Metallothioneins 1 and 2 Modulate Inflammation and Support Remodeling in Ischemic Cardiomyopathy in Mice.

Aims. Repetitive brief ischemia and reperfusion (I/R) is associated with left ventricular dysfunction during development of ischemic cardiomyopathy. We investigated the role of zinc-donor proteins metallothionein MT1 and MT2 in a closed-chest murine model of I/R. Methods. Daily 15-minute LAD-occlusion was performed for 1, 3, and 7 days in SV129 (WT)- and MT1/2 knockout (MT(-/-))-mice (n = 8-10/group). Hearts were examined with M-mode echocardiography and processed for histological and mRNA studies. Results. Expression of MT1/2 mRNA was transiently induced during repetitive I/R in WT-mice, accompanied by a transient inflammation, leading to interstitial fibrosis with left ventricular dysfunction without infarction. In contrast, MT(-/-)-hearts presented with enhanced apoptosis and small infarctions leading to impaired global and regional pump function. Molecular analysis revealed maladaptation of myosin heavy chain isoforms and antioxidative enzymes in MT1/2(-/-)-hearts. Despite their postponed chemokine induction we found a higher total neutrophil density and macrophage infiltration in small infarctions in MT(-/-)-hearts. Subsequently, higher expression of osteopontin 1 and tenascin C was associated with increased myofibroblast density resulting in predominately nonreversible fibrosis and adverse remodeling in MT1/2(-/-)-hearts. Conclusion. Cardioprotective effects of MT1/2 seem to be exerted via modulation of contractile elements, antioxidative enzymes, inflammatory response, and myocardial remodeling.

Impaired border zone formation and adverse remodeling after reperfused myocardial infarction in cannabinoid CB2 receptor deficient mice.

AIMS: Reperfusion ofmyocardial infarction is associated with inflammatory reaction and subsequentmyocardial remodeling with a rapid scar formation in mice. The cannabinoid receptor CB2 has been associated with cardioprotection and regulation ofmacrophage function.Weinvestigated its role in remodeling of reperfused infarction. MAIN METHODS: One hour LAD-occlusion was followed by reperfusion over 6 h and 1, 3 and 7 days in wild-type C57/BL6J (WT) and CB2 receptor-deficient (Cnr2−/−)mice (n=8/group). Hearts were processed for functional, morphological and mRNA/protein analysis, and tissue concentration of endocannabinoidswas determined using liquid chromatography-multiple reaction monitoring. KEY FINDINGS: In contrast to a rapid formation of granulation tissue and a compacted non-transmural scar inWT mice after 7 days of reperfusion, Cnr2−/− mice showed a non-compacted transmural scar. Millar® left ventricular catheter measurements revealed a significantly worse function in Cnr2−/− mice.We found no compensatory elevation of endocannabinoid concentration in Cnr2−/− hearts. Macrophage infiltration was significantly stronger in Cnr2−/− hearts and affected also the remote septum, when compared to WT hearts.We found a cytokine-driven inflammatory response in Cnr2−/− hearts with no significant induction of chemokines. Immunohistochemistry for thrombospondin-1 revealed a dysfunctional infarction border zone formation in Cnr2−/− hearts. Cnr2−/−hearts showed no significant induction of tenascin C, collagen-Iα or lysil oxidase, thereby indicating adversemyocardial remodeling. SIGNIFICANCE: Endocannabinoids act via CB2 receptor in the modulation of inflammatory response and myocardial remodeling after infarction. CB2 receptor plays an important role in the formation of infarction border zone, collagen deposition and organization of stable scar during remodeling.

CB2 receptor-mediated effects of pro-inflammatory macrophages influence survival of cardiomyocytes.

AIMS: The endocannabinoid system and cannabinoid receptor 2 (CB2 receptor) have been associated with modulation of inflammatory response and myocardial adaptation after ischemic injury. In order to elucidate CB2 receptor-related effects during cellular interactions, we investigated cardiomyocyte survival and macrophage function in vitro. MAIN METHODS: Murine embryonic (eCM) and adult (CM) cardiomyocytes, murine macrophages (MO), and their subtypes M1 (M1-MO) and M2 (M2-MO) were derived from wildtype- (WT) and CB2 receptor-deficient (Cnr2(-/-)) mice. Cells were cultured separately or in co-culture under normoxia or hypoxia (2% O2) and pro-inflammatory stimulation using interferon (IFN)γ. Besides immunohistochemistry, we also measured mRNA expression (Taqman®) and performed FACS-analysis of cardiomyocytes. Macrophage migration was assessed using Boyden chamber assay. KEY FINDINGS: We found a significant induction of CB2 receptor mRNA and protein in murine eCM as well as M1- and M2-MO in vitro following cultivation under hypoxia or stimulation with IFNγ. A significantly higher amount of apoptotic Cnr2(-/-)-CMs was found after incubation under hypoxia when compared to WT-CMs. We observed a significantly stronger migration potential in Cnr2(-/-)-M1-MOs towards the supernatant of apoptotic CM, than in corresponding WT-cells. Co-culture revealed a significantly higher loss of eCMs and induction of their apoptosis after cultivation with Cnr2(-/-)-M1-MOs. Production of TNF-α in M1-MOs was dependent on CB2 receptor stimulation by anandamide. SIGNIFICANCE: Our data provide novel insights into CB2 receptor-mediated protection of cardiomyocytes during hypoxia and pro-inflammatory stimulation. We show CB2 receptor-dependent effects on migration and function of M1-MOs in interaction with cardiomyocytes, thereby influencing their survival.