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Method Article
A detailed protocol is presented here to describe an in vitro organoid model from human nasal epithelial cells. The protocol has options for measurements requiring standard laboratory equipment, with additional possibilities for specialized equipment and software.
Individualized therapy for cystic fibrosis (CF) patients can be achieved with an in vitro disease model to understand baseline Cystic Fibrosis Transmembrane conductance Regulator (CFTR) activity and restoration from small molecule compounds. Our group recently focused on establishing a well-differentiated organoid model directly derived from primary human nasal epithelial cells (HNE). Histology of sectioned organoids, whole-mount immunofluorescent staining, and imaging (using confocal microscopy, immunofluorescent microscopy, and bright field) are essential to characterize organoids and confirm epithelial differentiation in preparation for functional assays. Furthermore, HNE organoids produce lumens of varying sizes that correlate with CFTR activity, distinguishing between CF and non-CF organoids. In this manuscript, the methodology for culturing HNE organoids are described in detail, focusing on the assessment of differentiation using the imaging modalities, including the measurement of baseline lumen area (a method of CFTR activity measurement in organoids that any laboratory with a microscope can employ) as well as the developed automated approach to a functional assay (which requires more specialized equipment).
Introduction to the technique
Ex vivo culture-based assays are an increasingly utilized tool for precision medicine and the study of disease pathophysiology. Primary human nasal epithelial (HNE) cell culture has been used in numerous studies of cystic fibrosis1,2,3,4,5,6,7,8,9,10,11,12,13, an autosomal recessive disease that affects epithelial cell function in multiple organs. HNE culture provides a renewable source of airway epithelia that may be obtained prospectively and recapitulates electrophysiological and biochemical qualities to test Cystic Fibrosis Transmembrane conductance Regulator (CFTR) activity. HNE cells can be sampled with minimal side effects14, similar to common viral respiratory swabs. Research work describing a model for cystic fibrosis study derived from HNE brush biopsies has been recently published11,13. While similar to other models using primary HNE2,3 and intestinal tissue15,16,17,18,19, detailed characterization of the differentiation and imaging of this model are described here for use in CF research and for aiding in the studies of other airways diseases13. The organoid model is not unlimited like immortalized cell lines but can be expanded by conditional reprogramming (using irradiated and inactivated feeder fibroblasts and Rho-kinase inhibitors) to a more stem cell-like state20,21,22,23. The processing of HNE brush biopsies using this method yields large numbers of epithelial cells for use in multiple applications at higher throughput while still retaining the ability to differentiate fully. While this protocol was developed using feeder cells, other methodologies may be used by investigators wishing to avoid feeder cell technology14,24.
Importance of the technique to pulmonary biology
A significant study has been devoted to understanding how the absence of regular, functioning CFTR in the cell membrane of epithelial cells results in dysfunction in the lungs, pancreas, liver, intestine, or other tissues. Dysfunctional epithelial ion transport, particularly that of chloride and bicarbonate, results in a decreased volume of the epithelial lining fluids and changes in mucous secretions, leading to mucous stasis and obstruction. In other airway diseases, such as primary ciliary dyskinesia, altered ciliary motion impairs mucociliary clearance and leads to mucous stasis and obstruction25. Therefore, the current HNE organoid model has been developed for various applications, depending on the investigator's experimental design and resources. This includes live-cell imaging using live-cell stains; fixation and sectioning to characterize the morphology; immunofluorescence staining with antibodies and whole-mount confocal imaging to avoid disrupting intraluminal structures; and bright-field imaging and micro-optical coherence tomography for quantitative measurements of ciliary beat frequency and mucociliary transport13. To facilitate expansion to other investigators, commercially available reagents and supplies were used for culturing. A functional assay was developed that used common microscope techniques and more specialized equipment. Overall, while the present model was designed to assess CFTR activity at baseline or in response to therapeutics, the techniques described in this protocol can be applied to other diseases involving epithelial cell function, especially epithelial cell fluid transport.
Comparison to other methodologies
Recently the utility of this organoid model was developed by correlating in vitro CFTR modulator responses of patients' organoids with their clinical response11. Notably, it is also demonstrated that the present model paralleled short-circuit current responses, the current gold standard for assessing CFTR function, in the same patients. Short-circuit current differs from the swelling assay because the former measures CFTR function via ion transport26. In contrast, this assay measures a more downstream effect with fluid transport, providing additional information about the overall function of CFTR27,28,29,30,31,32. Short-circuit current measurements have continued to be a common and reliable method for determining CFTR chloride channel activity1,33. These electrophysiological assays require specialized, expensive equipment, require many times more cells for each experimental replicate than the organoid assay, cannot be easily automated, and are not amenable to scaling up for higher throughput applications. Another organoid model derived from intestinal epithelia has additional advantages15,16,17,18, such as more excellent replicative capability, but is neither derived from an airway tissue nor is universally available. HNE brushings are obtained with inexpensive cytology brushes without the need for sedation and at minimal risk. Getting the brushing does not require a clinician and can be performed by trained research coordinators and other research staff14. The HNE organoid model can be cultured by any laboratory with primary cell culture capabilities, and some of the applications can be performed with standard microscopy techniques. Altogether, these advantages provide additional access to technology for assessing airway epithelial function that might otherwise be unavailable to some laboratories. Furthermore, HNE organoids can be utilized to study other disease states that affect the airway, such as primary ciliary dyskinesia25 or viral infection, which intestinal organoids cannot.
