Organoids and organ chips in ophthalmology

Postnatal development of rat retina: a continuous observation and comparison between the organotypic retinal explant model and in vivo development

JOURNAL/nrgr/04.03/01300535-202503000-00033/figure1/v/2024-06-17T092413Z/r/image-tiff The organotypic retinal explant culture has been established for more than a decade and offers a range of unique advantages compared with in vivo experiments and cell cultures. However, the lack of systematic and continuous comparison between in vivo retinal development and the organotypic retinal explant culture makes this model controversial in postnatal retinal development studies. Thus, we aimed to verify the feasibility of using this model for postnatal retinal development studies by comparing it with the in vivo retina. In this study, we showed that postnatal retinal explants undergo normal development, and exhibit a consistent structure and timeline with retinas in vivo. Initially, we used SOX2 and PAX6 immunostaining to identify retinal progenitor cells. We then examined cell proliferation and migration by immunostaining with Ki-67 and doublecortin, respectively. Ki-67- and doublecortin-positive cells decreased in both in vivo and explants during postnatal retinogenesis, and exhibited a high degree of similarity in abundance and distribution between groups. Additionally, we used Ceh-10 homeodomain-containing homolog, glutamate-ammonia ligase (glutamine synthetase), neuronal nuclei, and ionized calcium-binding adapter molecule 1 immunostaining to examine the emergence of bipolar cells, Müller glia, mature neurons, and microglia, respectively. The timing and spatial patterns of the emergence of these cell types were remarkably consistent between in vivo and explant retinas. Our study showed that the organotypic retinal explant culture model had a high degree of consistency with the progression of in vivo early postnatal retina development. The findings confirm the accuracy and credibility of this model and support its use for long-term, systematic, and continuous observation.

Generation of Anterior Segment of the Eye Cells from hiPSCs in Microfluidic Platforms

Ophthalmic diseases affect many people, causing partial or total loss of vision and a reduced quality of life. The anterior segment of the eye accounts for nearly half of all visual impairment that can lead to blindness. Therefore, there is a growing demand for ocular research and regenerative medicine that specifically targets the anterior segment to improve vision quality. This study aims to generate a microfluidic platform for investigating the formation of the anterior segment of the eye derived from human induced pluripotent stem cells (hiPSC) under various spatial-mechanoresponsive conditions. Microfluidic platforms are developed to examine the effects of dynamic conditions on the generation of hiPSCs-derived ocular organoids. The differentiation protocol is validated, and mechanoresponsive genes are identified through transcriptomic analysis. Several culture strategies is implemented for the anterior segment of eye cells in a microfluidic chip. hiPSC-derived cells showed anterior eye cell characteristics in mRNA and protein expression levels under dynamic culture conditions. The expression levels of yes-associated protein and transcriptional coactivator PDZ binding motif (YAP/TAZ) and PIEZO1, varied depending on the differentiation and growth conditions of the cells, as well as the metabolomic profiles under dynamic culture conditions.

Retinal Organoids: A Next-Generation Platform for High-Throughput Drug Discovery

Retinal diseases are leading causes of blindness globally. Developing new drugs is of great significance for preventing vision loss. Current drug discovery relies mainly on two-dimensional in vitro models and animal models, but translation to human efficacy and safety is biased. In recent years, the emergence of retinal organoid technology platforms, utilizing three-dimensional microenvironments to better mimic retinal structure and function, has provided new platforms for exploring pathogenic mechanisms and drug screening. This review summarizes the latest advances in retinal organoid technology, emphasizing its application advantages in high-throughput drug screening, efficacy and toxicity evaluation, and translational medicine research. The review also prospects the combination of emerging technologies such as organ-on-a-chip, 3D bioprinting, single cell sequencing, gene editing with retinal organoid technology, which is expected to further optimize retinal organoid models and advance the diagnosis and treatment of retinal diseases.

Single-cell transcriptomic analysis of corneal organoids during development

Corneal organoids are useful tools for disease modeling and tissue transplantation; however, they have not yet been well studied during maturation. We characterized human iPSC-derived corneal organoids at 1, 2, 3, and 4 months of development using single-cell RNA sequencing to determine the cellular heterogeneity at each stage. We found pluripotent cell clusters committed to epithelial cell lineage at 1 month; early corneal epithelial, endothelial, and stromal cell markers at 2 months; keratocytes as the largest cell population at 3 months; and a large epithelial cell population at 4 months. We compared organoid to fetal corneal development at different stages and found that 4-month organoids closely resemble the corneal cellular complexity of the fetal (16 post conception week) and adult cornea. Using RNA velocity trajectory analysis, we found that less differentiated cells appear to give rise to corneal epithelial cells during development.

