Calcitonin receptor, calcitonin gene-related peptide and amylin distribution in C1/2 dorsal root ganglia.

BACKGROUND: The upper cervical dorsal root ganglia (DRG) are important for the transmission of sensory information associated with the back of the head and neck, contributing to head pain. Calcitonin receptor (CTR)-based receptors, such as the amylin 1 (AMY1) receptor, and ligands, calcitonin gene-related peptide (CGRP) and amylin, have been linked to migraine and pain. However, the contribution of this system to nociception involving the cervical DRG is unclear. Therefore, this study aimed to determine the relative distribution of the CTR, CGRP, and amylin in upper cervical DRG. METHODS: CTR, CGRP, and amylin immunofluorescence was examined relative to neural markers in C1/2 DRG from male and female mice, rats, and human cases. Immunofluorescence was supported by RNA-fluorescence in situ hybridization examining amylin mRNA distribution in rat DRG. RESULTS: Amylin immunofluorescence was observed in neuronal soma and fibres. Amylin mRNA (Iapp) was also detected. Amylin and CGRP co-expression was observed in 19% (mouse), 17% (rat), and 36% (human) of DRG neurons in distinct vesicle-like neuronal puncta from one another. CTR immunoreactivity was present in DRG neurons, and both peptides produced receptor signalling in primary DRG cell cultures. CTR-positive neurons frequently co-expressed amylin and/or CGRP (66% rat; 84% human), with some sex differences. CONCLUSIONS: Amylin and CGRP could both be local peptide agonists for CTR-based receptors in upper cervical DRG, potentially acting through autocrine and/or paracrine signalling mechanisms to modulate neuron function. Amylin and its receptors could represent novel pain targets.

RIPK3 promotes islet amyloid-induced ß-cell loss and glucose intolerance in a humanized mouse model of type 2 diabetes.

OBJECTIVE: Aggregation of human islet amyloid polypeptide (hIAPP), a ß-cell secretory product, leads to islet amyloid deposition, islet inflammation and ß-cell loss in type 2 diabetes (T2D), but the mechanisms that underlie this process are incompletely understood. Receptor interacting protein kinase 3 (RIPK3) is a pro-death signaling molecule that has recently been implicated in amyloid-associated brain pathology and ß-cell cytotoxicity. Here, we evaluated the role of RIPK3 in amyloid-induced ß-cell loss using a humanized mouse model of T2D that expresses hIAPP and is prone to islet amyloid formation. METHODS: We quantified amyloid deposition, cell death and caspase 3/7 activity in islets isolated from WT, Ripk3-/-, hIAPP and hIAPP; Ripk3-/- mice in real time, and evaluated hIAPP-stimulated inflammation in WT and Ripk3-/- bone marrow derived macrophages (BMDMs) in vitro. We also characterized the role of RIPK3 in glucose stimulated insulin secretion (GSIS) in vitro and in vivo. Finally, we examined the role of RIPK3 in high fat diet (HFD)-induced islet amyloid deposition, ß-cell loss and glucose homeostasis in vivo. RESULTS: We found that amyloid-prone hIAPP mouse islets exhibited increased cell death and caspase 3/7 activity compared to amyloid-free WT islets in vitro, and this was associated with increased RIPK3 expression. hIAPP; Ripk3-/- islets were protected from amyloid-induced cell death compared to hIAPP islets in vitro, although amyloid deposition and caspase 3/7 activity were not different between genotypes. We observed that macrophages are a source of Ripk3 expression in isolated islets, and that Ripk3-/- BMDMs were protected from hIAPP-stimulated inflammatory gene expression (Tnf, Il1b, Nos2). Following 52 weeks of HFD feeding, islet amyloid-prone hIAPP mice exhibited impaired glucose tolerance and decreased ß-cell area compared to WT mice in vivo, whereas hIAPP; Ripk3-/- mice were protected from these impairments. CONCLUSIONS: In conclusion, loss of RIPK3 protects from amyloid-induced inflammation and islet cell death in vitro and amyloid-induced ß-cell loss and glucose intolerance in vivo. We propose that therapies targeting RIPK3 may reduce islet inflammation and ß-cell loss and improve glucose homeostasis in the pathogenesis of T2D.

Human islet amyloid polypeptide-induced ß-cell cytotoxicity is linked to formation of α-sheet structure.

