Detecting white adipose tissue browning in mice with in vivo R₂∗ mapping at 9.4T MRI

Area of Science:

• Biomedical Imaging
• Metabolic Disease Research
• Adipose Tissue Biology

Background:

• White adipose tissue (WAT) browning is a key strategy for combating obesity and metabolic disorders.
• Current methods like fat-water fraction (FWF) lack sensitivity and specificity for metabolic changes during browning.
• Iron metabolism plays a role in WAT browning, but is not adequately assessed by existing markers.

Purpose of the Study:

• To develop and validate a noninvasive preclinical imaging approach using R2* mapping to assess in vivo WAT browning.
• To investigate the correlation between R2* values, iron content, and UCP1 expression during WAT browning.
• To establish R2* as a potential imaging biomarker for evaluating WAT browning and related metabolic changes.

Main Methods:

• Investigated inguinal WAT (iWAT) browning induced by CL-316,243 (CL) in mice.
• Quantified in vivo R2*, FWF, and ex vivo UCP1 expression and iron content.
• Utilized H&E staining and immunohistochemistry for histological analysis.

Main Results:

• CL administration significantly increased R2* and decreased FWF in iWAT after 7 days.
• Ex vivo analysis revealed increased UCP1 expression and iron content in CL-treated iWAT.
• R2* strongly correlated with UCP1 expression and iron content, while inversely correlating with FWF.

Conclusions:

• R2* mapping offers a sensitive and specific noninvasive imaging biomarker for assessing WAT browning.
• This iron-based imaging approach provides a novel tool for diagnosing and evaluating metabolic diseases.
• R2* mapping could aid in the development and therapeutic evaluation of obesity treatments.