A pilot investigation of differential hydroxymethylation levels in patient-derived neural stem cells implicates altered cortical development in bipolar disorder

Introduction

Bipolar disorder (BD) is a chronic mental illness characterized by recurrent episodes of mania and depression and associated with social and cognitive disturbances. Environmental factors, such as maternal smoking and childhood trauma, are believed to modulate risk genotypes and contribute to the pathogenesis of BD, suggesting a key role in epigenetic regulation during neurodevelopment. 5-hydroxymethylcytosine (5hmC) is an epigenetic variant of particular interest, as it is highly expressed in the brain and is implicated in neurodevelopment, and psychiatric and neurological disorders.

Methods

Induced pluripotent stem cells (iPSCs) were generated from the white blood cells of two adolescent patients with bipolar disorder and their same-sex age-matched unaffected siblings (n = 4). Further, iPSCs were differentiated into neuronal stem cells (NSCs) and characterized for purity using immuno-fluorescence. We used reduced representation hydroxymethylation profiling (RRHP) to perform genome-wide 5hmC profiling of iPSCs and NSCs, to model 5hmC changes during neuronal differentiation and assess their impact on BD risk. Functional annotation and enrichment testing of genes harboring differentiated 5hmC loci were performed with the online tool DAVID.

Results

Approximately 2 million sites were mapped and quantified, with the majority (68.8%) located in genic regions, with elevated 5hmC levels per site observed for 3' UTRs, exons, and 2-kb shorelines of CpG islands. Paired t-tests of normalized 5hmC counts between iPSC and NSC cell lines revealed global hypo-hydroxymethylation in NSCs and enrichment of differentially hydroxymethylated sites within genes associated with plasma membrane (FDR = 9.1 × 10^-12) and axon guidance (FDR = 2.1 × 10^-6), among other neuronal processes. The most significant difference was observed for a transcription factor binding site for the KCNK9 gene (p = 8.8 × 10^-6), encoding a potassium channel protein involved in neuronal activity and migration. Protein-protein-interaction (PPI) networking showed significant connectivity (p = 3.2 × 10^-10) between proteins encoded by genes harboring highly differentiated 5hmC sites, with genes involved in axon guidance and ion transmembrane transport forming distinct sub-clusters. Comparison of NSCs of BD cases and unaffected siblings revealed additional patterns of differentiation in hydroxymethylation levels, including sites in genes with functions related to synapse formation and regulation, such as CUX2 (p = 2.4 × 10^-5) and DOK-7 (p = 3.6 × 10^-3), as well as an enrichment of genes involved in the extracellular matrix (FDR = 1.0 × 10^-8).

Discussion

Together, these preliminary results lend evidence toward a potential role for 5hmC in both early neuronal differentiation and BD risk, with validation and more comprehensive characterization to be achieved through follow-up study.

Bipolar depression in pediatric populations : epidemiology and management

Depression in children and adolescents with bipolar disorder is more commonly observed than mania or hypomania, and is associated with significant functional disability in multiple environmental realms. Optimal management of pediatric bipolar depression is often defined by its multimodal nature with emphasis on both psychopharmacological and psychosocial treatment. This article provides a brief overview of the epidemiology and clinical course of pediatric bipolar depression, a clinically-oriented guide to the evidence-based psychopharmacological and psychosocial management of bipolar depression in youth, and suggestions on how best to integrate medication and therapy. Recommended treatment for bipolar depression in pediatric populations usually includes both medication and psychosocial interventions given a paucity of double-blind, placebo-controlled psychopharmacological studies. Lithium and lamotrigine are feasible and tentatively efficacious options; however, treatment with quetiapine monotherapy may be no better than placebo. Furthermore, some youth may be at heightened risk for developing manic symptoms after treatment with selective serotonin reuptake inhibitors (SSRIs). Psychotherapy, either alone or adjunctively with medications, provides practitioners with a safe and feasible alternative. Interpersonal and Social Rhythm Therapy for Adolescents (IPSRT-A), Child- and Family-Focused Cognitive Behavioral Therapy (CFF-CBT), Dialectical Behavior Therapy for Adolescents (DBT-A), family psychoeducation, and Family Focused Therapy for Adolescents (FFT-A) are evidence-based treatments available to clinicians treating youth with bipolar depression.