Hyaluronan modulates growth factor induced mammary gland branching in a size dependent manner

A biological guide to glycosaminoglycans: current perspectives and pending questions

Mammalian glycosaminoglycans (GAGs), except hyaluronan (HA), are sulfated polysaccharides that are covalently attached to core proteins to form proteoglycans (PGs). This article summarizes key biological findings for the most widespread GAGs, namely HA, chondroitin sulfate/dermatan sulfate (CS/DS), keratan sulfate (KS), and heparan sulfate (HS). It focuses on the major processes that remain to be deciphered to get a comprehensive view of the mechanisms mediating GAG biological functions. They include the regulation of GAG biosynthesis and postsynthetic modifications in heparin (HP) and HS, the composition, heterogeneity, and function of the tetrasaccharide linkage region and its role in disease, the functional characterization of the new PGs recently identified by glycoproteomics, the selectivity of interactions mediated by GAG chains, the display of GAG chains and PGs at the cell surface and their impact on the availability and activity of soluble ligands, and on their move through the glycocalyx layer to reach their receptors, the human GAG profile in health and disease, the roles of GAGs and particular PGs (syndecans, decorin, and biglycan) involved in cancer, inflammation, and fibrosis, the possible use of GAGs and PGs as disease biomarkers, and the design of inhibitors targeting GAG biosynthetic enzymes and GAG-protein interactions to develop novel therapeutic approaches.

Going Full TeRM: The Seminal Role of Tissue-Resident Macrophages in Organ Remodeling during Pregnancy and Lactation

During pregnancy and lactation, the uterus and mammary glands undergo remarkable structural changes to perform their critical reproductive functions before reverting to their original dormant state upon childbirth and weaning, respectively. Underlying this incredible plasticity are complex remodeling processes that rely on coordinated decisions at both the cellular and tissue-subunit levels. With their exceptional versatility, tissue-resident macrophages play a variety of supporting roles in these organs during each stage of development, ranging from maintaining immune homeostasis to facilitating tissue remodeling, although much remains to be discovered about the identity and regulation of individual macrophage subsets. In this study, we review the increasingly appreciated contributions of these immune cells to the reproductive process and speculate on future lines of inquiry. Deepening our understanding of their interactions with the parenchymal or stromal populations in their respective niches may reveal new strategies to ameliorate complications in pregnancy and breastfeeding, thereby improving maternal health and well-being.

Functional delineation of the luminal epithelial microenvironment in breast using cell-based screening in combinatorial microenvironments

Microenvironment signals are potent determinants of cell fate and arbiters of tissue homeostasis, however understanding how different microenvironment factors coordinately regulate cellular phenotype has been experimentally challenging. Here we used a high-throughput microenvironment microarray comprised of 2640 unique pairwise signals to identify factors that support proliferation and maintenance of primary human mammary luminal epithelial cells. Multiple microenvironment factors that modulated luminal cell number were identified, including: HGF, NRG1, BMP2, CXCL1, TGFB1, FGF2, PDGFB, RANKL, WNT3A, SPP1, HA, VTN, and OMD. All of these factors were previously shown to modulate luminal cell numbers in painstaking mouse genetics experiments, or were shown to have a role in breast cancer, demonstrating the relevance and power of our high-dimensional approach to dissect key microenvironmental signals. RNA-sequencing of primary epithelial and stromal cell lineages identified the cell types that express these signals and the cognate receptors in vivo. Cell-based functional studies confirmed which effects from microenvironment factors were reproducible and robust to individual variation. Hepatocyte growth factor (HGF) was the factor most robust to individual variation and drove expansion of luminal cells via cKit+ progenitor cells, which expressed abundant MET receptor. Luminal cells from women who are genetically high risk for breast cancer had significantly more MET receptor and may explain the characteristic expansion of the luminal lineage in those women. In ensemble, our approach provides proof of principle that microenvironment signals that control specific cellular states can be dissected with high-dimensional cell-based approaches.

Disabled-2: a protein up-regulated by high molecular weight hyaluronan has both tumor promoting and tumor suppressor roles in ovarian cancer

Although the pro-tumorigenic functions of hyaluronan (HA) are well documented there is limited information on the effects and targets of different molecular weight HA. Here, we investigated the effects of 27 kDa, 183 kDa and 1000 kDa HA on ES-2 ovarian cancer cells overexpressing the stem cell associated protein, Notch3. 1000 kDA HA promoted spheroid formation in ES-2 cells mixed with ES-2 overexpressing Notch3 (1:3). We report disabled-2 (DAB2) as a novel protein regulated by 1000 kDa HA and further investigated its role in ovarian cancer. DAB2 was downregulated in ovarian cancer compared to normal tissues but increased in metastatic ovarian tumors compared to primary tumors. High DAB2 expression was associated with poor patient outcome and positively correlated with HA synthesis enzyme HAS2, HA receptor CD44 and EMT and macrophage markers. Stromal DAB2 immunostaining was significantly increased in matched ovarian cancer tissues at relapse compared to diagnosis and associated with reduced survival. The proportion of DAB2 positive macrophages was significantly increased in metastatic ovarian cancer tissues compared to primary cancers. However, DAB2 overexpression significantly reduced invasion by both A2780 and OVCAR3 cells in vivo. Our research identifies a novel relationship between HA signalling, Notch3 and DAB2. We highlight a complex relationship of both pro-tumorigenic and tumor suppressive functions of DAB2 in ovarian cancer. Our findings highlight that DAB2 has a direct tumor suppressive role on ovarian cancer cells. The pro-tumorigenic role of DAB2 may be mediated by tumour associated macrophages and requires further investigation.

