The Role and Mechanism of Transglutaminase 2 in Regulating Hippocampal Neurogenesis after Traumatic Brain Injury

Traumatic brain injury usually results in neuronal loss and cognitive deficits. Promoting endogenous neurogenesis has been considered as a viable treatment option to improve functional recovery after TBI. However, neural stem/progenitor cells (NSPCs) in neurogenic regions are often unable to migrate and differentiate into mature neurons at the injury site. Transglutaminase 2 (TGM2) has been identified as a crucial component of neurogenic niche, and significantly dysregulated after TBI. Therefore, we speculate that TGM2 may play an important role in neurogenesis after TBI, and strategies targeting TGM2 to promote endogenous neural regeneration may be applied in TBI therapy. Using a tamoxifen-induced Tgm2 conditional knockout mouse line and a mouse model of stab wound injury, we investigated the role and mechanism of TGM2 in regulating hippocampal neurogenesis after TBI. We found that Tgm2 was highly expressed in adult NSPCs and up-regulated after TBI. Conditional deletion of Tgm2 resulted in the impaired proliferation and differentiation of NSPCs, while Tgm2 overexpression enhanced the abilities of self-renewal, proliferation, differentiation, and migration of NSPCs after TBI. Importantly, injection of lentivirus overexpressing TGM2 significantly promoted hippocampal neurogenesis after TBI. Therefore, TGM2 is a key regulator of hippocampal neurogenesis and a pivotal therapeutic target for intervention following TBI.


Introduction
Traumatic brain injury, a form of brain damage caused by external mechanical forces [1], is a major health and socioeconomic issue worldwide [2,3]. Millions of survivors of TBI tend to have mental, physical, or intellectual disabilities [4]. TBI manifests in time-dependent ways and unfolds in phases following the traumatic event [5]. Primary brain damage is followed by a series of secondary molecular and cellular events that can result in cell death, tissue atrophy, and neurodegeneration over time [6,7]. Due to the heterogeneity and complexity of TBI, there is still no effective rehabilitation treatment for TBI [8]. Most clinical interventions focus on minimizing secondary injury, but neural repair and regeneration are very limited [1,9].
During the past few decades, endogenous neural stem/progenitor cells (NSPCs) have opened a new therapeutic avenue for brain injuries [10][11][12][13]. Unfortunately, endogenous NSPCs lose their abilities to migrate and differentiate into mature neurons at the injury sites in adult brain [14][15][16][17]. Therefore, developing new strategies to promote neural differentiation of endogenous NSPCs is crucial for replacing neurons lost in TBI.

Blade Penetrating Stab Wound to the Hippocampus
To produce a homogeneous hippocampal injury, male mice at 6-8 weeks of age were anesthetized with tribromoethanol (375 mg/kg) and received a blade penetrating stab wound injury in the right hippocampus according to published protocols [27,28]. Briefly, the scalp was disinfected and cut along the midline to expose the skull. A cranial window (4 mm in length, 1 mm in width) was opened on the right side of the skull, and a sterile scalpel blade #15 was inserted vertically into the hippocampus with the following coordinates (from bregma): AP (anterior-posterior) = 1.4 mm, ML (mediolateral) = 1.4 mm; AP = 4.3 mm, ML = 2.4 mm; DV (dorsal-ventral) = 3.5 mm. After surgery, a povidone-iodine solution was applied to prevent infections.

