title: SIK2 is involved in the negative modulation of insulin-dependent muller cell survival and implicated in hyperglycemia-induced cell death.
abstract: OBJECTIVE
  To investigate the role of the serine/threonine kinase SIK2, a member of the salt-inducible kinase (SIK) family, in insulin-dependent cell survival and hyperglycemia-induced cell death in Müller glia.
  
  
  METHODS
  Expression studies were performed by RT-PCR, immunostaining, Northern blotting, and immunoblotting. Insulin-dependent changes in SIK2 activity were investigated by in vitro kinase assays in MIO-M1 Müller cell line. Akt activation was studied by immunoblotting and cell death by TUNEL assay. The potential role of SIK2 in insulin signaling was explored by overexpression and sh-RNA knock-down approaches. Effects of hyperglycemia were studied in vitro and in vivo in streptozotocin-injected rats.
  
  
  RESULTS
  SIK2 expression was detected throughout adult retina, except for the outer nuclear layer. Insulin stimulation of MIO-M1 cells resulted in a rapid 2-fold increase of SIK2 activity, increased insulin receptor substrate 1 (IRS1)-SIK2 interaction, and reduced cell death. pAkt levels following insulin treatment were modulated by SIK2 activity. Under hyperglycemia, increased SIK2 activity/expression was concomitant to decreased Akt activation and enhanced apoptosis; whereas knockdown of SIK2 under normo- and hyperglycemic conditions resulted in a rapid increase in pAkt levels and blunted cell death. SIK2 overexpression under normoglycemia had an opposite effect. SIK2 activity increased significantly within 2 weeks of induction of hyperglycemia in the rat retina.
  
  
  CONCLUSIONS
  Results indicate that SIK2 functions as a negative modulator of the insulin-dependent survival pathway and contributes to hyperglycemia-induced cell death of Müller glia in vitro. Although still hypothetical at this point, our study suggests that SIK2 could serve a similar role during the development of diabetic retinopathy in vivo and that it represents a potential target to control disease progression.
authors.affiliation: Department of Medicine-Hematology/Oncology, Samuel Oschin Comprehensive Cancer Institute, Cedars-Sinai Medical Center, Los Angeles, California.
authors.forename: Gamze
authors.initials: G
authors.lastname: Küser-Abali
authors.forename: Ferruh
authors.initials: F
authors.lastname: Ozcan
authors.forename: Asli
authors.initials: A
authors.lastname: Ugurlu
authors.forename: Avni
authors.initials: A
authors.lastname: Uysal
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Fuss
authors.forename: Kuyas
authors.initials: K
authors.lastname: Bugra-Bilge
mesh_terms: D000367:Age Factors; D000818:Animals; D016923:Cell Death / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology; D002908:Chronic Disease; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism / Q000473:pathology; D003930:Diabetic Retinopathy / Q000378:metabolism / Q000473:pathology*; D020868:Gene Silencing; D006943:Hyperglycemia / Q000378:metabolism / Q000473:pathology*; D020287:In Situ Nick-End Labeling; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D008297:Male; D009457:Neuroglia / Q000166:cytology / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C583272:SIK2 protein, rat
keywords: Müller glia; SIK2; chronic hyperglycemia; insulin