Brain-Derived Neurotrophic Factor Attenuates Septic Myocardial Dysfunction via eNOS/NO Pathway in Rats

Abstract

Sepsis-induced myocardial dysfunction increases mortality in sepsis, yet the underlying mechanism is unclear. Brain-derived neurotrophic factor (BDNF) has been found to enhance cardiomyocyte function, but whether BDNF has a beneficial effect against septic myocardial dysfunction is unknown. Septic shock was induced by cecal ligation and puncture (CLP). BDNF was expressed in primary cardiomyocytes, and its expression was significantly reduced after sepsis. In rats with sepsis, a sharp decline in survival was observed after CLP, with significantly reduced cardiac BDNF expression, enhanced myocardial fibrosis, elevated oxidative stress, increased myocardial apoptosis, and decreased endothelial nitric oxide (NO) synthase (eNOS) and NO. Supplementation with recombined BDNF protein (rhBDNF) enhanced myocardial BDNF and increased survival rate with improved cardiac function, reduced oxidative stress, and myocardial apoptosis, which were associated with increased eNOS expression, NO production, and Trk-B, a BDNF receptor. Pretreatment with NOS inhibitor, N (omega)-nitro-L-arginine methyl ester, abolished the abovementioned BDNF cardioprotective effects without affecting BDNF and Trk-B. It is concluded that BDNF protects the heart against septic cardiac dysfunction by reducing oxidative stress and apoptosis via Trk-B, and it does so through activation of eNOS/NO pathway. These findings provide a new treatment strategy for sepsis-induced myocardial dysfunction.

Figure 1

BDNF expressed in cardiomyocytes was reduced after septic shock, and supplementation of BDNF improved survival rate in rats subjected to septic shock. (a) Schematic diagram of the protocol. (b) BDNF protein expression in isolated cardiomyocytes. (c) BDNF protein expression in heart tissues. (d) Survival rates in rats subjected to septic shock. Data are mean ± SEM, with n = 8 animals per group. ^∗P < 0.05 versus sham; ^#P < 0.05 versus CLP; ^∗∗P < 0.01. CLP: cecal ligation and puncture; rhBDNF: recombined BDNF protein.

Figure 2

BDNF reduced cardiac hypertrophy in septic shock rats that was attenuated by L-NAME. (a and b) Myocardial fibrosis content assessed by Masson's trichrome staining (400x magnification) and quantitation. (c) The cell size visualization by H&E staining (400x magnification). Data are mean ± SEM, with n = 8 animals per group. ^∗P < 0.05 versus sham; ^#P < 0.05 versus CLP; ^&P < 0.05 versus CLP + rhBDNF. CLP: cecal ligation and puncture; rhBDNF: recombined BDNF protein.

Figure 3

BDNF attenuated myocardial oxidative stress in septic shock rats that was abolished by L-NAME. (a and b) Visualization and quantitation of 4-HNE in heart tissue. (c) Superoxide dismutase (SOD) activity in heart tissue. (d) Free 15-F2t-isoprostane in heart tissue was measured by using an enzyme-linked immunoassay kit. Data are mean ± SEM, with n = 8 animals per group. ^∗P < 0.05 versus sham; ^#P < 0.05 versus CLP; ^&P < 0.05 versus CLP + rhBDNF. CLP: cecal ligation and puncture; rhBDNF: recombined BDNF protein.

Figure 4

BDNF reduced cardiomyocyte apoptosis after septic shock that was reduced by L-NAME. (a and b) Visualization (400x magnification) and quantitation of TUNEL positive cells in heart tissue. (c) Bax and Bcl-2 protein expression. (d) Total and cleaved caspase-3 protein expression. Data are mean ± SEM, with n = 8 animals per group. ^∗P < 0.05 versus sham; ^#P < 0.05 versus CLP; ^&P < 0.05 versus CLP + rhBDNF. CLP: cecal ligation and puncture; rhBDNF: recombined BDNF protein.

Figure 5

BDNF increased induction of eNOS-derived NO and enhanced Trk-B in septic shock rats. (a and b) Visualization (400x magnification) and quantitation of eNOS protein expression in heart tissue. (c) Nitric oxide (NO) production in heart tissue. (d and e) Visualization (400x magnification) and quantitation of Trk-B protein expression. Data are mean ± SEM, with n = 8 animals per group. ^∗P < 0.05 versus sham; ^#P < 0.05 versus CLP; ^&P < 0.05 versus CLP + rhBDNF. CLP: cecal ligation and puncture; rhBDNF: recombined BDNF protein.