An Ex Vivo Tissue Culture Model for Fibrovascular Complications in Proliferative Diabetic Retinopathy

Summary

Here, we present a protocol to study the pathophysiology of proliferative diabetic retinopathy by using patient-derived, surgically-excised, fibrovascular tissues for three-dimensional native tissue characterization and ex vivo culture. This ex vivo culture model is also amenable for testing or developing new treatments.

Abstract

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the leading causes of blindness in working-age adults. No current animal models of diabetes and oxygen-induced retinopathy develop the full-range progressive changes manifested in human proliferative diabetic retinopathy (PDR). Therefore, understanding of the disease pathogenesis and pathophysiology has relied largely on the use of histological sections and vitreous samples in approaches that only provide steady-state information on the involved pathogenic factors. Increasing evidence indicates that dynamic cell-cell and cell-extracellular matrix (ECM) interactions in the context of three-dimensional (3D) microenvironments are essential for the mechanistic and functional studies towards the development of new treatment strategies. Therefore, we hypothesized that the pathological fibrovascular tissue surgically excised from eyes with PDR could be utilized to reliably unravel the cellular and molecular mechanisms of this devastating disease and to test the potential for novel clinical interventions. Towards this end, we developed a novel method for 3D ex vivo culture of surgically-excised patient-derived fibrovascular tissue (FT), which will serve as a relevant model of human PDR pathophysiology. The FTs are dissected into explants and embedded in fibrin matrix for ex vivo culture and 3D characterization. Whole-mount immunofluorescence of the native FTs and end-point cultures allows thorough investigation of tissue composition and multicellular processes, highlighting the importance of 3D tissue-level characterization for uncovering relevant features of PDR pathophysiology. This model will allow the simultaneous assessment of molecular mechanisms, cellular/tissue processes and treatment responses in the complex context of dynamic biochemical and physical interactions within the PDR tissue architecture and microenvironment. Since this model recapitulates PDR pathophysiology, it will also be amenable for testing or developing new treatments.

Introduction

DR is a serious ocular complication of diabetes, a disease that has reached enormous proportions in the last three decades¹. Twenty years after diagnosis, virtually every patient with type 1 diabetes and 60% of patients with type 2 diabetes present signs of retinopathy, making diabetes per se one of the leading causes of blindness in working age adults². According to the level of microvascular degeneration and ischemic damage, DR is classified into non-proliferative DR (non-PDR) and proliferative DR (PDR). The end-stage disease, PDR, is characterized by ischemia- and inflammation-induced neovascularization and f....

Protocol

This research was approved by the Institutional Review Board and Ethical committee of Helsinki University Hospital. Signed informed consent was obtained from each patient.

1. Preparation of Solutions, Media and Equipment

1. Prepare the following equipment prior to collection of the fibrovascular tissue (FT) to ensure rapid processing.
   1. Sterile-autoclave two microdissection tweezers.
   2. Prepare 1x phosphate-buffered saline (PBS) by dissolving 1 pre-weighed PBS tablet (0.14 M NaCl, 0.0027 M KCl, 0.010 M PO₄^-3) in 900 mL of deionized water and stir to dissolve. Adjust the water volume up to 1 L....

Results

Deeper understanding of the PDR fibrovascular tissue properties and protein expression has relied mainly on vitreous samples and thin histological FT sections^3,15,16,17. To develop a method for thorough investigation of the 3D tissue organization and multicellular physiopathological processes of PDR, we set out to utilize the surgically excised, patient-derived .......

Discussion

Considering the importance of relevant tissue microenvironment for reliable functional cell and molecular mechanistic results, it is imperative to find appropriate experimental models that provide this tissue environment. The herein described ex vivo PDR culture model for the fibrin-embedded FTs allows the investigation of the mechanisms of PDR pathophysiology in the native, complex and multicellular context of the PDR clinical samples.

