title: Role of FAM18B in diabetic retinopathy.
abstract: OBJECTIVE
  Genome-wide association studies have suggested an association between a previously uncharacterized gene, FAM18B, and diabetic retinopathy. This study explores the role of FAM18B in diabetic retinopathy. An improved understanding of FAM18B could yield important insights into the pathogenesis of this sight-threatening complication of diabetes mellitus.
  
  
  METHODS
  Postmortem human eyes were examined with immunohistochemistry and immunofluorescence for the presence of FAM18B. Expression of FAM18B in primary human retinal microvascular endothelial cells (HRMECs) exposed to hyperglycemia, vascular endothelial growth factor (VEGF), or advanced glycation end products (AGEs) was determined with quantitative reverse-transcription PCR (qRT-PCR) and/or western blot. The role of FAM18B in regulating human retinal microvascular endothelial cell viability, migration, and endothelial tube formation was determined following RNAi-mediated knockdown of FAM18B. The presence of FAM18B was determined with qRT-PCR in CD34+/VEGFR2+ mononuclear cells isolated from a cohort of 17 diabetic subjects with and without diabetic retinopathy.
  
  
  RESULTS
  Immunohistochemistry and immunofluorescence demonstrated the presence of FAM18B in the human retina with prominent vascular staining. Hyperglycemia, VEGF, and AGEs downregulated the expression of FAM18B in HRMECs. RNAi-mediated knockdown of FAM18B in HRMECs contributed to enhanced migration and tube formation as well as exacerbating the hyperglycemia-induced decrease in HRMEC viability. The enhanced migration, tube formation, and decrease in the viability of HRMECs as a result of FAM18B downregulation was reversed with pyrrolidine dithiocarbamate (PDTC), a specific nuclear factor-kappa B (NF-κB) inhibitor. CD34+/VEGFR2+ mononuclear cells from subjects with proliferative diabetic retinopathy demonstrated significantly reduced mRNA expression of FAM18B compared to diabetic subjects without retinopathy.
  
  
  CONCLUSIONS
  FAM18B is expressed in the retina. Diabetic culture conditions decrease the expression of FAM18B in HRMECs. The downregulation of FAM18B by siRNA in HRMECs results in enhanced migration and tube formation, but also exacerbates the hyperglycemia-induced decrease in HRMEC viability. The pathogenic changes observed in HRMECs as a result of FAM18B downregulation were reversed with PDTC, a specific NF-κB inhibitor. This study is the first to demonstrate a potential role for FAM18B in the pathogenesis of diabetic retinopathy.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL.
authors.forename: Ai Ling
authors.initials: AL
authors.lastname: Wang
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL.
authors.forename: Vidhya R
authors.initials: VR
authors.lastname: Rao
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL.
authors.forename: Judy J
authors.initials: JJ
authors.lastname: Chen
authors.affiliation: Department of Medicine, University of Arizona, Tucson, AZ.
authors.forename: Yves A
authors.initials: YA
authors.lastname: Lussier
authors.affiliation: Departments of Medicine and Pharmacology, University of Illinois at Chicago, Chicago, IL.
authors.forename: Jalees
authors.initials: J
authors.lastname: Rehman
authors.affiliation: Section of Gastroenterology, Department of Medicine, University of Chicago, Chicago, IL.
authors.forename: Yong
authors.initials: Y
authors.lastname: Huang
authors.affiliation: University Retina, Oak Forest, IL.
authors.forename: Rama D
authors.initials: RD
authors.lastname: Jager
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Grassi
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D016022:Case-Control Studies; D002470:Cell Survival; D015331:Cohort Studies; D003930:Diabetic Retinopathy / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology; D055785:Gene Knockdown Techniques; D006801:Humans; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D055806:Microvessels / Q000378:metabolism / Q000473:pathology; D034622:RNA Interference; D015861:Retinal Neovascularization; D012171:Retinal Vessels / Q000378:metabolism / Q000473:pathology; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism; D021601:trans-Golgi Network
chemical_list: D018952:Antigens, CD34; D008565:Membrane Proteins; C000603301:TVP23B protein, human; C000588866:KDR protein, human; D040301:Vascular Endothelial Growth Factor Receptor-2