Ndrg2 regulates vertebral specification in differentiating somites

Whole-Genome Resequencing of Ujimqin Sheep Identifies Genes Associated with Vertebral Number

The number of vertebrae is a crucial economic trait that can significantly impact the carcass length and meat production in animals. However, our understanding of the quantitative trait loci (QTLs) and candidate genes associated with the vertebral number in sheep (Ovis aries) remains limited. To identify these candidate genes and QTLs, we collected 73 Ujimqin sheep with increased numbers of vertebrae (T13L7, T14L6, and T14L7) and 23 sheep with normal numbers of vertebrae (T13L6). Through high-throughput genome resequencing, we obtained a total of 24,130,801 effective single-nucleotide polymorphisms (SNPs). By conducting a selective-sweep analysis, we discovered that the most significantly selective region was located on chromosome 7. Within this region, we identified several genes, including VRTN, SYNDIG1L, LTBP2, and ABCD4, known to regulate the spinal development and morphology. Further, a genome-wide association study (GWAS) performed on sheep with increased and normal vertebral numbers confirmed that ABCD4 is a candidate gene for determining the number of vertebrae in sheep. Additionally, the most significant SNP on chromosome 7 was identified as a candidate QTL. Moreover, we detected two missense mutations in the ABCD4 gene; one of these mutations (Chr7: 89393414, C > T) at position 22 leads to the conversion of arginine (Arg) to glutamine (Gln), which is expected to negatively affect the protein's function. Notably, a transcriptome expression profile in mouse embryonic development revealed that ABCD4 is highly expressed during the critical period of vertebral formation (4.5-7.5 days). Our study highlights ABCD4 as a potential major gene influencing the number of vertebrae in Ujimqin sheep, with promising prospects for future genome-assisted breeding improvements in sheep.

The ndrg2 Gene Regulates Hair Cell Morphogenesis and Auditory Function during Zebrafish Development

Damages of sensory hair cells (HCs) are mainly responsible for sensorineural hearing loss, however, its pathological mechanism is not yet fully understood due to the fact that many potential deafness genes remain unidentified. N-myc downstream-regulated gene 2 (ndrg2) is commonly regarded as a tumor suppressor and a cell stress-responsive gene extensively involved in cell proliferation, differentiation, apoptosis and invasion, while its roles in zebrafish HC morphogenesis and hearing remains unclear. Results of this study suggested that ndrg2 was highly expressed in the HCs of the otic vesicle and neuromasts via in situ hybridization and single-cell RNA sequencing. Ndrg2 loss-of-function larvae showed decreased crista HCs, shortened cilia, and reduced neuromasts and functional HCs, which could be rescued by the microinjection of ndrg2 mRNA. Moreover, ndrg2 deficiency induced attenuated startle response behaviors to sound vibration stimuli. Mechanistically, there were no detectable HC apoptosis and supporting cell changes in the ndrg2 mutants, and HCs were capable of recovering by blocking the Notch signaling pathway, suggesting that ndrg2 was implicated in HC differentiation mediated by Notch. Overall, our study demonstrates that ndrg2 plays crucial roles in HC development and auditory sensory function utilizing the zebrafish model, which provides new insights into the identification of potential deafness genes and regulation mechanism of HC development.

Loss of ndrg2 Function Is Involved in Notch Activation in Neuromast Hair Cell Regeneration in Zebrafish

The regeneration of hair cells in zebrafish is a complex process involving the precise regulation of multiple signaling pathways, but this complicated regulatory network is not fully understood. Current research has primarily focused on finding molecules and pathways that can regulate hair cell regeneration and restore hair cell functions. Here, we show the role of N-Myc downstream regulated gene 2 (ndrg2) in zebrafish hair cell regeneration. We first found that ndrg2 was dynamically expressed in neuromasts of the developing zebrafish, and this expression was increased after neomycin-induced hair cell damage. Then, ndrg2 loss-of-function larvae showed reduced numbers of regenerated hair cells but increased numbers of supporting cells after neomycin exposure. By in situ hybridization, we further observed that ndrg2 loss of function resulted in the activation of Notch signaling and downregulation of atoh1a during hair cell regeneration in vivo. Additionally, blocking Notch signaling rescued the number of regenerated hair cells in ndrg2-deficient larvae. Together, this study provides evidence for the role of ndrg2 in regulating hair cell regeneration in zebrafish neuromasts.

