Examining How the MAFB Transcription Factor Affects Islet β-Cell Function Postnatally

Area of Science:

• Endocrinology
• Molecular Biology
• Genetics

Background:

• Human islet beta cells exhibit sustained MAFB transcription factor expression, unlike in mice.
• MAFA, another islet beta-cell enriched factor, shows delayed mRNA expression in humans, peaking after age 9.
• MAFA protein is minimally produced in juvenile human beta cells, and MafB expression is epigenetically silenced postnatally in mice.

Purpose of the Study:

• To investigate the functional role of MAFB in human islet beta cells.
• To compare the function of human MAFA/MAFB heterodimers with mouse MafA homodimers.
• To explore MafB's impact on maternal beta cell adaptation during pregnancy.

Main Methods:

• Developed a mouse model for ectopic MafB expression in adult beta cells using MafA regulatory elements.
• Analyzed beta cell function in mice with MafB coexpression and in MafA-deficient mutants.
• Assessed tryptophan hydroxylase 1 mRNA levels and serotonin biosynthesis in transgenic mice.

Main Results:

• Coexpression of MafB with MafA in adult mouse beta cells did not cause overt changes, suggesting functional equivalence to mouse MafA homodimers.
• MafB alone could not rescue beta cell defects in MafA-deficient mice.
• Transgenic MafB expression elevated tryptophan hydroxylase 1 mRNA during pregnancy, supporting serotonin biosynthesis for maternal beta cell adaptation.

Conclusions:

• The human adult MAFA/MAFB heterodimer appears functionally similar to the mouse MafA homodimer.
• MafB plays a distinct role in beta cells, particularly in supporting maternal adaptations during pregnancy via serotonin pathways.
• These findings offer new insights into MAFB's function in human islet beta cells.