Autocrine FGF1 signaling promotes glucose uptake in adipocytes

Abstract

Fibroblast growth factor 1 (FGF1) is an autocrine growth factor released from adipose tissue during over-nutrition or fasting to feeding transition. While local actions underlie the majority of FGF1's anti-diabetic functions, the molecular mechanisms downstream of adipose FGF receptor signaling are unclear. We investigated the effects of FGF1 on glucose uptake and its underlying mechanism in murine 3T3-L1 adipocytes and in ex vivo adipose explants from mice. FGF1 increased glucose uptake in 3T3-L1 adipocytes and epididymal WAT (eWAT) and inguinal WAT (iWAT). Conversely, glucose uptake was reduced in eWAT and iWAT of FGF1 knockout mice. We show that FGF1 acutely increased adipocyte glucose uptake via activation of the insulin-sensitive glucose transporter GLUT4, involving dynamic crosstalk between the MEK1/2 and Akt signaling proteins. Prolonged exposure to FGF1 stimulated adipocyte glucose uptake by MEK1/2-dependent transcription of the basal glucose transporter GLUT1. We have thus identified an alternative pathway to stimulate glucose uptake in adipocytes, independent from insulin, which could open new avenues for treating patients with type 2 diabetes.

Keywords: FGF1; adipocytes; fibroblast growth factors; glucose metabolism; insulin.

Fig. 1.

Acute stimulation of glucose uptake in adipocytes by FGF1. (A and B) Ex vivo FGF1-stimulated ³H-2-deoxy-d-glucose uptake in (A) epididymal WAT (eWAT) and (B) inguinal WAT (iWAT) 30 min after treatment. (C and D) Ex vivo ³H-2-deoxy-d-glucose uptake in (C) eWAT and (D) iWAT of wild-type (WT) and FGF1 knockout mice (FGF1KO) after 30 min incubation. (E) Dose–response curves of FGF1– and (F) FGF1+ insulin-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake in 3T3-L1 adipocytes 15 min after treatment. (G) Effect of insulin receptor (InsR) inhibition by 1 μM Osi-906 (30 min pretreatment), (H) FGF receptor (FGFR) inhibition by 5 nM LY2874455 (30 min pretreatment), or (I) GLUT4 inhibition by 100 μM indinavir (cotreatment) on FGF1- and insulin-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake in 3T3-L1 adipocytes 15 min after treatment. All data shown are mean ± SD (n = 4–6, *P < 0.05).

Fig. 2.

FGF1-stimulated glucose uptake is dependent on MEK-ERK activation. (A and B) Dose–response curves of PI3K inhibition by PIK-75 (0–10 µM, 30 min pretreatment) on insulin- and FGF1-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake in 3T3-L1 cells 15 min after treatment. (C and D) Dose–response curves of Akt inhibition by MK-2206 (0–10 µM, 30 min pretreatment) on insulin- and FGF1-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake in 3T3-L1 cells 15 min after treatment. (E and F) Dose–response curves of MEK1/2 inhibition by PD0325901 (0–10 µM, 30 min pretreatment) on insulin- and FGF1-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake in 3T3-L1 cells 15 min after treatment. All data shown are mean ± SD (n = 3).

Fig. 3.

Crosstalk between MEK-ERK and PI3K-Akt in FGF1-stimulated glucose uptake. (A) Time course (0-15 min) of Akt (Thr³⁰⁸, Ser⁴⁷³) and ERK (Thr²⁰²/Tyr²⁰⁴) phosphorylation by FGF1 in the absence and presence of MEK1/2 inhibitor PD0325901 (1 µM, 30 min pretreatment) in 3T3-L1 adipocytes. (B) Effect of MEK1/2 (1 µM PD0325901, 30 min pretreatment) and Akt (1 µM MK2206, 30 min pretreatment) inhibition on acute (15 min) FGF1-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake in 3T3-L1 cells. (C) Effect of MEK1/2 (1 µM PD0325901, 30 min pretreatment) and Akt (1 µM MK2206, 30 min pretreatment) inhibition on FGF1-stimulated ERK (Thr²⁰²/Tyr²⁰⁴) and Akt (Thr³⁰⁸, Ser⁴⁷³) phosphorylation in 3T3-L1 adipocytes. All data shown are mean ± SD (n = 6, *P < 0.05).

Fig. 4.

Chronic stimulation of glucose uptake by FGF1 in 3T3-L1 adipocytes is mediated via MEK-ERK-dependent control of GLUT1. (A) Dose–response curve of FGF1-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake 24 h after treatment. (B) Dose–response curve of acute (15 min) insulin-stimulated 2-deoxy-d-[¹⁴C]-glucose uptake and the effect of 24 h of FGF1 (100 ng/mL) treatment. (C) Time course analysis (2–8 h) of GLUT1 gene expression or (D) GLUT4 gene expression after treatment with FGF1. (E) Basal- and FGF1-induced GLUT1 gene expression upon 30 min pretreatment with 1 μM of the RNA synthesis Triptolide. (F) Effect of MEK1/2 inhibition by 1 μM PD0325901 (30 min pretreatment) on basal- and FGF1-stimulated GLUT1 gene expression (4 h), (G) GLUT1 protein levels, and (H) 2-deoxy-d-[¹⁴C]-glucose uptake (24 h) in 3T3-L1 adipocytes. (I) Basal- and FGF1-induced 2-deoxy-d-[¹⁴C]-glucose uptake after cotreatment with 100 μM GLUT4 blocker Indinavir in 3T3-L1 adipocytes. All data shown are mean ± SD (n = 4–8, *P < 0.05).