Screening Assays to Characterize Novel Endothelial Regulators Involved in the Inflammatory Response

Summary

Vascular endothelium tightly controls leukocyte recruitment. Inadequate leukocyte extravasation contributes to human inflammatory diseases. Therefore, searching for novel regulatory elements of endothelial activation is necessary to design improved therapies for inflammatory disorders. Here, we describe a comprehensive methodology to characterize novel endothelial regulators that can modify leukocyte trafficking during inflammation.

Abstract

The endothelial layer is essential for maintaining homeostasis in the body by controlling many different functions. Regulation of the inflammatory response by the endothelial layer is crucial to efficiently fight against harmful inputs and aid in the recovery of damaged areas. When the endothelial cells are exposed to an inflammatory environment, such as the outer component of gram-negative bacteria membrane, lipopolysaccharide (LPS), they express soluble pro-inflammatory cytokines, such as Ccl5, Cxcl1 and Cxcl10, and trigger the activation of circulating leukocytes. In addition, the expression of adhesion molecules E-selectin, VCAM-1 and ICAM-1 on the endothelial surface enables the interaction and adhesion of the activated leukocytes to the endothelial layer, and eventually the extravasation towards the inflamed tissue. In this scenario, the endothelial function must be tightly regulated because excessive or defective activation in the leukocyte recruitment could lead to inflammatory-related disorders. Since many of these disorders do not have an effective treatment, novel strategies with a focus on the vascular layer must be investigated. We propose comprehensive assays that are useful to the search of novel endothelial regulators that modify leukocyte function. We analyze endothelial activation by using specific expression targets involved in leukocyte recruitment (such as, cytokines, chemokines, and adhesion molecules) with several techniques, including: real-time quantitative polymerase chain reaction (RT-qPCR), western-blot, flow cytometry and adhesion assays. These approaches determine endothelial function in the inflammatory context and are very useful to perform screening assays to characterize novel endothelial inflammatory regulators that are potentially valuable for designing new therapeutic strategies.

Introduction

Inflammation is a beneficial biological response against infectious agents, with the major aim to eliminate the pathogen and repair damaged tissue. Under certain conditions, such as chronic infections or autoimmune diseases, inflammation does not resolve. Instead, there is an aberrant reaction with continuous infiltration of leukocytes, resulting in a prolonged immune response that leads to tissue damage, fibrosis, loss of function, and overall, disability and in some cases death of the patient. These human disorders, cataloged as inflammatory diseases, all involve the blood vessels for the control of leukocyte extravasation^1,

Protocol

1. Endothelial Cell Culture

1. Tissue culture treated plates
   1. Coat 100 mm tissue culture plates with 2.5 mL gelatin solution (autoclaved, 0.1% gelatin in distilled water) for 30 min at 37 °C; this can be extrapolated to the required well format. Aspirate the gelatin solution and leave plates to air-dry in the tissue culture hood.
2. Tissue culture conditions
   1. Cultivate the MLEC-04 cells inside a biological incubator (37 °C, 95% humidity, 5% CO₂). Grow the cells in complete media of Dulbecco's Modified Eagle Medium: Nutrient Mixture F-12 (DMEM/F-12) supplement....

Results

Evaluation of LPS-induced endothelial cell activation by RT-qPCR

The serum starved MLEC-04 cells were stimulated by 100 ng/mL of LPS for 6 h, and the endothelial gene expression was assessed using RT-qPCR by comparing the expression of activation markers to the resting condition. As shown in Figure 1A, the LPS-incubated MLEC-04 cells induced the mRNA expression of selected adhesion molecules involved i.......

