Macromolecular Crowding as a Tool to Screen Anti-fibrotic Drugs: The Scar-in-a-Jar System Revisited

Underestimated role of macromolecular crowding in bioengineered in vitro models of health and diseases

Macromolecular crowding (MMC) is a ubiquitous phenomenon in biological systems that is largely overlooked in bioengineered in vitro cellular models. This comprehensive review examines the significant impact of both intracellular and extracellular MMC on cellular and molecular processes under physiological and pathological conditions. By synthesizing current knowledge and identifying critical gaps in our understanding of MMC, this review highlights the need to incorporate crowding into the development of in vitro models for studying health and diseases, as well as for drug discovery platforms. The pervasive nature of MMC in biological systems underscores its potential importance in various physiological and pathological processes, including protein aggregation disorders, cancer, and vascular diseases. Recognizing the ubiquitous influence of MMC could open new avenues for therapeutic interventions and deepen our understanding of fundamental biological processes.

Regulation of fibronectin and collagens type I, III and VI by TNF-α, TGF-β, IL-13, and tofacitinib

Understanding how inflammatory cytokines influence profibrogenic wound healing responses in fibroblasts is important for understanding the pathogenesis of fibrosis. TNF-α and IL-13 are key cytokines in Th1 and Th2 immune responses, respectively, while TGF-β1 is the principal pro-fibrotic mediator. We show that 12-day fibroblast culture with TNF-α or IL-13 induces fibrogenesis, marked by progressively increasing type III and VI collagen formation, and that TGF-β1 co-stimulation amplifies these effects. Tofacitinib substantially reduced the formation of ECM proteins in response to IL-13, while fibrogenesis in response to TNF-α or TGF-β1 was marginally inhibited. The in vitro findings were supported by clinical observations in patients with active rheumatoid arthritis, which had elevated serum type III collagen formation, indicating ongoing fibrogenesis during inflammation. After 48-60 weeks of tofacitinib treatment, type III collagen degradation, aswell as formation, were significantly decreased compared to baseline, highlighting dual anti-inflammatory and anti-fibrogenic effects of tofacitinib. In contrast, other anti-inflammatory treatments including methotrexate, adalimumab and tocilizumab demonstrated anti-inflammatory effects only. Our results highlight fibro-inflammatory profiles associated with TNF-α or IL-13 stimulation, both alone and in combination with TGF-β1, and support the use of tofacitinib as an anti-fibrogenic treatment in chronic inflammatory conditions.

Harnessing the Biomimetic Effect of Macromolecular Crowding in the Cell-Derived Model of Clubfoot Fibrosis

Fibrotic changes in pediatric clubfoot provide an opportunity to improve corrective therapy and prevent relapses with targeted drugs. This study defines the parameters of clubfoot fibrosis and presents a unique analysis of a simple pseudo-3D in vitro model for disease-specific high-throughput drug screening experiments. The model combines clubfoot-derived fibroblasts with a biomimetic cultivation environment induced by the water-soluble polymers Ficoll and Polyvinylpyrrolidone, utilizing the principle of macromolecular crowding. We achieved higher conversion of soluble collagen into insoluble collagen, accelerated formation of the extracellular matrix layer and upregulated fibrosis-related genes in the mixed Ficoll environment. To test the model, we evaluated the effect of a potential antifibrotic drug, minoxidil, emphasizing collagen content and cross-linking. While the model amplified overall collagen deposition, minoxidil effectively blocked the expression of lysyl hydroxylases, which are responsible for the increased occurrence of specific collagen cross-linking in various fibrotic tissues. This limited the formation of collagen cross-link in both the model and control environments. Our findings provide a tool for expanding preclinical research for clubfoot and similar fibroproliferative conditions.

Human amniotic membrane modulates collagen production and deposition in vitro

Pathological fibrosis is a significant complication of surgical procedures resulting from the accumulation of excess collagen at the site of repair which can compromise the tissue architecture and severely impede the function of the affected tissue. Few prophylactic treatments exist to counteract this process; however, the use of amniotic membrane allografts has demonstrated promising clinical outcomes. This study aimed to identify the underlying mechanism of action by utilizing relevant models that accurately represent the pathophysiology of the disease state. This study employed a pro-fibrotic in vitro system using TGFβ1 stimulation and macromolecular crowding techniques to evaluate the mechanism by which amniotic membrane allografts regulate collagen biosynthesis and deposition. Following treatment with dehydrated human amnion chorion membrane (DHACM), subsequent RNA sequencing and functional enrichment with Reactome pathway analysis indicated that amniotic membranes are indeed capable of regulating genes associated with the composition and function of the extracellular matrix. Furthermore, macromolecular crowding was used in vitro to expand the evaluation to include both the effects of DHACM and a lyophilized human amnion/chorion membrane (LHACM). DHACM and LHACM regulate the TGFβ pathway and myofibroblast differentiation. Additionally, both DHACM and LHACM modulate the production, secretion, and deposition of collagen type I, a primary target for pathological fibrosis. These observations support the hypothesis that amniotic membranes may interrupt pathological fibrosis by regulating collagen biosynthesis and associated pathways.

