Resumen de Phenotyping of sigma-1 receptor knock-out rodents
The sigma-1 receptor is a chaperone that is primarily expressed in the mitochondria-associated endoplasmic reticulum (MAM). It was cloned years ago from different tissues of various species and recently its structure has been published.
In 2003, the first knock-out (KO) mouse for the sigma-1 receptor wasgenerated. These mice served to demonstrate the involvement of the sigma-1 receptor in acute and chronic pain. In addition to pain, the sigma-1 receptor has been implicated in other physiological processes and pathological conditions including depression and addiction. The sigma-1 receptor has also been shown to be associated with the regulation of other proteins, including dopamine transporters (DAT) and serotonin (SERT). Welab Barcelona has a KO line for the sigma-1 receiver in both mice and rats. In this work, the behavioural response of mice in two models of depression has been characterized, and the physiological and behavioural phenotyping of KO rats has been carried out, with special attention to the possible effects of the absence of the receptor in models of depression and addiction.
By means of CRISPR / Cas9 technology, two KO strains for the sigma-1 receptor with deletions of 218 bp and 7 bp were obtained. Neither strain showed significant differences in the Irwin test, spontaneous locomotor activity, open field test, startle response, or pre-pulse inhibition. In contrast, the results obtained in response to mechanical or thermal stimulation led us to select the strain with a deletion of 218 bp. Using this strain, WT (+/+), KO heterozygous (+/-) and KO homozygous (-/-) rats were phenotyped. No significant differences were found in growth or survival curves, nor in most of the assessed physiological or behavioural parameters. Regarding depression, no significant difference was found in the acute study after administration of fluoxetine (an antidepressant with sigma-1 affinity) or venlafaxine (without sigma-1 affinity) on the day of the test. This was an expected outcome, based on the literature and previous findings regarding the ineffectiveness of antidepressants in acute treatment. In the sub-acute study, the tendency for lower immobility during training observed in mice was confirmed. On test days 1 and 7, neither fluvoxamine nor venlafaxine showed any efficacy in reducing immobility. In contrast, at day 14, the two antidepressants significantly reduced immobility only in KO rats. Given that there is no sigma-1 receptor in these rats and that both antidepressants showed activity, regardless of whether they had sigma-1 affinity, it seems that the efficacy may be due to some change in their action on SERT.
Regarding locomotor activity, as a surrogate measure of addictive potential, the set of results seems to indicate a greater role of the sigma-1 receptor in rearing activity, especially as stereotyped behaviour rather than its merely exploratory activity. whereas the difference between the two genotypes occurs mainly at high doses. There have been fewer differences in locomotor activity and, surprisingly, no difference in cocaine, that has a sigma-1 affinity. Differences between mobility and rearing can be assigned to the dopaminergic pathways involved, meso-limbic for mobility, and nigro-striatal for stereotypes.
Regarding the expression levels of the transporters dopamine (DAT), serotonin (SERT) and norepinephrine (NET), in the Pre-frontal cortex the expression of both SERT and DAT was significantly increased, which could be behind the effects observed in the depression model and locomotor activity. In line with what has been described in the literature, regarding the regulatory role of the sigma-1 receptor on other proteins, the absence of the receptor may induce the regulation of associated proteins and conditioning the response to the evaluated drugs.
In conclusion, in rats, deletion of the gene encoding the sigma-1 receptor generates a viable phenotype very similar to the WT strain under normal conditions. Behavioural response under conditions of environmental stimulation and / or pharmacological treatment, reveals some differences between WT and KO, in both mice and rats. The absence of the receptor seems to lead to the adaptation of other proteins. The results further support that the sigma-1 receptor may be involved in the development and treatment of depression and addiction.