HNE samples were collected at the Children's of Alabama hospital. All procedures and methods described here have been approved by the IRB University of Alabama at Birmingham (UAB IRB #151030001). To facilitate the expansion and improve the function of human nasal epithelial cells (HNEs), the present culturing methods are adapted from the well-known air-liquid interface (ALI) culture method28,34. HNEs were initially collected by brush biopsy as previously described12,14, with the only difference being the use of a cytology brush. All sample processing steps and cell culture were performed in the biosafety cabinet.
1. Cell culture and expansion of nasal epithelial cells
2. Growth and differentiation of organoids in slides and culture inserts
3. Preparation and isolation of organoids for whole-mount immunofluorescence
4. Preparation and isolation of organoids for histological sectioning
5. Imaging of live organoids
NOTE: The following steps are carried out using an automated imaging system (see Table of Materials). Different imaging systems need to adapt these steps following their specific manufacturer's instructions. Regardless of the equipment utilized, imaging live organoids require a temperature-controlled and humidified environmental chamber with an accompanied CO2 gas controller.
6. Baseline lumen measurements
NOTE: This is done using manual imaging analysis software (see Table of Materials). A similar methodology can be followed using an open-source software38 or any software that can measure the area of a region on an image.
7. Pre-treatment and automated imaging of HNE organoids
NOTE: All pre-treatment steps are carried out in a clean biosafety cabinet. Pre-setup the automated imaging system and the software for recording the assay before step 7.1. The incubation with DAPI is optional but is recommended as a fail-safe if the quality of bright field images is compromised. In this case, the DAPI channel (377 nm) can be analyzed instead.
8. Automated analysis of forskolin-induced swelling assay on HNE organoids
HNEs expansion is essential for a thriving organoid culture. HNEs from a successful sample collection should expand to over 70% confluence around 10 days. An example of successful and unsuccessful samples is shown in Figure 1A and Figure 1B, respectively. The cells must be discarded if they cannot reach 70% confluence by 14 days after co-culture with irradiated 3T3 cells. Any contaminated cells are to be immediately discarded if unable to rescue...
This manuscript provides detailed methodologies for comprehensive live and fixed imaging of the airway epithelial organoids derived from HNE brush biopsy. It describes functional assays that can determine CFTR activity in an individual. HNEs provide a minimally invasive, primary tissue for a variety of applications. The expansion techniques offered here can be used for modeling airways disease, including organoids. Organoids can be used for precision therapeutic approaches and to monitor the stability of gene or mRNA-bas...
JSG is listed as an inventor on a patent application 20170242033 from the University of North Carolina that describes a similar model. When licensed technology from UNC produces royalties, the inventors receive a share of the revenue. Otherwise, the authors declare no conflicts of interest. The funders had no role in the study's design, in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.
We gratefully acknowledge the contributions of all the participants who donated HNE brush biopsies to develop this protocol. We thank Latona Kersh and Children's Research Unit staff for coordinating study volunteer recruitment and sample collections. We thank Lily Deng, Johnathan Bailey, and Stephen Mackay, former trainees in our laboratory, for technical assistance. We thank Zhong Liu and Rui Zhao for their technical help. Steven M. Rowe, Director of the CF Research Center at UAB, provides leadership and resources, without which this work would not be possible. We also would like to thank Sarah Guadiana at Biotek for assistance with instrument training, Robert Grabski for confocal microscopy assistance at the UAB High-Resolution Imaging Facility, and Dezhi Wang for histological assistance at the UAB Histology Core. This work was supported by the National Institutes of Health (NIH.) Grant K23HL143167 (to JSG), Cystic Fibrosis Foundation (CFF) Grant GUIMBE18A0-Q (to JSG), the Gregory Fleming James Cystic Fibrosis Center [NIH Grants R35HL135816 and DK072482 and the CFF University of Alabama at Birmingham (UAB) Research and Development Program (Rowe19RO)], and the UAB Center for Clinical and Translational Science (NIH Grant UL1TR001417).
Name | Company | Catalog Number | Comments |
Nasal brush | Medical Packaging CYB1 | CYB-1 | Length: 8 inches, width approximately 7 mm |
Large-Orifice Pipette Tips | ThermoFisher Scientific | 02-707-141 | Large bore pipette tips |
Accutase | ThermoFisher Scientific | A1110501 | Cell detachment solution |
0.05% trypsin -EDTA | Gibco | 25300-054 | |
Trypsin inhibitor from soybean | Sigma | T6522 | Working solution: 1mg/mL in 1XDPBS |
Matrigel matrix | Corning | 356255 | Extracellular matrix (EM) |
µ-Slide Angiogenesis | Ibidi | 81506 | 15-well slide |
24-Well Transwell | Corning | 7200154 | Culture insert |
Chambered Coverglass | ThermoFisher Scientific | 155409 | 8-well glass-bottom chamber slides |
Cell-Tak Cell and Tissue Adhesive | ThermoFisher Scientific | 354240 | Cell adhesive |
Paraformaldehyde | Electron Microscopy Sciences | 50980487 | |
Triton X-100 | Alfa Aesar | A16046 | |
BSA | ThermoFisher Scientific | BP1600-100 | |
NucBlue | ThermoFisher Scientific | R37605 | DAPI |
Eclipse Ts2-FL (Inverted Routine Microscope) | Nikon | Inverted epi-fluorescence microscope or bright-field microscope | |
Nikon A1R-HD25 | Nikon | Confocal microscope | |
NIS Elements- Basic Research | Nikon | manual imaging analysis software | |
Histogel | ThermoFisher Scientific | HG-4000-012 | |
Disposable Base Molds | ThermoFisher Scientific | 41-740 | |
Lionheart FX | BioTek | BTLFX | Automated image system |
Lionheart Cover | BioTek | BT1450009 | Environmental Control Lid |
Humidity Chamber | BioTek | BT1450006 | Stage insert (environmental chamber) |
Gas Controller for CO2 and O2 | BioTek | BT1210013 | Gas controller |
Microplate/Slide Stage Insert | BioTek | BT1450527 | Slide holder |
Gen5 Imaging Prime Software | BioTek | BTGEN5IPRIM | Automated imaging analysis software |
4x Phase Contrast Objective | BioTek | BT1320515 | |
10x Phase Contrast Objective | BioTek | BT1320516 | |
LED Cube | BioTek | BT1225007 | |
Filter Cube (DAPI) | BioTek | BT1225100 | DAPI |
CFTRinh-172 | Selleck Chemicals | S7139 | |
Forskolin | Sigma | F6886 | |
IBMX | Sigma | I5879 | |
Expansion Media | |||
DMEM | ThermoFisher Scientific | 11965 | |
F12 Nutrient mix | ThermoFisher Scientific | 11765 | |
Fetal Bovine Serum | ThermoFisher Scientific | 16140-071 | |
Penicillin/Streptomycin | ThermoFisher Scientific | 15-140-122 | |
Cholera Toxin | Sigma | C8052 | |
Epidermal Growth Factor (EGF) | ThermoFisher Scientific | PHG0314 | |
Hydrocortisone (HC) | Sigma | H0888 | |
Insulin | Sigma | I9278 | |
Adenine | Sigma | A2786 | |
Y-27632 | Stemgent | 04-0012-02 | |
Antibiotic Media | |||
Ceftazidime | Alfa Aesar | J66460-03 | |
Tobramycin | Alfa Aesar | J67340 | |
Vancomycin | Alfa Aesar | J67251 | |
Amphotericin B | Sigma | A2942 | |
Differentiation Media | |||
DMEM/F-12 (1:1) | ThermoFisher Scientific | 11330-32 | |
Ultroser-G | Pall | 15950-017 | |
Fetal Clone II | Hyclone | SH30066.03 | |
Bovine Brain Extract | Lonza | CC-4098 | |
Insulin | Sigma | I-9278 | |
Hydrocortisone | Sigma | H-0888 | |
Triiodothyronine | Sigma | T-6397 | |
Transferrin | Sigma | T-0665 | |
Ethanolamine | Sigma | E-0135 | |
Epinephrine | Sigma | E-4250 | |
O-Phosphorylethanolamine | Sigma | P-0503 | |
Retinoic Acid | Sigma | R-2625 | |
Primary antibodies | |||
Human CFTR antibody | R&D Systems | MAB1660 | Dilution: 100x |
ZO-1 antibody | Thermo Fisher | MA3-39100-A647 | Dilution: 1000x |
Anti-MUC5B antibody | Sigma | HPA008246 | Dilution: 100x |
Anti-acetylated tubulin | Sigma | T7451 | Dilution: 100x |
Anti-beta IV Tubulin antibody | Abcam | Ab11315 | Dilution: 100x |
Secondary antibodies | |||
Donkey anti-Mouse IgG (H+L), Alexa Fluor 488 | Invitrogen | A21202 | Dilution: 2000x |
Donkey anti-Rabbit IgG (H+L), Alexa Fluor 594 | Invitrogen | A21207 | Dilution: 2000x |
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