In multiple pathway analyses, signaling pathways were found in the top 10 rankings. GeneGo analysis of the up-regulated DEGs in BPD L neurons identified the wnt signaling pathway including GSK3β. Ingenuity Pathway Analysis of DEGs showed enrichment of receptor-mediated signaling pathways. One observation was that virtually all of the top pathways identified were associated with GSK3β. This may be due to over-prevalence of GSK3β in IPA pathways; however, GSK3β has been suggested to play a role in the therapeutic effects of lithium [42,47]. Lithium is the treatment of choice for preventing episodes of affective disorder in bipolar subjects and specifically in these Amish families, where good responsiveness and compliance has been documented over decades [24]. In particular, the BPD patients in our study were all good lithium responders based on medication histories recorded longitudinally (see Methods section). Quantitative RT-PCR analysis however failed to show a difference in GSK3β mRNA expression. Since the activity of this enzyme is largely regulated by posttranslational phosphorylation [58,59], future studies of BPD-derived iPS neurons might explore GSK3β protein expression and phosphorylation, as well as the response to lithium. Other components identified in our IPA pathway analysis should also be evaluated.
