Transgenic mice expressing beta-galactosidase in mature neurons under neuron-specific enolase promoter control

Charcot-Marie-Tooth type 2A in vivo models: Current updates

Charcot-Marie-Tooth type 2A (CMT2A) is an inherited sensorimotor neuropathy associated with mutations within the Mitofusin 2 (MFN2) gene. These mutations impair normal mitochondrial functioning via different mechanisms, disturbing the equilibrium between mitochondrial fusion and fission, of mitophagy and mitochondrial axonal transport. Although CMT2A disease causes a significant disability, no resolutive treatment for CMT2A patients to date. In this context, reliable experimental models are essential to precisely dissect the molecular mechanisms of disease and to devise effective therapeutic strategies. The most commonly used models are either in vitro or in vivo, and among the latter murine models are by far the most versatile and popular. Here, we critically revised the most relevant literature focused on the experimental models, providing an update on the mammalian models of CMT2A developed to date. We highlighted the different phenotypic, histopathological and molecular characteristics, and their use in translational studies for bringing potential therapies from the bench to the bedside. In addition, we discussed limitations of these models and perspectives for future improvement.

An ultra-compact promoter drives widespread neuronal expression in mouse and monkey brains

Promoters are essential tools for basic and translational neuroscience research. An ideal promoter should possess the shortest possible DNA sequence with cell-type selectivity. However, whether ultra-compact promoters can offer neuron-specific expression is unclear. Here, we report the development of an extremely short promoter that enables selective gene expression in neurons, but not glial cells, in the brain. The promoter sequence originates from the human CALM1 gene and is only 120 bp in size. The CALM1 promoter (pCALM1) embedded in an adeno-associated virus (AAV) genome directed broad reporter expression in excitatory and inhibitory neurons in mouse and monkey brains. Moreover, pCALM1, when inserted into an all-in-one AAV vector expressing SpCas9 and sgRNA, drives constitutive and conditional in vivo gene editing in neurons and elicits functional alterations. These data demonstrate the ability of pCALM1 to conduct restricted neuronal gene expression, illustrating the feasibility of ultra-miniature promoters for targeting brain-cell subtypes.

A novel transgenic mouse line with hippocampus-dominant and inducible expression of truncated human tau

BACKGROUND

Intraneuronal accumulation of hyperphosphorylated tau is a defining hallmark of Alzheimer's disease (AD). However, mouse models imitating AD-exclusive neuronal tau pathologies are lacking.

METHODS

We generated a new tet-on transgenic mouse model expressing truncated human tau N1-368 (termed hTau368), a tau fragment increased in the brains of AD patients and aged mouse brains. Doxycycline (dox) was administered in drinking water to induce hTau368 expression. Immunostaining and Western blotting were performed to measure the tau level. RNA sequencing was performed to evaluate gene expression, and several behavioral tests were conducted to evaluate mouse cognitive functions, emotion and locomotion.

RESULTS

Dox treatment for 1-2 months at a young age induced overt and reversible human tau accumulation in the brains of hTau368 transgenic mice, predominantly in the hippocampus. Meanwhile, the transgenic mice exhibited AD-like high level of tau phosphorylation, glial activation, loss of mature neurons, impaired hippocampal neurogenesis, synaptic degeneration and cognitive deficits.

CONCLUSIONS

This study developed a well-characterized and easy-to-use tool for the investigations and drug development for AD and other tauopathies.

The use of viral vectors to promote repair after spinal cord injury

Spinal cord injury (SCI) is a devastating event that can permanently disrupt multiple modalities. Unfortunately, the combination of the inhibitory environment at a central nervous system (CNS) injury site and the diminished intrinsic capacity of adult axons for growth results in the failure for robust axonal regeneration, limiting the ability for repair. Delivering genetic material that can either positively or negatively modulate gene expression has the potential to counter the obstacles that hinder axon growth within the spinal cord after injury. A popular gene therapy method is to deliver the genetic material using viral vectors. There are considerations when deciding on a viral vector approach for a particular application, including the type of vector, as well as serotypes, and promoters. In this review, we will discuss some of the aspects to consider when utilizing a viral vector approach to as a therapy for SCI. Additionally, we will discuss some recent applications of gene therapy to target extrinsic and/or intrinsic barriers to promote axon regeneration after SCI in preclinical models. While still in early stages, this approach has potential to treat those living with SCI.

