Extracellular matrix directs phenotypic heterogeneity of activated fibroblasts

Abstract

Activated fibroblasts are key players in the injury response, tumorigenesis, fibrosis, and inflammation. Dichotomous outcomes in response to varied stroma-targeted therapies in cancer emphasize the need to disentangle the roles of heterogeneous fibroblast subsets in physiological and pathophysiological settings. In wound healing, fibrosis, and myriad tumor types, fibroblast activation protein (FAP) and alpha-smooth muscle actin (αSMA) identify distinct, yet overlapping, activated fibroblast subsets. Prior studies established that FAP reactive fibroblasts and αSMA myofibroblasts can exert opposing influences in tumorigenesis. However, the factors that drive this phenotypic heterogeneity and the unique functional roles of these subsets have not been defined. We demonstrate that a convergence of ECM composition, elasticity, and transforming growth factor beta (TGF-β) signaling governs activated fibroblast phenotypic heterogeneity. Furthermore, FAP reactive fibroblasts and αSMA myofibroblasts exhibited distinct gene expression signatures and functionality in vitro, illuminating potentially unique roles of activated fibroblast subsets in tissue remodeling. These insights into activated fibroblast heterogeneity will inform the rational design of stroma-targeted therapies for cancer and fibrosis.

A framework for advancing our understanding of cancer-associated fibroblasts

“…Indeed, CAFs isolated from mouse PDAC can be switched from the αSMA-high and IL-6-producing states through manipulation of TGFβ and IL-1 signalling, arguing for considerable plasticity in fibroblast states 20 . Furthermore, the responsiveness of matrix production by fibroblasts and the αSMA promoter to a range of extracellular cues, including substrate stiffness, supports the idea that the αSMA-high, matrix producing-high state is rever sible 63,64,[137][138][139] . Once again, irreversible lineage marking approaches in mouse models should be informative in addressing the interconvertibility of different CAF subtypes, and improved understanding of the epigenetic regulation of CAF states should shed further light on the stability of CAFs.…”

“…Crosstalk and positive feedback involving Janus kinase (JAK)-STAT signalling, the contractile cytoskeleton and alterations in histone acetylation further promote CAF activation 59,60 . Physical changes in the ECM are also capable of activating CAFs 53,[61][62][63][64] . In vitro studies have shown that fibroblast stretching, which may result from the hyperproliferation of transformed epithelial cells, can activate SRF-driven transcription and Yes-associated protein 1 (YAP1)-TEAD-driven transcription 53,54,65,66 .…”

Cancer‐associated fibroblasts that restrain cancer progression: Hypotheses and perspectives

“…Recent studies have begun to reveal several signaling pathways that differentially induce various CAF subsets in vitro and in vivo. For example, ECM constituents and substratum stiffness are crucial for the regulation of FAPα expression, a representative pCAF marker, in primary cultured lung fibroblasts . A recent study on PDAC revealed that interleukin (IL)‐1 and transforming growth factor (TGF)‐β, possibly derived from tumor cells, induce the differentiation of quiescent pancreatic stellate cells (PSC), which are a source of CAF, into IL‐6 + CAF (iCAF) and α‐SMA + CAF (myCAF), respectively, yielding heterogeneous CAF subsets .…”

Single Cell Transcriptomics of Pancreatic Cancer Precursors Demonstrates Epithelial and Microenvironmental Heterogeneity as an Early Event in Neoplastic Progression

“…Heterogeneous fibroblast populations across histological subtypes were also identified potentially representing distinct stromal functions during tumorigenesis. For example, the fibroblast subtype known as "inflammatory" CAF (iCAF) is characterized by expression of VIM, FAP, COL3A1, DES, IL6, and CXCL12 and reduced expression of a-SMA (ACTA2) [32,33]. This subpopulation has been shown to be involved in immunosuppression, growth factor secretion, and promotion of pro-tumorigenic mechanisms facilitating invasion and metastasis [32], which might correlate with its exclusive representation in PDAC derived clusters, representing 10.5% (58/544) of single stromal cells profiled, and absence within non-invasive IPMNs.…”