Update: role of the angiotensin type-2 (AT(2)) receptor in blood pressure regulation

In the past, virtually all of the physiologic actions of angiotensin II (ANG II) were thought to be mediated by the type-1 ANG II receptor. However, there is now a compelling body of evidence suggesting that the type-2 (AT2) receptor is an important regulator of renal function and blood pressure (BP). The AT2 receptor stimulates a bradykinin (BK)-nitric oxide (NO)-cyclic GMP vasodilator cascade in blood vessels and in the kidney. Recent studies have shown that absence of the AT2 receptor lends to pressor and natriuretic hypersensitivity to ANG II. Furthermore, there is now excellent evidence that the AT2 receptor mediates pressure natriuresis. The AT2 receptor also stimulates the conversion of prostaglandin E2 (PGE2) to PGF2. In addition, it is now apparent that the therapeutic reduction in BP with AT1 receptor blockade (eg, losartan, valsartan, candesartan) is mediated by ANG II stimulation of the AT2 receptor, leading to increased levels of BK, NO, and cGMP. Current evidence predicts that AT2 receptor agonists would be beneficial in the treatment of hypertension.

Involvement of endogenous nitric oxide and c-kit-expressing cells in chronic intestinal pseudo-obstruction

BACKGROUND/PURPOSE

Chronic intestinal pseudo-obstruction (CIP) in infants and children is a motility disorder without apparent mechanical cause. Nitric oxide (NO), an inhibitory neurotransmitter and c-kit cells, essential for the intestinal pacemaker activity, both play a key role in the intestinal motility function. In the current study, the authors investigated the distributive change in the intestinal nitric oxide synthase (NOS) and c-kit cells of patients with CIP.

METHODS

Tissues were obtained from 4 patients undergoing bowel resection or biopsy for CIP at laparotomy. For controls, the intestinal specimens were obtained from 4 age-matched cases of intestinal stricture, intussusception, and autopsy with no evidence of gastrointestinal disease. Immunohistochemical studies were performed on paraffin-embedded tissue cross sections with neuronal NOS and inducible NOS monoclonal antibody as well as a rabbit polyclonal antibody against the human c-kit receptor.

RESULTS

Under immunohistochemical staining, a greatly increased density of neuronal NOS immunoreactivity and an evidently increased number of intense NOS immunoreactive nerve fibers were observed in the myenteric plexus and circular muscle layers compared with the control sections. In the submucosal plexus and longitudinal muscle layer, there was no change in NOS immunoreactivity. Inducible NOS immunoreactivity was not detected in the control cases. However, in tissues of CIP, almost all the epithelial cells were positively and strongly labeled for inducible NOS immunoreactivity. For c-kit cells staining, the number of c-kit-positive cells in the myenteric plexus and circular muscle layers were greatly less than that in the controls, especially in the myenteric plexus region.

CONCLUSION

These findings suggest that sustained production of NO by an increased NOS activity and a deficiency of c-kit cells in the intestine may be related to the pathogenesis of CIP.

Expression and localization of angiotensin subtype receptor proteins in the hypertensive rat heart

