In Vivo Study of Human Endothelial-Pericyte Interaction Using the Matrix Gel Plug Assay in Mouse

Summary

We present a protocol to study human endothelial-pericyte interactions in mouse using a variation of the matrix gel plug angiogenesis assay.

Abstract

Angiogenesis is the process by which new blood vessels are formed from existing vessels. New vessel growth requires coordinated endothelial cell proliferation, migration, and alignment to form tubular structures followed by recruitment of pericytes to provide mural support and facilitate vessel maturation. Current in vitro cell culture approaches cannot fully reproduce the complex biological environment where endothelial cells and pericytes interact to produce functional vessels. We present a novel application of the in vivo matrix gel plug assay to study endothelial-pericyte interactions and formation of functional blood vessels using severe combined immune deficiency mutation (SCID) mice. Briefly, matrix gel is mixed with a solution containing endothelial cells with or without pericytes followed by injection into the back of anesthetized SCID mice. After 14 days, the matrix gel plugs are removed, fixed and sectioned for histological analysis. The length, number, size and extent of pericyte coverage of mature vessels (defined by the presence of red blood cells in the lumen) can be quantified and compared between experimental groups using commercial statistical platforms. Beyond its use as an angiogenesis assay, this matrix gel plug assay can be used to conduct genetic studies and as a platform for drug discovery. In conclusion, this protocol will allow researchers to complement available in vitro assays for the study of endothelial-pericyte interactions and their relevance to either systemic or pulmonary angiogenesis.

Introduction

Angiogenesis is the process by which new blood vessels are formed from a pre-existing vascular network¹ and is the focus of ongoing research across many areas ranging from normal development to disease. This dynamic process involves the proliferation and migration of endothelial cells (ECs) and recruitment of pericytes to construct a vascular tube that is directed toward the site that needs oxygen and nutrient delivery². To study this process requires an equally dynamic assay, most importantly one that can recapitulate the three-dimensional nature of tube formation. In vitro 3D matrix assays have been developed to address this need and h....

Protocol

Ethics Statement: Procedures involving animal subjects have been approved by the Institutional Animal Care and Use Committee at Stanford University School of Medicine.

NOTE: Animals are under anesthetization with 3% vaporizer isoflurane and 3% supply of O₂ gas. Use of vet ointment on eyes may help to prevent dryness while under anesthesia.

1. Cell Preparation

1. Grow human endothelial and pericyte cell cultures in 100 mm plates with 10 ml of the appropriate media. Replace 10 ml of fresh medium every 2 - 3 days until cells reach 80% confluency.
   1. Culture endothelial cells (ECs) in complete endothelial cell media (ECM) supplem....

Results

Representative H&E and immunofluorescent staining of matrix gel plug sections are shown in Figure 2. Sections from EC only plugs display some vessels that are mostly not perfused with blood (Figure 2 top left, black arrows) whereas plugs containing both ECs and pericytes display several perfused vessels with larger diameters and complete pericyte coverage, as evidenced by positive SMA staining immediately adjacent to CD31-positive ECs. These results s.......

Discussion

The matrix gel plug assay has proven to be a convenient and powerful method to evaluate gene regulation in angiogenesis, angiogenic and antiangiogenic compounds in vivo, and to supplement in vitro tests. Here, we describe in detail a novel matrix gel plug assay of human angiogenesis that investigates the interaction between endothelial cells and pericytes during vessel formation.

There are a few novel and critical steps in this protocol. Cells in low passage (passage 1 - 4) a.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
PBS (Phosphate buffered saline)	Corning	21-031-CV
0.25% Trypsin/0.53 mM EDTA	Corning	25-053-CI
Endothelial Cell Media (ECM) kit	Sciencell	1001	includes media, EC growth supplement, and penicillin/streptomycin, each supplied at the appropriate volume for easy mixing
Pericyte Media (PM) kit	Sciencell	1201	includes media, Pericyte growth supplement, and penicillin/streptomycin, each supplied at the appropriate volume for easy mixing
primary human pulmonary microvascular endothelial cells	Pulmonary Hypertension Breakthrough Initiative		this cell type is also available commercially. Cells used at passage 1-4
primary human pulmonary pericytes	Pulmonary Hypertension Breakthrough Initiative		this cell type is not available commercially, but brain paricytes are.  Cells used at passage 1-4
bFGF (basic Fibroblast Growth Factor)	Peprotech	100-18B	stock solution is 50 μg/ml in 0.1% BSA in PBS, aliquots at 50 μl and stored at -20 degrees
Matrigel Basement Membrane Matrix	BD	356237
28 G 1 cc Insluin Syringe	BD	329410
SCID (Severe Combined Immune Deficiency) mice	The Jackson Laboratory	5557	NOD.SCID IL2R gamma knockout strain is the best strain; 4-6 weeks of age
1.5 ml microcentrifuge tubes, sterile	Thermo Fisher Scientific	05-408-129
15 ml screw top tubes, sterile	BD Biosciences	352096
PAP pen	Life Technologies	8899
hemocytometer	ThermoFisher Scientific	02-671-6
Nair hair removal cream	Walmart
anti-human CD31 primary antibody	LifeSpan Biosciences	LS-B4737	working solution is 1:50
anti-human Smooth Muscle actin CY3 primary fluorescent antibody	Sigma	C6198	working solution is 1:300
goat anti-rabbit secondary antibody; 488/green	ThermoFisher Scientific	A-11008	working solution is 1:250
Prolong Gold DAPI solution	Cell Signaling	8961S
microscope slides	VWR	48300-047
no. 1.5 cover slips	Thermo Fisher Scientific	12-544-D
citrate buffer 10x	Millipore	21545
extra fine surgical scissors	Fine Science Tools	14084-08
Formalin (paraformaldehyde)	Thermo Fisher Scientific	245-685
Tissue cassettes	Simport	M492-12
goat serum	Dako	X0907