Type 2 diabetes (T2D) results from insulin secretory dysfunction arising in part from the loss of pancreatic islet ß-cells. Several factors contribute to ß-cell loss, including islet amyloid formation, which is observed in over 90% of individuals with T2D. The amyloid is comprised of human islet amyloid polypeptide (hIAPP). Here we provide evidence that early in aggregation, hIAPP forms toxic oligomers prior to formation of amyloid fibrils. The toxic oligomers contain α-sheet secondary structure, a nonstandard secondary structure associated with toxic oligomers in other amyloid diseases. De novo, synthetic α-sheet compounds designed to be nontoxic and complementary to the α-sheet structure in the toxic oligomers inhibit hIAPP aggregation and neutralize oligomer-mediated cytotoxicity in cell-based assays. In vivo administration of an α-sheet design to mice for 4 weeks revealed no evidence of toxicity nor did it elicit an immune response. Furthermore, the α-sheet designs reduced endogenous islet amyloid formation and mitigation of amyloid-associated ß-cell loss in cultured islets isolated from an hIAPP transgenic mouse model of islet amyloidosis. Characterization of the involvement of α-sheet in early aggregation of hIAPP and oligomer toxicity contributes to elucidation of the molecular mechanisms underlying amyloid-associated ß-cell loss.

Polymeric micelles as potent islet amyloid inhibitors: Current advances and future perspectives.

Diabetes mellitus (DM) has become one of the most prevalent diseases across the globe, mainly because of the inability of existing treatment strategies to target its root cause (i.e., pancreatic ß cell damage). Polymeric micelles (PMs) have gained attention as a treatment option for DM by targeting misfolded islet amyloid polypeptide protein (IAPP), which is common in more than 90% of DM patients. Such misfolding could result from either oxidative stress or mutation in the gene encoding IAPP. In this review, we discuss progress in the designing of PMs to halt islet amyloidosis along with their mechanism and dynamics of interactions with IAPP. We also discuss the clinical challenges associated with the translation of PMs as anti-islet amyloidogenic agents.

Human IAPP is a contributor to painful diabetic peripheral neuropathy.

Peripheral neuropathy is a frequent complication of type 2 diabetes mellitus (T2DM). We investigated whether human islet amyloid polypeptide (hIAPP), which forms pathogenic aggregates that damage pancreatic islet ß cells in T2DM, is involved in T2DM-associated peripheral neuropathy. In vitro, hIAPP incubation with sensory neurons reduced neurite outgrowth and increased levels of mitochondrial reactive oxygen species. hIAPP-transgenic mice, which have elevated plasma hIAPP levels without hyperglycemia, developed peripheral neuropathy as evidenced by pain-associated behavior and reduced intraepidermal nerve fiber (IENF) density. Similarly, hIAPP Ob/Ob mice, which have hyperglycemia in combination with elevated plasma hIAPP levels, had signs of neuropathy, although more aggravated. In wild-type mice, intraplantar and intravenous hIAPP injections induced long-lasting allodynia and decreased IENF density. Non-aggregating murine IAPP, mutated hIAPP (pramlintide), or hIAPP with pharmacologically inhibited aggregation did not induce these effects. T2DM patients had reduced IENF density and more hIAPP oligomers in the skin compared with non-T2DM controls. Thus, we provide evidence that hIAPP aggregation is neurotoxic and mediates peripheral neuropathy in mice. The increased abundance of hIAPP aggregates in the skin of T2DM patients supports the notion that hIAPP is a potential contributor to T2DM neuropathy in humans.

Treatment with semaglutide, a GLP-1 receptor agonist, improves extracellular matrix remodeling in the pancreatic islet of diet-induced obese mice.

