title: Hypoxia regulates sumoylation pathways in intervertebral disc cells: implications for hypoxic adaptations.
abstract: To explore the hypoxic regulation of sumoylation pathways and cell viability in nucleus pulposus (NP) and annulus fibrosus (AF) cells.
  
  
  
  Expression of small ubiquitin-like modifier (SUMO) molecules, SUMO E1 activating enzymes SAE1 and SAE2, SUMO E2 conjugating enzyme UBC9, and de-sumoylation enzyme sentrin/SUMO-specific proteases (SENP)1 was immunolocalized in rat intervertebral disc (IVD) cells. NP and AF cells were cultured in hypoxia and cell viability was evaluated by quantifying cell proliferation, cellular senescence, apoptosis, and cell cycle distribution. Hypoxic regulation of sumoylation pathways was studied by analyzing the transcription and expression of SUMO molecules and sumoylation enzymes. Loss of function study using SENP1 siRNA was performed to investigate the regulatory role of sumoylation on the function of hypoxia inducible factor 1α (HIF-1α) and the hypoxic tolerance of IVD cells.
  
  
  
  Sumoylation pathways were expressed in IVD cells and localized predominantly in nuclei. Both NP and AF cells maintained viability under hypoxia and upregulated the expression of SENP1. In NP cells hypoxia transiently increased the expression of SUMO-1, SUMO-2/3, SAE2, and UBC9, whereas SUMO-1 was elevated while SUMO-2/3, SAE1, SAE2, and UBC9 were reduced by low oxygen tensions in AF cells. Although downregulation of SENP1 decreased the transcriptional activity of HIF-1α, the viability of disc cells showed no significant loss under hypoxia.
  
  
  
  NP and AF cells equally tolerate oxygen deficiency, but differently regulate the sumoylation pathways under hypoxia. The distinct sumoylation dynamics may help extend our understanding of the cell-specific regulation of the molecular basis that promotes cell survival in the hypoxic IVD.
authors.affiliation: Department of Spine Surgery, Zhongda Hospital, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China; Surgery Research Center, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China. Electronic address: wangfengspine@163.com.
authors.forename: F
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Spine Surgery, Zhongda Hospital, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China; Surgery Research Center, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China. Electronic address: fzzs_1987@163.com.
authors.forename: F
authors.initials: F
authors.lastname: Cai
authors.affiliation: Department of Spine Surgery, Zhongda Hospital, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China; Surgery Research Center, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China. Electronic address: 277834792@qq.com.
authors.forename: R
authors.initials: R
authors.lastname: Shi
authors.affiliation: Surgery Research Center, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China; Department of Orthopedics, Zhongda Hospital, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China. Electronic address: jinanwei@163.com.
authors.forename: J-N
authors.initials: JN
authors.lastname: Wei
authors.affiliation: Department of Spine Surgery, Zhongda Hospital, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China; Surgery Research Center, School of Medicine, Southeast University, 87# Dingjiaqiao Road, 210009 Nanjing, China. Electronic address: wuxiaotaospine@163.com.
authors.forename: X-T
authors.initials: XT
authors.lastname: Wu
mesh_terms: D000818:Animals; D015687:Cell Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007403:Intervertebral Disc; D051381:Rats; D058207:Sumoylation
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit
keywords: Hypoxia; Intervertebral disc; Posttranslational modulation; Sumoylation