Cyclic stretch reveals a mechanical role for intermediate filaments in a desminopathic cell model

Mechanics is now recognized as crucial in cell function. To date, the mechanical properties of cells have been inferred from experiments which investigate the roles of actin and microtubules ignoring the intermediate filaments (IFs) contribution. Here, we analyse myoblasts behaviour in the context of myofibrillar myopathy resulting from p.D399Y desmin mutation which disorganizes the desmin IF network in muscle cells. We compare the response of myoblasts expressing either mutated or wild-type desmin to cyclic stretch. Cells are cultivated on supports submitted to periodic uniaxial stretch of 20% elongation amplitude and 0.3 Hz frequency. We show that during stretching cycles, cells expressing mutated desmin reduce their mean amplitude both for the elongation and spreading area compared to those expressing wild-type desmin. Even more unexpected, the reorientation angles are altered in the presence of p.D399Y desmin. Yet, at rest, the whole set of those parameters are similar for the two cell populations. Thus, we demonstrate that IFs affect the mechanical properties and the dynamics of cell reorientation. Since these processes are known due to actin cytoskeleton, these results suggest the IFs implication in mechanics signal transduction. Further studies may lead to better understanding of their contribution to this process.

Adiponectin receptors are expressed in hypothalamus and colocalized with proopiomelanocortin and neuropeptide Y in rodent arcuate neurons

Adiponectin is involved in the control of energy homeostasis in peripheral tissues through Adipor1 and Adipor2 receptors. An increasing amount of evidence suggests that this adipocyte-secreted hormone may also act at the hypothalamic level to control energy homeostasis. In the present study, we observed the gene and protein expressions of Adipor1 and Adipor2 in rat hypothalamus using different approaches. By immunohistochemistry, Adipor1 expression was ubiquitous in the rat brain. By contrast, Adipor2 expression was more limited to specific brain areas such as hypothalamus, cortex, and hippocampus. In arcuate and paraventricular hypothalamic nuclei, Adipor1, and Adipor2 were expressed by neurons and astrocytes. Furthermore, using transgenic green fluorescent protein mice, we showed that Adipor1 and Adipor2 were present in pro-opiomelanocortin (POMC) and neuropeptide Y (NPY) neurons in the arcuate nucleus. Finally, adiponectin treatment by intracerebroventricular injection induced AMP-activated protein kinase (AMPK) phosphorylation in the rat hypothalamus. This was confirmed by in vitro studies using hypothalamic membrane fractions. In conclusion, Adipor1 and Adipor2 are both expressed by neurons (including POMC and NPY neurons) and astrocytes in the rat hypothalamic nuclei. Adiponectin is able to increase AMPK phosphorylation in the rat hypothalamus. These data reinforced a potential role of adiponectin and its hypothalamic receptors in the control of energy homeostasis.

A putative physiological role of hypothalamic CNTF in the control of energy homeostasis

Administration of CNTF durably reduces food intake and body weight in obese humans and rodent models. However, the involvement of endogenous CNTF in the central regulation of energy homeostasis needs to be elucidated. Here, we demonstrate that CNTF and its receptor are expressed in the arcuate nucleus, a key hypothalamic region controlling food intake, and that CNTF levels are inversely correlated to body weight in rats fed a high-sucrose diet. Thus endogenous CNTF may act, in some individuals, as a protective factor against weight gain during hypercaloric diet and could account for individual differences in the susceptibility to obesity.

Lack of cross-desensitization between leptin and prolactin signaling pathways despite the induction of suppressor of cytokine signaling 3 and PTP-1B

Hyperprolactinemia and hyperleptinemia occur during gestation and lactation with marked hyperphagia associated with leptin resistance. Prolactin (PRL) induces the expression of orexigenic neuropeptide Y (NPY) through the activation of JAK-2/STAT-3 signaling pathway in hypothalamic paraventricular nucleus (PVN) leading to hyperphagia. PRL may also act through the inhibition of anorexigenic effect of leptin via induction of suppressor of cytokine signaling 3 (SOCS-3). This paper aimed to co-localize PRL (PRL-R) and leptin (ObRb) receptors in the hypothalamus of female rats and investigate the possible cross-desensitization between PRL-R and ObRb. We showed that: 1) PRL-R and ObRb are expressed in the PVN and co-localized in the same neurons; 2) in lactating females leptin failed to activate JAK-2/STAT-3 signaling pathway; 3) in Chinese Hamster Ovary (CHO) stably co-expressing PRL-R and ObRb, overexposure to PRL did not affect leptin signaling but totally abolished PRL-dependent STAT-5 phosphorylation. The overexposure to leptin produces similar results with strong alteration of leptin-dependent STAT-3 phosphorylation, whereas PRL-dependent STAT-5 was not affected; and 4) CHO-ObRb/PRL-R cells overexposure to leptin or PRL induces the expression of negative regulators SOCS-3 and PTP-1B. Thus, we conclude that these negative regulators affect specifically the inducer signaling pathway; for instance, SOCS-3 induced by PRL will affect PRL-R signaling but not ObRb signaling and vice versa. Finally, the lack of cross-desensitization between PURL-R and ObRb suggests that hyperphagia observed during gestation and lactation may be attributed to a direct effect of PRL on NPYexpression, and is most likely exacerbated by the physiological leptin resistance state.