AIMS: The extracellular matrix (ECM) is fundamental for the normal endocrine functions of pancreatic islet cells and plays key roles in the pathophysiology of type 2 diabetes. Here we investigated the turnover of islet ECM components, including islet amyloid polypeptide (IAPP), in an obese mouse model treated with semaglutide, a glucagon-like peptide type 1 receptor agonist. MAIN METHODS: Male one-month-old C57BL/6 mice were fed a control diet (C) or a high-fat diet (HF) for 16 weeks, then treated with semaglutide (subcutaneous 40 µg/kg every three days) for an additional four weeks (HFS). The islets were immunostained and gene expressions were assessed. KEY FINDINGS: Comparisons refer to HFS vs HF. Thus, IAPP immunolabeling and beta-cell-enriched beta-amyloid precursor protein cleaving enzyme (Bace2, -40 %) and heparanase immunolabeling and gene (Hpse, -40 %) were mitigated by semaglutide. In contrast, perlecan (Hspg2, +900 %) and vascular endothelial growth factor A (Vegfa, +420 %) were enhanced by semaglutide. Also, semaglutide lessened syndecan 4 (Sdc4, -65 %) and hyaluronan synthases (Has1, -45 %; Has2, -65 %) as well as chondroitin sulfate immunolabeling, and collagen type 1 (Col1a1, -60 %) and type 6 (Col6a3, -15 %), lysyl oxidase (Lox, -30 %) and metalloproteinases (Mmp2, -45 %; Mmp9, -60 %). SIGNIFICANCE: Semaglutide improved the turnover of islet heparan sulfate proteoglycans, hyaluronan, chondroitin sulfate proteoglycans, and collagens in the islet ECM. Such changes should contribute to restoring a healthy islet functional milieu and should reduce the formation of cell-damaging amyloid deposits. Our findings also provide additional evidence for the involvement of islet proteoglycans in the pathophysiology of type 2 diabetes.

Novel Hominid-Specific IAPP Isoforms: Potential Biomarkers of Early Alzheimer's Disease and Inhibitors of Amyloid Formation.

(1) Background and aims: Amyloidosis due to aggregation of amyloid-ß (Aß42) is a key pathogenic event in Alzheimer's disease (AD), whereas aggregation of mature islet amyloid polypeptide (IAPP37) in human islets leads to ß-cell dysfunction. The aim of this study is to uncover potential biomarkers that might additionally point to therapy for early AD patients. (2) Methods: We used bioinformatic approach to uncover novel IAPP isoforms and developed a quantitative selective reaction monitoring (SRM) proteomic assay to measure their peptide levels in human plasma and CSF from individuals with early AD and controls, as well as postmortem cerebrum of clinical confirmed AD and controls. We used Thioflavin T amyloid reporter assay to measure the IAPP isoform fibrillation propensity and anti-amyloid potential against aggregation of Aß42 and IAPP37. (3) Results: We uncovered hominid-specific IAPP isoforms: hIAPPß, which encodes an elongated propeptide, and hIAPPγ, which is processed to mature IAPP25 instead of IAPP37. We found that hIAPPß was significantly reduced in the plasma of AD patients with the accuracy of 89%. We uncovered that IAPP25 and a GDNF derived DNSP11 were nonaggregating peptides that inhibited the aggregation of IAPP37 and Aß42. (4) Conclusions: The novel peptides derived from hIAPP isoforms have potential to serve as blood-derived biomarkers for early AD and be developed as peptide based anti-amyloid medicine.

Aß efflux impairment and inflammation linked to cerebrovascular accumulation of amyloid-forming amylin secreted from pancreas.

Impairment of vascular pathways of cerebral ß-amyloid (Aß) elimination contributes to Alzheimer disease (AD). Vascular damage is commonly associated with diabetes. Here we show in human tissues and AD-model rats that bloodborne islet amyloid polypeptide (amylin) secreted from the pancreas perturbs cerebral Aß clearance. Blood amylin concentrations are higher in AD than in cognitively unaffected persons. Amyloid-forming amylin accumulates in circulating monocytes and co-deposits with Aß within the brain microvasculature, possibly involving inflammation. In rats, pancreatic expression of amyloid-forming human amylin indeed induces cerebrovascular inflammation and amylin-Aß co-deposits. LRP1-mediated Aß transport across the blood-brain barrier and Aß clearance through interstitial fluid drainage along vascular walls are impaired, as indicated by Aß deposition in perivascular spaces. At the molecular level, cerebrovascular amylin deposits alter immune and hypoxia-related brain gene expression. These converging data from humans and laboratory animals suggest that altering bloodborne amylin could potentially reduce cerebrovascular amylin deposits and Aß pathology.

Understanding the mechanism of amylin aggregation: From identifying crucial segments to tracing dominant sequential events to modeling potential aggregation suppressors.

