Revised Genetic Classification of Limb Girdle Muscular Dystrophies

Limb girdle muscular dystrophies (LGMD) are a heterogeneous group of inherited progressive muscle disorders affecting predominantly the shoulder and pelvic girdle muscles. They present both with autosomal dominant and autosomal recessive patterns of inheritance. Recent development, including results from Next Generation Sequencing technology, expanded the number of recognised forms. Therefore a revised genetic classification that takes into account the novel entities is needed, allowing clinicians and researchers to refer to a common nomenclature for diagnostic and research purposes.

Constitutive activity of cannabinoid-2 (CB2) receptors plays an essential role in the protean agonism of (+)AM1241 and L768242

BACKGROUND AND PURPOSE

Cannabinoid-2 (CB(2)) receptor-selective agonists have shown anti-nociceptive activity in models of neuropathic and inflammatory pain, and the two agonists most widely used, (+/-)AM1241 [(2-iodo-5-nitrophenyl)-[1-(1-methylpiperidin-2-ylmethyl)-1H-indol-3-yl-methanone] and L768242 [(2,3-dichloro-phenyl)-[5-methoxy-2-methyl-3-(2-morpholin-4-yl-ethyl)-indol-1-yl]-methanone] (GW405833), have been suggested to be protean agonists. Here we investigated the role of the constitutive activity of CB(2) receptors in (+)AM1241 and L768242 protean agonism.

EXPERIMENTAL APPROACH

Pharmacological profiles of CB(2) receptor ligands were evaluated in Chinese hamster ovary cells expressing recombinant human (hCB(2)) or rat (rCB(2)) receptors, by measuring modulation of cAMP. To assess the influence of constitutive activity on pharmacological profile, constitutive activity was abolished by pretreatment with AM630 [(6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl](4-methoxyphenyl) methanone)], followed by extensive washing.

KEY RESULTS

In cell lines expressing either hCB(2) or rCB(2) receptors, (+)AM1241 did not reverse forskolin stimulation of cAMP levels. Conversely, L768242 was an inverse agonist at both hCB(2) and rCB(2) receptors. Abolition of constitutive activity disclosed (+)AM1241 and L768242 agonist activity, while activity of CP55940 [5-(1,1-dimethylheptyl)-2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxy-propyl)-cyclohexyl]-phenol] was unaffected and AM630 became a neutral antagonist. In presence of constitutively active CB(2) receptors, (+)AM1241 antagonized CP55940, but when constitutive activity was abolished, it acted as a partial agonist with additive or antagonistic behaviour, depending on concentration.

CONCLUSIONS AND IMPLICATIONS

These results show that (+)AM1241 and L768242 are protean agonists at both hCB(2) and rCB(2) receptors. Abolition of constitutive activity reveals the agonist activity of these compounds. Thus, differences between in vivo and in vitro profiles of CB(2) receptor agonists could be due to different levels of constitutive activity in recombinant versus native CB(2) receptors.

Presenilin-1 regulates the neuronal threshold to excitotoxicity both physiologically and pathologically

A direct pathophysiological role of Familial Alzheimer's Disease (FAD)-associated Presenilin 1 (PS1) mutations in neuronal vulnerability remains a controversial matter. We evaluated the relationship between PS1 and excitotoxicity in four different experimental models of neurotoxicity by using primary neurons from (i) transgenic (tg) mice overexpressing a human FAD-linked PS1 variant (L286V mutation), (ii) tg mice overexpressing human wild-type (wt) PS1, (iii) PS1 knockout mice, and (iv) wt mice in which PS1 gene expression was knocked down by antisense treatment. We found that primary neurons overexpressing mutated PS1 showed an increased vulnerability to both excitotoxic and hypoxic-hypoglycemic damage when compared with neurons obtained from either mice overexpressing human wt PS1 or in wt mice. In addition, reduced excitotoxic damage was obtained in neurons in which PS1 expression was absent or diminished. Data obtained in in vivo experimental models of excitotoxicity partially supported the in vitro observations. Accelerated neuronal death was demonstrated in the hippocampus of mice overexpressing mutated PS1 after peripheral administration of kainic acid in comparison with wt animals. However, measurement of the infarct volume after middle cerebral artery occlusion did not show significant difference between the two animal groups. The results altogether suggest that expression of FAD-linked PS1 variants increases the vulnerability of neurons to a specific type of damage in which excitotoxicity plays a relevant role. In addition, they support the view that reduction of endogenous PS1 expression results in neuroprotection.

