Crucial roles of neuronatin in insulin secretion and high glucose-induced apoptosis in pancreatic β-cells

Neuronatin (Nnat) was initially identified as a selectively-expressed gene in neonatal brains, but its expression has been also identified in pancreatic β-cells. Therefore, to investigate the possible functions that Nnat may serve in pancreatic β-cells, two Nnat isotypes (α and β) were expressed using adenoviruses in murine MIN6N8 pancreatic β-cells, and the cellular fates and the effects of Nnat on insulin secretion, high glucose-induced apoptosis, and functional impairment were examined. Nnatα and Nnatβ were primarily localized in the endoplasmic reticulum (ER), and their expressions increased insulin secretion by increasing intracellular calcium levels. However, under chronic high glucose conditions, the Nnatβ to Nnatα ratio gradually increased in proportion to the length of exposure to high glucose levels. Moreover, adenovirally-expressed Nnatβ was inclined to form aggresome-like structures, and we found that Nnatβ aggregation inhibited the function of the proteasome. Therefore, when glucose is elevated, the expression of Nnatβ sensitizes MIN6N8 cells to high glucose stress, which in turn, causes ER stress. As a result, expression of Nnatβ increased hyperglycemia-induced apoptosis. In addition, the expression of Nnatβ under high glucose conditions decreased the expression of genes important for β-cell function, such as glucokinase (GCK), pancreas duodenum homeobox-1 (PDX-1), and insulin. Collectively, Nnat may play a critical factor in normal β-cell function, as well as in the pathogenesis of type 2 diabetes

Expression of Myocilin Mutants Sensitizes Cells to Oxidative Stress-Induced Apoptosis : Implication for Glaucoma Pathogenesis

Mutations in the myocilin gene are associated with juvenile and adult-onset primary open-angle glaucoma. However, the pathogenic mechanisms of myocilin-induced glaucoma are still largely unknown. To investigate these mechanisms, we developed stably transfected HEK293 cell lines expressing wild-type or mutant (Y437H and I477N) myocilins under an inducible promoter. Expression of two mutant myocilins led to different levels of endoplasmic reticulum stress and increased apoptosis after treatment of cells with hydrogen peroxide. The Y437H mutant myocilin cell line showed the highest sensitivity to the oxidant treatment. Several antioxidant genes were down-regulated in the Y437H mutant myocilin cell line, but not in other cell lines. The Y437H mutant myocilin cell line also produced more reactive oxygen species than other cell lines examined. Consistent with the data obtained in cultured cells, the endoplasmic reticulum stress marker, 78 kDa glucose-regulated protein, was up-regulated, whereas antioxidant proteins, paraoxonase 2 and glutathione peroxidase 3, were down-regulated in the eye angle tissue of 18-month-old transgenic mice expressing Y437H myocilin mutant. In addition, a pro-apoptotic factor, CCAAT/enhancer-binding protein-homologous protein, was up-regulated in the aged transgenic mouse angle tissue. Our results suggest that expression of mutated myocilins may have a sensitization effect, which can lead to a severe phenotype in combination with oxidative stress. Mutant myocilins may confer different sensitivity to oxidative stress depending on the mutation

Erratum to: Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition) (Autophagy, 12, 1, 1-222, 10.1080/15548627.2015.1100356

non present