Silencing Epidermal Growth Factor Receptor in Hypothalamic Paraventricular Nucleus Reduces Extracellular Signal-regulated Kinase 1 and 2 Signaling and Sympathetic Excitation in Heart Failure Rats

Activation AMPK in Hypothalamic Paraventricular Nucleus Improves Renovascular Hypertension Through ERK1/2-NF-κB Pathway

Hypertension is a globally prevalent disease, but the pathogenesis remains largely unclear. AMP-activated protein kinase (AMPK) is a nutrition-sensitive signal of cellular energy metabolism, which has a certain influence on the development of hypertension. Previously, we found a down-regulation of the phosphorylated (p-) form of AMPK, and the up-regulation of the angiotensin II type 1 receptor (AT1-R) and that of p-ERK1/2 in the hypothalamic paraventricular nucleus (PVN) of hypertensive rats. However, the exact mechanism underlying the relationship between AMPK and AT1-R in the PVN during hypertension remains unclear. Thus, we hypothesized that AMPK modulates AT1-R through the ERK1/2-NF-κB pathway in the PVN, thereby inhibiting sympathetic nerve activity and improving hypertension. To examine this hypothesis, we employed a renovascular hypertensive animal model developed via two-kidney, one-clip (2K1C) and sham-operated (SHAM). Artificial cerebrospinal fluid (aCSF), used as vehicle, or 5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide (AICAR, an AMPK activator, 60 μg/day) was microinjected bilaterally in the PVN of these rats for 4 weeks. In 2K1C rats, there an increase in systolic blood pressure (SBP) and circulating norepinephrine (NE). Also, the hypertensive rats had lowered expression of p-AMPK and p-AMPK/AMPK, elevated expression of p-ERK1/2, p-ERK1/2/ERK1/2 and AT1-R, increased NF-κB p65 activity in the PVN compared with the levels of these biomarkers in SHAM rats. Four weeks of bilateral PVN injection of AMPK activator AICAR, attenuated the NE level and SBP, increased the expression of p-AMPK and p-AMPK/AMPK, lessened the NF-κB p65 activity, decreased the expression of p-ERK1/2, p-ERK1/2/ERK1/2 and AT1-R in the PVN of 2K1C rats. Data from this study imply that the activation of AMPK within the PVN suppressed AT1-R expression through inhibiting the ERK1/2-NF-κB pathway, decreased the activity of the sympathetic nervous system, improved hypertension.

Angiotensin II inhibits the A-type K+ current of hypothalamic paraventricular nucleus neurons in rats with heart failure: role of MAPK-ERK1/2 signaling

Angiotensin II (ANG II)-mediated sympathohumoral activation constitutes a pathophysiological mechanism in heart failure (HF). Although the hypothalamic paraventricular nucleus (PVN) is a major site mediating ANG II effects in HF, the precise mechanisms by which ANG II influences sympathohumoral outflow from the PVN remain unknown. ANG II activates the ubiquitous intracellular MAPK signaling cascades, and recent studies revealed a key role for ERK1/2 MAPK signaling in ANG II-mediated sympathoexcitation in HF rats. Importantly, ERK1/2 was reported to inhibit the transient outward potassium current (IA) in hippocampal neurons. Given that IA is a critical determinant of the PVN neuronal excitability, and that downregulation of IA in the brain has been reported in cardiovascular disease states, including HF, we investigated here whether ANG II modulates IA in PVN neurons via the MAPK-ERK pathway, and, whether these effects are altered in HF rats. Patch-clamp recordings from identified magnocellular neurosecretory neurons (MNNs) and presympathetic (PS) PVN neurons revealed that ANG II inhibited IA in both PVN neuronal types, both in sham and HF rats. Importantly, ANG II effects were blocked by inhibiting MAPK-ERK signaling as well as by inhibiting epidermal growth factor receptor (EGFR), a gateway to MAPK-ERK signaling. Although no differences in basal IA magnitude were found between sham and HF rats under normal conditions, MAPK-ERK blockade resulted in significantly larger IA in both PVN neuronal types in HF rats. Taken together, our studies show that ANG II-induced ERK1/2 activity inhibits IA, an effect expected to increase the excitability of presympathetic and neuroendocrine PVN neurons, contributing in turn to the neurohumoral overactivity that promotes progression of the HF syndrome.

