The regulatory effects of electroacupuncture on type 2 innate lymphoid cell (ILC2) function and browning of white adipose tissue in obese rats

Objective

To observe the effects of electroacupuncture (EA) on type 2 innate lymphoid cell (ILC2) function in white adipose tissue (WAT) of high-fat diet (HFD)-induced obese rats to reveal the mechanism underlying weight loss.

Methods

Male Winstar rats (n=15) were randomly divided into control, HFD, and HFD+EA groups, with five rats in each group. An obesity model was established by feeding rats with a HFD. EA (2 Hz, 1 mA) was applied to “Zhongwan (CV12)” bilateral “Tianshu (ST25)” “Zusanli (ST36)” and “Sanyinjiao (SP6)” for 15 min, 7 days a week, for a total of 5 weeks. During EA treatment, the HFD group was fed a HFD, whereas rats in the control group were maintained on a normal diet. There was no intervention in either the control or the HFD groups. Body weight was measured weekly. Full-field adipocyte morphology, adipocyte volume, and the number of abdominal WAT were observed under a microscope after sectioning and hematoxylin and eosin staining. The levels of IL-5 (interleukin-5), IL-13 (interleukin-13), IL-33 (interleukin-33), and ST2 (growth stimulating gene 2 protein) in the WAT were assayed using enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction (RT-PCR). The expression levels of browning markers including PGC1α（peroxisome proliferator-activated receptor gamma coactivator 1-alpha）, PPARγ (peroxisome proliferator-activated receptor gamma), PRDM16 (histone-lysine N-methyltransferase), and UCP1（uncoupling protein 1 in WAT were detected by western blot analysis and RT-PCR.

Results

After a 7-week induction period, rats in both the HFD and HFD+EA groups were 20% heavier than their initial weights before modeling (P<0.01, P<0.001). Following a 5-week EA intervention, the body mass and Lee index of obese rats were significantly reduced (P<0.05). The HE results showed that adipocytes in the HFD group displayed a significant increase in diameter and a decrease in number compared to the control group. However, in the HFD+EA group, white adipocytes exhibited reduced diameter and appeared more regular in shape. In the control group, the proportion of ILC2 was (86.53±2.55)%, whereas in the HFD group, it decreased to (73.62±2.52)%, indicating a significant reduction in ILC2 in the WAT of obese rats. Following EA treatment, the proportion of ILC2 was elevated to (80.54±4.25)%. This analysis revealed a significant decrease in the expression levels of IL-5, IL-13, IL-33, and ST2 in the WAT of obese rats in the HFD group; however, these levels increased after EA intervention. The mRNA levels of PPARγ, PGC1α, PRDM16, and protein levels of UCP1 were decreased in the HFD group (P<0.01, P<0.05, and P<0.001), and the trends were significantly reversed with EA manipulation (P<0.05). RT-PCR and western blotting results revealed that EA remarkably upregulated the mRNA expression of PGC1α, PPARγ, and PRDM16, as well as the protein expression of UCP1 induced by HFD. In the HFD group, PRDM16 expression showed a strong correlation with UCP1 expression, and ILCs were strongly correlated with PGC1α expression. However, these strong correlations did not occur in HFD+EA group. Following EA treatment, the expression of PPARγ displayed a strong correlation with ILC2s, indicating that the altered ILC2 proportion was closely related to browning in WAT.

Conclusion

EA treatment effectively alleviated obesity by restoring ILC2 function and promoting browning of white adipocytes. ILC2s may play an important role in the effects of EA treatment, but this requires further study.