Matrix metalloproteinase-9 reduces islet amyloid formation by degrading islet amyloid polypeptide
ABSTRACT Deposition of islet amyloid polypeptide (IAPP) as amyloid is a pathological hallmark of the islet in type 2 diabetes, which is toxic to β cells. We previously showed that the enzyme neprilysin reduces islet amyloid deposition, and thereby reduces β-cell apoptosis, by inhibiting fibril formation. Two other enzymes, matrix metalloproteinase (MMP)-2 and MMP-9, are extracellular gelatinases capable of degrading another amyloidogenic peptide, Aβ, the constituent of amyloid deposits in Alzheimers disease. We therefore investigated whether MMP-2 and MMP-9 play a role in reducing islet amyloid deposition. MMP-2 and MMP-9 mRNA were present in mouse islets but only MMP-9 activity was detectable. In an islet culture model where human IAPP (hIAPP) transgenic mouse islets develop amyloid but non-transgenic islets do not, a broad-spectrum MMP inhibitor (GM6001) and an MMP-2/9 inhibitor increased amyloid formation and the resultant β-cell apoptosis. In contrast, a specific MMP-2 inhibitor had no effect on either amyloid deposition or β-cell apoptosis. Mass spectrometry demonstrated that MMP-9 degraded amyloidogenic hIAPP but not non-amyloidogenic mouse IAPP. Thus, MMP-9 constitutes an endogenous islet protease that limits islet amyloid deposition and its toxic effects via degradation of hIAPP. As islet MMP-9 mRNA levels are decreased in type 2 diabetic subjects, islet MMP-9 activity may also be decreased in human type 2 diabetes, thereby contributing to increased islet amyloid deposition and β-cell loss. Approaches to increase islet MMP-9 activity could reduce or prevent amyloid deposition and its toxic effects in type 2 diabetes.
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- " Moreover, it was found that metal ion-induced aggregation of IAPP depends also on the origin of the peptide, i.e. if it is hu- man   or murine (m-IAPP),  and mass spectrometry (MS) has also been applied to elucidate the structure of copper(II)–IAPP complexes and the putative binding sites.  On the other hand, IAPP homeostasis seems to be regulated also by the action of some metalloproteases which have been found to be able to degrade    this hormone and/or to impede its aggre- gation.  In particular, more than 10 years ago, insulin-degrading enzyme (IDE) was suggested to have an important role in the regulation of IAPP homeostasis and aggregation. "
ABSTRACT: Amylin or islet amyloid polypeptide (IAPP) is a 37-residue peptide hormone secreted from the pancreatic islets into the blood circulation and is cleared by peptidases in the kidney. IAPP aggregates are strongly associated with β-cell degeneration in type 2 diabetes, as demonstrated by the fact that more than 95% of patients exhibit IAPP amyloid upon autopsy. Recently, it has been reported that metal ions such as copper(II) and zinc(II) are implicated in the aggregation of IAPP as well as able to modulate the proteolytic activity of IAPP degrading enzymes. For this reason, in this work, the role of the latter metal ions in the degradation of IAPP by insulin-degrading enzyme (IDE) has been investigated by a chromatographic and mass spectrometric combined method. The latter experimental approach allowed not only to assess the overall metal ion inhibition of the human and murine IAPP degradation by IDE but also to have information on copper- and zinc-induced changes in IAPP aggregation. In addition, IDE cleavage site preferences in the presence of metal ions are rationalized as metal ion-induced changes in substrate accessibility. Copyright © 2014 John Wiley & Sons, Ltd.Journal of Mass Spectrometry 04/2014; 49(4). DOI:10.1002/jms.3338 · 2.71 Impact Factor
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ABSTRACT: The DPP-4 inhibitor sitagliptin is an attractive therapy for diabetes as it increases insulin release and may preserve beta-cell mass. However, sitagliptin also increases beta-cell release of human islet amyloid polypeptide (hIAPP), the peptide component of islet amyloid, which is co-secreted with insulin. Thus, sitagliptin treatment may promote islet amyloid formation and its associated beta-cell toxicity. Conversely, metformin treatment decreases islet amyloid formation by decreasing beta-cell secretory demand, and could therefore offset sitagliptin's potential pro-amyloidogenic effects. Sitagliptin treatment has also been reported to be detrimental to the exocrine pancreas. We investigated whether long-term sitagliptin treatment, alone or with metformin, increased islet amyloid deposition and beta-cell toxicity, and induced pancreatic ductal proliferation, pancreatitis and/or pancreatic metaplasia/neoplasia. hIAPP transgenic and non-transgenic littermates were followed for one year on no treatment, sitagliptin, metformin, or the combination. Islet amyloid deposition, beta-cell mass, insulin release and measures of exocrine pancreas pathology were determined. Relative to untreated mice, sitagliptin treatment did not increase amyloid deposition, despite increasing hIAPP release, and prevented amyloid-induced beta-cell loss. Metformin treatment alone or with sitagliptin decreased islet amyloid deposition to a similar extent vs untreated mice. Ductal proliferation was not altered among treatment groups and no evidence of pancreatitis, ductal metaplasia or neoplasia, were observed. Therefore, long-term sitagliptin treatment stimulates beta-cell secretion without increasing amyloid formation and protects against amyloid-induced beta-cell loss. This suggests a novel effect of sitagliptin to protect the beta cell in type 2 diabetes which appears to occur without adverse effects on the exocrine pancreas.AJP Endocrinology and Metabolism 06/2013; 305(4). DOI:10.1152/ajpendo.00025.2013 · 4.09 Impact Factor
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ABSTRACT: Amylin is the 37-residue peptide hormone produced by the islet -cells in the pancreas and the formation of amylin aggregates is strongly associated with -cells degeneration in type 2 diabetes, as demonstrated by more than 95% of patients exhibiting amylin amyloid upon autopsy. It is widely recognized that metal ions such as copper(II) have been implicated in the aggregation process of amyloidogenic peptides such as A and -synuclein and there is evidence that also amylin self-assembly is largely affected by copper(II). For this reason, in this work, the role of copper(II) in the aggregation of amylin has been investigated by several different experimental approaches. Mass spectrometric investigations show that copper(II) induces significant changes in the amylin structure which decrease the protein fibrillogenesis as observed by ThT measurements. Accordingly, solid-state NMR experiments together with computational analysis carried out on a model amylin fragment confirmed the non fibrillogenic nature of the copper(II) induced aggregated structure. Finally, the presence of copper(II) is also shown to have a major influence on amylin proneness to be degraded by proteases and cytotoxicity studies on different cell cultures are reported.Metallomics 07/2014; 6(10). DOI:10.1039/C4MT00130C · 3.98 Impact Factor