Matrigel is required for efficient differentiation of isolated, stem cell-derived otic vesicles into inner ear organoids

Exploiting Matrix Stiffness to Overcome Drug Resistance

Drug resistance is arguably one of the biggest challenges facing cancer research today. Understanding the underlying mechanisms of drug resistance in tumor progression and metastasis are essential in developing better treatment modalities. Given the matrix stiffness affecting the mechanotransduction capabilities of cancer cells, characterization of the related signal transduction pathways can provide a better understanding for developing novel therapeutic strategies. In this review, we aimed to summarize the recent advancements in tumor matrix biology in parallel to therapeutic approaches targeting matrix stiffness and its consequences in cellular processes in tumor progression and metastasis. The cellular processes governed by signal transduction pathways and their aberrant activation may result in activating the epithelial-to-mesenchymal transition, cancer stemness, and autophagy, which can be attributed to drug resistance. Developing therapeutic strategies to target these cellular processes in cancer biology will offer novel therapeutic approaches to tailor better personalized treatment modalities for clinical studies.

Mapping the developmental potential of mouse inner ear organoids at single-cell resolution

Inner ear organoids recapitulate development and are intended to generate cell types of the otic lineage for applications such as basic science research and cell replacement strategies. Here, we use single-cell sequencing to study the cellular heterogeneity of late-stage mouse inner ear organoid sensory epithelia, which we validated by comparison with datasets of the mouse cochlea and vestibular epithelia. We resolved supporting cell sub-types, cochlear-like hair cells, and vestibular type I and type II-like hair cells. While cochlear-like hair cells aligned best with an outer hair cell trajectory, vestibular-like hair cells followed developmental trajectories similar to in vivo programs branching into type II and then type I extrastriolar hair cells. These results highlight the transcriptional accuracy of the organoid developmental program but will also inform future strategies to improve synaptic connectivity and regional specification.

Modeling, applications and challenges of inner ear organoid

More than 6% of the world's population is suffering from hearing loss and balance disorders. The inner ear is the organ that senses sound and balance. Although inner ear disorders are common, there are limited ways to intervene and restore its sensory and balance functions. The development and establishment of biologically therapeutic interventions for auditory disorders require clarification of the basics of signaling pathways that control inner ear development and the establishment of endogenous or exogenous cell-based therapeutic methods. In vitro models of the inner ear, such as organoid systems, can help identify new protective or regenerative drugs, develop new gene therapies, and be considered as potential tools for future clinical applications. Advances in stem cell technology and organoid culture offer unique opportunities for modeling inner ear diseases and developing personalized therapies for hearing loss. Here, we review and discuss the mechanisms for the establishment and the potential applications of inner ear organoids.

Current advances in biomaterials for inner ear cell regeneration

Inner ear cell regeneration from stem/progenitor cells provides potential therapeutic strategies for the restoration of sensorineural hearing loss (SNHL), however, the efficiency of regeneration is low and the functions of differentiated cells are not yet mature. Biomaterials have been used in inner ear cell regeneration to construct a more physiologically relevant 3D culture system which mimics the stem cell microenvironment and facilitates cellular interactions. Currently, these biomaterials include hydrogel, conductive materials, magneto-responsive materials, photo-responsive materials, etc. We analyzed the characteristics and described the advantages and limitations of these materials. Furthermore, we reviewed the mechanisms by which biomaterials with different physicochemical properties act on the inner ear cell regeneration and depicted the current status of the material selection based on their characteristics to achieve the reconstruction of the auditory circuits. The application of biomaterials in inner ear cell regeneration offers promising opportunities for the reconstruction of the auditory circuits and the restoration of hearing, yet biomaterials should be strategically explored and combined according to the obstacles to be solved in the inner ear cell regeneration research.

Morphogenesis and development of human telencephalic organoids in the absence and presence of exogenous extracellular matrix

The establishment and maintenance of apical-basal polarity is a fundamental step in brain development, instructing the organization of neural progenitor cells (NPCs) and the developing cerebral cortex. Particularly, basally located extracellular matrix (ECM) is crucial for this process. In vitro, epithelial polarization can be achieved via endogenous ECM production, or exogenous ECM supplementation. While neuroepithelial development is recapitulated in neural organoids, the effects of different ECM sources in tissue morphogenesis remain underexplored. Here, we show that exposure to a solubilized basement membrane matrix substrate, Matrigel, at early neuroepithelial stages causes rapid tissue polarization and rearrangement of neuroepithelial architecture. In cultures exposed to pure ECM components or unexposed to any exogenous ECM, polarity acquisition is slower and driven by endogenous ECM production. After the onset of neurogenesis, tissue architecture and neuronal differentiation are largely independent of the initial ECM source, but Matrigel exposure has long-lasting effects on tissue patterning. These results advance the knowledge on mechanisms of exogenously and endogenously guided morphogenesis, demonstrating the self-sustainability of neuroepithelial cultures by endogenous processes.

