This protocol describes methods for establishing whole mount and dissociated cultures of mouse Dorsal Root Ganglia (DRG) and their use to assess tumor-nerve interactions.
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Method Article
This protocol describes methods for establishing whole mount and dissociated cultures of mouse Dorsal Root Ganglia (DRG) and their use to assess tumor-nerve interactions.
The contribution of the nervous system to the tumor microenvironment and the importance of neural invasion as a route for cancer dissemination are being increasingly recognized. Interactions of cancer cells with neurons can promote their invasion around and into nerves, a feature of many cancers with poor clinical outcomes. In vitro models to study reciprocal interactions between neurons and cancer cells provide valuable tools for understanding cancer spread and identifying approaches to mitigate it.
Here, we describe a protocol for murine dorsal root ganglia (DRG) isolation and the establishment of both whole mount and dissociated monolayer cultures that can be used to visualize neuron morphology and neurite outgrowth over time. Whole DRGs mounted in Matrigel preserve nerve architecture and responses to stimuli in a heterogeneous environment more similar to the in vivo nerve, while dissociated nerve cultures allow assessment of direct cell-cell interactions more closely. Once DRG cultures are established, cancer cells can be added to generate co-cultures that can be used to visualize changes in neurite outgrowth and nerve morphology in response to cancer cells. Growth or motility of cancer cells in response to nerve-derived signals over time or under conditions of growth stimulation or inhibition can be assessed, as well as visualizing the effects of direct contact between cancer cells and nerve extensions.
As both co-culture models can be generated simultaneously, this protocol provides a more comprehensive view of the impact of cancer-neuron interactions and facilitates comparisons of treatment conditions and integration of information from the cellular level and whole ganglia. This protocol will facilitate the study of nerve-tumor interactions and can be used for a wide range of applications, including studies of cell signaling, drug screening, or study of the heterogeneity of the tumor-nerve environment and the mechanisms of tumor dissemination along nerves.
Tumor dissemination, through local invasion and regional or distant metastasis, is the primary cause of cancer-related death. Although research has focused on vascular or lymphatic routes of spread, neural invasion of tumor cells is frequently observed in many solid tumors, including pancreatic1,2, prostate3, head and neck4, breast5, and colorectal6 cancers. In recent years, numerous studies have highlighted the emerging role of nerves in promoting tumor growth and progression, and as routes of dissemination, driving metastasis development7,8. In this context, cancer neuroscience has emerged as a prominent research field, offering new perspectives in oncology by elucidating the interactions between tumor cells and the fundamental components of the peripheral nervous system (PNS) that may contribute to these processes8,9.
The PNS consists of both peripheral nerves and ganglia, which are heterogeneous structures composed of diverse cell types, including neurons of varying sizes and functions, Schwann and other glial cells, fibroblasts, macrophages, mast cells, melanocytes, and vascular endothelial cells that form the local vasculature10. The PNS is a critical component of the tumor microenvironment (TME), and reciprocal communication between cancer cells and nerves, either directly through physical contact or indirectly through the release of neurotrophic factors, neurotransmitters, growth factors, and other signals, can facilitate neural invasion and promote more aggressive phenotypes8.
In vitro models can be used to characterize the processes that contribute to nerve maintenance and repair and are increasingly being used to examine cellular interactions between nerves and cancer cells11,12. A frequently used in vitro model involves extracted mouse dorsal root ganglia (DRG) co-cultured with tumor cells11. These models often use two-dimensional (2D) monolayer culture of dissociated DRG cells to study neuronal biology in vitro and have been used to model cellular interactions in the PNS13,14. However, 2D cultures lack the complexity of the nerve microenvironment and poorly represent its in vivo architecture. Three-dimensional (3D) whole mounts of peripheral neurons or ganglia offer an alternative that more effectively recapitulates peripheral nerve physiology to represent nerve-environment interactions more holistically15,16,17,18. However, the heterogeneity of this model limits the ability to visualize or quantify cell-cell interactions, and these models are more effective for observing overall peripheral nerve responses than for exploring specific cellular interactions and mechanistic responses to stimuli. Thus, it is clear that dissociated and whole mount neuronal cultures are complementary and that evaluation of 2D and 3D models in parallel is optimal to assess both overall effects and individual cell responses to stimuli.