Interleukin-10 modulates neuronal threshold of vulnerability to ischaemic damage

Interleukin-10 (IL-10) is a powerful suppressor of cellular immune responses, with a postulated role in brain inflammation. First, we have evaluated the role of this cytokine in ischaemic brain damage using IL-10 knockout (IL-10-/-) mice. The middle cerebral artery (MCA) was occluded in either IL-10-/- or wild-type animals of corresponding strain (C57Bl/6) and age. Infarct volume was assessed 24 h later in serial brain sections. Brain infarct produced by MCA occlusion was 30% larger in the IL-10-/- than in wild-type mice (21. 8 +/- 1.2 vs. 16.9 +/- 1.0 mm3, respectively; P < 0.01; Student's t-test). To further characterize these findings, studies were extended to in vitro models. Primary neuronal cortical cultures derived from IL-10-/- animals were more susceptible to both excitotoxicity and combined oxygen-glucose deprivation compared with cell cultures from wild-type mice. Moreover, when added to the culture medium, recombinant murine IL-10 (0.1-100 ng/mL) exerted a concentration-dependent prevention of neuronal damage induced by excitotoxicity in both cortical and cerebellar granule cell cultures taken from either strain. The accordance of in vivo and in vitro data allows us to suggest a potential neuroprotective role of IL-10 against cerebral ischaemia when administered exogenously or made available from endogenous sources.

Genetically modified mice in neuropharmacology

Since the first transgenic mouse was reported in 1980, genetically engineered mice have become an invaluable biological tool for better understanding of physiological and pathological processes in many fields of biomedical research. The transgenic technology allows researchers to carry out specific genetic manipulation in all cells of a laboratory animal, and makes it possible to dissect gene function in a living organism. In the field of neurosciences these animals have contributed greatly to shed light on basic mechanisms of brain function as well as to generate useful animal models for studying human neurological disorders. In this review, the different techniques available for generating specific mutations in the mouse genome will be described, from pronuclear microinjection to gene targeting in embryonic stem cells, and to the second generation of inducible and conditional knockout mice. Then, the impact of transgenic mouse models as an alternative or additional approach to neuropharmacology will be discussed, not only for the study of molecular mechanisms in the central nervous system but also for the identification of new biological targets for innovative pharmacological therapy.

Neurological dysfunctions in mice expressing different levels of the Q/R site-unedited AMPAR subunit GluR-B

We generated mouse mutants with targeted AMPA receptor (AMPAR) GluR-B subunit alleles, functionally expressed at different levels and deficient in Q/R-site editing. All mutant lines had increased AMPAR calcium permeabilities in pyramidal neurons, and one showed elevated macroscopic conductances of these channels. The AMPAR-mediated calcium influx induced NMDA-receptor-independent long-term potentiation (LTP) in hippocampal pyramidal cell connections. Calcium-triggered neuronal death was not observed, but mutants had mild to severe neurological dysfunctions, including epilepsy and deficits in dendritic architecture. The seizure-prone phenotype correlated with an increase in the macroscopic conductance, as independently revealed by the effect of a transgene for a Q/R-site-altered GluR-B subunit. Thus, changes in GluR-B gene expression and Q/R site editing can affect critical architectural and functional aspects of excitatory principal neurons.

The murine Y1 receptor 5' upstream sequence directs cell-specific and developmentally regulated LacZ expression in transgenic mice CNS

The Y1 receptor for neuropeptide Y (NPY) is highly expressed in mammalian CNS where it mediates the activation of several neurobiological functions. We have previously demonstrated that a 1.3-kb fragment upstream of the transcription initiation sites of the murine Y1 receptor gene is able to direct specific expression of reporter genes in neuronal cell cultures. In the present study transgenic mice harbouring this putative promoter region linked to the LacZ reporter gene were generated and analysed for temporal and spatial distribution. Ten transgenic lines expressed beta-galactosidase in the CNS but not in other organs such as heart, liver and kidney. Histochemical analysis of brain from adult transgenic mice showed specific expression of the transgene in specific brain regions with little variation. Four transgenic lines showed characteristic patterns of beta-galactosidase activity in the brain that are consistent with the expression of the endogenous gene. Prominent LacZ activity was present in several telencephalic and diencephalic structures, including deeper layers of cerebral cortex, amygdaloid complex, hippocampus, preoptic area, several thalamic and hypothalamic nuclei and habenula. The ontogeny analysis indicates that the LacZ expression agrees with the temporal expression pattern of rat Y1 receptor mRNA. These data demonstrate that the 1.3-kb upstream region of the murine Y1 receptor gene contains the cis acting elements required for establishing a CNS-restricted and developmental stage-specific pattern of expression in vivo. Moreover they provide further information on the distribution of this NPY subtype receptor in mammalian brain.

Importance of the intracellular domain of NR2 subunits for NMDA receptor function in vivo

NMDA receptors, a class of glutamate-gated cation channels with high Ca2+ conductance, mediate fast transmission and plasticity of central excitatory synapses. We show here that gene-targeted mice expressing NMDA receptors without the large intracellular C-terminal domain of any one of three NR2 subunits phenotypically resemble mice made deficient in that particular subunit. Mice expressing the NR2B subunit in a C-terminally truncated form (NR2B(deltaC/deltaC) mice) die perinatally. NR2A(deltaC/deltaC) mice are viable but exhibit impaired synaptic plasticity and contextual memory. These and NR2C(deltaC/deltaC) mice display deficits in motor coordination. C-terminal truncation of NR2 subunits does not interfere with the formation of gateable receptor channels that can be synaptically activated. Thus, the phenotypes of our mutants appear to reflect defective intracellular signaling.