Tailoring biomaterials for biomimetic organs-on-chips

Organs-on-chips are microengineered microfluidic living cell culture devices with continuously perfused chambers penetrating to cells. By mimicking the biological features of the multicellular constructions, interactions among organs, vascular perfusion, physicochemical microenvironments, and so on, these devices are imparted with some key pathophysiological function levels of living organs that are difficult to be achieved in conventional 2D or 3D culture systems. In this technology, biomaterials are extremely important because they affect the microstructures and functionalities of the organ cells and the development of the organs-on-chip functions. Thus, herein, we provide an overview on the advances of biomaterials for the construction of organs-on-chips. After introducing the general components, structures, and fabrication techniques of the biomaterials, we focus on the studies of the functions and applications of these biomaterials in the organs-on-chips systems. Applications of the biomaterial-based organs-on-chips as alternative animal models for pharmaceutical, chemical, and environmental tests are described and highlighted. The prospects for exciting future directions and the challenges of biomaterials for realizing the further functionalization of organs-on-chips are also presented.

CAM Model: Intriguing Natural Bioreactor for Sustainable Research and Reliable/Versatile Testing

We are witnessing the revival of the CAM model, which has already used been in the past by several researchers studying angiogenesis and anti-cancer drugs and now offers a refined model to fill, in the translational meaning, the gap between in vitro and in vivo studies. It can be used for a wide range of purposes, from testing cytotoxicity, pharmacokinetics, tumorigenesis, and invasion to the action mechanisms of molecules and validation of new materials from tissue engineering research. The CAM model is easy to use, with a fast outcome, and makes experimental research more sustainable since it allows us to replace, reduce, and refine pre-clinical experimentation ("3Rs" rules). This review aims to highlight some unique potential that the CAM-assay presents; in particular, the authors intend to use the CAM model in the future to verify, in a microenvironment comparable to in vivo conditions, albeit simplified, the angiogenic ability of functionalized 3D constructs to be used in regenerative medicine strategies in the recovery of skeletal injuries of critical size (CSD) that do not repair spontaneously. For this purpose, organotypic cultures will be planned on several CAMs set up in temporal sequences, and a sort of organ model for assessing CSD will be utilized in the CAM bioreactor rather than in vivo.

Current microfluidic platforms for reverse engineering of cornea

According to the World Health Organization, corneal blindness constitutes 5.1% of global blindness population. Surgical outcomes have been improved significantly in the treatment of corneal blindness. However, corneal transplantation is limited by global shortage of donor tissue, prompting researchers to explore alternative therapies such as novel ocular pharmaceutics to delay corneal disease progression. Animal models are commonly adopted for investigating pharmacokinetics of ocular drugs. However, this approach is limited by physiological differences in the eye between animals and human, ethical issues and poor bench-to-bedside translatability. Cornea-on-a-chip (CoC) microfluidic platforms have gained great attention as one of the advanced in vitro strategies for constructing physiologically representative corneal models. With significant improvements in tissue engineering technology, CoC integrates corneal cells with microfluidics to recapitulate human corneal microenvironment for the study of corneal pathophysiological changes and evaluation of ocular drugs. Such model, in complement to animal studies, can potentially accelerate translational research, in particular the pre-clinical screening of ophthalmic medication, driving clinical treatment advancement for corneal diseases. This review provides an overview of engineered CoC platforms with respect to their merits, applications, and technical challenges. Emerging directions in CoC technology are also proposed for further investigations, to accentuate preclinical obstacles in corneal research.

Revolutionizing drug development: harnessing the potential of organ-on-chip technology for disease modeling and drug discovery

The inefficiency of existing animal models to precisely predict human pharmacological effects is the root reason for drug development failure. Microphysiological system/organ-on-a-chip technology (organ-on-a-chip platform) is a microfluidic device cultured with human living cells under specific organ shear stress which can faithfully replicate human organ-body level pathophysiology. This emerging organ-on-chip platform can be a remarkable alternative for animal models with a broad range of purposes in drug testing and precision medicine. Here, we review the parameters employed in using organ on chip platform as a plot mimic diseases, genetic disorders, drug toxicity effects in different organs, biomarker identification, and drug discoveries. Additionally, we address the current challenges of the organ-on-chip platform that should be overcome to be accepted by drug regulatory agencies and pharmaceutical industries. Moreover, we highlight the future direction of the organ-on-chip platform parameters for enhancing and accelerating drug discoveries and personalized medicine.

Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.