This protocol describes methods for generating complementary dissociated (2D) and whole-mount (3D) nerve cultures that can be used to evaluate nerve and cancer cell interactions at both cellular and tissue levels, providing a more comprehensive view of these interactions than methods using only one type of culture1,13. These models can be used to visualize and assess cellular processes, including nerve cell morphology and neurite outgrowth, as well as tumor cell responses to nerve-secreted chemotactic agents, such as neurotrophic factors, and crosstalk between sensory neurons and tumor cells. It also allows exploration of potential interactions between tumor cells and other components of the neural microenvironment, such as immune cells, fibroblasts, and glia. We highlight the application of these models to study nerve-cancer cell interactions over time, visualized by live cell staining or immunofluorescence, as examples of approaches to assess or quantify cell interactions and responses. Together, the results generated from the use of these methods can further our understanding of how the nervous system promotes the growth and spread of cancer, helping us to develop strategies to target these mechanisms.
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All mouse work was reviewed and approved by the Office of the University Animal Care Committee at Queen's University (Protocol number 2524). Animals were maintained and euthanized for tissue collection in compliance with Canadian Council on Animal Care, and National Centre for the Replacement, Refinement & Reduction on Animals in Research (UK) ethical guidelines. In this protocol, we used tissue isolated from C57BL/6 animals but also successfully used other genotypes, including Rag2IL2Rγc KO animals. Sections 1-6 can be performed in a clean environment on a surface-sterilized lab bench (see Figure 1), while sections 7-9 must be performed in a biological safety cabinet. For better understanding, schematic representations of the steps mentioned were created (Figure 1).
1. Preparation of stock solutions
2. Preparing reagents and materials for the dissection of DRGs (Figure 1A)
3. Preparing reagents and materials for whole-mount DRG culture
NOTE: Some steps in this section might require overnight preparation. Although any type of tissue culture plate can be used for DRG cultures, the volumes and instructions in this protocol were optimized for 8-well glass bottom slides, which provided optimal imaging quality for our analyses. Keep 8-well glass bottom slide, pipette tips, and Matrigel on ice at all times.
4. Preparing reagents and materials for dissociated DRG culture
5. Harvesting the spinal column (Figure 1B) and dissecting the DRGs (Figure 1C)
6. Dissecting the Dorsal Root Ganglia (DRGs)
7. Whole-mount DRG culture (Figure 2)
8. Dissociated DRG culture (Figure 4)
NOTE: Any multiwell plate can be used to seed the dissociated DRG neurons. However, in this protocol, 8-well glass-bottom slides were used because they provided better cell confluency and imaging quality for immunofluorescence analyses.
9. Preparing cancer cell suspensions and establishing co-cultures
NOTE: Adherent cancer cells of many kinds can be used. Growth media and cell numbers for co-cultures will be cell line-dependent. We recommend preliminary testing before the experiment to determine timing for cell collection and optimal cell seeding numbers. The protocol described here was based on the use of human pancreatic cancer cell lines PanC1, and MiaPaCa2, and prostate cancer cell line DU-145.
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Our protocol describes the isolation of primary mouse DRG-derived cells and the establishment of two complementary culture models: dissociated DRG and whole-mounted DRG cultures, which allow us to investigate nerve-cancer cell interactions at different levels of complexity. A key advantage of this protocol is that both types of culture can be generated using DRGs isolated from the same animal, which minimizes inter-animal and inter-experimental variability and allows the information gener...
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The protocol presented here describes improved methods to establish 2D and 3D DRG primary nerve cultures and their application in co-culture with cancer cells. This protocol advances on previous methods by establishing the two models in parallel. As 2D and 3D models are established at the same time, using primary nerves isolated from the same animals, interanimal and interexperimental variation is minimized, and data from both models can be more easily compared or integrated facilitating complementary observations of cel...
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The authors have no conflicts of interest to disclose.
This work was supported by operating grants from the Canadian Institutes for Health Research (PJT-178274) (LMM), and by an Ontario Graduate Scholarship (LCBO), and by a scholarship from the Coordination for the Improvement of Higher Education Personnel - Brazil (CAPES) - Finance Code 001 (ERP). LMM is the Bracken Chair in Genetics and Molecular Medicine at Queen's University. Some images were generated in part using Biorender.
