Mesenchymal Stem Cell-Like Properties of Orbital Fibroblasts in Graves' Orbitopathy.
OBJECTIVE
Graves' orbitopathy (GO) is a sight-threatening autoimmune disorder causing extraocular muscle fibrosis, upper lid retraction and eye bulging due to orbital fat expansion. These clinical features are mediated by aspects of orbital fibroblasts differentiation, including adipogenesis and fibrosis. Our previous work suggested that this dual phenotype might be a manifestation of mixed cell populations, partially linked to the expression of mesenchymal stem cell (MSC) marker CD90. Thus, we set out to determine whether GO orbital fibroblasts displayed MSC properties.


METHODS
Control and GO orbital fibroblasts previously characterized for CD90 and CD45 expression were analyzed by flow cytometry for classical MSC positive (CD73, CD105) and negative (CD14, CD19, HLA-DR, and CD34) markers. Graves' orbitopathy fibroblasts were tested further for their ability to undergo lineage specific differentiation following standard protocols.


RESULTS
Control and GO fibroblasts strongly expressed CD73 and CD105, with a higher percentage of positive cells and stronger expression levels in GO. Neither cell type expresses CD14, CD19, and HLA-DR. Protein CD34 was expressed at low levels by 45% to 70% of the cells, with its expression significantly lower in GO cells. Graves' orbitopathy fibroblasts displayed features of osteogenesis (calcium deposits, and osteocalcin [BGLAP] and osteonectin [SPARC] expression), chondrogenesis (glycosaminoglycan production; SOX9 and aggrecan [ACAN] expression), myogenesis (α-smooth muscle actin expression), and neurogenesis (β-III tubulin expression) upon differentiation.


CONCLUSIONS
Our findings suggest that orbital fibroblasts contain a population of cells that fulfil the criteria defining MSC. This subpopulation may be increased in GO, possibly underlying the complex differentiation phenotype of the disease.
Department of Cell Biology UCL Institute of Ophthalmology, London, United Kingdom.
Katarzyna
K
Kozdon
Department of Cell Biology UCL Institute of Ophthalmology, London, United Kingdom.
Caroline
C
Fitchett
Orbital clinic, Moorfields Eye Hospital and the National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
Geoffrey E
GE
Rose
Department of Cell Biology UCL Institute of Ophthalmology, London, United Kingdom 2Orbital clinic, Moorfields Eye Hospital and the National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and.
Daniel G
DG
Ezra
Department of Cell Biology UCL Institute of Ophthalmology, London, United Kingdom.
Maryse
M
Bailly
D053674:Aggrecans / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D016022:Case-Control Studies; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000502:physiology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D049970:Graves Ophthalmopathy / Q000378:metabolism* / Q000473:pathology; D006684:HLA-DR Antigens / Q000378:metabolism; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis / Q000502:physiology; D015676:Osteonectin / Q000378:metabolism; D055758:SOX9 Transcription Factor / Q000378:metabolism
D053674:Aggrecans; D015703:Antigens, CD; D015415:Biomarkers; D006684:HLA-DR Antigens; D015676:Osteonectin; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D015675:Osteocalcin