Hippocampal BMP signaling as a common pathway for antidepressant action

The benefits of current treatments for depression are limited by low response rates, delayed therapeutic effects, and multiple side effects. Antidepressants affect a variety of neurotransmitter systems in different areas of the brain, and the mechanisms underlying their convergent effects on behavior have been unclear. Here we identify hippocampal bone morphogenetic protein (BMP) signaling as a common downstream pathway that mediates the behavioral effects of five different antidepressant classes (fluoxetine, bupropion, duloxetine, vilazodone, trazodone) and of electroconvulsive therapy. All of these therapies decrease BMP signaling and enhance neurogenesis in the hippocampus. Preventing the decrease in BMP signaling blocks the effect of antidepressant treatment on behavioral phenotypes. Further, inhibition of BMP signaling in hippocampal newborn neurons is sufficient to produce an antidepressant effect, while chemogenetic silencing of newborn neurons prevents the antidepressant effect. Thus, inhibition of hippocampal BMP signaling is both necessary and sufficient to mediate the effects of multiple classes of antidepressants.

Animal Models of CMT2A: State-of-art and Therapeutic Implications

Charcot-Marie-Tooth disease type 2A (CMT2A), arising from mitofusin 2 (MFN2) gene mutations, is the most common inherited axonal neuropathy affecting motor and sensory neurons. The cellular and molecular mechanisms by which MFN2 mutations determine neuronal degeneration are largely unclear. No effective treatment exists for CMT2A, which has a high degree of genetic/phenotypic heterogeneity. The identification of mutations in MFN2 has allowed the generation of diverse transgenic animal models, but to date, their ability to recapitulate the CMT2A phenotype is limited, precluding elucidation of its pathogenesis and discovery of therapeutic strategies. This review will critically present recent progress in in vivo CMT2A disease modeling, discoveries, drawbacks and limitations, current challenges, and key reflections to advance the field towards developing effective therapies for these patients.

Early Restoration of Shank3 Expression in Shank3 Knock-Out Mice Prevents Core ASD-Like Behavioral Phenotypes

Several genes are associated with increased risk for autism spectrum disorder (ASD), neurodevelopmental disorders that present with repetitive movements and restricted interests along with deficits in social interaction/communication. While genetic alterations associated with ASD are present early in life, ASD-like behaviors are difficult to detect in early infancy. This raises the issue of whether reversal of an ASD-associated genetic alteration early in life can prevent the onset of ASD-like behaviors. Genetic alterations of SHANK3, a well-characterized gene encoding a postsynaptic scaffolding protein, are estimated to contribute to ∼0.5% of ASD and remain one of the more replicated and well-characterized genetic defects in ASD. Here, we investigate whether early genetic reversal of a Shank3 mutation can prevent the onset of ASD-like behaviors in a mouse model. Previously, we have demonstrated that mice deficient in Shank3 display a wide range of behavioral abnormalities such as repetitive grooming, social deficits, anxiety, and motor abnormalities. In this study, we replicate many of these behaviors in Shank3 mutant mice. With early genetic restoration of wild-type (WT) Shank3, we rescue behaviors including repetitive grooming and social, locomotor, and rearing deficits. Our findings support the idea that the underlying mechanisms involving ASD behaviors in mice deficient in Shank3 are susceptible to early genetic correction of Shank3 mutations.

