Reduction of TIP47 improves hepatic steatosis and glucose homeostasis in mice

Abstract

Lipid droplets in the liver are coated with the perilipin family of proteins, notably adipocyte differentiation-related protein (ADRP) and tail-interacting protein of 47 kDa (TIP47). ADRP is increased in hepatic steatosis and is associated with hyperlipidemia, insulin resistance, and glucose intolerance. We have shown that reducing ADRP in the liver via antisense oligonucleotide (ASO) treatment attenuates steatosis and improves insulin sensitivity and glucose tolerance. We hypothesized that TIP47 has similar effects on hepatic lipid and glucose metabolism. We found that TIP47 mRNA and protein levels were increased in response to a high-fat diet (HFD) in C57BL/6J mice. TIP47 ASO treatment decreased liver TIP47 mRNA and protein levels without altering ADRP levels. Low-dose TIP47 ASO (15 mg/kg) and high-dose TIP47 ASO (50 mg/kg) decreased triglyceride content in the liver by 35% and 52%, respectively. Liver histology showed a drastic reduction in hepatic steatosis following TIP47 ASO treatment. The high dose of TIP47 ASO significantly blunted hepatic triglyceride secretion, improved glucose tolerance, and increased insulin sensitivity in liver, adipose tissue, and muscle. These findings show that TIP47 affects hepatic lipid and glucose metabolism and may be a target for the treatment of nonalcoholic fatty liver and related metabolic disorders.

Fig. 1.

Effects of normal chow and high-fat diets on body weight (A), body fat (B), liver triglycerides (C), very low density lipoprotein (VLDL) secretion (D), liver tail-interacting protein of 47 kDa (TIP47) mRNA relative to phosphoriboprotein (36B4) (E), liver adipocyte differentiation-related protein (ADRP) mRNA relative to 36B4 (F), and immunoblots of TIP47, ADRP, and GPDH in liver (G). A–F: data are means ± SE. *P < 0.001 vs. NC; n = 8–10. NC, normal chow; HFD, high-fat diet.

Fig. 2.

Effects of TIP47 antisense oligonucleotide (ASO) on liver TIP47 mRNA expression relative to 36B4 (A), liver ADRP mRNA level relative to 36B4 (B), immunoblots of TIP47, ADRP, and GPDH protein levels in liver lysates (C). Data are expressed as means ± SE. *P < 0.001 vs. saline and control ASO. Cont, control ASO; LD, low-dose TIP47 ASO; HD, high-dose TIP47 ASO; GPDH, glycerol-3-phosphate dehydrogenase.

Fig. 3.

Liver sections showing the effects of saline, control ASO, and TIP47 ASO treatment on TIP47 immunostaining (A–C), and Oil Red O staining (D–F). Scale bar = 50 μm.

Fig. 4.

Effects of high-dose TIP47 ASO on TIP47 mRNA expression (A) and ADRP mRNA expression (B) relative to 36B4 in white adipose tissue (WAT). Data are expressed as means ± SE; n = 3–4. C: ADRP immunostaining in liver sections from mice treated with saline, control ASO, or TIP47 ASO. Arrows point to lipid droplets. Scale bar = 50 μm.

Fig. 5.

Effects of TIP47 ASO on liver triglycerides (A), VLDL secretion (B), and glucose tolerance test (C). Data are expressed as means ± SE. *P < 0.01; n = 6 or 7/group.

Fig. 6.

Effects of high-dose TIP47 ASO on hepatic mRNA expression of Acc1 (A), Fas (B), Dgat2 (C), Gpat (D), and Cpt1 (E). Gene expression was normalized to 36B4. Data are expressed as means ± SE. *P < 0.05 vs. control ASO; n = 5–8. Acc, acetyl-CoA carboxylase; Fas, fatty acid synthase; Dgat, diacylglycerol O-acyltransferase; Gpat, glycerol-3-phosphate acyltransferase; Cpt, carnitine palmitoyl-transferase.

Fig. 7.

Effects of TIP47 ASO on insulin sensitivity under fasting and clamp conditions. A: basal hepatic glucose production (HGP). B: glucose infusion rate (GIR). C: clamp HGP. D: rate of glucose disposal (R_d). E: glucose uptake in gastrocnemius muscle. F: glucose uptake in epidydimal white adipose tissue (WAT) under hyperinsulinemic-euglycemic clamp. Data are expressed as means ± SE; n = 5 or 6/group. *P < 0.5, **P < 0.01 ***P < 0.001.