OOCDB: A Comprehensive, Systematic, and Real-time Organs-on-a-chip Database

Organs-on-a-chip is a microfluidic microphysiological system that uses microfluidic technology to analyze the structure and function of living human cells at the tissue and organ levels in vitro. Organs-on-a-chip technology, as opposed to traditional two-dimensional cell culture and animal models, can more closely simulate pathologic and toxicologic interactions between different organs or tissues and reflect the collaborative response of multiple organs to drugs. Despite the fact that many organs-on-a-chip-related data have been published, none of the current databases have all of the following functions: searching, downloading, as well as analyzing data and results from the literature on organs-on-a-chip. Therefore, we created an organs-on-a-chip database (OOCDB) as a platform to integrate information about organs-on-a-chip from various sources, including literature, patents, raw data from microarray and transcriptome sequencing, several open-access datasets of organs-on-a-chip and organoids, and data generated in our laboratory. OOCDB contains dozens of sub-databases and analysis tools, and each sub-database contains various data associated with organs-on-a-chip, with the goal of providing researchers with a comprehensive, systematic, and convenient search engine. Furthermore, it offers a variety of other functions, such as mathematical modeling, three-dimensional modeling, and citation mapping, to meet the needs of researchers and promote the development of organs-on-a-chip. The OOCDB is available at http://www.organchip.cn.

Revolutionizing Disease Modeling: The Emergence of Organoids in Cellular Systems

Cellular models have created opportunities to explore the characteristics of human diseases through well-established protocols, while avoiding the ethical restrictions associated with post-mortem studies and the costs associated with researching animal models. The capability of cell reprogramming, such as induced pluripotent stem cells (iPSCs) technology, solved the complications associated with human embryonic stem cells (hESC) usage. Moreover, iPSCs made significant contributions for human medicine, such as in diagnosis, therapeutic and regenerative medicine. The two-dimensional (2D) models allowed for monolayer cellular culture in vitro; however, they were surpassed by the three-dimensional (3D) cell culture system. The 3D cell culture provides higher cell-cell contact and a multi-layered cell culture, which more closely respects cellular morphology and polarity. It is more tightly able to resemble conditions in vivo and a closer approach to the architecture of human tissues, such as human organoids. Organoids are 3D cellular structures that mimic the architecture and function of native tissues. They are generated in vitro from stem cells or differentiated cells, such as epithelial or neural cells, and are used to study organ development, disease modeling, and drug discovery. Organoids have become a powerful tool for understanding the cellular and molecular mechanisms underlying human physiology, providing new insights into the pathogenesis of cancer, metabolic diseases, and brain disorders. Although organoid technology is up-and-coming, it also has some limitations that require improvements.

Organoids of the male reproductive system: Challenges, opportunities, and their potential use in fertility research

Organoids are units of function of a given organ able to reproduce, in culture, a biological structure similar in architecture and function to its counterpart in vivo. Today, it is possible to develop an organoid from a fragment of tissue, a stem cell located in an adult organ, an embryonic stem cell, or an induced pluripotent stem cell. In the past decade, many organoids have been developed which mimic stomach, pancreas, liver and brain tissues, optic cups, among many others. Additionally, different male reproductive system organs have already been developed as organoids, including the prostate and testis. These 3D cultures may be of great importance for urological cancer research and have the potential to be used in fertility research for the study of spermatozoa production and maturation, germ cells-somatic cells interactions, and mechanisms of disease. They also provide an accurate preclinical pipeline for drug testing and discovery, as well as for the study of drug resistance. In this work, we revise the current knowledge on organoid technology and its use in healthcare and research, describe the male reproductive system organoids and other biomaterials already developed, and discuss their current application. Finally, we highlight the research gaps, challenges, and opportunities in the field and propose strategies to improve the use of organoids for the study of male infertility situations. This article is categorized under: Reproductive System Diseases > Stem Cells and Development Reproductive System Diseases > Biomedical Engineering.

The Chick Embryo and Its Structures as a Model System for Experimental Ophthalmology

The possibilities of using the chick embryo and its individual structures as a model system in experimental ophthalmology are considered. Cultures of the retina and spinal ganglia from chick embryos are used in the development of new methods for the treatment of glaucomatous optic neuropathy and ischemic optic neuropathy. The chorioallantoic membrane is used for modelling vascular pathologies of the eye, screening of anti-VEGF drugs, and assessing biocompatibility of implants. Co-culturing of chick embryo nervous tissue and human corneal cells makes it possible to study the processes of corneal reinnervation. The use of chick embryo cells and tissues in the "organ-on-a-chip" system opens up wide opportunities for fundamental and applied ophthalmological studies.