The cellular localization of the AT(2) receptor and the regulation of its expression in hypertrophied left ventricle are not well known. We compared the expression of the cardiac AT(1) and AT(2) receptor in spontaneously hypertensive rats/Izumo strain (SHR/Izm) and Wistar Kyoto rats/Izumo strain (WKY/Izm), ages 4, 12, and 20 wk, by means of immunohistochemistry and Western blot analysis. In SHR/Izm, compared with WKY/Izm, blood pressure (161 +/- 2 vs. 120 +/- 2 mmHg at 12 wk, P </= 0.01, and 199 +/- 3 vs. 123 +/- 3 mmHg at 20 wk, P </= 0.01) and heart-to-body weight ratio (3.76 +/- 0.07 vs. 3.06 +/- 0.06 mg/g at 12 wk, P </= 0.01, and 3.90 +/- 0.08 vs. 3.01 +/- 0.12 mg/g at 20 wk, P </= 0.01) were significantly elevated. There was no difference in these values between the two strains at 4 wk of age. Histologically, 20-wk-old SHR/Izm demonstrated myocardial hypertrophy, a thickening of the smooth muscle layer of the intracardiac arteries, and perivascular fibrosis. By immunohistochemistry, the AT(2) receptor was localized to cardiomyocytes and vascular endothelial cells, but not in the vascular smooth muscle cells. No major AT(2) receptor signal was observed in perivascular fibrosis at any age in either strain of rats. No difference was detected in this localization between the two strains. By Western blotting, a single 44-kDa band for the AT(2) receptor and a single 60-kDa band for the AT(1) receptor were detected in ventricles from both strains of rats at all ages. Densitometric analysis demonstrated that the AT(2) receptor 44-kDa band was decreased by 20% at 12 wk and 32% at 20 wk (P < 0.01) in SHR/Izm compared with WKY/Izm. The intensity of the AT(1) receptor 60-kDa band was increased by 57% in 20-wk-old SHR/Izm compared with WKY/Izm (P < 0.05). There was no significant difference in the intensity of the 44- or 60-kDa bands in 4-wk-old animals of either strain. We demonstrated a decrease in the AT(2) receptor and an increase in the AT(1) receptor protein with no change in their localizations in hypertrophied left ventricular myocytes of SHR/Izm.

Vitamin A antagonizes decreased cell growth and elevated collagen-degrading matrix metalloproteinases and stimulates collagen accumulation in naturally aged human skin

Damage to human skin due to ultraviolet light from the sun (photoaging) and damage occurring as a consequence of the passage of time (chronologic or natural aging) are considered to be distinct entities. Photoaging is caused in part by damage to skin connective tissue by increased elaboration of collagen-degrading matrix metalloproteinases, and by reduced collagen synthesis. As matrix metalloproteinase levels are known to rise in fibroblasts as a function of age, and as oxidant stress is believed to underlie changes associated with both photoaging and natural aging, we determined whether natural skin aging, like photoaging, gives rise to increased matrix metalloproteinases and reduced collagen synthesis. In addition, we determined whether topical vitamin A (retinol) could stimulate new collagen deposition in sun-protected aged skin, as it does in photoaged skin. Sun-protected skin samples were obtained from 72 individuals in four age groups: 18-29 y, 30-59 y, 60-79 y, and 80+ y. Histologic and cellular markers of connective tissue abnormalities were significantly elevated in the 60-79 y and 80+ y groups, compared with the two younger age groups. Increased matrix metalloproteinase levels and decreased collagen synthesis/expression were associated with this connective tissue damage. In a separate group of 53 individuals (80+ y of age), topical application of 1% vitamin A for 7 d increased fibroblast growth and collagen synthesis, and concomitantly reduced the levels of matrix-degrading matrix metalloproteinases. Our findings indicate that naturally aged, sun-protected skin and photoaged skin share important molecular features including connective tissue damage, elevated matrix metalloproteinase levels, and reduced collagen production. In addition, vitamin A treatment reduces matrix metalloproteinase expression and stimulates collagen synthesis in naturally aged, sun-protected skin, as it does in photoaged skin.

The effect of mutation at valine-45 on the stability and redox potentials of trypsin-cleaved cytochrome b5

