An Intronic Enhancer Element Regulates Angiotensin II Type 2 Receptor Expression during Satellite Cell...

Area of Science:

• Muscle biology and regeneration
• Cardiorenal disease pathophysiology
• Molecular mechanisms of gene regulation

Background:

• Advanced congestive heart failure (CHF) and chronic kidney disease (CKD) are linked to increased angiotensin II (Ang II) and muscle wasting (cachexia).
• Ang II acting through its type 1 receptor (AT1R) promotes muscle protein breakdown and inhibits regeneration, while its type 2 receptor (AT2R) expression is induced during muscle stem cell (SC) differentiation and enhances regeneration.
• Reduced muscle regeneration in CHF suggests dysregulation of pathways controlling AT2R expression.

Purpose of the Study:

• To investigate the regulatory mechanisms of AT2R expression in skeletal muscle during chronic disease.
• To elucidate the role of AT2R regulation in impaired muscle regeneration observed in a mouse model of CHF.
• To identify potential therapeutic targets for enhancing muscle regeneration in chronic conditions.

Main Methods:

• Utilized a mouse model of CHF to assess muscle regeneration and AT2R expression.
• Performed AT2R promoter reporter assays during SC differentiation to identify core promoter and enhancer regions.
• Conducted deletion/mutation analysis within the identified AT2R intron 2 enhancer region (+286/+690) to map transcription factor binding sites.

Main Results:

• Muscle regeneration was significantly reduced in CHF mice, correlating with a blunted increase in AT2R expression.
• A core AT2R promoter region was identified upstream of the transcription start site, while AT2R intron 2 functioned as a crucial transcriptional enhancer during SC differentiation.
• Multiple transcription factor binding sites within the +286/+690 region of intron 2 were found to regulate AT2R transcription, and this enhancer activity was suppressed in CHF skeletal muscle.

Conclusions:

• AT2R expression and subsequent muscle regeneration are suppressed in CHF, likely due to the inhibition of the AT2R intronic enhancer activity.
• The identified +286/+690 enhancer region in AT2R intron 2 represents a key regulatory element for AT2R induction during SC differentiation.
• Targeting this intron 2 enhancer element offers a potential novel therapeutic strategy to boost AT2R levels and improve skeletal muscle regenerative capacity in patients with chronic diseases like CHF and CKD.