Critical steps within the protocol are the prope.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Material
Microforceps	Medicon	07.60.03	Used for handling the FTs
Disposable Scalpels - Sterile	Swann-Morton	0513	Used for FT dissection
Culture dish, vented, 28 ml (60mm)	Greiner Bio-One	391-3210	Used for dissection and for testing fibrin gel formation
Cell culture plates, 12-well	Greiner Bio-One	392-0049	Used for FT dissection and whole-mount immunofluorescence
Reagent/centrifuge tube with screw cap, 15 mL	Greiner Bio-One	391-3477
Reagent/centrifuge tube with screw cap, 50 mL	Greiner Bio-One	525-0384
Millex-GV Syringe Filter Unit, 0.22 µm, PVDF	Millipore	SLGV033RS	Used to sterile-filter the fibrinogen solution
Syringe, 10 mL	Braun	4606108V	Used to sterile-filter the fibrinogen solution
Polypropylene Microcentrifuge Tubes, 1.5 mL	Fisher	FB74031
Cell-Culture Treated Multidishes, 24-well	Nunc	142475	Used for casting the FT/fibrin gels for native FT characterization and ex vivo culture
Cell culture plates, 96-well, U-bottom	Greiner Bio-One	392-0019	Used for whole-mount immunofluorescence
Round/Flat Spatulas, Stainless Steel	VWR	82027-528	Used for whole-mount immunofluorescence
Coverslips 22x22mm #1	Menzel/Fisher	15727582	Used for mounting
Microscope slides	Fisher	Kindler K102	Used for mounting
Absorbent paper	VWR	115-0202	Used for mounting
Name	Company	Catalog Number	Comments
Reagents
PBS tablets	Medicago	09-9400-100	Used for preparing 1x PBS
Fibrinogen, Plasminogen-Depleted, Human Plasma	Calbiochem	341578
Hanks Balanced Salt Solution	Sigma-Aldrich	H9394-500ML	Used for preparing the fibrinogen and TA solution
Fetal bovine serum	Gibco	10270106	Used for preparing the blocking solution
Human Serum	Sigma-Aldrich	H4522	Aliquoted in -20 °C, thaw before preparing the ex vivo culture media
Gentamicin Sulfate 10mg/ml	Biowest	L0011-100
Endothelial cell media MV Kit	Promocell	C-22120	Contains 500 ml of Endothelial Cell Growth Medium MV, 25 mL of fetal calf serum, 2 mL of endothelial cell growth supplement,  500 μL of recombinant human epidermal growth factor (10 μg/ mL) and 500 μL of hydrocortisone (1 g/ mL)
Sodium azide	Sigma-Aldrich	S2002	Used for storage of the native and ex vivo cultured FTs. TOXIC: wear protective gloves and/or clothing, and eye and/or face protection. Use in fume hood.
Acetone	Sigma-Aldrich	32201-2.5L-M	Used to prepare the post-fixation solution. HARMFUL: wear protective gloves and/or clothing. Use in fume hood.
Methanol	Sigma-Aldrich	32213	Used to prepare the post-fixation solution. TOXIC: wear protective gloves and/or clothing. Use in fume hood.
Triton X-100 (octyl phenol ethoxylate)	Sigma-Aldrich	T9284	Used for whole-mount immunofluorescence. HARMFUL: wear protective gloves and/or clothing.
Hoechst 33342, 20mM	Life Technologies	62249	For nuclei counterstaining. HARMFUL: wear protective gloves and/or clothing, and eye and/or face protection.
VECTASHIELD Antifade Mounting Medium	Vector Laboratories	H-1000	Wear protective gloves and/or clothing, and eye protection. Use in fume hood.
VECTASHIELD Antifade Mounting Medium with DAPI	Vector Laboratories	H-1200	Mounting medium with nuclei counterstaining. Wear protective gloves and/or clothing, and eye protection. Use in fume hood.
Eukitt Quick-hardening mounting medium	Sigma-Aldrich	03989-100ml	TOXIC: Wear protective gloves and/or clothing, and eye protection. Use in fume hood.
Thrombin from bovine plasma, lyophilized powder	Sigma-Aldrich	T9549-500UN	Dissolve at 100 units/ mL, aliquote and store at -20 °C, avoid repeated freeze/ thaw
Aprotinin from bovine lung, lyophilized powder	Sigma	A3428	Dissolve at 50 mg/ mL, aliquote and store at -20 °C, avoid repeated freeze/ thaw
Name	Company	Catalog Number	Comments
Growth factors
Recombinant human VEGFA	R&D Systems	293-VE-010	50 ng/ mL final concentration
Recombinant human VEGFC	R&D Systems	752-VC-025	200 ng/ mL final concentration
Recombinant human TGFβ	Millipore	GF346	1 ng/ mL final concentration
Recombinant human bFGF	Millipore	01-106	50 ng/ mL final concentration
Name	Company	Catalog Number	Comments
Primary antibodies
CD31 (JC70A)	Dako	M0823	Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab
CD34 (QBEND10)	Dako	M716501-2	Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab
CD45 (2B11+PD7/26)	Dako	M070129-2	Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab
CD68	ImmunoWay	RLM3161	Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab
Cleaved caspase-3 (5A1E)	Cell Signalling	9664	Used at 1:200 dilution, Goat anti Rabbit Alexa 594 Secondary Ab
ERG (EP111)	Dako	M731429-2	Used at 1:100 dilution, Goat anti Rabbit Alexa 594 Secondary Ab
GFAP	Dako	Z0334	Used at 1:100 dilution, Goat anti Rabbit Alexa 594 Secondary Ab
Ki67	Leica Microsystems	NCL-Ki67p	Used at 1:1500 dilution, Goat anti Rabbit Alexa 594 Secondary Ab
Lyve1	R&D Systems	AF2089	Used at 1:100 dilution, Donkey anti Goat Alexa 568 Secondary Ab
NG2	Millipore	AB5320	Used at 1:100 dilution, Goat anti Rabbit Alexa 594 Secondary Ab
Prox1	ReliaTech	102-PA32	Used at 1:200 dilution, Goat anti Rabbit Alexa 568 Secondary Ab
Prox1	R&D Systems	AF2727	Used at 1:40 dilution, Chicken anti Goat Alexa 594 Secondary Ab
VEGFR3 (9D9F9)	Millipore	MAB3757	Used at 1:100 dilution, Donkey anti Mouse Alexa 488 Secondary Ab
α-SMA (1A4)	Sigma	C6198	Used at 1:400 dilution, Cy3 conjugated
Name	Company	Catalog Number	Comments
Secondary antibodies
Alexa Fluor488 Donkey Anti-Mouse IgG	Life Technologies	A-21202	Used at 1:500 dilution
Alexa Fluor594 Goat Anti-Rabbit IgG	Invitrogen	A-11012	Used at 1:500 dilution
Alexa Fluor568 Donkey anti-Goat IgG	Thermo Scientific	A-11057	Used at 1:500 dilution
Alexa Fluor568 Goat anti-Rabbit IgG	Thermo Scientific	A-11036	Used at 1:500 dilution
Alexa Fluor594 Chicken Anti-Goat IgG	Molecular Probes	A-21468	Used at 1:500 dilution
Name	Company	Catalog Number	Comments
Microscopes
Axiovert 200 inverted epifluorescence microscope	Zeiss		For imaging of the fresh and fibrin-embedded FT
SZX9 upright dissection stereomicroscope	Olympus		For FT dissection
LSM 780 confocal microscope	Zeiss		For imaging of whole-mount immunostained FT
AxioImager.Z1 upright epifluorescence microscope with Apotome	Zeiss		For imaging of whole-mount immunostained FT