Charakterisierung der Einflüsse des Pituitary Adenylate Cyclase-Activating Polypeptides (PACAP) und seines Rezeptors PAC1 auf die strukturelle und zelluläre Morphologie des Herzens im murinen ApoE-Knock-Out Modell

Fibrosis is a hallmark of cardiac remodeling and occurs in a variety of cardiovascular diseases. In particular interstitial fibrosis has been identified as a key pathophysiological factor in the widely heterogeneous group of cardiac dysfunctions with preserved left ventricular ejection fraction (LVEF). According to recent studies comorbidities, particularly from the metabolic spectrum, promote chronic low grade systemic inflammation with secondary involvement of the heart, leading to fibrosis and thereby compromising its structure and subsequently function. The lack of effective antifibrotic treatment options underscores the urgent need for new therapeutic targets. Recent evidence on the antifibrotic effect of the pleiotropic neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) in radiation-induced myocardial injury provides a rationale for a focused investigation of possible antifibrotic effects of PACAP in the aforementioned context. Therefore, the aim of the present work is to elucidate the role of PACAP and its receptor PAC1 in myocardial fibrosis in a metabolic stress model. For this purpose, PACAP-/-- and PAC1-/-- C57/Bl6 N mice were crossed with an ApoE-/-- strain, and metabolic stress was induced by feeding a cholesterol-enriched diet (CED) for 10 weeks. Standard diet (SD) served as a control diet. Cardiac ventricle tissue samples were processed for FFPE histological analysis with hemalaun/eosin- and picro- sirius-red-staining and subjected to morphometric quantification of cardiomyocyte cross diameters and myocardial fibrosis using a software-based image analysis technique. In addition, the CED-group was examined for the presence of CD90 positive cells, which represent a fibroblast subpopulation, using immunohistochemical labeling. In the CED-group a significantly higher extent of myocardial fibrosis was observed in PACAP-/-/ApoE-/-- and PAC1-/-/ApoE-/--mice compared to ApoE-/--mice. The pattern of fibrous deposition resembled typical reactive interstitial fibrosis and affected both ventricles equally. In addition to the higher extent of myocardial fibrosis, PAC1-/-/ApoE-/- -mice also showed a significantly higher number of CD90 positive cells per cardiac area. Measurements of ventricular wall thickness and cardiomyocyte cross diameters revealed no macroscopic or cellular hypertrophy in PACAP-/-/ApoE-/-- and PAC1-/-/ApoE-/--mice compared with ApoE-/--mice after CED. Significant differences occurred exclusively after CED feeding and were not detectable with SD feeding. The present work provides novel evidence for a significant involvement of PACAP and its receptor PAC1 in the development of interstitial fibrosis induced by metabolic stress. Based on the present data, the antifibrotic effect of PACAP is mediated to a significant extent via the PAC1 receptor and occurs only under metabolic stress conditions. The absence of macro- and microscopic myocardial hypertrophy in PACAP-deficient or PAC1-deficient mice precludes relevant hemodynamic effects of PACAP or the PAC1- receptor in the studied model. Based on the present results, PACAP-analogues or PAC1-receptor-agonists may offer therapeutic potential to prevent or attenuate metabolic cardiac fibrosis.