Stable recombinant production of codon-scrambled lubricin and mucin in human cells

Advances in viscosupplementation and tribosupplementation for early-stage osteoarthritis therapy

Joint kinematic instability, arising from congenital or acquired musculoskeletal pathoanatomy or from imbalances in anabolism and catabolism induced by pathophysiological factors, leads to deterioration of the composition, structure and function of cartilage and, ultimately, progression to osteoarthritis (OA). Alongside articular cartilage degeneration, synovial fluid lubricity decreases in OA owing to a reduction in the concentration and molecular weight of hyaluronic acid and surface-active mucinous glycoproteins that form a lubricating film over the articulating joint surfaces. Minimizing friction between articulating joint surfaces by lubrication is fundamental for decreasing hyaline cartilage wear and for maintaining the function of synovial joints. Augmentation with highly viscous supplements (that is, viscosupplementation) offers one approach to re-establishing the rheological and tribological properties of synovial fluid in OA. However, this approach has varied clinical outcomes owing to limited intra-articular residence time and ineffective mechanisms of chondroprotection. This Review discusses normal hyaline cartilage function and lubrication and examines the advantages and disadvantages of various strategies for restoring normal joint lubrication. These strategies include contemporary viscosupplements that contain antioxidants, anti-inflammatory drugs or platelet-rich plasma and new synthetic synovial fluid additives and cartilage matrix enhancers. Advanced biomimetic tribosupplements offer promise for mitigating cartilage wear, restoring joint function and, ultimately, improving patient care.

Recombinant manufacturing of multispecies biolubricants

Lubricin, a lubricating glycoprotein abundant in synovial fluid, forms a low-friction brush polymer interface in tissues exposed to sliding motion including joints, tendon sheaths, and the surface of the eye. Despite its therapeutic potential in diseases such as osteoarthritis and dry eye disease, there are few sources available. Through rational design, we developed a series of recombinant lubricin analogs that utilize the species-specific tissue-binding domains at the N- and C-termini to increase biocompatibility while replacing the central mucin domain with an engineered variant that retains the lubricating properties of native lubricin. In this study, we demonstrate the tissue binding capacity of our engineered lubricin product and its retention in the joint space of rats. Next, we present a new bioprocess chain that utilizes a human-derived cell line to produce O-glycosylation consistent with that of native lubricin and a purification strategy that capitalizes on the positively charged, hydrophobic N- and C-terminal domains. The bioprocess chain is demonstrated at 10 L scale in industry-standard equipment utilizing commonly available ion exchange, hydrophobic interaction and size exclusion chromatography resins. Finally, we confirmed the purity and lubricating properties of the recombinant biolubricant. The biomolecular engineering and bioprocessing strategies presented here are an effective means of lubricin production and could have broad applications to the study of mucins in general.

Recombinant Production of Glycoengineered Mucins in HEK293-F Cells

Recombinant mucins are attractive polymeric building blocks for new biomaterials, biolubricants, and therapeutics. Advances in glycoengineered host cell systems now enable the recombinant production of mucins with tailored O-glycan side chains, offering new opportunities to tune the functionality of mucins and investigate the biology of specific O-glycan structures. Here, we provide a protocol for the scalable production of glycoengineered mucins and mucin-like glycoproteins in suspension-adapted HEK293-F cells. The protocol includes the preparation of engineered cell lines with homozygous knockout (KO) of glycosyltransferases using CRISPR/Cas9 and homology-directed repair (HDR) templates designed for efficient screening of clones. Strategies are provided for the stable introduction of mucin expression cassettes into the HEK293-F genome and the subsequent isolation of high-expressing cell populations. The high-titer production of recombinant mucins in conventional shaker flasks is described as an example production strategy using these cell lines.

A review of recent advances and applications of machine learning in tribology

In tribology, a considerable number of computational and experimental approaches to understand the interfacial characteristics of material surfaces in motion and tribological behaviors of materials have been considered to date. Despite being useful in providing important insights on the tribological properties of a system, at different length scales, a vast amount of data generated from these state-of-the-art techniques remains underutilized due to lack of analysis methods or limitations of existing analysis techniques. In principle, this data can be used to address intractable tribological problems including structure-property relationships in tribological systems and efficient lubricant design in a cost and time effective manner with the aid of machine learning. Specifically, data-driven machine learning methods have shown potential in unraveling complicated processes through the development of structure-property/functionality relationships based on the collected data. For example, neural networks are incredibly effective in modeling non-linear correlations and identifying primary hidden patterns associated with these phenomena. Here we present several exemplary studies that have demonstrated the proficiency of machine learning in understanding these critical factors. A successful implementation of neural networks, supervised, and stochastic learning approaches in identifying structure-property relationships have shed light on how machine learning may be used in certain tribological applications. Moreover, ranging from the design of lubricants, composites, and experimental processes to studying fretting wear and frictional mechanism, machine learning has been embraced either independently or integrated with optimization algorithms by scientists to study tribology. Accordingly, this review aims at providing a perspective on the recent advances in the applications of machine learning in tribology. The review on referenced simulation approaches and subsequent applications of machine learning in experimental and computational tribology shall motivate researchers to introduce the revolutionary approach of machine learning in efficiently studying tribology.