[Organoids-the key to novel therapies for the inner ear? German version]

The sensitivity and the complexity of the human inner ear in conjunction with the lack of regenerative capacity are the main reasons for hearing loss and tinnitus. Progress in the development of protective and regenerative therapies for the inner ear often failed in the past not least due to the fact that no suitable model systems for cell biological and pharmacological in vitro studies were available. A novel technology for creating "mini-organs", so-called organoids, could solve this problem and has now also reached inner ear research. It makes it possible to produce inner ear organoids from cochlear stem/progenitor cells, embryonic and induced pluripotent stem cells that mimic the structural characteristics and functional properties of the natural inner ear. This review focuses on the biological basis of these inner ear organoids, the current state of research and the promising prospects that are now opening up for basic and translational inner ear research.

Emerging organoid-immune co-culture models for cancer research: from oncoimmunology to personalized immunotherapies

In the past decade, treatments targeting the immune system have revolutionized the cancer treatment field. Therapies such as immune checkpoint inhibitors have been approved as first-line treatment in a variety of solid tumors such as melanoma and non-small cell lung cancer while other therapies, for instance, chimeric antigen receptor (CAR) lymphocyte transfer therapies, are still in development. Although promising results are obtained in a small subset of patients, overall clinical efficacy of most immunotherapeutics is limited due to intertumoral heterogeneity and therapy resistance. Therefore, prediction of patient-specific responses would be of great value for efficient use of costly immunotherapeutic drugs as well as better outcomes. Because many immunotherapeutics operate by enhancing the interaction and/or recognition of malignant target cells by T cells, in vitro cultures using the combination of these cells derived from the same patient hold great promise to predict drug efficacy in a personalized fashion. The use of two-dimensional cancer cell lines for such cultures is unreliable due to altered phenotypical behavior of cells when compared with the in vivo situation. Three-dimensional tumor-derived organoids, better mimic in vivo tissue and are deemed a more realistic approach to study the complex tumor-immune interactions. In this review, we present an overview of the development of patient-specific tumor organoid-immune co-culture models to study the tumor-specific immune interactions and their possible therapeutic infringement. We also discuss applications of these models which advance personalized therapy efficacy and understanding the tumor microenvironment such as: (1) Screening for efficacy of immune checkpoint inhibition and CAR therapy screening in a personalized manner. (2) Generation of tumor reactive lymphocytes for adoptive cell transfer therapies. (3) Studying tumor-immune interactions to detect cell-specific roles in tumor progression and remission. Overall, these onco-immune co-cultures might hold a promising future toward developing patient-specific therapeutic approaches as well as increase our understanding of tumor-immune interactions.

Growth and differentiation of human induced pluripotent stem cell (hiPSC)-derived kidney organoids using fully synthetic peptide hydrogels

Human induced pluripotent stem cell (hiPSC)-derived kidney organoids have prospective applications ranging from basic disease modelling to personalised medicine. However, there remains a necessity to refine the biophysical and biochemical parameters that govern kidney organoid formation. Differentiation within fully-controllable and physiologically relevant 3D growth environments will be critical to improving organoid reproducibility and maturation. Here, we matured hiPSC-derived kidney organoids within fully synthetic self-assembling peptide hydrogels (SAPHs) of variable stiffness (storage modulus, G'). The resulting organoids contained complex structures comparable to those differentiated within the animal-derived matrix, Matrigel. Single-cell RNA sequencing (scRNA-seq) was then used to compare organoids matured within SAPHs to those grown within Matrigel or at the air-liquid interface. A total of 13,179 cells were analysed, revealing 14 distinct clusters. Organoid compositional analysis revealed a larger proportion of nephron cell types within Transwell-derived organoids, while SAPH-derived organoids were enriched for stromal-associated cell populations. Notably, differentiation within a higher G' SAPH generated podocytes with more mature gene expression profiles. Additionally, maturation within a 3D microenvironment significantly reduced the derivation of off-target cell types, which are a known limitation of current kidney organoid protocols. This work demonstrates the utility of synthetic peptide-based hydrogels with a defined stiffness, as a minimally complex microenvironment for the selected differentiation of kidney organoids.