Transforming Growth Factor-α Acts in Hypothalamic Paraventricular Nucleus to Upregulate ERK1/2 Signaling and Expression of Sympathoexcitatory Mediators in Heart Failure Rats

Activation of epidermal growth factor receptor (EGFR) tyrosine kinase is associated with increased extracellular signal-regulated kinase (ERK) 1/2 signaling in the hypothalamic paraventricular nucleus (PVN), which contributes to the sympathetic excitation in heart failure (HF). Transforming growth factor (TGF)-α is a major endogenous ligand for EGFR. The present study sought to determine whether TGF-α increases in the PVN in HF and promotes the activation of EGFR to increase ERK1/2 activity. Male rats received bilateral PVN microinjections of an EGFR siRNA or a scrambled siRNA followed by an intracerebroventricular (ICV) injection of TGF-α or vehicle one week later. In rats pretreated with the scrambled siRNA, ICV TGF-α increased phosphorylated (p-) EGFR and upregulated the expression of p-ERK1/2 and mRNA levels of proinflammatory cytokines (PICs) and renin-angiotensin system (RAS) components in the PVN, when compared with the untreated age-matched control rats. These responses to ICV TGF-α were significantly attenuated in rats pretreated with the EGFR siRNA. Furthermore, bilateral PVN microinjection of a TGF-α siRNA in HF rats significantly decreased the elevated levels of TGF-α, p-EGFR, p-ERK1/2 and the mRNA expression of PICs and RAS components in the PVN, compared with the HF rats treated with a scrambled siRNA. The TGF-α siRNA-treated HF rats also exhibited lower plasma norepinephrine levels and improved peripheral manifestations of HF. These data suggest that TGF-α expression is upregulated in the PVN in HF and induces the activation of EGFR-mediated ERK1/2 signaling to augment the inflammation and RAS activity that drives sympathetic excitation in HF.

The Role of Epidermal Growth Factor Receptor Family of Receptor Tyrosine Kinases in Mediating Diabetes-Induced Cardiovascular Complications

Diabetes mellitus is a major debilitating disease whose global incidence is progressively increasing with currently over 463 million adult sufferers and this figure will likely reach over 700 million by the year 2045. It is the complications of diabetes such as cardiovascular, renal, neuronal and ocular dysfunction that lead to increased patient morbidity and mortality. Of these, cardiovascular complications that can result in stroke and cardiomyopathies are 2- to 5-fold more likely in diabetes but the underlying mechanisms involved in their development are not fully understood. Emerging research suggests that members of the Epidermal Growth Factor Receptor (EGFR/ErbB/HER) family of tyrosine kinases can have a dual role in that they are beneficially required for normal development and physiological functioning of the cardiovascular system (CVS) as well as in salvage pathways following acute cardiac ischemia/reperfusion injury but their chronic dysregulation may also be intricately involved in mediating diabetes-induced cardiovascular pathologies. Here we review the evidence for EGFR/ErbB/HER receptors in mediating these dual roles in the CVS and also discuss their potential interplay with the Renin-Angiotensin-Aldosterone System heptapeptide, Angiotensin-(1-7), as well the arachidonic acid metabolite, 20-HETE (20-hydroxy-5, 8, 11, 14-eicosatetraenoic acid). A greater understanding of the multi-faceted roles of EGFR/ErbB/HER family of tyrosine kinases and their interplay with other key modulators of cardiovascular function could facilitate the development of novel therapeutic strategies for treating diabetes-induced cardiovascular complications.