Constitutive expression of suppressor of cytokine signalling-3 in skeletal muscle leads to reduced mobility and overweight in mice.

AIMS/HYPOTHESIS: Due to their ability to regulate various signalling pathways (cytokines, hormones, growth factors), the suppressor of cytokine signalling (SOCS) proteins are thought to be promising therapeutic targets for metabolic and inflammatory disorders. Hence, their role in vivo has to be precisely determined. METHODS: We generated transgenic mice constitutively producing SOCS-3 in skeletal muscle to define whether the sole abundance of SOCS-3 is sufficient to induce metabolic disorders and whether SOCS-3 is implicated in physiological roles distinct from metabolism. RESULTS: We demonstrate here that chronic expression of SOCS-3 in skeletal muscle leads to overweight in mice and worsening of high-fat diet-induced systemic insulin resistance. Counter-intuitively, insulin sensitivity in muscle of transgenic mice appears to be unaltered. However, following constitutive SOCS-3 production, several genes had deregulated expression, among them other members of the SOCS family. This could maintain the insulin signal into skeletal muscle. Interestingly, we found that SOCS-3 interacts with calcineurin, which has been implicated in muscle contractility. In Socs-3 transgenic muscle, this leads to delocalisation of calcineurin to the fibre periphery. Relevant to this finding, Socs-3 transgenic animals had dilatation of the sarcoplasmic reticulum associated with swollen mitochondria and decreased voluntary activity. CONCLUSIONS/INTERPRETATION: Our results show that constitutive SOCS-3 production in skeletal muscle is not in itself sufficient to induce the establishment of metabolic disorders such as diabetes. In contrast, we reveal a novel role of SOCS-3, which appears to be important for muscle integrity and locomotor activity.

Peroxisome proliferator-activated receptor beta activation promotes myonuclear accretion in skeletal muscle of adult and aged mice.

We reported recently that peroxisome proliferator-activated receptor beta (PPARbeta) activation promotes a calcineurin-dependent exercise-like remodelling characterised by increased numbers of oxidative fibres and capillaries. As physical exercise also induces myonuclear accretion, we investigated whether PPARbeta activation alters myonuclear density. Transgenic muscle-specific PPARbeta over-expression induced 14% increase of myonuclear density. Pharmacological PPARbeta activation promoted rapid and massive myonuclear accretion (20% increase after 48 h), which is dependent upon calcineurin/nuclear factor of activated T cells signalling pathway. In vivo bromodeoxyuridine labelling and proliferating cell nuclear antigen immunodetection revealed that PPARbeta activation did not promote cell proliferation, suggesting that the PPARbeta-promoted myonuclear accretion involves fusion of pre-existing muscle precursor cells to myofibres rather than cell division. Finally, we showed that in skeletal muscle, ageing led to a down-regulation of PPARbeta accompanied by decrease of both oxidative fibre number and myonuclear density. PPARbeta pharmacological activation counteracts, at least in part, the ageing-driven muscle remodelling.

Alterations of peroxisome proliferator-activated receptor delta activity affect fatty acid-controlled adipose differentiation.

Fatty acids have been postulated to regulate adaptation of adipose mass to nutritional changes by controlling expression of genes implicated in lipid metabolism via activation of nuclear receptors. Ectopic expression of the nuclear receptors PPARgamma or PPARdelta promotes adipogenesis in fibroblastic cells exposed to thiazolidinediones or long-chain fatty acids. To investigate the role of PPARdelta in fatty acid regulation of gene expression and adipogenesis in a preadipose cellular context, we studied the effects of overexpressing the native receptor or the dominant-negative PPARdelta mutant in Ob1771 and 3T3-F442A cells. Overexpression of PPARdelta enhanced fatty acid induction of the adipose-related genes for fatty acid translocase, adipocyte lipid binding protein, and PPARgamma and fatty acid effects on terminal differentiation. A transactivation-deficient form of PPARdelta mutated in the AF2 domain severely reduced these effects. Findings are similar in Ob1771 or 3T3-F442A preadipose cells. These data demonstrate that PPARdelta plays a central role in fatty acid-controlled differentiation of preadipose cells. Furthermore, they suggest that modulation of PPARdelta expression or activity could affect adaptive responses of white adipose tissue to nutritional changes.

