α1-Antitrypsin Protects β-Cells From Apoptosis

Abstract

1␤-Cell apoptosis appears to represent a key event in the pathogenesis of type 1 diabetes. Previous studies have demonstrated that administration of the serine proteinase inhibitor ␣1-antitrypsin (AAT) prevents type 1 diabetes development in NOD mice and prolongs islet allograft survival in rodents; yet the mechanisms underlying this therapeutic benefit remain largely unclear. Herein we describe novel findings indicating that AAT significantly reduces cytokine-and streptozotocin (STZ)-induced ␤-cell apoptosis. Specifically, strong antiapoptotic activities for AAT (Prolastin, human) were observed when murine insulinoma cells (MIN6) were exposed to tumor necrosis factor-␣. In a second model system involving STZ-induced ␤-cell apoptosis, treatment of MIN6 cells with AAT similarly induced a significant increase in cellular viability and a reduction in apoptosis. Importantly, in both model systems, treatment with AAT completely abolished induced caspase-3 activity. In terms of its activities in vivo, treatment of C57BL/6 mice with AAT prevented STZ-induced diabetes and, in agreement with the in vitro analyses, supported the concept of a mechanism involving the disruption of ␤-cell apoptosis. These results propose a novel biological function for this molecule and suggest it may represent an effective candidate for attempts seeking to prevent or reverse type 1 diabetes. Diabetes 56:1316-1323, 2007 T ype 1 diabetes is an autoimmune disease resulting from destruction of the insulin-producing islet ␤-cells (1). Multiple lines of evidence indicate that antigen-presenting cells (APCs), especially dendritic cells, are pathologically active in orchestrating the process of insulitis (2). APCs within islets likely respond to micro-environmental triggers, including ␤-cell death and apoptosis, and initiate the insulitis process by migrating out of the islet and into the peripheral pancreatic lymph nodes. These APCs trigger the activation and proliferation of ␤-cell-reactive T-cells, which destroy islet cells at a rate that eventually results in type 1 diabetes. It has been shown that both direct cytotoxic (T-cell mediated) and indirect cytokine-dependent (e.g., interleukin-1, tumor necrosis factor-␣ [TNF-␣], and ␥-interferon) mechanisms are responsible for ␤-cell apoptosis (3).The direct cytotoxic mechanisms appear to involve the release of cytotoxic granule contents (e.g., perforin and granzymes) by cytotoxic T-cells (4). Granzymes play a critical role in triggering apoptotic cell death through mitochondrial pathways or by the activation of cellular caspases. Indeed, caspases (e.g., caspase-3) are key players in controlling the events leading to cellular apoptosis. Caspases are synthesized as inactive zymogens, which can be cleaved and activated by proteinases, including granzymes, cathepsins, and calpains. Granzymes and cathepsins are also members of a class of molecules known as serine proteinase inhibitor (serpin) proteinases. As for indirect mechanisms for ␤-cell apoptosis involving cytokines, signal transduction activities ...

Alpha-1-antitrypsin in cell and organ transplantation

“…Stabilization of mitochondrial membranes and decreasing release of Ca++, cytochrome c, and other constituents may explain how AAT protects against induction of diabetes by the mitochondrial poison, streptozotocin (STZ) 9, 10. This effect, and inhibition of pro‐apoptotic signaling induced by tumor necrosis factor‐α (TNF‐α),10, 11 likely contribute to stabilization of pancreatic islet β‐cells and to the prevention/treatment of diabetes reported in animal models and in some human studies 12. Preservation of islets is of obvious interest in pancreas and islet transplantation (discussed in section 3.1, Pancreatic Islet Transplantation).…”

“…Marcondes et al reported that AAT alters the cellular redox state and improves mitochondrial membrane potential while also increasing expression of antioxidant enzymes such as heme oxygenase 1 (Figure 1). 4, 5, 6, 7 Oxidative stress is important in inflammation and IRI, so these activities may contribute to the ability of AAT to promote cell and tissue survival and modulate inflammatory damage 10, 11, 13, 14, 15, 16, 17, 18, 19, 20. Because different types of lymphocytes, and cells in different activation states, differ in dependence on glycolysis vs oxidative phosphorylation, modulation of mitochondrial function may influence the balance between sensitization and tolerance 6…”

“…AAT has been shown to inhibit apoptosis in multiple in vitro and in vivo models 10, 11, 13, 14, 15, 16, 17, 18, 19, 20. Increased cell survival may result not only from stabilization of mitochondrial membranes, but also likely involves direct inhibition of caspases (Figure 1).…”

Anti‐inflammaging effects of human alpha‐1 antitrypsin

“…Human AAT has serine proteinase inhibitor activity, which can inhibit neutrophil elastase, proteinase 3, and cathepsin G. Human AAT can be chemically modified by nitric oxide (NO) and exhibits antibacterial and cysteine protease inhibitor activities (Miyamoto et al ., 2000). We and others have shown that hAAT directly inhibits caspase‐3 and prevents apoptosis (Petrache et al ., 2006; Zhang et al ., 2007). Increasing evidence indicates that hAAT is a multifunctional protein and may play an important role in modulating the immune system.…”

“…Increasing evidence indicates that hAAT is a multifunctional protein and may play an important role in modulating the immune system. First, application of hAAT has been shown to alleviate symptoms in many disease models whereby immunity and inflammation were implicated, such as type 1 diabetes (Lu et al ., 2006; Zhang et al ., 2007; Ma et al ., 2010), islet cell transplantation (Lewis et al ., 2008), rheumatoid arthritis (Grimstein et al ., 2010, 2011), stroke (Moldthan et al ., 2014), and bone loss (Cao et al ., 2011). A recent study indicated AAT treatment inhibited instant blood‐mediated inflammatory reaction (IBMIR) and islet apoptosis after islet cell transplantation (Wang et al ., 2017).…”