The mechanism of IAPP-induced apoptosis was investigated in INS-1 cells and human IAPP (HIP) transgenic rats. ER stress in humans was investigated by ␤-cell C/EBP homologous protein (CHOP) expression in 7 lean nondiabetic, 12 obese nondiabetic, and 14 obese type 2 diabetic human pancreata obtained at autopsy. To assure specificity for type 2 diabetes, we also examined pancreata from eight cases of type 1 diabetes.RESULTS-IAPP induces ␤-cell apoptosis by ER stress in INS-1 cells and HIP rats. Perinuclear CHOP was rare in lean nondiabetic (2.6 Ϯ 2.0%) and more frequent in obese nondiabetic (14.6 Ϯ 3.0%) and obese diabetic (18.5 Ϯ 3.6%) pancreata. Nuclear CHOP was not detected in lean nondiabetic and rare in obese nondiabetic (0.08 Ϯ 0.04%) but six times higher (P Ͻ 0.01) in obese diabetic (0.49 Ϯ 0.17%) pancreata. In type 1 diabetic pancreata, perinuclear CHOP was rare (2.5 Ϯ 2.3%) and nuclear CHOP not detected. B oth type 1 and type 2 diabetes are characterized by deficits in ␤-cell mass and increased ␤-cell apoptosis (1-6). The mechanism that initiates ␤-cell apoptosis in type 1 diabetes is believed to be autoimmune-mediated cytokine production (5). Several mechanisms have been proposed for increased ␤-cell apoptosis in type 2 diabetes, including oxygen free radicals (7), free fatty acid toxicity (8), interleukin-1␤ (9), and formation of islet amyloid polypeptide (IAPP) toxic oligomers (10 -12). CONCLUSIONS-ERProgrammed cell death, or apoptosis, is important in multicellular organisms to permit organ development and remodeling (13). In disease states, apoptosis permits selective removal of cells that are damaged, particularly in relation to cell cycle, so that damage is not propagated (3,14). Apoptosis may be initiated by a wide variety of cellular insults, which are currently thought to act through at least three pathways that converge to accomplish irreversible destruction of the cell's chromosomes. These three major pathways have been designated as the extrinsic and intrinsic pathways and endoplasmic reticulum (ER) stress pathway (15,16). The extrinsic pathway is classically exemplified by cytokine-induced cell death, mediated through cell surface death receptors (17). The intrinsic pathway is most often described as a response to mitochondrial disruption, for example, secondary to oxygen free radicals (18). ER stress-induced apoptosis is classically ascribed to aggregates of misfolded protein that are believed to compromise the ER membrane (15).The human pancreatic ␤-cell is vulnerable to al...

Both Rb and p130 are required for the recruitment of heterochromatin proteins that mediate silencing of proliferation genes in adult cardiac myocytes.

Multiple infections have been linked with the development of bronchiolitis obliterans syndrome (BOS) post-lung transplantation. Lung allograft airway colonization by Aspergillus species is common among lung transplant recipients. We hypothesized that Aspergillus colonization may promote the development of BOS and may decrease survival post-lung transplantation. We reviewed all lung transplant recipients transplanted in our center between 1/2000 and 6/2006. Bronchoscopy was performed according to a surveillance protocol and when clinically indicated. Aspergillus colonization was defined as a positive culture from bronchoalveolar lavage or two sputum cultures positive for the same Aspergillus species, in the absence of invasive pulmonary Aspergillosis. We found that Aspergillus colonization was strongly associated with BOS and BOS related mortality in Cox regression analyses. Aspergillus colonization typically preceded the development of BOS by a median of 261 days (95% CI 87 to 520). Furthermore, in a multivariate Cox regression model, Aspergillus colonization was a distinct risk factor for BOS, independent of acute rejection. These data suggest a potential causative role for Aspergillus colonization in the development of BOS post-lung transplantation and raise the possibility that strategies aimed to prevent Aspergillus colonization may help delay or reduce the incidence of BOS.

The islet in type 2 diabetes is characterized by an approximately 60% beta-cell deficit, increased beta-cell apoptosis, and islet amyloid derived from islet amyloid polypeptide (IAPP). Human IAPP (hIAPP) but not rodent IAPP (rIAPP) forms toxic oligomers and amyloid fibrils in an aqueous environment. We previously reported that overexpression of hIAPP in transgenic rats triggered endoplasmic reticulum (ER) stress-induced apoptosis in beta-cells. In the present study, we sought to establish whether the cytotoxic effects of hIAPP depend on its propensity to oligomerize, rather than as a consequence of protein overexpression. To accomplish this, we established a novel homozygous mouse model overexpressing rIAPP at a comparable expression rate and, on the same background, as a homozygous transgenic hIAPP mouse model previously reported to develop diabetes associated with beta-cell loss. We report that by 10 wk of age hIAPP mice develop diabetes with a deficit in beta-cell mass due to increased beta-cell apoptosis. The rIAPP transgenic mice counterparts do not develop diabetes or have decreased beta-cell mass. Both rIAPP and hIAPP transgenic mice have increased expression of BiP, but only hIAPP transgenic mice have elevated ER stress markers (X-box-binding protein-1, nuclear localized CCAAT/enhancer binding-protein homologous protein, active caspase-12, and accumulation of ubiquitinated proteins). These findings indicate that the beta-cell toxic effects of hIAPP depend on the propensity of IAPP to aggregate, but not on the consequence of protein overexpression.

