Cell Biology

Human neuromuscular diseases represent a diverse group of disorders with unmet clinical need, ranging from muscular dystrophies, such as Duchenne muscular dystrophy (DMD), to neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS). In many of these conditions, axonal and neuromuscular synapse dysfunction have been implicated as crucial pathological events, highlighting the need for in vitro disease models that accurately recapitulate these aspects of human neuromuscular physiology. The protocol reported here describes the co-culture of neural spheroids composed of human pluripotent stem cell (PSC)–derived motor neurons and astrocytes, and human PSC-derived myofibers in 3D compartmentalised microdevices to generate functional human neuromuscular circuits in vitro. In this microphysiological model, motor axons project from a central nervous system (CNS)–like compartment along microchannels to innervate skeletal myofibers plated in a separate muscle compartment. This mimics the spatial organization of neuromuscular circuits in vivo. Optogenetics, particle image velocimetry (PIV) analysis, and immunocytochemistry are used to control, record, and quantify functional neuromuscular transmission, axonal outgrowth, and neuromuscular synapse number and morphology. This approach has been applied to study disease-specific phenotypes for DMD and ALS by incorporating patient-derived and CRISPR-corrected human PSC-derived motor neurons and skeletal myogenic progenitors into the model, as well as testing candidate drugs for rescuing pathological phenotypes. The main advantages of this approach are: i) its simple design; ii) the in vivo–like anatomical separation between CNS and peripheral muscle; and iii) the amenability of the approach to high power imaging. This opens up the possibility for carrying out live axonal transport and synaptic imaging assays in future studies, in addition to the applications reported in this study.

Graphical abstract

Graphical abstract abbreviations: Channelrhodopsin-2 (CHR2+), pluripotent stem cell (PSC), motor neurons (MNs), myofibers (MFs), neuromuscular junction (NMJ).

A rigorous determination of effector contributions of tumor-infiltrating immune cells is critical for identifying targetable molecular mechanisms for the development of novel cancer immunotherapies. A tumor/immune cell–admixture model is an advantageous strategy to study tumor immunology as the fundamental methodology is relatively straightforward, while also being adaptable to scale to address increasingly complex research queries. Ultimately, this method can provide robust experimental information to complement more traditional murine models of tumor immunology. Here, we describe a tumor/macrophage-admixture model using bone marrow–derived macrophages to investigate macrophage-dependent tumorigenesis. Additionally, we provide commentary on potential branch points for optimization with other immune cells, experimental techniques, and cancer types.

Competition assays are a simple phenotyping strategy that confront two bacterial strains to evaluate their relative fitness. Because they are more accurate than single-strain growth assays, competition assays can be used to highlight slight differences that would not otherwise be detectable. In the frame of host-pathogens interactions, they can be very useful to study the contribution of individual bacterial genes to bacterial fitness and lead to the identification of new adaptive traits. Here, we describe how to perform such competition assays by taking the example of the model phytopathogenic bacterium Xanthomonas campestris pv. campestris during infection of the mesophyll of its cauliflower host. This phenotypic assay is based on the use of a Competitive Index (CI) that compares the relative abundance of co-inoculated strains before and after inoculation. Since multiplication is a direct proxy for bacterial fitness, the evolution of the ratio between both strains in the mixed population is a direct way to assess differences in fitness in a given environment. In this protocol, we exploit the blue staining of GUS-expressing bacteria to count blue vs. white colonies on plates and estimate the competitiveness of the strains of interest in plant mesophyll.

Methods to test both the functionality and mechanism of action for human recombinant proteins and antibodies in vitro have been limited by multiple factors. To test the functionality of a recombinant protein or antibody, the receptor, the receptor-associated ligand, or both must be expressed by the cells present within the in vitro culture. While the use of transfected cell lines can circumvent this gap, the use of transfected cell lines does not allow for studying the native signaling pathway(s) modulated by the specific recombinant protein or antibody in primary cells. The present protocol utilizes sort purified CD14⁺ monocytes and T cells, both CD4⁺ T cells and CD8⁺ T cells, from healthy donors in a co-culture system. This methodology is particularly relevant for testing recombinant proteins or antibodies that are putative therapeutics for the treatment of autoimmune disease and cancer. While the current protocol focuses on co-cultures containing B7-H4 expressing monocytes plus either autologous CD4⁺ T cells or CD8⁺ T cells, the protocol can be modified for the user’s specific needs.

The search for the origin of the first hematopoietic stem cells (HSCs) in the mouse embryo has been a hot topic in the field of developmental hematopoiesis. Detecting lymphoid potential is one of the supportive evidence to show the definitive hematopoietic activity of HSCs. However, the first B-lymphoid potential in the mouse embryos are reported to be biased to innate-like B-1 cell lineage that can develop from hemogenic endothelial cells (HECs) independently of HSCs. On the other hand, conventional adaptive immune B cells (B-2) cells are considered to be exclusively derived from HSCs. Therefore, segregating B-1 and B-2 progenitor potential is important to understand the developmental process of HSCs that are also produced from HECs through intermediate precursors referred to as pre-HSCs. Both HECs and pre-HSCs show endothelial surface phenotype and require stromal support to detect their hematopoietic activity. The method utilizing stromal cell culture followed by modified semisolid clonal culture enables us to detect the number of colony forming units for B-1/B-2 progenitors originally derived from HECs/pre-HSCs, which will reflect the potential of B-1 biased or multi-lineage repopulating HSCs.