Early-onset epilepsy and postnatal lethality associated with an editing-deficient GluR-B allele in mice

The arginine residue at position 586 of the GluR-B subunit renders heteromeric alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-sensitive glutamate receptor channels impermeable to calcium. The codon for this arginine is introduced at the precursor messenger RNA (pre-mRNA) stage by site-selective adenosine editing of a glutamine codon. Heterozygous mice engineered by gene targeting to harbor an editing-incompetent GluR-B allele synthesized unedited GluR-B subunits and, in principal neurons and interneurons, expressed AMPA receptors with increased calcium permeability. These mice developed seizures and died by 3 weeks of age, showing that GluR-B pre-mRNA editing is essential for brain function.

In primary neuronal cultures muscarinic m1 and m3 receptor mRNA levels are regulated by agonists, partial agonists and antagonists

The homologous regulation of the muscarinic m1 and m3 receptors mRNA was studied in rat corticostriatal neuronal cultures. In response to the full agonist carbachol the m1 and m3 receptor mRNA levels were modulated and showed different time-courses. The m1 receptor mRNA increased to 270% of prestimulation levels after 6 h, while the m3 receptor transcript transiently increased to 170% after 2 h. Conversely, the muscarinic receptor partial agonist oxotremorine caused a rapid and sustained increase in both mRNA species as soon as after 1 h of exposure. A comparable increase in both receptor mRNAs was induced by the partial agonist [4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethyl-ammonium chloride] (McN-A-343). The observation that 1 h exposure to the non selective antagonist N-methyl-scopolamine also enhanced the m1 and m3 receptor transcripts suggests that in corticostriatal neurons muscarinic receptor partial agonists exert an antagonist-like effect on the m1 and m3 receptor mRNAs.

Intracerebroventricular administration of nerve growth factor affects muscarinic cholinergic receptors in the cerebral cortex of neonatal rats

The repeated intracerebroventricular administration of nerve growth factor (5 micrograms/2.5 microliters) to neonatal rats induced the activation of choline acetyltransferase in forebrain cholinergic neurons that was paralleled by a concomitant change in the density of muscarinic cholinergic receptors in the cerebral cortex. The administration of nerve growth factor altered muscarinic binding sites in a biphasic fashion during postnatal development. A significant stimulation of the developmental increase in the density of muscarinic binding sites occurred in nerve growth factor-treated animals at days 2 and 3 after birth. Conversely, nerve growth factor induced a significant decrease in the receptor number at postnatal days 8 and 14. Muscarinic receptor number returned to control values after treatment, suggesting that nerve growth factor-induced changes to muscarinic cholinergic receptors are reversible. Nerve growth factor administration did not affect muscarinic cholinergic receptor density in striatal membranes and did not alter the relative content of cortical messenger RNAs encoding m1 and m3 muscarinic cholinergic receptor subtypes at postnatal day 14, as determined by reverse transcriptase-polymerase chain reaction. The up- and down-regulation of muscarinic cholinergic receptors induced by nerve growth factor during postnatal development may be temporally related events associated with concomitant changes in the activity of choline acetyltransferase.

[Erythrocyte zinc-protoporphyrin content in pregnancy]

The assessment of iron deficiency represents a major aspect of routine laboratory chemico-clinical analysis, but the results provided by traditional hemato-clinical tests (sideremia, transferrinemia, mean cell volume and red blood cell levels) may not prove conclusive. During pregnancy iron deficiency is common and it would be extremely valuable to obtain a precise method of evaluating anemia. The assay of erythrocytic zincoprotoporphyrin (ZNPP) offers further diagnostic possibilities. This study aimed to evaluate the behaviour of ZNPP and other common laboratory indices in pregnant and non-pregnant women in order to assess the value of assaying ZNPP levels. Some common parameters for the study of sideropenic anemia were determined using the methods employed in our laboratory: mean cell volume (MCV), hemoglobin (Hb), sideremia (Fe), ferrinemia and ZNPP in women of child-bearing age. The tests were prescribed for preventive tests prior to the administration of oral contraceptives and/or in pregnant women undergoing control tests. No tests were made to ascertain professional or environmental exposure to lead or its derivatives. Precision was evaluated by calculating the coefficient of variation (CV) for repeated tests. If a detailed analysis is made of the behaviour of some parameters during pregnancy it can be seen that there is a progressive diminution of sideremia and ferritin, accompanied by increased levels of ZNPP. The potentially most characteristic parameters are ferritin and ZNPP which do not have a Gaussian distribution.(ABSTRACT TRUNCATED AT 250 WORDS)