title: Identifying HIF activity in three-dimensional cultures of islet-like clusters.
abstract: OBJECTIVE
  Hypoxia is a major cause for failure of encapsulated islet grafts. Three-dimensional (3D) re-aggregation and hypoxic preconditioning are used to help overcome this obstacle. However, it is still difficult to identify hypoxic cells in a 3D system. We evaluate the efficacy of a fluorescent system for detecting HIF-1 activity in live β-cells. Identification of HIF-1 activity and correlation with insulin secretion and viability will allow for more informed implant construction and better prediction of post-transplantational function.
  
  
  METHODS
  MIN6 cells were infected with the marker virus and rotationally cultured to form clusters. Clusters were encapsulated in PEG hydrogels and incubated in 20%, 2%, or 1% O2. Gels were imaged daily for hypoxia marker signaling and for morphological observation. Daily GSIS was quantified by insulin ELSIA and cell viability was assessed by LIVE/DEAD staining.
  
  
  RESULTS
  Clusters cultured in 2% and 1% O2 displayed high levels of HIF activity compared to 20% O2  clusters. 20% O2 clusters maintained viability and achieved a smooth, islet-like morphology by  Day 14. Clusters in 2% and 1% O2 failed to associate cohesively and showed reduced viability. As a whole, constructs cultured in 20% O2 exhibited 10-fold higher GSIS than constructs in 2% and 1% O2.
  
  
  CONCLUSIONS
  Our marker is an effective approach for identifying cellular hypoxia in 3D cultures. β-cell clusters in 2% and 1% O2 are similarly affected by reduced oxygen tension, with HIF-1 activity correlating to reduced GSIS and impaired cell/cluster morphology. Simultaneous aggregative culture and hypoxic conditioning may not be beneficial to β-cell transplantation.
authors: Biomedical Engineering Program, University of South Carolina College of Engineering and Computing, Columbia, South Carolina, USA.
authors: Matthew L
authors: ML
authors: Skiles
authors: Nathan B
authors: NB
authors: Wilder
authors: Suchit
authors: S
authors: Sahai
authors: James O
authors: JO
authors: Blanchette
mesh_terms: D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology*; D045744:Cell Line, Tumor; D048430:Cell Shape; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D010190:Pancreatic Neoplasms / Q000378:metabolism
chemical_list: C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit