Combined Leptin Actions on Adipose Tissue and Hypothalamus Are Required to Deplete Adipocyte Fat in Lean Rats

Abstract

Intense hyperleptinemia completely depletes adipocyte fat of normal rats within 14 days. To determine the mechanism, epididymal fat pads from normal wild-type (؉/؉) and obese (fa/fa) Zucker Diabetic Fatty (ZDF) donor rats were transplanted into normal ؉/؉ and fa/fa ZDF recipients. Hyperleptinemia induced by adenovirus-leptin administration depleted all fat from native fat pads and from fat transplants from ؉/؉ donors but not from transplants from ZDF fa/fa donors with defective leptin receptors. In both native and transplanted ؉/؉ fat pads, large numbers of mitochondria were apparent, and genes involved in fatty acid oxidation were up-regulated. However, ؉/؉ fat pads transplanted into fa/fa recipients did not respond to hyperleptinemia, suggesting lack of an essential leptin-stimulated cohormone(s). In ؉/؉ but not in fa/fa rats, plasma catecholamine levels rose, and both P-STAT3 and P-CREB increased in adipose tissue, suggesting that both direct and indirect (hypothalamic) leptin receptor-mediated actions of hyperleptinemia are involved in depletion of adipocyte fat.In normal lean rodents, the induction of hyperleptinemia by administration of recombinant adenovirus containing the leptin cDNA (AdCMV-leptin) causes all visible fat to melt away within 7 days (1). In what is probably the most striking effect of this hormone, white adipocytes are transformed into fatless cells filled with small mitochondria (2). In addition, genes such as ucp-1 (uncoupling protein-1) and pgc-1␣ (peroxisome proliferator-activated receptor-␥-coactivator-1-␣), normally expressed in brown but not white adipocytes, are expressed at high levels, whereas adipocyte markers, such as leptin and aP2, are profoundly down-regulated (2). Despite their similarities to brown adipocytes, these transformed white adipocytes differ sufficiently to warrant designation as a novel derivative cell, the "post-adipocyte" (2). Although fat depletion of adipocytes by hyperleptinemia occurs only in lean and not in obese rodents, understanding of its mechanisms may have implications for the treatment of obesity.The fat depletion induced by experimental hyperleptinemia differs from that of naturally occurring catabolic states, such as starvation and insulin deficiency, in which free fatty acids are released from the adipocytes and oxidized in the liver. The fat depletion of experimental hyperleptinemia is unaccompanied by an increase in plasma free fatty acids or ketones (3, 4), and the molecular and morphologic changes (2) imply that the oxidation takes place within the transformed adipocytes.The pathway by which hyperleptinemia induces transformation of adipocytes to post-adipocytes has not been clearly identified. We know that leptin-responsive centers in the hypothalamus regulate energy metabolism and feeding behavior (3-8), but there is also evidence for direct leptin action on adipocytes (9 -11) and on other tissues (12-17). Here we report that the fat-depleting action of hyperleptinemia requires both direct leptin receptor (Lepr) 3 -mediated action on adi...

Leptin responsiveness restored by amylin agonism in diet-induced obesity: Evidence from nonclinical and clinical studies

“…Under the present experimental conditions, amylin pretreatment was not associated with altered Lep, Lepr, or Socs-3 gene expression or pSTAT3 levels in WAT; however, leptin-mediated fat depletion has been shown to follow a complex time course arising from a combination of paracrine, hypothalamic, and sympathetic (catecholaminergic) effects (19,34). Hence, the interrogation of selected downstream genes/effectors of leptin at a single time point does not exclude the possibility that different durations of amylin or amylinϩleptin treatment could enhance direct leptin receptor or postreceptor events at the level of the adipocyte.…”

“…Additional, complementary mechanisms underlying the observed synergy could include amylin potentiating leptin's direct effects at the level of the adipocyte (19,33,34). Under the present experimental conditions, amylin pretreatment was not associated with altered Lep, Lepr, or Socs-3 gene expression or pSTAT3 levels in WAT; however, leptin-mediated fat depletion has been shown to follow a complex time course arising from a combination of paracrine, hypothalamic, and sympathetic (catecholaminergic) effects (19,34).…”

“…The synergy between amylin and leptin could be explained in part by amylin restoring hypothalamic sensitivity to leptin and/or augmenting leptin activation in leptin-sensitive regions within the hindbrain. Likewise, because leptin, but not amylin (19,20), has a direct effect on adipocytes, amylin-induced weight loss could potentiate leptin action at the receptor or postreceptor level of the adipocyte. To explore these possibilities, vehicle-, PF(to the amylin group)-, or amylin-pretreated DIO rats (7 d) and a lean rat control group were injected with vehicle or leptin (15 mg/kg i.p., a dose eliciting diminished hypothalamic signaling in DIO-prone vs. DIO-resistant controls) (18).…”

Effect of high-fat diet feeding on leptin receptor expression in white adipose tissue in rats: depot- and sex-related differential response

“…Moreover, leptin resistance can be regarded as a main factor in the initiation and development of diet-induced obesity [19]; however, it seems that this effect may not only rely on the central level, but also on the peripheral level, in which the adipose tissue can be of great importance [14]. In this sense, Wang et al have previously shown that HF-diet feeding in male rats induced a decline in OB-Rb mRNA in the adipose tissue (the authors do not specify the type of fat depot analyzed) [25].…”

Effect of dermcidin, an antimicrobial peptide, on body fat mobilization in normal mice

“…In previous studies in which recombinant adenoviruses were administered to intact rodents, the reporter gene was primarily expressed in the liver (Herz & Gerard 1993, Chen et al 1996, Park et al 2006. We used real-time PCR and western blot analysis to examine the expression of DCD in various tissues of normal 5-week-old mice that had been injected with either Ad-b-gal or Ad-DCD virus.…”