In an attempt to elucidate the determinants of redox potential and protein stability in cytochrome b5, three mutants at a highly conserved residue Val45, which is a member of heme hydrophobic pocket residues have been characterized. The V45Y mutant was designed to introduce a bulkier residue and a hydroxyl group to the heme pocket. The mutants V45H and V45E were constructed to test the effect of positive and negative charge on the stability and redox potential of proteins. The influence of these mutants on the protein stability towards thermal, urea, acid, ethanol and on the redox potential were studied. It is concluded that the decrease of hydrophobic free energy and the larger volume of the tyrosine make the phenylhydroxyl group of tyrosine still sitting inside the hydrophobic pocket, while the side chain of the mutant V45E and V45H shift away from the heme pocket. The redox potentials of mutants V45Y, V45H, V45E and wild-type of cytochrome b5 are -35 mV, 8 mV, -26 mV and -3 mV, respectively. The bigger change of the V45Y on redox potential is due to the close contact between the hydroxyl group and the heme, while the changes of the V45E and V45H result from the alteration of charge density and distribution around the heme. Different relative stability of these mutants towards heat have been observed with the order: WT > V45Y-V45H > V45E being both in the oxidized and reduced state. The relative stability induced by addition of urea decreases in the order: WT > V45Y > V45H > V45E. These results suggest that the difference in the hydrophobic free energy is a major factor contributing to the stability of the Val45 mutants. Also the loose of the helix III in the mutant V45E makes it more unstable. These results indicate that residue Val45 plays an important role in the stability and redox potential of the protein.

Role of the angiotensin type 2 receptor in the regulation of blood pressure and renal function

The renin-angiotensin system is a major physiological regulator of body fluid volume, electrolyte balance, and arterial pressure. Virtually all of the biological actions of the principle effector peptide angiotensin II (ANG II) have been attributed to an action at the type 1 (AT(1)) ANG receptor. Until recently, the functional role of the type 2 (AT(2)) receptor, if any, has been unknown, possibly because the AT(2) receptor has a low degree of expression compared with that of the AT(1) receptor. Evidence has now accumulated that the AT(2) receptor opposes functions mediated by the AT(1) receptor. Whereas the AT(1) receptor stimulates cell proliferation, the AT(2) receptor inhibits proliferation and promotes cell differentiation. These differences in growth responses have been ascribed to different cell signaling pathways in which the AT(1) receptor stimulates protein phosphorylation and the AT(2) receptor dephosphorylation. During the past 5 years, studies have demonstrated that the AT(2) receptor is responsible for vasodilation and natriuresis, thus opposing the vasoconstrictor and antinatriuretic effects of ANG II mediated through the AT(1) receptor. Work from our laboratory and others indicates that the AT(2) receptor stimulates vasodilation and natriuresis by an autocrine cascade including bradykinin, nitric oxide, and cyclic GMP. The AT(2) receptor also has been found to control vasodilator prostaglandins, which have a role in blood pressure regulation. The AT(2) receptor appears to play a counterregulatory protective role in the regulation of blood pressure and sodium excretion that opposes the AT(1) receptor.

New approaches to understanding p53 gene tumor mutation spectra

The first p53 gene mutation arising in a human tumor was described a decade ago by Baker et al. [S.J. Baker, E.R. Fearon, J.M. Nigro, S.R. Hamilton, A.C. Preisinger, J.M. Jessup, P. van Tuinen, D.H. Ledbetter, D.F. Barker, Y. Nakamura, R. White, B. Vogelstein, Chromosome 17 deletions and p53 gene mutations in colorectal carcinomas, Science 244 (1989) 217-221]. There are now over 10,000 mutations extracted from the published literature in the IARC database of human p53 tumor mutations [P. Hainaut, T. Hernandez, A. Robinson, P. Rodriguez-Tome, T. Flores, M. Hollstein, C.C. Harris, R. Montesano, IARC database of p53 gene mutations in human tumors and cell lines: updated compilation, revised formats and new visualization tools, Nucleic Acids Res. 26 (1998) 205-213; Version R3, January 1999]. A large and diverse collection of tumor mutations in cancer patients provides important information on the nature of environmental factors or biological processes that are important causes of human gene mutation, since xenobiotic mutagens as well as endogenous mechanisms of genetic change produce characteristic types of patterns in target DNA [J.H. Miller, Mutational specificity in bacteria, Annu. Rev. Genet. 17 (1983) 215-238; T. Lindahl, Instability and decay of the primary structure of DNA, Nature 362 (1993) 709-715; S.P. Hussain, C.C. Harris, Molecular epidemiology of human cancer: contribution of mutation spectra studies of tumor suppressor genes, Cancer Res. 58 (1998) 4023-4037; P. Hainaut, M. Hollstein, p53 and human cancer: the first ten thousand mutations, Adv. Cancer Res. 2000]. P53 gene mutations in cancers can be compared to point mutation spectra at the HPRT locus of human lymphocytes from patients or healthy individuals with known exposure histories, and accumulated data indicate that mutation patterns at the two loci share certain general features. Hypotheses regarding specific cancer risk factors can be tested by comparing p53 tumor mutations typical of a defined patient group against mutations generated experimentally in rodents or in prokaryotic and eukaryotic cells in vitro. Refinements of this approach to hypothesis testing are being explored that employ human p53 sequences introduced artificially into experimental organisms used in laboratory mutagenesis assays. P53-specific laboratory models, combined with DNA microchips designed for high through-put mutation screening promise to unmask information currently hidden in the compilation of human tumor p53 mutations.

