Effects Of Exercise On Cardiac Sympathetic Nerve Remodeling And Paraventricular Nucleus Oxidative Stress In Rats With Myocardial Infarction And Its Relationship

Myocardial infarction (MI) is one of the most fateful diseases. Cardiac sympathetic nerve sprouting and the dysregulation of β-adrenergic receptor (β-AR) play a critical role in the deterioration of cardiac function after myocardial infarction (MI). And MI is characterized by central nervous system-driven sympathoexcitation and deteriorating cardiac function. The paraventricular nucleus (PVN) of the hypothalamus is a key regulator of sympathetic nerve activity and is implicated in MI. Redox signaling in the PVN and other central nervous system sites is a primary mechanism of neuro-cardiovascular regulation, New researches indicate that targeted inhibition of oxidant signaling in the PVN could provide a novel treatment for MI. Growing evidence indicates that exercise provides protection against MI. The aims of this study were to investigate whether exercise following MI could inhibit sympathetic nerve sprouting, restore the balance of β-AR, and reduce oxidative stress in the paraventricular nucleus after MI. This study wants to provide the evidence for protective effects of exercise training on cardiac function and cardiac rehabilitation in MI rats.Objective:The aims of this study were to investigate whether exercise following MI could inhibit sympathetic nerve sprouting, restore the balance of β-AR, and reduce oxidative stress in the paraventricular nucleus after MI. And study the protective effect of exercise training on myocardial infarction by oxidative stress reduction in the paraventricular nucleus.Methods:45 male Sprague-Dawley rats were randomly assigned to three groups in chapter 1:sham group (S), myocardial infarction group (MI), moderate-intensity exercise training with myocardial infarction group (ME). Rats were randomly assigned to five groups in chapter 2:sham group (S), myocardial infarction group (MI), exercise training with myocardial infarction group (ME), MI rats for continuous ICV infusion of Artificial cerebrospinal fluid (ACSF)(MI+A), MI rats for continuous ICV infusion of Tempol (MI+T). Rats were randomly assigned to five groups in chapter 3:Sham rats for continuous ICV infusion of artificial cerebrospinal fluid (ACSF) (S+A), MI rats for continuous ICV infusion of ACSF (MI+A), MI rats for continuous ICV infusion of Tempol (MI+T), myocardial infarction group (MI), exercise training training with myocardial infarction group (ME).ME group rats started exercising at 1 week post-MI using a motorized rodent treadmill. During this training period, rats were exercised 10 min/day at an initial treadmill speed of 10 m/min up a 0% grade. To ensure that a significant endurance ExT effect was produced, the treadmill grade and speed were gradually increased to 5-10% and 20-25 m/min, respectively, and the exercise duration was increased to 60 min/day. The exercise was performed 5 days per week for 4 weeks.MI+A group, MI+T group rats underwent intracerebroventricular (ICV) cannula surgery, at 1 week post-MI. An Alzet osmotic mini-pump was implanted subcutaneously in the back of the rats neck and attached to the cerebral ventricle cannula for chronic ICV infusion of the tempol (80μg/kg/h), a superoxide scavenger, or Artificial cerebrospinal fluid (ACSF,0.25μl/hr) for 4 weeks. After 4 weeks, the PVN and heart was taken for histologic section.After training, the following hemodynamic parameters were measured to detect cardiac function:LVSP, LVEDP, ±dp/dtmax.Then the heart was taken for histologic section and Masson and TTC dyeing. The sympathetic nerve marker-tyrosine hydroxylase (TH), the nerve sprouting marker-growth associated protein 43 (GAP-43) of the left ventricle were measured by immunohistochemistry. The expression of nerve growth factor (NGF), TrkA, p75NTR were measured by immunofluorescence. The protein expression of TH, GAP-43, NGF, TrkA, p75NTR was measured by Western blot. β2-AR in the left ventricle was examined by immunohistochemistry. The expression of β1-AR, p3-AR, NOS1, p-NOS1 were measured by immunofluorescence. The protein expression of β1-AR, β2-AR, β3-AR, Akt, p-Akt, NOS3, p-NOS3, NOS1 