Mucin-Like Glycoproteins Modulate Interfacial Properties of a Mimetic Ocular Epithelial Surface

Dry eye disease (DED) has high personal and societal costs, but its pathology remains elusive due to intertwined biophysical and biochemical processes at the ocular surface. Specifically, mucin deficiency is reported in a subset of DED patients, but its effects on ocular interfacial properties remain unclear. Herein a novel in vitro mucin-deficient mimetic ocular surface (Mu-DeMOS) with a controllable amount of membrane-tethered mucin molecules is developed to represent the diseased ocular surfaces. Contact angle goniometry on mimetic ocular surfaces reveals that high surface roughness, but not the presence of hydrophilic mucin molecules, delivers constant hydration over native ocular surface epithelia. Live-cell rheometry confirms that the presence of mucin-like glycoproteins on ocular epithelial cells reduces shear adhesive strength at cellular interfaces. Together, optimal surface roughness and surface chemistry facilitate sustainable lubrication for healthy ocular surfaces, while an imbalance between them contributes to lubrication-related dysfunction at diseased ocular epithelial surfaces. Furthermore, the restoration of low adhesive strength at Mu-DeMOS interfaces through a mucin-like glycoprotein, recombinant human lubricin, suggests that increased frictional damage at mucin-deficient cellular surfaces may be reversible. More broadly, these results demonstrate that Mu-DeMOS is a promising platform for drug screening assays and fundamental studies on ocular physiology.

Bioproduction of biomacromolecules for antiviral applications

The societal damage brought on by viral epidemics indicates that next-generation antiviral treatments must be developed and deployed. Biomacromolecules are a diverse class of compounds that can potentially exhibit potent antiviral activity. Their efficacy and mechanisms of action are dependent upon multiple structural factors, including molecular weight, degree and position of sulfation, and backbone stereochemistry. Extracting biomacromolecules from animals and plants for healthcare applications is undesirable, as these methods are unable to yield products with well-defined chemical structures. Modern advances utilizing recombinant microbes and metabolic pathway engineering can be a key step towards large-scale bioproduction of tailored biomacromolecules for targeted antiviral applications.

Synthetic Glycobiology: Parts, Systems, and Applications

Protein glycosylation, the attachment of sugars to amino acid side chains, can endow proteins with a wide variety of properties of great interest to the engineering biology community. However, natural glycosylation systems are limited in the diversity of glycoproteins they can synthesize, the scale at which they can be harnessed for biotechnology, and the homogeneity of glycoprotein structures they can produce. Here we provide an overview of the emerging field of synthetic glycobiology, the application of synthetic biology tools and design principles to better understand and engineer glycosylation. Specifically, we focus on how the biosynthetic and analytical tools of synthetic biology have been used to redesign glycosylation systems to obtain defined glycosylation structures on proteins for diverse applications in medicine, materials, and diagnostics. We review the key biological parts available to synthetic biologists interested in engineering glycoproteins to solve compelling problems in glycoscience, describe recent efforts to construct synthetic glycoprotein synthesis systems, and outline exemplary applications as well as new opportunities in this emerging space.

A Century of Cartilage Tribology Research Is Informing Lubrication Therapies

Articular cartilage is one of the most unique materials found in nature. This tissue's ability to provide low friction and low wear over decades of constant use is not surpassed, as of yet, by any synthetic materials. Lubrication of the body's joints is essential to mammalian locomotion, but breakdown and degeneration of cartilage is the leading cause of severe disability in the industrialized world. In this paper, we review how theories of cartilage lubrication have evolved over the past decades and connect how theories of cartilage lubrication have been translated to lubrication-based therapies. Here, we call upon these historical perspectives and highlight the open questions in cartilage lubrication research. Additionally, these open questions within the field's understanding of natural lubrication mechanisms reveal strategic directions for lubrication therapy.

Influence of Block Length on Articular Cartilage Lubrication with a Diblock Bottle-Brush Copolymer

We report how the tribological properties of a class of diblock copolymers with architecture and function inspired by the lubricating glycoprotein lubricin correlate to chemical composition. This class of diblock copolymers, consisting of a cationic cartilage-binding block and a brush-lubricating block, demonstrates that boundary lubrication of articular cartilage more strongly depends on the cartilage-binding block than the lubrication block. Specifically, the cartilage-binding functional groups (tertiary or quaternary amines) and cartilage-binding block length significantly influence the degree of lubrication under boundary mode experimental conditions. An optimal number (∼24 in this case) of cartilage-binding groups led to the lowest coefficient of friction, and an increase or decrease in the number of cations in the binding block led to partial (>24, and between 12 and 24) or complete (=12) loss of lubricating ability. The length of the lubricating block (DP = 200 or 400) chosen in this study had no effect on the degree of lubrication. These results are put into context in terms of binding affinity to the cartilage and the spatial packing density of the polymer on the cartilage surface and can serve as a useful guide for future designs of synthetic lubricants that rival the efficacy of natural lubricants.

Mucins and Pathogenic Mucin-Like Molecules Are Immunomodulators During Infection and Targets for Diagnostics and Vaccines

Mucins and mucin-like molecules are highly O-glycosylated proteins present on the cell surface of mammals and other organisms. These glycoproteins are highly diverse in the apoprotein and glycan cores and play a central role in many biological processes and diseases. Mucins are the most abundant macromolecules in mucus and are responsible for its biochemical and biophysical properties. Mucin-like molecules cover various protozoan parasites, fungi and viruses. In humans, modifications in mucin glycosylation are associated with tumors in epithelial tissue. These modifications allow the distinction between normal and abnormal cell conditions and represent important targets for vaccine development against some cancers. Mucins and mucin-like molecules derived from pathogens are potential diagnostic markers and targets for therapeutic agents. In this review, we summarize the distribution, structure, role as immunomodulators, and the correlation of human mucins with diseases and perform a comparative analysis of mucins with mucin-like molecules present in human pathogens. Furthermore, we review the methods to produce pathogenic and human mucins using chemical synthesis and expression systems. Finally, we present applications of mucin-like molecules in diagnosis and prevention of relevant human diseases.