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

Factors Affecting the Evaluation of Collagen Deposition and Fibrosis In Vitro

Immune responses to biomedical implants, wound healing, and diseased tissues often involve collagen deposition by fibroblasts and other stromal cells. Dysregulated collagen deposition can lead to complications, such as biomaterial fibrosis, cardiac fibrosis, desmoplasia, liver fibrosis, and pulmonary fibrosis, which can ultimately result in losses of organ function or failure of biomedical implants. Current in vitro methods to induce collagen deposition include growing the cells under macromolecular crowding conditions or on fibronectin-coated surfaces. However, the majority of these methods have been demonstrated with a single cell line, and the combined impacts of culture conditions and postculture processing on collagen deposition have not been explored in detail. In this work, the effects of macromolecular crowding versus fibronectin coating, fixation with methanol versus fixation with paraformaldehyde, and use of plastic substrates versus glass substrates were evaluated using the WI-38 human lung fibroblast cell line. Fibronectin coating was found to provide enhanced collagen deposition under macromolecular crowding conditions, while a higher plating density led to improved collagen I deposition compared with macromolecular crowding. Collagen deposition was found to be more apparent on plastic substrates than on glass substrates. The effects of primary cells versus cell lines, and mouse cells versus human cells, were evaluated using WI-38 cells, primary human lung fibroblasts, primary human dermal fibroblasts, primary mouse lung fibroblasts, primary mouse dermal fibroblasts, and the L929 mouse fibroblast cell line. Cell lines exhibited enhanced collagen I deposition compared with primary cells. Furthermore, collagen deposition was quantified with picrosirius red staining, and plate-based drug screening through picrosirius red staining of decellularized extracellular matrices was demonstrated. The results of this study provide detailed conditions under which collagen deposition can be induced in vitro in multiple cell types, with applications including material development, development of potential antifibrotic therapies, and mechanistic investigation of disease pathways. Impact Statement This study demonstrated the effects of cell type, biological conditions, fixative, culture substrate, and staining method on in vitro collagen deposition and visualization. Further the utility of plate-based picrosirius red staining of decellularized extracellular matrices for drug screening through collagen quantification was demonstrated. These results should provide clarity and a path forward for researchers who aim to conduct in vitro experiments on collagen deposition.

AP-1 signaling modulates cardiac fibroblast stress responses

Matrix remodeling outcomes largely dictate patient survival post myocardial infarction. Moreover, human-restricted noncoding regulatory elements have been shown to worsen fibrosis, but their mechanism of action remains elusive. Here, we demonstrate, using induced pluripotent stem cell-derived cardiac fibroblasts (iCFs), that inflammatory ligands abundant in the remodeling heart after infarction activate AP-1 transcription factor signaling pathways resulting in fibrotic responses. This observed signaling induces deposition of fibronectin matrix and is further capable of supporting immune cell adhesion; pathway inhibition blocks iCF matrix production and cell adhesion. Polymorphisms in the noncoding regulatory elements within the 9p21 locus (also referred to as ANRIL) redirect stress programs, and in iCFs, they transcriptionally silence the AP-1 inducible transcription factor GATA5. The presence of these polymorphisms modulate iCF matrix production and assembly and reduce cell-cell signaling. These data suggest that this signaling axis is a critical modulator of cardiac disease models and might be influenced by noncoding regulatory elements.

Tumour enzyme affinity mediated peptide molecular crowding for targeted disruption of hyperactivated glucose uptake

An unconventional environment-responsive molecular crowding via specific binding between small molecule peptide inhibitor derivatives and an overexpressed tumour enzyme has been developed. Assemblies of such short peptides selectively localize on tumour surfaces and exhibited unique functions in disrupting hyperactivated glucose uptake, providing novel insights towards strategic tumour treatment.

Macromolecular cryoprotectants for the preservation of mammalian cell culture: lessons from crowding, overview and perspectives

Cryopreservation is a process used for the storage of mammalian cells at a very low temperature, in a state of 'suspended animation.' Highly effective and safe macromolecular cryoprotectants (CPAs) have gained significant attention as they obviate the toxicity of conventional CPAs like dimethyl sulfoxide (DMSO) and reduce the risks involved in the storage of cultures at liquid nitrogen temperatures. These agents provide cryoprotection through multiple mechanisms, involving extracellular and intracellular macromolecular crowding, thereby impacting the biophysical and biochemical dynamics of the freezing medium and the cryopreserved cells. These CPAs vary in their structures and physicochemical properties, which influence their cryoprotective activities. Moreover, the introduction of polymeric crowders in the cryopreservation media enables serum-free storage at low-DMSO concentrations and high-temperature vitrification of frozen cultures (-80 °C). This review highlights the need for macromolecular CPAs and describes their mechanisms of cryopreservation, by elucidating the role of crowding effects. It also classifies the macromolecules based on their chemistry and their structure-activity relationships. Furthermore, this article provides perspectives on the factors that may influence the outcomes of the cell freezing process or may help in designing and evaluating prospective macromolecules. This manuscript also includes case studies about cellular investigations that have been conducted to demonstrate the cryoprotective potential of macromolecular CPAs. Ultimately, this review provides essential directives that will further improve the cell cryopreservation process and may encourage the use of macromolecular CPAs to fortify basic, applied, and translational research.

Improved epicardial cardiac fibroblast generation from iPSCs

Since the initial isolation of human embryonic stem cells and subsequent discovery of reprogramming methods for somatic cells, thousands of protocols have been developed to create each of the hundreds of cell types found in-vivo with significant focus on disease-prone systems, e.g., cardiovascular. Robust protocols exist for many of these cell types, except for cardiac fibroblasts (CF). Very recently, several competing methods have been developed to generate these cells through a developmentally conserved epicardial pathway. Such methods generate epicardial cells, but here we report that prolonged exposure to growth factors such as bFGF induces fibroblast spindle-like morphology and similar chromatin architecture to primary CFs. Media conditions for growth and assays are provided, as well as suggestions for seeding densities and timepoints for protein harvest of extracellular matrix. We demonstrate marker expression and matrix competency of resultant cells as shown next to primary human cardiac fibroblasts. These methods provide additional guidance to the original protocol and result in an increasingly stable phenotype.