Authors :
Presenting Author: Henry Lee, PhD – Boston Children's Hospital
Zijie Jin, MS – Boston Children's Hospital
Gabrielle McGinty, BS – Boston Children's Hospital
Amanda Liebhardt, BS – Boston Children's Hospital
Alexander Rotenberg, MD, PhD – Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
Rationale:
Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare hyper-GABAergic disorder due to impaired catabolism of the inhibitory neurotransmitter g-aminobutyric acid (GABA). Paradoxically, notwithstanding excess GABA, patients with SSADHD are often epileptic. We used RNA-seq coupled with Gene Ontology (GO) and Gene Set Enrichment Analysis (GSEA) in the reversible SSADHD mouse model, Aldh5a1lox-STOP, to analyze gene family expressions. Our objectives were to (1) obtain deeper mechanistic insight into epilepsy in SSADHD, and (2) identify novel anti-epilepsy drug targets for this disorder.
Methods:
Brain tissues were collected from homozygous Aldh5a1lox-STOP (Hom) mice (n=15) at symptomatic stage (postnatal days P16) and age-matched wild-type (WT) control (n=9). In a separate cohort (n=6), adeno-associated virus-encoding Cre (AAV-Cre) was injected at P14 to restore SSADH enzyme, rescuing Hom phenotype, and brain tissues collected at P100. Microdissected cerebral cortex and hippocampus were subjected to RNA-seq in a pilot study, with data mapped using Hisat2 (v2.0.5), analyzed by GO (PANTHER), and GSEA (v4.4.0) performed using MSigDB pre-ranked gene lists with 1000 permutations. Quantitative PCR validated results.
Results:
In the cortex, positive enrichment was found in the m2 gene set ‘neuron markers’ (FDR 0.14, p< 0.001) and ‘postmitotic neurons’ (FDR 0.36, p< 0.001) (Fig. 1A-B). Notable genes include Camk2a, Syp, Gria3, Grin2b, Syt1, and Scn8a, suggesting glutamatergic neurotransmission and excitatory synapse over-representation. Negative enrichment in m8 sets ‘Schwann cell precursors’ (FDR 0.0001, p< 0.001) and ‘inhibitory neurons’ (FDR 0.25, p=0.017), with down-regulated genes Adamts5, Grik3, and Dlx5, suggesting reduced extracellular matrix (ECM) turnover and delayed inhibitory neuron development (Fig. 1C-D). In the hippocampus, positive enrichment in m3 ‘Psip target genes’ (FDR 0.05, p=0.001) revealed mitochondrial tRNA family mt-T enhancement (Fig. 2A). Negative enrichment in m2 ‘oligodendrocytes’ (FDR 0.0, p< 0.001) and m3 ‘miR 7241 targets’ (FDR 0.19, p< 0.001), with down-regulated genes relevant for myelin/oligodendrocytes and protocadherin (