title: PPAR-γ activation restores pancreatic islet SERCA2 levels and prevents β-cell dysfunction under conditions of hyperglycemic and cytokine stress.
abstract: The maintenance of intracellular Ca(2+) homeostasis in the pancreatic β-cell is closely regulated by activity of the sarco-endoplasmic reticulum Ca(2+) ATPase (SERCA) pump. Our data demonstrate a loss of β-cell SERCA2b expression in several models of type 2 diabetes including islets from db/db mice and cadaveric diabetic human islets. Treatment of 832/13 rat INS-1-derived cells with 25 mm glucose and the proinflammatory cytokine IL-1β led to a similar loss of SERCA2b expression, which was prevented by treatment with the peroxisome proliferator-activated receptor (PPAR)-γ agonist, pioglitazone. Pioglitazone was able to also protect against hyperglycemia and cytokine-induced elevations in cytosolic Ca(2+) levels, insulin-secretory defects, and cell death. To determine whether PPAR-γ was a direct transcriptional regulator of the SERCA2 gene, luciferase assays were performed and showed that a -259 bp region is sufficient to confer PPAR-γ transactivation; EMSA and chromatin immunoprecipitation experiments confirmed that PPAR-γ directly binds a PPAR response element in this proximal region. We next sought to characterize the mechanisms by which SERCA2b was down-regulated. INS-1 cells were exposed to high glucose and IL-1β in time course experiments. Within 2 h of exposure, activation of cyclin-dependent kinase 5 (CDK5) was observed and correlated with increased serine-273 phosphorylation of PPAR-γ and loss of SERCA2 protein expression, findings that were prevented by pioglitazone and roscovitine, a pharmacological inhibitor of CDK5. We conclude that pioglitazone modulates SERCA2b expression through direct transcriptional regulation of the gene and indirectly through prevention of CDK5-induced phosphorylation of PPAR-γ.
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Tatsuyoshi
authors.initials: T
authors.lastname: Kono
authors.forename: Geonyoung
authors.initials: G
authors.lastname: Ahn
authors.forename: Dan R
authors.initials: DR
authors.lastname: Moss
authors.forename: Liann
authors.initials: L
authors.lastname: Gann
authors.forename: Angel
authors.initials: A
authors.lastname: Zarain-Herzberg
authors.forename: Yurika
authors.initials: Y
authors.lastname: Nishiki
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Fueger
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ogihara
authors.forename: Carmella
authors.initials: C
authors.lastname: Evans-Molina
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D001786:Blood Glucose; D002118:Calcium / Q000378:metabolism; D002453:Cell Cycle; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism; D016207:Cytokines / Q000494:pharmacology / Q000502:physiology*; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism / Q000473:pathology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D047495:PPAR gamma / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D000077205:Pioglitazone; D011485:Protein Binding; D051381:Rats; D020218:Response Elements; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological; D045162:Thiazolidinediones / Q000494:pharmacology
chemical_list: D001786:Blood Glucose; D016207:Cytokines; D007004:Hypoglycemic Agents; D007328:Insulin; D007527:Isoenzymes; D047495:PPAR gamma; D045162:Thiazolidinediones; D051360:Cyclin-Dependent Kinase 5; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium; D000077205:Pioglitazone