Mafa expression enhances glucose-responsive insulin secretion in neonatal rat beta cells

Area of Science:

• Endocrinology
• Molecular Biology
• Developmental Biology

Background:

• Neonatal beta cells exhibit immature function, lacking glucose-stimulated insulin secretion.
• This immaturity is linked to low expression of mature beta cell genes, including key transcription factors like Mafa and Pdx1.
• Mafa and Pdx1 are critical for regulating insulin synthesis and secretion and are implicated in late-stage beta cell development.

Purpose of the Study:

• To investigate the role of Mafa and Pdx1 in the postnatal functional maturation of beta cells.
• To determine if Mafa and/or Pdx1 regulate glucose responsiveness in neonatal beta cells.

Main Methods:

• Quantitative PCR was used to assess beta cell gene expression in neonatal and adult rats.
• Adenoviral vectors overexpressing MAFA or Pdx1 were used to manipulate gene expression in P2 rat islets.
• Insulin secretion was measured using static incubation and reverse hemolytic plaque assay (RHPA).

Main Results:

• Neonatal beta cells showed significantly lower Mafa expression compared to adults, persisting through P21.
• Overexpression of Pdx1 increased Mafa, Neurod1, glucokinase (Gck) mRNA, and insulin content but did not improve glucose responsiveness.
• Overexpression of MAFA led to increased Neurod1, Nkx6-1, Gck, and Glp1r mRNAs and importantly, conferred glucose-responsive insulin secretion, increasing both the percentage of secreting cells and insulin output.

Conclusions:

• Mafa plays a critical role in the functional maturation of neonatal beta cells, specifically in acquiring glucose-responsive insulin secretion.
• Functional maturation involves a coordinated gene expression program where Mafa is a key regulator.
• These findings provide insights into the molecular mechanisms driving beta cell development and functional maturation.