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Fibroblast behavior in the embryonic chick heart
1Division of Pediatric Cardiology, University of California at Davis 95616.
Insights
Chick heart fibroblasts exhibit distinct behaviors based on their location. Their characteristics are reversible and influenced by the local environment, not predetermined differentiation.
Area of Science:
- Developmental biology
- Cell biology
- Cardiac tissue engineering
Background:
- Intracardiac fibroblasts in chick embryos exist in two main populations: epicardial and atrioventricular.
- These fibroblast populations display differing characteristics in vivo regarding matrix production, proliferation, and interaction with myocytes.
Purpose of the Study:
- To investigate whether the distinct behaviors of epicardial and atrioventricular fibroblasts are predetermined or environmentally responsive.
- To elucidate the role of the local microenvironment in modulating fibroblast behavior during heart development.
Main Methods:
- Isolation of epicardial and atrioventricular fibroblast populations from Hamburger and Hamilton stage 36 chick hearts.
- Utilized a 3D cell aggregate culture system to simulate in vivo cell-cell and cell-matrix interactions.
- Cultured fibroblasts in serum-free medium and medium supplemented with chicken serum to assess environmental influences.
Main Results:
- In serum-free conditions, both fibroblast types showed low matrix production, minimal proliferation, and failed to segregate from myocytes.
- In the presence of chicken serum, both populations exhibited increased matrix production, heightened cell proliferation, and segregation from myocytes.
- These findings indicate that environmental factors significantly influence fibroblast behavior.
Conclusions:
- The observed differences between epicardial and atrioventricular fibroblasts in vivo are likely due to reversible responses to local environmental cues.
- Fibroblast behavior is not dictated by irreversible differentiation states but is plastic and adaptable to microenvironmental conditions.
- This suggests a dynamic model for fibroblast function in cardiac development and potentially in cardiac repair.
Abstract:
Intracardiac fibroblasts (mesenchymal cells) of Hamburger and Hamilton stage 36 chick heart reside in the epicardium and atrioventricular valves. The characteristics of the epicardial fibroblasts include segregation from the myocytes of the heart wall myocardium, voluminous extracellular matrix production, and some cell proliferation activity. The atrioventricular fibroblasts intermingle with myocytes at the mutual border between these tissues, produce smaller amounts of extracellular matrix, and show very active cell proliferation. Is the behavior of each population of fibroblasts predetermined or is each responding in a reversible fashion to local environment? A cell aggregate culture system, which permits 3-dimensional cell-cell and cell-matrix interactions, is used to study the behavior of each isolated population of fibroblasts in vitro. In the presence of serum-free medium, each population produces very little extracellular matrix, has relatively low mitotic activity, and does not segregate from myocytes when the aggregate is composed of randomly intermixed myocytes and fibroblasts. In the presence of chicken serum, each population increases matrix production, increases cell proliferation, and sorts from myocytes. Thus, we suggest that the two populations of fibroblasts in the developing heart are responding to local environments and the differences observed in vivo are not the consequence of irreversible states of cellular differentiation.