Sigma nonopioid intracellular receptor 1 mutations cause frontotemporal lobar degeneration-motor neuron disease

OBJECTIVE

Frontotemporal lobar degeneration (FTLD) is the most common cause of early-onset dementia. Pathological ubiquitinated inclusion bodies observed in FTLD and motor neuron disease (MND) comprise trans-activating response element (TAR) DNA binding protein (TDP-43) and/or fused in sarcoma (FUS) protein. Our objective was to identify the causative gene in an FTLD-MND pedigree with no mutations in known dementia genes.

METHODS

A mutation screen of candidate genes, luciferase assays, and quantitative polymerase chain reaction (PCR) was performed to identify the biological role of the putative mutation. Neuropathological characterization of affected individuals and western blot studies of cell lines were performed to identify the pathological mechanism of the mutation.

RESULTS

We identified a nonpolymorphic mutation (c.672*51G>T) in the 3'-untranslated region (UTR) of the Sigma nonopioid intracellular receptor 1 (SIGMAR1) gene in affected individuals from the FTLD-MND pedigree. The c.672*51G>T mutation increased gene expression by 1.4-fold, corresponding with a significant 1.5-fold to 2-fold change in the SIGMAR1 transcript or Sigma-1 protein in lymphocyte or brain tissue. Brains of SIGMAR1 mutation carriers displayed a unique pathology with cytoplasmic inclusions immunopositive for either TDP-43 or FUS but not Sigma-1. Overexpression of SIGMAR1 shunted TDP-43 and FUS from the nucleus to the cytoplasm by 2.3-fold and 5.2-fold, respectively. Treatment of cells with Sigma-1 ligands significantly altered translocation of TDP-43 by up to 2-fold.

INTERPRETATION

SIGMAR1 is a causative gene for familial FTLD-MND with a unique neuropathology that differs from other FTLD and MND cases. Our findings also suggest Sigma-1 drugs as potential treatments for the TDP-43/FUS proteinopathies.

Neuropharmacology of the anxiolytic drug opipramol, a sigma site ligand

Although opipramol is structurally related to imipramine, it does not represent a tricyclic antidepressant drug as it does not inhibit the neuronal uptake of norepinephrine and/or serotonin. Unlike imipramine it is a rather potent sigma ligand with modest subclass selectivity which is similar in vitro as well as ex vivo. Opipramol is active in several behavioural paradigms indicative of anxiolytic properties at doses (1-10 mg/kg), which are also needed to occupy sigma binding sites. Somewhat higher doses (10-20 mg/kg) are needed for "antidepressant like" effects. The data allow the conclusion that interaction with sigma sites is involved in the anxiolytic and antidepressant effects of opipramol albeit a contribution of its weaker D (2)-antagonistic and 5-HT2-antagonistic properties cannot be totally be excluded.

Specific modulation of sigma binding sites by the anxiolytic drug opipramol

The atypical anxiolytic and antidepressive drug opipramol binds with high affinity to sigma1 and somewhat lower affinity to sigma2 sites. After subchronic treatment, opipramol significantly down-regulated sigma2 but not sigma1 sites. This effect was not seen for imipramine, citalopram, and reboxetine under similar conditions. On the other hand, only imipramine reduced the number of sigma1 sites. It is suggested that effects at sigma2 sites are involved in the anxiolytic properties of opipramol.

Some behavioral effects of 1,3-di-o-tolylguanidine, opipramol and sertraline, the sigma site ligands