Peroxisome-proliferator-activated receptor delta mediates the effects of long-chain fatty acids on post-confluent cell proliferation.

Nutritional long-chain fatty acids control adipose tissue mass by regulating the number and the size of adipocytes. It is now established that peroxisome-proliferator-activated receptors (PPARs) play crucial functions in the control of gene expression and the level of cell differentiation. PPARgamma, which is activated by specific prostanoids, is a key factor in activating terminal differentiation and adipogenesis. We have recently demonstrated that PPARdelta, once activated by fatty acids, drives the expression of a limited set of genes, including that encoding PPARgamma, thereby inducing adipose differentiation. Thus far, the mechanism of action of fatty acids in the control of preadipocyte proliferation has remained unknown. We show here that PPARdelta is directly implicated in fatty acid-induced cell proliferation. Ectopic expression of PPARdelta renders 3T3C2 cells capable of responding to treatment with long-chain fatty acids by a resumption of mitosis, and this effect is limited to a few days after confluence. This response is restricted to PPARdelta activators and, for fatty acids, takes place within the range of concentrations found to trigger differentiation of preadipocytes both in vitro and in vivo. Furthermore, the use of a mutated inactive PPARdelta demonstrated that transcriptional activity of the nuclear receptor is required to mediate fatty acid-induced proliferation. These data demonstrate that PPARdelta, as a transcription factor, is directly implicated in fatty acid-induced proliferation, and this could explain the hyperplastic development of adipose tissue that occurs in high-fat-fed animals.

Expression of peroxisome proliferator-activated receptor PPARdelta promotes induction of PPARgamma and adipocyte differentiation in 3T3C2 fibroblasts.

Nutritional long chain fatty acids control adipose tissue mass by regulating the number and the size of adipocytes. The molecular mechanisms implicated in this action of fatty acids remain poorly understood. It has been well established that peroxisome proliferator-activated receptor (PPAR) gamma, activated by specific prostanoids, plays a central role in the control of adipocyte gene expression and terminal differentiation. Thus far, the role of PPARdelta in the control of adipose tissue mass has remained unclear. Herein, we report the effects of ectopically expressed PPARdelta on the control of adipose-related gene expression and adipogenesis of 3T3C2 fibroblasts. Treatment of PPARdelta-expressing fibroblasts with fatty acids alone did not stimulate adipogenesis, whereas exposure of cells to a combination of fatty acids and PPARgamma activators promoted lipid accumulation and expression of a typical adipocyte program. At the molecular level, activation of PPARdelta by fatty acids induced transcription of the genes encoding fatty acid transporter, adipocyte lipid-binding protein, and PPARgamma. Subsequent activation of PPARgamma by specific agonists appeared to be required to promote terminal differentiation. These data demonstrate that PPARgamma gene expression is under the control of PPARdelta activated by fatty acids and could explain, at least partially, the adipogenic action of nutritional fatty acids.

Oral inflammatory pseudotumour: immunohistochemical investigation of a case involving the submandibular gland and review of the literature.

Inflammatory pseudotumours (IPs) are rare lesions. Most commonly reported in the lung, they are almost ubiquitous, but few oral cases have been described. Their rapid growth, local invasiveness and recurrence, and their ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) aspects are confusing and mimic benign or malignant neoplasms. Their recognition and distinction from malignant tumors is of importance but their histopathological diagnosis may represent a challenge. In the case reported involving the submandibular gland, the spindle cells had the immunohistochemical profile of myofibroblasts, broader cells with a larger nucleus were CD68 and/or Mac387 positive and the dense plasmacytic infiltrate was polyclonal. Histopathology of IPs covers a spectrum of appearances according to the cellularity and the degree of fibrosis. The recognition of a variable mixture of three main cell types: histiocytes or macrophages, myofibroblasts or fibroblasts and abundant plasma cells, with low mitotic activity and absence of cytological abnormalities in an ill circumscribed and rather fibrous lesion is recommended for the diagnosis of oral IP.

[Buccal dryness, xerostomia and measurement of salivary secretory activity]. / Sécheresse buccale, xérostomie et mesure de l'activité sécrétoire salivaire.