Prime Editing Strategy to Install the PRPH2 c.828+1G>A Mutation

Mutations in peripherin 2 (PRPH2) are associated with a spectrum of inherited retinal diseases (IRDs) including retinitis pigmentosa (RP) and macular degeneration. As PRPH2 is localized to cone and rod outer segments, mutations in PRPH2 lead the disorganization or absence of photoreceptor outer segments. Here, we report on a patient with PRPH2-linked RP who exhibited widespread RPE atrophy with a central area of macular atrophy sparing the fovea. In future studies, we plan to model the pathobiology of PRPH2-based RP using induced pluripotent stem cell (iPSC)-derived retinal organoids. To effectively model rare mutations using iPSC-derived retinal organoids, we first require a strategy that can install the desired mutation in healthy wild-type iPSC, which can efficiently generate well-laminated retinal organoids. In this study, we developed an efficient prime editing strategy for the installation of the pathogenic PRPH2 c.828+1 G>A splice-site mutation underlying our patient's disease.

Retinogenesis in a Dish: Bibliometric Analysis and Visualization of Retinal Organoids From 2011 to 2022

Retinal organoid (RO) is the three-dimensional (3D) retinal culture derived from pluripotent or embryonic stem cells which recapitulates organ functions, which was a revolutionary milestone in stem cell technology. The purpose of this study is to explore the hotspots and future directions on ROs, as well as to better understand the fields of greatest research opportunities. Eligible publications related to RO from 2011 to 2022 were acquired from the Web of Science (WoS) Core Collection database. Bibliometric analysis was performed by using software including VOSviewer, CiteSpace, and ArcGIS. A total of 520 articles were included, and the number of annual publications showed a rapid increase with an average rate of 40.86%. The United States published the most articles (241/520, 46.35%) with highest total citation frequencies (5,344). University College London (UK) contributed the largest publication output (40/520, 7.69%) and received highest total citation frequencies. Investigative Ophthalmology & Visual Science was the most productive journal with 129 articles. Majlinda Lako contributed the most research with 32 articles, while Olivier Goureau has the strongest collaboration work. Research could be subdivided into four keyword clusters: "culture and differentiation," "morphogenesis and modeling," "gene therapy," and "transplantation and visual restoration," and evolution of keywords was identified. Last decade has witnessed the huge progress in the field of RO, which is a young and promising research area with extensive and in-depth studies. More attention should be paid to RO-related models and therapies based on specific retinal diseases, especially inherited retinopathies.

[Application of the organ-on-a-chip technology in experimental ophthalmology]

Organ-on-chip is a microfluidic device that can reproduce in vitro the minimal functional unit of an organ or system of organs and model various physiological processes and body structures with high accuracy. This review covers the main approaches to the use of the organ-on-chip technology in modern experimental ophthalmology. The analysis of literature sources revealed the following main applications of the organ-on-chip technology in ophthalmology; the technology allows modeling the anterior eye surface and its diseases, such as dry eye syndrome, as well as disorders of the posterior segment of the eye such as age-related macular degeneration, diabetic macular edema, diabetic retinopathy, glaucoma. Culturing of eye tissues in microfluidic systems helps identify the toxic effects and pharmacological activity of new compounds, and provides an opportunity for deeper understanding of the normal physiology of the eye and the pathogenesis of ocular diseases. In addition, the technology can reduce the cost and duration of experiments. Thus, the organ-on-a-chip technology has a great potential in the field of experimental ophthalmology and preclinical trials of new ophthalmic drugs.

Generation of CRB1 RP Patient-Derived iPSCs and a CRISPR/Cas9-Mediated Homology-Directed Repair Strategy for the CRB1 c.2480G>T Mutation

Mutations in the Crumbs-homologue-1 (CRB1) gene lead to a spectrum of severe inherited retinal diseases, including retinitis pigmentosa (RP). The establishment of a genotype-phenotype correlation in CRB1 patients has been difficult due to the substantial variability and phenotypic overlap between CRB1-associated diseases. This phenotypic modulation may be due to several factors, including genetic modifiers, deep intronic mutations, isoform diversity, and copy number variations. Induced pluripotent stem cell (iPSC)-derived patient retinal organoids are novel tools that can provide sensitive, quantitative, and scalable phenotypic assays. CRB1 RP patient iPSC-derived retinal organoids have shown reproducible phenotypes compared to healthy retinal organoids. However, having genetically defined iPSC isogenic controls that take into account potential phenotypic modulation is crucial. In this study, we generated iPSC from an early-onset CRB1 patient and developed a correction strategy for the c.2480G>T, p.(Gly827Val) CRB1 mutation using CRISPR/Cas9-mediated homology-directed repair.

