Inhibition of Brain Mitogen-Activated Protein Kinase Signaling Reduces Central Endoplasmic Reticulum Stress and Inflammation and Sympathetic Nerve Activity in Heart Failure Rats

Abstract

Mitogen-activated protein kinase (MAPK) signaling and endoplasmic reticulum (ER) stress in the brain have been implicated in the pathophysiology of hypertension. This study determined whether ER stress occurs in subfornical organ and hypothalamic paraventricular nucleus in heart failure (HF) and how MAPK signaling interacts with ER stress and other inflammatory mediators. HF rats had significantly higher levels of the ER stress biomarkers (glucose-regulated protein 78, activating transcription factor 6, activating transcription factor 4, X-box binding protein 1, P58(IPK), and C/EBP homologous protein) in subfornical organ and paraventricular nucleus, which were attenuated by a 4-week intracerebroventricular infusion of inhibitors selective for p44/42 MAPK (PD98059), p38 MAPK (SB203580), or c-Jun N-terminal kinase (SP600125). HF rats also had higher mRNA levels of tumor necrosis factor-α, interleukin-1β, cyclooxygenase-2, and nuclear factor-κB p65, and a lower mRNA level of IκB-α, in subfornical organ and paraventricular nucleus, compared with SHAM rats, and these indicators of increased inflammation were attenuated in the HF rats treated with the MAPK inhibitors. Plasma norepinephrine level was higher in HF rats than in SHAM rats but was reduced in the HF rats treated with PD98059 and SB203580. A 4-week intracerebroventricular infusion of PD98059 also improved some hemodynamic and anatomic indicators of left ventricular function in HF rats. These data demonstrate that ER stress increases in the subfornical organ and paraventricular nucleus of rats with ischemia-induced HF and that inhibition of brain MAPK signaling reduces brain ER stress and inflammation and decreases sympathetic excitation in HF. An interaction between MAPK signaling and ER stress in cardiovascular regions of the brain may contribute to the development of HF.

Keywords: brain; endoplasmic reticulum stress; heart failure; hypothalamic paraventricular nucleus; subfornical organ; sympathetic nerve activity.

Figure 1

Quantitative analysis by real-time PCR showing the mRNA expression of ER stress biomarkers GRP78, ATF6, P58^IPK and CHOP in subfornical organ (SFO), hypothalamic paraventricular nucleus (PVN) and cerebral cortex in heart failure (HF) rats treated ICV for 4 weeks with the p44/42 MAPK inhibitor PD98059 (HF+PD), the p38 MAPK inhibitor SB203580 HF+SB), the JNK inhibitor SP600125 (HF+SP) or vehicle (VEH, HF+VEH) and VEH-treated SHAM (SHAM+VEH) rats. Values are mean ± SEM (n=6 for each group) and expressed as a fold change relative to SHAM+VEH control. * p<0.05, vs SHAM+VEH; † p< 0.05, HF+PD, HF+SB, and HF+SP vs HF+VEH.

Figure 2

Quantitative analysis by real-time PCR showing the mRNA expression of the inflammatory mediators TNF-α, IL-1β, COX-1, COX-2, NF-kB p65 and IkB-α in subfornical organ (SFO), hypothalamic paraventricular nucleus (PVN) and cerebral cortex in heart failure (HF) rats treated ICV for 4 weeks with the p44/42 MAPK inhibitor PD98059 (HF+PD), the p38 MAPK inhibitor SB203580 (HF+SB), the JNK inhibitor SP600125 (HF+SP) or VEH (HF+VEH) and VEH-treated SHAM rats (SHAM+VEH). Values are mean ± SEM (n=6 for each group) and expressed as a fold change relative to SHAM+VEH control. * p<0.05, vs SHAM+VEH; † p< 0.05, HF+PD, HF+SB, and HF+SP vs HF+VEH.

Figure 3

Plasma NE level in VEH-treated SHAM (SHAM+VEH) rats and heart failure (HF) rats treated ICV for 4 weeks with the p44/42 MAPK inhibitor PD98059 (HF+PD), the p38 MAPK inhibitor SB203580 (HF+SB), the JNK inhibitor SP600125 (HF+SP) or VEH. Values are expressed as means ± SEM. * p<0.05, vs SHAM+VEH; † p<0.05, HF+PD, HF+SB, and HF+SP vs HF+VEH.

Figure 4

Western blot analysis showing the expression of ER stress biomarkers GRP78, XBP-1 and ATF4 in subfornical organ (SFO) and hypothalamic paraventricular nucleus (PVN) in VEH-treated SHAM (SHAM+VEH) rats and heart failure (HF) rats treated for 4 weeks with ICV p44/42 MAPK inhibitor PD98059 (HF+PD) or VEH (HF+VEH). Values are expressed as means ± SEM and normalized to β-actin (n=6 in each group). * p<0.05, vs SHAM+VEH; † p< 0.05, HF+PD vs HF+VEH. Representative Western bands are shown above the bar group.

Figure 5

Laser confocal images showing the immunofluorescent staining of ER stress biomarkers GRP78, XBP-1 and ATF4 in subfornical organ (SFO) and hypothalamic paraventricular nucleus (PVN) in VEH-treated heart failure (HF+VEH) rats and HF rats treated ICV for 4 weeks with the p44/42 MAPK inhibitor PD98059 (HF+PD).

Figure 6

Echocardiographic, hemodynamic and anatomical measurements in VEH-treated SHAM (SHAM+VEH) rats and heart failure (HF) rats treated ICV for 4 weeks with the p44/42 MAPK inhibitor PD98059 (HF+PD) or VEH (HF+VEH). Values are expressed as means ± SEM. * p<0.05, vs SHAM+VEH; † p<0.05, HF+PD vs HF+VEH, # p<0.05, 24 hrs vs 4 wks. LVEF: left ventricular (LV) ejection fraction; BW: body weight; RV: right ventricular weight; HW: heart weight; LW: Lung weight; LVEDP: LV end-diastolic pressure; LV dP/dt max: maximum rate of rise of LV pressure; LV vol/mass: the ratio of LV volume to LV myocardial mass.