Focus on fibroblasts : development, plasticity, and therapeutic challenges in the cardiac fibroblast lineage

Abstract

Cardiac fibroblasts (CFs) are cells of mesenchymal origin and represent a heterogeneous population in the mammalian heart. They secrete extracellular matrix (ECM) molecules providing structural support during heart development and homeostasis. In response to injury, CFs are activated and undergo phenotypic conversion to myofibroblasts (myoFBs). MyoFBs, in turn, produced high levels of ECM proteins which can lead to cardiac fibrosis, thereby contributing to tissue stiffness, reduced contractility, and eventually heart failure (HF). Currently, there are no effective treatments for HF. However, a better understanding of CF biology and the mechanisms of cardiac pathology may lead to novel therapeutic strategies for treatment of heart disease. The overall aim of this thesis was further our understanding of CFs, with particular emphasis on their embryonic development, their plasticity, and the therapeutic challenges and opportunities presented by CFs.

In study I, we defined the transcriptional profiles of cardiac cells of mesenchymal origin during embryonic development in the mouse heart. The results suggested a new model for cell fate acquisition and differentiation within the mesenchymal lineage of the heart. In study II, we developed a novel approach for the reprogramming of mouse CFs into an immature, scalable cardiac progenitor cells (CPCs) that could be differentiated into other cardiac cell types that may be more beneficial for cardiac function. In study III, we established cell culture conditions that supported extracellular deposition of mature collagen from primary human CFs. This method was then used to develop an in vitro cardiac fibrosis assay that allows high-throughput screening to identify compounds with anti-fibrotic activity. In study IV, we presented a new methodology for cell encapsulation, where human cells were encapsulated in microparticles made of new polymer materials and a new synthesis method that enables the delivery of secreted molecules for therapeutic use.

In summary, the work presented in this thesis contributes to a better understanding of CFs at the cellular and molecular level, and points to how they can be targeted for therapeutic purposes for treatment of heart diseases.