The islet in type 2 diabetes mellitus (T2DM) is characterized by a deficit in ␤ cells and islet amyloid derived from islet amyloid polypeptide (IAPP), a protein coexpressed with insulin by ␤ 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 ␤ cell function and mass with increased ␤ 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 ␤ 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 ␤ 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 ␤ 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.

In type II diabetes (T2DM), there is a deficit in b-cells, increased b-cell apoptosis and formation of intracellular membranepermeant oligomers of islet amyloid polypeptide (IAPP). Human-IAPP (h-IAPP) is an amyloidogenic protein co-expressed with insulin by b-cells. IAPP expression is increased with obesity, the major risk factor for T2DM. In this study we report that increased expression of human-IAPP led to impaired autophagy, due at least in part to the disruption of lysosome-dependant degradation. This action of IAPP to alter lysosomal clearance in vivo depends on its propensity to form toxic oligomers and is independent of the confounding effect of hyperglycemia. We report that the scaffold protein p62 that delivers polyubiquitinated proteins to autophagy may have a protective role against human-IAPP-induced apoptosis, apparently by sequestrating protein targets for degradation. Finally, we found that inhibition of lysosomal degradation increases vulnerability of b-cells to h-IAPPinduced toxicity and, conversely, stimulation of autophagy protects b-cells from h-IAPP-induced apoptosis. Collectively, these data imply an important role for the p62/autophagy/lysosomal degradation system in protection against toxic oligomer-induced apoptosis. Cell Death and Differentiation (2011) 18, 415-426; doi:10.1038/cdd.2010.111; published online 3 September 2010In type II diabetes (T2DM), hyperglycemia is because of inadequate insulin secretion in response to relative insulin resistance. The islet in T2DM is characterized by a deficit in b-cells, 1,2 increased b-cell apoptosis attributable to endoplasmic reticulum (ER) stress 3,4 and intracellular b-cell toxic aggregates of the amyloidogenic protein islet amyloid polypeptide (IAPP), 5 the expression of which increases with insulin resistance. 6 IAPP is co-expressed and co-secreted with insulin by b-cells 7 with its best-characterized physiological role being to inhibit insulin secretion through a direct paracrine effect on b-cells. 8 IAPP has the propensity to form amyloid fibrils in species at risk of T2DM (humans, non-human primates and cats). 9 In contrast to human-IAPP (h-IAPP), the rodent form of IAPP (r-IAPP) is non-amyloidogenic. Transgenic expression of h-IAPP in b-cells of rodents at rates present in insulin resistance leads to the development of diabetes because of ER stress-induced b-cell apoptosis with formation of membrane-damaging intracellular IAPP oligomers comparable to those present in humans with T2DM. 3,5,[10][11][12] Conserved mechanisms protect long-lived cells with a high protein synthetic burden (such as b-cells) from accumulation of intracellular protein aggregates and the adverse consequences termed proteotoxicity. 9 A quality control system in the ER recognizes misfolded proteins and targets them for degradation by the ubiquitin/proteasome system. 13 A second pathway of protein degradation, autophagy, also implies a role for ubiquitin in removal of misfolded proteins. 14 Macroautophagy (hereafter referred to as autophagy) permits selective autodi...

OBJECTIVEThe islet in type 2 diabetes is characterized by β-cell apoptosis, β-cell endoplasmic reticulum stress, and islet amyloid deposits derived from islet amyloid polypeptide (IAPP). Toxic oligomers of IAPP form intracellularly in β-cells in humans with type 2 diabetes, suggesting impaired clearance of misfolded proteins. In this study, we investigated whether human-IAPP (h-IAPP) disrupts the endoplasmic reticulum–associated degradation/ubiquitin/proteasome system.RESEARCH DESIGN AND METHODSWe used pancreatic tissue from humans with and without type 2 diabetes, isolated islets from h-IAPP transgenic rats, isolated human islets, and INS 832/13 cells transduced with adenoviruses expressing either h-IAPP or a comparable expression of rodent-IAPP. Immunofluorescence and Western blotting were used to detect polyubiquitinated proteins and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) protein levels. Proteasome activity was measured in isolated rat and human islets. UCH-L1 was knocked down by small-interfering RNA in INS 832/13 cells and apoptosis was evaluated.RESULTSWe report accumulation of polyubiquinated proteins and UCH-L1 deficiency in β-cells of humans with type 2 diabetes. These findings were reproduced by expression of oligomeric h-IAPP but not soluble rat-IAPP. Downregulation of UCH-L1 expression and activity to reproduce that caused by h-IAPP in β-cells induced endoplasmic reticulum stress leading to apoptosis.CONCLUSIONSOur results indicate that defective protein degradation in β-cells in type 2 diabetes can, at least in part, be attributed to misfolded h-IAPP leading to UCH-L1 deficiency, which in turn further compromises β-cell viability.