Streptozotocin (STZ), a glucose analogue known to induce diabetes in experimental animals, causes DNA strand breaks and subsequent activation of poly(ADPribose) polymerase (Parp). Because Parp uses NAD as a substrate, extensive DNA damage will result in reduction of cellular NAD level. In fact, STZ induces NAD depletion and cell death in isolated pancreatic islets in vitro. Activation of Parp therefore is thought to play an important role in STZ-induced diabetes. In the present study, we established Parp-deficient (Parp ؊/؊ ) mice by disrupting Parp exon 1 by using the homologous recombination technique. These mice were used to examine the possible involvement of Parp in STZ-induced ␤-cell damage in vivo. The wild-type (Parp ؉/؉ ) mice showed significant increases in blood glucose concentration from 129 mg͞dl to 218, 370, 477, and 452 mg͞dl on experimental days 1, 7, 21, and 60, respectively, after a single injection of 180 mg STZ͞kg body weight. In contrast, the concentration of blood glucose in Parp ؊/؊ mice remained normal up to day 7, slightly increased on day 21, but returned to normal levels on day 60. STZ injection caused extensive necrosis in the islets of Parp ؉/؉ mice on day 1, with subsequent progressive islet atrophy and loss of functional ␤ cells from day 7. In contrast, the extent of islet ␤-cell death and dysfunction was markedly less in Parp ؊/؊ mice. Our findings clearly implicate Parp activation in islet ␤-cell damage and glucose intolerance induced by STZ in vivo.Various types of DNA damage produced by many environmental chemicals or reactive oxygen species generated by inflammatory reactions contribute to insulin-dependent diabetes mellitus (IDDM) through the induction of ␤-cell death in pancreatic islets (1-3). Acute exposure to streptozotocin [2-deoxy-2-(3-methyl-3-nitrosourea)l-D-glucopyranose, STZ] induces massive ␤-cell death and diabetes mellitus in experimental animals (4, 5). STZ also causes a rapid depletion of cellular NAD in islets (6-9), but this depletion is prevented by injection of nicotinamide immediately before or soon after the administration of STZ (10). Okamoto and colleagues (2, 11) demonstrated that STZ induces DNA strand breaks and activation of poly(ADP-ribose) polymerase (Parp) with subsequent reduction of NAD levels in the isolated pancreatic islets in vitro. These findings suggest the involvement of Parp as a key molecule in STZ-induced ␤-cell death and diabetes through extensive poly(ADP-ribose) formation and NAD depletion, leading to reduction of ATP level and cell death. In agreement with this hypothesis, Parp inhibitors such as 3-aminobenzamide or nicotinamide prevent the depletion of NAD and induction of STZ-induced ␤-cell death (12, 13). However, because Parp inhibitors possess other effects, such as scavenging hydrogen peroxide (14), it is not clear whether and how Parp activity contributes to ␤-cell death and the development of diabetes in vivo. Thus, engineering of a Parp-deficient animal model would be useful for investigating the role of Parp in S...

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Embryonic stem (ES) cells deficient in the enzyme poly(ADP-ribose) polymerase (Parp1) develop into teratocarcinoma-like tumors when injected subcutaneously into nude mice that contain cells with giant cell-like morphology. We show here that these cells express genes characteristic of trophoblast giant cells and thus belong to the trophectoderm lineage. In addition, Parp1(-/-) tumors contained other trophoblast subtypes as revealed by expression of spongiotrophoblast-specific marker genes. The extent of giant cell differentiation was enhanced, however, as compared with spongiotrophoblast. A similar shift toward trophoblast giant cell differentiation was observed in cultures of Parp1-deficient ES cells and in placentae of Parp1(-/-) embryos. Analysis of other cell lineage markers demonstrated that Parp1 acts exclusively in trophoblast to suppress differentiation. Surprisingly, trophoblast derivatives were also detected in wildtype tumors and cultured ES cells, albeit at significantly lower frequency. These data show that wildtype ES cells contain a small population of cells with trophectoderm potential and that absence of Parp1 renders ES cells more susceptible to adopting a trophoblast phenotype.

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