title: Enhanced endoplasmic reticulum stress in bone marrow angiogenic progenitor cells in a mouse model of long-term experimental type 2 diabetes.
abstract: OBJECTIVE
  Bone marrow-derived circulating angiogenic cells (CACs) play an important role in vascular repair. In diabetes, compromised functioning of the CACs contributes to the development of diabetic retinopathy; however, the underlying mechanisms are poorly understood. We examined whether endoplasmic reticulum (ER) stress, which has recently been linked to endothelial injury, is involved in diabetic angiogenic dysfunction.
  
  
  METHODS
  Flow cytometric analysis was used to quantify bone marrow-derived progenitors (Lin(-)/c-Kit(+)/Sca-1(+)/CD34(+)) and blood-derived CACs (Sca-1(+)/CD34(+)) in 15-month-old Lepr (db) (db/db) mice and in their littermate control (db/+) mice used as a model of type 2 diabetes. Markers of ER stress in diabetic (db/db) and non-diabetic (db/+) bone marrow-derived early outgrowth cells (EOCs) and retinal vascular density were measured.
  
  
  RESULTS
  The numbers of bone-marrow progenitors and CACs were significantly reduced in db/db mice. Vascular density was markedly decreased in the retinas of db/db mice, and this was accompanied by vascular beading. Microglial activation was enhanced, as was the production of hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF). The production of ER stress markers (glucose-regulated protein-78 [GRP-78], phosphorylated inositol-requiring enzyme-1α [p-IRE-1α], phosphorylated eukaryotic translation initiation factor-2α [p-eIF2α], activating transcription factor-4 [ATF4], C/EBP homologous protein [CHOP] and spliced X-box binding protein-1 [XBP1s]) was significantly increased in bone marrow-derived EOCs from db/db mice. In addition, mouse EOCs cultured in high-glucose conditions demonstrated higher levels of ER stress, reduced colony formation, impaired migration and increased apoptosis, all of which were largely prevented by the chemical chaperone 4-phenylbutyrate.
  
  
  CONCLUSIONS
  Taken together, our results indicate that diabetes increases ER stress in bone marrow angiogenic progenitor cells. Thus, targeting ER stress may offer a new approach to improving angiogenic progenitor cell function and promoting vascular repair in diabetes.
authors.affiliation: Department of Ophthalmology, University at Buffalo, State University of New York, 3435 Main Street, Buffalo, NY, 14214, USA.
authors.forename: Maulasri
authors.initials: M
authors.lastname: Bhatta
authors.forename: Jacey Hongjie
authors.initials: JH
authors.lastname: Ma
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Wang
authors.forename: Jonna
authors.initials: J
authors.lastname: Sakowski
authors.forename: Sarah X
authors.initials: SX
authors.lastname: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis; D001786:Blood Glucose / Q000378:metabolism; D001854:Bone Marrow Cells / Q000166:cytology*; D002465:Cell Movement; D002469:Cell Separation; D003921:Diabetes Mellitus, Experimental / Q000473:pathology*; D003924:Diabetes Mellitus, Type 2 / Q000473:pathology*; D059865:Endoplasmic Reticulum Stress; D042783:Endothelial Cells / Q000166:cytology; D005434:Flow Cytometry; D051379:Mice; D009389:Neovascularization, Pathologic; D010654:Phenylbutyrates / Q000737:chemistry; D012171:Retinal Vessels / Q000473:pathology; D013234:Stem Cells / Q000166:cytology*
chemical_list: D001786:Blood Glucose; D010654:Phenylbutyrates; C075773:4-phenylbutyric acid