Blockade of Wnt Secretion Attenuates Myocardial Ischemia-Reperfusion Injury by Modulating the Inflammatory Response.

Wnt (a portmanteau of Wingless and Int-1) signaling in the adult heart is largely quiescent. However, there is accumulating evidence that it gets reactivated during the healing process after myocardial infarction (MI). We here tested the therapeutic potential of the Wnt secretion inhibitor LGK-974 on MI healing. Ischemia/reperfusion (I/R) injury was induced in mice and Wnt signaling was inhibited by oral administration of the porcupine inhibitor LGK-974. The transcriptome was analyzed from infarcted tissue by using RNA sequencing analysis. The inflammatory response after I/R was evaluated by flow cytometry. Heart function was assessed by echocardiography and fibrosis by Masson's trichrome staining. Transcriptome and gene set enrichment analysis revealed a modulation of the inflammatory response upon administration of the Wnt secretion inhibitor LGK-974 following I/R. In addition, LGK-974-treated animals showed an attenuated inflammatory response and improved heart function. In an in vitro model of hypoxic cardiomyocyte and monocyte/macrophage interaction, LGK974 inhibited the activation of Wnt signaling in monocytes/macrophages and reduced their pro-inflammatory phenotype. We here show that Wnt signaling affects inflammatory processes after MI. The Wnt secretion inhibitor LGK-974 appears to be a promising compound for future immunomodulatory approaches to improve cardiac remodeling after MI.

Silencing the CSF-1 Axis Using Nanoparticle Encapsulated siRNA Mitigates Viral and Autoimmune Myocarditis.

Myocarditis is an inflammatory disease of the heart muscle most commonly caused by viral infection and often maintained by autoimmunity. Virus-induced tissue damage triggers chemokine production and, subsequently, immune cell infiltration with pro-inflammatory and pro-fibrotic cytokine production follows. In patients, the overall inflammatory burden determines the disease outcome. Following the aim to define specific molecules that drive both immunopathology and/or autoimmunity in inflammatory heart disease, here we report on increased expression of colony stimulating factor 1 (CSF-1) in patients with myocarditis. CSF-1 controls monocytes originating from hematopoietic stem cells and subsequent progenitor stages. Both, monocytes and macrophages are centrally involved in mediating tissue damage and fibrotic scarring in the heart. CSF-1 influences monocytes via engagement of CSF-1 receptor, and it is also produced by cells of the mononuclear phagocyte system themselves. Based on this, we sought to modulate the virus-triggered inflammatory response in an experimental model of Coxsackievirus B3-induced myocarditis by silencing the CSF-1 axis in myeloid cells using nanoparticle-encapsulated siRNA. siCSF-1 inverted virus-mediated immunopathology as reflected by lower troponin T levels, a reduction of accumulating myeloid cells in heart tissue and improved cardiac function. Importantly, pathogen control was maintained and the virus was efficiently cleared from heart tissue. Since viral heart disease triggers heart-directed autoimmunity, in a second approach we investigated the influence of CSF-1 upon manifestation of heart tissue inflammation during experimental autoimmune myocarditis (EAM). EAM was induced in Balb/c mice by immunization with a myocarditogenic myosin-heavy chain-derived peptide dissolved in complete Freund's adjuvant. siCSF-1 treatment initiated upon established disease inhibited monocyte infiltration into heart tissue and this suppressed cardiac injury as reflected by diminished cardiac fibrosis and improved cardiac function at later states. Mechanistically, we found that suppression of CSF-1 production arrested both differentiation and maturation of monocytes and their precursors in the bone marrow. In conclusion, during viral and autoimmune myocarditis silencing of the myeloid CSF-1 axis by nanoparticle-encapsulated siRNA is beneficial for preventing inflammatory tissue damage in the heart and preserving cardiac function without compromising innate immunity's critical defense mechanisms.

Calcification of myocardial necrosis is common in mice.

Independent of the severity, phenotypes and clinical outcomes of myocardial infarction may vary considerably in patients, suggesting a strong genetic influence on healing and adaptive processes. Since little is known about these genetic determinants, we examined the tissue response to myocardial injury in seven inbred mouse strains, including those employed for gene targeting or transgenic overexpression. Myocardial necrosis was produced by non-ischemic, trans-diaphragmal freeze-thaw injury in strains C57BL/6, C3H/He, DBA/2, BALB/c, 129S1, FVB/n and A/J. Two days after injury, necrotic cardiomyocytes calcified in C3H/He, DBA/2, BALB/c and 129S1, a phenotype known as dystrophic cardiac calcinosis (DCC). The susceptibility to DCC of 129S1 was determined by Dyscalc1, a locus on chromosome 7, which was identified previously in C3H/He and DBA/2. DCC was also observed in C3H/He following ischemic injury by permanent coronary artery ligation, indicating that DCC was independent of the mode of injury. In contrast, strains C57BL/6, FVB and A/J were resistant to DCC, showing formation of a fibrous scar without calcification. The development of DCC was studied in detail in C3H/He and C57BL/6. In both strains, no calcium deposition and only little structural disintegration were noted in necrotic myocardium 24 h after injury upon calcium-sensitive fluorescence staining. Ultrastructural examination revealed calcified mitochondria in C3H/He that may have served later as a nidus for rapid intracellular calcification of cardiomyocytes. We concluded that the susceptibility to calcification of myocardial necrosis may be common among inbred strains and should be recognised as a strong genetic modifier of experimental myocardial injury.