1,3-Di-o-tolylguanidine (DTG), opipramol (OPI) and sertraline (SER), sigma site ligands, were studied in Wistar rats and Albino Swiss mice, mainly with regard to their interaction with dopamine drugs. DTG and SER (at the highest doses only) decreased the spontaneous locomotor activity. DTG did not change the amphetamine locomotor hyperactivity, while OPI and SER decreased it. The amphetamine stereotypy was slightly increased (prolonged) by all the three drugs. OPI antagonized the locomotor hyperactivity, stereotypy, aggression and climbing, all those being induced by apomorphine; DTG inhibited only the aggression, while SER-the aggression and climbing (the latter was also inhibited by paroxetine, which showed no affinity for sigma sites). DTG and SER (but not paroxetine) were able to increase the locomotor hyperactivity induced by quinpirole. That effect was antagonized by OPI which-when given alone-did not affect the quinpirole hyperlocomotion. The reserpine-induced akinesia was not affected by DTG, OPI or SER; the L-DOPA hyperactivity in reserpinized rats was changed (increased) by DTG only. DTG and SER (also paroxetine and citalopram), but not OPI, increased the cocaine locomotor hyperactivity. All the three sigma ligands given alone did not evoke catalepsy; the haloperidol- and spiperone-induced catalepsy was attenuated by DTG and OPI, but increased by SER. The MK-801-induced hyperactivity was decreased by DTG, but increased by OPI and SER. In the forced swimming test, only DTG slightly reduced the immobility time; the reduction of the immobility time induced by MK-801 was not changed by DTG, but increased by OPI and SER. Only DTG evoked a dose-dependent decrease in the body temperature, which was not changed by rimcazole. The above results indicate that the sigma site ligands studied differ in their pharmacological profile; however, it is still difficult to determine unequivocally whether they show agonistic or antagonistic properties.

Opipramol, a potent sigma ligand, is an anti-ischemic agent: neurochemical evidence for an interaction with the N-methyl-D-aspartate receptor complex in vivo by cerebellar cGMP measurements

Opipramol, a potent sigma ligand and a tricyclic antidepressant compound, provided significant neuronal protection (P less than 0.0001) against ischemia-induced neuronal cell loss in the hippocampus in Mongolian gerbils, at a dose of 50 mg/kg (30 min pretreatment). However, opipramol did not offer protection when given 60 min after the ischemic insult. Opipramol decreased basal levels of cGMP in the cerebellum of the mouse and harmaline-induced increases in levels of cGMP, with approximate ED50 values of 4 and 27 mg/kg. Opipramol antagonized methamphetamine- and pentylenetetrazol-induced increases in levels of cGMP. Parenteral administration of opipramol also antagonized the increases in levels of cGMP in the cerebellum of the mouse after the local administration of D-serine, an agonist at the N-methyl-D-aspartate (NMDA)-associated, strychnine-insensitive glycine receptor. These results indicate that opipramol attenuates responses mediated through the NMDA receptor complex. These results further support the functional modulation of the NMDA receptor complex by sigma ligands and provide a neurochemical correlate for the observed anti-ischemic properties of opipramol.

Neurochemical characterization of dopaminergic effects of opipramol, a potent sigma receptor ligand, in vivo

Opipramol, a tricyclic antidepressant drug, potently interacted with sigma recognition sites labelled by [3H](+)-3-hydroxyphenyl)N-(1-propyl)piperidine [( 3H](+)-3-PPP) with a Ki value of 50 +/- 8 nM and with minimal affinity for phencyclidine receptors (Ki greater than 30,000 nM). Opipramol potently increased the metabolism of dopamine in the striatum, olfactory tubercle and pyriform cortex of the rat and increased the release of dopamine from the striatum of the mouse, as measured by increases in the levels of 3-methoxytyramine in vivo. Opipramol increased plasma prolactin in the rat, only at a dose as large as 50 mg/kg dose. Irreversible inactivation of dopamine receptors by EEDQ (N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline) did not affect the opipramol-induced increases in levels of dihydroxyphenylacetic acid (DOPAC) in the striatum of the rat, indicating a predominant role of activation of sigma receptors in the dopaminergic effects of opipramol. However, pretreatment with the putative sigma ligand, rimcazole, markedly potentiated the ability of opipramol to increase the metabolism of release of DA in the striatum of the mouse in vivo. These results suggest that rimcazole and opipramol interact at two distinct receptors, the pharmacological significance of which is yet to be elucidated.

