Brain Network Analysis of EEG Recordings Can Be Used to Assess Cognitive Function in Teenagers With 15q13.3 Microdeletion Syndrome

Augmented hippocampal up-regulation of immune modulators following a peripheral immune challenge in a hemizygous mouse model of the 15q13.3 microdeletion

The strongest known genetic risk factor for generalized epilepsy is the human hemizygous 15q13.3 microdeletion (MD). This 1.5 Mb MD encompasses six genes, including CHRNA7 encoding the alpha7 subunit that forms the homo-pentameric nicotinic acetylcholine receptor, a known regulator of the immune system. In the CNS, hyper activation of neuroimmune responses contributes to increased seizure susceptibility. In a mouse model with a hemizygous deletion of the orthologous region (Df(h15q13)/+) (Het), we previously demonstrated increased hippocampal expression of inflammatory cytokines compared to wildtype (WT) mice following a mild peripheral immune challenge. To further characterize neuroimmune responses, hippocampal mRNA expression of the chemokines CXCL2 and CXCL10, and the Gap junction protein connexin 43 (GJA1), all of which are implicated in neuronal hyperexcitability, were determined along with additional immune related targets. Three hours after a lipopolysaccharide (LPS, 0.1 mg/kg) or polyinosinic:polycytidylic acid (Poly(I:C), 5 mg/kg) injection (i.p.), hippocampi were collected, mRNA extracted, and cDNA prepared for qPCR. The results demonstrate extensive upregulation of CXCL2 and CXCL10 expression by LPS and Poly(I:C) (up to 200-fold CXCL2, up to 600-fold CXCL10) (p < 0.0001) with genotype x treatment interactions for CXCL2 by LPS (p < 0.007). Responses to treatment were far smaller in magnitude for all other targets. LPS and Poly(I:C) induced statistically similar increases for Toll-like receptor (TLR)2, TLR4, HMGB1, and C3, but Poly(I:C) had stronger effects on GJA1, TLR3, C1qA and MARCO expression. Remarkably, TLR3 was the only target with significant downregulation of expression after Poly(I:C) (p < 0.0001). In addition, genotype x treatment interactions were detected for TLR3, TLR4, HMGB1, and C1qA (p < 0.02). Thus, a peripheral immune challenge caused extensive increases for CXCL2 and CXCL10, and the genotype-treatment interactions that was seen for several targets, underscored the augmented neuroinflammatory response in mice carrying the MD. Of note is the dramatic upregulation of CXCL10 by low dose Poly(I:C). CXCL10 causes hyperexcitability via neuronal CXCR3 activation. Thus, even an asymptomatic viral infection may increase seizure susceptibility. In summary, a peripheral immune challenge causes strong upregulation of hippocampal inflammatory mediators implicated in neuronal excitability which is particularly detrimental for individuals with high seizure susceptibility, such as carriers of the 15q13.3 MD.

Peripheral immune challenges elicit differential up-regulation of hippocampal cytokine and chemokine mRNA expression in a mouse model of the 15q13.3 microdeletion syndrome

The human heterozygous 15q13.3 microdeletion is associated with neuropathological disorders, most prominently with epilepsy and intellectual disability. The 1.5 Mb deletion encompasses six genes (FAN1 [MTMR15], MTMR10, TRPM1, KLF13, OTUD7A, and CHRNA7); all but one (TRPM1) are expressed in the brain. The 15q13.3 microdeletion causes highly variable neurological symptoms, and confounding factors may contribute to a more severe phenotype. CHRNA7 and KLF13 are involved in immune system regulation and altered immune responses may contribute to neurological deficits. We used the Df[h15q13]/+ transgenic mouse model with a heterozygous deletion of the orthologous region (Het) to test the hypothesis that the microdeletion increases innate immune responses compared to wild type (WT). Male and female mice were acutely challenged with the bacteriomimetic lipopolysaccharide (LPS, 0.1 mg/kg, i.p.) or the viral mimetic polyinosinic:polycytidylic acid (Poly(I:C), 5 mg/kg). Hippocampal mRNA expression of pro-inflammatory cytokines and chemokines were determined three hours after injection using quantitative PCR analysis. In controls, expression was not affected by sex or genotype. LPS and Poly(I:C) resulted in significantly increased hippocampal expression of cytokines, chemokines, and interferon-γ (IFNγ), with more robust increases for TNF-α, IL-6, IL-1β, CXCL1, and CCL2 by LPS, higher induction of IFNγ by Poly(I:C), and similar increases of CCL4 and CCL5 by both agents. Generally, Hets exhibited stronger responses than WT mice, and significant effects of genotype or genotype × treatment interactions were detected for CXCL1 and CCL5, and IL-6, IL-1β, and CCL4, respectively, after LPS. Sex differences were detected for some targets. LPS but not Poly(I:C), reduced overnight burrowing independent of sex or genotype, suggesting that LPS induced sickness behavior. Thus, mice carrying the microdeletion have an increased innate immune response following a LPS challenge, but further studies will have to determine the extent and mechanisms of altered immune activation and subsequent contributions to 15q13.3 microdeletion associated deficits.