| Background:Hypertrophy of myocardium, proliferation of fibroblasts, excessive deposition of collagen are main pathological changes after myocardial infarction(MI), which lead to impairment of cardiac function, stiffiness of myocardium, arrhythmia, and sudden death. A variety of cytokines and growth factors are involved in the pathology of myocardial fibrosis. Transforming growth factor-beta (TGF-β) is considered the most important cytokine relating to myocardial fibrosis. TGF-β is a crucial mediator in the pathogenesis of post-infarction remodeling. Increased TGF-β levels in the remodeling heart are associated with activation of TGF-P signaling. High-mobility group box1(HMGB1) has been reported to attenuate ventricular remodeling. However, the mechanism by which HMGB1attenuates fibrosis and prevents post-infarct ventricular remodeling has not yet been studied in detail. Our study was designed to investigate whether HMGB1attenuate cardiac remodeling through the TGF-β/Smad signaling pathway.Objective:To observed the effect of HMGB1on myocardial fibrosis and left ventricle remodeling after myocardial infarction in rats, and explored whether or not these effects were depended upon the TGF-β signaling pathway.Methods:60male Sprague Dawley (SD) rats (200-250g) were randomized to following group:Sham group(15Sham-operated animals were underwent thoracotomy without LAD ligation).45MI animals were randomly assigned to tow groups:MI control group, HMGB1implantation group.3weeks after inducing myocardial infarction,100μl PBS without HMGB1or containing2.5μg HMGB1was injected into4sites (25μL per site) of the ventricular wall bordering the viable myocardium through a32-gauge needle. At4weeks after the treatment, The left ventricular (LV) function was assessed by echocardiography.8rats of each group were sacrificed at4weeks post-MI. We assessed the infarct size by masson staining. We also observed the expression of MMP2, MMP9, TIMP2, TIMP3, collagenⅠ, collagenⅢ, TGF-β1, pSmad2, Smad2, pSmad3, Smad3, Smad7, p38by western blot; the mRNA expression of TGF-β1by Real Time-PCR. Results:(1) At4weeks after the treatment, HMGB1significantly increased the left ventricular ejection fraction (LVEF)(P<0.05), decreased the left ventricular end diastolic dimension (LVEDD)(P<0.05), left ventricular end systolic dimension (LVESD)(P<0.05) and the infarct size (P<0.05) compared with control group.(2) The expressions of collagen Ⅰ, collagen Ⅲ and tissue inhibitor of metalloproteinase2(TIMP2) were also decreased, while the matrix metalloproteinases2(MMP2) and MMP9expressions were upregulated by HMGB1injection (P<0.05) compared with control group. No effect on TIMP3was observed.(3) Furthermore, TGF-β1and phosphor-Smad2(p-Smad2) were significantly suppressed and Smad7was increased in HMGB1-treated group (P<0.05) compared with control group, no effects on p-Smad3and p-p38were observed.Conclusion:(1)HMGB1could improve the heart function and reverse the LV remodeling;(2) These benifical effect may function through the possible inhibition of TGF-β1/pSmad2signaling pathway and increased Smad7expression. Background:MI is associated with a great loss of cardiomyocytes, and likely to develop into heart failure. In recent years, researchers found that transplantation of stem cells such as bone-marrow-derived stem cells (BMSCs) and endothelial progenitor cells (EPCs) into the ischemic myocardium has been shown to improve cardiac function following myocardial infarction. However, the pure stem cell transplantation is challenged by low cell retention and survival, leading to little improvement of heart function. A new method to induce cardiac cell regeneration in situ remains a major challenge for cardiologists. HMGB1, a nuclear protein, has been recently reported to improve heart function by inducing cardiac stem cells proliferation and differentiation in suit. However, administration of HMGB1alone is hampered by rapid clearance and relatively high doses needed to exert a therapeutic effect. Thermosensitive hydrogels are cross-linked polymer network which is both biocompatible and biodegradable, and has no apparent cytotoxicity. It was widely applied for controlled drug delivery and cell growth in reacent years.Object:This study was designed to investigate whether the benifical effect of HMGB1could be strengthened by local intramyocardial injection of HMGB1along with a novel Dex-PCL-HEMA/PNIPAAm hydrogel and ascertain its possible mechanism of action.Methods:Rat models were induced by coronary artery ligation. Five rats underwent sham operation without LAD ligation. Eighty five MI animals were randomly assigned to groups receiving multiple intramyocardial injections of100μL phosphate buffered saline without HMGB1(PBS, group-1),100μL hydrogel without HMGB1(hydrogel, group-2),100μL PBS containing2.5μg HMGB1(PBS+HMGB1, group-3), or100μL hydrogel containing2.5μg HMGB1(hydrogel+HMGB1, group-4). Each group had a minimum of5animals available for testing. The injection was made via a32-gauge needle into4sites (25μL per injection) of the peri-infarct zone immediately after coronary ligation.4weeks after injection, LV function and dimensions were assessed with echocardiography. Myocardial cells regeneration, Collagen deposition and neovascularization following MI were evaluated by histopathological examinations. mRNA expression of MEF2C and Nkx2.5were evaluated by RT-PCR.Results:The injection of HMGB1along with hydrogel improved cardiac function reduced collagen content and increased arterial density in the peri-infarct area at4 weeks after MI. Additionally, the number of c-Kit+/Ki67+, a-sarcomeric+/MEF2C+and a-sarcomeric+/Ki67+cells were increased significantly compared with the results of using either agent alone. mRNA expression of MEF2C, as well as Nkx2.5, an early transcription factor of cardiomyocyte lineage, was significantly increased in the peri-infarct area of the heart1week following MI hydrogel+HMGB1group, compared with the other three groups.Conclusions:HMGB1injection with Dex-PCL-HEMA/PNIPAAm hydrogel attenuates cardiac remodeling and improves cardiac function after MI by inducing myocardial regeneration. |
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