Chromosomal aberrations in PARP(-/-) mice: genome stabilization in immortalized cells by reintroduction of poly(ADP-ribose) polymerase cDNA

Depletion of poly(ADP-ribose) polymerase (PARP) increases the frequency of recombination, gene amplification, sister chromatid exchanges, and micronuclei formation in cells exposed to genotoxic agents, implicating PARP in the maintenance of genomic stability. Flow cytometric analysis now has revealed an unstable tetraploid population in immortalized fibroblasts derived from PARP(-/-) mice. Comparative genomic hybridization detected partial chromosomal gains in 4C5-ter, 5F-ter, and 14A1-C1 in PARP(-/-)mice and immortalized PARP(-/-)fibroblasts. Neither the chromosomal gains nor the tetraploid population were apparent in PARP(-/-) cells stably transfected with PARP cDNA [PARP(-/-)(+PARP)], indicating negative selection of cells with these genetic aberrations after reintroduction of PARP cDNA. Although the tumor suppressor p53 was not detectable in PARP(-/-) cells, p53 expression was partially restored in PARP(-/-) (+PARP) cells. Loss of 14D3-ter that encompasses the tumor suppressor gene Rb-1 in PARP(-/-) mice was associated with a reduction in retinoblastoma(Rb) expression; increased expression of the oncogene Jun was correlated with a gain in 4C5-ter that harbors this oncogene. These results further implicate PARP in the maintenance of genomic stability and suggest that altered expression of p53, Rb, and Jun, as well as undoubtedly many other proteins may be a result of genomic instability associated with PARP deficiency.

A nonpeptidyl mimic of superoxide dismutase with therapeutic activity in rats

Many human diseases are associated with the overproduction of oxygen free radicals that inflict cell damage. A manganese(II) complex with a bis(cyclohexylpyridine)-substituted macrocyclic ligand (M40403) was designed to be a functional mimic of the superoxide dismutase (SOD) enzymes that normally remove these radicals. M40403 had high catalytic SOD activity and was chemically and biologically stable in vivo. Injection of M40403 into rat models of inflammation and ischemia-reperfusion injury protected the animals against tissue damage. Such mimics may result in better clinical therapies for diseases mediated by superoxide radicals.

Diffraction properties of transmission photorefractive volume gratings in a cerium-doped potassium sodium strontium barium niobate crystal

The diffraction efficiency of volume gratings written by two-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) photorefractive crystal is studied. It is found that the diffraction efficiency strongly depends on the polarization of writing beams and exhibits loop behavior with respect to the fringe modulation. The fringe modulations before and behind the crystal are compared. Modified coupled-wave theory is used to fit the experimental data. This research presents data that are relevant to the application of Ce:KNSBN crystals to holographic recording and optical information processing.

