Differential effects of leptin on adiponectin expression with weight gain versus obesity

Abstract

Background/objective: Adiponectin exerts beneficial effects by reducing inflammation and improving lipid metabolism and insulin sensitivity. Although the adiponectin level is lower in obese individuals, whether weight gain reduces adiponectin expression in humans is controversial. We sought to investigate the role of weight gain, and consequent changes in leptin, on altering adiponectin expression in humans.

Methods/results: Forty-four normal-weight healthy subjects were recruited (mean age 29 years; 14 women) and randomized to either gain 5% of body weight by 8 weeks of overfeeding (n=34) or maintain weight (n=10). Modest weight gain of 3.8±1.2 kg resulted in increased adiponectin level (P=0.03), whereas weight maintenance resulted in no changes in adiponectin. Further, changes in adiponectin correlated positively with changes in leptin (P=0.0085). In-vitro experiments using differentiated human white preadipocytes showed that leptin increased adiponectin mRNA and protein expression, whereas a leptin antagonist had opposite effects. To understand the role of leptin in established obesity, we compared adipose tissue samples obtained from normal-weight versus obese subjects. We noted, first, that leptin activated cellular signaling pathways and increased adiponectin mRNA in the adipose tissue from normal-weight participants, but did not do so in the adipose tissue from obese participants. Second, we noted that obese subjects had increased caveolin-1 expression, which attenuates leptin-dependent increases in adiponectin.

Conclusions: Modest weight gain in healthy individuals is associated with increases in adiponectin levels, which correlate positively with changes in leptin. In vitro, leptin induces adiponectin expression, which is attenuated by increased caveolin-1 expression. In addition, the adipose tissue from obese subjects shows increased caveolin-1 expression and impaired leptin signaling. This leptin signal impairment may prevent concordant increases in adiponectin levels in obese subjects despite their high levels of leptin. Therefore, impaired leptin signaling may contribute to low adiponectin expression in obesity and may provide a target for increasing adiponectin expression, hence improving insulin sensitivity and cardio-metabolic profile in obesity.

Figure 1. Effects of overfeeding-induced weight gain versus weight maintenance in normal weight subjects

Heat map depicting individual responses of the study subjects at baseline (TP1) and after 8 week of weight gain or maintenance (TP2) (A). The heat map highlights the inter-individual variations in response to overfeeding-induced changes in weight, fat mass, leptin and adiponectin in weight gainers along with variations observed in the subjects assigned to the weight maintainer group. Relation between relative changes in adiponectin and leptin with modest weight gain in study participants (B). Circles represent data from weight gainers (n=34), and triangles represent data from weight maintainers (n=10). Changes in adiponectin correlated positively only with changes in leptin (Pearson coefficient, r = 0.39, P = 0.008; n = 44), but not with any other variable.

Figure 2. Leptin regulates adiponectin expression in differentiated human white preadipocytes (HWP)

In-vitro treatment of differentiated HWP with increasing concentrations of leptin increases adiponectin mRNA (A) and protein (B) in a dose-dependent manner. However, leptin does not increase adiponectin secretion (C). Treatment of differentiated HWP with leptin antagonist decreases adiponectin mRNA (D), protein (E), and secretion (F). Data presented as mean ± SEM (n=4). *P ≤ 0.05 compared with control as determined by Wilcoxon rank-sum test. Total adiponectin: grey bars; high molecular weight adiponectin: black bars.

Figure 3. Activation of ERK pathway is required for leptin-dependent increases in adiponectin

In-vitro treatment of differentiated HWP with leptin in presence of ERK and STAT3 pathway inhibitor prevented leptin-dependent increases in adiponectin (A). However, treatment with leptin-antagonist attenuated leptin-dependent activation of ERK1/2 (B). Leptin-antagonist does not prevent leptin-dependent activation of STAT3 pathways (C). Data presented as mean ± SEM (n=4). *P ≤ 0.05 compared with control as determined by Wilcoxon rank-sum test. Grey bars present data from leptin treatment. Black bars present data from leptin-antagonist and leptin treatment.

Figure 4. Leptin-dependent activation of cellular signaling pathways is evident in normal weight subjects (N, white bars) but impaired in adipose tissue from obese (Ob, black bars) participants

Ex-vivo treatment of adipose tissue with leptin (100 ng/ml) for 15 min activated STAT3 (A), and ERK (B) pathways in samples obtained from normal weight participants. Activation of these pathways was impaired in adipose tissue samples obtained from obese subjects. Furthermore, adiponectin protein expression was elevated in adipose tissue from normal weight subjects (C). The impaired cellular signaling prevented leptin-dependent increases in adiponectin mRNA in adipose tissue from obese participants (D). Data presented as mean ± SEM. *P ≤ 0.05 compared with percent activation in normal weight participants as determined by Wilcoxon rank-sum test.

Figure 5. Increased caveolin-1 expression contributes to impaired leptin-dependent activation of cellular signaling pathways in adipose tissue from obese (Ob, black bars) subjects

The expression of leptin receptor (Ob-R) (A), and SOCS-3 (B) was not different in adipose tissue from obese participants, but caveolin-1 protein expression (C) was increased significantly. Furthermore, caveolin-1 overexpression impaired leptin-dependent increases in adiponectin mRNA in cultured differentiated HWP (D, checkered bars). Data presented as mean ± SEM. *P ≤ 0.05 compared to normal weight subjects (N) / control (Leptin: 0 ng/ml) as determined by Wilcoxon rank-sum test.