Comparative anticonvulsant activity and neurotoxicity of 4-amino-N-(2,6-dimethylphenyl)phthalimide and prototype antiepileptic drugs in mice and rats

We compared the anticonvulsant activity and neurotoxicity of 4-amino-N-(2,6-dimethylphenyl)phthalimide (ADD 213063) with those of phenytoin (PHT), carbamazepine (CBZ), phenobarbital (PB), ethosuximide (ESM), valproate (VPA), and felbamate (FBM). Evaluation of anticonvulsant properties performed according to well-established procedures in rats and mice showed that ADD 213063 is most effective in protecting animals against maximal electroshock seizures (MES). This anti-MES activity is achieved with nontoxic doses, with the optimal effect recorded in rats dosed orally with anti-MES ED50 and protective index (PI) values of 25.2 mumol/kg and > 75, respectively. ADD 213063 protects to a lesser extent against seizures induced by subcutaneous (s.c.) picrotoxin and subcutaneous pentylenetetrazol (PTZ) in mice dosed intraperitoneally and orally, respectively. The profile of anticonvulsant action of ADD 213063 closely parallels that of CBZ.

Synthesis and anticonvulsant activity of two N-(2,6- dimethylphenyl)pyridinedicarboximides

Two N-(2,6-dimethylphenyl)pyridinedicarboximides were synthesized and evaluated for anticonvulsant properties and neurotoxicity. These compounds were mainly active against maximal electroshock (MES) induced seizures in animal models. In rats dosed orally, N-(2,6-dimethylphenyl-2,3-pyridinedicarboximide 1 exhibited an anti-MES ED50 of 54.2 mumol/kg and a protective index (PI = TD50/ED50) superior to 27.4. In mice dosed intraperitoneally, compound 1 is less active against MES induced seizure (ED50 = 160.9 mumol/kg) and more neurotoxic as evidenced by a low protective index (1.93). Comparison with published data on phenytoin reveals that compound 1 is, in rats dosed orally, two-fold more potent than this antiepileptic drug against MES induced seizures.

Synthesis and anticonvulsant activity of some N-phenylphthalimides

The anticonvulsant potential of a series of N-phenylphthalimide derivatives has been screened in subcutaneous pentylenetetrazole seizure (scPTZ) and maximal electroshock seizure (MES) tests. Intraperitoneal 4-amino-N-phenylphthalimides were the most potent agents against MES in mice. Referring to the N-(2,6-dimethyl-phenyl)phthalimide structure, the order of anticonvulsant activity appears to correspond to the phthalimide ring substitution pattern of 4-amino > 4-nitro > 4-methyl; H > 3-nitro; 3-amino. The 4-amino-N-(2-methylphenyl)-phthalimide displays an anti-MES ED50 of 47.61 mumol/kg with a protective index (PI) of 4.2. Oral administration to rats of the compounds found to be active in mice showed that the 4-amino-N-(2,6-dimethylphenyl)phthalimide is the most potent anti-MES agent in rats, exhibiting an ED50 of 25.2 mumol/kg and a PI greater than 75. Regarding the nature of the 2 and 6 substituents of the N-phenyl ring, the anticonvulsant efficiencies may be ordered as follows: 2,6-dimethyl > 2-methyl > 2-ethyl > 2-ethyl-6-methyl > 2,6-diethyl > unsubstituted phenyl ring. N-Phenylphthalimide derivatives seem to have great potential as candidate anticonvulsant drugs.

Anticonvulsant activity of some 4-amino-N-phenylphthalimides and N-(3-amino-2-methylphenyl)phthalimides

A series of fifteen N-phenylphthalimides including 12 4-amino-N-phenylphthalimides and three N-(3-amino-2-methylphenyl)phthalimides was prepared and evaluated for anticonvulsant properties. The compounds were tested against seizures induced by electroshock (MES) and pentylenetetrazol (scPTZ) in mice dosed intraperitoneally. Their neurologic toxicity was assessed using the rotorod assay procedure. The most potent 4-amino-N-phenylphthalimides against MES were those possessing small lipophilic groups in either 2 or 2 and 6 positions of the N-phenyl ring. They also exhibited some activity against scPTZ and were the most toxic of the series. By contrast, no activity against scPTZ or neurotoxicity could be observed up to 300 mg/kg for members of the N-(3-amino-2- methylphenyl)phthalimide series. In this series, the order of anti-MES activity appears to correspond to the phthalimide ring substitution pattern of 4-amino > H > 4-methyl. Quantitation of anticonvulsant properties and toxicity of 4-amino-N-(2,6-dimethylphenyl)phthalimide (ADD 213063) previously initiated in rats has been, here, extended to mice dosed intraperitoneally but also orally. The confrontation of the two modes of administration in mice suggests that ADD 213063 presents with a good bioavailability.