Localization of exercise- and denervation-responsive elements in the mouse GLUT4 gene

Area of Science:

• Molecular Biology
• Genetics
• Physiology

Background:

• Exercise training enhances glucose uptake in skeletal muscle, largely mediated by increased expression of glucose transporter type 4 (GLUT4).
• Previous research localized exercise-responsive elements of the murine GLUT4 gene to a region between -1001 and -442 bp relative to the transcription start site.

Purpose of the Study:

• To further delineate the specific regulatory elements within the GLUT4 gene responsible for exercise-induced expression and tissue-specific regulation.
• To investigate the role of the myocyte enhancer factor 2 (MEF2) binding site in GLUT4 gene regulation in response to exercise and denervation.

Main Methods:

• Generation and analysis of transgenic mice harboring GLUT4 minigenes with varying lengths of the 5'-flanking region (-701, -551, -442, and -423 bp).
• Assessment of minigene expression in skeletal muscle, heart, and brown adipose tissue.
• Evaluation of the impact of exercise training (swimming, treadmill running) and denervation on minigene mRNA levels.

Main Results:

• All minigenes, including the -423 construct lacking the MEF2-binding domain, showed expression in skeletal muscle and heart.
• Expression in brown adipose tissue was observed for -701 and -551 constructs but not for -442 or -423 constructs.
• Exercise training up-regulated GLUT4 minigene mRNA in -701 and -551 transgenic mice, but not in -442 or -423 mice. Denervation down-regulated expression in all constructs.

Conclusions:

• Exercise-responsive elements and brown adipocyte-specific elements are located within the -551 to -442 bp region of the GLUT4 gene.
• The MEF2 binding site (-437 to -428 bp) is not essential for GLUT4 expression in skeletal muscle and heart.
• The cis-element mediating denervation-induced down-regulation of GLUT4 is located downstream of -423 bp.