Effects of fingolimod administration in a genetic model of cognitive deficits

Abstract

Notwithstanding recent advances, cognitive impairments are among the most difficult-to-treat symptoms in neuropsychiatric disorders. Deficits in information processing contributing to memory and sociability impairments are found across neuropsychiatric-related disorders. Previously, we have shown that mutations in the DTNBP1 gene (encoding dystrobrevin-binding protein 1 [dysbindin-1]) lead to abnormalities in synaptic glutamate release in the prefrontal cortex (PFC) and hippocampus and to cognitive deficits; glutamatergic transmission is important for cortical recurrent excitation that allows information processing in the PFC. To investigate possible means of restoring glutamate release and improving cognitive impairments, we assess the effects of increasing endogenous levels of brain-derived neurotrophic factor (BDNF) in a dysbindin-1-deficient mouse model. Increasing endogenous levels of BDNF may aid in remediating cognitive deficits, given the roles of BDNF in synaptic transmission, plasticity, and neuroprotection. To increase BDNF, we use a novel strategy, repeated intraperitoneal injections of fingolimod (Gilenya). Sphingolipids have recently been shown to have therapeutic value in several neurology-related disorders. Both wild-type (WT) and mutant (MUT) genotypes were tested for sociability and recognition memory, followed by measuring endogenous BDNF levels and presynaptic [Ca²⁺ ]_i within the PFC. Both genotypes were treated for 1 week with either saline or fingolimod. Relative to WT mice, MUT mice demonstrated impairments in sociability and recognition memory and lower presynaptic calcium. After fingolimod treatment, MUT mice exhibited significant improvements in sociability and recognition memory and increases in presynaptic calcium and endogenous concentrations of BDNF. These results show promise for counteracting the cognitive impairments seen in neuropsychiatric disorders and may shed light on the role of dysbindin-1. © 2016 Wiley Periodicals, Inc.

Keywords: dysbindin; fingolimod; glutamate; prefrontal cortex.

Fig. 1.

A: Sociability of dysbindin-1 MUT mice as measured by the social choice/approach task. Relative to WT mice (n = 12), dysbindin-1 MUT mice (n = 12) exhibited lower interaction times with NM1 (★P < 0.0109). After fingolimod treatment, dysbindin-1 MUT mice (n = 13) showed normalized levels of interaction with NM1; the interaction is significantly greater compared with saline-treated counterparts (n = 12; ★P < 0.018). B: Assessing preference for social novelty in dysbindin-1 MUT mice. Given the choice between a past and a novel social interaction, dysbindin-1 MUT mice (n = 9) exhibited significantly lower interaction times with NM2 (★P = 0.0104) compared with WT mice (n = 9). After fingolimod treatment, dysbindin-1 MUT mice (n = 10) showed normalized levels of interaction with NM2, significantly greater compared with saline treatment (n = 9; ★P = 0.0173). C: Recognition ratio as a measure of memory function in dysbindin-1 MUT mice. WT mice showed no deficits in recognition memory when given the choice between a past and a novel social interaction, as measured by the recognition ratio. However, relative to WT mice, dysbindin-1 MUT mice exhibited significant reductions (★★P < 0.001) in recognition. After treatment with fingolimod, dysbindin-1 MUT mice showed significant improvement in recognition ratio (★P < 0.05) compared with the saline-treatment group. SAL, saline.

Fig. 2.

ELISA measuring levels of endogenous BDNF in the PFC across both genotype and treatment groups. Dysbindin-1 MUT mice (n = 8) showed slightly lower levels of BDNF in the PFC compared with their WT counterparts (n = 7) and a significant increase (n = 9; paired t-test, ★P < 0.022) after fingolimod treatment. SAL, saline.

Fig. 3.

Effect of fingolimod treatment on PFC presynaptic calcium concentration as measured by fluorescent calcium indicators. Baseline levels of intracellular calcium did not significantly differ between genotype, as measured by fluo-4 and fluo-3 (WT SAL, n = 9; MUT SAL, n = 6). After treatment, fluo-4 measures showed significant increases in intracellular calcium in both WT (n = 9; ★★P = 0.001) and dysbindin-1 MUT (n = 6; ★★★P < 0.0001) mice. Both dyes indicate a near doubling of intracellular calcium for both genotypes after treatment with fingolimod. SAL, saline.