Mechanisms underlying prorenin actions on hypothalamic neurons implicated in cardiometabolic control

Abstract

BackgroundHypertension and obesity are highly interrelated diseases, being critical components of the metabolic syndrome. Despite the growing prevalence of this syndrome in the world population, efficient therapies are still missing. Thus, identification of novel targets and therapies are warranted. An enhanced activity of the hypothalamic renin-angiotensin system (RAS), including the recently discovered prorenin (PR) and its receptor (PRR), has been implicated as a common mechanism underlying aberrant sympatho-humoral activation that contributes to both metabolic and cardiovascular dysregulation in the metabolic syndrome. Still, the identification of precise neuronal targets, cellular mechanisms and signaling pathways underlying PR/PRR actions in cardiovascular- and metabolic related hypothalamic nuclei remain unknown.Methods and resultsUsing a multidisciplinary approach including patch-clamp electrophysiology, live calcium imaging and immunohistochemistry, we aimed to elucidate cellular mechanisms underlying PR/PRR actions within the hypothalamic supraoptic (SON) and paraventricular nucleus (PVN), key brain areas previously involved in cardiometabolic regulation. We show for the first time that PRR is expressed in magnocellular neurosecretory cells (MNCs), and to a lesser extent, in presympathetic PVN neurons (PVNPS). Moreover, we show that while PRR activation efficiently stimulates the firing activity of both MNCs and PVNPS neurons, these effects involved AngII-independent and AngII-dependent mechanisms, respectively. In both cases however, PR excitatory effects involved an increase in intracellular Ca2+ levels and a Ca2+-dependent inhibition of a voltage-gated K+ current.ConclusionsWe identified novel neuronal targets and cellular mechanisms underlying PR/PRR actions in critical hypothalamic neurons involved in cardiometabolic regulation. This fundamental mechanistic information regarding central PR/PRR actions is essential for the development of novel RAS-based therapeutic targets for the treatment of cardiometabolic disorders in obesity and hypertension.

A-type K+ channels contribute to the prorenin increase of firing activity in hypothalamic vasopressin neurosecretory neurons

“…In a recent study, we showed that PRR is highly expressed in VP neurons and that their activation by PR evoked membrane depolarization and increased firing discharge. These effects were ANG II-independent and involved an increase in intracellular Ca 2ϩ levels and a Ca 2ϩ -dependent inhibition of a voltage-gated K ϩ current (34). Thus, our previous studies support that intracellular signaling cascades triggered by PR/PRR, rather than ANG II-AT 1 R indirect effects, mediate PR actions on VP neurons and VP release.…”

“…In a recent study, we showed that PR stimulates the firing discharge of hypothalamic VP and presympathetic neurons through distinct ANG II-independent and -dependent mechanisms, respectively (34). PR effects on both cell types, however, involved binding of PR to PRR and the inhibition of a voltage-gated K ϩ channel in a Ca 2ϩ -dependent manner.…”

“…Prorenin inhibition of I A increases neuronal firing activity and affects AP properties. We previously reported that focal application of PR stimulates firing activity of VP neurons (34). On the basis of our current results showing that PR inhibits I A , we repeated current-clamp experiments in the presence of the K ϩ channel blocker 4-AP to determine the contribution of I A to this effect.…”

“…Recordings were obtained from neurons in the SON (15 eGFP and 26 non-eGFP) and the lateral magnocellular subdivision of the PVN (16 eGFP and 2 non-eGFP). Since in our previous study (34) we reported that PR evoked a similar response involving the same mechanism in both eGFP and non-eGFP magnocellular neurosecretory cells from the SON and PVN, data were pooled together for analysis. The voltage output was digitized at 16-bit resolution and 10 kHz and was filtered at 2 kHz (Digidata 1440A, Axon Instruments).…”

“…On the basis of our current results showing that PR inhibits I A , we repeated current-clamp experiments in the presence of the K ϩ channel blocker 4-AP to determine the contribution of I A to this effect. Given our previous results showing a very slow or lack of recovery after a single PR application (34), experiments were performed in separate neurons preincubated in either control aCSF or 5 mM 4-AP, a concentration known to more specifically inhibit I A over other voltage-gated K ϩ currents (46). As shown in Fig.…”