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Spermatogenesis is a cyclical process in which different generations of spermatids undergo a series of developmental steps at a fixed time and finally produce spermatids. Here, we report that overexpression of PD-L1 (B7 homolog1) in the testis causes sperm developmental disorders and infertility in male mice, with severe malformation and sloughing during spermatid development, characterized by disorganized and collapsed seminiferous epithelium structure. PD-L1 needs to be simultaneously expressed on Sertoli cells and spermatogonia to cause spermatogenesis failure. After that, we excluded the influence of factors such as the PD-L1 receptor and humoral regulation, confirming that PD-L1 has an intrinsic function to interact with PD-L1. Studies have shown that PD-L1 not only serves as a ligand but also plays a receptor-like role in signal transduction. PD-L1 interacts with PD-L1 to affect the adhesive function of germ cells, causing malformation and spermatid sloughing. Taken together, these results indicate that PD-L1 can interact with PD-L1 to cause germ cell detachment and male infertility.

Traumatic brain injury (TBI) is one of the leading causes of disability and paralysis around the world. Secondary injury, characterized by progressive neuronal loss and astrogliosis, plays important roles in the post-TBI cognitive impairment and mood disorder. Unfortunately, there still lacks effective treatments, particularly surgery interferences for it. Recent findings of intercellular mitochondria transfer implies a potential therapeutic value of mitochondria transplantation for TBI, which has not been tested yet. In the present study, we demonstrated a quick dysfunction of mitochondria, up-regulation of Tom20 in the injured cortex and subsequent cognitive and mood impairment. Our data demonstrated that mitochondria derived from allogeneic liver or autogeneic muscle stimulated similar microglial activation in brain parenchyma. In vitro experiments showed that exogenous mitochondria could be easily internalized by neurons, astrocytes, and microglia, except for oligodendrocytes. Mitochondria transplantation effectively rescued neuronal apoptosis, restored the expression of Tom20 and the phosphorylation of JNK. Further analysis revealed that mitochondria transplantation in injured cortex induced a significant up-regulation of BDNF in reactive astrocytes, improved animals' spatial memory and alleviated anxiety. In together, our data indicate that mitochondria transplantation may has the potential of clinical translation for TBI treatment, in combination with surgery.

Spinster homolog 2 (SPNS2) is the membrane transporter of sphingosine-1-phosphate (S1P), and it participates in several physiologic processes by activating different S1P receptors (S1PRs). However, its functions in the nervous system remain largely unclear. We explored the important role of SPNS2 in the process of retinal morphogenesis using a spns2-deficient rat model. In the absence of the functional SPNS2 transporter, we observed progressively aggravating laminar disorganization of the epithelium at the postnatal stage of retinal development. Disrupted cell polarity, delayed cell-cycle exit of retinal progenitor cells, and insufficient migration of newborn neurons were proposed in this study as potential mechanisms accounting for this structural disorder. In addition, we analyzed the expression profiles of spns2 and s1prs, and proposed that SPNS2 regulated retinal morphogenesis by establishing the S1P level in the eye and activating S1PR3 signaling. These data indicate that SPNS2 is indispensable for normal retinal morphogenesis and provide new insights on the role of S1P in the developing retina using an established in vivo model.-Fang, C., Bian, G., Ren, P., Xiang, J., Song, J., Yu, C., Zhang, Q., Liu, L., Chen, K., Liu, F., Zhang, K., Wu, C., Sun, R., Hu, D., Ju, G., Wang, J. S1P transporter SPNS2 regulates proper postnatal retinal morphogenesis.

In many mammals, the eyelids migrate over the eye and fuse during embryogenesis to protect the cornea from damage during birth and early life. Loss-of-function mutations affecting the epidermal growth factor receptor (EGFR) signaling pathway cause an eyes-open-at-birth (EOB) phenotype in rodents. We identified an insertional mutation in Spinster homolog 2 (Spns2) in a strain of transgenic rats exhibiting the EOB phenotype. Spns2, a sphingosine 1-phosphate (S1P) transporter that releases S1P from cells, was enriched at the tip of developing eyelids in wild-type rat embryos. Spns2 expression or treatment with S1P or any one of several EGFR ligands rescued the EOB Spns2 mutant phenotype in vivo and in tissue explants in vitro and rescued the formation of stress fibers in primary keratinocytes from mutants. S1P signaled through the receptors S1PR1, S1PR2, and S1PR3 to activate extracellular signal-regulated kinase (ERK) and EGFR-dependent mitogen-activated protein kinase kinase kinase 1 (MEKK1)-c-Jun signaling. S1P also induced the nuclear translocation of the transcription factor MAL in a manner dependent on EGFR signaling. MAL and c-Jun stimulated the expression of the microRNAs miR-21 and miR-222, both of which target the metalloprotease inhibitor TIMP3, thus promoting metalloprotease activity. The metalloproteases ADAM10 and ADAM17 stimulated EGFR signaling by cleaving a membrane-anchored form of EGF to release the ligand. Our results outline a network by which S1P transactivates EGFR signaling through a complex mechanism involving feedback between several intra- and extracellular molecules to promote eyelid fusion in the developing rat.

Programmed cell death 1 ligand 1 (PD-L1) plays a critical role in mediating autoimmune diseases, including type I diabetes (T1D). B cells are important antigen-presenting cells (APCs) that make a major contribution to T1D development. However, B cells expressing low levels of PD-L1 that infiltrate insulitic islets in NOD mice may not inhibit effector T cells and prevent T1D. Here, we generated PD-L1 transgenic NOD (NOD.PD-L1Tg) mice, in which most immune cells overexpress PD-L1, to investigate the ability of B cells overexpressing PD-L1 to inhibit diabetic CD4+ T cells and prevent T1D. The severity of insulitis in NOD.PD-L1Tg mice was significantly lower than in NOD mice and none developed diabetes. In addition, there were no differences in expression of activity markers by APCs following LPS stimulation between two groups. In vitro studies revealed that B cells expressing high levels of PD-L1 inhibited proliferation of and cytokine secretion by pre-diabetic CD4+ T cells, whereas in vivo studies showed that NOD/SCID mice receiving diabetic CD4+ T cells mixed with B cells overexpressing PD-L1 became diabetic at a slower rate. Thus, we propose that B cells showing high expression of PD-L1 protect NOD mice against T1D and downregulate diabetogenic CD4+ T cells.

The inhibitory co-receptor programmed death 1 (PD-1, encoded by pdcd1) and its two ligands PD-L1 and PD-L2 comprise an important immune inhibitory signaling pathway for defense against microbes and for self-tolerance. Unlike other members of the B7-CD28 family, expression of PD-L1 and PD-L2 is not limited to the immune system. In this study, we determined that a polyclonal antibody (pAb) (R&D Systems) against extracellular domains of mouse PD-L2 (mPD-L2) could recognize antigen(s) in diverse mouse tissues, including the anterior and intermediate pituitary gland, olfactory bulbs and olfactory epithelium, tongue epithelium, keratinized epithelial cells and skin and whisker hair follicles. These findings differed from previous reports of mPD-L2 localization. Reverse transcription PCR and Western blot analyses, however, were unable to detect any mPD-L2 transcripts or proteins of the 25-kD predicted molecular weight in RNA and protein extracts, respectively, from the above tissues, suggesting that the anti-mPD-L2 pAb cross-reacts with certain novel antigen(s). Developmental studies revealed that the earliest expression of mPD-L2-like antigen was in the olfactory epithelium at embryonic day 12.5 (E12.5). At E14.5, mPD-L2-like antigen was present in the skin, tongue and follicles of the skin and whiskers. The distribution patterns of mPD-L2-like antigen remained similar from E18.5 to adulthood. The results of bioinformatic analysis and other experiments suggested neural cell adhesion molecule and hemicentin-1 as candidate proteins with cross-reactivity to the anti-mPD-L2 pAb. These results demonstrate that care is required in interpreting staining patterns generated when anti-PD-L2 pAb is used to locate PD-L2-expressing cells in the central nervous system and epithelial tissues, such as the olfactory epithelium. In addition, this anti-PD-L2 pAb may be used as an alternative antibody for labeling the olfactory epithelium during embryonic development in mice.

A single microRNA (miRNA) can regulate expression of multiple proteins and expression of an individual protein may be controlled by numerous miRNAs. This regulatory pattern strongly suggests that synergistic effects of miRNAs play critical roles in regulating biological processes. miR-9 and miR-124, two of the most abundant miRNAs in the mammalian nervous system, have important functions in neuronal development. In this study, we identified the small GTP-binding protein Rap2a as a common target of both miR-9 and miR-124. miR-9 and miR-124 together, but neither miRNA alone, strongly suppressed Rap2a, thereby promoting neuronal differentiation of neural stem cells (NSCs) and dendritic branching of differentiated neurons. Rap2a also diminished the dendritic complexity of mature neurons by decreasing the levels of pAKT and pGSK3β. Our results reveal a novel pathway in which miR-9 and miR-124 synergistically repress expression of Rap2a to sustain homeostatic dendritic complexity during neuronal development and maturation.