Transgenic models for investigating the nervous system: Currently available neurofluorescent reporters and potential neuronal markers

Recombinant DNA technologies have enabled the development of transgenic animal models for use in studying a myriad of diseases and biological states. By placing fluorescent reporters under the direct regulation of the promoter region of specific marker proteins, these models can localize and characterize very specific cell types. One important application of transgenic species is the study of the cytoarchitecture of the nervous system. Neurofluorescent reporters can be used to study the structural patterns of nerves in the central or peripheral nervous system in vivo, as well as phenomena involving embryologic or adult neurogenesis, injury, degeneration, and recovery. Furthermore, crucial molecular factors can also be screened via the transgenic approach, which may eventually play a major role in the development of therapeutic strategies against diseases like Alzheimer's or Parkinson's. This review describes currently available reporters and their uses in the literature as well as potential neural markers that can be leveraged to create additional, robust transgenic models for future studies.

Molecular Imaging of Stem Cells

Regenerative medicine with the use of stem cells has appeared as a potential therapeutic alternative for many disease states. Despite initial enthusiasm, there has been relatively slow transition to clinical trials. In large part, numerous questions remain regarding the viability, biology and efficacy of transplanted stem cells in the living subject. The critical issues highlighted the importance of developing tools to assess these questions. Advances in molecular biology and imaging have allowed the successful non-invasive monitoring of transplanted stem cells in the living subject. Over the years these methodologies have been updated to assess not only the viability but also the biology of transplanted stem cells. In this review, different imaging strategies to study the viability and biology of transplanted stem cells are presented. Use of these strategies will be critical as the different regenerative therapies are being tested for clinical use.

Selective Activation of N,N'-Diacyl Rhodamine Pro-fluorophores Paired with Releasing Enzyme, Porcine Liver Esterase (PLE)

This study reports the synthesis and testing of a family of rhodamine pro-fluorophores and an enzyme capable of converting pro-fluorophores to Rhodamine 110. We prepared a library of simple N,N'-diacyl rhodamines and investigated porcine liver esterase (PLE) as an enzyme to activate rhodamine-based pro-fluorophores. A PLE-expressing cell line generated an increase in fluorescence rapidly upon pro-fluorophore addition demonstrating the rhodamine pro-fluorophores are readily taken up and fluorescent upon PLE-mediated release. Rhodamine pro-fluorophore amides trifluoroacetamide (TFAm) and proponamide (PAm) appeared to be the best substrates using a cell-based assay using PLE expressing HEK293. Our pro-fluorophore series showed diffusion into live cells and resisted endogenous hydrolysis. The use of our engineered cell line containing the exogenous enzyme PLE demonstrated the rigorousness of amide masking when compared to cells not containing PLE. This simple and selective pro-fluorophore rhodamine pair with PLE offers the potential to be used in vitro and in vivo fluorescence based assays.

Combined experience of six independent laboratories attempting to create an Ewing sarcoma mouse model

Ewing sarcoma (ES) involves a tumor-specific chromosomal translocation that produces the EWS-FLI1 protein, which is required for the growth of ES cells both in vitro and in vivo. However, an EWS-FLI1-driven transgenic mouse model is not currently available. Here, we present data from six independent laboratories seeking an alternative approach to express EWS-FLI1 in different murine tissues. We used the Runx2, Col1a2.3, Col1a3.6, Prx1, CAG, Nse, NEFL, Dermo1, P0, Sox9 and Osterix promoters to target EWS-FLI1 or Cre expression. Additional approaches included the induction of an endogenous chromosomal translocation, in utero knock-in, and the injection of Cre-expressing adenovirus to induce EWS-FLI1 expression locally in multiple lineages. Most models resulted in embryonic lethality or developmental defects. EWS-FLI1-induced apoptosis, promoter leakiness, the lack of potential cofactors, and the difficulty of expressing EWS-FLI1 in specific sites were considered the primary reasons for the failed attempts to create a transgenic mouse model of ES.