Generation of Human iPSC-Derived Retinal Organoids for Assessment of AAV-Mediated Gene Delivery

Human retinal organoids derived from induced pluripotent stem cells (iPSCs) serve as a promising preclinical model for testing the safety and efficacy of viral gene therapy. Retinal organoids recapitulate the stratified multilayered epithelium structure of the developing and maturating human retina. As such, retinal organoids are unique tools to model retinal disease and to test therapeutic interventions toward their amelioration. Here, we describe a method for the generation of human iPSC-derived retinal organoids and how they can be utilized for the assessment of recombinant adeno-associated viral (rAAV)-mediated gene delivery.

Retinal organoid light responsivity: current status and future opportunities

The ability to generate human retinas in vitro from pluripotent stem cells opened unprecedented opportunities for basic science and for the development of therapeutic approaches for retinal degenerative diseases. Retinal organoid models not only mimic the histoarchitecture and cellular composition of the native retina, but they can achieve a remarkable level of maturation that allows them to respond to light stimulation. However, studies evaluating the nature, magnitude, and properties of light-evoked responsivity from each cell type, in each retinal organoid layer, have been sparse. In this review we discuss the current understanding of retinal organoid function, the technologies used for functional assessment in human retinal organoids, and the challenges and opportunities that lie ahead.

Biomechanical analysis of ocular diseases and its in vitro study methods

Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment.

Precision genome editing in the eye

CRISPR-Cas-based genome editing technologies could, in principle, be used to treat a wide variety of inherited diseases, including genetic disorders of vision. Programmable CRISPR-Cas nucleases are effective tools for gene disruption, but they are poorly suited for precisely correcting pathogenic mutations in most therapeutic settings. Recently developed precision genome editing agents, including base editors and prime editors, have enabled precise gene correction and disease rescue in multiple preclinical models of genetic disorders. Additionally, new delivery technologies that transiently deliver precision genome editing agents in vivo offer minimized off-target editing and improved safety profiles. These improvements to precision genome editing and delivery technologies are expected to revolutionize the treatment of genetic disorders of vision and other diseases. In this Perspective, we describe current preclinical and clinical genome editing approaches for treating inherited retinal degenerative diseases, and we discuss important considerations that should be addressed as these approaches are translated into clinical practice.

Looking into the Eyes—In Vitro Models for Ocular Research

Animal research undoubtedly provides scientists with virtually unlimited data but inflicts pain and suffering on animals. Currently, legislators and scientists alike are promoting alternative in vitro approaches allowing for an accurate evaluation of processes occurring in the body without animal sacrifice. Historically, one of the most infamous animal tests is the Draize test, mainly performed on rabbits. Even though this test was considered the gold standard for around 50 years, the Draize test fails to mimic human response mainly due to human and rabbit eye physiological differences. Therefore, many alternative assays were developed to evaluate ocular toxicity and drug effectiveness accurately. Here we review recent achievements in tissue engineering of in vitro 2D, 2.5D, 3D, organoid and organ-on-chip ocular models, as well as in vivo and ex vivo models in terms of their advantages and limitations.

Lacrimal gland regeneration: The unmet challenges and promise for dry eye therapy

DED (Dry eye disease) is a common multifactorial disease of the ocular surface and the tear film. DED has gained attention globally, with millions of people affected.. Although treatment strategies for DED have shifted towards Tear Film Oriented Therapy (TFOT), all the existing strategies fall under standard palliative care when addressed as a long-term goal. Therefore, different approaches have been explored by various groups to uncover alternative treatment strategies that can contribute to a full regeneration of the damaged lacrimal gland. For this, multiple groups have investigated the role of lacrimal gland (LG) cells in DED based on their regenerating, homing, and differentiating capabilities. In this review, we discuss in detail therapeutic mechanisms and regenerative strategies that can potentially be applied for lacrimal gland regeneration as well as their therapeutic applications. This review mainly focuses on Aqueous Deficiency Dry Eye Disease (ADDE) caused by lacrimal gland dysfunction and possible future treatment strategies. The current key findings from cell and tissue-based regenerative therapy modalities that could be utilised to achieve lacrimal gland tissue regeneration are summarized. In addition, this review summarises the available literature from in vitro to in vivo animal studies, their limitations in relation to lacrimal gland regeneration and the possible clinical applications. Finally, current issues and unmet needs of cell-based therapies in providing complete lacrimal gland tissue regeneration are discussed.

