title: Tiam1-Rac1 Axis Promotes Activation of p38 MAP Kinase in the Development of Diabetic Retinopathy: Evidence for a Requisite Role for Protein Palmitoylation.
abstract: OBJECTIVE
  Evidence in multiple tissues, including retina, suggests generation of reactive oxygen species (ROS) and the ensuing oxidative stress as triggers for mitochondrial defects and cell apoptosis. We recently reported novel roles for Tiam1-Rac1-Nox2 axis in retinal mitochondrial dysfunction and cell death leading to the development of diabetic retinopathy. Herein, we tested the hypothesis that activation of p38 MAP kinase, a stress kinase, represents the downstream signaling event to Rac1-Nox2 activation in diabetes-induced metabolic stress leading to capillary cell apoptosis.
  
  
  METHODS
  Activation of p38 MAP kinase was quantified by Western blotting in retinal endothelial cells incubated with high glucose (20 mM) for up to 96 hours, a duration where mitochondrial dysfunction and capillary cell apoptosis can be observed. NSC23766 and 2-bromopalmitate (2-BP) were used to assess the roles of Tiam1-Rac1 and palmitoylation pathways, respectively.
  
  
  RESULTS
  Activation of p38 MAP kinase was observed as early as 3 hours after high glucose exposure, and continued until 96 hours. Consistent with this, p38 MAP kinase activation was significantly higher in the retina from diabetic mice compared to age-matched normal mice. NSC23766 markedly attenuated hyperglycemia-induced activation of p38 MAP kinase. Lastly, 2-BP inhibited glucose-induced Rac1, Nox2 and p38 MAP kinase activation in endothelial cells.
  
  
  CONCLUSIONS
  Tiam1-Rac1-mediated activation of Nox2 and p38 MAP kinase constitutes early signaling events leading to mitochondrial dysfunction and the development of diabetic retinopathy. Our findings also provide the first evidence to implicate novel roles for protein palmitoylation in this signaling cascade.
authors.affiliation: Ophthalmology, Wayne State University, Detroit, MI, USA.
authors.forename: Rajakrishnan
authors.initials: R
authors.lastname: Veluthakal
authors.forename: Binit
authors.initials: B
authors.lastname: Kumar
authors.forename: Ghulam
authors.initials: G
authors.lastname: Mohammad
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Kowluru
authors.forename: Renu A
authors.initials: RA
authors.lastname: Kowluru
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D002417:Cattle; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000150:complications* / Q000378:metabolism; D003930:Diabetic Retinopathy / Q000378:metabolism* / Q000473:pathology; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D054878:Lipoylation; D008297:Male; D051379:Mice; D009479:Neuropeptides / Q000378:metabolism*; D010168:Palmitates / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D012160:Retina / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000634:Aminoquinolines; D020662:Guanine Nucleotide Exchange Factors; C487513:NSC 23766; D009479:Neuropeptides; D010168:Palmitates; D011743:Pyrimidines; C484602:Rac1 protein, mouse; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; C022776:2-bromopalmitate; D048051:p38 Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein; D005947:Glucose