Molecular Imaging Of LXR Agonist On Adipose-derived Mesenchymal Stem Cells’ Survival And Mechanism In Myocardial Infarcted Hearts

Background and aimsStem cell transplantation has emerged as a promising therapeutic strategy forischemic cardiomyopathy. Among all types of stem cell candidates for cardiacregeneration, AD-MSCs which can be easily obtained from adipose tissue areconsidered as one of the optimal cell types for clinical application. However,low retention and poor survival of injected AD-MSCs are the major obstacles toachieving agreeable therapeutic effect. It is revealed that approaching90%ofthe stem cells may not survive within the first4days after cell delivery, becauseof ischemia surroundings and local inflammation. Previous studies in our grouphave also demonstrated that improvement of the myocardial microenvironmentcould increase the survival of injected AD-MSCs. Therefore, there is a need forsuppressing excessive inflammatory responses in infarcted myocardium andimproving harmful local microenvironment.Liver X receptors (LXRα and LXRβ) are members of the nuclear receptor super family which have been recently recognized as novel pharmacologicaltargets for cardiovascular diseases therapy. LXRα is expressed predominantly inliver, kidney, intestine, macrophages and adipose tissue. Whereas, LXRβ isexpressed ubiquitously. LXR ligands affect the level of inflammatory mediatorssuch as inducible nitric oxide synthase (iNOS), MCP-1and cyclooxygenase-2(COX-2). In addition, it was also reported that LXR agonists also suppressinflammatory response via several assays in vivo,(e.g. murine models of contactdermatitis and atherosclerosis). Some recent studies also demonstrated that LXRagonists could inhibit ischemia and reperfusion injury.This study was designed to investigate effects and mechanisms of LXRagonist T0901317on the survival of adipose-derived mesenchymal stem cells(AD-MSCs) after intramyocardial transplantation by molecular imagingmethods.MethodsPart one: isolation, culture and characterized of AD-MSCs. Adipose-derivedmesenchymal stem cells which stably express Fluc were isolated fromβ-actin-luc transgenic mice and characterized by flow cytometry and BLI.Part two: the effect of LXR agonists on AD-MSCs after transplanted intomyocardial infracted hearts. Male FVB mice were randomly allocated into thefollowing four groups (n=10each):(1) sham group;(2) MI+PBS group;(3) MI+AD-MSCs group;(4) MI+AD-MSCs+LXR agonist T0901317group.AD-MSCs were injected intramyocardially into peri-infarcted region of miceheart after permanent left anterior descending (LAD) artery ligation. BLI wasperformed for quantification of injected cells retention and survival.Echocardiography was used to evaluate the cardiac function.Part three: the effects and mechanisms of LXR agonists on AD-MSCs under Hypoxia and Reperfusion (H/R) injury. AD-MSCs were individually subjectedto (1) normal control;(2) Hypoxia6hours and Reperfusion2hours (H/R);(3)H/R+DMSO;(4) H/R+different doses of LXR agonists (1μmol/L,5μmmol/L,10μmol/L,15μmol/L). BLI was used to assessed AD-MSCs survival. ELISAand Western blot assay were applied to detect TNF-α、IL-6and NF-κBexpression.Results1. Flow cytometry demonstrated that AD-MSCs were positive for CD44andCD90. Bioluminescence imaging and luciferase assay proved that the Flucexpression was correlated with AD-MSCs numbers well.2. The results of BLI in vivo revealed that LXR agonists improved the survivalof AD-MSCs at day7, day14and day21after cell transplantationcompared with AD-MSCs alone group. Cardiac function was improved andmyocardial fibrosis area obviously decreased in combination therapy groupcompared with AD-MSCs alone group.3. LXR agonists improved the survival of AD-MSCs fromHypoxia/Reperfusion injury. ELISA analysis and western blot assayshowed that TNF-α、IL-6secretion and NF-κB expression were inhibittedby T0901317in AD-MSCs.ConclusionsLXR agonist T0901317can improve the retention and survival ofintramyocardial injected AD-MSCs through inhibiting NF-κB signaling pathway.Combination therapy of T0901317and AD-MSCs has a synergetic effect oncardiac function improvement.