Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. This study focuses on the GAG molecules chondroitin sulfate (CS), dermatan sulfate (DS), and hyaluronic acid (HA). CS and DS are stereoisomers while HA is the only non-sulfated GAG. We characterized and decoupled the effects of these GAG molecules on the stiffness, transport, and matrix microarchitecture properties of type I collagen hydrogels using mechanical indentation testing, microfluidics, and confocal reflectance imaging, respectively. We complement these biophysical measurements with turbidity assays to profile collagen aggregate formation. Surprisingly, only HA enhanced the ECM indentation modulus, while all three GAGs had no effect on hydraulic permeability. Strikingly, we show that CS, DS, and HA differentially regulate the matrix microarchitecture of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs define key physical properties of the ECM, this work shows new ways in which stiffness measurements, microfluidics, microscopy, and turbidity kinetics can be used complementarily to reveal details of collagen self-assembly and structure. STATEMENT OF SIGNIFICANCE: Collagen and glycosaminoglycans (GAGs) are integral to the structure, function, and bioactivity of the extracellular matrix (ECM). Despite widespread interest in collagen-GAG composite hydrogels, there is a lack of quantitative understanding of how different GAGs alter the biophysical properties of the ECM across tissue, cellular, and subcellular length scales. Here we show using mechanical, microfluidic, microscopy, and analytical methods and measurements that the GAG molecules chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially regulate the mechanical, transport, and microstructural properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. As such, these results will inform improved design and utilization of collagen-based scaffolds of tailored composition, mechanical properties, molecular availability due to mass transport, and microarchitecture.

Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. Here we characterized and decoupled the effects of the GAG molecules chondroitin sulfate (CS) dermatan sulfate (DS) and hyaluronic acid (HA) on the stiffness (indentation modulus), transport (hydraulic permeability), and matrix microarchitecture (pore size and fiber radius) properties of collagen-based hydrogels. We complement these biophysical measurements of collagen hydrogels with turbidity assays to profile collagen aggregate formation. Here we show that CS, DS, and HA differentially regulate the biophysical properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs play significant roles in defining key physical properties of the ECM, this work shows new ways in which stiffness measurements, microscopy, microfluidics, and turbidity kinetics can be used complementary to reveal details of collagen self-assembly and structure.

Vessel-on-a-chip models for studying microvascular physiology, transport, and function in vitro

To understand how the microvasculature grows and remodels, researchers require reproducible systems that emulate the function of living tissue. Innovative contributions toward fulfilling this important need have been made by engineered microvessels assembled in vitro with microfabrication techniques. Microfabricated vessels, commonly referred to as "vessels-on-a-chip," are from a class of cell culture technologies that uniquely integrate microscale flow phenomena, tissue-level biomolecular transport, cell-cell interactions, and proper three-dimensional (3-D) extracellular matrix environments under well-defined culture conditions. Here, we discuss the enabling attributes of microfabricated vessels that make these models more physiological compared with established cell culture techniques and the potential of these models for advancing microvascular research. This review highlights the key features of microvascular transport and physiology, critically discusses the strengths and limitations of different microfabrication strategies for studying the microvasculature, and provides a perspective on current challenges and future opportunities for vessel-on-a-chip models.

Abstract 37: RNA-seq comparisons of in vitro and in vivo cancer model platforms: Monolayer, spheroids, immunodeficient, and syngeneic mouse model

Preclinical cancer models have been vital contributors in minimizing this burden as well as understanding basic cancer cell biology, however conventional and modern cancer models do not accurately or reliably recapitulate the complex in vivo tumor environment. Clinical significance of discoveries made using in vitromodels requires an understanding of the limitations imparted from cancer cells in a non-native environment. An ideal pre-clinical cancer platform that mimicks in vivo molecular phenotypes is essential for achieving effective drug screening and personalized treatments. This study aims to elucidate biological processes deficient in conventional in vitro methods from in vivo grown allograft cancer cells via transcriptome analysis.

The effects of culturing conditions on cancer cells were analyzed via whole transcriptome RNA sequencing on a mouse mammary carcinoma (4T1) cell line grown in multiple culture conditions: 2D (monolayer) or 3D (spheroid) constructs under static or dynamic flow in addition to 4T1 cells isolated from subcutaneous or orthotopically grown tumors into the mammary fat pad of immune-competent, BALB/c mice.

Comparative analysis of whole transcriptomic profiles of 4T1 cells in differing culturing conditions reveals distinct biological processes fostered by their environment. Monolayer culture shows enrichment in gene ontologies promoting proliferation, cell cycle progression, and protein synthesis. Compared to monolayer culture all 3-dimensional culturing methods encouraged the expression of proteins known to be critical to tumor progression such as extracellular matrix remodeling, adhesion, and differentiation. Furthermore, spheroid culture introduced heterogeneity as evidenced by upregulation of hypoxic induced genes and regulation of multicellular organism development processes. As expected, 4T1 cells expanded in vivo upregulated genes associated with processes difficult to recapitulate in vitro such as cell migration, inflammatory response, and angiogenesis.

3D culturing methods are able to recapitulate aspects of tumor heterogeneity yet fail to incorporate the complex heterogeneous cell composition and transient fluxes in nutrients and drugs found in vivo. Findings from this study demonstrate the behavioral and transcriptional alterations imparted from environmental factors. Additionally, clinically relevant in vitro testing can be improved by the incorporation of factors found in the native tumor microenvironment to existing 3D culturing approaches.

This study received funding from LLNL LDRD grant 19-SI-003. This work was conducted under the auspices of the USDOE by LLNL (DE-AC52-07NA27344).

Citation Format: Nicholas Hum, Aimy Sebastian, Wei He, Monica L. Moya, William F. Hynes, Jonathan J. Adorno, Aubree Hinckley, Elizabeth K. Wheeler, Matthew A. Coleman, Gabriela G. Loots. RNA-seq comparisons of in vitro and in vivo cancer model platforms: Monolayer, spheroids, immunodeficient, and syngeneic mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 37.