and p-NOS1 was measured by Western blot. The levels of cardiac NO, XOD were assessed by biochemical analysis.The levels of NE in plasma and the heart were quantified using ELISA kit.The levels of MDA, T-AOC and SOD in the PVN were assessed by biochemical analysis.while DHE staining was used to detect PVN superoxide anion (O2-)-The expression of NADPH oxidase subunits-Nox1, Nox2, Nox4 mRNA was measured by quantitative real-time PCR. The expression of Nox1, Nox4 in the PVN was measured by immunofluorescence. Immunohistochemical studies were performed to assess the PVN neuronal activation. The expression of SOD1, SOD2 in the PVN was measured by immunohistochemistry. The protein expression of Nox1, Nox2, Nox4, SOD1, SOD2 was measured by Western blot.Result:1 Exercise inhibits cardiac sympathetic nerve sprouting, restores β-AR balance, improves cardiac function after MI(1) Exercise training is effective in reducing infarct size, and attenuating the deterioration in cardiac function after MI.The result of TTC staining showed that the infarct area was significantly reduced in the ME group (P<0.05) compared with the MI group. In the MI group, the cardiac structure was disordered with extensive fibrotic tissue (blue staining) compared with the S group. After 4 weeks of exercise training, there was a trend towards reduction in cardiac fibrosis compared with the MI group. CVF, an indicator of interstitial fibrosis, was significantly higher in the MI group (P<0.01) than in the S group.exercise training(32.7±3.55%, ME group, P<0.01) significantly reduced CVF compared with the MI group. The changes of hemodynamic parameters following MI indicated a severe cardiac dysfunction, as evidenced by a significant increase in LVEDP and Tau (P<0.01, P<0.05), and a decrease in LVSP and ±dp/dtmax (both P<0.01) compared with the S group. However,4 weeks of aerobic exercise resulted in a significant reduction in LVEDP (P<0.01), and an increase in LVSP (P<0.01) compared with the MI group.(2) Exercise training inhibits cardiac sympathetic nerve sprouting after MI.The protein expression of TH, GAP-43 in the LV was significantly increased after MI (P<0.05, P<0.01), which was normalized by aerobic exercise (P<0.01). the protein expression of NGF and TrKA in the LV was significantly increased after MI (P<0.05), which was normalized by aerobic exercise (P<0.05).the protein expression of p75NTR in the LV was significantly reduced after MI (P<0.01), which was normalized by aerobic exercise (P<0.05).(3) Exercise Training restores cardiac P-adrenergic receptor balance after MI, increases 03-AR expression through the activation of NOS3 and NOS1 after MI.MI resulted in increased ratios of p2-AR/β1-AR and β3-AR/β1-AR (P<0.01 vs. S). Importantly, after 4 weeks of exercise, the protein expression of cardiac β1-AR and β3-AR was increased, while β2-AR expression did not change, implying that the β2-AR/β1-AR and β3-AR/β1-AR ratios (P<0.01, P<0.05) were correspondingly restored. After training, NOS3 was activated through Ser1177 phosphorylation (P<0.01 vs. MI) by exercise in the failing heart, whereas the expression of total NOS3 was unaltered. Cardiac NO content was reduced after MI(P<0.01), which was normalized by exercise(P<0.05). Exercise training activated NOS3 signaling in the failing heart. After training, NOS1 was activated through Ser1412 phosphorylation (P<0.01 vs. MI), Akt was activated (P<0.01 vs. MI) by exercise in the failing heart, whereas the expression of total NOS3 and total Akt was unaltered. The activity of cardiac xanthine oxidase was significantly up-regulated after MI(P<0.01), which was normalized by exercise(P<0.01). Exercise training activated Akt-NOS1 signaling in the failing heart.2 Exercise Training reduces MI-induced oxidative damage in the PVN, minimize MI-induced central neural excitation.