Hes5 Expression in the Postnatal and Adult Mouse Inner Ear and the Drug-Damaged Cochlea

The Notch signaling pathway is known to have multiple roles during development of the inner ear. Notch signaling activates transcription of Hes5, a homologue of Drosophila hairy and enhancer of split, which encodes a basic helix-loop-helix transcriptional repressor. Previous studies have shown that Hes5 is expressed in the cochlea during embryonic development, and loss of Hes5 leads to overproduction of auditory and vestibular hair cells. However, due to technical limitations and inconsistency between previous reports, the precise spatial and temporal pattern of Hes5 expression in the postnatal and adult inner ear has remained unclear. In this study, we use Hes5-GFP transgenic mice and in situ hybridization to report the expression pattern of Hes5 in the inner ear. We find that Hes5 is expressed in the developing auditory epithelium of the cochlea beginning at embryonic day 14.5 (E14.5), becomes restricted to a particular subset of cochlear supporting cells, is downregulated in the postnatal cochlea, and is not present in adults. In the vestibular system, we detect Hes5 in developing supporting cells as early as E12.5 and find that Hes5 expression is maintained in some adult vestibular supporting cells. In order to determine the effect of hair cell damage on Notch signaling in the cochlea, we damaged cochlear hair cells of adult Hes5-GFP mice in vivo using injection of kanamycin and furosemide. Although outer hair cells were killed in treated animals and supporting cells were still present after damage, supporting cells did not upregulate Hes5-GFP in the damaged cochlea. Therefore, absence of Notch-Hes5 signaling in the normal and damaged adult cochlea is correlated with lack of regeneration potential, while its presence in the neonatal cochlea and adult vestibular epithelia is associated with greater capacity for plasticity or regeneration in these tissues; which suggests that this pathway may be involved in regulating regenerative potential

LRH-1 NUTRIGENOMICS: The Provision of Lauric Acid Results in the Endogenous Production of the Liver Receptor Homolog-1 Ligand, Dilauroylphosphatidylcholine, and LRH-1 Transactivation

ABSTRACTBackgroundThe unusual phosphatidylcholine species, dilauroylphosphatidylcholine (DLPC), has been reported to bind and activate the orphan nuclear receptor, liver receptor homolog-1 (LRH-1). To date, DLPC has not been reported endogenously in metabolomic databases.ObjectiveHerein, we test the hypothesis that the provision of the acyl constituent of DLPC, lauric acid (C12:0), a saturated fatty acid rich in tropical oils such as coconut oil, will 1) result in endogenous DLPC production and 2) enhance LRH-1 transcriptional activity.MethodsWe measured DLPC following provision of C12:0 to HepG2 cells, C57/BL6J mice, and to healthy human participants in an acute, randomized, controlled cross-over trial. LRH-1fl/fl and LRH-1fl/fl Albumin-Cre mice were used in ex vivo and in vivo approaches. to assess the impact of C12:0 on LRH-1 target gene expression. 1-13C-lauric acid and methyl-d9-choline were used to assess DLPC production dynamics.ResultsDLPC was not observed in any C12:0-free approach. Provision of C12:0 in the culture media or to C57/BL6J mice resulted in the rapid production of DLPC, including DLPC’s presence in multiple LRH-1 expressing tissues. Coconut oil-fed human participants exhibited DLPC in postprandial serum samples. Ex vivo and in vivo C12:0 provision resulted in increased mRNA expression of LRH-1 target genes, an effect that was not observed in hepatic knockout mice. Methyl-d9-choline administration revealed a complex reliance on CDP-choline-derived DLPC.ConclusionC12:0 provision results in endogenous production of the LRH-1 ligand, DLPC, and LRH-1 transcriptional activation phenotypes. Our findings highlight pleiotropic effects of lauric acid, a common hypercholesterolemic dietary saturated fatty acid, secondary to LRH-1 agonism.</jats:sec