Effects of Hyaluronan on Breast Cancer Aggressiveness

The expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) in breast cancer cells is critical for determining tumor aggressiveness and targeting therapies. The presence of such receptors allows for the use of antagonists that effectively reduce breast cancer growth and dissemination. However, the absence of such receptors in triple-negative breast cancer (TNBC) reduces the possibility of targeted therapy, making these tumors very aggressive with a poor outcome. Cancers are not solely composed of tumor cells, but also include several types of infiltrating cells, such as fibroblasts, macrophages, and other immune cells that have critical functions in regulating cancer cell behaviors. In addition to these cells, the extracellular matrix (ECM) has become an important player in many aspects of breast cancer biology, including cell growth, motility, metabolism, and chemoresistance. Hyaluronan (HA) is a key ECM component that promotes cell proliferation and migration in several malignancies. Notably, HA accumulation in the tumor stroma is a negative prognostic factor in breast cancer. HA metabolism depends on the fine balance between HA synthesis by HA synthases and degradation yielded by hyaluronidases. All the different cell types present in the tumor can release HA in the ECM, and in this review, we will describe the role of HA and HA metabolism in different breast cancer subtypes.

Receptor for hyaluronan-mediated motility (RHAMM) defines an invasive niche associated with tumor progression and predicts poor outcomes in breast cancer patients

Breast cancer invasion and metastasis result from a complex interplay between tumor cells and the tumor microenvironment (TME). Key oncogenic changes in the TME include aberrant synthesis, processing, and signaling of hyaluronan (HA). Hyaluronan-mediated motility receptor (RHAMM, CD168; HMMR) is an HA receptor enabling tumor cells to sense and respond to this aberrant TME during breast cancer progression. Previous studies have associated RHAMM expression with breast tumor progression; however, cause and effect mechanisms are incompletely established. Focused gene expression analysis of an internal breast cancer patient cohort confirmed that increased RHAMM expression correlates with aggressive clinicopathological features. To probe mechanisms, we developed a novel 27-gene RHAMM-related signature (RRS) by intersecting differentially expressed genes in lymph node (LN)-positive patient cases with the transcriptome of a RHAMM-dependent model of cell transformation, which we validated in an independent cohort. We demonstrate that the RRS predicts for poor survival and is enriched for cell cycle and TME-interaction pathways. Further analyses using CRISPR/Cas9-generated RHAMM-/- breast cancer cells provided direct evidence that RHAMM promotes invasion in vitro and in vivo. Immunohistochemistry studies highlighted heterogeneous RHAMM protein expression, and spatial transcriptomics associated the RRS with RHAMM-high microanatomic foci. We conclude that RHAMM upregulation leads to the formation of 'invasive niches', which are enriched in RRS-related pathways that drive invasion and could be targeted to limit invasive progression and improve patient outcomes. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Conditional expression of endorepellin in the tumor vasculature attenuates breast cancer growth, angiogenesis and hyaluronan deposition

The tumor stroma of most solid malignancies is characterized by a pathological accumulation of pro-angiogenic and pro-tumorigenic hyaluronan driving tumorigenesis and metastatic potential. Of all three hyaluronan synthase isoforms, HAS2 is the primary enzyme that promotes the build-up of tumorigenic HA in breast cancer. Previously, we discovered that endorepellin, the angiostatic C-terminal fragment of perlecan, evokes a catabolic mechanism targeting endothelial HAS2 and hyaluronan via autophagic induction. To explore the translational implications of endorepellin in breast cancer, we created a double transgenic, inducible Tie2CreERT2;endorepellin(ER)Ki mouse line that expresses recombinant endorepellin specifically from the endothelium. We investigated the therapeutic effects of recombinant endorepellin overexpression in an orthotopic, syngeneic breast cancer allograft mouse model. First, adenoviral delivery of Cre evoking intratumor expression of endorepellin in ERKi mice suppressed breast cancer growth, peritumor hyaluronan and angiogenesis. Moreover, tamoxifen-induced expression of recombinant endorepellin specifically from the endothelium in Tie2CreERT2;ERKi mice markedly suppressed breast cancer allograft growth, hyaluronan deposition in the tumor proper and perivascular tissues, and tumor angiogenesis. These results provide insight into the tumor suppressing activity of endorepellin at the molecular level and implicate endorepellin as a promising cancer protein therapy that targets hyaluronan in the tumor microenvironment.

Hyaluronan and Reactive Oxygen Species Signaling—Novel Cues from the Matrix?

Hyaluronan (HA) is a naturally occurring non-sulfated glycosaminoglycan (GAG) localized to the cell surface and the tissue extracellular matrix (ECM). It is composed of disaccharides containing glucuronic acid and N-acetylglucosamine, is synthesized by the HA synthase (HAS) enzymes and is degraded by hyaluronidase (HYAL) or reactive oxygen and nitrogen species (ROS/RNS) actions. HA is deposited as a high molecular weight (HMW) polymer and degraded to low molecular weight (LMW) fragments and oligosaccharides. HA affects biological functions by interacting with HA-binding proteins (hyaladherins). HMW HA is anti-inflammatory, immunosuppressive, and antiangiogenic, whereas LMW HA has pro-inflammatory, pro-angiogenetic, and oncogenic effects. ROS/RNS naturally degrade HMW HA, albeit at enhanced levels during tissue injury and inflammatory processes. Thus, the degradation of endothelial glycocalyx HA by increased ROS challenges vascular integrity and can initiate several disease progressions. Conversely, HA exerts a vital role in wound healing through ROS-mediated HA modifications, which affect the innate immune system. The normal turnover of HA protects against matrix rigidification. Insufficient turnover leads to increased tissue rigidity, leading to tissue dysfunction. Both endogenous and exogenous HMW HA have a scavenging capacity against ROS. The interactions of ROS/RNS with HA are more complex than presently perceived and present an important research topic.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

Low molecular weight hyaluronan inhibits lung epithelial ion channels by activating the calcium-sensing receptor

Herein, we tested the hypothesis that low molecular weight hyaluronan (LMW-HA) inhibits lung epithelial ions transport in-vivo, ex-vivo, and in-vitro by activating the calcium-sensing receptor (CaSR). Twenty-four hours post intranasal instillation of 50-150 µg/ml LMW-HA to C57BL/6 mice, there was a 75% inhibition of alveolar fluid clearance (AFC), a threefold increase in the epithelial lining fluid (ELF) depth, and a 20% increase in lung wet/dry (W/D) ratio. Incubation of human and mouse precision cut lung slices with 150 µg/ml LMW-HA reduced the activity and the open probability (Po) of epithelial sodium channel (ENaC) in alveolar epithelial type 2 (ATII) cells, and in mouse tracheal epithelial cells (MTEC) monolayers as early as 4 h. The Cl- current through cystic fibrosis transmembrane conductance regulator (CFTR) and the activity of Na,K-ATPase were both inhibited by more than 66% at 24 h. The inhibitory effects of LMW-HA on ion channels were reversed by 1 µM NPS-2143, or 150 µg/ml high molecular weight hyaluronan (HMW-HA). In HEK-293 cells expressing the calcium-sensitive Cl- channel TMEM16-A, CaSR was required for the activation of the Cl- current by LMW-HA. This is the first demonstration of lung ions and water transport inhibition by LMW-HA, and its mediation through the activation of CaSR.