Tamoxifen Induction and BrdU Labeling
Tamoxifen (Sigma-Aldrich, St. Louis, MO, USA, T5648) was dissolved in corn oil (Sigma-Aldrich, C8267). Adult mice (6-8 weeks old) received three intraperitoneal injections of tamoxifen to initiate genetic recombination at a dose of 180 mg/kg, each injection was separated by 24 h. For BrdU labeling, mice received daily intraperitoneal BrdU (Sigma-Aldrich, B5002-5G) injections after TBI or sham surgery at a dose of 100 mg/kg for three consecutive days.
Microglia was cultured as described previously [30]. Briefly, P3 cortices were dissociated and digested at 37 • C for 10 min with TrypLE Express. After that, DMEM/F12 medium supplemented with 10% FBS was used to culture mixed glial cells for 2 weeks. Microglia were then purified by shaking flasks for 2 h at 130 rpm. For collecting microglial conditioned medium, primary microglia were treated with 100 ng/mL of LPS (Sigma-Aldrich, L2630) for 24 h. Medium were collected and centrifuged for 5 min at 500 rcf. Finally, the supernatants were aliquoted and stored at 80 • C until use.
For co-localization analysis of marked proteins in cells, z-stack images were taken with a LSM880 confocal microscope (Zeiss, Oberkochen, Gernany). Co-localization was determined as overlap with orthogonal view from different planes (x/y, x/z, and y/z). For quantifying the fluorescence intensity, images from all groups were captured at the same exposure time. The mean fluorescence of small areas that had no positive signals was measured as the background reading for every image. The corrected total square fluorescence was calculated with the following equation: the Corrected Total Frame Fluorescence = Integrated Density − (Mean Fluorescence of Background readings × Area of Selected Frame).  Total RNA from cells or tissues was extracted with TRIzol reagent (Invitrogen, Carlsbad, CA, USA, 15596018). The Transcript One-Step gDNA Removal and cDNA Synthesis Kit (TransGen Biotech, Beijing, China, 11104ES70) was used to reverse-transcribed RNA into cDNA. For each sample, quantitative RT-PCR (qRT-PCR) reactions were run in triplicate in a 20 µL system with the SYBR Green Master Mix (Yeasen Biotech, Shanghai, China, 11201ES08). β-actin was used as an endogenous control. The 2 −∆∆CT method was used to measure relative expression levels of genes. PCR reactions were run at 95 • C for 30 s, followed by 45 cycles of denaturation at 94 • C for 10 s, annealing at 60 • C for 30 s, and elongation at 72 • C for 30 s. All qRT-PCR experiments were repeated at least three times. The primers for qRT-PCR are listed in Table 1.

Lentivirus Production and In Vivo Grafting
Lentiviral vectors were constructed and packaged as described previously [31,32]. For overexpressing Tgm2, Tgm2 cDNA was amplified from mouse cerebral cortex by PCR, and then subcloned into the construction of pCD511B-copGFP vector containing CMV promoter. For knocking down Tgm2, a U6 promoter-driven Tgm2 shRNA (5 -CCAAGTATGATGCACCCTT-3 ) hairpin loop sequence was inserted into the lentiviral construct.
To produce lentivirus, HEK293T cells were co-transfected with lentiviral vector and packaging plasmids (pMDLg/pRRE, pRSV-Rev, and pMD2.VSV-G) using polyethylenimine. Lentiviral supernatants were collected at 48 h and 72 h after transfection and filtered through a 0.22 µm filter, then centrifuged at 19 k rpm for 2 h at 4 • C. After dissolving in PBS, lentivirus with a titer of 1 × 10 9 TU/mL was aliquoted and stored at −80 • C until use.

Proliferation, Differentiation, Self-Renewal, and Migration Analyses of Cultured NSPCs
Analyses of proliferation, differentiation, self-renewal, and migration were performed as previously described [32,33]. To examine the proliferation ability of NSPCs, cells were plated on poly-L-ornithine/laminin (PLL)-coated coverslips at a density of 5 × 10 4 cells per well. Lentivirus was added into the proliferation medium at 6 h post-plating. Following lentiviral transduction for 48 h, 5 µM BrdU was added into the culture medium for 6 h. NSPCs were fixed with 4% PFA for 20 min at room temperature, and then washed with PBS and immunostained with anti-BrdU.
To examine the self-renewal ability, we plated NSPCs in uncoated 12-well plates at a density of 5 × 10 4 cells/well. Following lentiviral transduction for 48 h, the sizes of primary and secondary neurospheres were measured.
Scratch wound healing assay was carried out to evaluate the migration capacity of NSPCs. NSPCs were seeded on PLL-coated coverslips at a density of 1 × 10 5 cells/well in 24-well plates, and treated with lentiviral transduction for at least 48 h. After cell confluency reached more than 90%, scratch wounds were generated using a 200 µL micropipette tip. Cells were then allowed to grow for additional 48 h, and the closure of wound was photographed at 0 h and 48 h, respectively.

