PDX1 deficiency causes mitochondrial dysfunction and defective insulin secretion through TFAM suppression
Benoit R Gauthier1, Andreas Wiederkehr, Mathurin Baquié
1Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland. benoit.gauthier@cabimer.es
Cell Metabolism
|August 7, 2009
Summary
Transcription factor Pdx1 controls mitochondrial factor A (TFAM) expression, crucial for beta cell function. Restoring TFAM or blocking mitochondrial calcium exchange improves insulin secretion in diabetes models.
Area of Science:
- Molecular biology
- Endocrinology
- Genetics
Background:
- Mutations in the transcription factor Pdx1 are linked to maturity-onset diabetes of the young 4 (MODY4).
- Impaired mitochondrial metabolism and glucose-stimulated insulin secretion (GSIS) are observed following Pdx1 inhibition.
- Transcript profiling indicates suppression of nuclear-encoded mitochondrial factor A (TFAM) under these conditions.
Purpose of the Study:
- To investigate the regulatory relationship between Pdx1 and TFAM in pancreatic beta cells.
- To determine if TFAM is a direct target of Pdx1 and its role in maintaining mitochondrial function and insulin secretion.
- To explore therapeutic strategies targeting mitochondrial metabolism for diabetes.
Main Methods:
- Utilized dominant-negative Pdx1 (RIPDN79PDX1) in mouse models and isolated rat INS1 cells and human islets.
- Performed transcript profiling to identify downstream targets of Pdx1.
- Employed adenoviral overexpression of TFAM and pharmacological inhibition of the mitochondrial Na(+)/Ca(2+) exchanger (CGP37157).
Main Results:
- Pdx1 suppression in adult mice reduced islet TFAM expression and caused hyperglycemia.
- TFAM was confirmed as a direct transcriptional target of Pdx1 in both rodent and human beta cell models.
- Overexpression of TFAM rescued mitochondrial DNA (mtDNA) copy number, restored respiratory chain activity, and normalized glucose-induced ATP synthesis and insulin secretion.
- CGP37157 treatment restored ATP generation and GSIS in islets with Pdx1 deficiency, bypassing the transcriptional defect.
Conclusions:
- Pdx1 directly regulates TFAM, a key factor for maintaining beta cell mitochondrial DNA and function.
- TFAM is essential for mitochondrial ATP production and normal glucose-stimulated insulin secretion.
- Targeting mitochondrial calcium handling offers a potential therapeutic avenue for diabetes associated with Pdx1 dysfunction.
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