One of the most abundant, prevailing, and life-threatening human diseases that are currently baffling the scientific community is type 2 diabetes (T2D). The self-association of human amylin has been implicated in the pathogenesis of T2D, though with an inconclusive understanding of the mechanism. Hence, we focused on the characterization of the conformational ensembles of all the species that are believed to define the structural polymorphism of the aggregation process - the functional monomeric, the initially self-associated oligomeric, and the structured protofibril - by employing near-equilibrium, non-equilibrium, and equilibrium atomistic simulations on the sporadic, two familial variants (S20G and G33R), and their proline-substituted forms (S20P and G33P). The dynamic near-equilibrium assays hint toward - the abundance of helical conformation in the monomeric state, the retainment of the helicity in the initial self-associated oligomeric phase pointing toward the existence of the helix-helix association mechanism, the difference in preference of specific segments to have definite secondary structural features, the phase-dependent variability in the dominance of specific segments and mutation sites, and the simultaneous presence of generic and unique features among various sequences. Furthermore, the non-equilibrium pulling assays exemplify a generic sequential unzipping mechanism of the protofibrils, however, the sequence-dependent uniqueness comes from the difference in location and magnitude of the control of a specific terminus. Importantly, the equilibrium thermodynamic assays efficiently rank order the potential of aggregability among sequences and consequently suggests the probability of designing effective aggregation suppressors against sporadic and familial amylin variants incorporating proline as the mutation.

On the plasticity of amyloid formation: The impact of destabilizing small to large substitutions on islet amyloid polypeptide amyloid formation.

Amyloids are partially ordered, proteinaceous, ß-sheet rich deposits that have been implicated in a wide range of diseases. An even larger set of proteins that do not normally form amyloid in vivo can be induced to do so in vitro. A growing number of structures of amyloid fibrils have been reported and a common feature is the presence of a tightly packed core region in which adjacent monomers pack together in extremely tight interfaces, often referred to as steric zippers. A second common feature of many amyloid fibrils is their polymorphous nature. We examine the consequences of disrupting the tight packing in amyloid fibrils on the kinetics of their formation using the 37 residue polypeptide hormone islet amyloid polypeptide (IAPP, amylin) as a model system. IAPP forms islet amyloid in vivo and is aggressively amyloidogenic in vitro. Six Cryo-EM structures of IAPP amyloid fibrils are available and in all Gly24 is in the core of the structured region and makes tight contacts with other residues. Calculations using the ff14SBonlysc forcefield in Amber20 show that substitutions with larger amino acids significantly disrupt close packing and are predicted to destabilize the various fibril structures. However, Gly to 2-amino butyric acid (2-carbon side chain) and Gly to Leu substitutions actually enhance the rate of amyloid formation. A Pro substitution slows, but does not prevent amyloid formation.

Differential Effects of Aromatic Residues on Amyloid Formation and Cytotoxicity of Human IAPP.

Islet amyloid polypeptide (IAPP) is a 37-residue polypeptide hormone secreted by the pancreatic ß-cells. IAPP plays a role in glycemic regulation, but in the pre-type-2 diabetic state, it aggregates to form an islet amyloid. The process of islet amyloid formation contributes to ß-cell dysfunction and disease progression. The features of the IAPP sequence that modulate amyloid formation are still not understood. Human IAPP contains three aromatic residues, F15, F23, and Y37. F15 and Y37 are highly conserved, while F23 is more commonly a Leu or Ile in other species. The role of the aromatic residues in modulating the time course of amyloid formation and the cytotoxicity was examined using aromatic to Leu mutations. All three single and double mutants and the triple mutant were studied. F23 plays a dominant role in both amyloid formation and toxicity. An F15L mutant accelerated amyloid formation, a Y37L mutant had little effect, while an F23L replacement slowed amyloid formation by a factor of 2.6. Double mutants, which contained an F23L replacement, had a larger effect than those that did not, and there are non-additive effects between pairs of aromatic residues. F23 also plays a key role in toxicity. Single or multiple mutants that contain the F23L replacement were noticeably less toxic than the wild-type or mutants which did not include the F23L substitution. In contrast, the F15L mutant was more toxic than the wild-type one. The implications for IAPP amyloid formation and for the design of non-aggregating analogues of IAPP are discussed.

SORLA mediates endocytic uptake of proIAPP and protects against islet amyloid deposition.