Characterization of Hyaluronan Localization in the Developing Mammary Gland and Mammary Tumors

The extracellular matrix (ECM) is biochemically and biomechanically important for the structure and function of the mammary gland, which undergoes vast structural changes throughout pubertal and reproductive development. Although hyaluronan (HA) is a ubiquitous glycosaminoglycan (GAG) of the mammary gland ECM, extensive characterization of HA deposition in the mammary gland is lacking. Understanding physiologic HA metabolism is critical as this tightly controlled system is often hijacked in cancer. In the current studies, we characterize HA regulation throughout mammary gland development to better understand subsequent dysregulation of HA in mammary tumors. Using immunofluorescence (IF) imaging, we demonstrate that organized HA-rich septa exist in the mammary gland stroma throughout puberty, pregnancy, and involution. Furthermore, we find heterogeneous HA deposition within two murine models of breast cancer. Using cell specific isolation techniques, we characterize expression of genes associated with HA binding, synthesis, and degradation within EpCAM + epithelial cells, CD90.2 + fibroblasts, and F4/80 + macrophages isolated from mammary glands and tumors. Most notably, we identify elevated levels of the hyaluronidases Hyal1 and Hyal2 in tumor-association macrophages (TAMs), suggesting a role for TAM-mediated turnover of HA in the tumor microenvironment (TME). Gene expression is supported functionally by in vitro experiments in which macrophages treated with tumor-cell conditioned media exhibit increased hyaluronidase activity. These findings link TAMs to the direct degradation of HA within the TME of mammary tumors, which has negative implications for patient survival.

A Comprehensive Review of Electrospun Fibers, 3D-Printed Scaffolds, and Hydrogels for Cancer Therapies

Anticancer therapies and regenerative medicine are being developed to destroy tumor cells, as well as remodel, replace, and support injured organs and tissues. Nowadays, a suitable three-dimensional structure of the scaffold and the type of cells used are crucial for creating bio-inspired organs and tissues. The materials used in medicine are made of non-degradable and degradable biomaterials and can serve as drug carriers. Developing flexible and properly targeted drug carrier systems is crucial for tissue engineering, regenerative medicine, and novel cancer treatment strategies. This review is focused on presenting innovative biomaterials, i.e., electrospun nanofibers, 3D-printed scaffolds, and hydrogels as a novel approach for anticancer treatments which are still under development and awaiting thorough optimization.

Selective isolation of hyaluronan by solid phase adsorption to silica

A solid phase adsorption method for selective isolation of hyaluronan (HA) from biological samples is presented. Following enzymatic degradation of protein, HA can be separated from sulfated glycosaminoglycans, other unsulfated glycosaminoglycans, nucleic acids, and proteolytic fragments by adsorption to amorphous silica at specific salt concentrations. The adsorbed HA can be released from silica using neutral and basic aqueous solutions. HA ranging in size from ∼9 kDa to MDa polymers has been purified by this method from human serum and conditioned medium of cultured cells.

Hyaluronan network: a driving force in cancer progression

Hyaluronan is one of the most abundant macromolecules of the extracellular matrix and regulates several physiological cell and tissue properties. However, hyaluronan has been shown to accumulate together with its receptors in various cancers. In tumors, accumulation of hyaluronan system components (hyaluronan synthesizing/degrading enzymes and interacting proteins) associates with poor outcomes of the patients. In this article, we review the main roles of hyaluronan in normal physiology and cancer, and further discuss the targeting of hyaluronan system as an applicable therapeutic strategy.

Methods for isolating and analyzing physiological hyaluronan: a review

The carbohydrate hyaluronan (or hyaluronic acid, HA) is found in all human tissues and biofluids where it has wide-ranging functions in health and disease that are dictated by both its abundance and size. Consequently, hyaluronan evaluation in physiological samples has significant translational potential. Although the analytical tools and techniques for probing other biomolecules such as proteins and nucleic acids have become standard approaches in biochemistry, those available for investigating hyaluronan are less well established. In this review, we survey methods related to the assessment of native hyaluronan in biological specimens, including protocols for separating it from biological matrices and technologies for determining its concentration and molecular weight.

Mechanical control of tissue shape: Cell-extrinsic and -intrinsic mechanisms join forces to regulate morphogenesis

During vertebrate development, cells must proliferate, move, and differentiate to form complex shapes. Elucidating the mechanisms underlying the molecular and cellular processes involved in tissue morphogenesis is essential to understanding developmental programmes. Mechanical stimuli act as a major contributor of morphogenetic processes and impact on cell behaviours to regulate tissue shape and size. Specifically, cell extrinsic physical forces are translated into biochemical signals within cells, through the process of mechanotransduction, activating multiple mechanosensitive pathways and defining cell behaviours. Physical forces generated by tissue mechanics and the extracellular matrix are crucial to orchestrate tissue patterning and cell fate specification. At the cell scale, the actomyosin network generates the cellular tension behind the tissue mechanics involved in building tissue. Thus, understanding the role of physical forces during morphogenetic processes requires the consideration of the contribution of cell intrinsic and cell extrinsic influences. The recent development of multidisciplinary approaches, as well as major advances in genetics, microscopy, and force-probing tools, have been key to push this field forward. With this review, we aim to discuss recent work on how tissue shape can be controlled by mechanical forces by focusing specifically on vertebrate organogenesis. We consider the influences of mechanical forces by discussing the cell-intrinsic forces (such as cell tension and proliferation) and cell-extrinsic forces (such as substrate stiffness and flow forces). We review recently described processes supporting the role of intratissue force generation and propagation in the context of shape emergence. Lastly, we discuss the emerging role of tissue-scale changes in tissue material properties, extrinsic forces, and shear stress on shape establishment.

