Bioprinting of exosomes: Prospects and challenges for clinical applications.

453Three-dimensional bioprinting (3DBP) is an additive manufacturing technique that has emerged as a promising strategy for the fabrication of scaffolds, which can successfully recapitulate the architectural, biochemical, and physical cues of target tissues. More importantly, 3DBP offers fine spatiotemporal control and high submicron scale resolution, which can be leveraged for the incorporation and directional gradient release of single or multiple biomimetic cues, including cell-derived exosomes (EXOs). EXOs are extracellular vesicles that originate from the endosomal compartment of various cell types, with sizes ranging from 30 to120 nm. They act as cell mediators and contain discrete cell constituents, including growth factors, cytokines, lipid moieties, nucleic acids, metabolites, and cell surface markers, depending on the cell type. Essentially, owing to their therapeutic potential, EXOs derived from mesenchymal stem cells (MSCs) have been recently investigated in several clinical trials for the treatment of various conditions, including cancer, diabetes, dry eyes, periodontitis, and acute ischemic stroke. The 3DBP strategy of EXOs is especially useful in tissue engineering and regenerative medicine applications, as tissues can be biofabricated to closely mimic the complex microarchitecture and developmental profiles of native heterogeneous tissues for restoring biological functions. Moreover, EXOs can be manipulated to carry exogenous cargo such as genes or proteins of therapeutic interest, confer multifunctional attributes, and further enhance their tissue regenerative potential. However, significant challenges, including the selection of appropriate bioink, pattern resolution, engineering-defined exosomal gradient, spatial presentation and modulation of EXO release kinetics, as well as EXO stability and storage conditions, must be addressed for the successful translation of therapeutic grade EXOs to clinical settings. In this review, we highlight the recent advances and offer future perspectives on the bioprinting of EXOs as regenerative biotherapeutics for the fabrication of complex heterogeneous tissues that are suitable for clinical transplantation.

Infectious Keratitis: An Update on Role of Epigenetics.

Epigenetic mechanisms modulate gene expression and function without altering the base sequence of DNA. These reversible, heritable, and environment-influenced mechanisms generate various cell types during development and orchestrate the cellular responses to external stimuli by regulating the expression of genome. Also, the epigenetic modifications influence common pathological and physiological responses including inflammation, ischemia, neoplasia, aging and neurodegeneration etc. In recent past, the field of epigenetics has gained momentum and become an increasingly important area of biomedical research As far as eye is concerned, epigenetic mechanisms may play an important role in many complex diseases such as corneal dystrophy, cataract, glaucoma, diabetic retinopathy, ocular neoplasia, uveitis, and age-related macular degeneration. Focusing on the epigenetic mechanisms in ocular diseases may provide new understanding and insights into the pathogenesis of complex eye diseases and thus can aid in the development of novel treatments for these diseases. In the present review, we summarize the clinical perspective of infectious keratitis, role of epigenetics in infectious keratitis, therapeutic potential of epigenetic modifiers and the future perspective.

Mini Review: Current Trends and Understanding of Exosome Therapeutic Potential in Corneal Diseases.

Exosomes are a subset of extracellular vesicles (EVs) that are secreted by most cell types. They are nanosized EVs ranging from 30 to 150 nm. The membrane-enclosed bodies originate by the process of endocytosis and mainly comprise DNA, RNA, protein, and lipids. Exosomes not only act as cell-to-cell communication signaling mediators but also have the potential to act as biomarkers for clinical application and as a promising carrier for drug delivery. Unfortunately, the purification methods for exosomes remain an obstacle. While most of the exosome researches are mainly focused on cancer, there are limited studies highlighting the importance of exosomes in ocular biology, specifically cornea-associated pathologies. Here, we summarize a brief description of exosome biogenesis, roles of exosomes and exosome-based therapies in corneal pathologies, and exosome bioengineering for tissue-specific therapy.

Human Cadaveric Donor Cornea Derived Extra Cellular Matrix Microparticles for Minimally Invasive Healing/Regeneration of Corneal Wounds.

Biological materials derived from extracellular matrix (ECM) proteins have garnered interest as their composition is very similar to that of native tissue. Herein, we report the use of human cornea derived decellularized ECM (dECM) microparticles dispersed in human fibrin sealant as an accessible therapeutic alternative for corneal anterior stromal reconstruction. dECM microparticles had good particle size distribution (≤10 µm) and retained the majority of corneal ECM components found in native tissue. Fibrin-dECM hydrogels exhibited compressive modulus of 70.83 ± 9.17 kPa matching that of native tissue, maximum burst pressure of 34.3 ± 3.7 kPa, and demonstrated a short crosslinking time of ~17 min. The fibrin-dECM hydrogels were found to be biodegradable, cytocompatible, non-mutagenic, non-sensitive, non-irritant, and supported the growth and maintained the phenotype of encapsulated human corneal stem cells (hCSCs) in vitro. In a rabbit model of anterior lamellar keratectomy, fibrin-dECM bio-adhesives promoted corneal re-epithelialization within 14 days, induced stromal tissue repair, and displayed integration with corneal tissues in vivo. Overall, our results suggest that the incorporation of cornea tissue-derived ECM microparticles in fibrin hydrogels is non-toxic, safe, and shows tremendous promise as a minimally invasive therapeutic approach for the treatment of superficial corneal epithelial wounds and anterior stromal injuries.

Structural Basis for Draxin-Modulated Axon Guidance and Fasciculation by Netrin-1 through DCC.

Axon guidance involves the spatiotemporal interplay between guidance cues and membrane-bound cell-surface receptors, present on the growth cone of the axon. Netrin-1 is a prototypical guidance cue that binds to deleted in colorectal cancer (DCC), and it has been proposed that the guidance cue Draxin modulates this interaction. Here, we present structural snapshots of Draxin/DCC and Draxin/Netrin-1 complexes, revealing a triangular relationship that affects Netrin-mediated haptotaxis and fasciculation. Draxin interacts with DCC through the N-terminal four immunoglobulin domains, and Netrin-1 through the EGF-3 domain, in the same region where DCC binds. Netrin-1 and DCC bind to adjacent sites on Draxin, which appears to capture Netrin-1 and tether it to the DCC receptor. We propose the conformational flexibility of the single-pass membrane receptor DCC is used to promote fasciculation and regulate axon guidance through concerted Netrin-1/Draxin binding. VIDEO ABSTRACT.