P6295
Role of angiotensin II receptor type 1 in TGF-beta-mediated fibrogenesis in mouse model of experimental autoimmune myocarditis

Extract

Background/Introduction: Heart-specific inflammation called myocarditis is a common cause of pathological fibrogenesis, which leads to tissue stiffening of ventricles and impaired heart function. TGFβ and angiotensin II have been identified as critical factors involved in pathological cardiac fibrogenesis, but the interplay between these two profibrotic pathways is poorly understood. The role of angiotensin II signalling in mouse model of experimental autoimmune myocarditis (EAM) has not been addressed so far.

Purpose: Using EAM model and angiotensin II receptor type 1 (AT1) deficient mice (AT1−/−) we aimed to elucidate the role of AT1 during the acute (inflammatory) and chronic (fibrotic) stage of the disease. We investigated also the role of AT1 signalling in TGFβ-mediated transformation of heart-inflammatory progenitors into pathogenic myofibroblasts.

Methods and results: EAM was induced in BALB/c mice by immunization with alpha myosin heavy chain (αMyHC) combined with Complete Freund's Adjuvant. We demonstrated that AT1−/− mice showed equal extent of inflammation in the cardiac muscle and similar immune response during the acute phase (d21), but significantly reduced fibrotic tissue area at the late stage (d40) of the disease in comparison to wild type animals. Bone marrow transplantation experiments revealed that bone marrow compartment was the major source of pathological fibrotic tissue as wild type animals reconstituted with AT1−/− bone marrow failed to develop heart fibrosis at the post-inflammatory stage of EAM. Isolated heart inflammatory CD133+ cells from AT−/− mice showed reduced expression of profibrotic genes such as Acta2 and Fn1 and inefficient differentiation towards myofibroblast phenotype in response TGFβ stimulation. Moreover, we showed that TGFβ-dependent profibrotic Wnt signalling activation was reduced in AT1−/− cells. Furthermore, AT1 was also required to transduce and sustain TGFβ signalling via small GTPase RhoA, as demonstrated by reduced formation of Rho-GTP complex in AT1−/− cells after long-term (24h), but not after short-term (30 min) stimulation with TGFβ. Finally, we identified A-kinase anchoring protein-Lbc (AKAP-Lbc) as a critical factor involved in AT1-dependent signal transduction of TGFβ-induced RhoA activation.