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Amylin and beta amyloid proteins interact to form amorphous heterocomplexes with enhanced toxicity in neuronal cells.

ABSTRACT: Human pancreatic islet amyloid polypeptide (hIAPP) and beta amyloid (A?) can accumulate in Type 2 diabetes (T2D) and Alzheimer's disease (AD) brains and evidence suggests that interaction between the two amyloidogenic proteins can lead to the formation of heterocomplex aggregates. However, the structure and consequences of the formation of these complexes remains to be determined. The main objective of this study was to characterise the different types and morphology of A?-hIAPP heterocomplexes and determine if formation of such complexes exacerbate neurotoxicity. We demonstrate that hIAPP promotes A? oligomerization and formation of small oligomer and large aggregate heterocomplexes. Co-oligomerized A?42-hIAPP mixtures displayed distinct amorphous structures and a 3-fold increase in neuronal cell death as compared to A? and hIAPP alone. However, in contrast to hIAPP, non-amyloidogenic rat amylin (rIAPP) reduced oligomer A?-mediated neuronal cell death. rIAPP exhibited reductions in A? induced neuronal cell death that was independent of its ability to interact with A? and form heterocomplexes; suggesting mediation by other pathways. Our findings reveal distinct effects of IAPP peptides in modulating A? aggregation and toxicity and provide new insight into the potential pathogenic effects of A?-IAPP hetero-oligomerization and development of IAPP based therapies for AD and T2D.

SUBMITTER: Bharadwaj P

PROVIDER: S-EPMC7316712 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Amylin and beta amyloid proteins interact to form amorphous heterocomplexes with enhanced toxicity in neuronal cells.

Bharadwaj Prashant P Solomon Tanya T Sahoo Bikash R BR Ignasiak Katarzyna K Gaskin Scott S Rowles Joanne J Verdile Giuseppe G Howard Mark J MJ Bond Charles S CS Ramamoorthy Ayyalusamy A Martins Ralph N RN Newsholme Philip P

Scientific reports 20200625 1

Human pancreatic islet amyloid polypeptide (hIAPP) and beta amyloid (Aβ) can accumulate in Type 2 diabetes (T2D) and Alzheimer's disease (AD) brains and evidence suggests that interaction between the two amyloidogenic proteins can lead to the formation of heterocomplex aggregates. However, the structure and consequences of the formation of these complexes remains to be determined. The main objective of this study was to characterise the different types and morphology of Aβ-hIAPP heterocomplexes ...[more]

PMID: 32587390

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Project description:BackgroundNeuroinflammation in the brain consequent to activation of microglia is viewed as an important component of Alzheimer's disease (AD) pathology. Amyloid beta (A?) protein is known to activate microglia and unleash an inflammatory cascade that eventually results in neuronal dysfunction and death. In this study, we sought to identify the presence of amylin receptors on human fetal and murine microglia and determine whether A? activation of the inflammasome complex and subsequent release of cytokines is mediated through these receptors.MethodsThe presence of dimeric components of the amylin receptor (calcitonin receptor and receptor activity modifying protein 3) were first immunohistochemically identified on microglia. Purified human fetal microglial (HFM) cultures were incubated with an in vivo microglial marker, DyLight 594-conjugated tomato lectin, and loaded with the membrane-permeant green fluorescent dye, Fluo-8L-AM for measurements of intracellular calcium [Ca2+]i. HFM and BV-2 cells were primed with lipopolysaccharide and then exposed to either human amylin or soluble oligomeric A?1-42 prior to treatment with and without the amylin receptor antagonist, AC253. Changes in the inflammasome complex, NLRP3 and caspase-1, were examined in treated cell cultures with Western blot and fluorometric assays. RT-PCR measurements were performed to assess cytokine release. Finally, in vivo studies were performed in transgenic mouse model of AD (5xFAD) to examine the effects of systemic administration of AC253 on markers of neuroinflammation in the brain.ResultsAcute applications of human amylin or A?1-42 resulted in an increase in [Ca2+]i that could be blocked by the amylin receptor antagonist, AC253. Activation of the NLRP3 and caspase-1 and subsequent release of cytokines, TNF? and IL-1?, was diminished by AC253 pretreatment of HFMs and BV2 cells. In vivo, intraperitoneal administration of AC253 resulted in a reduction in microglial markers (Iba-1 and CD68), caspase-1, TNF?, and IL-1?. These reductions in inflammatory markers were accompanied by reduction in amyloid plaque and size in the brains of 5xFAD mice compared to controls.ConclusionMicroglial amylin receptors mediate A?-evoked inflammation, and amylin receptor antagonists therefore offer an attractive therapeutic target for intervention in AD.

Project description:Human amylin-derived oligomers and aggregates are believed to play an important role in the pathogenesis of type II diabetes mellitus (T2DM). In addition to amylin-evoked cell attrition, T2DM is often accompanied by elevated serum copper levels. Although previous studies have shown that human amylin, in the course of its aggregation, produces hydrogen peroxide (H2O2) in solution, and that this process is exacerbated in the presence of copper(ii) ions (Cu(2+)), very little is known about the mechanism of interaction between Cu(2+) and amylin in pancreatic ?-cells, including its pathological significance. Hence, in this study we investigated the mechanism by which Cu(2+) and human amylin catalyze formation of reactive oxygen species (ROS) in cells and in vitro, and examined the modulatory effect of Cu(2+) on amylin aggregation and toxicity in pancreatic rat insulinoma (RIN-m5F) ?-cells. Our results indicate that Cu(2+) interacts with human and rat amylin to form metalo-peptide complexes with low aggregative and oxidative properties. Human and non-amyloidogenic rat amylin produced minute (nM) amounts of H2O2, the accumulation of which was slightly enhanced in the presence of Cu(2+). In a marked contrast to human and rat amylin, and in the presence of the reducing agents glutathione and ascorbate, Cu(2+) produced ?M concentrations of H2O2 surpassing the amylin effect by several fold. The current study shows that human and rat amylin not only produce but also quench H2O2, and that human but not rat amylin significantly decreases the amount of H2O2 in solution produced by Cu(2+) and glutathione. Similarly, human amylin was found to also decrease hydroxyl radical formation elicited by Cu(2+) and glutathione. Furthermore, Cu(2+) mitigated the toxic effect of human amylin by inhibiting activation of pro-apoptotic caspase-3 and stress-kinase signaling pathways in rat pancreatic insulinoma cells in part by stabilizing human amylin in its native conformational state. This sacrificial quenching of metal-catalyzed ROS by human amylin and copper's anti-aggregative and anti-apoptotic properties suggest a novel and protective role for the copper-amylin complex.

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Amylin and beta amyloid proteins interact to form amorphous heterocomplexes with enhanced toxicity in neuronal cells.

Publications

Amylin and beta amyloid proteins interact to form amorphous heterocomplexes with enhanced toxicity in neuronal cells.

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