Modulation of Cell-Cycle Progression by Hydrogen Peroxide-Mediated Cross-Linking and Degradation of Cell-Adhesive Hydrogels

The cell cycle is known to be regulated by features such as the mechanical properties of the surrounding environment and interaction of cells with the adhering substrates. Here, we investigated the possibility of regulating cell-cycle progression of the cells on gelatin/hyaluronic acid composite hydrogels obtained through hydrogen peroxide (H₂O₂)-mediated cross-linking and degradation of the polymers by varying the exposure time to H₂O₂ contained in the air. The stiffness of the hydrogel varied with the exposure time. Human cervical cancer cells (HeLa) and mouse mammary gland epithelial cells (NMuMG) expressing cell-cycle reporter Fucci2 showed the exposure-time-dependent different cell-cycle progressions on the hydrogels. Although HeLa/Fucci2 cells cultured on the soft hydrogel (Young’s modulus: 0.20 and 0.40 kPa) obtained through 15 min and 120 min of the H₂O₂ exposure showed a G2/M-phase arrest, NMuMG cells showed a G1-phase arrest. Additionally, the cell-cycle progression of NMuMG cells was not only governed by the hydrogel stiffness, but also by the low-molecular-weight HA resulting from H₂O₂-mediated degradation. These results indicate that H₂O₂-mediated cross-linking and degradation of gelatin/hyaluronic acid composite hydrogel could be used to control the cell adhesion and cell-cycle progression.

Heterogeneity and function of macrophages in the breast during homeostasis and cancer

Macrophages are diverse immune cells populating all tissues and adopting a unique tissue-specific identity. Breast macrophages play an essential role in the development and function of the mammary gland over one's lifetime. In the recent years, with the development of fate-mapping, imaging and scRNA-seq technologies we grew a better understanding of the origin, heterogeneity and function of mammary macrophages in homeostasis but also during breast cancer development. Here, we aim to provide a comprehensive review of the latest improvements in studying the macrophage heterogeneity in healthy mammary tissues and breast cancer.

Hyaluronic acid and proliferation/cellular death amount in the female rats mammary gland after estroprogestative therapy

AIMS

To evaluate the concentration of hyaluronan acid and proliferation/cellular death in mammary gland of ovariectomized female rat after estroprogestative therapy.

MATERIALS AND METHODS

Forty ovariectomized female rats were divided into four groups with 10 animals/each: OG (vehicle); EG: (Estradiol, 7 days of treatment), PG (Progesterone acetate, 23 days of treatment), and EPG: (Estradiol, 7 days of treatment, and next Progesterone acetate, 23 days of treatment). Twenty-four hours after the last treatment, all animals were euthanized, the mammary gland removed, then, a fragment was immersed in acetone to quantifying of the hyaluronan acid biochemical method (ELISA-Like fluorometric assay), and a fragment fixed for 24 h in 10% formaldehyde in phosphate-buffered saline (PBS) processed for immunohistochemistry method for detection of the cell marker proliferation (Ki67) and cellular marker death by DNA fragmentation the TUNEL method.

RESULTS

The estradiol-treatment alone (EG) or associated with progesterone (EPG) affected the concentration of hyaluronan acid, increased cell proliferation, and decreased cell death compared to OG and PG (p < .05) in the mammary tissue.

CONCLUSIONS

Our results suggest that the excessive reduction of HA in mammary tissue, as occurred with progesterone treatment, can lead to a breakdown of the extracellular matrix. These changes may be indicative of mammary pathology such as the development of tumor.

The Impact of Hyaluronan on Tumor Progression in Cutaneous Melanoma

The incidence of cutaneous melanoma is rapidly increasing worldwide. Cutaneous melanoma is an aggressive type of skin cancer, which originates from malignant transformation of pigment producing melanocytes. The main risk factor for melanoma is ultraviolet (UV) radiation, and thus it often arises from highly sun-exposed skin areas and is characterized by a high mutational burden. In addition to melanoma-associated mutations such as BRAF, NRAS, PTEN and cell cycle regulators, the expansion of melanoma is affected by the extracellular matrix surrounding the tumor together with immune cells. In the early phases of the disease, hyaluronan is the major matrix component in cutaneous melanoma microenvironment. It is a high-molecular weight polysaccharide involved in several physiological and pathological processes. Hyaluronan is involved in the inflammatory reactions associated with UV radiation but its role in melanomagenesis is still unclear. Although abundant hyaluronan surrounds epidermal and dermal cells in normal skin and benign nevi, its content is further elevated in dysplastic lesions and local tumors. At this stage hyaluronan matrix may act as a protective barrier against melanoma progression, or alternatively against immune cell attack. While in advanced melanoma, the content of hyaluronan decreases due to altered synthesis and degradation, and this correlates with poor prognosis. This review focuses on hyaluronan matrix in cutaneous melanoma and how the changes in hyaluronan metabolism affect the progression of melanoma.

Hyaluronan Functions in Wound Repair That Are Captured to Fuel Breast Cancer Progression

Signaling from an actively remodeling extracellular matrix (ECM) has emerged as a critical factor in regulating both the repair of tissue injuries and the progression of diseases such as metastatic cancer. Hyaluronan (HA) is a major component of the ECM that normally functions in tissue injury to sequentially promote then suppress inflammation and fibrosis, a duality in which is featured, and regulated in, wound repair. These essential response-to-injury functions of HA in the microenvironment are hijacked by tumor cells for invasion and avoidance of immune detection. In this review, we first discuss the numerous size-dependent functions of HA and emphasize the multifunctional nature of two of its receptors (CD44 and RHAMM) in regulating the signaling duality of HA in excisional wound healing. This is followed by a discussion of how HA metabolism is de-regulated in malignant progression and how targeting HA might be used to better manage breast cancer progression.

