Identification of Urop11, a novel leptin-modulated gene that is upregulated in the hypothalamus of mice with virus-induced obesity.

Obesity results from disturbances of tightly regulated interactions between the nervous, endocrine, and metabolic systems that can be caused by external factors, such as viral infections. A mouse model of obesity induced by brain infection with a morbillivirus, canine distemper virus, allowed us to identify obesity-related genes. Using a subtractive library for the hypothalamus, the main brain structure regulating energy homeostasis, we identified a new gene on mouse chromosome 19 which we named upregulated obese product (Urop) 11 and, which has no homology with any known mRNA. A step-by-step molecular approach allowed us to isolate the full-length mRNA, predict the protein sequence, and identify consensus sites. Urop11 was mainly detected in the hypothalamus and adipocytes, and was dramatically upregulated in these central and peripheral structures in obese mice. Urop11 was also expressed in human neural and lymphoid samples and its expression seemed to be regulated by the state of lymphocyte activation. Interestingly, Urop11 expression was strongly upregulated both in vivo in mouse hypothalamus and in vitro in mouse neural cell lines, after leptin treatment. Taken together, our data show that Urop11 is a target of leptin, the satiety factor produced by adipocytes, in physiological and pathological conditions, including obesity. This new gene can be considered a key molecule in the hypothalamic integration pathway and demonstrates the importance of Urop11 as a target of leptin action.

[Cellular dynamics of pathogenesis induced by bovine leukemia virus]. / Dynamique cellulaire de la pathogenèse induite par le virus de la leucémie bovine.

Bovine leukemia virus (BLV) is the etiological agent of a lymphoproliferative disease in cattle. This retrovirus can also be experimentally transmitted to sheep, in which the pathology is more rapid and more frequent. This review summarizes the current knowledge on the BLV virus and more particularly on its role in lymphocyte homeostasis and induction of pathogenesis. This system has been informative for understanding pathogenesis induced by human T-lymphotropic virus type I (HTLV-1).

Morbillivirus infection of the mouse central nervous system induces region-specific upregulation of MMPs and TIMPs correlated to inflammatory cytokine expression.

Viral infection of the central nervous system (CNS) can result in perturbation of cell-to-cell communication involving the extracellular matrix (ECM). ECM integrity is maintained by a dynamic balance between the synthesis and proteolysis of its components, mainly as a result of the action of matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs). An MMP/TIMP imbalance may be critical in triggering neurological disorders, in particular in virally induced neural disorders. In the present study, a mouse model of brain infection using a neurotropic strain of canine distemper virus (CDV) was used to study the effect of CNS infection on the MMP/TIMP balance and cytokine expression. CDV replicates almost exclusively in neurons and has a unique pattern of expression (cortex, hypothalamus, monoaminergic nuclei, hippocampus, and spinal cord). Here we show that although several mouse brain structures were infected, they exhibited a differential pattern in terms of MMP, TIMP, and cytokine expression, exemplified by (i) a large increase in pro-MMP9 levels, in particular in the hippocampus, which occurred mainly in neurons and was associated with in situ gelatinolytic activity, (ii) specific and significant upregulation of MT1-MMP mRNA expression in the cortex and hypothalamus, (iii) an MMP/TIMP imbalance, suggested by the upregulation of TIMP-1 mRNA in the cortex, hippocampus, and hypothalamus and of TIMP-3 mRNA in the cortex, and (iv) a concomitant region-specific large increase in expression of Th1-like cytokines, such as gamma interferon, tumor necrosis factor alpha, and interleukin 6 (IL-6), contrasting with weaker induction of Th2-like cytokines, such as IL-4 and IL-10. These data indicate that an MMP/TIMP imbalance in specific brain structures, which is tightly associated with a local inflammatory process as shown by the presence of immune infiltrating cells, differentially impairs CNS integrity and may contribute to the multiplicity of late neurological disorders observed in this viral mouse model.

Down regulation of melanin concentrating hormone in virally induced obesity.

Obesity is a complex disease involving genetic components and environmental factors and probably associated with the dysregulation of central homeostasis normally maintained by the hypothalamic neuroendocrine/neurotransmitter network. We previously reported that canine distemper virus (CDV), which is closely related to human measles virus, can target hypothalamic nuclei, and lead to obesity syndrome in the late stages of infection. Here, using differential display PCR, we demonstrate specific down-regulation of melanin-concentrating hormone precursor mRNA (ppMCH) in infected-obese mice. Although ppMCH was down-regulated in all infected mice during the acute stage of infection, this was only seen during the late stage of infection in infected-obese mice. In addition, ppMCH mRNA and protein expression in the lateral hypothalamus was decreased in the absence of neuronal death. These results show the importance of ppMCH in the establishment and maintenance of obesity and the involvement of a virus as an environmental factor.

Alteration of the leptin network in late morbid obesity induced in mice by brain infection with canine distemper virus.

Viruses can induce progressive neurologic disorders associated with diverse pathological manifestations, and therefore, viral infection of the brain can impair differentiated neural functions, depending on the initial viral tropism. We have previously reported that canine distemper virus (CDV) targets certain mouse brain structures, including the hypothalamus, early and selectively. Infected mice exhibit acute encephalitis, with late disease, characterized by motor impairment or obesity syndrome, appearing in some of the surviving mice several months after the initial viral replication. In the present study, we show viral persistence in the hypothalami of obese mice, as demonstrated by low, but still significant, levels of CDV nucleoprotein transcripts, associated with a dramatic decrease in F gene mRNAs. Given the pivotal role of the hypothalamus in obesity (eating behavior, energy consumption, and neuroendocrine function) and that of leptin, the adipose tissue-derived satiety factor acting through hypothalamic receptors, we analyzed the leptin networks in both obese and nonobese mice. The discrepancy found between the chronic and dramatic increase in blood leptin levels and the occurrence of obesity may be due to leptin resistance in the brain. In fact, expression of the long leptin receptor isoform, representing the functional leptin receptor, was specifically downregulated in the hypothalami of obese mice, explaining their inability to generate an adequate response to leptin in the brain. Intriguingly, during the acute phase of infection, its expression was increased in CDV-targeted structures in all infected mice and remained high in obese mice in all CDV-targeted structures, except for the hypothalamus. The biphasic change in hypothalamic leptin receptor expression seen during the progression of CDV-induced obesity provides a new paradigm for understanding mechanisms of neuroendocrinological, virus-induced abnormalities.