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| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Tools | |||
| 70 µm Cell Strainer | Progene | 71-229483-ULT | Used for filtering cell suspension |
| 8-well glass bottom slides | IBidi, Munich, Germany | 80807 | |
| Dumont #5 - Fine Forceps | Fine Science Tools, Foster City, USA | 11254-20 | |
| Dumont #5 Forceps | Fine Science Tools, Foster City, USA | 11252-20 | |
| Fine Scissors | Fine Science Tools, Foster City, USA | 91460-11 | |
| Pattern Forceps | Fine Science Tools, Foster City, USA | 91121-12 | |
| Spring Scissors | Fine Science Tools, Foster City, USA | 91500-09 | |
| Reagents | |||
| 1x Phosphate buffered saline | Sigma, St. Louis, USA | D8662-500ML | Used for dissolving enzymes |
| B-27 Supplement (50x) | Thermo Fisher Scientific, Massachusetts, USA | 17504044 | Used at 2% concentration in F12 media |
| Bovine Type I Collagen | Corning Incorporated, New York, USA | 354231 | Used for coating plates, Working solution 50 µg/mL in 0.01 M HCl |
| Collagenase Type IV | Sigma-Aldrich, St. Louis, USA | C4-BIOC | Dissolve in PBS at 1.25 mg/mL, aliquot, store at -20 °C |
| Dispase II | Roche, Basel, Switzerland | 4942078001 | Dissolve in PBS at 2.5 mg/mL, aliquot, store at -20 °C |
| DNase I | Roche, Basel, Switzerland. | 11284932001 | Added at final concentration of 0.2 mg/mL during dissociation |
| Fetal Bovine Serum (FBS) | Sigma-Aldrich, St. Louis, USA | F1051 | Used at 10% concentration in F12 media |
| HBSS (Hank's Balanced Salt Solution) | Sigma, St. Louis, USA | H6648-500ML | Prepared with 1% Penicillin-Streptomycin |
| Matrigel Growth Factor Reduced | Corning Incorporated, New York, USA | 356231 | Thaw at 4 °C overnight, keep on ice |
| Nutrient Mixture F-12 Ham | Sigma-Aldrich, St. Louis, USA | N6658-500ML | Basal medium for preparation of supplemented culture media |
| Papain | Roche, Basel, Switzerland. | 10108014001 | Dissolve in PBS at 30 U/mL, aliquot, store at -20 °C |
| Penicillin-Streptomycin (100x) | Sigma-Aldrich, St. Louis, USA | P4333-100ML | Used at 1% concentration in media |
| Trypan Blue Solution | Sigma-Aldrich, St. Louis, USA | T8154-100ML | To assess cell viability |
| TrypLE Express | Thermo Fisher Scientific, Massachusetts, USA | 12605-028 | For harvesting cancer cells |
| Antibodies | |||
| β-Tubulin III antibody | Abcam (Cambridge, UK) | AB15568 | Dilution 1:200 |
| Alexa Fluor 488 | Thermo Fisher Scientific, Massachusetts, USA | A-11008 | Dilution 1:2000 |
| Alexa Fluor 594 | Thermo Fisher Scientific, Massachusetts, USA | A-21442 | Dilution 1:2000 |
| Alexa Fluor 647 | Thermo Fisher Scientific, Massachusetts, USA | A-21245 | Dilution 1:2000 |
| NeuN antibody | Sigma-Aldrich, St. Louis, USA | MAB377 | Dilution 1:100 |
| Fluorescent Dyes & Probes | |||
| ActinGreen 488 ReadyProbes Reagent (Phalloidin) | Thermo Fisher Scientific, Massachusetts, USA | R37110 | Dilution 1:40 |
| CellTrace Calcein Red-Orange | Thermo Fisher Scientific, Massachusetts, USA | C34851 | Cell tracker used to visualize neurons under fluorescence microscope |
| Hoechst 33342 | Thermo Fisher Scientific, Massachusetts, USA | H3570 | Dilution 1:5000 |
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