Expansion of murine and human olfactory epithelium/mucosa colonies and generation of mature olfactory sensory neurons under chemically defined conditions

Establishment of nasal and olfactory epithelium organoids for unveiling mechanism of tissue regeneration and pathogenesis of nasal diseases

Organoid is an ideal in vitro model with cellular heterogeneity and genetic stability when passaging. Currently, organoids are exploited as new tools in a variety of preclinical researches and applications for disease modeling, drug screening, host-microbial interactions, and regenerative therapy. Advances have been made in the establishment of nasal and olfactory epithelium organoids that are used to investigate the pathogenesis of smell-related diseases and cellular/molecular mechanism underlying the regeneration of olfactory epithelium. A set of critical genes are identified to function in cell proliferation and neuronal differentiation in olfactory epithelium organoids. Besides, nasal epithelium organoids derived from chronic rhinosinusitis patients have been established to reveal the pathogenesis of this disease, potentially applied in drug responses in individual patient. The present article reviews recent research progresses of nasal and olfactory epithelium organoids in fundamental and preclinical researches, and proposes current advances and potential future direction in the field of organoid research and application.

Multimodal spatiotemporal monitoring of basal stem cell-derived organoids reveals progression of olfactory dysfunction in Alzheimer's disease

Olfactory dysfunction (OD) is a highly prevalent symptom and an early sign of neurodegenerative diseases in humans. However, the roles of peripheral olfactory system in disease progression and the mechanisms behind neurodegeneration remain to be studied. Olfactory epithelium (OE) organoid is an ideal model to study pathophysiology in vitro, yet the reliance on 3D culture condition limits continual in situ monitoring of organoid development. Here, we combined impedance biosensors and live imaging for real-time spatiotemporal analysis of OE organoids morphological and physiological features during Alzheimer's disease (AD) progression. The impedance measurements showed that organoids generated from basal stem cells of APP/PS1 transgenic mice had lower proliferation rate than that from wild-type mice. In concert with the biosensor measurements, live imaging enabled to visualize the spatial and temporal dynamics of organoid morphology. Abnormal protein aggregation and accumulation, including amyloid plaques and neurofibrillary tangles, was found in AD organoids and increased as disease progressed. This multimodal in situ bioelectrical measurement and imaging provide a new platform for investigating onset mechanisms of OD, which would shed new light on early diagnosis and treatment of neurodegenerative disease.

Immunohistological study of the unexplored vomeronasal organ of an endangered mammal, the dama gazelle (Nanger dama)

Dama gazelle is a threatened and rarely studied species found primarily in northern Africa. Human pressure has depleted the dama gazelle population from tens of thousands to a few hundred individuals. Since 1970, a founder population consisting of the last 17 surviving individuals in Western Sahara has been maintained in captivity, reproducing naturally. In preparation for the future implementation of assisted reproductive technology, certain aspects of dama gazelle reproductive biology have been established. However, the role played by semiochemical-mediated communications in the sexual behavior of dama gazelle remains unknown due partially to a lack of a neuroanatomical or morphofunctional characterization of the dama gazelle vomeronasal organ (VNO), which is the sensory organ responsible for pheromone processing. The present study characterized the dama gazelle VNO, which appears fully equipped to perform neurosensory functions, contributing to current understanding of interspecies VNO variability among ruminants. By employing histological, lectin-histochemical, and immunohistochemical techniques, we conducted a detailed morphofunctional evaluation of the dama gazelle VNO along its entire longitudinal axis. Our findings of significant structural and neurochemical transformation along the entire VNO suggest that future studies of the VNO should take a similar approach. The present study contributes to current understanding of dama gazelle VNO, providing a basis for future studies of semiochemical-mediated communications and reproductive management in this species. RESEARCH HIGHLIGHTS: This exhaustive immunohistological study of the vomeronasal organ (VNO) of the dama gazelle provides the first evidence of notable differences in the expression of neuronal markers along the rostrocaudal axis of the VNO. This provides a morphological basis for the implementation of pheromones in captive populations of dama gazelle.

