LAUSR

OBJECTIVE To investigate the role and mechanism of microRNA-499 (miR-499) regulating α-myosin heavy chain (α-MHC) and β-myosin heavy chain (β-MHC) gene axis in septic myocardial dysfunction (SMD) and its significance. METHODS Sixty healthy adult male Sprague-Dawley (SD) rats were divided into phosphate buffered saline (PBS) control group (PBS group), lipopolysaccharide (LPS) induced SMD model group (LPS group), miR-499 agonist pretreatment group (agomir+LPS group), and miR-499 inhibitor pretreatment group (antagomir+LPS group) by random number table, with 15 rats in each group. SMD rat model was reproduced by intraperitoneal injection of LPS 10 mg/kg. The PBS group was intraperitoneally injected with the same amount of PBS. The two pretreatment groups were injected with agomir 30 mg/kg or antagomir 80 mg/kg through the caudal vein for 3 days, once a day. PBS group and LPS group were not pretreated. Echocardiography was detected 5 hours after LPS injection, and relevant indexes were recorded. The expression of miR-499 in plasma and myocardial tissue was detected by real-time quantitative polymerase chain reaction (qPCR). Western blotting was used to detect the protein expressions of α-MHC and β-MHC in myocardial tissue. Plasma N-terminal pro-brain natriuretic peptide (NT-proBNP), a marker of heart failure, was measured by electrochemiluminescence. RESULTS Compared with the PBS group, the rats in LPS group were depressed. Additionally, LPS down-regulated the level of miR-499 in plasma and myocardial tissue, decreased α-MHC expression in myocardial tissue and up-regulated the expression of β-MHC. Echocardiography showed that left ventricular ejection fraction (LVEF), left ventricle fractional shortening (LVFS), cardiac output (CO), stroke volume (SV) and heart rate (HR) decreased by 49.1%, 59.2%, 48.8%, 39.4% and 15.9%, respectively, and the level of plasma NT-proBNP increased significantly in LPS group, indicating that LPS could induce cardiac dysfunction in rats. Compared with the LPS group, after pretreatment with agomir to overexpress the miR-499, LVEF and LVFS were significantly increased [LVEF: 0.662±0.020 vs. 0.323±0.024, LVFS: (36.16±1.43)% vs. (20.20±1.32)%, both P < 0.01], which suggested that the cardiac function of rats was improved in agomir+LPS group. At the same time, pretreatment with agomir significantly down-regulated the β-MHC protein expression (β-MHC/GAPDH: 0.74±0.04 vs. 2.97±0.34, P < 0.01), significantly up-regulated α-MHC protein expression (α-MHC/GAPDH: 1.59±0.05 vs. 0.74±0.14, P < 0.01), and significantly decreased the plasma NT-proBNP level (ng/L: 114.49±6.85 vs. 334.13±4.36, P < 0.01). After pretreatment with antagomir to inhibit the expression of miR-499, echocardiography showed that LVEF and LVFS were significantly lower than those in the LPS group [LVEF: 0.297±0.021 vs. 0.323±0.024, LVFS: (19.38±1.52)% vs. (21.20±1.32)%, both P < 0.01], which suggested that the cardiac function of rats was significantly inhibited. At the same time, pretreatment with antagomir significantly down-regulated α-MHC protein expression in myocardial tissue (α-MHC/GAPDH: 0.63±0.03 vs. 0.74±0.14, P < 0.01), significantly up-regulated β-MHC protein expression (β-MHC/GAPDH: 3.03±0.47 vs. 2.97±0.34, P < 0.01), and significantly increased the level of plasma NT-proBNP (ng/L: 373.91±4.23 vs. 334.13±4.36, P < 0.05). CONCLUSIONS miR-499 could regulate the expression of α-MHC and β-MHC which improved cardiac dysfunction caused by sepsis. Targeted regulation of miR-499 expression may be an effective way to treat SMD.