Functions of poly(ADP-ribose) polymerase in controlling telomere length and chromosomal stability

In most eukaryotes, poly(ADP-ribose) polymerase (PARP) recognizes DNA strand interruptions generated in vivo. DNA binding by PARP triggers primarily its own modification by the sequential addition of ADP-ribose units to form polymers; this modification, in turn, causes the release of PARP from DNA ends. Studies on the effects of the disruption of the gene encoding PARP (Adprt1, formerly Adprp) in mice have demonstrated roles for PARP in recovery from DNA damage and in suppressing recombination processes involving DNA ends. Telomeres are the natural termini of chromosomes and are, therefore, potential targets of PARP. Here, by the use of two different techniques, we show that mice lacking PARP display telomere shortening compared with wild-type mice. Telomere shortening is seen in different genetic backgrounds and in different tissues, both from embryos and adult mice. In vitro telomerase activity, however, is not altered in Adprt1-/- mouse fibroblasts. Furthermore, cytogenetic analysis of mouse embryonic fibroblasts reveals that lack of PARP is associated with severe chromosomal instability, characterized by increased frequencies of chromosome fusions and aneuploidy. The absence of PARP does not affect the presence of single-strand overhangs, naturally present at the ends of telomeres. This study therefore reveals an unanticipated role for PARP in telomere length regulation and provides insights into its functions in maintaining genomic integrity.

Failure of poly(ADP-ribose) polymerase cleavage by caspases leads to induction of necrosis and enhanced apoptosis

Activation of poly(ADP-ribose) polymerase (PARP) by DNA breaks catalyzes poly(ADP-ribosyl)ation and results in depletion of NAD+ and ATP, which is thought to induce necrosis. Proteolytic cleavage of PARP by caspases is a hallmark of apoptosis. To investigate whether PARP cleavage plays a role in apoptosis and in the decision of cells to undergo apoptosis or necrosis, we introduced a point mutation into the cleavage site (DEVD) of PARP that renders the protein resistant to caspase cleavage in vitro and in vivo. Here, we show that after treatment with tumor necrosis factor alpha, fibroblasts expressing this caspase-resistant PARP exhibited an accelerated cell death. This enhanced cell death is attributable to the induction of necrosis and an increased apoptosis and was coupled with depletion of NAD+ and ATP that occurred only in cells expressing caspase-resistant PARP. The PARP inhibitor 3-aminobenzamide prevented the NAD+ drop and concomitantly inhibited necrosis and the elevated apoptosis. These data indicate that this accelerated cell death is due to NAD+ depletion, a mechanism known to kill various cell types, caused by activation of uncleaved PARP after DNA fragmentation. The present study demonstrates that PARP cleavage prevents induction of necrosis during apoptosis and ensures appropriate execution of caspase-mediated programmed cell death.

Methanol-induced unfolding and refolding of cytochrome b5 and its P40V mutant monitored by UV-visible, CD, and fluorescence spectra

In order to illustrate the structural importance of proline-40 of cytochrome b5 (Cyt b5), the P40V mutant gene was constructed. Unfolding and refolding of Cyt b5 induced by methanol was investigated by means of the UV-visible spectrum, circular dichroism, and the fluorescence spectrum. Methanol denaturation of Cyt b5 is a cooperative process, that is, the heme group dissociates from the heme pocket accompanied by unfolding of the polypeptide chain both in the secondary and tertiary structures. Substitution of proline by valine reduces the stability of the mutant under methanol denaturation. The unfolding process is almost reversible by dilution. During refolding, the denatured polypeptide must be folded to a more ordered structure prior to the heme capture. Pro40 plays an important role in modulating the protein's stability. The role of tyrosine in the unfolding and refolding of Cyt b5 is evaluated for the first time. A mechanism of methanol denaturation is also proposed.

