Poly(ADP-ribose) polymerase-deficient mice are protected from streptozotocin-induced diabetes

Abstract

Streptozotocin (STZ) selectively destroys insulin-producing beta islet cells of the pancreas providing a model of type I diabetes. Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme whose overactivation by DNA strand breaks depletes its substrate NAD ؉ and then ATP, leading to cellular death from energy depletion. We demonstrate DNA damage and a major activation of PARP in pancreatic islets of STZ-treated mice. These mice display a 500% increase in blood glucose and major pancreatic islet damage. In mice with homozygous targeted deletion of PARP (PARP ؊͞؊), blood glucose and pancreatic islet structure are normal, indicating virtually total protection from STZ diabetes. Partial protection occurs in PARP ؉͞؊ animals. Thus, PARP activation may participate in the pathophysiology of type I diabetes, for which PARP inhibitors might afford therapeutic benefit.Type I diabetes (insulin-dependent diabetes mellitus) is a chronic metabolic disorder characterized by a loss of pancreatic islet B cell mass, decreased serum insulin, and hyperglycemia. Although the pathogenic mechanisms of this disease have not been fully characterized, genetic, environmental, and autoimmune factors have been postulated. In particular, development of this disorder is postulated to proceed through generation of oxygen radicals during prediabetic pancreatic islet inflammation (1, 2). One possible mechanism is that autoimmune activation of macrophages damages B cells through release of massive amounts of NO after inducible NO synthase activation, as damage elicited when islets are cocultured with macrophages is prevented by inhibition of NO synthase (3).Focal cerebral ischemic damage is also associated with NO release leading to DNA damage elicited by reactive oxygen species, including peroxynitrite formed from NO. Downstream of this DNA damage, the enzyme poly(ADP-ribose) polymerase (PARP, EC 2.4.2.30) is stimulated. Nuclear PARP is activated by DNA fragments to transfer branched chains of up to 200 ADP ribose groups from NAD ϩ to acceptor proteins in the nucleus, including histones and PARP itself. PARP activation plays a role in DNA repair, particularly the base excision repair process (4-8), in response to moderate amounts of DNA damage. With excessive DNA damage, however, PARP is so highly activated that its substrate NAD ϩ is critically depleted (9). NAD ϩ is an important enzyme in energy metabolism, and its depletion results in lower ATP production. As ATP is also consumed in efforts to resynthesize NAD ϩ , cells can die from energy loss. Cerebral ischemic damage is greatly diminished in mice with targeted deletion of PARP (PARP Ϫ͞Ϫ) (10, 11) and in animals treated with PARP inhibitors (12, 13). A role of PARP activation in pancreatic damage is also suggested by protection through PARP inhibition of pancreatic islet cells from NO-mediated killing (14, 15). Furthermore, in vitro pancreatic islet cells from PARP Ϫ͞Ϫ mice are resistant to NAD ϩ depletion after exposure to either NO or other reactive oxygen intermediates generated th...

Genetic control of non obese diabetic mice susceptibility to high-dose streptozotocin-induced diabetes

“…Whereas PARP-1 activation and subsequent NAD + depletion have been implicated as a major mechanism of HDS-induced pancreatic beta-cell destruction [27,28,29], we did not detect any linkage of NOD HDSsusceptiblity to the D1Mit36 (92.3 cM) and D1Mit407 (101.5 cM) markers surrounding the corresponding gene at 98.6 cM in chromosome 1. This result is not really surprising since our previous studies showed that, in the NOD mouse, PARP-1 activation was not required for HDS-induced diabetes [6].…”

Excessive stimulation of poly(ADP‐ribosyl)ation contributes to endothelial dysfunction in pre‐eclampsia

“…In endothelial cells treated with high glucose, as well as in diabetes and hyperglycaemia, a sequence of events has been proposed whereby reactive nitrogen and oxygen species trigger DNA single-strand breaks, which in turn induce the rapid and excessive activation of PARP, an event which quickly depletes the intracellular stores of NAD þ (Soriano et al, 2001;Virag & Szabo, 2002). This depletion slows glycolysis, electron transport and ATP formation, and finally initiates acute endothelial dysfunction and vascular instability (Eliasson et al, 1997;Szabo et al, 1997;Burkart et al, 1999;Pieper et al, 1999a;.…”

“…However, in contrast to these cytoprotective functions, overstimulation of PARP is associated with pathophysiological effects resulting from rapid depletion of the intracellular NAD þ and ATP pools; this slows the rate of glycolysis and mitochondrial respiration and leads to cellular dysfunction (Eliasson et al, 1997;Szabo et al, 1997;Zingarelli et al, 1998;Burkart et al, 1999;Oliver et al, 1999;Pieper et al, 1999a, b;Soriano et al, 2001). PARP activation is implicated in the pathogenesis of stroke (Eliasson et al, 1997), autoimmune b-cell destruction (Burkart et al, 1999;Pieper et al, 1999a), shock and inflammation (Szabo et al, 1997;Oliver et al, 1999) and diabetic vascular dysfunction (Soriano et al, 2001).…”

The mechanisms of alloxan- and streptozotocin-induced diabetes

“…Also, mice deficient in PARP are resistant to beta cell death mediated by streptozotocin, in spite of DNA fragmentation. The absence of PARP prevents the depletion of the cofactor NAD + and the subsequent loss of ATP [84,[88][89][90] and thus cell death.…”