Radix Astragali Improves Dysregulated Triglyceride Metabolism and Attenuates Macrophage Infiltration in Adipose Tissue in High-Fat Diet-Induced Obese Male Rats through Activating mTORC1-PPAR γ Signaling Pathway

Abstract

Increased levels of free fatty acids (FFAs) and hypertriglyceridemia are important risk factors for cardiovascular disease. The effective fraction isolated from radix astragali (RA) has been reported to alleviate hypertriglyceridemia. The mechanism of this triglyceride-lowering effect of RA is unclear. Here, we tested whether activation of the mTORC1-PPAR γ signaling pathway is related to the triglyceride-lowering effect of RA. High-fat diet-induced obese (DIO) rats were fed a high-fat diet (40% calories from fat) for 9-10 weeks, and 4 g/kg/d RA was administered by gavage. RA treatment resulted in decreased fasting triglyceride levels, FFA concentrations, and adipocyte size. RA treated rats showed improved triglyceride clearance and fatty acid handling after olive oil overload. RA administration could also decrease macrophage infiltration and expression of MCP-1 and TNF α , but it may also increase the expression of PPAR γ in epididymal adipose tissue from RA treated rats. Consistently, expressions of PPAR γ and phospho-p70S6K were increased in differentiated 3T3-L1 adipocytes treated with RA. Moreover, RA couldnot upregulate the expression of PPAR γ at the presence of rapamycin. In conclusion, the mTORC1-PPAR γ signaling pathway is a potential mechanism through which RA exerts beneficial effects on the disturbance of triglyceride metabolism and dysfunction of adipose tissue in DIO rats.

Figure 1

RA treatment has no effect on body weight and intra-abdominal white adipose tissue mass but decreases adipocyte size. (a) Body weights of rats fed standard chow without RA administration (NFD-C) and with RA administration (NFD-RA), high-fat diet without RA administration (HFD-C) and high-fat diet with RA administration (HFD-RA) (20 weeks, here and throughout, except as noted, n = 5–8/group) (b) epididymal (epi), perirenal (peri), and epi + peri fat pad weights (normalized to body weights here) in rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups (20 weeks, n = 5–8/group). (c) Histology of epididymal adipose tissue from rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups. Scale bar: 50 μm. (d) Mean adipocyte size in rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups (n = 5/group). *P < 0.05 (HFD-C group versus NFD-C group) and ^# P < 0.05 (HFD-RA group versus HFD-C group).

Figure 2

RA treatment decreases TG and FFA levels after a 5-hour fast and olive oil gavage. (a) TG concentrations in rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups after a 5-hour fast (n = 5–8/group). (b) TG concentrations in rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups after olive oil gavage (n = 5–8/group). (c) The AUC of TG levels during olive oil challenge is shown. (d) FFA concentrations in rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups after a 5-hour fast (n = 5–8/group). (e) FFA concentrations in rats in the NFD-C, NFD-RA, HFD-C, and HFD-RA groups after olive oil gavage (n = 5–8/group). (f) AUC of FFA levels during olive oil challenge is shown. *P < 0.05 (HFD-C group versus NFD-C group) and ^# P < 0.05 (HFD-RA group versus HFD-C group).

Figure 3

RA treatment improves the inflammatory state in intra-abdominal white adipose tissue. (a) Immunohistochemical staining of epididymal adipose tissue with anti-F4/80 antibodies. qRT-PCR analysis of TNFα (b) and MCP-1 (c) in the epididymal fat pad. *P < 0.05 (HFD-C group versus NFD-C group) and ^# P < 0.05 (HFD-RA group versus HFD-C group). (d) Protein levels of MCP-1 and TNFα in the epididymal fat pad.

Figure 4

RA upregulates the expression of PPARγ in the intra-abdominal white adipose tissue. (a) mRNA levels of PPARγ from epididymal fat pad were measured by qRT-PCR. *P < 0.05 (HFD-C group versus NFD-C group) and ^# P < 0.05 (HFD-RA group versus HFD-C group). (b) Protein levels of PPARγ in epididymal fat pad.

Figure 5

The mTORC1 signaling pathway plays an important role in the upregulation of PPARγ expression by RA. (a) Differentiated 3T3-L1 cells were cultured with 0, 1, 2, and 4 mg/mL RA for 48 hours. Cell extracts were then subjected to western blot analysis with antibodies specific for total and phosphorylated p70S6K (Thr389), PPARγ, and β-actin. (b) Differentiated 3T3-L1 cells were cultured with rapamycin (0 or 30 nM) and RA (0 or 2 mg/mL) for 2 or 48 hours. Cell extracts were then subjected to western blot analysis with antibodies specific for total and phosphorylated p70S6K (Thr389), PPARγ, TNFα, and β-actin.