Effect of high fat diet on pulmonary expression of parathyroid hormone-related protein and its downstream targets

Abstract

Aims: Parathyroid hormone-related protein (PTHrP) is involved in lung development and surfactant production. The latter one requires a paracrine interaction between type II alveolar cells and lipofibroblasts in which leptin triggers PTHrP-induced effects. Whether increased plasma leptin levels, as they occur in high fat diet, modify the expression of PTHrP remains unclear. Furthermore, the effect of high fat diet under conditions of forced pulmonary remodelling such as response to post myocardial infarction remains to be defined.

Materials and methods: C57 bl/6 mice were randomized to either normal diet or high fat diet at an age of 6 weeks. Seven months later, the mice were euthanized and the lung was removed and frozen in fluid nitrogen until use. Samples were analyzed by real-time RT-PCR and western blot. Leptin deficient mice were used to investigate the effect of leptin on pulmonary expression of PTHrP more directly. A subgroup of mice with and without high fat diet underwent in vivo ischemia (45 min) and reperfusion (4 weeks). Finally, experiments were repeated with prolonged high-fat diet.

Key findings: High fat diet increased plasma leptin levels by 30.4% and the pulmonary mRNA expression of PTHrP (1,447-fold), PTH-1 receptor (4.21-fold), and PTHrP-downstream targets ADRP (7.54-fold) and PPARγ (5.27-fold). Pulmonary PTHrP expression was reduced in leptin deficient mice by 88% indicating leptin dependent regulation. High fat diet further improved changes in pulmonary adaptation caused by ischemia/reperfusion (1.48-fold increased PTH-1 receptor protein expression). These effects were lost during prolonged high fat diet.

Significance: This study established that physiological regulation of leptin plasma levels by high fat diet affects the pulmonary PTHrP expression and of PTHrP downstream targets. Modification of pulmonary expression of PTH-1 receptors by high fat diet after myocardial infarction suggests that the identified interaction may participate in the obesity paradox.

Keywords: Medicine; Physiology.

Fig. 1

Pulmonary mRNA expression of PTHrP, PTH-1 receptor, ADRP, and PPARγ in seven months old mice that were fed with either normal diet (ND, n = 12) or high fat diet (HFD, n = 7). Data are expressed as means ± S.D. *, p < 0.05 vs. ND.

Fig. 2

Pulmonary mRNA expression of PTHrP, PTH-1 receptor, ADRP, and PPARγ in leptin deficient mice (Lep^ob/ob). Data are expressed as means ± S.D. and normalized to wild-type littermates. n = 4 mice each. *, p < 0.05 vs. wild-type littermates.

Fig. 3

Pulmonary mRNA expression of PTHrP, PTH-1 receptor, ADRP, and PPARγ in thirteen months old mice that were fed with either normal diet (ND, n = 6), high fat diet (HFD, n = 5). Data are expressed as means ± S.D. all values p > 0.05 vs. ND.

Fig. 4

Pulmonary protein expression of PTHrP and the corresponding PTH-1 receptor in mice. A + B) Representative western blots from seven months old (A) or thirteen months old (B) mice; HFD = high fat diet; I/R = ischemia/reperfusion; The original full size blots are given in the supplementary material as Fig. 4a-PTHrP, Fig. 4a-PTH-1R, Fig. 4a-Actin, Fig. 4b-PTH-1R, Fig. 4b-PTHrP; and Fig. 4b-Actin; C-F) Mean protein expression of PTHrP and PTH-1 receptor in seven months old mice (C,D) or thirteen months old mice (E,F). Data are expressed as means ± S.D. and normalized to age-matched mice under normal diet (always n = 3); *, p < 0.05 vs. normal diet.

Fig. 5

Pulmonary mRNA expression of PTHrP, PTH-1 receptor, ADRP, and PPARγ in seven months old mice that underwent ischemia/reperfusion (I/R) with normal diet (n = 9) or high fat diet (HFD), n = 10). Data are expressed as means ± S.D. and normalized to sham mice with normal diet *, p < 0.05 vs. sham, #, p < 0.05 vs. I/R.

Fig. 6

Pulmonary mRNA expression of PTHrP, PTH-1 receptor, ADRP, and PPARγ in thirteen months old mice that underwent ischemia/reperfusion (I/R) with normal diet (n = 8) or high fat diet (HFD), n = 6). Data are expressed as means ± S.D. and normalized to sham mice with normal diet. #, p < 0.05 vs. I/R.

Fig. 7

Pulmonary mRNA expression of TGF-β₁, elastin and fibronectin in seven months old mice. (A) Comparison of the effect of nomrla diet (ND) versus high fat diet (HFD) (B) Comparison of the effect of ischemia/reperfusion (I/R) to sham I/R plus HFD. Data are expressed as means ± S.D. from n = 6–12 mice (see Fig. 1 and 5 for exact numbers) *, p < 0.05 vs. ND of seven months old mice.