Adipose tissue cellularity and apoptosis after intracerebroventricular injections of leptin and 21 days of recovery in rats

Abstract

OBJECTIVE:To determine the effect of leptin and post-treatment recovery on adipose tissue cellularity and apoptosis. In addition, to investigate whether Bcl-2 and/or Bax is involved in the mechanism of leptin-induced adipose tissue apoptosis. DESIGN: A total of 24 adult male Sprague-Dawley rats were injected i.c.v. with either 10 mg mouse leptin or 10 ml vehicle once per day for 4 days. At 24 h after the last injection, one group was killed while the other was monitored for 21 days. MEASUREMENTS: DNA fragmentation and Bcl-2 and Bax protein levels were determined in inguinal (ING), epididymal (EPI) and retroperitoneal (RP) white adipose tissues and the interscapular brown adipose tissue (BAT). Cellularity was determined in ING and EPI. RESULTS: Leptin significantly reduced the masses of all white fat pads [RP>ING>EPI] but not BAT. Cell volume was significantly reduced in EPI and ING. Only ING had a significantly reduced cell number from leptin treatment plus exhibited apoptosis by increased DNA fragmentation and DNA laddering, and upregulation of pro-apoptosis Bax protein. The other fat pads exhibited a general trend to increase the Bcl-2/Bax ratio. Recovery allowed for normalization of white fat pad mass, cell number and cell volume; however, BAT mass increased 42% over control. After recovery, apoptosis was not detected, Bcl-2 protein had increased in ING, and the Bcl-2/Bax ratio had risen overall. CONCLUSIONS: Central administration of mouse leptin in the rat targets white fat depots individually to reduce mass by a reduction in cell volume plus adipocyte deletion in, at least, the ING fat pad by Bax-mediated apoptosis. Even after a dramatic loss in adipose tissue mass and change in cellularity, the rat demonstrates a resilient return to control levels together with an increase in factors that prevent adipocyte loss.

Chronological changes in metabolism and functions of cultured adipocytes: a hypothesis for cell aging in mature adipocytes

“…Finally, there is some evidence that reagents that are capable of modifying adipocyte aging or turnover process can cause improvement in compositional and functional profiles of adipose tissue. In this regard, both leptin and the thiazolidinediones improve adipose function by promoting apoptosis of aged adipocytes (15,33) and by stimulating de novo production of young adipocytes (16,30), respectively. Future investigations would require careful monitoring and characterization of the adipocyte aging process and changes in turnover rates under these and various other conditions.…”

“…To monitor the aging process, we quantified the gene expression of Bax and lipopolysaccharide-induced TNF-␣ factor (LITAF). Bax is a member of the Bcl-2 family and a proapoptotic polypeptide that is elevated in dying adipocytes (15,20). LITAF is an inducible gene by proapoptotic protein p53 (27,29).…”

Injections of leptin into rat ventromedial hypothalamus increase adipocyte apoptosis in peripheral fat and in bone marrow

“…We have recently shown that leptin deficiency increases bone marrow adipogenesis in ob/ob mice (Hamrick et al 2004), and that peripheral leptin treatment decreases bone marrow adipocyte number (Hamrick et al 2005). In addition, we have demonstrated that intracerebroventricular administration of leptin in rats causes adipose tissue to undergo apoptosis in addition to activating lipolysis (Qian et al 1998;Gullicksen et al 2003). Adipose tissue from leptin-treated rats exhibits a loss of adipocytes and the appearance of adipocytes with condensed chromatin, a characteristic feature of apoptotic cells (Gullicksen et al 2003).…”

High-fat diet-induced obesity in animal models

“…Another study in adult male C57BL/6J mice fed a high-fat diet (45 % of energy, Research Diets, New Brunswick, NJ, USA) for 10 weeks and then switched to chow for 2 weeks had similar results (308) . Centrally administered leptin (10 mg, ICV) for 4 d in normal-weight adult male Sprague-Dawley rats caused a decrease in the number of inguinal fat cells (309) . Leptin injections (5 mg; ICV) over 5 d decreased the number of fat cells in young (aged 3 months) male Sprague-Dawley rats, but not in mature (aged 8 months) animals (310) .…”