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A potential role for somatostatin signaling in regulating retinal neurogenesis.

ABSTRACT: Neuropeptides have been reported to regulate progenitor proliferation and neurogenesis in the central nervous system. However, these studies have typically been conducted using pharmacological agents in ex vivo preparations, and in vivo evidence for their developmental function is generally lacking. Recent scRNA-Seq studies have identified multiple neuropeptides and their receptors as being selectively expressed in neurogenic progenitors of the embryonic mouse and human retina. This includes Sstr2, whose ligand somatostatin is transiently expressed by immature retinal ganglion cells. By analyzing retinal explants treated with selective ligands that target these receptors, we found that Sstr2-dependent somatostatin signaling induces a modest, dose-dependent inhibition of photoreceptor generation, while correspondingly increasing the relative fraction of primary progenitor cells. These effects were confirmed by scRNA-Seq analysis of retinal explants but abolished in Sstr2-deficient retinas. Although no changes in the relative fraction of primary progenitors or photoreceptor precursors were observed in Sstr2-deficient retinas in vivo, scRNA-Seq analysis demonstrated accelerated differentiation of neurogenic progenitors. We conclude that, while Sstr2 signaling may act to negatively regulate retinal neurogenesis in combination with other retinal ganglion cell-derived secreted factors such as Shh, it is dispensable for normal retinal development.

SUBMITTER: Weir K

PROVIDER: S-EPMC8155210 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Purpose: Neuropeptide signaling has been reported to impact neurogenesis in the central nervous system. However, these studies have typically been conducted using pharmacological agents in ex vivo preparations, and in vivo evidence for their developmental function is generally lacking. The goal of this study is to identify the impact of somatostatin signaling on retinal neurogenesis and development both ex vivo and in vivo. Methods: Mouse retinal explants grown ex vivo from E14-P0 and treated with a range of doses of agonist for the somatostatin receptor Sstr2 were multiplexed according to the MULTI-seq protocol and used to generate a single scRNA-seq expression library. Retinas from P0 littermates representing an allelic series (+/+, +/-, -/-) of Sstr2 KO mice were mutliplexed according to the MULTI-seq protocol and used to generate a single scRNA-seq expression library. Retinas from P14 littermates representing an allelic series (+/+, +/-, -/-) of Sstr2 KO mice were mutliplexed according to the MULTI-seq protocol and used to generate a single scRNA-seq expression library. Sequencing was performed on an illumina sequencer. Bcl files were analyzed by Cellranger. Samples were deconvoluted with the deMULTIplex r package and clustering and gene expression analysis were performed with the Seurat and Monocle2 r packages. Results: Cell type proportions were found to be impacted by Sstr2 signaling ex vivo with increasing levels of Sstr2 agonist found to decrease photoreceptor proportion and increase primary progenitor proportion. Sstr2 KO was not found to have an impact on cell type proportion in vivo at either P0 or P14. Sstr2 pharmacologic manipulation and Sstr2 KO did produce complementary gene expression changes in neurogenic progenitors indicating that somatostatin signaling downregulates neurogenesis. Conclusions: Our study demonstrates a role for somatostatin in retinal development by downregulating neurogenesis in neurogenic progenitors. However, it also demonstrates that somatostatin signaling is dispensable for in vivo retinal development and likely redundant with other cell extrinsic signals released during the same period.

Project description:Stress and glucocorticoid hormones regulate hippocampal neurogenesis, but the molecular mechanisms underlying their effects are unknown. We, therefore, investigated the molecular signaling pathways mediating the effects of cortisol on proliferation, neuronal differentiation, and astrogliogenesis, in an immortalized human hippocampal progenitor cell line. In addition, we examined the molecular signaling pathways activated in the hippocampus of prenatally stressed rats, characterized by persistently elevated glucocorticoid levels in adulthood. In human hippocampal progenitor cells, we found that low concentrations of cortisol (100 nM) increased proliferation (+16%), decreased neurogenesis into microtubule-associated protein 2 (MAP2)-positive neurons (-24%) and doublecortin (Dcx)-positive neuroblasts (-21%), and increased differentiation into S100?-positive astrocytes (+23%). These effects were dependent on the mineralocorticoid receptor (MR) as they were abolished by the MR antagonist, spironolactone, and mimicked by the MR-agonist, aldosterone. In contrast, high concentrations of cortisol (100 ?M) decreased proliferation (-17%) and neuronal differentiation into MAP2-positive neurons (-22%) and into Dcx-positive neuroblasts (-27%), without regulating astrogliogenesis. These effects were dependent on the glucocorticoid receptor (GR), blocked by the GR antagonist RU486, and mimicked by the GR-agonist, dexamethasone. Gene expression microarray and pathway analysis showed that the low concentration of cortisol enhances Notch/Hes-signaling, the high concentration inhibits TGF?-SMAD2/3-signaling, and both concentrations inhibit Hedgehog signaling. Mechanistically, we show that reduced Hedgehog signaling indeed critically contributes to the cortisol-induced reduction in neuronal differentiation. Accordingly, TGF?-SMAD2/3 and Hedgehog signaling were also inhibited in the hippocampus of adult prenatally stressed rats with high glucocorticoid levels. In conclusion, our data demonstrate novel molecular signaling pathways that are regulated by glucocorticoids in vitro, in human hippocampal progenitor cells, and by stress in vivo, in the rat hippocampus.

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A potential role for somatostatin signaling in regulating retinal neurogenesis.

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