Protective effects of a superoxide dismutase mimetic and peroxynitrite decomposition catalysts in endotoxin-induced intestinal damage

1. The relative contributions of superoxide anion (O2-) and peroxynitrite (PN) were evaluated in the pathogenesis of intestinal microvascular damage caused by the intravenous injection of E. coli lipopolysaccharide (LPS) in rats. The superoxide dismutase mimetic (SODm) SC-55858 and the active peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-disulphonatophenyl)-por phyrinato iron (III) and 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)-porphyrinato iron (III) (FeTMPS, FeTMPyP respectively) were used to assess the roles of O2- and PN respectively. 2. The intravenous injection of LPS elicited an inflammatory response that was characterized by a time-dependent infiltration of neutrophils, lipid peroxidation, microvascular leakage (indicative of microvascular damage), and epithelial cell injury in both the duodenum and jejunum. 3. Administration of the SODm SC-55858, FeTMPS or FeTMPyP at 3 h post LPS reduced the subsequent increase in microvascular leakage, lipid peroxidation and epithelial cell injury. Inactive peroxynitrite decomposition catalysts exhibited no protective effects. Only, SC-55858 inhibited neutrophil infiltration. 4. Our results suggest that O2 and peroxynitrite play a significant role in the pathogenesis of duodenal and intestinal injury during endotoxaemia and that their remoyal by SODm and peroxynitrite decomposition catalysts offers a novel approach to the treatment of septic shock or clinical conditions of gastrointestinal inflammation. Furthermore, the remarkable protection of the intestinal epithelium by these agents suggests their use during chemo- and radiation therapy, cancer treatments characterized by gastrointestinal damage. Potential mechanisms through which these radicals evoke damage are discussed.

Poly(ADP-ribose) polymerase activation mediates 1-methyl-4-phenyl-1, 2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that causes parkinsonism in humans and nonhuman animals, and its use has led to greater understanding of the pathogenesis of Parkinson's disease. However, its molecular targets have not been defined. We show that mice lacking the gene for poly(ADP-ribose) polymerase (PARP), which catalyzes the attachment of ADP ribose units from NAD to nuclear proteins after DNA damage, are dramatically spared from MPTP neurotoxicity. MPTP potently activates PARP exclusively in vulnerable dopamine containing neurons of the substantia nigra. MPTP elicits a novel pattern of poly(ADP-ribosyl)ation of nuclear proteins that completely depends on neuronally derived nitric oxide. Thus, NO, DNA damage, and PARP activation play a critical role in MPTP-induced parkinsonism and suggest that inhibitors of PARP may have protective benefit in the treatment of Parkinson's disease.

MHC class I molecules on CD4 T cells regulate receptor-mediated activation signals

Three T cell populations can be distinguished based on their response to antigen receptor engagement. A sizable fraction dies within hours of TCR ligation, a smaller fraction enters the mitotic cycle, and the remaining T cells merely upregulate the expression of certain cell surface markers. An MHC-I-controlled regulatory mechanism has been identified. MHC I MAbs, or Fab fragments, prevent T cells from mounting a proliferative mitogen response but do not inhibit the mitogen-induced deletion of T cells. IFN-gamma enlarges the fraction of T cells which proliferate in response to mitogen stimulation but, in the presence of MHC I MAb, these cells fail to clonally expand and enter the deletion pathway. Phenotypically, MHC I MAb Fab fragments induce T cells to upregulate the expression of the apoptosis marker CD95, even in the absence of TCR ligand, and prevent the upregulation of costimulatory CD28 molecule expression.

