Serotonin receptor 2C regulates neurite growth and is necessary for normal retinal processing of visual information

Abstract

Serotonin (5HT) is present in a subpopulation of amacrine cells, which form synapses with retinal ganglion cells (RGCs), but little is known about the physiological role of retinal serotonergic circuitry. We found that the 5HT receptor 2C (5HTR2C) is upregulated in RGCs after birth. Amacrine cells generate 5HT and about half of RGCs respond to 5HTR2C agonism with calcium elevation. We found that there are on average 83 5HT+ amacrine cells randomly distributed across the adult mouse retina, all negative for choline acetyltransferase and 90% positive for tyrosine hydroxylase. We also investigated whether 5HTR2C and 5HTR5A affect RGC neurite growth. We found that both suppress neurite growth, and that RGCs from the 5HTR2C knockout (KO) mice grow longer neurites. Furthermore, 5HTR2C is subject to post-transcriptional editing, and we found that only the edited isoform's suppressive effect on neurite growth could be reversed by a 5HTR2C inverse agonist. Next, we investigated the physiological role of 5HTR2C in the retina, and found that 5HTR2C KO mice showed increased amplitude on pattern electroretinogram. Finally, RGC transcriptional profiling and pathways analysis suggested partial developmental compensation for 5HTR2C absence. Taken together, our findings demonstrate that 5HTR2C regulates neurite growth and RGC activity and is necessary for normal amplitude of RGC response to physiologic stimuli, and raise the hypothesis that these functions are modulated by a subset of 5HT+/ChAT-/TH+ amacrine cells as part of retinal serotonergic circuitry. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Single cell transcriptome profiling of retinal ganglion cells identifies cellular subtypes

“…RGCs were purified from both sexes of postnatal day 5 mice eyes single-cell suspension (separately for the left and right eyes) by immunopanning for Thy1 (CD90, MCA02R, Serotec) after depletion of macrophages (using anti-mouse macrophage antibody, AIA31240, Accurate Chemical) and washing off the nonadherent cells, following our established protocol 19 . To confirm purity and survivability of RGCs, cells were plated and cultured in defined growth medium 19 , 21 , 24 , and immunostained after 12 h with an RGC marker RBPMS (1832-RBPMS, PhosphoSolutions), neuronal marker Tuj1 (MMS-435P, BioLegend), and DAPI (Thermo Fisher Scientific). As shown in Fig.…”

“…Here, we purified RGCs in large numbers from pre-eye-opening age 3 , 19 – 21 , and performed scRNA-seq profiling with an improved, next generation droplet-based method 22 . We detected, on average, 5000 genes at a depth of ~100,000 reads per cell in 6225 RGCs, which represent over 10% of total RGC population.…”

Effects of antipsychotic drugs on neurites relevant to schizophrenia treatment

“…5‐HT2C receptors have nonedited and edited forms . The edited isoform of 5‐HT2C receptor has a suppressive effect on neurite growth, which could be reversed by a 5‐HT2C receptor inverse agonist . Commonly prescribed atypical antipsychotic drugs including olanzapine, clozapine, and risperidone are potent 5‐HT2A receptors ( p Ki = < 8 nM, < 8 nM, but > 9 nM, respectively) and 5‐HT2C receptor ( p Ki = < 9 nM, < 8 nM, and < 8 nM, respectively) antagonists .…”

The Role of Axon Transport in Neuroprotection and Regeneration

“…In the case of KLFs, where developmental upregulation of KLF9 and KLF4 and downregulation of KLF6 and KLF7 are coincident with the reduction of intrinsic regenerative capacity of RGCs, reversing these expression patterns in adult RGCs or in other CNS neuron pathways after injury allows sprouting or long‐distance regeneration (Moore et al, ; Blackmore et al, ; Apara et al, ; Wang et al, ). Exploring the molecular mechanisms of the KLFs further, identification of co‐factors such as JNK3 and STAT3, and downstream targets such as serotonin receptors and dual‐specificity phosphatase 14 (DUSP14) (Qin et al, ; Apara et al, ; Trakhtenberg et al, ; Galvao et al, ) have led to broader understanding of the biology of intrinsic capacity for axon growth. What other molecular targets do KLF family transcription factors and other intrinsic regulators of axon growth affect?…”