In salt-sensitive hypertension, the accumulation of Na(+) in tissue has been presumed to be accompanied by a commensurate retention of water to maintain the isotonicity of body fluids. We show here that a high-salt diet (HSD) in rats leads to interstitial hypertonic Na(+) accumulation in skin, resulting in increased density and hyperplasia of the lymphcapillary network. The mechanisms underlying these effects on lymphatics involve activation of tonicity-responsive enhancer binding protein (TonEBP) in mononuclear phagocyte system (MPS) cells infiltrating the interstitium of the skin. TonEBP binds the promoter of the gene encoding vascular endothelial growth factor-C (VEGF-C, encoded by Vegfc) and causes VEGF-C secretion by macrophages. MPS cell depletion or VEGF-C trapping by soluble VEGF receptor-3 blocks VEGF-C signaling, augments interstitial hypertonic volume retention, decreases endothelial nitric oxide synthase expression and elevates blood pressure in response to HSD. Our data show that TonEBP-VEGF-C signaling in MPS cells is a major determinant of extracellular volume and blood pressure homeostasis and identify VEGFC as an osmosensitive, hypertonicity-driven gene intimately involved in salt-induced hypertension.

BackgroundAgonistic autoantibodies directed at the α1-adrenergic receptor (α1-AAB) have been described in patients with hypertension. We implied earlier that α1-AAB might have a mechanistic role and could represent a therapeutic target.Methodology/Principal FindingsTo pursue the issue, we performed clinical and basic studies. We observed that 41 of 81 patients with refractory hypertension had α1-AAB; after immunoadsorption blood pressure was significantly reduced in these patients. Rabbits were immunized to generate α1-adrenergic receptor antibodies (α1-AB). Patient α1-AAB and rabbit α1-AB were purified using affinity chromatography and characterized both by epitope mapping and surface plasmon resonance measurements. Neonatal rat cardiomyocytes, rat vascular smooth muscle cells (VSMC), and Chinese hamster ovary cells transfected with the human α1A-adrenergic receptor were incubated with patient α1-AAB and rabbit α1-AB and the activation of signal transduction pathways was investigated by Western blot, confocal laser scanning microscopy, and gene expression. We found that phospholipase A2 group IIA (PLA2-IIA) and L-type calcium channel (Cacna1c) genes were upregulated in cardiomyocytes and VSMC after stimulation with both purified antibodies. We showed that patient α1-AAB and rabbit α1-AB result in protein kinase C alpha activation and transient extracellular-related kinase (EKR1/2) phosphorylation. Finally, we showed that the antibodies exert acute effects on intracellular Ca2+ in cardiomyocytes and induce mesentery artery segment contraction.Conclusions/SignificancePatient α1-AAB and rabbit α1-AB can induce signaling pathways important for hypertension and cardiac remodeling. Our data provide evidence for a potential clinical relevance for α1-AAB in hypertensive patients, and the notion of immunity as a possible cause of hypertension.

Hypertension is one of the major health care problems worldwide since it markedly increases the risk for development of heart disease, stroke, generalized vascular disease, and renal failure. The renin-angiotensin system (RAS) with its major end-product angiotensin II (Ang II) plays a fundamental role in blood pressure regulation through direct and indirect mechanisms. Pharmacologically, we can inhibit the RAS using angiotensin-converting enzyme inhibitors and AT1 receptor blocker. Inhibiting renin directly with a clinically useful drug eluded pharmacologists until recently. However, the once-daily, orally effective, small-molecule, direct renin inhibitor aliskiren has recently changed this state of affairs. Aliskiren, with its 40-h half-life and ideal pharmacokinetics, can now address angiotensin production directly at its rate-limiting step. A novel transgenic rat model outfitted with the human renin and angiotensinogen genes allowed the testing of aliskiren in an animal model. Preclinical data demonstrated that aliskiren prolonged survival, decreased cardiac hypertrophy and the inducibility of arrhythmias, proteinuria, and attenuated inflammation. All these features might result in improved target-organ damage. Studies in humans attest to an effective blood pressure-lowering action, a largely side effect-free profile, and the option of several combination therapies. Aliskiren is the first of a novel antihypertensive drug class. The preclinical data is very promising. Nevertheless, for the evaluation of its potency in humans, we have to wait for more clinical data.

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