Calcineurin Controls Hypothalamic NMDA Receptor Activity and Sympathetic Outflow

Abstract

Rationale: Hypertension is a common and serious adverse effect of calcineurin inhibitors, including cyclosporine and tacrolimus (FK506). Although increased sympathetic nerve discharges are associated with calcineurin inhibitor–induced hypertension, the sources of excess sympathetic outflow and underlying mechanisms remain elusive. Calcineurin (protein phosphatase-2B) is broadly expressed in the brain, including the paraventricular nuclear (PVN) of the hypothalamus, which is critically involved in regulating sympathetic vasomotor tone. Objective: We determined whether prolonged treatment with the calcineurin inhibitor causes elevated sympathetic output and persistent hypertension by potentiating synaptic N-methyl-D-aspartate (NMDA) receptor activity in the PVN. Methods and Results: Telemetry recordings showed that systemic administration of FK506 (3 mg/kg per day) for 14 days caused a gradual and profound increase in arterial blood pressure in rats, which lasted at least 7 days after discontinuing FK506 treatment. Correspondingly, systemic treatment with FK506 markedly reduced calcineurin activity in the PVN and circumventricular organs, but not rostral ventrolateral medulla, and increased the phosphorylation level and synaptic trafficking of NMDA receptors in the PVN. Immunocytochemistry labeling showed that calcineurin was expressed in presympathetic neurons in the PVN. Whole-cell patch-clamp recordings in brain slices revealed that treatment with FK506 increased baseline firing activity of PVN presympathetic neurons; this increase was blocked by the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist. Also, treatment with FK506 markedly increased presynaptic and postsynaptic NMDA receptor activity of PVN presympathetic neurons. Furthermore, microinjection of the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist into the PVN of anesthetized rats preferentially attenuated renal sympathetic nerve discharges and blood pressure elevated by FK506 treatment. In addition, systemic administration of memantine, a clinically used NMDA receptor antagonist, effectively attenuated FK506 treatment–induced hypertension in conscious rats. Conclusions: Our findings reveal that normal calcineurin activity in the PVN constitutively restricts sympathetic vasomotor tone via suppressing NMDA receptor activity, which may be targeted for treating calcineurin inhibitor–induced hypertension.

Brain α2δ-1–Bound NMDA Receptors Drive Calcineurin Inhibitor–Induced Hypertension

“…Calcineurin Inhibition Promotes the α2δ-1-NMDAR Interaction and Synaptic Trafficking of α2δ-1-Bound NMDARs in the PVN Systemic treatment with the calcineurin inhibitor FK506 diminishes calcineurin activity in the forebrain and increases NMDAR phosphorylation in the PVN. 5 is a phospho-binding protein and preferentially interacts with phosphorylated NMDARs independently of VGCCs in the cell line and spinal cord. 26 We first determined whether calcineurin inhibition affects the synaptic protein levels of α2δ-1 and NMDARs in the PVN.…”

“…17,20,21 Systemic treatment with FK506 diminishes calcineurin activity in the PVN, which augments phosphorylation and activity of synaptic NMDARs in the PVN, leading to increased glutamatergic excitatory synaptic input and firing activity of presympathetic neurons and sympathetic outflow. 5 Correspondingly, NMDAR antagonists are effective in reducing CIH in the animal model. 5 However, it is unclear how synaptic NMDAR activity in the PVN is augmented in CIH.…”

“…5 Correspondingly, NMDAR antagonists are effective in reducing CIH in the animal model. 5 However, it is unclear how synaptic NMDAR activity in the PVN is augmented in CIH. Furthermore, NMDARs in the central nervous system are involved in many physiological functions, including learning and memory.…”

“…25 For induction of CIH, FK506 was injected intraperitoneally at a dose of 3 mg/kg once daily for 14 consecutive days in rats and mice. 5 Final experiments were conducted 5 to 7 days after the last FK506 injection. Animals received the same amount of dimethyl sulfoxide as the vehicle group.…”

Calcineurin Controls Hypothalamic NMDA Receptor Activity and Sympathetic Outflow

“…In light of the previous literature showing that CNI causes increase in arterial pressure acutely, Zhou et al 16 in this issue of Circulation Research postulated that prolonged treatment with CNIs causes an increase in sympatho-excitation and hypertension by potentiating synaptic NMDA receptor activity, specifically within the PVN. They observed a gradual and significant increase in arterial pressure following systemic administration of CNIs for 2 weeks, which lasted even after treatment was terminated.…”