The Mitochondrial Peptidase Pitrilysin Degrades Islet Amyloid Polypeptide in Beta-Cells

Abstract

Amyloid formation and mitochondrial dysfunction are characteristics of type 2 diabetes. The major peptide constituent of the amyloid deposits in type 2 diabetes is islet amyloid polypeptide (IAPP). In this study, we found that pitrilysin, a zinc metallopeptidase of the inverzincin family, degrades monomeric, but not oligomeric, islet amyloid polypeptide in vitro. In insulinoma cells when pitrilysin expression was decreased to 5% of normal levels, there was a 60% increase in islet amyloid polypeptide-induced apoptosis. In contrast, overexpression of pitrilysin protects insulinoma cells from human islet amyloid polypeptide-induced apoptosis. Since pitrilysin is a mitochondrial protein, we used immunofluorescence staining of pancreases from human IAPP transgenic mice and Western blot analysis of IAPP in isolated mitochondria from insulinoma cells to provide evidence for a putative intramitochondrial pool of IAPP. These results suggest that pitrilysin regulates islet amyloid polypeptide in beta cells and suggest the presence of an intramitochondrial pool of islet amyloid polypeptide involved in beta-cell apoptosis.

The association between renal accumulation of pancreatic amyloid-forming amylin and renal hypoxia

“…In vitro study with INS1F cells showed exogenous human amylin induces mitochondrial dysfunction and cell apoptosis ( 107 ). Mitochondrial peptidase pitrilysin regulates human amylin in beta cells’ mitochondria, and the intra-mitochondrial pool of amylin causes beta-cell apoptosis and mitochondrial dysfunction ( 108 ). Thus, diabetes-associated hyperamylinemia could promote hypoxic-renal injury by creating mitochondrial dysfunction and ROS.…”

Islet amyloid toxicity: From genesis to counteracting mechanisms

“…Although insulin sensitizers did not prevent islet amyloid formation, they decreased hIAPP secretion and the extent of islet amyloid in hIAPP transgenic mice (Hull et al, 2005). Improving hIAPP degradation is another way to counteract the hyperamylinemia and to prevent islet amyloid toxicity, as degrading enzymes overexpression protected β-cells from hIAPP-induced apoptosis (Guan et al, 2013(Guan et al, , 2015 (Figure 3a). Alternatively, several amyloid inhibitors have been reported as efficient to block toxic oligomers formation and/or convert the fibrils into nontoxic intermediates (Figure 3b).…”

“…Reduced expression or activity of IDE (Bennett et al, 2003), neprilysin (Zraika et al, 2010), MMP‐9 (Aston‐mourney et al, 2013), and pitrilysin (Guan et al, 2015), induced amyloidogenesis and impaired islets or β‐cells viability. In contrast, neprilysin (Guan et al, 2013) and pitrilysin (Guan et al, 2015) overexpression protected INS 832/13 cells from hIAPP‐induced toxicity. Hence, hIAPP degradation is another critical step to trigger amyloid formation.…”

“…These enzymes are zinc metallopeptidases ubiquitously expressed. IDE is located mainly in the cytoplasm (Bennett et al, 2000), neprilysin in the cell membrane (Zraika et al, 2007), pitrilysin in the mitochondria (Guan et al, 2015), and MMP‐9 in the extracellular compartment (Aston‐mourney et al, 2013). The proper IAPP degradation ensures normal concentrations of the hormone, which is very important to IAPP homeostasis.…”

“…IAPP is degraded by several enzymes including insulin-degrading enzyme (IDE) (Bennett et al, 2000), neprilysin (Zraika et al, 2007), pitrilysin (Guan et al, 2015), and metalloproteinase-9 (MMP-9) (Aston-mourney et al, 2013). These enzymes are zinc metallopeptidases ubiquitously expressed.…”