title: The unconventional role of acid sphingomyelinase in regulation of retinal microangiopathy in diabetic human and animal models.
abstract: OBJECTIVE
  Acid sphingomyelinase (ASM) is an important early responder in inflammatory cytokine signaling. The role of ASM in retinal vascular inflammation and vessel loss associated with diabetic retinopathy is not known and represents the goal of this study.
  
  
  METHODS
  Protein and gene expression profiles were determined by quantitative RT-PCR and Western blot. ASM activity was determined using Amplex Red sphingomyelinase assay. Caveolar lipid composition was analyzed by nano-electrospray ionization tandem mass spectrometry. Streptozotocin-induced diabetes and retinal ischemia-reperfusion models were used in in vivo studies.
  
  
  RESULTS
  We identify endothelial caveolae-associated ASM as an essential component in mediating inflammation and vascular pathology in in vivo and in vitro models of diabetic retinopathy. Human retinal endothelial cells (HREC), in contrast with glial and epithelial cells, express the plasma membrane form of ASM that overlaps with caveolin-1. Treatment of HREC with docosahexaenoic acid (DHA) specifically reduces expression of the caveolae-associated ASM, prevents a tumor necrosis factor-α-induced increase in the ceramide-to-sphingomyelin ratio in the caveolae, and inhibits cytokine-induced inflammatory signaling. ASM is expressed in both vascular and neuroretina; however, only vascular ASM is specifically increased in the retinas of animal models at the vasodegenerative phase of diabetic retinopathy. The absence of ASM in ASM(-/-) mice or inhibition of ASM activity by DHA prevents acellular capillary formation.
  
  
  CONCLUSIONS
  This is the first study demonstrating activation of ASM in the retinal vasculature of diabetic retinopathy animal models. Inhibition of ASM could be further explored as a potential therapeutic strategy in treating diabetic retinopathy.
authors.affiliation: Department of Physiology, Michigan State University, East Lansing, Michigan, USA.
authors.forename: Madalina
authors.initials: M
authors.lastname: Opreanu
authors.forename: Maria
authors.initials: M
authors.lastname: Tikhonenko
authors.forename: Svetlana
authors.initials: S
authors.lastname: Bozack
authors.forename: Todd A
authors.initials: TA
authors.lastname: Lydic
authors.forename: Gavin E
authors.initials: GE
authors.lastname: Reid
authors.forename: Kelly M
authors.initials: KM
authors.lastname: McSorley
authors.forename: Andrew
authors.initials: A
authors.lastname: Sochacki
authors.forename: Gloria I
authors.initials: GI
authors.lastname: Perez
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Esselman
authors.forename: Timothy
authors.initials: T
authors.lastname: Kern
authors.forename: Richard
authors.initials: R
authors.lastname: Kolesnick
authors.forename: Maria B
authors.initials: MB
authors.lastname: Grant
authors.forename: Julia V
authors.initials: JV
authors.lastname: Busik
mesh_terms: D000818:Animals; D002196:Capillaries / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002199:Capillary Permeability / Q000187:drug effects; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000378:metabolism*; D003930:Diabetic Retinopathy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004281:Docosahexaenoic Acids / Q000494:pharmacology; D020869:Gene Expression Profiling; D006801:Humans; D008297:Male; D051379:Mice; D051381:Rats; D017207:Rats, Sprague-Dawley; D012171:Retinal Vessels / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics / Q000378:metabolism*
chemical_list: D004281:Docosahexaenoic Acids; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase