Reduced cell proliferation and increased apoptosis in the hippocampal formation in a rat model of Hirschsprung's disease

The Impact of Mutant EDNRB on the Two-End Black Coat Color Phenotype in Chinese Local Pigs

Endothelin Receptor Type B (EDNRB) is expressed in a variety of cells during embryonic stage, including melanocyte precursors cells. Our previous studies found that 11 bp deletion of EDNRB caused the two-end black (TEB) coat color in Chinese pigs. In this study, we aimed to explore the mutant EDNRB on the formation of TEB coat color in Chinese pigs. We constructed recombinant plasmid for wild and mutant EDNRB and EDN1, respectively, and transfected the recombinant plasmid into mouse B16 melanoma cells in groups. Real-time fluorescent quantitative PCR (RT-qPCR) was performed to detect expression of genes that participate in melanin pathway, including PLCγ, Raf, MITF. Comparing to the wild-type EDNRB cells, expression of the three genes in the cell line expressing mutant EDNRB cells was significantly reduced. We measured the melanin content produced by transfected recombinant granulocytes of wild and mutant EDNRB and found that the amount of melanin in mutant EDNRB cells was significantly lower than that of the wild. Wound-healing assay confirmed that the migration and mobility rate of mutant EDNRB cells were significantly lower than the wild. Co-immunoprecipitation further confirmed that mutant EDNRB could not interact with the EDN1 protein. In conclusion, this study revealed that the 11 bp deletion of EDNRB reduced the melanin production, which may be caused by inhibiting the expression of PLCγ, Raf, and MITF. The mutant EDNRB reduced melanocyte migration and could not interact with the EDN1 protein. We explored the effect of mutant EDNRB in Chinese pigs with TEB coat color, and the results provided a reference for exploring molecular mechanism of mutant EDNRB on the formation of TEB coat color pigs.

Colostomy Delays Cell Loss in the Brain and Improves Juvenile Survival in a Neonatal Rat Model of Hirschsprung's Disease

Hirschsprung's disease is a congenital malformation characterized by the absence of enteric ganglia in the distal intestine and gut obstruction. Our previous study indicates the brain pathology during the disease progression. A subpopulation of Hirschsprung's disease patients is also associated with anomalies of the central nervous system. In the investigation, we studied a rat model of Hirschsprung's disease, known as spotting lethal (sl/sl) ETB-/- rats, which carries a spontaneous deletion in endothelin receptor B (human gene name: EDNRB) and manifests a similar phenotype as humans with Hirschsprung's disease. Homozygous mutant sl/sl rats were successfully rescued from premature death by performing colostomy and dramatically survived to their juvenile age. By the body weight measured, their body growth was not revealed to be significantly different between ETB-/- and wildtype ETB+/+ or heterozygous (+/sl) ETB+/- groups while all underwent the same colostomy. Cell loss was investigated in several brain regions by using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay (TUNEL) in ETB+/+, ETB-/-, and ETB+/- rats. Number of TUNEL-positive cells in the cerebellum and the hippocampus of ETB-/- rats was significantly increased compared with that of the ETB+/+ and ETB+/- rats. TUNEL-positive cells were observed in the molecular layer and granular cell layers of the cerebellum. In contrast, no significant difference in the density of TUNEL-positive cells was revealed in the cerebral cortex. These results suggest that either endothelin receptor B sl mutation or colostomy has predominant lasting effects on the cell survival/loss in the cerebellum and hippocampus of adult ETB-/- rats. Our findings provide the information on cellular changes in the brains of patients with Hirschsprung's disease due to congenital EDNRB mutation as well as clinically relevant interventions.

Brain size reductions associated with endothelin B receptor mutation, a cause of Hirschsprung's disease

Background

ET_B has been reported to regulate neurogenesis and vasoregulation in foetal development. Its dysfunction was known to cause HSCR, an aganglionic colonic disorder with syndromic forms reported to associate with both small heads and developmental delay. We therefore asked, "is CNS maldevelopment a more general feature of ET_B mutation?" To investigate, we reviewed the micro-CT scans of an ET_B^−/− model animal, sl/sl rat, and quantitatively evaluated the structural changes of its brain constituents.

Methods

Eleven neonatal rats generated from ET_B^+/− cross breeding were sacrificed. Micro-CT scans were completed following 1.5% iodine-staining protocols. All scans were reviewed for morphological changes. Selected organs were segmented semi-automatically post-NLM filtering: TBr, T-CC, T-CP, OB, Med, Cer, Pit, and S&I Col. Volumetric measurements were made using Drishti rendering software. Rat genotyping was completed following analysis. Statistical comparisons on organ volume, organ growth rate, and organ volume/bodyweight ratios were made between sl/sl and the control groups based on autosomal recessive inheritance. One-way ANOVA was also performed to evaluate potential dose-dependent effect.

Results

sl/sl rat has 16.32% lower body weight with 3.53% lower growth rate than the control group. Gross intracranial morphology was preserved in sl/sl rats. However, significant volumetric reduction of 20.33% was detected in TBr; similar reductions were extended to the measurements of T-CC, T-CP, OB, Med, and Pit. Consistently, lower brain and selected constituent growth rates were detected in sl/sl rat, ranging from 6.21% to 11.51% reduction. Lower organ volume/bodyweight ratio was detected in sl/sl rats, reflecting disproportional neural changes with respect to body size. No consistent linear relationships exist between ET_B copies and intracranial organ size or growth rates.

Conclusion

Although ET_B^−/− mutant has a normal CNS morphology, significant size reductions in brain and constituents were detected. These structural changes likely arise from a combination of factors secondary to dysfunctional ET-1/ET-3/ET_B signalling, including global growth impairment from HSCR-induced malnutrition and dysregulations in the neurogenesis, angiogenesis, and cerebral vascular control. These changes have important clinical implications, such as autonomic dysfunction or intellectual delay. Although further human study is warranted, our study suggested comprehensive managements are required for HSCR patients, at least in ET_B^−/− subtype.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-021-00646-z.

Permanent Whisker Removal Reduces the Density of c-Fos+ Cells and the Expression of Calbindin Protein, Disrupts Hippocampal Neurogenesis and Affects Spatial-Memory-Related Tasks

Facial vibrissae, commonly known as whiskers, are the main sensitive tactile system in rodents. Whisker stimulation triggers neuronal activity that promotes neural plasticity in the barrel cortex (BC) and helps create spatial maps in the adult hippocampus. Moreover, activity-dependent inputs and calcium homeostasis modulate adult neurogenesis. Therefore, the neuronal activity of the BC possibly regulates hippocampal functions and neurogenesis. To assess whether tactile information from facial whiskers may modulate hippocampal functions and neurogenesis, we permanently eliminated whiskers in CD1 male mice and analyzed the effects in cellular composition, molecular expression and memory processing in the adult hippocampus. Our data indicated that the permanent deprivation of whiskers reduced in 4-fold the density of c-Fos+ cells (a calcium-dependent immediate early gene) in cornu ammonis subfields (CA1, CA2 and CA3) and 4.5-fold the dentate gyrus (DG). A significant reduction in the expression of calcium-binding proteincalbindin-D_28k was also observed in granule cells of the DG. Notably, these changes coincided with an increase in apoptosis and a decrease in the proliferation of neural precursor cells in the DG, which ultimately reduced the number of Bromodeoxyuridine (BrdU)+NeuN+ mature neurons generated after whisker elimination. These abnormalities in the hippocampus were associated with a significant impairment of spatial memory and navigation skills. This is the first evidence indicating that tactile inputs from vibrissal follicles strongly modify the expression of c-Fos and calbindin in the DG, disrupt different aspects of hippocampal neurogenesis, and support the notion that spatial memory and navigation skills strongly require tactile information in the hippocampus.

