Reduced androgen receptor gene expression with first exon CAG repeat expansion

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Spinal/bulbar muscular atrophy (SBMA) is an adult-onset neurodegenerative disease.
• Partial androgen insensitivity is a characteristic of SBMA.
• The role of androgen receptor (AR) gene CAG repeat length in SBMA pathogenesis requires further elucidation.

Purpose of the Study:

• To investigate the molecular basis of partial androgen insensitivity in SBMA.
• To determine the relationship between CAG repeat length in the AR gene and AR expression levels.
• To assess the impact of CAG repeat expansion on AR functional activity.

Main Methods:

• Transient transfection of human AR expression vectors with varying CAG repeat lengths.
• Quantification of AR mRNA and protein levels.
• Measurement of AR binding affinity and transcriptional activity using reporter assays.

Main Results:

• An inverse correlation was found between CAG repeat length and AR mRNA and protein levels.
• CAG repeat lengths of 43 and 65 reduced AR expression but did not alter binding affinity or transcriptional activity.
• Glutamine expansion up to 66 residues did not impair AR functional activity.

Conclusions:

• CAG repeat expansion in the AR gene's first exon reduces AR mRNA and protein expression.
• This reduction in AR expression is a key mechanism underlying androgen resistance in SBMA.
• The study identifies a novel molecular mechanism contributing to SBMA pathogenesis.