OS057. Pathophysiological role of elevated tissue transglutaminase in autoantibody-induced features of preeclampsia in pregnant mice

INTRODUCTION

Preeclampsia (PE) is highly associated with the presence of autoantibodies that activate the major angiotensin receptor, AT1R. These autoantibodies (termed AT1-AA) cause most features of PE when introduced into pregnant mice and are believed to contribute to disease pathogenesis. Tissue transglutaminase (tTG) is a prominent member of a family of enzymes that crosslink proteins by catalyzing the formation of an isopeptide bond between the amide group of glutamine and the free amino group of lysine and is believed to play a role in AT1R activation.

OBJECTIVES

To test the hypothesis that tTG plays a role in autoantibody-mediated AT1R activation and thereby contributes to the pathophyhsiology of PE.

METHODS

Western blotting was used to quantify tTG in placentas of normotensive pregnant women and those with PE. Immunohistochemistry was used to determine cellular localization of tTG, AT1R and glutamyl-lysine isopeptides in placenta tissue. Co-immunoprecipitation experiments were used to explore the possible association of tTG and AT1R. Finally, in an effort to determine the role of tTG in AT1-AA-induced features of PE in vivo, we treated autoantibody-injected pregnant mice with cystamine, a potent tTG inhibitor.

RESULTS

Western blot analysis showed elevated tTG in placentas of women with PE. Immunohistochemical analysis revealed that increased levels of tTG, glutamyl-lysineisopeptides, AT1R co-localized in the microvillous membrane of PE placentas. Immunoprecipitation of tTG from human trophoblast cell (HTR) lysates resulted in the co-immunoprecipitation of AT1R, thereby providing evidence for an interaction between tTG and AT1R in HTR cells. Finally, we found that cystamine treatment significantly attenuated key features associated with PE including hypertension and proteinuria in the PE-IgG-injected pregnant mice.

CONCLUSION

Taken together, we identified a previously unrecognized role of elevated tTG in PE likely by activating or stabilizing AT1Rs. These studies provide novel mechanisms of autoantibody-induced AT1R activation by elevated placental tTG, highlight the role of tTG in the pathogenesis of PE and suggest novel therapeutic strategies for the disease.

OS069. Light, a TNF superfamily member, contributes to pathophysiology in a mouse model of preeclampsia

INTRODUCTION

Preeclampsia (PE) is associated with alterations in the renin-angiotensin system due to the presence of autoantibodies that activate the major angiotensin receptor, AT1R. The resulting chronic activation of the AT1 receptor is believed to contribute to a pro-inflammatory state that is also characteristic of PE. Microarray analysis revealed a pronounced increase in the abundance of LIGHT, a potent member of the TNF superfamily that has emerged as a key factor mediating strong T-cell inflammatory responses and a contributor to autoimmune disease pathogenesis.

OBJECTIVES

The goal of research described here is to determine the contribution of LIGHT to the pathophysiology of PE.

METHODS

An ELISA, specific for LIGHT was used to validate the results of the initial microarray analysis. Infusion experiments were used to determine the effects of elevated LIGHT in pregnant and non-pregnant mice. An adoptive transfer model of PE in pregnant mice was used to determine if AT1R agonistic autoantibodies (AT1AA) stimulate LIGHT production. The potential contribution of increased LIGHT to clinical features of PE in pregnant mice was evaluated by the use of neutralizing antibodies directed to the LIGHT receptors, HVEM and LTβR.

RESULTS

The use of a LIGHT-specific ELISA showed that the cytokine was significantly increased in the circulation and placentas of women with PE. The infusion of recombinant LIGHT into pregnant mice induced major clinical features of PE, including hypertension and proteinuria. Such changes were not observed when LIGHT was infused into not non-pregnant mice. LIGHT was significantly elevated in a pregnant mouse model of PE based on the introduction of IgG from women with PE. In this autoantibody-injection model of PE, the use of neutralizing antibodies to the LIGHT receptors, HVEM and LTβR, blocked autoantibody-induced hypertension, proteinuria, elevated sFlt-1 production, impaired placental angiogenesis and endothelial dysfunction.

CONCLUSION

Overall, our studies show that LIGHT is significantly elevated in women with PE and that elevated LIGHT contributes to pathophysiology of PE in an antibody-injection model of PE in pregnant mice. LIGHT-induced pathophysiology can be abrogated by the use of neutralizing antibodies directed at its receptors, HVEM and LTβR. These results indicate that LIGHT may have a previously unrecognized role in the pathophysiology of PE and that its detrimental effects are pregnancy-dependent. These findings immediately suggest novel therapeutic possibilities.

The functional role of the renin-angiotensin system in pregnancy and preeclampsia

During normal pregnancy, the renin-angiotensin system (RAS) plays a vitally important role in salt balance and subsequent well-being of mother and fetus. In this balance, one must consider not only the classical renal RAS but also that of the uteroplacental unit, where both maternal and fetal tissues contribute to the signaling cascade. Many studies have shown that in normal pregnancy there is an increase in almost all of the components of the RAS. In derangements of pregnancy this delicate equilibrium can become unbalanced. Preeclampsia is one such case. It is a disorder of pregnancy characterized by hypertension, proteinuria and placental abnormalities associated with shallow trophoblast invasion and impaired spiral artery remodeling. Despite being a leading cause of maternal death and a major contributor to maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of preeclampsia are poorly understood. Immunological mechanisms and the RAS have been long considered to be involved in the development of preeclampsia. Numerous recent studies demonstrate the presence of the angiotensin II type I receptor agonistic autoantibody (AT1-AA). This autoantibody can induce many key features of the disorder and upregulate molecules involved in the pathogenesis of preeclampsia. Here we review the functional role of the RAS during pregnancy and the impact of AT1-AA on preeclampsia.

Cu/Zn superoxide dismutase mutants associated with amyotrophic lateral sclerosis show enhanced formation of aggregates in vitro

Mutations in Cu/Zn superoxide dismutase (SOD) are associated with the fatal neurodegenerative disorder amyotrophic lateral sclerosis (ALS). There is considerable evidence that mutant SOD has a gain of toxic function; however, the mechanism of this toxicity is not known. We report here that purified SOD forms aggregates in vitro under destabilizing solution conditions by a process involving a transition from small amorphous species to fibrils. The assembly process and the tinctorial and structural properties of the in vitro aggregates resemble those for aggregates observed in vivo. Furthermore, the familial ALS SOD mutations A4V, G93A, G93R, and E100G decrease protein stability, which correlates with an increase in the propensity of the mutants to form aggregates. These mutations also increase the rate of protein unfolding. Our results suggest three possible mechanisms for the increase in aggregation: (i) an increase in the equilibrium population of unfolded or of partially unfolded states, (ii) an increase in the rate of unfolding, and (iii) a decrease in the rate of folding. Our data support the hypothesis that the gain of toxic function for many different familial ALS-associated mutant SODs is a consequence of protein destabilization, which leads to an increase in the formation of cytotoxic protein aggregates.