Modelling inner ear development and disease using pluripotent stem cells - a pathway to new therapeutic strategies

The sensory epithelia of the mammalian inner ear enable sound and movement to be perceived. Damage to these epithelia can cause irreversible sensorineural hearing loss and vestibular dysfunction because they lack regenerative capacity. The human inner ear cannot be biopsied without causing permanent damage, significantly limiting the tissue samples available for research. Investigating disease pathology and therapeutic developments have therefore traditionally relied on animal models, which often cannot completely recapitulate the human otic systems. These challenges are now being partly addressed using induced pluripotent stem cell-derived cultures, which generate the sensory epithelial-like tissues of the inner ear. Here, we review how pluripotent stem cells have been used to produce two-dimensional and three-dimensional otic cultures, the strengths and limitations of these new approaches, and how they have been employed to investigate genetic and acquired forms of audiovestibular dysfunction. This Review provides an overview of the progress in pluripotent stem cell-derived otic cultures thus far, focusing on their applications in disease modelling and therapeutic trials. We survey their current limitations and future directions, highlighting their prospective utility for high-throughput drug screening and developing personalised medicine approaches.

Advancements in inner ear development, regeneration, and repair through otic organoids

The vertebrate inner ear contains a diversity of unique cell types arranged in a particularly complex 3D cytoarchitecture. Both of these features are integral to the proper development, function, and maintenance of hearing and balance. Since the elucidation of the timing and delivery of signaling molecules to produce inner ear sensory cells, supporting cells, and neurons from human induced pluripotent stem cells, we have entered a revolution using organ-like 'otic organoid' cultures to explore inner ear specific genetic programs, developmental rules, and potential therapeutics. This review aims to highlight a selection of reviews and primary research papers from the past two years of particular merit that use otic organoids to investigate the broadly defined topics of cell reprogramming, regeneration, and repair.

Mimicking the Natural Basement Membrane for Advanced Tissue Engineering

Advancements in the field of tissue engineering have led to the elucidation of physical and chemical characteristics of physiological basement membranes (BM) as specialized forms of the extracellular matrix. Efforts to recapitulate the intricate structure and biological composition of the BM have encountered various advancements due to its impact on cell fate, function, and regulation. More attention has been paid to synthesizing biocompatible and biofunctional fibrillar scaffolds that closely mimic the natural BM. Specific modifications in biomimetic BM have paved the way for the development of in vitro models like alveolar-capillary barrier, airway models, skin, blood-brain barrier, kidney barrier, and metastatic models, which can be used for personalized drug screening, understanding physiological and pathological pathways, and tissue implants. In this Review, we focus on the structure, composition, and functions of in vivo BM and the ongoing efforts to mimic it synthetically. Light has been shed on the advantages and limitations of various forms of biomimetic BM scaffolds including porous polymeric membranes, hydrogels, and electrospun membranes This Review further elaborates and justifies the significance of BM mimics in tissue engineering, in particular in the development of in vitro organ model systems.

Hydrogel, Electrospun and Composite Materials for Bone/Cartilage and Neural Tissue Engineering

Injuries of the bone/cartilage and central nervous system are still a serious socio-economic problem. They are an effect of diversified, difficult-to-access tissue structures as well as complex regeneration mechanisms. Currently, commercially available materials partially solve this problem, but they do not fulfill all of the bone/cartilage and neural tissue engineering requirements such as mechanical properties, biochemical cues or adequate biodegradation. There are still many things to do to provide complete restoration of injured tissues. Recent reports in bone/cartilage and neural tissue engineering give high hopes in designing scaffolds for complete tissue regeneration. This review thoroughly discusses the advantages and disadvantages of currently available commercial scaffolds and sheds new light on the designing of novel polymeric scaffolds composed of hydrogels, electrospun nanofibers, or hydrogels loaded with nano-additives.

Deafness-in-a-dish: modeling hereditary deafness with inner ear organoids

Sensorineural hearing loss (SNHL) is a major cause of functional disability in both the developed and developing world. While hearing aids and cochlear implants provide significant benefit to many with SNHL, neither targets the cellular and molecular dysfunction that ultimately underlies SNHL. The successful development of more targeted approaches, such as growth factor, stem cell, and gene therapies, will require a yet deeper understanding of the underlying molecular mechanisms of human hearing and deafness. Unfortunately, the human inner ear cannot be biopsied without causing significant, irreversible damage to the hearing or balance organ. Thus, much of our current understanding of the cellular and molecular biology of human deafness, and of the human auditory system more broadly, has been inferred from observational and experimental studies in animal models, each of which has its own advantages and limitations. In 2013, researchers described a protocol for the generation of inner ear organoids from pluripotent stem cells (PSCs), which could serve as scalable, high-fidelity alternatives to animal models. Here, we discuss the advantages and limitations of conventional models of the human auditory system, describe the generation and characteristics of PSC-derived inner ear organoids, and discuss several strategies and recent attempts to model hereditary deafness in vitro. Finally, we suggest and discuss several focus areas for the further, intensive characterization of inner ear organoids and discuss the translational applications of these novel models of the human inner ear.