Differential regulation of depression associated interferon-inducible genes identified in HCV patients during IFN-alpha therapy in hippocampal and prefrontal cortex mouse neurons

Aims: In previous studies, 16 genes strongly associated with the development of severe depressive side effects during the standard therapy with IFN-α and ribavirin were identified in the peripheral blood of HCV patients. In addition, an enhanced expression of such genes was found in psychiatric patients undergoing severe depression and in autopsy brain tissue from suicidal individuals.

Aims: The present study elucidates the effects of IFN-α and Poly I:C costimulation, which would promote the activation of INF-α and TLR3 pathways, on the expression of the identified interferon-inducible genes and inflammatory-related cytokines in two brain areas closely related to depression development, hippocampus (HP) and prefrontal cortex (PC), by using primary cultured mouse neurons.

Methods: Hippocampal and PC neurons were isolated from 17-day-old embryos of C57 BL/6 mice, and cultured at 1,2×10⁵ cells/well, initially in DMEM and 10% FCS and later in Neurobasal medium. At day 9 of culture, stimulation was performed using 1000 IU of mouse IFN-αA and 100µg/ml of Poly I:C, and cells were collected after 24 hours. The expression of 10 of the depression-related interferon-inducible genes (DRIIs), as well as of Isg15, IFN-β, IL-6, Ip-10 and Ccl5 was assessed using real time PCR.

Results: The stimulation with mouse IFN promoted a significant ISG15, IFN-β, IL-6, Ip-10 and Ccl5 upregulation in both brain areas. Regarding to the DRIIs, differenzial responses to the treatment were observed, ranging from a non- or mild response in one or both studied areas (i.e. Dynlt1, showed a significant increase in PC but not in HP), to a strong upregulation, as found in Stat1, Rtp4, Gbp1 and Ube2L6.

Conclusions: Exposition of murine neurons of HP and PC to IFN-α and Poly I:C treatment induces an increase of Isg15 and the proinflammatory cytokines IFN-β, IL-6, Ip-10 and Ccl5 expression. The double treatment is also associated to the modulation of the expression of most of the studied DRIIs, meanwhile others might be under the regulation of different factor(s) absent in this in vitro system. Linked to our previous findings, the upregulation of some DRIIs may be involved in the physiopathological mechanisms underlying IFN-α therapy-associated depression.