Osteocalcin protects pancreatic beta cell function and survival under high glucose conditions.
Diabetes is characterized by progressive beta cell dysfunction and loss due in part to oxidative stress that occurs from gluco/lipotoxicity. Treatments that directly protect beta cell function and survival in the diabetic milieu are of particular interest. A growing body of evidence suggests that osteocalcin, an abundant non-collagenous protein of bone, supports beta cell function and proliferation. Based on previous gene expression data by microarray, we hypothesized that osteocalcin protects beta cells from glucose-induced oxidative stress. To test our hypothesis we cultured isolated rat islets and INS-1E cells in the presence of normal, high, or high glucose ± osteocalcin for up to 72 h. Oxidative stress and viability/mitochondrial function were measured by H2O2 assay and Alamar Blue assay, respectively. Caspase 3/7 activity was also measured as a marker of apoptosis. A functional test, glucose stimulated insulin release, was conducted and expression of genes/protein was measured by qRT-PCR/western blot/ELISA. Osteocalcin treatment significantly reduced high glucose-induced H2O2 levels while maintaining viability/mitochondrial function. Osteocalcin also significantly improved glucose stimulated insulin secretion and insulin content in rat islets after 48 h of high glucose exposure compared to untreated islets. As expected sustained high glucose down-regulated gene/protein expression of INS1 and BCL2 while increasing TXNIP expression. Interestingly, osteocalcin treatment reversed the effects of high glucose on gene/protein expression. We conclude that osteocalcin can protect beta cells from the negative effects of glucose-induced oxidative stress, in part, by reducing TXNIP expression, thereby preserving beta cell function and survival.
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA. Electronic address: kkover@cmh.edu.
Karen
K
Kover
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
Yun
Y
Yan
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
Pei Ying
PY
Tong
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
Dara
D
Watkins
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
Xiaoyu
X
Li
Kansas City University Medical Biosciences, Kansas City, MO, USA.
James
J
Tasch
Kansas City University Medical Biosciences, Kansas City, MO, USA.
Melissa
M
Hager
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
Mark
M
Clements
Division of Endocrine/Diabetes, Children's Mercy Hospital & Clinics, Kansas City, MO 64108, USA; University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108, USA.
Wayne V
WV
Moore
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000235:genetics / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D015675:Osteocalcin / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D007328:Insulin; D019253:Proto-Oncogene Proteins c-bcl-2; C493796:TXNIP protein, rat; D015675:Osteocalcin; D053148:Caspase 3; D053179:Caspase 7; D005947:Glucose
Diabetes; Glucose toxicity; Osteocalcin; Oxidative stress; Pancreatic beta cells