NDRG2 regulates the formation of reactive astrocyte-derived progenitor cells via Notch signaling pathway after brain traumatic injury in rats

In response to traumatic brain injury, a subpopulation of cortical astrocytes is activated, resulting in acquisition of stem cell properties, known as reactive astrocytes-derived progenitor cells (Rad-PCs). However, the underlying mechanisms remain largely unknown during this process. In this study, we examined the role of N-myc downstream-regulated gene 2 (NDRG2), a differentiation- and stress-associated molecule, in Rad-PCs after cortical stab injury in adult rats. Immunohistochemical analysis showed that in the cerebral cortex of normal adult rats, NDRG2 was exclusively expressed in astrocytes. After liu cortical injury, the expression of NDRG2 was significantly elevated around the wound and most cells expressing NDRG2 also expressed GFAP, a reactive astrocyte marker. Importantly, NDRG2-expressing cells were co-labeled with Nestin, a marker for neural stem cells, some of which also expressed cell proliferation marker Ki67. Overexpression of NDRG2 further increased the number of NDRG2/Nestin double-labeling cells around the lesion. In contrast, shRNA knockdown of NDRG2 decreased the number of NDRG2+/Nestin+ cells. Intracerebroventricular administration of stab-injured rats with a Notch antagonist, DAPT, led to a significant decrease in Nestin+/NDRG2+ cells around the injured boundary, but did not affect NDRG2+ cells. Moreover, overexpression or knockdown of NDRG2 led to up- and down-regulation of the expression of Notch intracellular domain NICD and Notch target gene Hes1, respectively. Taken together, these results suggest that NDRG2 may play a role in controlling the formation of Rad-PCs in the cerebral cortex of adult rats following traumatic injury, and that Notch signaling pathway plays a key role in this process.

EZH2 regulates the balance between osteoclast and osteoblast differentiation to inhibit arthritis-induced bone destruction

Enhancer of zeste homolog 2 (EZH2) has been noted to contribute to the pathogenesis of autoimmune diseases. This study sought to investigate the mechanism of EZH2 in osteoclast (OCL) and osteoblast (OBL) differentiation (OCLD/OBLD) and bone destruction in RA. The animal model of collagen-induced arthritis (CIA) was established, followed by arthritis index (AI) scoring and histological staining, and measurements of inflammatory cytokines levels. The number of OCLs was detected via Tartrate-resistant acid phosphatase (TRAP) staining, and levels of OBL markers were determined by Western blot analysis. Trimethylated histone H3 at lysine 27 (H3K27me3) expression and its enrichment in the Ndrg2 promoter were detected. Collaborative experiments were performed with GSK-J1 or sh-Ndrg2 in CIA mice with EZH2 knockdown. EZH2 was upregulated while Ndrg2 was downregulated in knee joint tissues of CIA mice. Silencing EZH2 reduced AI scores, pathological injury of the knee joint, levels of inflammatory cytokines, and TRAP-positive cells, and increased protein levels of RUNX2 and BMP2. EZH2 promoted H3K27me3 level in the Ndrg2 promoter to inhibit Ndrg2 transcription. H3K27me3 upregulation or Ndrg2 downregulation reversed the role of silencing EZH2 in bone destruction. Overall, EZH2 repressed OBLD and promoted OCLD to aggravate bone destruction in CIA mice through H3K27me3/Ndrg2.

Whole-genome resequencing identified candidate genes associated with the number of ribs in Hu sheep

The number of ribs is an important economic trait in the sheep industry when the sheep are raised for mutton. However, in sheep, the genetic mechanisms regulating rib number are poorly understood. In the present study, we aimed to identify important candidate genes that affect the increase in rib number in sheep. Whole-genome resequencing of 36 Hu sheep with an increased number of ribs (R14) and 36 sheep with normal (R13) rib numbers was carried out. Analysis using three methods (fixation index (F_ST), Fisher's exact test, and Chi-squared test) showed that 219 single nucleotide polymorphism sites overlapped among the results of the three methods, which represented 206 genes. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses indicated that the genes were mainly associated with regulation of developmental process, inorganic anion transport, cellular biosynthetic process, tight junction, the oxytocin signaling pathway, and arrhythmogenic right ventricular cardiomyopathy. Four mutations were selected according to the significantly selected genomic regions and important pathways for genotyping and association analysis. The result demonstrated that three synonymous mutations correlated significantly with the rib number. Importantly, we revealed that the CPOX (encoding coproporphyrinogen oxidase), KCNH1 (encoding potassium voltage-gated channel subfamily H member 1), and CPQ (encoding carboxypeptidase Q) genes have a combined effect on rib number in Hu sheep. Our results identified candidate molecular markers for rib number in sheep breeding.

Abnormal social behavior and altered gene expression in mice lacking NDRG2

N-myc downstream-regulated gene 2 (NDRG2), a member of the NDRG family, has multiple functions in cell proliferation, differentiation, and stress responses, and is predominantly expressed by astrocytes in the central nervous system. Previous studies including ours demonstrated that NDRG2 is involved in various central nervous system pathologies. However, the significance of NDRG2 in neurodevelopment is not fully understood. Here, we investigated the expression profile of NDRG2 during postnatal brain development, the role of NDRG2 in social behavior, and transcriptome changes in the brain of NDRG2-deficient mice. NDRG2 expression in the brain increased over time from postnatal day 1 to adulthood. Deletion of NDRG2 resulted in abnormal social behavior, as indicated by reduced exploratory activity toward a novel mouse in a three-chamber social interaction test. Microarray analysis identified genes differentially expressed in the NDRG2-deficient brain, and upregulated gene expression of Bmp4 and Per2 was confirmed by quantitative PCR analysis. Expression of both these genes and the encoded proteins increased over time during postnatal brain development, similar to NDRG2. Gene expression of Bmp4 and Per2 was upregulated in cultured astrocytes isolated from NDRG2-deficient mice. These results suggest that NDRG2 contributes to brain development required for proper social behavior by modulating gene expression in astrocytes.

Genome-Wide Association Analysis Identified BMPR1A as a Novel Candidate Gene Affecting the Number of Thoracic Vertebrae in a Large White × Minzhu Intercross Pig Population

Simple Summary

The number of thoracic vertebrae (NTV) and number of vertebrae (NV) varies among pig breeds with a high correlation of about 0.8. It is important to discover variants associated with the NTV by considering the effect of the NV in pig. The results suggest that regulation variants on SSC7 might play crucial roles in the NTV and the FOS on SSC7 should be further studied as a critical candidate gene. In addition, BMPR1A was identified as a novel candidate gene affecting the NTV in pigs.

Abstract

The number of vertebrae (NV), especially the number of thoracic vertebrae (NTV), varies among pig breeds. The NTV is controlled by vertebral segmentation and the number of somites during embryonic development. Although there is a high correlation between the NTV and NV, studies on a fixed NV have mainly considered the absolute numbers of thoracic vertebrae instead of vertebral segmentation. Therefore, this study aimed to discover variants associated with the NTV by considering the effect of the NV in pigs. The NTV and NV of 542 F2 individuals from a Large White × Minzhu pig crossbreed were recorded. All animals were genotyped for VRTN g.19034 A > C, LTBP2 c.4481A > C, and 37 missense or splice variants previously reported in a 951-kb interval on SSC7 and 147 single nucleotide polymorphisms (SNPs) on SSC14. To identify NTV-associated SNPs, we firstly performed a genome-wide association study (GWAS) using the Q + K (population structure + kinship matrix) model in TASSEL. With the NV as a covariate, the obtained data were used to identify the SNPs with the most significant genome-wide association with the NTV by performing a GWAS on a PorcineSNP60K Genotyping BeadChip. Finally, a conditional GWAS was performed by fixing this SNP. The GWAS showed that 31 SNPs on SSC7 have significant genome-wide associations with the NTV. No missense or splice variants were found to be associated with the NTV significantly. A linkage disequilibrium analysis suggested the existence of quantitative trait loci (QTL) in a 479-Kb region on SSC7, which contained a critical candidate gene FOS for the NTV in pigs. Subsequently, a conditional GWAS was performed by fixing M1GA0010658, the most significant of these SNPs. Two SNPs in BMPR1A were found to have significant genome-wide associations and a significant dominant effect. The leading SNP, S14_87859370, accounted for 3.86% of the phenotypic variance. Our study uncovered that regulation variants in FOS on SSC7 and in BMPR1A on SSC14 might play important roles in controlling the NTV, and thus these genetic factors may be harnessed for increasing the NTV in pigs.

Roles of N-myc downstream-regulated gene 2 in the central nervous system: molecular basis and relevance to pathophysiology

N-myc downstream-regulated gene 2 (NDRG2) is a member of the NDRG family, whose members have multiple functions in cell proliferation, differentiation, and stress responses. NDRG2 is widely distributed in the central nervous system and is uniquely expressed by astrocytes; however, its role in brain function remains elusive. The clinical relevance of NDRG2 and the molecular mechanisms in which it participates have been reported by studies using cultured cells and specimens of patients with neurological disorders. In recent years, genetic tools, including several lines of Ndrg2-knockout mice and virus-mediated gene transfer, have improved understanding of the roles of NDRG2 in vivo. This review aims to provide an update of recent growing in vivo evidence that NDRG2 is involved in brain function, focusing on research of Ndrg2-knockout mice with neurological disorders such as brain tumors, chronic neurodegenerative diseases, and acute brain insults including brain injury and cerebral stroke. These studies demonstrate that NDRG2 plays diverse roles in the regulation of astrocyte reactivity, blood-brain barrier integrity, and glutamate excitotoxicity. Further elucidation of the roles of NDRG2 and their molecular basis may provide novel therapeutic approaches for various neurological disorders.

NDRG2 attenuates ischemia-induced astrocyte necroptosis via the repression of RIPK1

Cerebral ischemia results in severe brain damage, and is a leading cause of death and long-term disability. Previous studies have investigated methods to activate astrocytes in order to promote repair in injured brain tissue and inhibit cell death. It has previously been shown that N-myc downstream-regulated gene 2 (NDRG2) was highly expressed in astrocytes and associated with cell activity, but the underlying mechanism is largely unknown. The present study generated NDRG2 conditional knockout (Ndrg2-/-) mice to investigate whether NDRG2 can block ischemia-induced astrocyte necroptosis by suppressing receptor interacting protein kinase 1 (RIPK1) expression. This study investigated astrocyte activity in cerebral ischemia, and identified that ischemic brain injuries could trigger RIP-dependent astrocyte necroptosis. The depletion of NDRG2 was found to accelerate permanent middle cerebral artery occlusion-induced necroptosis in the brain tissue of Ndrg2-/- mice, indicating that NDRG2 may act as a neuroprotector during cerebral ischemic injury. The present study suggested that NDRG2 attenuated astrocytic cell death via the suppression of RIPK1. The pharmacological inhibition of astrocyte necroptosis by necrostatin-1 provided neuroprotection against ischemic brain injuries after NDRG2 knockdown. Therefore, NDRG2 could be considered as a potential target for the treatment of cerebral ischemia.

Astrocyte-specific NDRG2 gene: functions in the brain and neurological diseases

In recent years, the roles of astrocytes of the central nervous system in brain function and neurological disease have drawn increasing attention. As a member of the N-myc downstream-regulated gene (NDRG) family, NDRG2 is principally expressed in astrocytes of the central nervous system. NDRG2, which is involved in cell proliferation and differentiation, is commonly regarded as a tumor suppressor. In astrocytes, NDRG2 affects the regulation of apoptosis, astrogliosis, blood-brain barrier integrity, and glutamate clearance. Several preclinical studies have revealed that NDRG2 is implicated in the pathogenesis of many neurological diseases not limited to tumors (mostly glioma in the nervous system), such as stroke, neurodegeneration (Alzheimer's disease and Parkinson's disease), and psychiatric disorders (depression and attention deficit hyperactivity disorder). This review summarizes the biological functions of NDRG2 under physiological and pathological conditions, and further discusses the roles of NDRG2 during the occurrence and development of neurological diseases.

N-myc Downstream-Regulated Gene 2 (NDRG2) Promotes Bone Morphogenetic Protein 2 (BMP2)-Induced Osteoblastic Differentiation and Calcification by Janus Kinase 3 (JAK3)/Signal Transducer and Activator of Transcription 3 (STAT3) Signaling Pathway

Background

Osteoporosis is an osteolytic disease resulted from imbalance in bone homeostasis. Studies indicated that N-myc downstream-regulated gene 2 (NDRG2) could affect the osteoclast differentiation. However, the effect of NDRG2 on osteoblastic differentiation and calcification remains unknown. Hence, we aimed to analyze the effect of NDRG2 on the proliferation and differentiation of osteoblasts.

Material/Methods

The differentiation of bone morphogenetic protein 2 (BMP2) induced MC3T3-E1 cells was observed by the microscope. Real-time quantitative polymerase chain reaction (RT-qPCR) and western blot analysis detected the expression of BMP2, NDRG2, runt-related transcription factor 2 (Runx2), osteoprotegerin (OPG), osterix (OSX), and osteocalcin (OCN). Alkaline phosphatase (ALP) activity assay was detecting the ALP activity and alizarin red staining assay was analyzing intracellular calcium salt deposition. The cell transfection was also verified by RT-qPCR analysis.

Results

The results demonstrated that BMP2 promoted the osteoblastic differentiation with the increasing expression of Runx2, OPG, OSX, and OCN. NDRG2 expression was upregulated during osteogenic differentiation. NDRG2 overexpression promoted the expression of Runx2, OPG, OSX, and OCN, and increased the ALP activity while NDRG2 inhibition reversed the changes. NDRG2 overexpression increased the intracellular calcium salt deposition and NDRG2 inhibition reversed the changes. The role of NDRG2 in osteoblastic differentiation and calcification was played through the JAK3/STAT3 signal pathway.

Conclusions

The presented data indicated that NDRG2 promoted BMP2-induced osteoblastic differentiation and calcification by activating the JAK3/STAT3 signal pathway.

Whole-Genome Resequencing Reveals Loci Associated With Thoracic Vertebrae Number in Sheep

The number of vertebrae, especially thoracic vertebrae, is an important economic trait that may influence carcass length and meat production in animals. However, the genetic basis of vertebrae number in sheep is still poorly understood. To detect the candidate genes, 400 increased number of thoracic vertebrae (T14L6) and 200 normal (T13L6) Kazakh sheep were collected. We generated and sequenced 60 pools of genomic DNA (each pool prepared by mixing genomic DNA from 10 sheep with the same thoracic traits), with an average depth of coverage of 25.65×. We identified a total of 42,075,402 SNPs and 11 putatively selected genomic regions, including the VRTN gene and the HoxA gene family that regulate vertebral development. The most prominent areas of selective elimination were located in a region of chromosome 7, including VRTN, which regulates spinal development and morphology. Further investigation indicated that the expression level of the VRTN gene during fetal development was significantly higher in sheep with more thoracic vertebrae than in those with a normal number of thoracic vertebrae. A genome-wide comparison between sheep with increased and normal numbers of thoracic vertebrae showed that the VRTN gene is the major selection locus for the number of thoracic vertebrae in sheep and has the potential to be utilized in sheep breeding in the future.