RHAMM Is a Multifunctional Protein That Regulates Cancer Progression

The functional complexity of higher organisms is not easily accounted for by the size of their genomes. Rather, complexity appears to be generated by transcriptional, translational, and post-translational mechanisms and tissue organization that produces a context-dependent response of cells to specific stimuli. One property of gene products that likely increases the ability of cells to respond to stimuli with complexity is the multifunctionality of expressed proteins. Receptor for hyaluronan-mediated motility (RHAMM) is an example of a multifunctional protein that controls differential responses of cells in response-to-injury contexts. Here, we trace its evolution into a sensor-transducer of tissue injury signals in higher organisms through the detection of hyaluronan (HA) that accumulates in injured microenvironments. Our goal is to highlight the domain and isoform structures that generate RHAMM's function complexity and model approaches for targeting its key functions to control cancer progression.

Molecular mechanisms of mammary gland remodeling: A review of the homeostatic versus bisphenol a disrupted microenvironment

Mammary gland (MG) undergoes critical points of structural changes throughout a woman's life. During the perinatal and pubertal stages, MG develops through growth and differentiation to establish a pre-mature feature. If pregnancy and lactation occur, the epithelial compartment branches and differentiates to create a specialized structure for milk secretion and nurturing of the newborn. However, the ultimate MG modification consists of a regression process aiming to reestablish the smaller and less energy demanding structure until another production cycle happens. The unraveling of these fascinating physiologic cycles has helped the scientific community elucidate aspects of molecular regulation of proliferative and apoptotic events and remodeling of the stromal compartment. However, greater understanding of the hormonal pathways involved in MG developmental stages led to concern that endocrine disruptors such as bisphenol A (BPA), may influence these specific development/involution stages, called "windows of susceptibility". Since it is used in the manufacture of polycarbonate plastics and epoxy resins, BPA is a ubiquitous chemical present in human everyday life, exerting an estrogenic effect. Thus, descriptions of its deleterious effects on the MG, especially in terms of serum hormone concentrations, hormonal receptor expression, molecular pathways, and epigenetic alterations, have been widely published. Therefore, allied to a didactic description of the main physiological mechanisms involved in different critical points of MG development, the current review provides a summary of key mechanisms by which the endocrine disruptor BPA impacts MG homeostasis at different windows of susceptibility, causing short- and long-term effects.

Molar mass effect in food and health

It is demanded to supply foods with good quality for all the humans. With the advent of aging society, palatable and healthy foods are required to improve the quality of life and reduce the burden of finance for medical expenditure. Food hydrocolloids can contribute to this demand by versatile functions such as thickening, gelling, stabilising, and emulsifying, controlling texture and flavour release in food processing. Molar mass effects on viscosity and diffusion in liquid foods, and on mechanical and other physical properties of solid and semi-solid foods and films are overviewed. In these functions, the molar mass is one of the key factors, and therefore, the effects of molar mass on various health problems related to noncommunicable diseases or symptoms such as cancer, hyperlipidemia, hyperglycemia, constipation, high blood pressure, knee pain, osteoporosis, cystic fibrosis and dysphagia are described. Understanding these problems only from the viewpoint of molar mass is limited since other structural characteristics, conformation, branching, blockiness in copolymers such as pectin and alginate, degree of substitution as well as the position of the substituents are sometimes the determining factor rather than the molar mass. Nevertheless, comparison of different behaviours and functions in different polymers from the viewpoint of molar mass is expected to be useful to find a common characteristics, which may be helpful to understand the mechanism in other problems.

Autophagic degradation of HAS2 in endothelial cells: A novel mechanism to regulate angiogenesis

Hyaluronan plays a key role in regulating inflammation and tumor angiogenesis. Of the three transmembrane hyaluronan synthases, HAS2 is the main pro-angiogenic enzyme responsible for excessive hyaluronan production. We discovered that HAS2 was degraded in vascular endothelial cells via autophagy evoked by nutrient deprivation, mTOR inhibition, or pro-autophagic proteoglycan fragments endorepellin and endostatin. Using live-cell and super-resolution confocal microscopy, we found that protracted autophagy evoked a dynamic interaction between HAS2 and ATG9A, a key transmembrane autophagic protein. This regulatory axis of HAS2 degradation occurred in various cell types and species and in vivo upon nutrient deprivation. Inhibiting in vivo autophagic flux via chloroquine showed increased levels of HAS2 in the heart and aorta. Functionally, autophagic induction via endorepellin or mTOR inhibition markedly suppressed extracellular hyaluronan production in vascular endothelial cells and inhibited ex vivo angiogenic sprouting. Thus, we propose autophagy as a novel catabolic mechanism regulating hyaluronan production in endothelial cells and demonstrate a new link between autophagy and angiogenesis that could lead to potential therapeutic modalities for angiogenesis.

Tissue-resident macrophages promote extracellular matrix homeostasis in the mammary gland stroma of nulliparous mice

Tissue-resident macrophages in the mammary gland are found in close association with epithelial structures and within the adipose stroma, and are important for mammary gland development and tissue homeostasis. Macrophages have been linked to ductal development in the virgin mammary gland, but less is known regarding the effects of macrophages on the adipose stroma. Using transcriptional profiling and single-cell RNA sequencing approaches, we identify a distinct resident stromal macrophage subpopulation within the mouse nulliparous mammary gland that is characterized by the expression of Lyve-1, a receptor for the extracellular matrix (ECM) component hyaluronan. This subpopulation is enriched in genes associated with ECM remodeling and is specifically associated with hyaluronan-rich regions within the adipose stroma and fibrous capsule of the virgin mammary gland. Furthermore, macrophage depletion leads to enhanced accumulation of hyaluronan-associated ECM in the adipose-associated stroma, indicating that resident macrophages are important for maintaining homeostasis within the nulliparous mammary gland stroma.