RNA Sequencing
Total RNA was extracted from the primary cultured E13.5 NSPCs using TRIzol reagent. Libraries were constructed and sequenced on Illumina 2500 HiSeq platforms at Annoroad Gene Technology (Beijing, China) Data quality was assessed using FastQC, and adapter sequencing was removed with FASTX-Toolkit. Salmon (v1.0.0, SAF Pattern) was used for alignment-based quantification of mappings. Through GENCODE vM23, clean reads were mapped to the reference genome of the mouse. DESeq2 was used to identify differences in gene expression across all samples. Differentially expressed genes were determined with p < 0.05, and log2FC > 1.5 or < −1.5. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were subsequently performed. As described previously, a pseudoreplication analysis of all samples was conducted to reduce the influence from libraries construction bias and sequencing depth [34]. The RNA-seq data have been deposited in the Genome Sequence Archive in the National Genomics Data Center, Beijing Institute of Genomics, Chinese Academy of Sciences with accession number CRA009304.

Statistical Analysis
To determine statistical significance, either unpaired two-tailed t-test (to compare the mean of two independent groups) or two-way ANOVA test (to determine the effect of two variables on an outcome) were performed using GraphPad Prism v8.01. All data are shown as mean ± SEM (standard error of the mean). p-values less than 0.05 were considered as statistically significant.

Tgm2 Is Upregulated in NSPCs following TBI
To examine whether Tgm2 is expressed in hippocampal NSPCs, we performed immunofluorescent staining of TGM2 in hippocampal tissues of 1-month-old Nestin-creER T2 ;tdTamato mice which had tamoxifen-induced tdTamato labeling of nestinexpressing stem cells and their progeny in neurogenic regions. We found that TGM2 was highly expressed in NSPCs (tdTamato + ) in the subgranular zone (SGZ) of the hippocampus (Figure 1a). Using a mouse model of hippocampal stab wound injury (Figure 1b), we observed that both Tgm2 mRNA and protein expression levels were significantly elevated in SGZ at 7 days after injury (Figure 1c-e), suggesting that TGM2 might play a pivotal role in neurogenesis following TBI.
highly expressed in NSPCs (tdTamato + ) in the subgranular zone (SGZ) of the hippocampus (Figure 1a). Using a mouse model of hippocampal stab wound injury (Figure 1b), we observed that both Tgm2 mRNA and protein expression levels were significantly elevated in SGZ at 7 days after injury (Figure 1c-e), suggesting that TGM2 might play a pivotal role in neurogenesis following TBI.

Deletion of TGM2 in NSPCs Inhibits Hippocampal Neurogenesis
To explore the function of TGM2 in NSPCs, we generated the NSPCs-specific TAMinducible Tgm2 knockout (iKO) mice by crossing Nestin-creER T2 mice with Tgm2 fl/fl mice ( Figure S1a). Upon TAM administration to 6-8 weeks-old mice for three consecutive days, our qRT-PCR analysis demonstrated that the mRNA level of Tgm2 was significantly reduced in the dentate gyrus of Tgm2 iKO mice compared to that of WT mice ( Figure S1b). Consistently, TGM2 fluorescence signal was almost undetectable in Tgm2-iKO NSPCs in SGZ by immunohistochemistry staining assays (Figure S1c-f). These results indicated that Tgm2 could be specifically deleted in NSPCs upon TAM treatment.
Next, we applied a unilateral hippocampal stab wound injury to 6-8 weeks-old Tgm2 WT and iKO mice to examine whether TGM2 depletion affects proliferation and differentiation of NSPCs after TBI. Following intraperitoneal administration of TAM for three consecutive days, animals were subjected to TBI and administered BrdU (200 mg/kg body

Deletion of TGM2 in NSPCs Inhibits Hippocampal Neurogenesis
To explore the function of TGM2 in NSPCs, we generated the NSPCs-specific TAMinducible Tgm2 knockout (iKO) mice by crossing Nestin-creER T2 mice with Tgm2 fl/fl mice ( Figure S1a). Upon TAM administration to 6-8 weeks-old mice for three consecutive days, our qRT-PCR analysis demonstrated that the mRNA level of Tgm2 was significantly reduced in the dentate gyrus of Tgm2 iKO mice compared to that of WT mice ( Figure S1b). Consistently, TGM2 fluorescence signal was almost undetectable in Tgm2-iKO NSPCs in SGZ by immunohistochemistry staining assays (Figure S1c-f). These results indicated that Tgm2 could be specifically deleted in NSPCs upon TAM treatment.