Discussion

This endothelial protocol describes a stepwise technology that establishes the groundwork for exploring novel mechanisms involved in the regulation of the inflammatory response. These approaches are based on the study of the endothelial activity stimulated by LPS and evaluate the critical steps involved in leukocyte recruitment during the inflammatory response, specifically: endothelial cytokines release, endothelial adhesion molecules expression and leukocyte adhesion to the vascular layer. Once the endothelial paramete.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Gelatin	Sigma	G9391
DMEM-F12	Lonza	BE12-719F
Fetal Bovine Serum	Sigma	A4503
Penicillin streptomycin	Lonza	DE17-602E
Trypsine	Lonza	BE17-160E
EDTA	Sigma	ED2SS
LPS	Sigma	L2880
Trizol	Sigma	T9424	RNA extraction buffer
Isopropanol	Sigma	33539
Ethanol absoluto	Panreac	1,310,861,612
Pure H2O	Qiagen	1017979	RNAse free
Agarose	Pronadisa	8020
Stain for agarose gels	Invitrogen	s33102
SuperScript III First-Strand Synth	Invitrogen	18080051	Reagents for RT-PCR
Fast SYBR Green Master Mix	Applied Biosystems	4385610	Fluorescent stain for qPCR
MicroAmp Fast Optical 96-Well	Applied Biosystems	4346906	Plates for qPCR
U-bottom 96 well plates	Falcon	353072
Cytometry tubes	Falcon	352054
TX100	Panreac	212314	Non-ionic surfactant
Tris-HCl	Panreac	1,319,401,211
Sodium chloride	Merck	1,064,041,000
Sodium pyrophosphate	Sigma	221368
Sodium fluoride	Sigma	S7920
Sodium orthovanadate	sigma	13721-39-6
Protease inhibitor cocktail	sigma	P8340
Pierce BCA Protein Assay Kit	Pierce	23225	Reagents for bicinchoninic acid assay
β-mercaptoethanol	merck	805,740
PVDF Transfer Membrane, 0.45 µm	Thermo Scientific	88518
Tween-20	Panreac	1,623,121,611	Polysorbate 20
PBS	Lonza	BE17-515Q
ECL	Millipore	WBKLS0500
Fibronectin	Sigma	F1141
Laminin	Sigma	L2020
Collagen type I	Sigma	c8919
Acetic acid	Panreac	1,310,081,611
Trypan blue	Sigma	T8154
Paraformaldehyde	Sigma	P6148
Methanol	Panreac	1,310,911,612
Crystal violet	Sigma	HT90132
Sodium citrate	Sigma	C7254
Ethanol 96%	Panreac	1,410,851,212
CFSE	Sigma	21888
RPMI	Lonza	BE12-115F
SDS	Bio-Rad	161-0418
Infinite M200	Tecan	M200	Multi mode microplate reader
Gel Doc 2000	Bio-Rad	2000	Gel documentation system
StepOnePlus	Applied Biosystems	StepOnePlus	qPCR system
MACSQuant Analyzer 10	Miltenyi Biotec	Analyzer 10	Cytometry equipment
ChemiDoc MP	Bio-Rad	MP	Chemiluminescence detection system
Name	Company	Catalog Number	Comments
Antibodies
PECAM-1	BD Biosciences	553370	Use at 10 µg/mL
ICAM-2	Biolegend	1054602	Use at 10 µg/mL
E-selectin	BD Biosciences	553749	Use at 10 µg/mL
VCAM-1	BD Biosciences	553330	Use at 10 µg/mL
ICAM-1	Becton Dickinson	553250	Use at 10 µg/mL
anti-rat IgG-FITC	Jackson Immuno Research	112-095-006	Use at 10 µg/mL
anti armenian hamster-FITC	Jackson Immuno Research	127-095-160	Use at 10 µg/mL
Rat IgG isotyope control	Invitrogen	10700	Use at 10 µg/mL
Armenian hamster IgG isotype control	Invitrogen	PA5-33220	Use at 10 µg/mL
P-IκΒ-α	Cell Signaling	2859	Use at 10 µg/mL
β-Actin	Sigma	A5441	Use at 10 µg/mL
P-ERK	Cell Signaling	9101	Use at 10 µg/mL
anti-mouse HRP	GE Healthcare	LNXA931/AE	Use at 1:10,000
anti-rabbit HRP	GE Healthcare	LNA934V/AG	Use at 1:10,000
anti-rat HRP	Santa Cruz	Sc-3823	Use at 1:10,000