[Electroacupuncture activates PKA / CREB signaling pathway to promote browning of white fat in obese rats]

Abstract

Objectives: To observe the effect of electroacupuncture (EA) on lipid metabolism and cyclic adenosine monophosphate-dependent protein kinase A (PKA)/cyclic adenosine monophosphate-responsive element binding protein (CREB) signalling pathway in obese rats, so as to explore its possible mechanism in promoting browning of white fat in obese rats.

Methods: Forty 8-week-old male SD rats were randomly divided into blank, model and EA groups (n=10 per group). The obesity model was established by feeding the rats with high-fat diet for 12 weeks. For the EA group, EA (2 Hz/15 Hz, 1.5 mA) was applied to "Zhongwan" (CV12), "Guanyuan" (CV4) and bilateral "Tianshu" (ST25) and "Fenglong" (ST40) for 20 min, once a day, 6 days a week for 6 weeks. After the treatment, the body weight, body length and abdominal circumference of rats were evaluated, and Lee's index was calculated. The weight of inguinal white adipose tissue, epididymal white adipose tissue, white adipose tissue and scapular brown adipose tissue of rats were weighed. The contents of serum total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) were measured by the microplate method. HE staining was used to detect the morphology of inguinal white adipose tissue and scapular brown adipose tissue. Western blot was used to detect the expression levels of PKA, CREB, phosphorylated (p)-CREB, mitochondrial uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor γ-coactivator 1-α (PGC-1α) and sterol regulatory element binding protein 1 (SREBP-1) and immunohistochemistry was used to dectect the positive expressions of PKA、CREB、p-CREB、UCP1、PGC-1α in inguinal white adipose tissue and scapular brown adipose tissue. The mRNA expressions of UCP1, PGC-1α, PR domain-containing protein 16 (PRDM16), peroxisome proliferator-activated receptor gamma (PPARγ), cytochrome c oxidase subunit 7a1 (Cox7a1), cytochrome c oxidase subunit 8b (Cox8b), iodothyronine deiodinase 2 (DIO2), ELOVL3 fatty acid elongase 3 (ELOVL3), cell death-inducing DFFA-like effector a (Cidea), T-box transcription factor 1 (Tbx1), transmembrane protein 26 (Tmem26), and 4-1BB receptor (CD137) in the inguinal white adipose tissue and interscapular brown adipose tissue of rats from various groups were detected by quantitative real-time PCR.

Results: Compared with the blank group, the body weight, abdominal circumference, Lee's index, TG, TC and LDL-C contents, white fat mass in the inguinal, epididymal and perirenal regions, and SREBP-1 protein expression were significantly increased in the model group (P<0.001, P<0.01);whereas brown fat mass in the scapular region, serum HDL-C content, PKA, p-CREB, UCP1, PGC-1α protein expression, as well as mRNA expressions of browning-related genes such as UCP1, PGC-1α, and PRDM16 were significantly decreased (P<0.001, P<0.01, P<0.05). H.E. staining showed an increase of the volume of white adipose tissues, disordered arrangement of cells with vague boundary, meanwhile an enlarge of vacuoles and an increase volume of brown adipose tissues, present white adipocyte-like changes in the model group. Compared with the model group, EA can effectively improve the above indicators of lipid metabolism and white fat browning (P<0.01, P<0.001, P<0.05), and reverse the morphology of adipose tissues in the obese rats.

Conclusions: EA can effectively reduce the body weight and improve lipid metabolism in obesity rats, which is possibly associated with its functions in activating the PKA/CREB signalling pathway, up-regulating the white fat browning markers UCP1 and PGC-1α protein expressions and white fat browning-related genes, and down-regulating the expression of the lipid regulatory protein SREBP-1.

Keywords: Electroacupuncture; Lipid metabolism; Obesity; PKA/CREB signalling pathway; White adipose tissue browning.