Isolation of Valvular Endothelial Cells

Summary

We provide a method for isolating and culturing pure populations of heart valve endothelial cells (VEC). VEC can be isolated from either side of the cusp or leaflet and immediately following, underlying interstitial cell (VIC) isolation is straightforward.

Abstract

Heart valves are solely responsible for maintaining unidirectional blood flow through the cardiovascular system. These thin, fibrous tissues are subjected to significant mechanical stresses as they open and close several billion times over a lifespan. The incredible endurance of these tissues is due to the resident valvular endothelial (VEC) and interstitial cells (VIC) that constantly repair and remodel in response to local mechanical and biological signals. Only recently have we begun to understand the unique behaviors of these cells, for which in vitro experimentation has played a key role. Particularly challenging is the isolation and culture of VEC. Special care must be used from the moment the tissue is removed from the host through final plating. Here we present protocols for direct isolation, side specific isolation, culture, and verification of pure populations of VEC. We use enzymatic digestion followed by a gentle swab scraping technique to dislodge only surface cells. These cells are then collected into a tube and centrifuged into a pellet. The pellet is then resuspended and plated into culture flasks pre-coated with collagen I matrix. VEC phenotype is confirmed by contact inhibited growth and the expression of endothelial specific markers such as PECAM1 (CD31), Von Willebrand Factor (vWF), and negative expression of alpha-smooth muscle actin (α-SMA). The functional characteristics of VEC are associated with high levels of acetylated LDL. Unlike vascular endothelial cells, VEC have the unique capacity to transform into mesenchyme, which normally occurs during embryonic valve formation¹. This can also occur during significantly prolonged post confluent in vitro culture, so care should be made to passage at or near confluence. After VEC isolation, pure populations of VIC can then be easily acquired.

Protocol

1. Preparation

1. Autoclave in a covered instrument tray the following items:
   1. Serrated tissue forceps - For handling the leaflet tissue
   2. Tissue scissors (8 cm) - For trimming leaflet tissue and cusps
   3. Cotton Swabs - For isolating the endothelial layer from the leaflet or cusp
2. Make sterile collagenase solution
   1. Add 4.0 grams of powdered DMEM to 250 mL of 18 MΩ water.
   2. Add 1.11 grams of sodium bicarbonate.
   3. Add (600 U/mL) 180,000 units of collagenase.
   4. Add 1% (3mL) Penicillin/Streptomycin.
   5. Adjust the pH of the solution to 7.2.

Discussion

An understanding of valvular biology has been impaired by technical difficulties isolating and culturing pure populations of valvular endothelial cells. Typical isolation techniques involve enzymatic digestion of the underlying basal matrix or chemical dissociation of endothelial adhesive bonds^2,3. Preliminary isolation experiments were qualitatively assessed by varying dissociation agents and incubation periods. The results of these experiments showed that EDTA (or Trypsin-EDTA) incubation for up to 60 min.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Dulbecco’s Modified Eagle Medium	Mediatech, Inc.	50-103-PB
Fetal Bovine Serum	GIBCO, by Life Technologies	26140
Penicillin Streptomycin	GIBCO, by Life Technologies	15140-122
0.25% Trypsin-EDTA	GIBCO, by Life Technologies	25200
Heparin Sodium Salt	Sigma-Aldrich	H4784-1G
Collagenase Type 2	Worthington Biochemical	LS004176
DPBS	GIBCO, by Life Technologies	21300-058
Rat Tail Collagen	BD Biosciences	354236
Critical Swabs	VWR international	89031-270
Sodium Bicarbonate	Sigma-Aldrich	55761
T25 Flasks	BD Biosciences	353018
T75 Flasks	BD Biosciences	353136
24 Well Plate	Falcon BD	353047
60x15 mm Dishes	VWR international	25384-092
60x15 Glass Dishes	VWR international	89000-310
Paraffin Embedding Wax	Electron Microscopy Sciences	19304-01
Precision Glide Needles	BD Biosciences	305165
500 mL Nalgene Filters	VWR international	73520-985
1L Nalgene Filters	VWR international	73520-986
Tissue Forceps	Fine Science Tools	11023-15
FSC Tweezers #5	Fine Science Tools	11295-00