Crosstalk between neurons and oligodendrocytes is important for proper brain functioning. Multiple co-culture methods have been developed to study oligodendrocyte maturation, myelination or the effect of oligodendrocytes on neurons. However, most of these methods contain cells derived from animal models. In the current protocol, we co-culture human neurons with human oligodendrocytes. Neurons and oligodendrocyte precursor cells (OPCs) were differentiated separately from pluripotent stem cells according to previously published protocols. To study neuron-glia cross-talk, neurons and OPCs were plated in co-culture mode in optimized conditions for additional 28 days, and prepared for OPC maturation and neuronal morphology analysis. To our knowledge, this is one of the first neuron-OPC protocols containing all human cells. Specific neuronal abnormalities not observed in mono-cultures of Tuberous Sclerosis Complex (TSC) neurons, became apparent when TSC neurons were co-cultured with TSC OPCs. These results show that this co-culture system can be used to study human neuron-OPC interactive mechanisms involved in health and disease.

Myofiber isolation followed with ex vivo culture could recapitulate and visualize satellite cells (SCs) activation, proliferation, and differentiation. This approach could be taken to understand the physiology of satellite cells and the molecular mechanism of regulatory factors, in terms of the involvement of intrinsic factors over SCs quiescence, activation, proliferation and differentiation. Single myofiber culture has several advantages that the traditional approach such as FASC and cryosection could not compete with. For example, myofiber isolation and culture could be used to observe SCs activation, proliferation and differentiation at a continuous manner within their physiological “niche” environment while FACS or cryosection could only capture single time-point upon external stimulation to activate satellite cells by BaCl₂, Cardiotoxin or ischemia. Furthermore, in vitro transfection with siRNA or overexpression vector could be performed under ex vivo culture to understand the detailed molecular function of a specific gene on SCs physiology. With these advantages, the physiological state of SCs could be analyzed at multiple designated time-points by immunofluorescence staining. In this protocol, we provide an efficient and practical protocol to isolate single myofiber from EDL muscle, followed with ex vivo culture and immunostaining.

Endothelial cells (ECs) sustain the self-renewal and regeneration of adult hematopoietic stem and progenitor cells (HSPCs) via deployment of EC-derived paracrine factors, termed as angiocrine factors. Generation of durable ex vivo vascular niche that maintains EC identity and preserves the angiocrine profile of organ of origin offers platforms for in vitro dissection of the mechanism by which angiocrine factors execute their instructive function for stem cell maintenance and tissue regeneration. This protocol describes detailed methods to isolate primary bone marrow ECs (BMECs), to subsequently transduce lentiviral vector carrying myristoylated-Akt1 into primary BMECs, and to use the Akt1-BMECs to expand engraftable murine HSPCs. The BMEC-HSPC co-culture system serves as bioreactor prototype to generate scalable populations of the blood and immune systems.

One fundamental property of the TNR receptor (TNFR) family relates to how ‘signal quality’ (the extent of receptor ligation or cross-linking) influences the outcome of receptor ligation, for instance the induction of death in tumour cells. It is unequivocal that membrane-presented ligand (delivered to target cells via cell-surface presentation by co-culture with ligand-expressing third-party cells) induces a greater extent of carcinoma cell death in vitro in comparison to non-cross-linked agonists (agonistic antibodies and/or recombinant ligands). The CD40 receptor epitomises this fundamental property of TNF receptor-ligand interactions, as the extent of CD40 cross-linking dictates cell fate. Membrane-presented CD40 ligand (mCD40L), but not soluble agonists (e.g., agonistic anti-CD40 antibody), induces high level of pro-inflammatory cytokine secretion and causes extensive cell death (apoptosis) in malignant (but not normal) epithelial cells. In this article, we describe a co-culture system for the activation of CD40 by mCD40L and subsequent detection of various features of apoptosis (including cell membrane permeabilisation, DNA fragmentation, caspase activation) as well as detection of intracellular mediators of cell death (including adaptor proteins, pro-apoptotic kinases and reactive oxygen species, ROS).

Bone Marrow Hematopoietic Stem Cells (HSCs) require bone marrow microenvironment for their maintenance and proliferation. Culture of Bone Marrow Mesenchymal Stromal Cells (MSCs) provides appropriate environmental signals for HSCs survival in vitro. Here, we provide a detailed protocol that describes culture conditions for MSCs, flow cytometric isolation of HSCs from mouse bone marrow, and perform co-culture of MSCs and HSCs known as Cobblestone area-forming cell (CAFC) assay. Altogether, CAFC assays can be used as a high-throughput in vitro screening model where efforts are made to understand and develop therapies for complex bone marrow diseases. This protocol needs 3 to 4 weeks starting from culturing MSCs, isolating LSK cells (HSCs), and to performing limited dilution CAFC assay.