Insulin Stimulates Both Leptin Secretion and Production by Rat White Adipose Tissue

Abstract

Leptin, the peptide encoded by the obese gene, is secreted by adipose cells and plays a role in regulating food intake, energy expenditure, and adiposity. Because earlier studies suggested that insulin increases the expression of leptin, we investigated the effect of insulin on leptin secretion by adipose tissue. Epididymal fat pads were incubated in vitro in the presence or absence of insulin over a 4-h time course. Insulin increased leptin secretion by about 80% at all time points studied. After 10 min of insulin treatment, the amount of tissue-associated leptin was lower in insulin-stimulated tissue, presumably due to the increased secretion. At later times, both tissue-associated leptin and total leptin production were higher in insulin-treated tissue. In untreated, isolated adipose cells, immunostaining of leptin was detected in the endoplasmic reticulum by confocal microscopy. After insulin treatment, there were two populations of cells. In many cells, leptin staining became fainter and was restricted to a narrow band near the plasma membrane. However, in other cells the leptin-staining pattern was unchanged. Leptin did not colocalize with GLUT4, the glucose transporter isoform found primarily in insulin-responsive cells, in either basal or insulin-stimulated adipose cells. In this study, insulin increased both secretion and production of leptin by adipose tissue fragments. Interestingly, insulin appeared to stimulate the transport of leptin from the endoplasmic reticulum rather than acting on a pool of regulated secretory vesicles. (Endocrinology 138: 4463-4472, 1997)

Estradiol-induced hypophagia is associated with the differential mRNA expression of hypothalamic neuropeptides

“…These data suggest that food intake may modulate leptin secretion and reinforce the notion that it may play a role in the process of satiety, modulating meal size (22). The increase in plasma leptin levels after feeding may be mediated, in part, by insulin, which directly stimulates the synthesis and secretion of leptin by adipocytes (23).…”

A novel PPARα agonist ameliorates insulin resistance in dogs fed a high-fat diet

“…Therefore, these effects could be associated at least in part with decreased visceral fat weight. We cannot exclude the possibility that circulating levels of adipokines are regulated by other factors, such as insulin and PPAR (3,10,22), independent of fat cell size, because the improvement effects reached their values before feeding a high-fat diet.…”

Golgin-160 Is Required for the Golgi Membrane Sorting of the Insulin-responsive Glucose Transporter GLUT4 in Adipocytes

“…In adipocytes, it has been reported that constitutive as well as regulated secretion of adipokines can occur independently from TGN trafficking. For example, it has been reported that leptin is directly secreted from the endoplasmic reticulum and adiponection from the Golgi cisternae (Barr et al, 1997;Xie et al, 2006). Although these latter two proteins are soluble luminal proteins, adipocytes also display complex patterns of integral membrane protein transport with several proteins undergoing various degrees of insulin responsiveness.…”