Abstract P533: Distinct Molecular Compositions of Circulating Microparticles in Hypertension and Diabetes

Background: Microparticles (MPs) are emerging as novel markers and mediators of vascular pathology. The purpose of this study was to examine the effect of hypertension and diabetes on the molecular composition of circulating MPs. Methods: We studied circulating MPs isolated from transgenic mice expressing active human renin in the liver (TtRhRen, a model of hypertension), OVE26 type 1 diabetic mice, and their wild-type (WT) littermates. At 20 weeks of age mice were sacrificed and blood samples were obtained by cardiac puncture. MPs were subsequently isolated from platelet-free plasma via differential centrifugation and protein content was assessed via mass spectrometry (MS). Results: TtRhRen mice exhibited increased blood pressure compared with OVE26 mice or their WT littermates. (144.2±7.6 vs 123.5±4.9 [OVE26] vs. 114.6±5.7 mmHg [WT], p<0.05). MS identified 300 independent proteins with at least 2 peptides per protein. Of these, 167 were found in all groups studied, 27 were exclusive to WT mice, 4 were exclusive to TtRhRen mice and 46 were exclusive to OVE26 mice. In addition, 16 proteins were found in MPs from WT and OVE26 mice but absent from TtRhRen mice while 40 were found in MPs from TtRhRen and OVE26 mice but absent in MPs from WT mice. Interestingly, proteins exclusive to MPs derived from hypertensive TtRhRen mice included two proteins previously implicated in the pathogenesis of hypertension: insulin-like growth factor-binding protein 5 and haptoglobin. Conclusions: Taken together our results suggest that circulating MPs display a distinct molecular composition, reflective of pathogenic state. Further examination of these changes may lead to the identification of novel biomarkers of vascular injury in hypertension and diabetes.

Evidence for intraventricular secretion of angiotensinogen and angiotensin by the subfornical organ using transgenic mice

Direct intracerebroventricular injection of angiotensin II (ANG II) causes increases in blood pressure and salt and water intake, presumably mimicking an effect mediated by an endogenous mechanism. The subfornical organ (SFO) is a potential source of cerebrospinal fluid (CSF), ANG I, and ANG II, and thus we hypothesized that the SFO has a secretory function. Endogenous levels of angiotensinogen (AGT) and renin are very low in the brain. We therefore examined the immunohistochemical localization of angiotensin peptides and AGT in the SFO, and AGT in the CSF in two transgenic models that overexpress either human AGT (A+ mice), or both human AGT (hAGT) and human renin (SRA mice) in the brain. Measurements were made at baseline and following volumetric depletion of CSF. Ultrastructural analysis with immunoelectron microscopy revealed that superficially located ANG I/ANG II and AGT immunoreactive cells in the SFO were vacuolated and opened directly into the ventricle. Withdrawal of CSF produced an increase in AGT in the CSF that was accompanied by a large decline in AGT immunoreactivity within SFO cells. Our data provide support for the hypothesis that the SFO is a secretory organ that releases AGT and possibly ANG I/ANG II into the ventricle at least under conditions when genes that control the renin-angiotensin system are overexpressed in mice.