Control of cardiogenesis and homeostasis by cardiac fibroblasts

by Sumon Sur
Doctoral thesis
Date of Examination:2016-05-04
Date of issue:2016-07-12
Advisor:Prof. Dr. Wolfram-Hubertus Zimmermann
Referee:Prof. Dr. Dörthe Katschinski
Referee:Prof. Dr. Peter Rehling
Persistent Address: http://dx.doi.org/10.53846/goediss-5712

 

 

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Abstract

English

The mammalian heart is a complex multicellular organ which undergoes many critical changes during development and under pathological conditions. Cardiac fibroblasts (cFBs) represent the predominant non-myocyte population in the adult heart and play essential roles in heart muscle development and homeostasis. The mechanisms how cFBs communicate with cardiomyocytes (CMs) in contributing to the formation of a cardio-instructive environment remain unclear. In this study, we hypothesized that the mechanical and paracrine effects of cFBs and its secreted extracellular matrix (ECM) influence cardiac tissue formation and CM maturation. We utilized the 3D Engineered Heart Muscle (EHM) model of heart muscle development to investigate the role of cFBs in cardiac muscle formation in mouse and human systems. As collagen type I produced by cFBs comprises the main ECM protein in the heart, we furthermore investigated the influence of the collagen-specific molecular chaperone Heat Shock Protein 47 (HSP47) on CM maturation and assembly into functional syncytia, utilizing HSP47 knockout (KO) mouse FBs on 2D and 3D EHM culture platforms. By use of genetically engineered mouse and human embryonic stem cell (ESC) lines, we were firstly able to successfully generate by directed differentiation highly purified CMs to exclusively define the cellular constituents (CMs to non-myocytes) in EHMs. The generation of mature compact cardiac tissue with organotypic morphology and functionality was only feasible with the supplementation of FBs to EHMs. These observations can be explained by several identified mechanisms: FBs facilitate (1) cardiac tissue formation via integrin mediated signalling, (2) the secretion of a cardio-instructive ECM environment, important in mediating heart muscle maturation. Utilizing HSP47 KO FBs, we demonstrated the absence of HSP47 in FBs impairs both ECM-collagen deposition and CM morphology and functionality in both 2D and 3D EHM mouse culture systems. We were able to furthermore recently establish the generation of two mutant HSP47 human ESC lines via the CRISPR/Cas9 system. In conclusion, FBs play a prerequisite role in controlling and inducing cardiac tissue formation and maturation. Furthermore, we identified HSP47 to be an important regulator of cardiac tissue maturation.
Keywords: ECM; Collagen; HSP47; Tissue engineering; Fibroblast; Cardiomyocyte
 
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