Emerging tissue engineering strategies for the corneal regeneration

Cornea as the outermost layer of the eye is at risk of various genetic and environmental diseases that can damage the cornea and impair vision. Corneal transplantation is among the most applicable surgical procedures for repairing the defected tissue. However, the scarcity of healthy tissue donations as well as transplantation failure has remained as the biggest challenges in confront of corneal grafting. Therefore, alternative approaches based on stem-cell transplantation and classic regenerative medicine have been developed for corneal regeneration. In this review, the application and limitation of the recently-used advanced approaches for regeneration of cornea are discussed. Additionally, other emerging powerful techniques such as 5D printing as a new branch of scaffold-based technologies for construction of tissues other than the cornea are highlighted and suggested as alternatives for corneal reconstruction. The introduced novel techniques may have great potential for clinical applications in corneal repair including disease modeling, 3D pattern scheming, and personalized medicine.

Transcending Dimensions in Apicomplexan Research: from Two-Dimensional to Three-Dimensional In Vitro Cultures

Parasites belonging to the Apicomplexa phylum are among the most successful pathogens known in nature. They can infect a wide range of hosts, often remain undetected by the immune system, and cause acute and chronic illness. In this phylum, we can find parasites of human and veterinary health relevance, such as Toxoplasma, Plasmodium, Cryptosporidium, and Eimeria. There are still many unknowns about the biology of these pathogens due to the ethical and practical issues of performing research in their natural hosts. Animal models are often difficult or nonexistent, and as a result, there are apicomplexan life cycle stages that have not been studied. One recent alternative has been the use of three-dimensional (3D) systems such as organoids, 3D scaffolds with different matrices, microfluidic devices, organs-on-a-chip, and other tissue culture models. These 3D systems have facilitated and expanded the research of apicomplexans, allowing us to explore life stages that were previously out of reach and experimental procedures that were practically impossible to perform in animal models. Human- and animal-derived 3D systems can be obtained from different organs, allowing us to model host-pathogen interactions for diagnostic methods and vaccine development, drug testing, exploratory biology, and other applications. In this review, we summarize the most recent advances in the use of 3D systems applied to apicomplexans. We show the wide array of strategies that have been successfully used so far and apply them to explore other organisms that have been less studied.

Organ-on-a-Chip systems for new drugs development

Research on alternatives to the use of animal models and cell cultures has led to the creation of organ-on-a-chip systems, in which organs and their physiological reactions to the presence of external stimuli are simulated. These systems could even replace the use of human beings as subjects for the study of drugs in clinical phases and have an impact on personalized therapies. Organ-on-a-chip technology present higher potential than traditional cell cultures for an appropriate prediction of functional impairments, appearance of adverse effects, the pharmacokinetic and toxicological profile and the efficacy of a drug. This potential is given by the possibility of placing different cell lines in a three-dimensional-arranged polymer piece and simulating and controlling specific conditions. Thus, the normal functioning of an organ, tissue, barrier, or physiological phenomenon can be simulated, as well as the interrelation between different systems. Furthermore, this alternative allows the study of physiological and pathophysiological processes. Its design combines different disciplines such as materials engineering, cell cultures, microfluidics and physiology, among others. This work presents the main considerations of OoC systems, the materials, methods and cell lines used for their design, and the conditions required for their proper functioning. Examples of applications and main challenges for the development of more robust systems are shown. This non-systematic review is intended to be a reference framework that facilitates research focused on the development of new OoC systems, as well as their use as alternatives in pharmacological, pharmacokinetic and toxicological studies.

Organ-On-A-Chip: A Survey of Technical Results and Problems

Organ-on-a-chip (OoC), also known as micro physiological systems or “tissue chips” have attracted substantial interest in recent years due to their numerous applications, especially in precision medicine, drug development and screening. Organ-on-a-chip devices can replicate key aspects of human physiology, providing insights into the studied organ function and disease pathophysiology. Moreover, these can accurately be used in drug discovery for personalized medicine. These devices present useful substitutes to traditional preclinical cell culture methods and can reduce the use of in vivo animal studies. In the last few years OoC design technology has seen dramatic advances, leading to a wide range of biomedical applications. These advances have also revealed not only new challenges but also new opportunities. There is a need for multidisciplinary knowledge from the biomedical and engineering fields to understand and realize OoCs. The present review provides a snapshot of this fast-evolving technology, discusses current applications and highlights advantages and disadvantages for biomedical approaches.

The link between Keratoconus and posterior segment parameters: An updated, comprehensive review

Keratoconus (KCN) has been typically known as a disorder with effects limited to the cornea. Because of this viewpoint, less attention has been devoted to its effects on the posterior segment structures. We aimed to provide a comprehensive review of the literature to understand the potential link between KCN and posterior segment structures and their functions. It is clear from the extensive evidence in the literature that KCN can be associated with morphological and functional changes in different parts of the posterior segment. It is worth noting that anatomical changes have been not only noted in several layers of the retina but also in the optic nerve head and the choroid. Several mechanisms have been proposed to explain this observation, including incidents induced by oxidative stress in keratoconic corneas and retinal adaptions to the distorted image that lands on the retina. Consequently, when KCN has been diagnosed, it seems practical to consider assessing the retinal and choroidal profile using optical coherence tomography and potentially functional abnormalities through electrophysiology procedures.