5-Hydroxytryptamine uptake and imipramine binding sites in neurotumor NCB-20 cells

NCB-20 cells (neuroblastoma X fetal Chinese hamster brain hybrids) are equipped with a [3H]5-hydroxytryptamine [( 3H]5-HT) uptake system and [3H]imipramine recognition sites. Approximately 80% of the radioactivity taken up by cells incubated with [3H]5-HT was identified with 5-HT. [3H]5-HT uptake was temperature-dependent, partially sodium-dependent, saturable (Km = 7.3 +/- 0.6 microM; Vmax = 2.0 +/- 0.6 pmol/min/mg), and inhibited by clomipramine, imipramine, fluoxetine, and desipramine, but not by iprindole, mianserin, or opipramol. Lineweaver-Burk plots showed a competitive type of inhibition by imipramine and fluoxetine. [3H]5-HT uptake was not inhibited by nisoxetine or benztropine. [3H]Imipramine binding sites had a KD of 12 +/- 2 nM and a Bmax of 22 +/- 7 pmol/mg protein. The binding was sodium-sensitive although to a lesser extent than that found with brain membranes. Imipramine binding was displaced by tricyclic antidepressants with the following order of potency: clomipramine greater than imipramine greater than fluoxetine greater than desipramine much greater than iprindole = mianserin greater than opipramol. These results suggest that imipramine binding sites are present together with the 5-HT uptake sites in NCB-20 cells and that these sites interact functionally but are different biochemically.

On the central antiserotonin activity of benzoctamine and opipramol

Benzoctamine inhibited the head twitch reaction induced by L-5-hydroxytryptophan (5-HTP) in mice and by 5-methoxytryptamine (5-MT) in rats pretreated with tranylcypromine. It also antagonized tryptamine (TRP)-induced clonic convulsions of forepaws in rats. Opipramol had no effect in the 5-MT test and appeared to be a weak antagonist in the 5-HTP and TRP tests. Both drugs, of which benzoctamine was a more potent antagonist, inhibited hyperthermia induced by LSD in rabbits. Benzoctamine abolished also LSD-or quipazine-induced stimulation of the flexor reflex in spinal rats; the above effect did not depend on noradrenolytic action of the drug. Opipramol was ineffective as an LSD or quipazine antagonist in this test. These results suggest that benzoctamine blocks the central postsynaptic serotonin receptors. This effect may contribute to the anxiolytic effect of the drug.

A quantitative study of the anticholinergic action of several tricyclic antidepressants on the rat isolated fundal strip

1. Investigations were carried out on the antagonism of the action of carbamylcholine chloride on the isolated fundus of the rat stomach by several tricyclic antidepressants.2. The anticholinergic potency of the compounds was in the order: GP 45437>amitriptyline>protriptyline>desmethylimipramine>opipramol. All of the antagonists were less effective than atropine.3. Statistical analysis was carried out to determine whether the theory of competitive antagonism would fit the data obtained.

Analysis of the inhibition of pethidine N-demethylation by monoamine oxidase inhibitors and some other drugs with special reference to drug interactions in man

1. N-Demethylation of pethidine was studied in microsomal suspensions from unstarved male rat liver and the N-demethylase identified as belonging to the class of hepatic microsomal mixed function oxidases.2. A study of the structure/action relationships of compounds inhibiting pethidine N-demethylase revealed that hydrazine derivatives including phenylhydrazine, methylphenylhydrazine and mebanazine were all potent competitive inhibitors.3. Pethidine N-demethylase was only slightly inhibited by histamine and amphetamine but not by adrenaline and ephedrine nor by several miscellaneous compounds including piperidine, N-ethylpiperidine, N-methylpiperidine, N-methylammonium, hydrallazine or pethidinic acid.4. Several psychotropic drugs were all found to be potent competitive inhibitors of pethidine N-demethylase. These included monoaminoxidase inhibitors (the most active being nialamide and phenoxypropazine [K(i)=0.01 mM]; the least active iproniazid [K(i)=1.05 mM]); the tranquillizers promazine, propiomazine and chlorpromazine and tricyclic antidepressants (opipramol [K(i)=0.01 mM], imipramine [K(i)=0.03 mM], desipramine [K(i)=0.03 mM] and amitryptyline [K(i)=0.03 mM]). Hydrocortisone [K(i)=0.3 mM], prednisolone [2.8 mM] and nalorphine [0.07 mM] were also inhibitors, whilst SKF 525A was the most active of all [K(i)=0.002 mM].5. These results are discussed in relation to the clinically observed drug interactions which may occur between monoamineoxidase inhibitors and pethidine. It is concluded that since many different groups of drugs, including monoamineoxidase inhibitors, tranquillizers, tricyclic antidepressants, steroids, nalorphine, SKF 525A and barbiturates compete for cytochrome P(450) reductase, it is possible that this mechanism may account, at least in part, for the observed interactions of these various drugs in man.