Novel actions of angiotensin II via its renal type-2 (AT(2)) receptor

The vast majority of the biologic effects of angiotensin II have been considered to be mediated by the subtype-1 (AT(1)) receptor. The AT(2) receptor is expressed to a low degree in most adult cells and tissues, and its function has not been understood. Recent studies, however, have identified novel actions of angiotensin II mediated by the AT(2) receptor in the kidney. These AT(2) receptor actions have importance in the control of blood pressure and hypertension. The AT(2) receptor mediates a renal vasodilator cascade, including generation of bradykinin, nitric oxide, and cyclic GMP. This action of angiotensin II occurs when the renin-angiotensin system is activated, as in sodium depletion. The AT(2) receptor also appears to mediate prostaglandin (PG) F(2)(a) formation, probably by stimulating conversion of PGE2 to PGF(2)(a). The AT(2) receptor plays a counter-regulatory vasodilator role opposing the vasoconstrictor actions of angiotensin II. The AT(1) and AT(2) receptors engage in inter-receptor "cross-talk." In the absence of the AT(2) receptor, sustained angiotensin II pressor and antinatriuretic hypersensitivity occurs, mediated by a deficiency of bradykinin, nitric oxide, and cyclic GMP. The AT(2) receptor may play an important role in stimulating pressure natriuresis, but definitive studies are required to resolve this issue. The AT(2) receptor mediates several renal actions of angiotensin II, appears to be important in the physiologic regulation of blood pressure, and may be involved in the pathophysiology of hypertension.

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

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.

Mice lacking the poly(ADP-ribose) polymerase gene are resistant to pancreatic beta-cell destruction and diabetes development induced by streptozocin

Human type 1 diabetes results from the selective destruction of insulin-producing pancreatic beta cells during islet inflammation. Cytokines and reactive radicals released during this process contribute to beta-cell death. Here we show that mice with a disrupted gene coding for poly (ADP-ribose) polymerase (PARP-/- mice) are completely resistant to the development of diabetes induced by the beta-cell toxin streptozocin. The mice remained normoglycemic and maintained normal levels of total pancreatic insulin content and normal islet ultrastructure. Cultivated PARP-/- islet cells resisted streptozocin-induced lysis and maintained intracellular NAD+ levels. Our results identify NAD+ depletion caused by PARP activation as the dominant metabolic event in islet-cell destruction, and provide information for the development of strategies to prevent the progression or manifestation of the disease in individuals at risk of developing type 1 diabetes.

Compensatory expression of p73 in PARP-deficient mouse fibroblasts as response to a reduced level of regularly spliced wild-type p53 protein

We have investigated the effect of PARP gene inactivation on the expression of wild-type (wt) p53 protein. Using immortalized fibroblasts from control and PARP knock-out mice we have found by immunoblotting with the PAb421 antibody a profound decrease of the p53 expression to a barely detectable level in PARP knock-out cells. Surprisingly, longer exposure of immunoblots revealed an immunoreactive band at about 75 kD which was stronger in PARP-deficient cells than in wt cells and was not affected upon doxorubicin treatment. The size of the PAb421 immunoreactive protein and the lack of its inducibility in response to DNA damage resembled those of p73, the first described p53 homologue. Therefore, we examined the reactivity of anti-p53 antibodies with in vitro translated p73 protein. Interestingly, p73 was efficiently immunoprecipitated with distinct antibodies recognizing the carboxy-terminus of p53. In Northern blots we observed p73 signals of comparable intensity in controls and PARP-deficient cells. We conclude that elevated expression of p73 may compensate the reduced level of p53 in PARP-deficient cells.

JunB is essential for mammalian placentation

Lack of JunB, an immediate early gene product and member of the AP-1 transcription factor family causes embryonic lethality between E8.5 and E10.0. Although mutant embryos are severely retarded in growth and development, cellular proliferation is apparently not impaired. Retardation and embryonic death are caused by the inability of JunB-deficient embryos to establish proper vascular interactions with the maternal circulation due to multiple defects in extra-embryonic tissues. The onset of the phenotypic defects correlates well with high expression of junB in wild-type extra-embryonic tissues. In trophoblasts, the lack of JunB causes a deregulation of proliferin, matrix metalloproteinase-9 (MMP-9) and urokinase plasminogen activator (uPA) gene expression, resulting in a defective neovascularization of the decidua. As a result of downregulation of the VEGF-receptor 1 (flt-1), blood vessels in the yolk sac mesoderm appeared dilated. Mutant embryos which escape these initial defects finally die from a non-vascularized placental labyrinth. Injection of junB-/- embryonic stem (ES) cells into tetraploid wild-type blastocysts resulted in a partial rescue, in which the ES cell-derived fetuses were no longer growth retarded and displayed a normal placental labyrinth. Therefore, JunB appears to be involved in multiple signaling pathways regulating genes involved in the establishment of a proper feto-maternal circulatory system.