Hyaluronic acid induction on breast cancer stem cells unfolds subtype specific variations in stemness and epithelial-to-mesenchymal transition

The reoccurrence of breast cancer is a major concern due to presence of cancer stem cells (CSCs). Considering the key role of hyaluronic acid (HA) in modulating the inflammation and cellular migration in cancer, the response of high molecular weight (HMW) and low molecular weight (LMW) HA towards various subtypes of breast cancer and breast cancer stem cells remain elusive. The aim of this study is to determine the effect of exogenous HMW-HA and LMW-HA on stemness of CSCs and epithelial-to-mesenchymal transition which may help in designing HA based therapeutic strategies. LMW-HA induces EMT in MCF-7 more prominently as compared to MDA-MB-231. However, HMW-HA did not show significant changes in the expression of EMT genes. Surprisingly, both HMW-HA and LMW-HA have shown to decrease the expression of EpCAM in MCF-7 cells and decrease the expression of CD44 in MDAMB-231 cells. HA has maintained the native stem cells phenotype of bCSCs isolated from MCF-7 only. The bCSCs isolated form MDAMB-231 showed a decrease in CD44. Luminal subtype has shown to follow Wnt/β-catenin whereas in the basal subtype localization of CD44 from surface to cytosol was observed in response to HA. Our study has demonstrated that bCSCs in luminal and basal cells follow differential intracellular signaling mechanisms in response to HA. This study could significantly influence the therapeutics involving HA in breast cancer.

Hyaluronan Degradation Promotes Cancer via Hippo-YAP Signaling: An Intervention Point for Cancer Therapy

High-molecular-weight hyaluronan acts as a ligand of the tumor-suppressive Hippo signal, whereas degradation of hyaluronan from a high-molecular-weight form to a low-molecular-weight forms by hyaluronidase 2 inhibits Hippo signal activation and thereby activates the pro-oncogenic transcriptional coactivator yes-associated protein (YAP), which creates a cancer-predisposing microenvironment and drives neoplastic transformation of cells through both cell-autonomous and non-cell-autonomous mechanisms. In fact, accumulation of low-molecular-weight hyaluronan in tissue stroma is observed in many types of cancers. Since inhibition of YAP activity suppresses tumor growth in vivo, pharmacological intervention of the Hippo-YAP signal is an attractive approach for future drug development. In this review, pharmacological intervention of excessive hyaluronan degradation as a novel approach for inhibition of the Hippo-YAP signal is also discussed. Development of hyaluronidase inhibitors may provide novel therapeutic strategies for human malignant tumors.

Creating a Favorable Microenvironment for Fat Grafting in a Novel Model of Radiation-Induced Mammary Fat Pad Fibrosis

BACKGROUND

Radiofibrosis of breast tissue compromises breast reconstruction by interfering with tissue viability and healing. Autologous fat transfer may reduce radiotherapy-related tissue injury, but graft survival is compromised by the fibrotic microenvironment. Elevated expression of receptor for hyaluronan-mediated motility (RHAMM; also known as hyaluronan-mediated motility receptor, or HMMR) in wounds decreases adipogenesis and increases fibrosis. The authors therefore developed RHAMM peptide mimetics to block RHAMM profibrotic signaling following radiation. They propose that this blocking peptide will decrease radiofibrosis and establish a microenvironment favoring adipose-derived stem cell survival using a rat mammary fat pad model.

METHODS

Rat mammary fat pads underwent a one-time radiation dose of 26 Gy. Irradiated (n = 10) and nonirradiated (n = 10) fat pads received a single intramammary injection of a sham injection or peptide NPI-110. Skin changes were examined clinically. Mammary fat pad tissue was processed for fibrotic and adipogenic markers using quantitative polymerase chain reaction and immunohistochemical analysis.

RESULTS

Clinical assessments and molecular analysis confirmed radiation-induced acute skin changes and radiation-induced fibrosis in rat mammary fat pads. Peptide treatment reduced fibrosis, as detected by polarized microscopy of picrosirius red staining, increased collagen ratio of 3:1, reduced expression of collagen-1 crosslinking enzymes lysyl-oxidase, transglutaminase 2, and transforming growth factor β1 protein, and increased adiponectin, an antifibrotic adipokine. RHAMM was expressed in stromal cell subsets and was downregulated by the RHAMM peptide mimetic.

CONCLUSION

Results from this study predict that blocking RHAMM function in stromal cell subsets can provide a postradiotherapy microenvironment more suitable for fat grafting and breast reconstruction.

Molecular size-dependent specificity of hyaluronan on functional properties, morphology and matrix composition of mammary cancer cells

High levels of hyaluronan (ΗΑ), a major extracellular matrix (ECM) glycosaminoglycan, have been correlated with poor clinical outcome in several malignancies, including breast cancer. The high and low molecular weight HΑ forms exert diverse biological functions. Depending on their molecular size, ΗΑ forms either promote or attenuate signaling cascades that regulate cancer progression. In order to evaluate the effects of different ΗΑ forms on breast cancer cells' behavior, ΗΑ fragments of defined molecular size were synthesized. Breast cancer cells of different estrogen receptor (ER) status - the low metastatic, ERα-positive MCF-7 epithelial cells and the highly aggressive, ERβ-positive MDA-MB-231 mesenchymal cells - were evaluated following treatment with HA fragments. Scanning electron microscopy revealed that HA fragments critically affect the morphology of breast cancer cells in a molecular-size dependent mode. Moreover, the ΗΑ fragments affect cell functional properties, the expression of major ECM mediators and epithelial-to-mesenchymal transition (ΕΜΤ) markers. Notably, treatment with 200 kDa ΗΑ increased the expression levels of the epithelial marker Ε-cadherin and reduced the expression levels of HA synthase 2 and mesenchymal markers, like fibronectin and snail2/slug. These novel data suggest that the effects of HA in breast cancer cells depend on the molecular size and the ER status. An in-depth understanding on the mechanistic basis of these effects may contribute on the development of novel therapeutic strategies for the pharmacological targeting of aggressive breast cancer.

Dissecting the role of hyaluronan synthases in the tumor microenvironment

The tumor microenvironment is becoming a crucial factor in determining the aggressiveness of neoplastic cells. The glycosaminoglycan hyaluronan is one of the principal constituents of both the tumor stroma and the cancer cell surfaces, and its accumulation can dramatically influence patient survival. Hyaluronan functions are dictated by its ability to interact with several signaling receptors that often activate pro-angiogenic and pro-tumorigenic intracellular pathways. Although hyaluronan is a linear, non-sulfated polysaccharide, and thus lacks the ability of the other sulfated glycosaminoglycans to bind and modulate growth factors, it compensates for this by the ability to form hyaluronan fragments characterized by a remarkable variability in length. Here, we will focus on the role of both high and low molecular weight hyaluronan in controlling the hallmarks of cancer cells, including cell proliferation, migration, metabolism, inflammation, and angiogenesis. We will critically assess the multilayered regulation of HAS2, the most critical hyaluronan synthase, and its role in cancer growth, metabolism, and therapy.

