Human alpha 2A-adrenergic receptor gene expressed in transgenic mouse adipose tissue under the control of its regulatory elements.

Catecholamines regulate white adipose tissue function and development by acting through beta- and alpha2-adrenergic receptors (ARs). Human adipocytes express mainly alpha 2A- but few or no beta 3-ARs while the reverse is true for rodent adipocytes. Our aim was to generate a mouse model with a human-like alpha2/beta-adrenergic balance in adipose tissue by creating transgenic mice harbouring the human alpha 2A-AR gene under the control of its own regulatory elements in a combined mouse beta 3-AR-/- and human beta 3-AR+/+ background. Transgenic mice exhibit functional human alpha 2A-ARs only in white fat cells. Interestingly, as in humans, subcutaneous adipocytes expressed higher levels of alpha2-AR than perigonadal fat cells, which are associated with a better antilipolytic response to epinephrine. High-fat-diet-induced obesity was observed in transgenic mice in the absence of fat cell size modifications. In addition, analysis of gene expression related to lipid metabolism in isolated adipocytes suggested reduced lipid mobilization and no changes in lipid storage capacity of transgenic mice fed a high-fat diet. Finally, the development of adipose tissue in these mice was not associated with significant modifications of glucose and insulin blood levels. Thus, these transgenic mice constitute an original model of diet-induced obesity for in vivo physiological and pharmacological studies with respect to the alpha2/beta-AR balance in adipose tissue

Identification of a novel role for autotaxin in microglial cells submitted to oxidative stress

International audienc

Identification of a novel role for autotaxin in microglial cells submitted to oxidative stress

International audienc

Alpha2-adrenergic receptor-mediated release of lysophosphatidic acid by adipocytes. A paracrine signal for preadipocyte growth.

In the search for the existence of adrenergic regulation of the autocrine/paracrine function of the white adipose tissue, it was observed that conditioned media from isolated adipocytes or dialysates obtained by in situ microdialysis of human subcutaneous adipose tissue increased spreading and proliferation of 3T3F442A preadipocytes. These effects were amplified when an alpha2-adrenergic agonist was present during the obtention of conditioned media and microdialysates. This alpha2-adrenergic-dependent trophic activity was completely abolished by pretreatment of the conditioned media or microdialysates with the lysophospholipase, phospholipase B. Among the different lysophospholipids tested only lysophosphatidic acid (LPA) was able to induce spreading and proliferation of 3T3F442A preadipocytes. Moreover, previous chronic treatment of 3T3F442A preadipocytes with LPA which led to a specific desensitization of LPA responsiveness, abolished the alpha2-adrenergic-dependent trophic activities of the conditioned media and microdialysates. Finally, alpha2-adrenergic stimulation led to a rapid, sustained, and pertussis toxin-dependent release of [32P]LPA from [32P]-labeled adipocytes. Based upon these results it was proposed that in vitro and in situ stimulation of adipocyte alpha2-adrenergic receptors provokes the extracellular release of LPA leading, in turn, to regulation of preadipocyte growth

Phosphatidic acid mediates demyelination in Lpin1 mutant mice

Lipids play crucial roles in many aspects of glial cell biology, affecting processes ranging from myelin membrane biosynthesis to axo-glial interactions. In order to study the role of lipid metabolism in myelinating glial cells, we specifically deleted in Schwann cells the Lpin1 gene, which encodes the Mg2+-dependent phosphatidate phosphatase (PAP1) enzyme necessary for normal triacylglycerol biosynthesis. The affected animals developed pronounced peripheral neuropathy characterized by myelin degradation, Schwann cell dedifferentiation and proliferation, and a reduction in nerve conduction velocity. The observed demyelination is mediated by endoneurial accumulation of the substrate of the PAP1 enzyme, phosphatidic acid (PA). In addition, we show that PA is a potent activator of the MEK-Erk pathway in Schwann cells, and that this activation is required for PA-induced demyelination. Our results therefore reveal a surprising role for PA in Schwann cell fate determination and provide evidence of a direct link between diseases affecting lipid metabolism and abnormal Schwann cell functio