Chellappa, A. | bioRxiv Science

bioRxiv2019

Studying cellular functions in bipolar disorder: Are there specific predictors of lithium response?

BackgroundLithium is the first-line mood stabilizer for the treatment of bipolar disorder (BD). In order to interrogate cellular phenotypes related to disease and lithium treatment response, this study used neural precursor cells (NPCs) and lymphoblastoid cell lines (LCLs) from BD patients who are well characterized for clinical lithium response.\n\nMethodsBD patients diagnosed according to the DSM-IV criteria; were recruited from the outpatient services of the National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India. Clinical lithium response was assessed using the \"Alda scale\" and \"NIMH Retrospective Life chart method\". The controls were ethnically matched healthy subjects with no family history of neuropsychiatric illness. NPCs from two BD patients from the same family who clearly differed in their clinical response to lithium were chosen, and compared with healthy population controls. Whole transcriptome sequencing (RNA-Seq) and analysis were performed, with and without in vitro lithium (1mM for 7 days). In addition, mitochondrial membrane potential (MMP), cell viability and cell proliferation parameters were examined. Experiments were also performed in 25 LCLs from BD patients (16 lithium responders and 9 lithium non-responders), and 12 healthy control LCLs, to evaluate them in a system amenable to clinical translation.\n\nResultsRNA-Sequencing and analysis did not reveal differences in NPCs on in vitro lithium treatment. MMP was lower in BD, both in NPCs and LCLs; reversal with in vitro lithium happened only in LCLs and was unrelated to lithium response. Cell proliferation was higher in BD compared to controls, and there was no change on lithium addition. Cell viability assays indicated greater cell death in BD; which could only be rescued in LCLs of clinical lithium responders. The latter finding was associated with enhanced BCL2 and GSK3B expression with in vitro lithium.\n\nDiscussionOverall, our study findings indicate that there are cellular phenotypes related to the disease (mitochondrial potential, cell proliferation) in NPCs and LCLs. We also observed clinical lithium response related phenotypes (cell viability, BCL2/ GSK3B expression) in LCLs. The next step would be to evaluate a larger set of PBMCs from clinical lithium response groups of BD to derive cellular phenotypes related to direct clinical application.

neuroscience↗

bioRxiv2018

Novel KCNJ10 mutation identified in a SeSAME family compromise channel function and impairs Drosophila locomotor behavior

Dysfunction in inwardly-rectifying potassium channel Kir4.1 has been implicated in SeSAME syndrome, an autosomal-recessive (AR), rare, multi-systemic disorder. However, not all neurological, intellectual disability and comorbid phenotypes in SeSAME syndrome can be mechanistically linked solely to Kir4.1 dysfunction. We therefore performed whole exome sequencing and identified additional genetic risk-elements that might exert causative effects either alone or in concert with Kir4.1 in a family diagnosed with SeSAME syndrome. Two variant prioritization pipelines based on AR inheritance and runs of homozygosity (ROH), identified two novel homozygous variants in KCNJ10 and PI4KB and five rare homozygous variants in PVRL4, RORC, FLG2, FCRL1, NIT1 and one common homozygous variant in HSPA6 segregating in all four patients. The novel mutation in KCNJ10 resides in the cytoplasmic domain of Kir4.1, a seat of phosphatidyl inositol bisphosphate (PIP2) binding. The mutation altered the subcellular localization and stability of Kir4.1 in patient-specific lymphoblastoid cells (LCLs) compared to parental controls. Barium-sensitive endogenous K+ currents in patient-specific LCLs using whole-cell patch clamp electrophysiology revealed membrane depolarization and defects in inward K+ ion conductance across the membrane, thereby suggesting a loss-of-function effect of KCNJ10 variant. Altogether our findings implicate the role of new genes in SeSAME syndrome without electrolyte imbalance and thereby speculate the regulation of Kir4.1 channel activity by PIP2 and integrin-mediated adhesion signaling mechanisms.

neuroscience↗