Role of Oxidative Stress in Ocular Diseases Associated with Retinal Ganglion Cells Degeneration

Ocular diseases associated with retinal ganglion cell (RGC) degeneration is the most common neurodegenerative disorder that causes irreversible blindness worldwide. It is characterized by visual field defects and progressive optic nerve atrophy. The underlying pathophysiology and mechanisms of RGC degeneration in several ocular diseases remain largely unknown. RGCs are a population of central nervous system neurons, with their soma located in the retina and long axons that extend through the optic nerve to form distal terminals and connections in the brain. Because of this unique cytoarchitecture and highly compartmentalized energy demand, RGCs are highly mitochondrial-dependent for adenosine triphosphate (ATP) production. Recently, oxidative stress and mitochondrial dysfunction have been found to be the principal mechanisms in RGC degeneration as well as in other neurodegenerative disorders. Here, we review the role of oxidative stress in several ocular diseases associated with RGC degenerations, including glaucoma, hereditary optic atrophy, inflammatory optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and drug toxicity. We also review experimental approaches using cell and animal models for research on the underlying mechanisms of RGC degeneration. Lastly, we discuss the application of antioxidants as a potential future therapy for the ocular diseases associated with RGC degenerations.

The Communication between Ocular Surface and Nasal Epithelia in 3D Cell Culture Technology for Translational Research: A Narrative Review

There is a lack of knowledge regarding the connection between the ocular and nasal epithelia. This narrative review focuses on conjunctival, corneal, ultrastructural corneal stroma, and nasal epithelia as well as an introduction into their interconnections. We describe in detail the morphology and physiology of the ocular surface, the nasolacrimal ducts, and the nasal cavity. This knowledge provides a basis for functional studies and the development of relevant cell culture models that can be used to investigate the pathogenesis of diseases related to these complex structures. Moreover, we also provide a state-of-the-art overview regarding the development of 3D culture models, which allow for addressing research questions in models resembling the in vivo situation. In particular, we give an overview of the current developments of corneal 3D and organoid models, as well as 3D cell culture models of epithelia with goblet cells (conjunctiva and nasal cavity). The benefits and shortcomings of these cell culture models are discussed. As examples for pathogens related to ocular and nasal epithelia, we discuss infections caused by adenovirus and measles virus. In addition to pathogens, also external triggers such as allergens can cause rhinoconjunctivitis. These diseases exemplify the interconnections between the ocular surface and nasal epithelia in a molecular and clinical context. With a final translational section on optical coherence tomography (OCT), we provide an overview about the applicability of this technique in basic research and clinical ophthalmology. The techniques presented herein will be instrumental in further elucidating the functional interrelations and crosstalk between ocular and nasal epithelia.

Multiocular organoids from human induced pluripotent stem cells displayed retinal, corneal, and retinal pigment epithelium lineages

BACKGROUND

Recently, great efforts have been made to design protocols for obtaining ocular cells from human stem cells to model diseases or for regenerative purposes. Current protocols generally focus on isolating retinal cells, retinal pigment epithelium (RPE), or corneal cells and fail to recapitulate the complexity of the tissue during eye development. Here, the generation of more advanced in vitro multiocular organoids from human induced pluripotent stem cells (hiPSCs) is demonstrated.

METHODS

A 2-step method was established to first obtain self-organized multizone ocular progenitor cells (mzOPCs) from 2D hiPSC cultures within three weeks. Then, after the cells were manually isolated and grown in suspension, 3D multiocular organoids were generated to model important cellular features of developing eyes.

RESULTS

In the 2D culture, self-formed mzOPCs spanned the neuroectoderm, surface ectoderm, neural crest, and RPE, mimicking early stages of eye development. After lifting, mzOPCs developed into different 3D multiocular organoids composed of multiple cell lineages including RPE, retina, and cornea, and interactions between the different cell types and regions of the eye system were observed. Within these organoids, the retinal regions exhibited correct layering and contained all major retinal cell subtypes as well as retinal morphological cues, whereas the corneal regions closely resembled the transparent ocular-surface epithelium and contained of corneal, limbal, and conjunctival epithelial cells. The arrangement of RPE cells also formed organoids composed of polarized pigmented epithelial cells at the surface that were completely filled with collagen matrix.

