Reduced adiposity and high-fat diet-induced adipose inflammation in mice deficient for phosphodiesterase 4B

Abstract

The concept that obesity is an inflammatory state has changed our understanding of this condition and suggested that pharmacological interventions targeting inflammation may be useful strategies to improve metabolic complications of obesity. Phosphodiesterase 4 (PDE4) inhibitors exhibit profound antiinflammatory effects, but whether PDE4 inhibition suppresses obesity-induced inflammation is unknown. Among PDE4 isoforms, PDE4B is the major species mediating inflammatory responses. We therefore examined obesity-related phenotypes in mice deficient for PDE4B. Compared with wild-type littermates, PDE4B-null mice were leaner, with lower fat pad weights, smaller adipocytes, and decreased serum leptin levels on both chow and high-fat diets (HFDs). PDE4B deficiency suppressed TNF-alpha mRNA levels and macrophage infiltration in white adipose tissue in mice on HFD, but insulin sensitivity was unaltered. PDE4B-null mice on HFDs had increased locomotor activity. These results suggest a previously unappreciated role for PDE4B in the regulation of energy balance and that PDE4B inhibitors could have utility in treatment of obesity and for suppression of obesity-induced inflammation in white adipose tissue.

Figure 1

Reduced fat content and fat pad weights in PDE4B^−/− mice. Body weight curves (A), fat content determined by MRI for mice at 24 wk of age (B), and weights of total fat pads (C), epididymal fat pads (D), perirenal fat pads (E), sc fat pads (F), brown fat (G), heart (H), and liver (I) for PDE4B^−/− (KO) and WT mice on either chow or HFD at 28 wk of age (n = 6–8/group). Data are expressed as mean ± sem. *, P < 0.05; #, P < 0.01.

Figure 2

Reduced size of adipocytes in PDE4B^−/− mice. A, Representative H&E staining of epididymal adipose tissue sections from PDE4B^−/− (KO) and WT mice on either chow or HFD at 28 wk of age. B, Distribution of adipocyte diameters for mice on chow diet. C, Distribution of adipocyte diameters for mice on HFD. Dotted lines denote the mean of adipocyte diameters. Diameters of 100 adipocytes from four mice were quantified per genotype on each diet. Wilcoxon signed-rank tests were used to compare adipocyte diameter distributions. #, P < 0.01.

Figure 3

Reduced serum leptin levels in PDE4B^−/− mice. Serum levels of leptin (A), adiponectin (B), fasting glucose (C), and fasting insulin (D) in PDE4B^−/− (KO) and WT mice. Serum samples were taken from mice at 25 wk of age (n = 6–8/group). Data are expressed as mean ± sem. *, P < 0.05.

Figure 4

Reduced TNF-α expression and macrophage infiltration in WAT of PDE4B^−/− mice. A, Expression of TNF-α mRNA in epididymal adipose tissue. Representative immunohistochemical staining of epididymal adipose tissue sections using an antibody against the macrophage marker F4/80 for WT (B) and PDE4B^−/− (KO) (C) mice on HFD at 28 wk of age. D, Quantification of percentage of macrophages present in epididymal adipose tissue sections. E, Expression of F/80 mRNA in epididymal adipose tissue for mice on HFD. For macrophage quantification, four adipose tissue sections for each of the four PDE4B^−/− or WT littermates were counted. Percentages of F4/80-positive cells were calculated as the number of nuclei of F4/80-positive cells divided by the total number of nuclei. For mRNA expression, Taqman-based real-time PCR was performed and Cyclophilin was used as an internal control (n = 6–8/group). Data are expressed as mean ± sem. *, P < 0.05. AU, Arbitrary units.

Figure 5

Increased ISO-induced intracellular cAMP levels in PDE4B^−/− mice. A, Intracellular cAMP levels in adipocytes treated with 1 μm ISO at the indicated time points. Adipocytes were isolated from either PDE4B^−/− (KO) or WT mice. B, Adipocyte lipolysis as assessed by glycerol released into the medium for adipocytes treated with 1 μm ISO at the indicated time points. #, P < 0.01.

Figure 6

Increased locomotor activity of PDE4B^−/− mice on HFD. Locomotor activity (A) and oxygen consumption (B) of PDE4B^−/− (KO) and WT mice on either chow or HFD during light and dark cycles (n = 6–8/group). Data are expressed as mean ± sem. *, P < 0.05.