Inflammatory reactions are the most critical pathological processes occurring after spinal cord injury (SCI). Activated microglia/macrophages have either detrimental or beneficial effects on neural regeneration based on their functional polarized M1/M2 subsets. However, the mechanism of microglia/macrophage polarization to M1/M2 at the injured spinal cord environment remains unknown. In this study, wild-type (WT) or aldose reductase (AR)-knockout (KO) mice were subjected to SCI by a spinal crush injury model. The expression pattern of AR, behavior tests for locomotor activity, and lesion size were assessed at between 4 h and 28 days after SCI. We found that the expression of AR is upregulated in microglia/macrophages after SCI in WT mice. In AR KO mice, SCI led to smaller injury lesion areas compared to WT. AR deficiency-induced microglia/macrophages induce the M2 rather than the M1 response and promote locomotion recovery after SCI in mice. In the in vitro experiments, microglia cell lines (N9 or BV2) were treated with the AR inhibitor (ARI) fidarestat. AR inhibition caused 4-hydroxynonenal (HNE) accumulation, which induced the phosphorylation of the cAMP response element-binding protein (CREB) to promote Arg1 expression. KG501, the specific inhibitor of phosphorylated CREB, could cancel the upregulation of Arg1 by ARI or HNE stimulation. Our results suggest that AR works as a switch which can regulate microglia by polarizing cells to either the M1 or the M2 phenotype under M1 stimulation based on its states of activity. We suggest that inhibiting AR may be a promising therapeutic method for SCI in the future.

Diabetes mellitus is associated with adverse complications in many organ systems including the brain. Accumulating evidence indicates that diabetes, regardless of its type, impairs adult neurogenesis in the dentate gyrus (DG) of the hippocampus (HPC). However, the effects of the disease on neurogenesis in the subventricular zone (SVZ) are not well established. We induced diabetes in male NOD/SCID (non-obese diabetic/severe combined immunodeficiency) mice and C57BL/6 mice with a single intraperitoneal injection of streptozotocin (STZ). On day 7 or day 21 after STZ injection mice received the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) for labeling of proliferative cells. Mice were sacrificed 24h later and brain coronal sections were stained with anti-BrdU antibodies. Neural stem/progenitor cell (NSC/NPC) proliferation, as revealed by BrdU-labeled cells, was markedly decreased in the subgranular zone of the DG in STZ-treated diabetic mice. A similar reduction of NSC/NPC proliferation was seen in the SVZ. Reduced DG and SVZ cell proliferation was also found in diabetic NOD mice, a model of spontaneous diabetes, and the reduction was attenuated by bilateral adrenalectomy (Adx). Adx did not alter blood glucose or insulin levels in either prediabetic or diabetic NOD mice, but Adx partly increased mRNA levels of hippocampal and SVZ brain-derived neurotrophic factor (BDNF), a crucial regulator of NSC/NPC proliferation. Moreover, NOD and NOD/SCID mice showed a more rapid reduction of NSC/NPC proliferation than C57BL/6 mice in response to diabetes. Thus, we conclude that diabetes inhibits cell proliferation in both the SVZ and HPC, and inhibition was associated with elevated glucocorticoid levels and reduced BDNF expression.

It has been reported that autoimmune inflammatory processes in human multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), may induce an alteration in neurogenesis. Studies with transgenic EAE mice have demonstrated an enhancement of neurogenesis in the subventricular zone (SVZ). In contrast, a reduction of stem cell proliferation in the same region has been observed by Pluchino et al. [Brain 2008;131:2564-2578] in myelin oligodendrocyte glycoprotein (MOG)-induced EAE mice. We immunized female C57BL/6 mice with MOG 35-55 peptide and successfully developed chronic/nonremitting EAE, which is believed to be analogous to the progressive form of MS. On day 21 postimmunization, coronal brain sections were collected and stained with anti-5-bromo-2'-deoxyuridine (BrdU) antibody. By counting the number of BrdU-labeled cells, we demonstrated that the neural stem/progenitor cell (NSC/NPC) proliferation decreased in the SVZ, which basically confirms the study of Pluchino et al. on the changes in the SVZ. A reduction of NSC/NPC proliferation also occurred in the hippocampal subgranular zone of the dentate gyrus. The hippocampus is well known to be an important region involved in learning and memory; thus, our finding may offer a possible explanation for the cognitive impairment in human chronic MS.

Spinal cord injury (SCI) frequently provokes serious detrimental outcomes because neuronal regeneration is limited in the central nervous system (CNS). Thus, the creation of a permissive environment for transplantation therapy with neural stem/progenitor cells (NS/PCs) is a promising strategy to replace lost neuronal cells, promote repair, and stimulate functional plasticity after SCI. Macrophages are important SCI-associated inflammatory cells and a major source of secreted factors that modify the lesion milieu. Here, we used conditional medium (CM) from bone marrow-derived M1 or M2 polarized macrophages to culture murine NS/PCs. The NS/PCs showed enhanced astrocytic versus neuronal/oligodendrocytic differentiation in the presence of M1- versus M2-CM. Similarly, cotransplantation of NS/PCs with M1 and M2 macrophages into intact or injured murine spinal cord increased the number of engrafted NS/PC-derived astrocytes and neurons/oligodendrocytes, respectively. Furthermore, when cotransplantated with M2 macrophages, the NS/PC-derived neurons integrated into the local circuitry and enhanced locomotor recovery following SCI. Interesting, engrafted M1 macrophages promoted long-distance rostral migration of NS/PC-derived cells in a chemokine (C-X-C motif) receptor 4 (CXCR4)-dependent manner, while engrafted M2 macrophages resulted in limited cell migration of NS/PC-derived cells. Altogether, these findings suggest that the cotransplantation of NS/PCs together with polarized macrophages could constitute a promising therapeutic approach for SCI repair.

