Stromal PDGFR-α Activation Enhances Matrix Stiffness, Impedes Mammary Ductal Development, and Accelerates Tumor Growth

Abstract

The extracellular matrix (ECM) is critical for mammary ductal development and differentiation, but how mammary fibroblasts regulate ECM remodeling remains to be elucidated. Herein, we used a mouse genetic model to activate platelet derived growth factor receptor-alpha (PDGFRα) specifically in the stroma. Hyperactivation of PDGFRα in the mammary stroma severely hindered pubertal mammary ductal morphogenesis, but did not interrupt the lobuloalveolar differentiation program. Increased stromal PDGFRα signaling induced mammary fat pad fibrosis with a corresponding increase in interstitial hyaluronic acid (HA) and collagen deposition. Mammary fibroblasts with PDGFRα hyperactivation also decreased hydraulic permeability of a collagen substrate in an in vitro microfluidic device assay, which was mitigated by inhibition of either PDGFRα or HA. Fibrosis seen in this model significantly increased the overall stiffness of the mammary gland as measured by atomic force microscopy. Further, mammary tumor cells injected orthotopically in the fat pads of mice with stromal activation of PDGFRα grew larger tumors compared to controls. Taken together, our data establish that aberrant stromal PDGFRα signaling disrupts ECM homeostasis during mammary gland development, resulting in increased mammary stiffness and increased potential for tumor growth.

Hyaluronan, Cancer-Associated Fibroblasts and the Tumor Microenvironment in Malignant Progression

“…CAFs are most commonly identified by their expression of fibroblast activation protein (FAP) and alpha smooth muscle actin (∂-SMA), however, additional markers including platelet derived growth factor receptor b (PDGFRB), fibroblast specific protein (FSP) and vimentin (VIM), all of whose expression in tumor stroma have, like ∂-SMA, been linked to poor outcome of many cancers, can also be expressed in CAFs (Jacob et al, 2012 ; Folgueira et al, 2013 ; Paulsson and Micke, 2014 ; Han et al, 2015 ; Peiris-Pagès et al, 2015 ; Corvigno et al, 2016 ; Gascard and Tlsty, 2016 ; Kuzet and Gaggioli, 2016 ; Hammer et al, 2017 ; Tao et al, 2017 ; von Ahrens et al, 2017 ). The roles of CAFs as promoters of tumor initiation, progression, epithelial to mesenchymal transition, stemness, tumor invasion, angiogenesis, metastasis and drug resistance are well established (Kalluri and Zeisberg, 2006 ; Shekhar et al, 2007 ; Straussman et al, 2012 ) Experimentally, CAFs exhibit activity in all Hallmarks of Cancer categories (Salo et al, 2014 ; Tommelein et al, 2015 ; Attieh and Vignjevic, 2016 ; Mezawa and Orimo, 2016 ).…”

Disruption of stromal hedgehog signaling initiates RNF5-mediated proteasomal degradation of PTEN and accelerates pancreatic tumor growth

“…Fibroblasts are major contributors to the distinct desmoplastic reaction in PDAC that alter the architecture and mechanics of the ECM ( Provenzano et al, 2012 ; Stylianopoulos et al, 2013 ). We designed an in vitro assay using a microfluidic device ( Hammer et al, 2017 ) to test whether PTEN in tumor fibroblasts affects the hydraulic permeability (K), which is a characteristic of the ECM that relates interstitial fluid velocity to the fluid pressure gradient ( Wiig & Swartz, 2012 ) ( Fig S6A–D ). This in vitro assay demonstrated that human pancreatic tumor fibroblasts with PTEN knockdown had increased resistance to flow (i.e., decreased K) compared with control ( Fig 6D and E ).…”

A pleiotropic role for FGF signaling in mammary gland stromal fibroblasts

“…For example, patterning of collagen fibers in the mammary gland stroma regulates the orientation of TEBs during branching morphogenesis (Brownfield et al, 2013). Recent publications reported important role of fibroblasts in regulation of ECM composition, abundance and organization, and thereby in regulation of mammary epithelial branching morphogenesis (Feinberg et al, 2018;Hammer et al, 2017;Koledova et al, 2016;Morsing et al, 2016;Peuhu et al, 2017). We found that FGF signaling in fibroblasts regulates expression of several ECM genes, including collagens.…”

“…Stromal fibroblasts are important regulators of mammary epithelial morphogenesis (Hammer et al, 2017;Koledova et al, 2016;Morsing et al, 2016;Peuhu et al, 2017). Therefore, we investigated the role of FGF2 signaling in fibroblasts in epithelial branching morphogenesis using 3D cultures of mammary organoids alone, fibroblasts alone, and co-cultures of organoids with fibroblasts.…”

“…Fibroblasts were found essential for formation of mammary epithelial ductal structures upon transplantation of human mammary organoids into humanized mouse fat pads (Kuperwasser et al, 2004) and in 3D co-culture of MCF10A cells (Krause et al, 2008). Genetic mouse models demonstrated critical roles of fibroblast-mediated paracrine signaling and ECM remodeling in mammary gland development (Hammer et al, 2017;Jones et al, 2019;Koledova et al, 2016;Peuhu et al, 2017) and revealed regulation of these functions by receptor tyrosine kinase signaling, including PDGFR and EGFR-ERK1/2 pathways (Hammer et al, 2017;Koledova et al, 2016).…”