Xerostomia is a marked reduction in saliva production and may occur as an early symptom of various systemic diseases. It is also secondary to the administration of numerous drugs. Severity of salivary gland dysfunction cannot be predicted from subjective reports of oral dryness by patient, and accurate assessments of salivary gland function should be managed. Several procedures for saliva samplings and secretory activity measurements have been reported. In normal individuals, the mean values of unstimulated whole saliva was slightly higher in males (0.42 ml/min) than in females (0.37 ml/min). Corresponding mean values for stimulated whole saliva are 1.77 ml/min and 1.38 ml/min. Unstimulated whole saliva collection during 15 min is recommended as the most reliable test for clinical diagnosis. It is found that an unstimulated salivary flow of 0.1 ml/min represents the cut-off limit for the diagnosis of xerostomia.

[Drug-induced xerostomia]. / Les hyposialies d'origine médicamenteuse.

Hyposalivation is related to decreased salivary flow, with xerostomia as an ultimate degree. Prolonged severe hyposalivation or xerostomia may induce oral pain, poor tolerance to dentures, loss in taste acuity and increased incidence of oral infections: gingivitis, periodontitis, oral candidosis, infectious sialadenitis and multiple dental caries. Most of the time hyposalivation is a reversible drug-induced side-effect. Hyposalivation is frequent, particularly in elderly people with numerous drugs prescribed on a long-term continuous basis, and in psychiatric patients. It remains a neglected clinical problem. Besides the well-known antimuscarinics, antihistaminics, imipraminic antidepressants and phenothiazic neuroleptics, many drugs may induce hyposalivation. This work aims to review drug-induced xerostomia in 1997 (French pharmacopeae), and high-risk associations.

Comparison of immunological and molecular hybridization detection methods for the detection of hepatitis A virus in sewage.

Immune electron microscopy (IEM), radioimmunoassay (RIA) and molecular hybridization with a digoxigenin-labelled cDNA probe were compared for the detection of wild-type human hepatitis A virus (HAV) in raw and treated sewage. In the same experiments, classic tests for culturable enteroviruses were carried out. With the hybridization probes, HAV was detected in three of the 13 affluent samples (23%) and in eight out of 13 effluent samples (61%). For four of the effluent samples, positivity revealed by IEM was confirmed by the cDNA probe. In contrast, two of the samples shown as positive by IEM were negative with the probes. Detection of HAV by RIA was negative in all cases. Demonstration of HAV was higher in effluent than in affluent. No particular relationship was established between demonstration of HAV, on the one hand, and the various concentrations of enteroviruses observed in the same samples on the other. Overall, if all the results, irrespective of the type of water (affluent or effluent), are taken together, 50% of the sewage samples tested were found to contain HAV by one or another method of detection.

Occurrence of faecal bacteria, Salmonella and antigens associated with hepatitis A virus in shellfish.

An investigation was carried out over a one year period to examine jointly the occurrence of faecal bacteria, salmonella and the presence of antigens associated with the hepatitis A virus (HAV) in oysters (Crassostrea gigas), mussels (Mytilus edulis, Mytilus galloprovincialis) and cockles (Cerastoderma edule), taken from 8 shellfish farming areas or natural beds along the French coast. For the faecal coliforms (FC) and faecal streptococci (FS), statistical analysis of the 176 samples examined shows a statistically significant difference between sampling stations (F = 44.39 and F = 26.69 respectively, p less than 0.001): 4 of the 8 stations are more highly contaminated. Salmonella and antigens associated with HAV were detected in 5% and 1.7% respectively of the samples analysed. Frequency of isolation of salmonella is higher for the group of sampling stations where the mean levels of contamination by FC and FS are highest. The presence of HAV associated antigens was detected for the group of stations showing the lowest mean contamination levels. Taking all sample stations together, the percentage of isolation of salmonella differs significantly (chi 2 = 7.28, p less than 0.01) for the two classes of FC established on the basis of the threshold value (300 FC). There is no difference between the two classes of FS. For the HAV-associated antigens, detection percentages are similar for the two classes of results for FC and FS. Within each sampling station, considered independently, no particular correlation was found between the various viral and bacterial markers investigated.