Pericyte–fibroblast transition promotes tumor growth and metastasis

Kayoko Hosaka

Yunlong Yang

Takahiro Seki

Carina Fischer

Hiromasa Morikawa+7 authors

^{Department of Microbiology, Tumor and Cell Biology, Karolinska Institute, 171 77 Stockholm, Sweden;}

^{Key Laboratory of International Collaborations, Second People’s Hospital of Shenzhen, First Affiliated Hospital of Shenzhen University, Shenzhen 518035, China;}

^{Department of Oncology-Pathology, Karolinska Institute, 171 77 Stockholm, Sweden;}

^{Center for Molecular Medicine, Department of Medicine, Solna, Karolinska Institute, 171 76 Stockholm, Sweden;}

^{Unit of Computational Medicine, Department of Medicine, Center for Molecular Medicine, Karolinska Institute, 171 76 Stockholm, Sweden;}

^{Department of Pathology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan;}

^{Department of Cell and Developmental Biology, University College London, London WC1E 6DE, United Kingdom;}

^{Department of Cardiovascular Sciences, University of Leicester, and National Institute for Health Research Leicester Cardiovascular Biomedical Research Unit, Glenfield Hospital, Leicester LE1 7RH, United Kingdom}

^{To whom correspondence should be addressed. Email:}es.ik@oac.iahiy.

Edited by Tadamitsu Kishimoto, Osaka University, Suita, Japan, and approved July 26, 2016 (received for review May 25, 2016)

Author contributions: K.H. and Y.C. designed research; K.H., Y.Y., T.S., C.F., O.D., E.F., P.R., H.M., Y.I., O.L., R.C., and S.L. performed research; J.H., M.S., and G.C. contributed new reagents/analytic tools; E.F., H.M., and O.L. analyzed microarray data; J.H. and P.R. provided clinical samples; M.S. and G.C. provided genetic mice; K.H. and Y.C. analyzed data; and Y.C. wrote the paper.

Edited by Tadamitsu Kishimoto, Osaka University, Suita, Japan, and approved July 26, 2016 (received for review May 25, 2016)

Significance

We show that vascular pericytes significantly contribute to cancer invasion and metastasis by the mechanism of the pericyte–fibroblast transition (PFT). This study proposes this concept and indicates the vascular pericyte’s role. Vascular pericytes were considered to remodel tumor vessels toward a mature phenotype. However, once dissociated from tumor vessels their functions within the tumor tissue are not known. In the present study, we show that pericytes, once detached from tumor microvasculatures, underwent differentiation to become stromal fibroblasts, which are known to contribute to tumor invasion and metastasis. Our results show that vascular pericytes are the important source of stromal fibroblasts and targeting PFT may offer a new treatment option in cancer metastasis.

Keywords: pericyte, PDGF, fibroblast, metastasis, mesenchymal cell

Significance

Abstract

Vascular pericytes, an important cellular component in the tumor microenvironment, are often associated with tumor vasculatures, and their functions in cancer invasion and metastasis are poorly understood. Here we show that PDGF-BB induces pericyte–fibroblast transition (PFT), which significantly contributes to tumor invasion and metastasis. Gain- and loss-of-function experiments demonstrate that PDGF-BB-PDGFRβ signaling promotes PFT both in vitro and in in vivo tumors. Genome-wide expression analysis indicates that PDGF-BB–activated pericytes acquire mesenchymal progenitor features. Pharmacological inhibition and genetic deletion of PDGFRβ ablate the PDGF-BB–induced PFT. Genetic tracing of pericytes with two independent mouse strains, TN-AP-CreERT2:R26R-tdTomato and NG2-CreERT2:R26R-tdTomato, shows that PFT cells gain stromal fibroblast and myofibroblast markers in tumors. Importantly, coimplantation of PFT cells with less-invasive tumor cells in mice markedly promotes tumor dissemination and invasion, leading to an increased number of circulating tumor cells and metastasis. Our findings reveal a mechanism of vascular pericytes in PDGF-BB–promoted cancer invasion and metastasis by inducing PFT, and thus targeting PFT may offer a new treatment option of cancer metastasis.

Abstract

The tumor microenvironment possesses diverse cellular components including malignant cells, inflammatory cells, stromal fibroblasts, various progenitor cells, endothelial cells, and perivascular cells. These tumor-associated cellular components constantly change their identities and functions to cope with tumor growth and invasiveness (1). Tumor cells often produce various growth factors and cytokines as instrumental signals to manipulate host cells that in most cases facilitate tumor growth and metastasis. Although the role of endothelial, inflammatory, and mesenchymal cells in tumor growth and invasion have been extensively studied (2 –10), functions of pericytes in the tumor microenvironment remain largely unknown.