CONCLUSIONS

This approach clearly demonstrated the advantages of the combined 2D-3D construction tissue model as it provided a more ocular native-like cellular environment than that of previous models. In this complex preparations, multiocular organoids may be used to model the crosstalk between different cell types in eye development and disease.

Fluidics system for resolving concentration-dependent effects of dissolved gases on tissue metabolism

Oxygen (O2) and other dissolved gases such as the gasotransmitters H2S, CO, and NO affect cell metabolism and function. To evaluate effects of dissolved gases on processes in tissue, we developed a fluidics system that controls dissolved gases while simultaneously measuring parameters of electron transport, metabolism, and secretory function. We use pancreatic islets, retina, and liver from rodents to highlight its ability to assess effects of O2 and H2S. Protocols aimed at emulating hypoxia-reperfusion conditions resolved a previously unrecognized transient spike in O2 consumption rate (OCR) following replenishment of O2, and tissue-specific recovery of OCR following hypoxia. The system revealed both inhibitory and stimulatory effects of H2S on insulin secretion rate from isolated islets. The unique ability of this new system to quantify metabolic state and cell function in response to precise changes in dissolved gases provides a powerful platform for cell physiologists to study a wide range of disease states.

Retinal organoids as models for development and diseases

The evolution of pluripotent stem cell-derived retinal organoids (ROs) has brought remarkable opportunities for developmental studies while also presenting new therapeutic avenues for retinal diseases. With a clear understanding of how well these models mimic native retinas, such preclinical models may be crucial tools that are widely used for the more efficient translation of studies into novel treatment strategies for retinal diseases. Genetic modifications or patient-derived ROs can allow these models to simulate the physical microenvironments of the actual disease process. However, we are currently at the beginning of the three-dimensional (3D) RO era, and a general quantitative technology for analyzing ROs derived from numerous differentiation protocols is still missing. Continued efforts to improve the efficiency and stability of differentiation, as well as understanding the disparity between the artificial retina and the native retina and advancing the current treatment strategies, will be essential in ensuring that these scientific advances can benefit patients with retinal disease. Herein, we briefly discuss RO differentiation protocols, the current applications of RO as a disease model and the treatments for retinal diseases by using RO modeling, to have a clear view of the role of current ROs in retinal development and diseases.

Traumatic brain injury and sight loss in military and veteran populations- a review

War and combat exposure pose great risks to the vision system. More recently, vision related deficiencies and impairments have become common with the increased use of powerful explosive devices and the subsequent rise in incidence of traumatic brain injury (TBI). Studies have looked at the effects of injury severity, aetiology of injury and the stage at which visual problems become apparent. There was little discrepancy found between the frequencies or types of visual dysfunctions across blast and non-blast related groups, however complete sight loss appeared to occur only in those who had a blast-related injury. Generally, the more severe the injury, the greater the likelihood of specific visual disturbances occurring, and a study found total sight loss to only occur in cases with greater severity. Diagnosis of mild TBI (mTBI) is challenging. Being able to identify a potential TBI via visual symptoms may offer a new avenue for diagnosis.

Lens regeneration: scientific discoveries and clinical possibilities

In the process of exploring new methods for cataract treatment, lens regeneration is an ideal strategy for effectively restoring accommodative vision and avoiding postoperative complications and has great clinical potential. Lens regeneration, which is not a simple repetition of lens development, depends on the complex regulatory network comprising the FGF, BMP/TGF-β, Notch, and Wnt signaling pathways. Current research mainly focuses on in situ and in vitro lens regeneration. On the one hand, the possibility of the autologous stem cell in situ regeneration of functional lenses has been confirmed; on the other hand, both embryonic stem cells and induced pluripotent stem cells have been induced into lentoid bodies in vitro which are similar to the natural lens to a certain extent. This article will briefly summarize the regulatory mechanisms of lens development, describe the recent progress of lens regeneration, explore the key molecular signaling pathways, and, more importantly, discuss the prospects and challenges of their clinical applications to provide reference for clinical transformations.

Recent Microfluidic Innovations for Sperm Sorting

Sperm selection is a clinical need for guided fertilization in men with low-quality semen. In this regard, microfluidics can provide an enabling platform for the precise manipulation and separation of high-quality sperm cells through applying various stimuli, including chemical agents, mechanical forces, and thermal gradients. In addition, microfluidic platforms can help to guide sperms and oocytes for controlled in vitro fertilization or sperm sorting using both passive and active methods. Herein, we present a detailed review of the use of various microfluidic methods for sorting and categorizing sperms for different applications. The advantages and disadvantages of each method are further discussed and future perspectives in the field are given.