Increased Expression of NDRG3 in Mouse Uterus During Embryo Implantation and in Mouse Endometrial Stromal Cells During In Vitro Decidualization

Decidualization is an indispensable event in the embryo implantation process, but its underlying molecular mechanisms remain elusive. In this study, we showed that in mice, the uterine expression of N-myc downstream-regulated gene 3 (NDRG3), a member of the α/β hydrolase superfamily, was induced by estradiol and progesterone. During the embryo implantation process, uterine Ndrg3 expression was remarkably upregulated, and its expression level at implantation sites (IS) was significantly higher than that at inter-IS. Increased uterine expression of Ndrg3 was associated with artificial decidualization and the activation of delayed implantation. The in vitro decidualization of mouse endometrial stromal cells (ESCs) induced by estradiol and progesterone was also accompanied by increased Ndrg3 expression, and downregulated Ndrg3 expression in ESCs effectively inhibited decidualization. miR-290b-5p was identified as an upstream regulator of Ndrg3, and the uterine expression level of miR-290b-5p was decreased during the implantation process. Furthermore, overexpression of miR-290b-5p in mouse ESCs inhibited their in vitro decidualization. Taken together, these data suggested that Ndrg3 might play an important role in embryo implantation by regulating decidualization potentially via the estrogen/progesterone/miR-290b-5p pathway.

Ndrg3 gene regulates DSB repair during meiosis through modulation the ERK signal pathway in the male germ cells

The N-myc downstream regulated gene (NDRG) family consists of 4 members, NDRG-1, -2, -3, -4. Physiologically, we found Ndrg3, a critical gene which led to homologous lethality in the early embryo development, regulated the male meiosis in mouse. The expression of Ndrg3 was enhanced specifically in germ cells, and reached its peak level in the pachytene stage spermatocyte. Haplo-insufficiency of Ndrg3 gene led to sub-infertility during the male early maturation. In the Ndrg3^+/- germ cells, some meiosis events such as DSB repair and synaptonemal complex formation were impaired. Disturbances on meiotic prophase progression and spermatogenesis were observed. In mechanism, the attenuation of pERK1/2 signaling was detected in the heterozygous testis. With our primary spermatocyte culture system, we found that lactate promoted DSB repair via ERK1/2 signaling in the male mouse germ cells in vitro. Deficiency of Ndrg3 gene attenuated the activation of ERK which further led to the aberrancy of DSB repair in the male germ cells in mouse. Taken together, we reported that Ndrg3 gene modulated the lactate induced ERK pathway to facilitate DSB repair in male germ cells, which further regulated meiosis and subsequently fertility in male mouse.

Postnatal lethality and abnormal development of foregut and spleen in Ndrg4 mutant mice

NDRG4 is a member of the NDRG family (N-myc downstream-regulated gene), which is highly expressed in brain and heart. Previous studies showed that Ndrg1-deficient mice exhibited a progressive demyelinating disorder of peripheral nerves and Ndrg4-deficient mice had spatial learning deficits and vulnerabilities to cerebral ischemia. Here, we report generation of Ndrg4 mutant alleles that exhibit several development defects different from those previously reported. Our homozygous mice showed growth retardation and postnatal lethality. Spleen and thymuses of Ndrg4(-/-) mice are considerably reduced in size from 3 weeks of age. Histological analysis revealed abnormal hyperkeratosis in the squamous foregut and abnormal loss of erythrocytes in the spleen of Ndrg4(-/-) mice. In addition, we observed an abnormal hind limb clasping phenotype upon tail suspension suggesting neurological abnormalities. Consistent to these abnormalities, Ndrg4 is expressed in smooth muscle cells of the stomach, macrophages of the spleen and neurons. Availability of the conditional allele for Ndrg4 should facilitate further detailed analyses of the potential roles of Ndrg4 in gut development, nervous system and immune system.

