Microenvironmental sensing by fibroblasts controls macrophage population size

Area of Science:

• Cell biology
• Tissue homeostasis
• Immunology

Background:

• Mechanisms controlling cell type numbers in tissues are largely unknown.
• Different cell types exhibit unique population control strategies.
• Fibroblasts and macrophages have distinct proliferation constraints.

Purpose of the Study:

• To investigate how fibroblast density influences macrophage population.
• To identify signaling pathways connecting fibroblast and macrophage regulation.
• To understand the role of YAP1 in coordinating cell numbers.

Main Methods:

• Analysis of density-dependent gene expression in fibroblasts.
• Investigating the Hippo signaling pathway and YAP1 activity.
• Assessing the regulation of Csf1 enhancer activity in fibroblasts.
• Measuring macrophage population dynamics following YAP1 activation.

Main Results:

• Fibroblast proliferation is limited by space, while macrophage proliferation depends on growth factors.
• YAP1 in fibroblasts directly regulates Csf1 (macrophage growth factor) expression.
• Fibroblast YAP1 activation increases Csf1 and elevates macrophage numbers.
• Fibroblast gene expression changes with density may involve mechanical force sensing.

Conclusions:

• Distinct cell population control mechanisms are interconnected.
• Fibroblast YAP1 signaling coordinates macrophage numbers via Csf1.
• Tissue environment sensing is a key strategy for maintaining tissue composition.