Hyaluronan: molecular size-dependent signaling and biological functions in inflammation and cancer

Hyaluronan (HA) is a linear nonsulfated glycosaminoglycan of the extracellular matrix that plays a pivotal role in a variety of biological processes. High-molecular weight HA exhibits different biological properties than oligomers and low-molecular weight HA. Depending on their molecular size, HA fragments can influence cellular behavior in a different mode of action. This phenomenon is attributed to the different manner of interaction with the HA receptors, especially CD44 and RHAMM. Both receptors can trigger signaling cascades that regulate cell functional properties, such as proliferation migration, angiogenesis, and wound healing. HA fragments are able to enhance or attenuate the HA receptor-mediated signaling pathways, as they compete with the endogenous HA for binding to the receptors. The modulation of these pathways could be crucial for the development of pathological conditions, such as inflammation and cancer. The primary goal of this review is to critically present the importance of HA molecular size on cellular signaling, functional cell properties, and morphology in normal and pathological conditions, including inflammation and cancer. A deeper understanding of these mechanisms could contribute to the development of novel therapeutic strategies.

Methods for Monitoring Matrix-Induced Autophagy

A growing body of research demonstrates modulation of autophagy by a variety of matrix constituents, including decorin, endorepellin, and endostatin. These matrix proteins are both pro-autophagic and anti-angiogenic. Here, we detail a series of methods to monitor matrix-induced autophagy and its concurrent effects on angiogenesis. We first discuss cloning and purifying proteoglycan fragment and core proteins in the laboratory and review relevant techniques spanning from cell culture to treatment with these purified proteoglycans in vitro and ex vivo. Further, we cover protocols in monitoring autophagic progression via morphological and microscopic characterization, biochemical western blot analysis, and signaling pathway investigation. Downstream angiogenic effects using in vivo approaches are then discussed using wild-type mice and the GFP-LC3 transgenic mouse model. Finally, we explore matrix-induced mitophagy via monitoring changes in mitochondrial DNA and permeability.

Methods for Hyaluronan Molecular Mass Determination by Agarose Gel Electrophoresis

The average molecular mass of hyaluronan (HA) in most healthy biological fluids and tissues is usually about 6000-8000 kDa, but the biosynthetic mechanism results in a polydisperse mixture of sizes. Subsequent enzymatic degradation, or the action of reactive oxygen and nitrogen species, can further increase polydispersity and decrease the average size. Fragmented HA can be a biomarker of inflammation. In addition, reductions in HA size are associated with tissue remodeling and repair processes. Some cell-surface receptor proteins have been reported to have HA-binding affinities that are size specific, and participate in activation of signaling cascades controlling multiple aspects of cell behavior. Here we describe simple agarose gel electrophoresis protocols for the determination of the molecular mass distribution of HA isolated from tissues and fluids.

Differing Roles of Hyaluronan Molecular Weight on Cancer Cell Behavior and Chemotherapy Resistance

Hyaluronan (HA), a glycosaminoglycan located in the extracellular matrix, is important in embryo development, inflammation, wound healing and cancer. There is an extensive body of research demonstrating the role of HA in all stages of cancer, from initiation to relapse and therapy resistance. HA interacts with multiple cell surface receptors, including CD44, receptor for hyaluronan mediated motility (RHAMM) and intracellular signaling pathways, including receptor tyrosine kinase pathways, to promote the survival and proliferation of cancer cells. Additionally, HA promotes the formation of cancer stem cell (CSC) populations, which are hypothesized to be responsible for the initiation of tumors and therapy resistance. Recent studies have identified that the molecular weight of HA plays differing roles on both normal and cancer cell behavior. This review explores the role of HA in cancer progression and therapy resistance and how its molecular weight is important in regulating CSC populations, epithelial to mesenchymal transition (EMT), ATP binding cassette (ABC) transporter expression and receptor tyrosine kinase pathways.

Hyaluronic acid, CD44 and RHAMM regulate myoblast behavior during embryogenesis

Hyaluronic acid (HA) is an extracellular matrix (ECM) component that has been shown to play a significant role in regulating muscle cell behavior during repair and regeneration. For instance, ECM remodeling after muscle injury involves an upregulation in HA expression that is coupled with skeletal muscle precursor cell recruitment. However, little is known about the role of HA during skeletal muscle development. To gain insight into the way in which HA mediates embryonic myogenesis, we first determined the spatial distribution and gene expression of CD44, RHAMM and other HA related proteins in embryonic day (E)10.5 to E12.5 murine forelimbs. While HA and CD44 expression remained high, RHAMM decreased at both the protein (via immunohistochemistry) and RNA (via qPCR) levels. Next, we determined that 4-methylumbelliferone-mediated knockdown of HA synthesis inhibited the migration and proliferation of E11.5/E12.5 forelimb-derived cells. Then, the influence of CD44 and RHAMM on myoblast and connective tissue cell behavior was investigated using antibodies against these receptors. Anti-RHAMM, but not anti-CD44, significantly decreased the total distance myogenic progenitors migrated over 24 h, whereas both inhibited connective tissue cell migration. In contrast, anti-CD44 inhibited the proliferation of connective tissue cells and muscle progenitors, but anti-RHAMM had no effect. However, when myoblasts and connective tissue cells were depleted of CD44 and RHAMM by shRNA, motility and proliferation were significantly inhibited in both cells indicating that blocking cell surface-localized CD44 and RHAMM does not have as pronounced effect as global shRNA-mediated depletion of these receptors. These results show, for the first time, the distribution and activity of RHAMM in the context of skeletal muscle. Furthermore, our data indicate that HA, through interactions with CD44 and RHAMM, promotes myogenic progenitor migration and proliferation. Confirmation of the role of HA and its receptors in directing myogenesis will be useful for the design of regenerative therapies that aim to promote the restoration of damaged or diseased muscle.

