Hypertension (HTN) is the single most prevalent risk factor for cardiovascular disease, diabetes, obesity, and metabolic syndrome. Despite advances in lifestyle modification and multi-drug based therapies, 20-30% of all hypertensive patients remain resistant with uncontrolled high blood pressure. These patients exhibit autonomic dysregulation due to elevated sympathetic activity and norepinephrine (NE) spillover, and low parasympathetic activity, indicating that their HTN is of "neurogenic origin". Thus, we believe that a mechanism-based breakthrough is imperative to develop novel strategies to prevent and perhaps even cure neurogenic hypertension. Our evidence of a dysfunctional neural-bone marrow (BM) communication in neurogenic hypertension represents this breakthrough. Based on our published and preliminary data and evidence from the literature, we propose the following hypothesis: hypertensive signals such as increased angiotensin II are recognized by the hypothalamic paraventricular nucleus (PVN), resulting in activation of resident microglia, an increase in activity of pre-autonomic neurons, and enhancement of sympathetic drive to the BM. This autonomic imbalance to the BM leads to an increase in inflammatory cells that mobilize to the brain, differentiate into activated microglia, and perpetuate the hypertensive state.
Four specific aims are proposed to support/refute the "brain-BM axis" hypothesis and provide "conceptual support" for its translation into a formal clinical trial:
Aim 1 investigates the hypothesis that Ang II-induced increases in microglial activation in the PVN, mediated by the CCL2/CCR2 chemokine system, are key early events in enhancing SNA in HTN.
Aim 2 investigates the hypothesis that sympathetic nerve activity to the BM is increased in Ang II-induced HTN.
Aim 3 evaluates the hypothesis that extravasation of BM inflammatory progenitor cells to the PVN contributes to overall increase in activated microglia in HTN.
Aim 4 investigates the hypothesis that minocycline treatment would produce antihypertensive effects in drug-resistant hypertensive patients by decreasing cerebral microglia activity. These studies will utilize state-of-the-art integrative physiological genomic techniques including chronic brain and bone marrow cell/tissue specific gene modification, imaging in animals and humans, electrophysiological recordings of sympathetic fibers to the BM and pre-autonomic neurons, to support our novel hypothesis. Thus, outcomes of this investigation will be valuable for paradigm changing approaches for the treatment of resistant neurogenic hypertension.

Public Health Relevance

Hypertension (HTN) is the single biggest risk factor for cardiovascular disease, diabetes, obesity, and metabolic syndrome, and despite changes in lifestyle and the availability of multi-drug based therapies, 20- 30% of hypertensive patients stil have uncontrolled or neurogenic high blood pressure characterized by sustained activation of the sympathetic nerves that ultimately tell blood vessels to constrict and raise blood pressure. In this project we first aim to understand why the sympathetic nerves become permanently overactive, and our studies are focusing on the role of the brain and peripheral immune system in causing this overactivity. We will further determine whether administration of a drug that inhibits the activity of these immune cells will lower blood pressure in patients with uncontrolled neurogenic hypertension, and so we believe that this work will have an immediate impact in developing innovative strategies for the treatment of currently uncontrollable resistant hypertension.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Hypertension and Microcirculation Study Section (HM)
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Maric-Bilkan, Christine
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University of Florida
Schools of Medicine
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