Hibernoma development in transgenic mice identifies brown adipose tissue as a novel target of aldosterone action.

Abstract

Aldosterone is a major regulator of salt balance and blood pressure, exerting its effects via the mineralocorticoid receptor (MR). To analyze the regulatory mechanisms controlling tissue-specific expression of the human MR (hMR) in vivo, we have developed transgenic mouse models expressing the SV40 large T antigen (TAg) under the control of each of the two promoters of the hMR gene (P1 or P2). Unexpectedly, all five P1-TAg founder animals died prematurely from voluminous malignant liposarcomas originating from brown adipose tissue, as evidenced by the expression of the mitochondrial uncoupling protein ucp1, indicating that the proximal P1 promoter was transcriptionally active in brown adipocytes. No such hibernoma occurred in P2-TAg transgenic mice. Appropriate tissue-specific usage of P1 promoter sequences was confirmed by demonstrating the presence of endogenous MR in both neoplastic and normal brown adipose tissue. Several cell lines were derived from hibernomas; among them, the T37i cells can undergo terminal differentiation into brown adipocytes, which remain capable of expressing ucp1 upon adrenergic or retinoic acid stimulation. These cells possess endogenous functional MR, thus providing a new model to explore molecular mechanisms of mineralocorticoid action. Our data broaden the known functions of aldosterone and suggest a potential role for MR in adipocyte differentiation and regulation of thermogenesis.

Prolactin potentiates insulin-stimulated leptin expression and release from differentiated brown adipocytes

“…All products were purchased from Invitrogen. Differentiation into mature brown adipocytes was achieved by incubating subconfluent undifferentiated T37i cells with complete medium supplemented with 2 nM T3 (Sigma) and 20 nM insulin (Invitrogen) for 7 days (Zennaro et al 1998). Before each hormonal treatment, T37i cells were subsequently cultured for 18 h in the same medium without any serum named 'minimum medium'.…”

“…These cells are capable of differentiating into mature brown adipocytes upon insulin and triiodothyronine (T3) exposure as assessed by their ability to display multilocular intracytoplasmic lipid droplets and by the occurrence of specific adipogenic gene activation (Penfornis et al 2000). Importantly, expression of UCP1, but also of leptin, resistin and adiponectin were demonstrated in this cell line (Zennaro et al 1998, Buyse et al 2001, Viengchareun et al 2002.…”

“…With the aim of better understanding the specific role of PRL in BAT, we used both the brown adipocyte T37i cell line (Zennaro et al 1998) and the PRLR knockout mouse model (Ormandy et al 1997). T37i cells were derived from a hibernoma developed in a transgenic mouse in which the expression of SV40 large T antigen was placed under the control of the proximal promoter of the human mineralocorticoid receptor gene.…”

Transforming functions of Simian Virus 40

“…The role of the J domain has been less studied in transgenic models, and the reports so far indicate an important -although tissue-speci®c-dependency on the J domain to induce tumors (Chen et al, 1992;Ratineau et al, 2000;Symonds et al, 1993). In each of these cases, the amino-terminal fragment of LT is su cient to drive Fox et al, 1989;Zennaro et al, 1998;Le Menuet et al, 2000Bone Behringer et al, 1988Knowles et al, 1990;Jensen et al, 1993;Wilkie et al, 1994 Brain andnervous system Brinster et al, 1984;Reynolds et al, 1988;Chen et al, 1989;Theuring et al, 1990;Chen and Van Dyke, 1991;Perraud et al, 1992;Smith et al, 1992;Jensen et al, 1993;Chiu et al, 2000Cartilage Cheah et al, 1995Digestive system Li et al, 1995Kim et al, 1994;Hauft et al, 1992;Asa et al, 1996Eye Theuring et al, 1990Penna et al, 1998;Beermann et al, 1999Heart Behringer et al, 1988Kidney Theuring et al, 1990Liver Dyer and Messing, 1989Sandgren et al, 1989;Sepulveda et al, 1989;Butel et al, 1990;Manickan et al, 2001Lung Sandmoller et al, 1994Wikenheiser et al, 1992Lymphoid tissue Reynolds et al, 1988Chen et al, 1989Mammary...…”

Alteration of Cardiac and Renal Functions in Transgenic Mice Overexpressing Human Mineralocorticoid Receptor

“…MR was found initially to be expressed in sodium-transporting epithelia such as the distal nephron, colon, salivary, and sweat glands. It is now well established that MR is also expressed in a large variety of non-epithelial tissues including the hippocampus (4), the cardiovascular system (5), and brown adipose tissue (6). In tight epithelia, aldosterone is an important regulator of electrolyte and water homeostasis via its binding to MR, inducing sodium reabsorption, and potassium excretion (7).…”