Mouse Mammary Gland Whole Mount Preparation and Analysis

The mammary gland undergoes extensive remodeling during pregnancy and is also subject to neoplastic processes both of which result in histological changes of the gland epithelial structure. Since the mammary tree is a complex three-dimensional structure a method is needed that provides an overview of the entire gland. Whole mounts provide this information, are inexpensive and do not require specialized equipment. This protocol describes mammary gland isolation, whole mount preparation and analysis. Mammary gland tissue, which is removed postmortem, is stained with Carmine Alum, a nuclear stain, allowing detection of epithelial structures embedded in the adipose tissue of the mammary fat pad. Stained mammary glands are imaged by light microscopy or embedded and sectioned for histological examination. Image analysis software such as Image J can be used to quantify extensity of branching complexity, epithelial structure remodeling or hyperplastic changes.

Hyaluronan Isolation from Mouse Mammary Gland

The glycosaminoglycan hyaluronan (HA) is a key component of the extracellular matrix. The molecular weight of HA is heterogeneous and can reach from several million to several hundred daltons. The effect of HA on cell behavior is size dependent; fragmented HA acts as a danger signal, stimulates cell migration and proliferation and is proinflammatory, native high molecular weight HA suppresses inflammation. Therefore, it is important to analyze HA size distribution when studying the role of HA in tissue homeostasis and pathology. This protocol describes isolation of HA from mouse mammary glands but can also be applied to other tissues. The quality of the isolated HA is sufficient to analyze size distribution by gel electrophoresis ( Calabro et al., 2000 ).

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

This review summarizes the roles of CAFs in forming a “cancerized” fibrotic stroma favorable to tumor initiation and dissemination, in particular highlighting the functions of the extracellular matrix component hyaluronan (HA) in these processes. The structural complexity of the tumor and its host microenvironment is now well appreciated to be an important contributing factor to malignant progression and resistance-to-therapy. There are multiple components of this complexity, which include an extensive remodeling of the extracellular matrix (ECM) and associated biomechanical changes in tumor stroma. Tumor stroma is often fibrotic and rich in fibrillar type I collagen and hyaluronan (HA). Cancer-associated fibroblasts (CAFs) are a major source of this fibrotic ECM. CAFs organize collagen fibrils and these biomechanical alterations provide highways for invading carcinoma cells either under the guidance of CAFs or following their epithelial to mesenchymal transition (EMT). The increased HA metabolism of a tumor microenvironment instructs carcinoma initiation and dissemination by performing multiple functions. The key effects of HA reviewed here are its role in activating CAFs in pre-malignant and malignant stroma, and facilitating invasion by promoting motility of both CAFs and tumor cells, thus facilitating their invasion. Circulating CAFs (cCAFs) also form heterotypic clusters with circulating tumor cells (CTC), which are considered to be pre-cursors of metastatic colonies. cCAFs are likely required for extravasation of tumors cells and to form a metastatic niche suitable for new tumor colony growth. Therapeutic interventions designed to target both HA and CAFs in order to limit tumor spread and increase response to current therapies are discussed.

Extracellular matrix: The driving force of mammalian diseases

Like the major theme of a Mozart concerto, the immense and pervasive extracellular matrix drives each movement and ultimately closes the symphony, embracing a unique role as the fundamental mediator for most, if not all, ensuing intracellular events. As such, it comes as no surprise that the mechanism of just about every known disease can be traced back to some part of the matrix, typically in the form of an abnormal amount or activity level of a particular matrix component. These defects considerably affect downstream signaling axes leading to overt cellular dysfunction, organ failure, and death. From skin to bone, from vessels to brain, from eyes to all the internal organs, the matrix plays an incredible role as both a cause and potential means to reverse diseases. Human malaises including connective tissue disorders, muscular dystrophy, fibrosis, and cancer are all extracellular matrix-driven diseases. The ability to understand and modulate these matrix-related mechanisms may lead to the future discovery of novel therapeutic options for these patients.

Design of peptide mimetics to block pro-inflammatory functions of HA fragments

Hyaluronan is a simple extracellular matrix polysaccharide that actively regulates inflammation in tissue repair and disease processes. The native HA polymer, which is large (>500 kDa), contributes to the maintenance of homeostasis. In remodeling and diseased tissues, polymer size is strikingly polydisperse, ranging from <10 kDa to >500 kDa. In a diseased or stressed tissue context, both smaller HA fragments and high molecular weight HA polymers can acquire pro-inflammatory functions, which result in the activation of multiple receptors, triggering pro-inflammatory signaling to diverse stimuli. Peptide mimics that bind and scavenge HA fragments have been developed, which show efficacy in animal models of inflammation. These studies indicate both that HA fragments are key to driving inflammation and that scavenging these is a viable therapeutic approach to blunting inflammation in disease processes. This mini-review summarizes the peptide-based methods that have been reported to date for blocking HA signaling events as an anti-inflammatory therapeutic approach.

Hyaluronan and Hyaluronan Fragments

The glycosaminoglycan hyaluronan (HA) is a key component of the microenvironment surrounding cells. In healthy tissues, HA molecules have extremely high molecular mass and consequently large hydrodynamic volumes. Tethered to the cell surface by clustered receptor proteins, HA molecules crowd each other, as well as other macromolecular species. This leads to severe nonideality in physical properties of the biomatrix, because steric exclusion leads to an increase in effective concentration of the macromolecules. The excluded volume depends on both polymer concentration and hydrodynamic volume/molecular mass. The biomechanical properties of the extracellular matrix, tissue hydration, receptor clustering, and receptor-ligand interactions are strongly affected by the presence of HA and by its molecular mass. In inflammation, reactive oxygen and nitrogen species fragment the HA chains. Depending on the rate of chain degradation relative to the rates of new synthesis and removal of damaged chains, short fragments of the HA molecules can be present at significant levels. Not only are the physical properties of the extracellular matrix affected, but the HA fragments decluster their primary receptors and act as endogenous danger signals. Bioanalytical methods to isolate and quantify HA fragments have been developed to determine profiles of HA content and size in healthy and diseased biological fluids and tissues. These methods have potential use in medical diagnostic tests. Therapeutic agents that modulate signaling by HA fragments show promise in wound healing and tissue repair without fibrosis.

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

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.