Pericytes are mainly described as mural cells that are associated with vasculatures in various healthy and pathological tissues (11). Recruitment of pericytes to newly formed angiogenic vessels prevents excessive sprouting, stabilizes the nascent vasculature, prevents vascular leakiness, and remodels primitive vasculatures toward mature vasculatures (12, 13). It is believed that these vasculature-related pericyte functions could possibly impede tumor invasion and metastasis. Recent studies show that pericytes retain progenitor cell properties and can differentiate into other cells, including adipocytes, chondrocytes, osteoblasts, phagocytes, granulocytes, and skeletal muscle (14 –18). Under pathological conditions, pericytes may differentiate into myofibroblasts, contributing to kidney fibrosis (19, 20). Unlike most host cells in tumors, pericytes exhibit unique features by expressing a number of surface markers and respond to certain growth factors. The PDGF-BB-PDGFRβ signaling pathway is best known for its modulation of pericyte coverage on microvessels, and endothelial cells are the primary source of PDGF-BB (11). Endothelial cell-derived PDGF-BB recruits pericytes onto angiogenic vessels through activation of PDGFRβ. Deletion of Pdgfb or Pdgfrß genes in mice resulted in vascular defect-related embryonic lethality due to lack of pericytes (21, 22), indicating the pivotal role of PDGF-BB-PDGFRβ signaling in pericyte biology. Various tumors also express a high level of PDGF-BB and the impact of tumor cell-derived PDGF-BB on pericytes is controversial. In contrast to endothelial cells, tumor cell-derived PDGF-BB may potentially attract pericytes to migrate from vessels through a chemoattractant gradient mechanism (23). The fate of vessel disassociated pericyte (PC) has not been clearly investigated. PDGF receptor signaling has been suggested to contribute to pericyte–myofibrolast transition in kidney fibrosis (19).

CAFs, especially myofibroblasts, are known to facilitate tumor invasion and metastasis (6). In certain tumor types such as pancreatic cancers, CAFs dominate tumor cellular components and constitute a major part of the tumor mass (24). Unresolved key issues include the origin of CAFs and the signaling pathways that control the CAF population in tumor tissues. Could it be possible that other host cells in tumors differentiate into CAFs under the influence of specific signaling systems? In the present study, we provide evidence to demonstrate that vascular pericytes are an important source of CAFs, which markedly promote cancer metastasis. The pericyte–CAF transition is modulated by PDGF-BB-PDGFRβ signaling through the mechanism of pericyte–fibroblast transition (PFT). Gain- and loss-of-function experiments using genetic and pharmacological approaches validate that PFT in tumors is the primary driving force for cancer invasion and metastasis. Genetic tracing in tumor-bearing mice demonstrates that a significant number of pericytes undergo PFT. Finally, we provide evidence that PDGF-BB expression levels and fibroblast components correlate with poor survival in patients with different cancer types. Thus, our findings are clinically relevant and shed mechanistic insights on pericyte-mediated cancer metastasis and suggest that targeting PFT may potentially offer a new therapeutic option for cancer treatment.

Acknowledgments

We thank Funeng Jiang, Xiaojuan Yang, Yin Zhang, and Hideki Iwamoto for technical assistance; and Dr. Funa Keiko (Gothenburg University) and Dr. Xuri Li (Zhongshan Ophthalmology Center, Sun Yat-sen University) for providing tumor cell lines. Y.C.’s laboratory is supported through research grants from the Swedish Research Council, the Swedish Cancer Foundation, the Karolinska Institute Foundation, a Karolinska Institute distinguished professor award, the Torsten Soderbergs Foundation, the Tore Nilsons Foundation, the Ruth and Richard Julin Foundation, the Ogonfonden Foundation, the Martin Rinds Foundation, the Maud and Birger Gustavssons Foundation, the Lars Hiertas Minne Foundation, the Alex and Eva Wallströms Foundation, the Robert Lundbergs Memorial Foundation, the Swedish Diabetes Foundation, the Swedish Children Cancer Foundation, European Research Council Advanced Grant ANGIOFAT (Project 250021), the Knut Alice Wallenberg Foundation, and an advanced grant from NOVO Nordisk Foundation.

Acknowledgments

Footnotes

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

Data deposition: The sequences reported in this paper have been deposited in the Gene Expression Omnibus (GEO) database, www.ncbi.nlm.nih.gov/geo (accession nos. {"type":"entrez-geo","attrs":{"text":"GSE85955","term_id":"85955","extlink":"1"}}GSE85955 and {"type":"entrez-geo","attrs":{"text":"GSE33717","term_id":"33717","extlink":"1"}}GSE33717).

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1608384113/-/DCSupplemental.

Footnotes

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