Molecular Cloning of a Major mRNA Species in Murine 3T3 Adipocyte Lineage

Abstract

In an effort to identify novel mRNAs modulated during the course of adipose conversion, we have used a simplified differential display technique and have isolated a cDNA encoding an amine oxidase tremendously expressed in the adipocyte, the semicarbazide-sensitive amine oxidase (SSAO). The predicted amino acid sequence (765 amino acids) is likely to be the homologue of the human placental amine oxidase and of the partially known sequence of the rat adipocyte membrane amine oxidase. SSAO mRNAs are present in several tissues, but strikingly, the highest levels of gene expression are found in adipose tissue and aorta. Enzyme transcript levels are barely detectable in preadipocytes but are induced several hundred-fold during the adipocyte differentiation of 3T3-L1 or 3T3-F442A cells and of rat precursor primary cultures. These changes in transcript levels parallel a sharp increase in SSAO enzyme activity. The biochemical properties of the SSAO present in 3T3-L1 or 3T3-F442A adipocytes closely resemble the features of the SSAO activity previously described in white and brown adipose tissues. Interestingly, SSAO mRNA levels and enzyme activity drop in response to effectors of the cAMP pathway and to the cytokine tumor necrosis factor-␣, indicating that two major signaling molecules of adipose tissue development and metabolism can control SSAO function. Moreover, the expression of SSAO transcripts and activity are clearly down-regulated in white adipose tissue from obese Zü cker rats. Because of its known stimulatory effect on glucose transport, its biochemical properties and its pattern of expression and regulation, SSAO could play an important role in the regulation of adipocyte homeostasis.Adipose tissue is the primary site for triacylglycerol storage in mammals and exerts a key role in the control of energy balance. To perform these essential functions, adipocytes express a large pattern of enzymes and accessory proteins that concur in lipogenesis or lipolysis. Moreover, these metabolic pathways are under the tight control of a variety of hormones.Several major discoveries have supported the idea that, besides its classical energetic functions, the adipocyte is also able to exert regulatory functions through the secretion of paracrine or endocrine factors.In vivo a process of recruitment and conversion of mesenchymal cells into adipocytes can occur throughout life. Studies on adipogenesis have been greatly facilitated by the availability of established preadipose cell lines (1-3). When cultured under appropriate conditions, committed preadipocytes differentiate into adipocytes mimicking the white phenotype. The highly specialized functions of the mature adipocyte are acquired during the course of adipose differentiation. The emergence of the adipocyte phenotype is linked to the coordinated expression of a large number of genes and proteins. So far, a great number of genes have been identified and related to the molecular mechanisms of fat cell differentiation. They include genes coding for enzymes and structural pr...

Immunopurification and Characterization of Rat Adipocyte Caveolae Suggest Their Dissociation from Insulin Signaling

“…SSAO is found in many tissues, but it is particularly abundant in caveolae-rich tissues including fat, lungs, and muscle (29,77). SSAO is estimated to represent 2% of total protein in the PM of adipocytes (29), and accordingly it seems highly likely that it must have an important function for those cells, but what this function might be is not clear for any cell type (30).…”

Cloning of BUG demonstrates the existence of a brown preadipocyte distinct from a white one

“…It has been successfully used to compare mRNAs patterns in 3T3-L1 preadipocytes and differentiated adipocytes, resulting in the cloning of genes whose expression is increased during the differentiation. 18,19 Applying this technique to typically WAT and BAT in rats, we cloned a cDNA fragment corresponding to a transcript preferentially expressed in brown adipocyte precursor.…”

Semicarbazide-Sensitive Amine Oxidase in Vascular Smooth Muscle Cells

“…8 SSAO is also highly expressed in white and brown adipose cells from different species, 9,10 an observation that is in agreement with the large induction of SSAO mRNA and activity levels during the course of adipose conversion. 4 SSAO is also abundantly found in vascular smooth muscle cells (VSMCs) and non-VSMCs. 1,11 The high activity of SSAO in the aorta has been ascribed to its strong expression in the tunica media, which mainly contains smooth muscle cells.…”

“…At a molecular level, SSAO, which has recently been cloned in different species, [2][3][4] is identical to vascular adhesion protein-1 (VAP-1), which displays adhesive and enzymatic properties. 5,6 SSAO activities are found in blood plasma and are associated with membranes in several mammalian tissues.…”