Abstract 249: High Salt and Aldosterone Increase (pro)renin Receptor Expression Through Enac α Activation in Neuronal Cells

Abstract

Activation of the brain renin-angiotensin-aldosterone system plays an essential role in hyperactivity of the sympathetic nervous system during salt sensitive hypertension. We previously reported an up-regulation of (pro)renin receptor (PRR) expression levels in DOCA-salt hypertensive mice brain. However, the mechanism by which PRR is regulated in DOCA-salt hypertension remains unknown. We hypothesize that aldosterone increases PRR expression by activation of epithelial sodium channel (ENaC). To test this hypothesis, we used neuro-2A cell line from brain hypothalamus which expresses all ENaC α, β, and γ subunits, as well as mineralocorticoid receptor (MR). Cells were incubated in normal salt (NS, 142 mM) or high salt (HS, 160 mM) culture medium for 1, 3, or 5 days, with or without the addition of aldosterone (1μM) for 2 hours. Interestingly, the combination of HS (5 days) with aldosterone significantly increased PRR mRNA levels (fold change) (3.28 ± 0.11) compared to NS (1.00 ± 0.01), HS (1.23 ± 0.01), or aldosterone (1.40 ± 0.01) alone in Neuro-2A cells. The PRR expression levels (1.253 ± 0.006; 1.89 ± 0.002) were significantly attenuated by ENaC inhibition (amiloride, 10μM) or MR inhibition (eplernone, 10μM) respectively (P<0.05), suggesting that ENaC and MR activation mediates the up-regulation of PRR expression in neuronal cells. Furthermore, HS increased ENaC α (2.42 ± 0.01), while decreased ENaC β (0.05 ± 0.01), and ENaC γ (0.03 ± 0.01) mRNA expression levels compared to NS treatment (1.00 ±0.01) in Neuro-2A cells suggesting an increase in synthesis rate of α subunit following HS treatment. In summary, HS and aldosterone increase PRR expression levels via activation of ENaC. ENaC α may be the regulating subunit in the assembly of functional ENaC in neuronal cells. We conclude that regulation of PRR expression by high salt and aldosterone may be the critical step to activate angiotensinergic sympatho-excitatory pathways leading to salt sensitive hypertension.