OBJECTIVE: Sorting-related receptor with type A repeats (SORLA) is a neuronal sorting receptor that prevents accumulation of amyloid-beta peptides, the main constituent of senile plaques in Alzheimer disease. Recent transcriptomic studies show that SORLA transcripts are also found in beta cells of pancreatic islets, yet the role of SORLA in islets is unknown. Based on its protective role in reducing the amyloid burden in the brain, we hypothesized that SORLA has a similar function in the pancreas via regulation of amyloid formation from islet amyloid polypeptide (IAPP). METHODS: We generated human IAPP transgenic mice lacking SORLA (hIAPP:SORLA KO) to assess the consequences of receptor deficiency for islet histopathology and function in vivo. Using both primary islet cells and cell lines, we further investigated the molecular mechanisms whereby SORLA controls the cellular metabolism and accumulation of IAPP. RESULTS: Loss of SORLA activity in hIAPP:SORLA KO resulted in a significant increase in islet amyloid deposits and associated islet cell death compared to hIAPP:SORLA WT animals. Aggravated islet amyloid deposition was observed in mice fed a normal chow diet, not requiring high-fat diet feeding typically needed to induce islet amyloidosis in mouse models. In vitro studies showed that SORLA binds to and mediates the endocytic uptake of proIAPP, but not mature IAPP, delivering the propeptide to an endolysosomal fate. CONCLUSIONS: SORLA functions as a proIAPP-specific clearance receptor, protecting against islet amyloid deposition and associated cell death caused by IAPP.

Role of Autophagy in the Pathogenesis of Diabetes and Therapeutic Potential of Autophagy Modulators in the Treatment of Diabetes and Metabolic Syndrome.

Autophagy is critically involved in the maintenance of intracellular nutrient homeostasis and organelle function. Dysregulated autophagy is likely to play a role in the development of metabolic disorders and diabetes because autophagy is critical in the rejuvenation of dysfunctional or stressed endoplasmic reticulum and mitochondria that play a crucial role in the development of diabetes. Indeed, systemic autophagy insufficiency led to the increased tissue lipid content, aggravated metabolic and finally more severe diabetes when metabolic stress was imposed, suggesting that autophagy insufficiency of dysfunction of lysosome, an effector organelle of autophagy, due to aging, genetic predisposition or environmental factors could be an underlying cause of diabetes. Conversely, autophagy enhancer could improve metabolic profile of obese mice by reducing tissue lipid content and ameliorating metabolic inflammation. Furthermore, clearance of human islet amyloid polypeptide (hIAPP) oligomer and amyloid that accumulate in pancreatic islets of > 90% of diabetes patients was also dependent on autophagy. Consistently, autophagy enhancer could improve glucose profile and ß-cell function of transgenic mice expressing amyloidogenic hIAPP in pancreatic ß-cells, which was accompanied by reduced accumulation of hIAPP oligomer or amyloid, ameliorated ß-cell apoptosis and increased ß-cell mass. These results suggest that autophagy enhancer could be a novel therapeutic modality against diabetes associated with lipid overload and human diabetes characterized by islet amyloid accumulation.

Amylin-Calcitonin receptor signaling in the medial preoptic area mediates affiliative social behaviors in female mice.

Social animals actively engage in contact with conspecifics and experience stress upon isolation. However, the neural mechanisms coordinating the sensing and seeking of social contacts are unclear. Here we report that amylin-calcitonin receptor (Calcr) signaling in the medial preoptic area (MPOA) mediates affiliative social contacts among adult female mice. Isolation of females from free social interactions first induces active contact-seeking, then depressive-like behavior, concurrent with a loss of Amylin mRNA expression in the MPOA. Reunion with peers induces physical contacts, activates both amylin- and Calcr-expressing neurons, and leads to a recovery of Amylin mRNA expression. Chemogenetic activation of amylin neurons increases and molecular knockdown of either amylin or Calcr attenuates contact-seeking behavior, respectively. Our data provide evidence in support of a previously postulated origin of social affiliation in mammals.

Common variants in genes involved in islet amyloid polypeptide (IAPP) processing and the degradation pathway are associated with T2DM risk: A Chinese population study.