Overexpression of TGM2 in NSPCs Promotes Neurogenesis In Vitro
To further explore the role of TGM2 in neurogenesis, we constructed specific lentiviral vectors with GFP expression to up-or down-regulate TGM2. Transduction of TGM2 overexpression (lenti-Tgm2-OE) and downregulation (lenti-shTgm2) lentiviral vectors in cultured E13.5 NSPCs led to robust upregulation and reduction of TGM2 expression, respectively ( Figure S3a-d).
To analyze the role of TGM2 in NSPCs differentiation in vitro, the ratios of newborn neurons (GFP + Tuj1 + ) and new-formed astrocytes (GFP + GFAP + ) to lentivirus-transduced NSPCs (GFP + ) were quantified under pro-inflammatory conditions in vitro (Figure 3d

Overexpression of TGM2 Enhance Adult Neurogenesis after TBI
To examine whether TGM2 regulates adult neurogenesis in vivo, we grafted lenti-NC, lenti-Tgm2-OE, or lenti-shTgm2 into DG of 6-8 weeks old Nestin-CreER T2 ;tdTomato mice, which were then received intraperitoneal administration of TAM for three consecutive days. On the day after the last TAM injection, mice were received a stab wound injury in the hippocampus, as well as BrdU (200 mg/kg body weight) injection daily for three consecutive days (Figure 4a). At 7 days after the last BrdU injection, overexpression of TGM2 resulted in a significant increase in the proportion of BrdU + GFP + tdTomato + cells among GFP + tdTomato + cells as well as in the proportion of DCX + BrdU + GFP + tdTomato + cells among BrdU + GFP + tdTomato + cells, while knockdown of TGM2 significantly reduced the proliferation and neural differentiation of NSPCs compared to lenti-NC-transduced NSPCs (Figure 4b,d,e).

TGM2 Regulates the Expression of Genes Associated with Proliferation and Differentiation of NSPCs
To explore the molecular mechanism on how TGM2 regulates the proliferation and differentiation of NSPCs, we performed a transcriptional analysis of Tgm2-WT and Tgm2-iKO NSPCs that were cultured in the differentiation or proliferation medium for 48 h, respectively (Figure 5a). Results from the Pearson correlations and principal components and quantification (d-g) of BrdU (blue), DCX (pink) or NeuN (pink) immunostaining of hippocampal sections from Nestin-CreER T2 ;tdTomato mice which were injected with lentivirus, tamoxifen, and BrdU at given time windows. Percentages of BrdU + GFP + tdTamato + cells among GFP + tdTamato + cells were quantified to examine proliferative potential of lentivirus-transduced NSPCs at 7 dpi (c) and 21 dpi (f), respectively. Percentages of BrdU + GFP + tdTamato + DCX + cells (newborn immature neurons) or BrdU + GFP + tdTamato + NeuN + cells (newborn mature neurons) among BrdU + GFP + tdTamato + cells were quantified to determine the ability of neuronal differentiation of lentivirus-transduced NSPCs at 7 dpi (d) and 21 dpi (g), respectively. Scale bars: 50 µm. n = 4 mice per group. Data are represented as means ± SEM; two-tailed t-test, * p < 0.05, ** p < 0.01, *** p < 0.001.

