Stimulation of Notch Signaling in Mouse Osteoclast Precursors

Summary

Notch signaling is a form of cellular communication that relies upon direct contact between cells. To properly induce Notch signaling in vitro, Notch ligands must be presented to cells in an immobilized state. This protocol describes methods for in vitro stimulation of Notch signaling in mouse osteoclast precursors.

Abstract

Notch signaling is a key component of multiple physiological and pathological processes. The nature of Notch signaling, however, makes in vitro investigation of its varying and sometimes contradictory roles a challenge. As a component of direct cell-cell communication with both receptors and ligands bound to the plasma membrane, Notch signaling cannot be activated in vitro by simple addition of ligands to culture media, as is possible with many other signaling pathways. Instead, Notch ligands must be presented to cells in an immobilized state.

Variations in methods of Notch signaling activation can lead to different outcomes in cultured cells. In osteoclast precursors, in particular, differences in methods of Notch stimulation and osteoclast precursor culture and differentiation have led to disagreement over whether Notch signaling is a positive or negative regulator of osteoclast differentiation. While closer comparisons of osteoclast differentiation under different Notch stimulation conditions in vitro and genetic models have largely resolved the controversy regarding Notch signaling and osteoclasts, standardized methods of continuous and temporary stimulation of Notch signaling in cultured cells could prevent such discrepancies in the future.

This protocol describes two methods for stimulating Notch signaling specifically in cultured mouse osteoclast precursors, though these methods should be applicable to any adherent cell type with minor adjustments. The first method produces continuous stimulation of Notch signaling and involves immobilizing Notch ligand to a tissue culture surface prior to the seeding of cells. The second, which uses Notch ligand bound to agarose beads allows for temporary stimulation of Notch signaling in cells that are already adhered to a culture surface. This protocol also includes methods for detecting Notch activation in osteoclast precursors as well as representative transcriptional markers of Notch signaling activation.

Introduction

The mammalian Notch signaling pathway is homologous to the same pathway in Drosophila melanogaster and consists of four transmembrane Notch receptors (Notch1-4) and five membrane-bound ligands of the Jagged (JAG1 & JAG2) and Delta-like (DLL1, 3,& 4) families¹. Notch signaling is initiated when Notch receptor on a receiving cell is bound by ligand on a transmitting cell². During this trans-activation, the membrane-bound Notch ligand produces a stretching force on the membrane-bound Notch receptor^3,4. The stretching force of ligand binding induces ....

Protocol

All research involving vertebrate animals was performed in accordance with protocols approved by the University of Pennsylvania Institutional Animal Care and Use Committee (IACUC).

1. Culture Media Preparation

1. Prepare α-MEM by dissolving minimum essential medium (MEM) powder and 1.9 g sodium bicarbonate in 900 ml H₂O and supplement with 2 mM L-glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin, and 100 ml heat-inactivated fetal bovine serum. Sterilize using a 0.22 µm polyethersulfone (PES) filter.
2. Prepare macrophage medium by supplementing α-MEM with 35 ng/ml recombinant mouse Mac....

Results

The aim of this method is to culture and stimulate Notch signaling in osteoclast precursors. When properly cultured, osteoclast precursors exhibit a primarily elongated spindle-shaped morphology with smooth cytoplasm (Figure 1A). Care should be taken to avoid immunological activation of the osteoclast precursors. Upon activation, precursors spread and become flattened with foamy cytoplasm (Figure 1B). These "fried egg" cells are resistant to RANK signalin.......

Discussion

Critical steps within the protocol

Culture and in vitro differentiation of osteoclast precursors provides a useful platform for investigation of molecular mechanisms of osteoclastogenesis and identification of therapeutic targets for bone regeneration and preservation of bone mass. When culturing mouse osteoclast precursors, the most critical element is maintenance of precursors in a naïve state. As macrophage-like cells, osteoclast precursors are primed to respond to bacterial comp.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Recombinant mouse M-CSF	Biolegend	576402	Available from multiple suppliers, test activity before experiments
Recombinant mouse RANKL	Shenandoah Biotechnology	200-04	Available from multiple suppliers, test activity before experiments
Recombinant human Jagged1-Fc	R&D Systems	1277-JG-050	Available from multiple suppliers, test activity before experiments
Protein G agarose beads	InvivoGen	gel-agg-2
Goat anti-human IgG Fc	Jackson ImmunoResearch	109-001-008
Minimum Essential Medium powder	Sigma-Aldrich	M0894
Accutase cell dissociation reagent	ThermoFisher	A1110501	Used to lift osteoclast precursors
Acid Phosphatase, Leukocyte (TRAP) Kit	Sigma-Aldrich	387A-1KT	Used to stain differentiated osteoclasts