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Chronic thromboembolic pulmonary hypertension (CTEPH) is an entity of PH that not only limits patients quality of life but also causes significant morbidity and mortality. The treatment of choice is pulmonary endarterectomy. However numerous patients do not qualify for pulmonary endarterectomy or present with residual vasculopathy post pulmonary endarterectomy and require specific vasodilator treatment. Currently, there is no available specific small animal model of CTEPH that could serve as tool to identify targetable molecular pathways and to test new treatment options. Thus, we generated and standardized a rat model that not only resembles functional and histological features of CTEPH but also emulates thrombi fibrosis. The pulmonary embolism protocol consisted of 3 sequential tail vein injections of fibrinogen/collagen-covered polystyrene microspheres combined with thrombin and administered to 10-week-old male Wistar rats. After the third embolism, rats developed characteristic features of CTEPH including elevated right ventricular systolic pressure, right ventricular cardiomyocyte hypertrophy, pulmonary artery remodeling, increased serum brain natriuretic peptide levels, thrombi fibrosis, and formation of pulmonary cellular-fibrotic lesions. The current animal model seems suitable for detailed study of CTEPH pathophysiology and permits preclinical testing of new pharmacological therapies against CTEPH.

Cardiac functionality is dependent on a balanced protein turnover. Accordingly, regulated protein decay is critical to maintain cardiac function. Here we demonstrate that deficiency of SPRED2, an intracellular repressor of ERK-MAPK signaling markedly expressed in human heart, resulted in impaired autophagy, heart failure, and shortened lifespan. SPRED2-/- mice showed cardiomyocyte hypertrophy, cardiac fibrosis, impaired electrical excitability, and severe arrhythmias. Mechanistically, cardiomyocyte dysfunction resulted from ERK hyperactivation and dysregulated autophagy, observed as accumulation of vesicles, vacuolar structures, and degenerated mitochondria. The diminished autophagic flux in SPRED2-/- hearts was reflected by a reduced LC3-II/LC3-I ratio and by decreased Atg7, Atg4B and Atg16L expression. Furthermore, the autophagosomal adaptors p62/SQSTM1 and NBR1 and lysosomal Cathepsin D accumulated in SPRED2-/- hearts. In wild-type hearts, SPRED2 interacted physically with p62/SQSTM1, NBR1, and Cathepsin D, indicating that SPRED2 is required for autophagolysosome formation in regular autophagy. Restored inhibition of MAPK signaling by selumetinib led to an increase in autophagic flux in vivo. Therefore, our study identifies SPRED2 as a novel, indispensable regulator of cardiac autophagy. Vice versa, SPRED2 deficiency impairs autophagy, leading to cardiac dysfunction and life-threatening arrhythmias.

Introduction: TNF-related weak inducer of apoptosis (TWEAK) triggers multiple cellular responses involved in left ventricular remodelling after myocardial infarction (MI), including cytokine production, inflammation, and wound healing. We therefore hypothesized that TWEAK-Fn14 interactions improve wound healing after experimental MI. Methods/Results: We investigated the effects of exogenous TWEAK by applying (1) cross-linked TWEAK - activating the classical NF-kB-signalling pathway, (2) TWEAK and (3) human serum albumin-tagged (HSA)-TWEAK - both activating the alternative NFkB-signalling pathway, or (4) placebo after the induction of experimental MI. Treatment with TWEAK and HSA-TWEAK surprisingly resulted in significantly higher mortality after MI (survival, placebo vs. TWEAK vs. HSA-TWEAK, 66.7 (10 of 15) vs. 14.3 (4 of 26) vs. 7.1 % (1 of 19)) due to cardiac ruptures in the TWEAK- and HSA-TWEAK groups. Ruptures were not related to changes in cardiac architecture since left ventricular dimensions as measured by echocardiography were identical between HSA-TWEAK and the placebo group three days after MI, a time point where cardiac ruptures had not taken place yet. We rule out direct remodelling defects, since MMP9 mRNA expression and proteolytic activity (gelatine zymography), and collagen1α1 mRNA expression were not altered between the groups. HSA-TWEAK induced an exaggerated inflammatory response: Infiltration of neutrophils into the border zone was significantly increased as assessed by immunohistochemistry (placebo vs. HSA-TWEAK, 297.91 vs. 455.75 neutrophils/ mm2, p < 0.001). FACS-Analysis showed a significant up-regulation of CD45+-cells in the infarcted area (CD45+-cells, placebo vs. HSA-TWEAK, 4.52 vs. 9.38 %, p < 0.05). This was associated with the up-regulation of genes important for the recruitment (MIP2, MCP-1 and MCP-5) and differentiation (IL5, IL12 and IFN-γ) of leukocytes (pg/ml, placebo vs. HSA-TWEAK: p < 0.05: MIP2, 1.41 vs. 7.83; IL5, 4.13 vs. 18.75; p < 0.001: MCP-1, N.D. vs. 28.72; MCP-5, N.D. vs. 7.36; IL12, 2.07 vs. 44.51; IFN-γ, N.D. vs. 7.47). Conclusion: Treatment with TWEAK reduces survival after experimental MI due to left ventricular rupture. This may be mediated by an exaggerated inflammatory response.

Background Atrial natriuretic peptide (ANP), via its guanylyl cyclase A (GC-A) receptor and cyclic GMP formation, exerts cardiac antihypertrophic and antifibrotic actions. Conversely, aldosterone promotes pathological cardiac remodeling via the mineralocorticoid receptor (MR). To investigate whether local cardiac ANP/GC-A signaling counteracts the effects of aldosterone during experimental hypertensive cardiac remodeling. Results We studied the impact of the MR antagonist eplerenone (100 mg/kg/day) on cardiac remodeling after transverse aortic constriction (TAC) in mice with conditional, cardiomyocyte-restricted deletion of GC-A (CM GC-A KO) [1] or cGMP-dependent protein kinase I (CM cGK I KO) [2] and respective controls (n=10 in each group). Left ventricular (LV) hypertrophy and interstitial fibrosis were significantly exacerbated in both CM GC-A KO and cGK I KO mice after TAC. These histological changes were accompanied by decreased LV SERCA2a expression, increased CTGF and LV dilatation together with contractile dysfunction. Eplerenone had no effect on systemic blood pressure but fully prevented these pressure-overload induced cardiac morphological, molecular and functional alterations in both CM GC-A KO and CM cGK I KO mice. However, eplerenone did not inhibit TACinduced MAPK ERK1/2 phosphorylation/activation, suggesting that the non-genomic effects of aldosterone are not involved in exacerbated hypertensive cardiac remodeling of the KO mice. Intriguingly, in transfected HEK 293 cells, ANP inhibited the aldosterone-induced nuclear translocation of the MR. Conclusion ANP, via GC-A/cGMP/cGKI signaling in cardiac myocytes, attenuates hypertensive cardiac remodeling and dysfunction. These protective ANP effects seem to be mediated at least in part by counterregulation of the deleterious genomic (MR-mediated) cardiac actions of aldosterone.