TGM2 Regulates the Expression of Genes Associated with Proliferation and Differentiation of NSPCs
To explore the molecular mechanism on how TGM2 regulates the proliferation and differentiation of NSPCs, we performed a transcriptional analysis of Tgm2-WT and Tgm2-iKO NSPCs that were cultured in the differentiation or proliferation medium for 48 h, respectively (Figure 5a). Results from the Pearson correlations and principal components analysis (PCA) demonstrated that there was a clear discrimination between Tgm2-WT and Tgm2-iKO NSPCs, indicating that deletion of Tgm2 lead distinctly to gene expression pattern in both differentiating and proliferating NSPCs (Figure S4a,b). analysis (PCA) demonstrated that there was a clear discrimination between Tgm2-WT and Tgm2-iKO NSPCs, indicating that deletion of Tgm2 lead distinctly to gene expression pattern in both differentiating and proliferating NSPCs ( Figure S4a,b). In differentiating NSPCs, TGM2-deletion led to upregulation of 1583 genes as well as downregulation of 1529 genes (Figure 5b). To identify the biological functions perturbed by TGM2 deletion, we subjected the differentially expressed genes (DEGs) to gene ontology (GO) analysis of biological processes and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. GO analysis showed that genes downregulated on TGM2 ablation are involved in neurogenesis and neuronal maturation including gliogenesis, synapse organization, axonogenesis, GABAergic neuron differentiation, and central nervous system neuron differentiation (Figure 5c). KEGG analysis showed that genes associated with MAPK signaling pathway, PI3K-Akt signaling pathway, and notch signaling pathway are significantly down-regulated by TGM2 deletion (Figure 5c).
In proliferating NSPCs, TGM2 deletion led to decreased expression of 579 genes as well as increased expression of 291 genes (Figure 5d). GO analysis showed that downregulated genes were associated with DNA replication-dependent nucleosome assembly, DNA packaging, and protein-DNA complex assembly, suggesting that TGM2 might mediate histone modification through transamidation [35][36][37]. KEGG analysis showed that Notch signaling pathway was significantly down-regulated in proliferating Tgm2-iKO NSPCs (Figure 5e).
The upregulated genes in Tgm2-iKO NSPCs were associated with regulation of angiogenesis, inactivation of MAPK activity, regulation of vasculature development, chemokinmediated signaling pathway, and TNF, p53 and HIF-1 pathways ( Figure S5c,d), suggesting that TGM2 might play a pivotal role in the crosstalk between NSPCs and other cell types after TBI.

Discussion
TBI is a serious global health problem with deficiencies in prevention, care, and research [1]. The hippocampus plays a critical role in cognitive and behavioral functions and is highly susceptible to damage after TBI [38]. Since neuronal death is often observed in the hippocampus of TBI patients [39,40], the enhancement of endogenous hippocampal neurogenesis has been considered as a potential therapeutic approach for neuronal repair in the damaged hippocampus [41][42][43]. Immediately after TBI, microglia are the primary innate immune cells of the brain that rapidly respond within minutes and secrete inflammatory cytokines, neurotransmitters, chemokines, and reactive oxygen species, which produce either detrimental or favorable conditions for neurogenesis [6,[44][45][46]. Lipopolysaccharide (LPS), an endotoxin from Gram-negative bacteria, can induce robust microglial inflammatory activation. The addition of conditioned medium derived from LPS-stimulated microglia to cultured NSPCs has been widely used to study the inflammatory blockade in the process of neurogenesis [47,48]. Using both a mouse model of hippocampal stab wound injury and an in vitro cell culture model, this study elucidates a novel role of TGM2 in regulating hippocampal neurogenesis following TBI. We find that deletion or knockdown of TGM2 depletes proliferating NSPCs and inhibits neuronal differentiation in the (b-d) Quantitative PCR analysis validated the downregulation of genes associated with Notch signaling (b), MAPK and PI3-Akt signaling pathways (c) and co-downregulated genes in both proliferation and differentiation processes (d) using a new culture of Tgm2 iKO NSPCs under differentiating conditions. n = 4 cultures. Data are represented as means ± SEM; two-tailed t-test, * p < 0.05, ** p < 0.01, *** p < 0.001.

