Experimental evidence for the involvement of PDLIM5 in mood disorders in hetero knockout mice

Abstract

Background: Reports indicate that PDLIM5 is involved in mood disorders. The PDLIM5 (PDZ and LIM domain 5) gene has been genetically associated with mood disorders; it's expression is upregulated in the postmortem brains of patients with bipolar disorder and downregulated in the peripheral lymphocytes of patients with major depression. Acute and chronic methamphetamine (METH) administration may model mania and the evolution of mania into psychotic mania or schizophrenia-like behavioral changes, respectively.

Methods: To address whether the downregulation of PDLIM5 protects against manic symptoms and cause susceptibility to depressive symptoms, we evaluated the effects of reduced Pdlim5 levels on acute and chronic METH-induced locomotor hyperactivity, prepulse inhibition, and forced swimming by using Pdlim5 hetero knockout (KO) mice.

Results: The homozygous KO of Pdlim5 is embryonic lethal. The effects of METH administration on locomotor hyperactivity and the impairment of prepulse inhibition were lower in Pdlim5 hetero KO mice than in wild-type mice. The transient inhibition of PDLIM5 (achieved by blocking the translocation of protein kinase C epsilon before the METH challenge) had a similar effect on behavior. Pdlim5 hetero KO mice showed increased immobility time in the forced swimming test, which was diminished after the chronic administration of imipramine. Chronic METH treatment increased, whereas chronic haloperidol treatment decreased, Pdlim5 mRNA levels in the prefrontal cortex. Imipramine increased Pdlim5 mRNA levels in the hippocampus.

Conclusion: These findings are partially compatible with reported observations in humans, indicating that PDLIM5 is involved in psychiatric disorders, including mood disorders.

Figure 1. Gene-trap mutagenesis of Pdlim5.

(A) Insertion site of the gene-trap cassette in intron 8 of the Pdlim5 gene. The inserted sequence (gray box) includes a splice acceptor (SA), β-geo, which is a fusion of β-galactosidase and neomycin phosphotransferase II, and is followed by a stop codon and a polyadenylation signal (pA). (B) Schematic of the gene trap cassette. C) RT-PCR results and genomic genotyping of Pdlim5+/+, Pdlim5+/−. Samples were extracted from the brain and tail. (D) Expected domain structures of wild-type and PDLIM5 mutant proteins. (E) Real-time PCR analysis of Pdlim5 in the prefrontal brains of Pdlim5+/+ (n = 6) and Pdlim5+/− (n = 8) mice [F(1, 12) = 14.0, p = 0.003]. Values are shown as mean ± SD. (F) Representative western blots of Pdlim5 in the prefrontal brains of Pdlim5+/+ and Pdlim5+/−.

Figure 2. Effect of METH administration on locomotor activity and prepulse inhibition.

Relative locomotor activity and prepulse inhibition after acute (A, B, C) and chronic (D, E, F) administration of METH in Pdlim5+/+ and Pdlim5+/− mice. Values are shown as mean ± SD. * p<0.05 and ** p<0.01 by ANOVA.

Figure 3. Effects of PKCε-TIP on locomotor activity and prepulse inhibition response to METH.

Relative locomotor activity (A, B) and prepulse inhibition (C) by the treatment of PKCε-TIP after chronic METH administration. Values are shown as mean ± SD. P values are based on ANOVA. * p<0.05 and ** p<0.01 by ANOVA.

Figure 4. Effect of imipramine treatment on forced swimming.

Immobility time of Pdlim5 hetero KO and wild-type mice in the forced swimming test with saline or chronic imipramine administration. Values are shown as mean ± SD. * p<0.05 and ** p<0.01 by ANOVA.

Figure 5. Relative Pdlim5 expression levels after METH, haloperidol and imipramine administrations in mice brains.

Seven-week-old C57BL/6J male mice were treated with an intraperitoneal injection (i.p.) of METH (3.0 mg/kg, once daily for 14 days) (A, B), haloperidol (1 mg/kg, once daily for 49 days) (C), imipramine (20 mg/kg, once daily for 14 days) (D), or vehicle-saline. The upregulated Pdlim5 expression in the prefrontal cortex of chronic METH-administered mice (A) was confirmed by a separate experiment using a different mice cohort (B). Values are shown as mean ± SD. * p<0.05 and ** p<0.01 by Student’s t test.