A Morphometric and Cellular Analysis Method for the Murine Mandibular Condyle

Summary

This manuscript presents methods for analyzing morphometric and cellular changes within the mandibular condyle of rodents.

Abstract

The temporomandibular joint (TMJ) has the capacity to adapt to external stimuli, and loading changes can affect the position of condyles, as well as the structural and cellular components of the mandibular condylar cartilage (MCC). This manuscript describes methods for analyzing these changes and a method for altering the loading of the TMJ in mice (i.e., compressive static TMJ loading). The structural evaluation illustrated here is a simple morphometric approach that uses the Digimizer software and is performed in radiographs of small bones. In addition, the analysis of cellular changes leading to alterations in collagen expression, bone remodeling, cell division, and proteoglycan distribution in the MCC is described. The quantification of these changes in histological sections - by counting the positive fluorescent pixels using image software and measuring the distance mapping and stained area with Digimizer - is also demonstrated. The methods shown here are not limited to the murine TMJ, but could be used on additional bones of small experimental animals and in other regions of endochondral ossification.

Introduction

The TMJ is a unique load-bearing joint located in the craniofacial region and is formed of fibrocartilage. The MCC of the TMJ is essential for joint function, including unhindered jaw movement while speaking and masticating, but it is commonly affected by degenerative diseases, including osteoarthritis¹. The TMJ has the capacity to adapt to external stimuli and loading alterations, leading to structural and cellular changes to the components of the MCC^2,3,4,5. The load-bearing properties of the MCC can be explained by....

Protocol

The institutional animal care committee of the University of Connecticut Health Center approved all animal procedures.

1. Compressive Static TMJ Loading: Mouth Forced Open

Note: Four-week-old transgenic mice harboring fluorescent reporters for collagen (Col2a1XCol10a1), kindly provided by Dr. David Rowe (University of Connecticut), were used for the experiments described in this manuscript (n = 8; 4 males and 4 females). The Col2a1 cyan (blue) transgene is expressed in cells at the prehypertrophic zone of the MCC, while the Col10a1 cherry (red) cells are present in the hypertrophic region⁸ (....

Results

Descriptive statistics were performed to examine the distribution of morphometric measurements (mandibular length, condylar length, condylar width) and histological analyses. Outcomes were compared between the loaded group (i.e., mice subjected to compressive loading with the beta titanium spring) and the control group (i.e., matching control mice that did not receive any procedure). Statistically significant differences between means were determined by unpaired t-test, .......

Discussion

This manuscript described methods for the morphometric measurement and cellular analysis of murine mandibular condyles and mandibles. The radiographic morphometric measurements can also be used to analyze other bones from small experimental animals. In addition, the cellular analysis (cell quantification and cartilage distance mapping) are not limited to the rodent mandibular condyle, but can be used to quantify histological sections of numerous tissues.

Transgenic mouse models expressing flu.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
MX20 Radiography System	Faxitron X-Ray LLC
Digimizer Image software	MedCalc Software
Shandon Cryomatrix embedding resin	Thermo Scientific	6769006
Manual microscope Axio Imager Z1	Carl Zeiss	208562
yellow fluorescent protein filter  - EYFP	Chroma Technology Corp	49003
cyan fluorescent protein filter - ECFP	Chroma Technology Corp	49001
red fluoresecent protein filter - Cy5	Chroma Technology Corp	49009
sodium acetate anhydrous	Sigma-Aldrich	S2889
sodium L-tartrate dibasic dihydrate	Sigma-Aldrich	228729
sodium nitrite	Sigma-Aldrich	237213
ELF97 substrate	Thermo Fisher Scientific	E6600
ClickiT EdU Alexa Fluor 594 HCS kit	Life Technologies	C10339	includes EdU (5-ethynyl-2'-deoxyuridine)
DAPI (4',6-Diamidino-2-Phenylindole, Dihydrochloride)	Thermo Scientific	D1306
Sodium phosphate dibasic	Sigma-Aldrich	S3264
Sodium phosphate monobasic	Sigma-Aldrich	71505
Toluidine Blue O	Sigma-Aldrich	T3260
Adobe Photoshop	Adobe Systems Incorporated
Phosphate buffered saline tablets (PBS)	Research Products International	P32080-100T
CNA Beta III Nickel-Free Archwire	Ortho Organizers, Inc.
GraphPad Prism	GraphPad Software, Inc.