(1) Exercise Training reduces MI-induced oxidative damage in the PVN.The mRNA and protein expression of Nox2, Nox4, the activity of NADPH oxidase in the PVN was significantly up-regulated after MI(P<0.01). which was normalized by exercise(P<0.01). Compared with the MI+A group, the mRNA and protein expression of Nox2, Nox4, the activity of NADPH oxidase in the PVN was significantly reduced compared with MI rats treated with ACSF (P<0.01,P<0.01,P<0.05). After MI, the production of superoxide anion in the PVN was significantly increased (P<0.01). But after 4 weeks of exercise, the superoxide anion production was significantly reduced (P<0.05).Compared with the MI+A group,the production of superoxide anion was significantly reduced in MI rats with chronic ICV infusion of Tempol(P<0.01).Compared with the S group, The levels of MDA in the PVN were increased(P<0.05), SOD/MDA and SOD were reduced after MI(P<0.01). Exercise significantly reduce the MDA content (P<0.05), increase the levels of SOD,T-AOC and SOD/MDA, and SOD1 and SOD2 protein expression (P<0.01, P<0.05, P<0.01, P<0.05, P<0.01) in the PVN. Compared with the MI+A group, MDA content in the PVN were reduced(P<0.0), the levels of SOD,T-AOC and SOD/MDA, and SOD1 and SOD2 protein expression were increased compared with MI rats treated with ACSF(P<0.01, P<0.05, P<0.01).(2) Exercise Training minimize Mi-induced central neural excitation.The expression of Fra-like (Fra-LI) (fos family gene) activity was used as an indicator of chronic neuronal activation. Plasma NE was used as humoral Indicators. Fra-LI immunostaining in the PVN in MI rats were higher (P<0.01)than SHAM, confirmed that the PVN neurons has been significantly activised. Compared with the MI group, Exercise rats had fewer Fra-LI-positive PVN neurons(P<0.01). Compared with the MI+A group, MI+T rats had fewer Fra-LI-positive PVN neurons(P<0.01).3 Reducing oxidative stress in the paraventricular nucleus improves myocardial infarction-induced cardiac sympathetic nerve sprouting and β-adrenergic receptor dysregulation(1) ICV continue infusion Tempol improves MI-induced cardiac sympathetic nerve sprouting.Compared with the S+A group, the production of superoxide anion in the PVN was significantly increased in MI rats treated with ACSF(P<0.01). ICV continue infusion. Tempol reduce MI-induced oxidative damage in the PVN(P<0.01).Compared with the S+A group, the protein expression of GAP-43 and NGF in the LV was significantly increased in MI rats treated with ACSF (both P<0.01), which was normalized by in MI rats treated with ACSF (both P<0.05).Exercise training downregulate cardiac NGF and GAP-43 protein expression following MI(both P<0.01).The production of superoxide anion in the PVN in ME rats was positively correlated with cardiac GAP-43 expression(R=0.496, P<0.05), suggesting that ROS formation in the PVN was associate with cardiac sympathetic nerve sprouting.(2) ICV continue infusion Tempol improves MI-induced cardiac β-adrenergic receptor dysregulation.The protein expression of β1-AR was significantly down-regulated in MI rats treated with ACSF (P<0.05 vs. S+A). Whereas β2-AR was unaffected after MI. Compared with MI+A group, MI was associated with a significant increase in the ratios of β2-AR/β1-AR (P<0.05 vs. S+A). Importantly, ICV continue infusion Tempol was able to normalize the β2-AR/β1-AR ratios (P<0.05 vs. MI+A). β3-AR protein expression was up-regulated (P<0.05 vs. S+A) in MI rats treated with ACSF. Compared with MI+A group,β3-AR protein expression was up-regulated (P<0.05 vs. MI+A) following ICV continue infusion Tempol.There is no difference between ME and MI+T group.Conclusions:1 Exercise training can inhibit cardiac NGF-TrkA passway, increase the expression of p75NTR, inhibit cardiac sympathetic nerve sprouting after MI. Exercise training restores β-adrenergic receptor balance, activated β3-AR-NOS3 signaling, and activated Akt-NOS 1 signaling, improve cardiac function after MI.2 Exercise Training inhibits NADPH oxidase-ROS passway in the PVN, reduces Mi-induced oxidative damage, minimize MI-induced central neural excitation. There is no difference between exercise and Tempol treatment of MI rats.3 Reducing oxidative stress in the paraventricular nucleus improves myocardial infarction-induced cardiac sympathetic nerve sprouting and β-adrenergic receptor dysregulation.4 Exercise training can improve cardiac function after MI and that the underlying mechanisms may be related to the oxidative stress reduction in the paraventricular nucleus, the inhibition of sympathetic nerve sprouting and the restoring of β-AR balance.