ABSTRACT: Endogenous bioelectric signaling via changes in cellular resting potential (Vmem) is a key regulator of patterning during regeneration and embryogenesis in numerous model systems. Depolarization of Vmem has been functionally implicated in de-differentiation, tumorigenesis, anatomical re-specification, and appendage regeneration. However, no unbiased analyses have been performed to understand genome-wide transcriptional responses to Vmem change in vivo. Moreover, it is unknown which genes or gene networks represent conserved targets of bioelectrical signaling across different patterning contexts and species. Here, we use microarray analysis to comparatively analyze transcriptional responses to specific Vmem depolarization. We compare the response of the transcriptome during embryogenesis (Xenopus development), regeneration (Axolotl regeneration), and stem cell differentiation (human mesenchymal stem cells in culture) to identify common networks across model species that are associated with depolarization. Both sub-network enrichment and PANTHER analyses identified a number of key genetic modules as targets of Vmem change, and also revealed important (well-conserved) commonalities in bioelectric signal transduction, despite highly diverse experimental contexts and species. Depolarization regulates specific transcriptional networks across all three germ layers (ectoderm, mesoderm and endoderm) such as cell differentiation and apoptosis, and this information will be used for developing mechanistic models of bioelectric regulation of patterning. Moreover, our analysis reveals that Vmem change regulates transcripts related to important disease pathways such as cancer and neurodegeneration, which may represent novel targets for emerging electroceutical therapies. Whole bone marrow aspirate from a 25 year-old healthy man was purchased from Lonza through their Research Bone Marrow Donor Program, following approved guidelines of informed consent as previously documented (Sundelacruz et al. 2008, 2013b). Aspirate was plated at a density of 10 mL of aspirate per cm2 in control medium (DMEM with 10% fetal bovine serum (FBS), penicillin (100 U/mL), streptomycin (100 mg/mL), and 0.1 mM nonessential amino acids) supplemented with basic fibroblast growth factor (1 ng/mL) (Invitrogen). Cells were maintained in a humidified incubator at 37°C with 5% CO2. The hMSCs were isolated on the basis of their adherence to tissue culture plastic and were used for experiments between passages two and four. Undifferentiated hMSCs were cultured in control medium. Osteogenic (OS) differentiation medium consisted of αMEM medium supplemented with 10% FBS, penicillin (100 U/mL), streptomycin (100 mg/mL), 10mM β-glycerophosphate, 0.05mM L-ascorbic acid-2-phosphate, and 100nM dexamethasone (Sigma-Aldrich). Vmem was depolarized by (1) addition of Na+/K+ - ATPase-inhibitor ouabain (OB, 10 nM; Sigma-Aldrich) to differentiation medium or (2) elevation of extracellular K+ by adding potassium gluconate (High K+, HK, 40 mM; Sigma-Aldrich) to differentiation medium. Depolarization induced by these concentrations of OB and K+ has been confirmed using voltage-sensitive dyes and/or sharp intracellular recordings [(Sundelacruz et al. 2008) and unpublished data]. OS cells were pre-differentiated for three weeks before the addition of OB or HK for an additional three weeks of culture. The depolarizers were added to the differentiation medium and replenished in subsequent media changes.