Inhibition of osteoclast differentiation by overexpression of NDRG2 in monocytes

N-Myc downstream-regulated gene 2 (NDRG2), a member of the NDRG family of differentiation-related genes, has been characterized as a regulator of dendritic cell differentiation from monocytes, CD34(+) progenitor cells, and myelomonocytic leukemic cells. In this study, we show that NDRG2 overexpression inhibits the differentiation of U937 cells into osteoclasts in response to stimulation with a combination of macrophage colony-stimulating factor (M-CSF) and soluble receptor activator of NF-κB ligand (RANKL). U937 cells stably expressing NDRG2 are unable to differentiate into multinucleated osteoclast-like cells and display reduced tartrate-resistant acid phosphatase (TRAP) activity and resorption pit formation. Furthermore, NDRG2 expression significantly suppresses the expression of genes that are crucial for the proliferation, survival, differentiation, and function of osteoclasts, including c-Fos, Atp6v0d2, RANK, and OSCAR. The activation of ERK1/2 and p38 is also inhibited by NDRG2 expression during osteoclastogenesis, and the inhibition of osteoclastogenesis by NDRG2 correlates with the down-regulation of the expression of the transcription factor PU.1. Taken together, our results suggest that the expression of NDRG2 potentially inhibits osteoclast differentiation and plays a role in modulating the signal transduction pathway responsible for osteoclastogenesis.

NDRG2 as a marker protein for brain astrocytes

The protein NDRG2 (N-myc downregulated gene 2) is expressed in astrocytes. We show here that NDRG2 is located in the cytosol of protoplasmic and fibrous astrocytes throughout the mammalian brain, including Bergmann glia as observed in mouse, rat, tree shrew, marmoset and human. NDRG2 immunoreactivity is detectable in the astrocytic cell bodies and excrescencies including fine distal processes. Glutamatergic and GABAergic nerve terminals are associated with NDRG2 immunopositive astrocytic processes. Müller glia in the retina displays no NDRG2 immunoreactivity. NDRG2 positive astrocytes are more abundant and more evenly distributed in the brain than GFAP (glial fibrillary acidic protein) immunoreactive cells. Some regions with very little GFAP such as the caudate nucleus show pronounced NDRG2 immunoreactivity. In white matter areas, NDRG2 is less strong than GFAP labeling. Most NDRG2 positive somata are immunoreactive for S100ß but not all S100ß cells express NDRG2. NDRG2 positive astrocytes do not express nestin and NG2 (chondroitin sulfate proteoglycan 4). The localization of NDRG2 overlaps only partially with that of aquaporin 4, the membrane-bound water channel that is concentrated in the astrocytic endfeet. Reactive astrocytes at a cortical lesion display very little NDRG2, which indicates that expression of the protein is reduced in reactive astrocytes. In conclusion, our data show that NDRG2 is a specific marker for a large population of mature, non-reactive brain astrocytes. Visualization of NDRG2 immunoreactive structures may serve as a reliable tool for quantitative studies on numbers of astrocytes in distinct brain regions and for high-resolution microscopy studies on distal astrocytic processes.

Deletion of N-myc downstream-regulated gene 2 attenuates reactive astrogliosis and inflammatory response in a mouse model of cortical stab injury

N-myc downstream-regulated gene 2 (Ndrg2) is a differentiation- and stress-associated molecule predominantly expressed in astrocytes in the CNS. In this study, we examined the expression and the role of Ndrg2 after cortical stab injury. We observed that Ndrg2 expression was elevated in astrocytes surrounding the wounded area as early as day 1 after injury in wild-type mice. Deletion of Ndrg2 resulted in lower induction of reactive astroglial and microglial markers in the injured cortex. Histological analysis showed reduced levels of hypertrophic changes in astrocytes, accumulation of microglia, and neuronal death in Ndrg2(-/-) mice after injury. Furthermore, activation of the IL-6/signal transducer and activator of transcription 3 (STAT3) pathway, including the expression of IL-6 family cytokines and phosphorylation of STAT3, was markedly reduced in Ndrg2(-/-) mice after injury. In a culture system, both of Il6 and Gfap were up-regulated in wild-type astrocytes treated with forskolin. Deletion of Ndrg2 attenuated induction of these genes, but did not alter proliferation or migration of astrocytes. Adenovirus-mediated reexpression of Ndrg2 rescued the reduction of IL-6 expression after forskolin stimulation. These findings suggest that Ndrg2 plays a key role in reactive astrogliosis after cortical stab injury through a mechanism involving the positive regulation of IL-6/STAT3 signaling.