Diet-induced obese mice are leptin insufficient after weight reduction

Abstract

Behavioral therapies aimed at reducing excess body fat result in limited fat loss after dieting. To understand the causes for maintenance of adiposity, high-fat (HF) diet-induced obese (DIO) mice were switched to a low-fat chow diet, and the effects of chow on histological and molecular alterations of adipose tissue and metabolic parameters were examined. DIO mice reduced and stabilized their body weights after being switched to chow (HF-chow), but retained a greater amount of adiposity than chow-fed mice. Reduction in adipocyte volume, not number, caused a decrease in fat mass. HF-chow mice showed normalized circulating insulin and leptin levels, improved glucose tolerance, and reduced inflammatory status in white adipose tissue (WAT). Circulating leptin levels corrected for fat mass were lower in HF-chow mice. Leptin administration was used to test whether reduced leptin level of HF-chow mice inhibited further fat loss. Leptin treatment led to an additional reduction in adiposity. Finally, HF-HF mice had lower mRNA levels of beta(3) adrenergic receptor (beta(3)-AR) in epididymal WAT (EWAT) compared to chow-fed mice, and diet change led to an increase in the WAT beta(3)-AR mRNA levels that were similar to the levels of chow-fed mice, suggesting an elevation in sympathetic activation of WAT during diet switch relative to HF-HF mice leading to the reduced leptin level and proinflammatory cytokine content. In summary, HF-chow mice were resistant to further fat loss due to leptin insufficiency. Diet alteration from HF to low fat improved metabolic state of DIO mice, although their adiposity was defended at a higher level.

Figure 1. HF-chow mice lost weight but retained excess body adiposity compared to chow-fed mice. HF-chow mice had reduced fat cell size but not fat cell number

Body fat percentage (A), epididymal white adipose tissue (EWAT) mass (B), fat cell volume (C), and fat cell number (D) of HF-HF, HF-chow, and chow-fed mice. Representative images of EWAT of HF-HF and HF-chow mice (E). Scale bar = 100 μm. Linear regression of cellularity between histological prepared and osmium tetroxide fixed samples (F). * p < 0.05 comparing to HF-HF mice. ^†p < 0.05 comparing to HF-chow mice.

Figure 2. HF-chow mice improved steototic livers and glucose tolerance

HF-HF mice had fatty liver that was recovered in HF-chow DIO mice. Liver histological analysis of HF-HF (A), HF-chow (B), and chow-fed (C) mice using oil red O staining. HF-HF mice had impaired whereas HF-chow mice had normal glucose tolerance similar as chow-fed mice (D). *p < 0.05 comparing to HF-HF mice.

Figure 3. HF-chow but not HF-HF mice were leptin sensitive

Body weight curves after diet switch and before leptin administration (A). * p < 0.05 HF-HF mice comparing to chow-fed mice. ^†p < 0.05 HF-chow mice comparing to chow-fed mice. Plasma leptin levels following leptin treatment (B). * p < 0.05 comparing to chow-fed PBS mice. ^†p < 0.05 comparing to HF-HF PBS mice. Food intake (C) and body weight (D) of vehicle (PBS)- or leptin-treated HF-HF mice. Food intake (E) and body weight (F) of vehicle (PBS)- or leptin-treated HF-chow mice and PBS-treated chow-fed mice. *p < 0.05 comparing to chow-fed mice.

Figure 4. HF-chow mice decreased total body fat, epididymal white adipose tissue (EWAT) mass and fat cell number after leptin treatment

Body fat change (A), EWAT mass (B), and fat cell size (C) and fat cell number (D) of vehicle (PBS)- or leptin-treated HF-chow mice. * p < 0.05 comparing to PBS-treated HF-chow mice. ^†p < 0.05 comparing to 10 mg/kg leptin-treated HF-chow mice.