Axonal Regrowth of Olfactory Sensory Neurons In Vitro

One of the most prevalent causes of olfactory loss includes traumatic brain injury with subsequent shearing of olfactory axons at the level of the cribriform plate (anterior skull base). Scar tissue at this level may prevent axonal regrowth toward the olfactory bulb. Currently, there is no cure for this debilitating and often permanent condition. One promising therapeutic concept is to implant a synthetic scaffold with growth factors through the cribriform plate/scar tissue to induce neuroregeneration. The first step toward this goal is to investigate the optimum conditions (growth factors, extracellular matrix proteins) to boost this regeneration. However, the lack of a specifically tailored in vitro model and an automated procedure for quantifying axonal length limits our ability to address this issue. The aim of this study is to create an automated quantification tool to measure axonal length and to determine the ideal growth factors and extracellular proteins to enhance axonal regrowth of olfactory sensory neurons in a mouse organotypic 2D model. We harvested olfactory epithelium (OE) of C57BL/6 mice and cultured them during 15 days on coverslips coated with various extracellular matrix proteins (Fibronectin, Collagen IV, Laminin, none) and different growth factors: fibroblast growth factor 2 (FGF2), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), nerve growth factor (NGF), retinoic acid (RA), transforming growth factor β (TGFβ), and none. We measured the attachment rate on coverslips, the presence of cellular and axonal outgrowth, and finally, the total axonal length with a newly developed automated high-throughput quantification tool. Whereas the coatings did not influence attachment and neuronal outgrowth rates, the total axonal length was enhanced on fibronectin and collagen IV (p = 0.001). The optimum growth factor supplementation media to culture OE compared to the control condition were as follows: FGF2 alone and FGF2 from day 0 to 7 followed by FGF2 in combination with NGF from day 7 to 15 (p < 0.0001). The automated quantification tool to measure axonal length outperformed the standard Neuron J application by reducing the average analysis time from 22 to 3 min per specimen. In conclusion, robust regeneration of murine olfactory neurons in vitro can be induced, controlled, and efficiently measured using an automated quantification tool. These results will help advance the therapeutic concept closer toward preclinical studies.

TMEM59 ablation leads to loss of olfactory sensory neurons and impairs olfactory functions via interaction with inflammation

The olfactory epithelium undergoes constant neurogenesis throughout life in mammals. Several factors including key signaling pathways and inflammatory microenvironment regulate the maintenance and regeneration of the olfactory epithelium. In this study, we identify TMEM59 (also known as DCF1) as a critical regulator to the epithelial maintenance and regeneration. Single-cell RNA-Seq data show downregulation of TMEM59 in multiple epithelial cell lineages with aging. Ablation of TMEM59 leads to apparent alteration at the transcriptional level, including genes associated with olfactory transduction and inflammatory/immune response. These differentially expressed genes are key components belonging to several signaling pathways, such as NF-κB, chemokine, etc. TMEM59 deletion impairs olfactory functions, attenuates proliferation, causes loss of both mature and immature olfactory sensory neurons, and promotes infiltration of inflammatory cells, macrophages, microglia cells and neutrophils into the olfactory epithelium and lamina propria. TMEM59 deletion deteriorates regeneration of the olfactory epithelium after injury, with significant reduction in the number of proliferative cells, immature and mature sensory neurons, accompanied by the increasing number of inflammatory cells and macrophages. Anti-inflammation by dexamethasone recovers neuronal generation and olfactory functions in the TMEM59-KO animals, suggesting the correlation between TMEM59 and inflammation in regulating the epithelial maintenance. Collectively, TMEM59 regulates olfactory functions, as well as neuronal generation in the olfactory epithelium via interaction with inflammation, suggesting a potential role in therapy against olfactory dysfunction associated with inflamm-aging.

Cisplatin attenuates taste cell homeostasis and induces inflammatory activation in the circumvallate papilla

Rationale: Gustation is important to several biological functions in mammals. However, chemotherapy drugs often harm taste perception in cancer patients, while the underlying mechanism is still unclear for most drugs and there is no effective way to restore taste function. This study investigated the effects of cisplatin on the taste cell homeostasis and gustatory function. Methods: We used both mice and taste organoid models to study the effect of cisplatin on taste buds. Gustometer assay, gustatory nerve recording, RNA-Sequencing, quantitative PCR, and immunohistochemistry was performed to analyze the cisplatin-induced alteration in taste behavior and function, transcriptome, apoptosis, cell proliferation and taste cell generation. Results: Cisplatin inhibited proliferation and promoted apoptosis in the circumvallate papilla, leading to significant impairment in taste function and receptor cell generation. The transcriptional profile of genes associated with cell cycle, metabolic process and inflammatory response was significantly altered after cisplatin treatment. Cisplatin inhibited growth, promoted apoptosis, and deferred taste receptor cell differentiation in taste organoids. LY411575, a γ-secretase inhibitor, reduced the number of apoptotic cells and increased the number of proliferative cells and taste receptor cells, potentially suggesting as a taste tissue protective agent against chemotherapy. LY411575 treatment could offset the increased number of Pax1⁺ or Pycr1⁺ cells induced by cisplatin in the circumvallate papilla and taste organoids. Conclusion: This study highlights the inhibitory effects of cisplatin on taste cell homeostasis and function, identifies critical genes and biological processes regulated by chemotherapy, and proposes potential therapeutic targets and strategy for taste dysfunction in cancer patients.

