A low-protein, high-carbohydrate diet increases browning in perirenal adipose tissue but not in inguinal adipose...

The aim of this study was to evaluate the browning and origin of fatty acids (FAs) in the maintenance of triacylglycerol (TG) storage and/or as fuel for thermogenesis in perirenal adipose tissue (periWAT) and inguinal adipose tissue (ingWAT) of rats fed a low-protein, high-carbohydrate (LPHC) diet.

LPHC (6% protein, 74% carbohydrate) or control (C; 17% protein, 63% carbohydrate) diets were administered to rats for 15 d. The tissues were stained with hematoxylin and eosin for histologic analysis. The content of uncoupling protein 1 (UCP1) was determined by immunofluorescence. Levels of T-box transcription factor (TBX1), PR domain containing 16 (PRDM16), adipose triacylglycerol lipase (ATGL), hormone-sensitive lipase, lipoprotein lipase (LPL), glycerokinase, phosphoenolpyruvate carboxykinase (PEPCK), glucose transporter 4, β₃-adrenergic receptor (AR), β₁-AR, protein kinase A (PKA), adenosine-monophosphate-activated protein kinase (AMPK), and phospho-AMPK were determined by immunoblotting. Serum fibroblast growth factor 21 (FGF21) was measured using a commercial kit (Student's t tests, P < 0.05).

The LPHC diet increased FGF21 levels by 150-fold. The presence of multilocular adipocytes, combined with the increased contents of UCP1, TBX1, and PRDM16 in periWAT of LPHC-fed rats, suggested the occurrence of browning. The contents of β₁-AR and LPL were increased in the periWAT. The ingWAT showed higher ATGL and PEPCK levels, phospho-AMPK/AMPK ratio, and reduced β₃-AR and PKA levels.

These findings suggest that browning occurred only in the periWAT and that higher utilization of FAs from blood lipoproteins acted as fuel for thermogenesis. Increased glycerol 3-phosphate generation by glyceroneogenesis increased FAs reesterification from lipolysis, explaining the increased TG storage in the ingWAT.