AIM: To explore the genetic effects of SLC30A8, IAPP, PCSK1, PCSK2, CPE, PAM and IDE, key genes involved in IAPP processing and degradation pathway on T2DM risk and metabolic traits in Chinese population. METHODS: Common variants were genotyped in 10936 Chinese subjects by Asian Screening Array and Multi-Ethnic Global Array. Associations of SNPs with occurrences of T2DM and related traits were evaluated through logistic and multiple linear regression. Genetic risk score (GRS) model was constructed based on 6 T2DM-variants, and its relationship with T2DM and related traits was assessed. RESULTS: SLC30A8-rs13266634, PCSK1-rs155980, PCSK2-rs6136035, CPE-rs532192464, PAM-rs7716941, and IDE-rs117929184 were the top SNPs significantly associated with T2DM after adjusting for age, sex, and BMI, associated with blood glucose level, insulin secretion, and insulin sensitivity (all FDR p < 0.05). GRS calculated based on the above SNPs was remarkably correlated with T2DM, blood glucose, and insulin secretion. Furthermore, there was a significant interaction between SLC30A8 and IAPP in patients with T2DM (P = 0.0083). CONCLUSION: Our study showed that common variants in genes involved in IAPP processing and the degradation pathway were associated with T2DM in Chinese population. Subjects with high GRS exhibited poorer glucose metabolism and insulin secretion.

Islet amyloid toxicity: From genesis to counteracting mechanisms.

Islet amyloid polypeptide (IAPP or amylin) is a hormone co-secreted with insulin by pancreatic ß-cells and is the major component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes (T2D) and may be involved in ß-cell dysfunction and death, observed in this disease. Thus, investigating the aspects related to amyloid formation is relevant to the development of strategies towards ß-cell protection. In this sense, IAPP misprocessing, IAPP overproduction, and disturbances in intra- and extracellular environments seem to be decisive for IAPP to form islet amyloid. Islet amyloid toxicity in ß-cells may be triggered in intra- and/or extracellular sites by membrane damage, endoplasmic reticulum stress, autophagy disruption, mitochondrial dysfunction, inflammation, and apoptosis. Importantly, different approaches have been suggested to prevent islet amyloid cytotoxicity, from inhibition of IAPP aggregation to attenuation of cell death mechanisms. Such approaches have improved ß-cell function and prevented the development of hyperglycemia in animals. Therefore, counteracting islet amyloid may be a promising therapy for T2D treatment.

IAPP-induced beta cell stress recapitulates the islet transcriptome in type 2 diabetes.

AIMS/HYPOTHESIS: Type 2 diabetes is characterised by islet amyloid and toxic oligomers of islet amyloid polypeptide (IAPP). We posed the questions, (1) does IAPP toxicity induce an islet response comparable to that in humans with type 2 diabetes, and if so, (2) what are the key transcriptional drivers of this response? METHODS: The islet transcriptome was evaluated in five groups of mice: beta cell specific transgenic for (1) human IAPP, (2) rodent IAPP, (3) human calpastatin, (4) human calpastatin and human IAPP, and (5) wild-type mice. RNA sequencing data was analysed by differential expression analysis and gene co-expression network analysis to establish the islet response to adaptation to an increased beta cell workload of soluble rodent IAPP, the islet response to increased expression of oligomeric human IAPP, and the extent to which the latter was rescued by suppression of calpain hyperactivation by calpastatin. Rank-rank hypergeometric overlap analysis was used to compare the transcriptome of islets from human or rodent IAPP transgenic mice vs humans with prediabetes or type 2 diabetes. RESULTS: The islet transcriptomes in humans with prediabetes and type 2 diabetes are remarkably similar. Beta cell overexpression of soluble rodent or oligomer-prone human IAPP induced changes in islet transcriptome present in prediabetes and type 2 diabetes, including decreased expression of genes that confer beta cell identity. Increased expression of human IAPP, but not rodent IAPP, induced islet inflammation present in prediabetes and type 2 diabetes in humans. Key mediators of the injury responses in islets transgenic for human IAPP or those from individuals with type 2 diabetes include STAT3, NF-κB, ESR1 and CTNNB1 by transcription factor analysis and COL3A1, NID1 and ZNF800 by gene regulatory network analysis. CONCLUSIONS/INTERPRETATION: Beta cell injury mediated by IAPP is a plausible mechanism to contribute to islet inflammation and dedifferentiation in type 2 diabetes. Inhibition of IAPP toxicity is a potential therapeutic target in type 2 diabetes.