Characterization of human nasal organoids from chronic rhinosinusitis patients

Patient-derived organoids grown in three-dimensional cultures provide an excellent platform for phenotypic high-throughput screening and drug-response research. Organoid technology has been applied to study stem cell biology and various human pathologies. This study investigates the characteristics and cellular morphology of organoids derived from primary human nasal epithelial cells (HNECs) of chronic rhinosinusitis (CRS) patients. Nasal organoids were cultured up to 20 days and morphological, cell composition and functional parameters were measured by immunofluorescence, RT-qPCR, western blot and FACS analysis. The results showed that nasal organoids expressed the stem cell marker leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), and markers for apical junction genes, goblet cells and ciliated cells. Moreover, we were able to regrow and expand the nasal organoids well after freezing and thawing. This study provides an effective and feasible method for development of human nasal organoids, suitable for the phenotypic high-throughput screening and drug response research.

Reprogramming of Rat Fibroblasts into Induced Neurons by Small-Molecule Compounds In Vitro and In Vivo

Cell replacement is a promising approach for neurodegenerative disease treatment. Somatic cells such as fibroblasts can be induced to differentiate into neurons by specific transcription factors; however, the potential of viral vectors used for reprogramming to integrate into the genome raises concerns about the potential clinical applications of this approach. Here, we directly reprogrammed rat embryonic skin fibroblasts into induced neurons (iNs) via six small-molecule compounds (SMs) (VPA, CHIR99021, forskolin, Y-27632, Repsox, and P7C3-A20). iNs exhibit typical neuronal morphology, and immunofluorescence showed that more than 96% of the iNs expressed the early neuronal marker class III beta-tubulin (TUJ1) and that more than 91% of iNs expressed the mature neuronal marker neuron-specific enolase (NSE) after 10 days of reprogramming. Quantitative real-time polymerase chain reaction also showed that most iNs expressed the dopaminergic neuron marker tyrosine hydroxylase, the neural marker Nur correlation factor 1, the (γ-aminobutyric acid, GABA) GABAergic neuronal marker GABA, and the cholinergic neuron marker choline acetyltransferase. In addition, we found that cell proliferation decreased during reprogramming and that protein synthesis increased initially and then decreased. SMs were mixed with hydrogels, and the hydrogels were implanted subcutaneously into the backs of rats. After 7 days, the TUJ1 and NSE proteins were expressed in surrounding tissues, indicating that SMs caused reprogramming in vivo. In summary, rat skin fibroblasts can be efficiently reprogrammed into iNs by SMs in vitro and in vivo.

Bioelectric Potential in Next-Generation Organoids: Electrical Stimulation to Enhance 3D Structures of the Central Nervous System

Pluripotent stem cell-derived organoid models of the central nervous system represent one of the most exciting areas in in vitro tissue engineering. Classically, organoids of the brain, retina and spinal cord have been generated via recapitulation of in vivo developmental cues, including biochemical and biomechanical. However, a lesser studied cue, bioelectricity, has been shown to regulate central nervous system development and function. In particular, electrical stimulation of neural cells has generated some important phenotypes relating to development and differentiation. Emerging techniques in bioengineering and biomaterials utilise electrical stimulation using conductive polymers. However, state-of-the-art pluripotent stem cell technology has not yet merged with this exciting area of bioelectricity. Here, we discuss recent findings in the field of bioelectricity relating to the central nervous system, possible mechanisms, and how electrical stimulation may be utilised as a novel technique to engineer “next-generation” organoids.

Pharmacological Manipulation of Wnt/β-Catenin Signaling Pathway in Human Neural Precursor Cells Alters Their Differentiation Potential and Neuronal Yield

The canonical Wnt/β-catenin pathway is a master-regulator of cell fate during embryonic and adult neurogenesis and is therefore a major pharmacological target in basic and clinical research. Chemical manipulation of Wnt signaling during in vitro neuronal differentiation of stem cells can alter both the quantity and the quality of the derived neurons. Accordingly, the use of Wnt activators and blockers has become an integral part of differentiation protocols applied to stem cells in recent years. Here, we investigated the effects of the glycogen synthase kinase-3β inhibitor CHIR99021, which upregulates β-catenin agonizing Wnt; and the tankyrase-1/2 inhibitor XAV939, which downregulates β-catenin antagonizing Wnt. Both drugs and their potential neurogenic and anti-neurogenic effects were studied using stable lines human neural precursor cells (hNPCs), derived from embryonic stem cells, which can be induced to generate mature neurons by chemically-defined conditions. We found that Wnt-agonism by CHIR99021 promotes induction of neural differentiation, while also reducing cell proliferation and survival. This effect was not synergistic with those of pro-neural growth factors during long-term neuronal differentiation. Conversely, antagonism of Wnt by XAV939 consistently prevented neuronal progression of hNPCs. We show here how these two drugs can be used to manipulate cell fate and how self-renewing hNPCs can be used as reliable human in vitro drug-screening platforms.