The inflammatory response following spinal cord injury (SCI) involves the activation of resident microglia and the infiltration of macrophages. Macrophages and microglia can be polarized into the classically activated proinflammatory M1 phenotype or the alternatively activated anti-inflammatory M2 phenotype. Programmed cell death 1 (PD-1) is a critical immune inhibitory receptor involved in innate and adaptive immune responses. However, whether PD-1 is involved in the modulation of macrophage/microglial polarization is unknown. In this study, the mRNA levels of pd1 gradually increased after SCI, and PD-1 protein was found in macrophages/microglia in injured spinal cord sections. PD-1 knockout (KO) mice showed poor locomotor recovery after spinal cord crushing compared with wild-type mice. M1-type macrophages/microglia accumulated in greater numbers in the injured spinal cord of PD-1-KO mice. Under polarized stimulation, induced expression of PD-1 occurred in cultured macrophages and microglia. PD-1 suppressed M1 polarization by reducing the phosphorylation of signal transducer and activator of transcription 1 (STAT1) and promoted M2 polarization by increasing STAT6 phosphorylation. In PD-1-KO mice, the M1 response was enhanced via the activation of STAT1 and nuclear factor-kappa B. Furthermore, PD-1 played various roles in phagocytosis in macrophages and microglia. Therefore, our results suggest that PD-1 signaling plays an important role in the regulation of macrophage/microglial polarization. Thus, deregulated PD-1 signaling may induce the polarization of macrophages/microglia toward the M1 phenotype. Overall, our results provide new insights into the modulatory mechanisms of macrophage/microglial polarization, thereby possibly facilitating the development of new therapies for SCI via the regulation of macrophage/microglial polarization through PD-1 signaling. Electronic supplementary material The online version of this article (doi:10.1007/s13311-013-0254-x) contains supplementary material, which is available to authorized users.

In a previous study, we generated two monoclonal antibodies (mAbs) in mice, aNogoA-N and aNogo-66 mAb, which were raised against recombinant N-terminal fragments of rat NogoA and Nogo-66, respectively. When compared with the commercial rabbit anti-rat NogoA polyclonal antibody (pAb), which can specifically recognise NogoA, the two mAbs were also specific for the NogoA antigen in immunofluorescence histochemical (IHC) staining and Western blot (WB) analysis. Serial truncations of NogoA covering the N-terminal region of NogoA (aa 570-691) and Nogo-66 (aa 1026-1091) were expressed in E. coli. The epitopes recognised by aNogoA-N and aNogo-66 are located in the aa 634-668 and aa 1026-1055 regions of NogoA, respectively. Both mAbs remarkably enhanced the axon growth and branching of cultured hippocampal neurons in vitro. These results suggest that the antibodies that bind to aa 634-668 and aa 1026-1055 of NogoA may have stimulatory effects on axon growth and branching. Additionally, the two mAbs that we generated are specific for NogoA and significantly block NogoA function. In conclusion, two sites in NogoA located within aa 634-668 and aa 1026-1055 are recognised by our two antibodies and are novel and potentially promising targets for repair after central nervous system (CNS) injury.

MicroRNA-124 (miR-124) is abundantly expressed in neurons in the mammalian central nervous system, and plays critical roles in the regulation of gene expression during embryonic neurogenesis and postnatal neural differentiation. However, the expression profile of miR-124 after spinal cord injury and the underlying regulatory mechanisms are not well understood. In the present study, we examined the expression of miR-124 in mouse brain and spinal cord after spinal cord injury using in situ hybridization. Furthermore, the expression of miR-124 was examined with quantitative RT-PCR at 1, 3 and 7 days after spinal cord injury. The miR-124 expression in neurons at the site of injury was evaluated by in situ hybridization combined with NeuN immunohistochemical staining. The miR-124 was mainly expressed in neurons throughout the brain and spinal cord. The expression of miR-124 in neurons significantly decreased within 7 days after spinal cord injury. Some of the neurons in the peri-lesion area were NeuN(+)/miR-124(-). Moreover, the neurons distal to the peri-lesion site were NeuN(+)/miR-124(+). These findings indicate that miR-124 expression in neurons is reduced after spinal cord injury, and may reflect the severity of spinal cord injury.