In vivo leptin expression in cartilage and bone cells of growing rats and adult humans

Abstract

The present investigation was carried out to analyse, immunohistochemically, in vivo leptin expression in cartilage and bone cells, the latter restricted to the elements of the osteogenic system (stromal cells, osteoblasts, osteocytes, bone lining cells). Observations were performed on the first lumbar vertebra, tibia and femur of four rats and on the humerus, femur and acromion of four patients. Histological sections of paraffin-embedded bone samples were immunostained using antibody to leptin. The results showed that, in growing rat bone, leptin is expressed in chondrocytes and stromal cells, but not in osteoblasts; bone lining cells were not found in the microscopic fields examined. In adult human bone, leptin is expressed in chondrocytes, stromal cells and bone lining cells; osteoblasts were not found in the microscopic fields examined. Osteocytes were found to be leptin positive only occasionally and focally in both rat and human bone. The in vivo findings reported show, for the first time, that leptin appears to be expressed only in the cells of the osteogenic lineage (stromal cells, bone lining cells, osteocytes) that, with respect to osteoblasts, are permanent and inactive, i.e. in those cells that according to our terminology constitute the bone basic cellular system (BBCS). Because the BBCS seems to be primarily involved in sensing and integrating mechanical strains and biochemical factors and then in triggering and driving bone formation and/or bone resorption, it appears that leptin seems to be mainly involved in modulating the initial phases of bone modelling and remodelling processes.

The adipose organ of obesity-prone C57BL/6J mice is composed of mixed white and brown adipocytes

“…MRI and histological studies in rats have documented the plasticity of interscapular BAT, suggesting the reversibility of this phenomenon ( 43,44 ). Such tissue plasticity does not seem to be confi ned to these types of stimuli, as mammary gland adipocytes are able to transform reversibly into milk-secreting glands during pregnancy and lactation ( 45,46 ).…”

Inhibition of Leptin and Leptin Receptor Gene Expression by Silibinin-Curcumin Combination

“…It has central roles in the energy expenditure, food intake, many reproductive processes, regulation of energy homeostasis, neuroendocrine function, and metabolism (Kelesidis et al, 2010). Beside the synthesis by adipose tissue as the main source (Go et al, 2013), there have been indentified other sources of leptin in the body including testicles (Soyupek et al, 2005), ovaries (Löffler et al, 2001), placenta (Maymó et al, 2011), cartilage and bone cells (Morroni et al, 2004), skeletal muscle (Solberg et al, 2005) and stomach (Mix et al, 2004). Furthermore, the mitogenic, transforming or migration-induced properties of leptin have been revealed in many different cell types such as smooth muscle cells (Oda et al, 2001), normal and neoplastic colon cells (Hardwick et al, 2001;Liu et al, 2001); and also normal and malignant mammary epithelial cells (Dieudonne et al, 2002;Laud et al, 2002).…”

Leptin and Inflammation

“…Structurally, leptin is a 16 kDa non-glycosylated polypeptide found primarily in adipocytes, although it can be also detected (at lower levels) in the hypothalamus, pituitary [7], stomach and intestine [8], skeletal muscle [9], mammary epithelium [10], chondrocytes [11], placenta [12], cartilage and bone cells [13], and immune cells [14][15].…”