Discussion
TBI is a serious global health problem with deficiencies in prevention, care, and research [1]. The hippocampus plays a critical role in cognitive and behavioral functions and is highly susceptible to damage after TBI [38]. Since neuronal death is often observed in the hippocampus of TBI patients [39,40], the enhancement of endogenous hippocampal neurogenesis has been considered as a potential therapeutic approach for neuronal repair in the damaged hippocampus [41][42][43]. Immediately after TBI, microglia are the primary innate immune cells of the brain that rapidly respond within minutes and secrete inflammatory cytokines, neurotransmitters, chemokines, and reactive oxygen species, which produce either detrimental or favorable conditions for neurogenesis [6,[44][45][46]. Lipopolysaccharide (LPS), an endotoxin from Gram-negative bacteria, can induce robust microglial inflammatory activation. The addition of conditioned medium derived from LPS-stimulated microglia to cultured NSPCs has been widely used to study the inflammatory blockade in the process of neurogenesis [47,48]. Using both a mouse model of hippocampal stab wound injury and an in vitro cell culture model, this study elucidates a novel role of TGM2 in regulating hippocampal neurogenesis following TBI. We find that deletion or knockdown of TGM2 depletes proliferating NSPCs and inhibits neuronal differentiation in the hippocampus under both physiological and TBI conditions. In contrast, overexpression of TGM2 by lentiviral transduction promotes NSPCs migration and promotes hippocampal neurogenesis after TBI. Our data suggest that TGM2 may be a therapeutic target for the enhancement of endogenous neurogenesis in the injured hippocampus.
TGM2 is widely expressed in a variety of cell types. In A431 tumor cells, TGM2 activates PI3K/Akt signaling pathway that results in the upregulation of MMP-9 and an increase in cell adhesion, migration, invasion, and cancer metastasis [49]. TGM2 overexpression triggers stem cell differentiation via PI3K/Akt signaling in glioma [50]. We find that dozens of genes associated with PI3K-Akt signaling pathway, MAPK signaling pathway, and Notch signaling pathway are significantly down-regulated in NSPCs with TGM2-deletion, suggesting these dysregulated genes may be direct or indirect downstream targets of TGMS in regulation hippocampal neurogenesis. For example, the transcription factor SP1 can be crosslinked by TGM2, which results in Sp1 inactivation [51][52][53]. Moreover, Sp1 knockdown promotes the activation of Notch signaling pathway [54]. We speculate that TGM2 may regulate Notch signaling pathway through suppressing SP1.TGM2 has a multifunctional enzyme activity of isopeptidase, GTPase, and ATPase, deamidation, crosslinking, as well as adapter/scaffold activity [55]. TGM2 plays a prosurvival role in injured liver [56] as well as in ischemic stroke [57,58], while TGM2 accumulation results in cell death in hepatocytes [59], neuroglastoma cells [60], and neurons [61]. Although our data support that TGM2 has a prosurvival role in NSPCs by promoting their proliferation and neuronal differentiation, future studies are needed to determine the domains, conformations, and intracellular localizations of TGM2 that its function relies upon.
TBI is composed of both primary and secondary injuries that cause a series of structural damage and functional deficits in the brain [62]. Although various animal models of TBI have been developed, none of them can fully recapitulate all the pathophysiological aspects of human TBI patients [5,63]. Our previous study demonstrates that unilateral hippocampal blade stab injury (HBSI) can capture hemorrhage, neuroinflammation, and neuronal apoptosis in the injured hippocampus, but HBSI belongs to mainly focal, not diffuse type of injury [30]. In the diffuse type of TBI (such as controlled cortical impact, CCI), most newly generated neurons do not survive, and only a few of them connect with neural circuits [64,65]. Moreover, some newborn neurons are reported to aberrantly migrate in the outer granular cell layer of the hippocampus in adult mice 48 h after a moderate CCI [66]. Given that diffuse TBI is the most common type of brain injuries and tissue TGM2 has been identified as a key regulator for histone glutamine modifications, either serotonylation in the context of cellular differentiation or dopaminylation in the dopaminergic reward pathway [35,67], it will be interesting and important to investigate whether and how tissue and intracellular TGM2 play essential roles in every kinds of brain cells in various TBI models before translating findings from animals to human patients with neurotrauma.
Many specific inhibitors have been developed against TGM2 [68]. For example, ERW1041E is a TGM2-specific irreversible inhibitor that has been used to explore the role of TGM2 in hypoxia-induced pulmonary, celiac disease and cardiac fibrosis [69][70][71]. TGM2 inhibitors should be very useful to further support the role of TGM2 in cell cultures. Given that TGM2 is ubiquitously expressed in the central nervous system, technique for allowing the specific delivery of TGM2 inhibitors to NSPCS in the brain still remains a challenge. Moreover, additional experiments are required to ascertain the role and mechanisms of TGM2 in the pathogenesis of TBI, such as blocking TGM2 with specific inhibitors, profiling of proteome, rescuing TGM2-knockout phenotype, as well as evaluating possible crosstalk between different sources of TGM2.
In conclusion, the present study provides evidence showing that TGM2 is a key regulator for promoting hippocampal neurogenesis under both physiological and TBI conditions. We have also proposed some signaling pathways and gene candidates that are worthy to further explore the mechanisms of altered neurogenesis and to develop cell-based therapeutic strategies for treating brain trauma as well as other neurodegenerative diseases.
Hence, this study fills the gap of TGM2 in adult neurogenesis and proves the feasibility of endogenous NSPCs-based therapeutics for brain repair.