Eye Drops for Delivery of Bioactive Compounds and BrdU to Stimulate Proliferation and Label Mitotically Active Cells in the Adult Rodent Retina

Eye drop treatments are typically used to apply drugs to the anterior structures of the eye. Recently, however, studies have demonstrated that eye drops can reach the retina in the back of the eye if pharmacological agents are carried in appropriate vehicles. Here, we introduce an eye drop procedure to deliver a drug (PNU-282987), in combination with BrdU, to stimulate cell cycle re-entry and label dividing cells in the retinas of adult rodents. This procedure avoids potential systemic complications of repeated intraperitoneal injections, as well as the retinal damage that is induced by repeated intravitreal injections. Although the delivery of PNU-282987 and BrdU is the focus of this article, many different proliferating compounds could be delivered to the retina using this procedure.

Differing intrinsic biological properties between forebrain and spinal oligodendroglial lineage cells

Differentiation of oligodendroglial progenitor cells (OPCs) into myelinating oligodendrocytes is known to be regulated by the microenvironment where they differentiate. However, current research has not verified whether or not oligodendroglial lineage cells (OLCs) derived from different anatomical regions of the central nervous system (CNS) respond to microenvironmental cues in the same manner. Here, we isolated pure OPCs from rat neonatal forebrain (FB) and spinal cord (SC) and compared their phenotypes in the same in vitro conditions. We found that although FB and SC OLCs responded differently to the same external factors; they were distinct in proliferation response to mitogens, oligodendrocyte phenotype after differentiation, and cytotoxic responses to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-type glutamate receptor-mediated excitotoxicity at immature stages of differentiation in a cell-intrinsic manner. Moreover, transcriptome analysis identified genes differentially expressed between these OPC populations, including those encoding transcription factors (TFs), cell surface molecules, and signaling molecules. Particularly, FB and SC OPCs retained the expression of FB- or SC-specific TFs, such as Foxg1 and Hoxc8, respectively, even after serial passaging in vitro. Given the essential role of these TFs in the regional identities of CNS cells along the rostrocaudal axis, our results suggest that CNS region-specific gene regulation by these TFs may cause cell-intrinsic differences in cellular responses between FB and SC OLCs to extracellular molecules. Further understanding of the regional differences among OPC populations will help to improve treatments for demyelination in different CNS regions and to facilitate the development of stem cell-derived OPCs for cell transplantation therapies for demyelination. Cover Image for this issue: doi. 10.1111/jnc.13809.

Altered differentiation of enteric neural crest-derived cells from endothelin receptor-B null mouse model of Hirschsprung's disease

PURPOSE

Hirschsprung's disease (HD) is caused by a failure of enteric neural crest-derived cells (ENCC) to colonize the bowel, resulting in an absence of the enteric nervous system (ENS). Previously, we developed a Sox10 transgenic version of the Endothelin receptor-B (Ednrb) mouse to visualize ENCC with the green fluorescent protein, Venus. The aim of this study was to isolate Sox10-Venus⁺ cells, which are differentiated neurons and glial cells in the ENS, and analyze these cells using Sox10-Venus mice gut.

METHODS

The mid-and hindgut of Sox10-Venus⁺/Ednrb ^+/+ and Sox10-Venus⁺/Ednrb ^-/- at E13.5 and E15.5 were dissected and cells were dissociated. Sox10-Venus⁺ cells were then isolated. Expression of PGP9.5 and GFAP were evaluated neurospheres using laser scanning microscopy.

RESULTS

7 days after incubation, Sox10-Venus⁺ cells colonized the neurosphere. There were no significant differences in PGP9.5 expressions on E13.5 and E15.5. GFAP was significantly increased in HD compared to controls on E15.5 (P < 0.05).

CONCLUSIONS

Our results suggest increased glial differentiation causes an imbalance in ENCC lineages, leading to a disruption of normal ENS development in this HD model. Isolation of ENCC provides an opportunity to investigate the ENS with purity and might be a useful tool for modeling cell therapy approaches to HD.