Leptin receptor is expressed by tissue mast cells

Leptin, the adipose tissue-derived product of the obese (ob) gene, is known to function as the hormone of energy expenditure. It has also been established that leptin regulates immune and inflammatory processes. All leptin-induced biological activities depend on binding to the membrane-spanning leptin receptor (Ob-R), belonging to the class I cytokine receptor family. The available data relating to the Ob-R on mature mast cells (MCs), and consequently leptin significance in the modulation of MC activity within the tissue, are limited. Immunohistochemistry was used to establish Ob-R expression by MCs in the mesenteric adipose tissue. Flow cytometry and confocal microscopy were used to evaluate both constitutive and leptin-induced expression of Ob-R on freshly isolated peritoneal MCs. MCs in the mesenteric adipose tissue and native peritoneal MCs express Ob-R constitutively. Additionally, leptin influences its receptor expression on these cells. Leptin at lower concentrations caused Ob-R expression increase both at the cell surface and in the cell interior. MC stimulation with higher concentrations of leptin results in a decline of Ob-R from the cell surface and significant enhancement of this receptor not only in the nuclear region but also in the endoplasmic reticulum. In conclusion, one can be assumed that leptin regulates MC activity within tissues. These findings might provide an additional link among the leptin, innate immune function, and inflammatory processes and diseases.