The secretory function of adipocytes in the physiology of white adipose tissue

Abstract

White adipose tissue, previously regarded as a passive lipid storage site, is now viewed as a dynamic tissue. It has the capacity to actively communicate by sending and receiving different types of signals. An overview of these signals, the external modulators that affect adipose tissue and the secreted signaling molecules, the adipokines, is presented. The secretory function is highlighted in relation to energy metabolism, inflammation and the extracellular matrix and placed in the context of adipose tissue biology. We observe that the endocrine function of adipocytes receives much attention, while its paracrine and autocrine functions are underestimated. Also, we provide examples that species specificity should not be neglected. We conclude that adipose tissue primarily is an energy storage organ, well supported by its secretory function.

Expression of NGF, BDNF and their high-affinity receptors in ovine mammary glands during development and lactation

“…This is consistent again with the role of the mammary fat pad and the loose intralobular stroma as source of paracrine and endocrine molecules (Sternlicht et al 2005;Wang et al 2008;Hovey and Aimo 2010), with the abundant cell proliferation occurring in the prepubertal period of mammary development and with the autocrine proliferative action of neurotrophins in breast cancer (Hondermarck 2012). In fact, NGF and BDNF may constitute an important local regulator of mammary gland development playing a central role in promoting survival of mammary cells via phosphatidylinositol 3-kinase (PI3K) and protein kinase B (AKT), as IGF1 does, or via mitogen-activated protein kinase (MEK1/2), like epidermal growth factor (EGF) through its ErbB receptor that is also a tyrosine kinase.…”

“…It should be noted that, differently from mice, in prepubertal ewes growing epithelial cells are separated from adipocytes by multiple layers of fibroblastic connective tissue (Hovey et al 1999). Depots of adipose tissue have been recognized as a site for the synthesis of several molecules (Wang et al 2008) and a source of neurotrophins (Celis et al 2005;Hausman et al 2008). In prepubertal glands, NGF and BDNF showed an intense immunoreactivity in adipocytes of fat pad and in loose connective tissue surrounding epithelial cells composing TDUs.…”

β-Carotene conversion products and their effects on adipose tissue

“…To perform this function it is in active communication with other organs, receiving and sending signals [74]. Alterations in the secretion of these molecules, and also in the ability of adipose tissue to expand appropriately under conditions of positive energy balance, have been shown to influence the aetiology of several pathologies including type II diabetes and cardiovascular diseases.…”

“…More than 50 different adipokines have been identified so far, including: adiponectin, leptin, resistin, acylation stimulating protein, fasting-induced adipose factor, enzymes involved in lipoprotein metabolism and various cytokines, chemokines and acute phase proteins [59,62,69,74]. In 2005, vitamin A plasma transporter RBP4 (retinol binding protein-4) of adipose origin was identified as a new adipokine favouring insulin resistance in mice through effects on liver and muscle [79], which are more likely independent of vitamin A.…”

Expression of NGF, BDNF and their receptors in subcutaneous adipose tissue of lactating cows

“…Currently, adipose tissue is also considered an endocrine organ capable of releasing a variety of bioactive substances known as adipose-derived secreted factors or adipokines (Wang et al, 2008;Colitti and Grasso, 2014). The WAT is innervated by the sympathetic nervous system (SNS), although less extensively than brown adipose tissue (BAT) (Bartness et al, 2001).…”