Sfrp5 is an anti-inflammatory adipokine that modulates metabolic dysfunction in obesity

Abstract

Adipose tissue secretes proteins referred to as adipokines, many of which promote inflammation and disrupt glucose homeostasis. Here we show that secreted frizzled-related protein 5 (Sfrp5), a protein previously linked to the Wnt signaling pathway, is an anti-inflammatory adipokine whose expression is perturbed in models of obesity and type 2 diabetes. Sfrp5-deficient mice fed a high-calorie diet developed severe glucose intolerance and hepatic steatosis, and their adipose tissue showed an accumulation of activated macrophages that was associated with activation of the c-Jun N-terminal kinase signaling pathway. Adenovirus-mediated delivery of Sfrp5 to mouse models of obesity ameliorated glucose intolerance and hepatic steatosis. Thus, in the setting of obesity, Sfrp5 secretion by adipocytes exerts salutary effects on metabolic dysfunction by controlling inflammatory cells within adipose tissue.

Fig. 1

Expression of Sfrp5 in white adipose tissue in lean and obese mice. (A) Expression of Sfrp5 and Wnt5a in epididymal fat tissue in WT and ob/ob mice at the age of 20 weeks. (B) Expression of Sfrp5 and Wnt5a in epididymal adipose tissue of WT mice fed normal diet (ND) or HF-HS diet for 24 weeks. Sfrp5 transcript levels were measured by quantitative real-time polymerase chain reaction analysis and expressed relative to a reference gene, 36B4 (n = 6 or 7 mice). Expression of Sfrp5 and Wnt5a protein was determined by immunoblot analysis.

Fig. 2

Sfrp5-deficiency exacerbates metabolic dysfunction in mice fed a HFHS diet. Sfrp5^–/– (KO) and WT mice were given normal feed or a HF-HS diet for 12 weeks. (A) (Left) Glucose tolerance and (right) insulin tolerance tests (n = 9 in each group). *P < 0.01 versus corresponding WT mice. (B) Histological sections of oil red O–stained liver from the HF-HS–fed WT and KO mice. Scale bars, 100 μm. (Right) Triglyceride (TG) content of liver from HF-HS diet–fed WT and KO mice (n = 6). (C) Histological analysis of hematoxylin and eosin (H&E)–stained epididymal white adipose tissue of the HF-HS–fed WT and KO mice. Scale bars, 100 μm. Adipocyte cross-sectional areas were determined using the ImageJ program (n = 7). (D) Macrophage accumulation in epididymal adipose tissues in WT and KO mice when fed a HF-HS diet. Histological sections were stained with antibody against F4/80. Macrophage infiltration was determined as the number of F4/80-positive cells per mm² (n = 8). Scale bars, 50 μm.

Fig. 3

JNK1 activation contributes to diet-induced metabolic dysfunction in Sfrp5-deficient mice and Wnt5a-mediated cell activation in vitro. Sfrp5^–/– (KO) and WT mice were maintained on a HF-HS diet for 12 weeks. (A) Phosphorylation of JNK (Thr¹⁸³/Tyr¹⁸⁵), cJUN (Ser⁶³), and IRS-1 (Ser³⁰⁷) in fat tissue of WT and KO mice as determined by immunoblot analysis. (B) Akt phosphorylation in adipose tissues of WT and KO mice after insulin administration. (C) Effect of Sfrp5 on Wnt5a-stimulated JNK phosphorylation in adipocytes. 3T3-L1 adipocytes were transduced with Ad–β-gal or Ad-Sfrp5 in the presence of AdCMV-tTA, which uses a cytomegalovirus promoter sequence to drive a tetracycline transactivator and activate β-galactosidase or Sfrp5, followed by treatment with Wnt5a or vehicle for 30 min. (D) Effect of the conditioned medium from Sfrp5-transfected adipocytes on Wnt5a-induced JNK activation in macrophages. Peritoneal macrophages were stimulated with Wnt5a or vehicle for 30 min in the presence of the conditioned media from 3T3-L1 adipocyte transduced with Ad–β-gal or Ad-Sfrp5 along with AdCMV-tTA. (E) Contribution of JNK1 to severe insulin resistance caused by Sfrp5 deficiency. WT, Sfrp5^–/– (Sfrp5-KO), Jnk1^–/– (Jnk1-KO), and Sfrp5^–/– Jnk1^–/– (Sfrp5/Jnk1-DKO) mice were maintained on a HF-HS diet for 12 weeks. (Left) Glucose tolerance and (right) insulin tolerance tests were performed (n = 6 or 7 in each group). *P < 0.01 versus WT mice. **P < 0.01 versus Sfrp5-KO mice.

Fig. 4

Systemic delivery of Sfrp5 is protective against metabolic dysfunction in obese mice. (A) (Left) Glucose tolerance and (right) insulin tolerance assays. Ad–β-gal and Ad-Sfrp5 along with AdCMV-tTA, or Ad-APN were intravenously administered to ob/ob mice at the age of 20 weeks. Two weeks after supplementation of adenoviral reagents (β-gal, Sfrp5, or APN), glucose tolerance and insulin tolerance tests were performed (n = 5 or 6 in each group). *P < 0.01 versus β-gal treatment. **P < 0.05 versus β-gal treatment. (B and C) Representative histological sections of (B) fat pads stained with H&E and (C) liver stained with oil red O in β-gal– or Sfrp5-treated ob/ob mice. Scale bars, 100 μm. (B) (Right) Quantification of adipocyte size (n = 6). (C) (Right) Triglyceride (TG) content of liver (n = 6).