Identification, tissue distribution, and anorexigenic effect of amylin in Siberian sturgeon (Acipenser baeri).

Amylin is a 37-amino acid polypeptide that has been found to be involved in feeding regulation in some mammals, birds, and goldfish. We cloned amylin of Siberian sturgeon and detected its distribution pattern in 15 tissues. The expression levels in the periprandial period (pre-and post-feeding), the changes in the food intake, and the expression levels of related appetite factors after the intraperitoneal injection of amylin were detected. The expression of amylin was found to be the highest in the hypothalamus. Compared with 1 h pre-feeding, the expression levels of amylin in the hypothalamus and duodenum were increased significantly 1 h post-feeding. Compared with the control group (saline), intraperitoneal injection of 50 ng/g, 100 ng/g, and 200 ng/g of amylin significantly inhibited food intake at 1 h post injection, but not at 3 h and 6 h. The injection of 50 ng/g, 100 ng/g, and 200 ng/g amylin significantly inhibited the cumulative feed. After 1 h of 50 ng/g amylin injection, the levels of MC4R and somatostatin in the hypothalamus increased significantly, while the levels of amylin and NPY decreased significantly. The levels of CCK in the valvular intestine were increased significantly. Insulin in the duodenum was also increased significantly, but there was no significant change in ghrelin in the duodenum. These results show that amylin inhibits feeding in Siberian sturgeon by down-regulating the appetite-stimulating factor NPY and up-regulating the appetite-suppressing factors somatostatin, MC4R, CCK, and insulin. This study provides a theoretical basis for studying the feeding function and action mechanisms of amylin in Siberian sturgeon.

The Amyloid Forming Peptides Islet Amyloid Polypeptide and Amyloid ß Interact at the Molecular Level.

Epidemiological studies support a connection between the two common disorders, type-2 diabetes and Alzheimer's disease. Both conditions have local amyloid formation in their pathogenesis, and cross-seeding between islet amyloid polypeptide (IAPP) and amyloid ß (Aß) could constitute the link. The bimolecular fluorescence complementation (BiFC) assay was used to investigate the occurrence of heterologous interactions between IAPP and Aß and to compare the potential toxic effects of IAPP/Aß, IAPP/IAPP, and Aß/Aß expression in living cells. Microscopy was used to confirm the fluorescence and determine the lysosomal, mitochondrial areas and mitochondrial membrane potential, and a FACS analysis was used to determine ROS production and the role for autophagy. Drosophila melanogaster expressing IAPP and Aß was used to study their co-deposition and effects on longevity. We showed that the co-expression of IAPP and Aß resulted in fluorophore reconstitution to the same extent as determined for homologous IAPP/IAPP or Aß/Aß expression. The BiFC(+)/BiFC(-) ratio of lysosomal area calculations increased in transfected cells independent of the vector combinations, while only Aß/Aß expression increased mitochondrial membrane potential. Expression combinations containing Aß were necessary for the formation of a congophilic amyloid. In Drosophila melanogaster expressing IAPP/Aß, co-deposition of the amyloid-forming peptides caused reduced longevity. The BiFC results confirmed a heterologous interaction between IAPP and Aß, while co-deposits in the brain of Drosophila suggest mixed amyloid aggregates.

Cryo-EM structures of hIAPP fibrils seeded by patient-extracted fibrils reveal new polymorphs and conserved fibril cores.

Amyloidosis of human islet amyloid polypeptide (hIAPP) is a pathological hallmark of type II diabetes (T2D), an epidemic afflicting nearly 10% of the world's population. To visualize disease-relevant hIAPP fibrils, we extracted amyloid fibrils from islet cells of a T2D donor and amplified their quantity by seeding synthetic hIAPP. Cryo-EM studies revealed four fibril polymorphic atomic structures. Their resemblance to four unseeded hIAPP fibrils varies from nearly identical (TW3) to non-existent (TW2). The diverse repertoire of hIAPP polymorphs appears to arise from three distinct protofilament cores entwined in different combinations. The structural distinctiveness of TW1, TW2 and TW4 suggests they may be faithful replications of the pathogenic seeds. If so, the structures determined here provide the most direct view yet of hIAPP amyloid fibrils formed during T2D.