Resorption Pit Assay: An In Vitro Technique to Quantify Calcium Resorption Activity of Mature Osteoclasts using Calcium Phosphate-Coated Culture Plates

Abstract

Source: Cen, W., et al. A Simple Pit Assay Protocol to Visualize and Quantify Osteoclastic Resorption In Vitro. J. Vis. Exp. (2022)

In this video, we describe an in vitro osteoclastic resorption assay on calcium phosphate-coated cell culture plates cultured with human peripheral blood mononuclear cell-derived osteoclasts. The osteoclasts form a characteristic actin ring on the calcium phosphate-coated matrix of the cell culture plate and degrade the matrix within the actin ring region to release calcium and phosphate ions, resulting in the formation of distinct resorption pits within the degraded matrix.

Protocol

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human welfare and have been reviewed by the local institutional review board.

1. Expansion of OC progenitors

1. Resuspend PBMCs in complete α-MEM (10% FBS, 1% Pen/Strep, 1% amphotericin B) containing 20 ng/mL M-CSF. Seed PBMCs at a density of 2.5 x 10⁵ cells/cm². Usually, cells isolated from 15-20 mL fresh blood can be seeded in one 75 cm² flask (1.5-2 x 10⁷ cells).
2. Feed the cells with fresh complete α-MEM containing 20 ng/mL ....

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
α-MEM	Gibco	32561-029	MEM alpha, GlutaMAX, no nucleosides
amphotericin B	Biochrom	03-028-1B	Amphotericin B Solution
Calcein	Sigma-Aldrich	C0875	Calcein
FBS	Sigma-Aldrich	F7524	fetal bovine serum
Fixation buffer	Biolegend	420801	Paraformaldehyde
Hoechst 33342	Promokine	PK-CA707-40046	Hoechst 33342
M-CSF	PeproTech	300-25	Recombinant Human M-CSF
PBS	Lonza	17-512F	Dulbecco's Phosphate Buffered Saline (1X), DBPS without Calcium and Magnesium
Pen-Strep	Lonza	DE17-602E	Penicillin-Streptomycin Mixture
Phalloidin-Alexa Fluor 546	Invitrogen	A22283	Alexa Fluor 546 Phalloidin
RANKL	PeproTech	310-01	Recombinant Human sRANK Ligand (E.coli derived)
Triton X-100	Sigma-Aldrich	T8787	Alkyl Phenyl Polyethylene Glycol
TrypLE Express	Gibco	12605010	Recombinant cell-dissociation enzymes