Increased nonenzymatically glycosylated proteins in the vitreous humor of diabetic animals

One of the earliest pathologic changes of diabetes mellitus is increased nonenzymatic glycosylation (i.e., glycation) of proteins, which results in abnormal aggregation of collagen fibrils and production of superoxide radicals. These abnormalities may be responsible for the precocious senescence of connective tissue associated with the disease. We sought to determine whether glycation is increased in the vitreous humor of short-term diabetic cats (6 months' duration) and rabbits (2 months' duration), using a nitroblue tetrazolium colorimetric assay for fructosamine. Vitreous protein fructosamine concentration was significantly higher in diabetic cats and rabbits, compared with that in control (nondiabetic) animals. These results indicate that glycation is increased in the vitreous humor of short-term diabetic animals, and therefore may be one of the initial triggers for clinically apparent diabetic retinopathy.

Reduced stability of regularly spliced but not alternatively spliced p53 protein in PARP-deficient mouse fibroblasts

The interaction between poly(ADP-ribose) polymerase (PARP) and the product of the tumor suppressor gene p53 has been described previously. Here, we have investigated whether PARP deficiency may affect the expression and regulation of wild-type (wt) p53. For this purpose, we have used immortalized cells derived from wt and PARP knockout mice. We have found a clearly reduced basal level of PAb421 immunoreactive wt p53 protein in PARP-deficient cells. The monoclonal antibody PAb421 is known to recognize an epitope in the COOH terminus of normally spliced p53 protein. Under indirect immunofluorescence, this antibody stained nuclei in normal but not in PARP-deficient cells. Despite marked reduction of wt p53 protein in PARP knockout cells, no significant difference of the p53 transcription rate was observed between wt and PARP-deficient cells. Interestingly, in both cell types, an additional p53 transcript representing the alternatively spliced (AS) p53 form was detected. Because of its reactivity with different specific anti-p53 antibodies, we have determined that the p53 protein present in PARP knockout mouse cells possesses characteristic features of AS p53. Our results clearly show that PARP-deficient cells constitutively express the AS form of wt p53 and indicate that the regularly spliced p53 is extremely unstable in the absence of PARP. Moreover, PARP-/- cells fail to transactivate p53-responsive genes. Treatment of PARP-/- cells with genotoxic agents primarily leads to the activation of AS p53 protein.

Differential regulation of renal angiotensin subtype AT1A and AT2 receptor protein in rats with angiotensin-dependent hypertension

-This study was designed to investigate distribution and regulation of the renal AT1A and AT2 subtype receptors in rats with either systemic angiotensin II (Ang II)-induced hypertension or acute phase renal hypertension (2-kidney, 1-clip [2K1C] or 2-kidney, 1-figure-of-8-wrap [2K1W]). In normal rat kidneys, positive immunostaining for the AT1A receptor was observed in the intrarenal vasculature, glomeruli, proximal and distal tubules, and collecting ducts. The AT2 receptor was localized mainly to the glomeruli. The AT1A but not AT2 receptor protein expression was significantly reduced in rats with 10-day systemic Ang II-induced hypertension. In both 7-day 2K1C and 3-day 2K1W rats, the AT1A receptor was significantly reduced in ischemic and contralateral kidneys compared with sham-operated control rats. Reduction in AT2 receptor expression was observed only in the ischemic kidneys in 2K1C and 2K1W renal hypertensive rats. These results demonstrate that the AT1A receptor is widely distributed in the glomerulus and all other nephron segments of the rat kidney. Renal AT1A but not AT2 receptor protein is downregulated in rats with Ang II-induced hypertension. In renal hypertensive rats, the AT1A receptor is bilaterally downregulated and the AT2 receptor is downregulated only in the ischemic kidney.