MicroRNA-21 Modulates White Adipose Tissue Browning and Altered Thermogenesis in a Mouse Model of Polycystic Ovary Syndrome
Authors: Rezq Samar , Huffman Alexandra M , Syed Maryam , Basnet Jelina , do Carmo Jussara M , Moak Sydney P , Cardozo Licy L Yanes , Romero Damian G 
Published: May 2021

Abstract
Background and Aim: Polycystic ovary syndrome (PCOS) is associated with obesity, and white adipose tissue (WAT) and brown adipose tissue (BAT) dysregulation. However, the molecular mechanisms that mediate WAT and BAT derangements in PCOS are poorly understood. Subcutaneous (SC) WAT (SC-WAT) can transition to a beige/brite adipose tissue phenotype (browning) under altered thermogenic conditions. MicroRNAs play critical functions in brown adipocyte differentiation and maintenance. We aim to study the role of microRNA-21 (miR-21) in androgen-mediated browning and beiging derangements in both SC-WAT and BAT. Methods: Three week-old miR-21 knockout (miR21KO) or wild type (WT) female mice were treated with dihydrotestosterone (DHT, 8 mg/silastic tube) or vehicle for 90 days (n=12/grp). Body composition was measured by EchoMRI. Energy expenditure (EE), oxygen consumption (VO2), and carbon dioxide production (VCO2) were measured by indirect calorimetry. Glucose homeostasis was measured by oral glucose tolerance test (OGTT). HOMA-IR index was calculated from fasting serum glucose and insulin levels. Gene expression for browning (UCP1, Cox7a1, Elov3, Dio2 and Cidea) and beiging (Hspb7 and Txb1) markers was quantified by RT-qPCR in SC-WAT and BAT. Results: DHT increased body weight (25.07 ± 0.52 vs 21.79 ± 0.47 g, p&lt;0.05) and fat mass (4.60 ± 0.46 vs 1.98 ± 0.12 g, p&lt;0.05), impaired OGTT (186.10 ± 5.99 vs 250.70 ± 14.76 mg.min/dL, p&lt;0.05), and did not significantly change EE, VO2 or VCO2 in WT mice. All browning markers were downregulated by DHT in SC-WAT; however, only iodothyronine deiodinase 2 (Dio2) downregulation reached significance in both SC-WAT and BAT (by 53 and 40%, respectively) compared with the vehicle-treated mice. Beiging markers were significantly upregulated in SC-WAT and did not change in BAT. DHT-treated miR21KO mice showed attenuated DHT-mediated increase in body weight (23.84 ± 0.99 vs 25.07 ± 0.52 g, p&lt;0.05) compared with WT mice. MiR-21 ablation did not modify DHT-mediated increase in fat mass or OGTT but worsened insulin resistance as calculated by the HOMA-IR index. Additionally, DHT-treated miR21KO mice showed a trend to reduced EE, VO2 and VCO2 values compared with DHT-treated WT. Gene expression analysis showed an exacerbation in DHT-mediated reduction in browning markers expression in the SC-WAT. Additionally, the induction in the adaptive beiging response was abolished in SC-WAT. Conclusion and Significance: These findings suggest that adipose tissue miR-21 may have a protective role in PCOS and ameliorate the DHT-mediated decrease in energy expenditure. Adipose tissue-specific modulation of miR-21 levels could be a novel therapeutic approach for the treatment of PCOS-associated metabolic derangements. (Supported by NIH grants NIGMS P20GM121334 to LLYC and DGR, NIDDK R21DK113500 to DGR, NIGMS P20GM104357 and NHLBI P01HL51971).