Maintenance of the Innate Seizure Threshold by Cyclooxygenase-2 is Not Influenced by the Translational Silencer, T-cell Intracellular Antigen-1

Activity of neuronal cyclooxygenase-2 (COX-2), a primary source of PG synthesis in the normal brain, is enhanced by excitatory neurotransmission and this is thought to be involved in seizure suppression. Results herein showing that the incidence of pentylenetetrazole (PTZ)-induced convulsions is suppressed in transgenic mice overexpressing COX-2 in neurons support this notion. T-cell intracellular antigen-1 (TIA-1) is an mRNA binding protein that is known to bind to COX-2 mRNA and repress its translation in non-neuronal cell types. An examination of the expression profile of TIA-1 protein in the normal brain indicated that it is expressed broadly by neurons, including those that express COX-2. However, whether TIA-1 regulates COX-2 protein levels in neurons is not known. The purpose of this study was to test the possibility that deletion of TIA-1 increases basal COX-2 expression in neurons and consequently raises the seizure threshold. Results demonstrate that neither the basal nor seizure-induced expression profiles of COX-2 were altered in mice lacking a functional TIA-1 gene suggesting that TIA-1 does not contribute to regulation of COX-2 protein expression in neurons. The acute PTZ-induced seizure threshold was also unchanged in mice lacking TIA-1 protein, indicating that this RNA binding protein does not influence the innate seizure threshold. Nevertheless, the results raise the possibility that the level of neuronal COX-2 expression may be a determinant of the innate seizure threshold and suggest that a better understanding of the regulation of COX-2 expression in the brain could provide new insight into the molecular mechanisms that suppress seizure induction.

Characterization of neural stem cells modified with hypoxia/neuron-specific VEGF expression system for spinal cord injury

Spinal cord injury (SCI) is an incurable disease causing an ischemic environment and functional defect, thus a new therapeutic approach is needed for SCI treatment. Vascular endothelial growth factor (VEGF) is a potent therapeutic gene to treat SCI via angiogenesis and neuroprotection, and both tissue-specific gene expression and high gene delivery efficiency are important for successful gene therapy. Here we design the hypoxia/neuron dual-specific gene expression system (pEpo-NSE) and efficient gene delivery platform can be achieved by the combination ex vivo gene therapy with erythropoietin (Epo) enhancer, neuron-specific enolase (NSE) promoter and neural stem cells (NSCs). An in vitro model, NSCs transfected with pEpo-NSE were consistently and selectively overexpressing therapeutic genes in response to neural differentiation and hypoxic conditions. Also, in SCI model, ex vivo gene therapy using pEpo-NSE system with NSCs significantly enhanced gene delivery efficiency compared with pEpo-NSE system gene therapy alone. However, microarray analysis reveals that introducing exogenous pEpo-NSE and VEGF triggers biological pathways in NSCs such as glycolysis and signaling pathways such as Ras and mitogen-activated protein kinase, leading to cell proliferation, differentiation and apoptosis. Collectively, it indicates that the pEpo-NSE gene expression system works stably in NSCs and ex vivo gene therapy using pEpo-NSE system with NSCs improves gene expression efficiency. However, exogenously introduced pEpo-NSE system has an influence on gene expression profiles in NSCs. Therefore, when we consider ex vivo gene therapy for SCI, the effects of changes in gene expression profiles in NSCs on safety should be investigated.

Tracking Adventitial Fibroblast Contribution to Disease: A Review of Current Methods to Identify Resident Fibroblasts

Cells present in the adventitia, or outermost layer of the blood vessel, contribute to the progression of vascular diseases, such as atherosclerosis, hypertension, and aortic dissection. The adventitial fibroblast of the aorta is the prototypic perivascular fibroblast, but the adventitia is composed of multiple distinct cell populations. Therefore, methods for uniquely identifying the fibroblast are critical for a better understanding of how these cells contribute to disease processes. A popular method for distinguishing adventitial cell types relies on the use of genetic tools in the mouse to trace and manipulate these cells. Because lineage tracing relying on Cre-recombinase expressing mice is used more frequently in studies of vascular disease, it is important to outline the advantages and limitations of these genetic tools. The purpose of this article is to provide an overview of the various genetic tools available in the mouse for the study of resident adventitial fibroblasts.

Physiological Exploration of the Long Term Evolutionary Selection against Expression of N-Glycolylneuraminic Acid in the Brain

All vertebrate cell surfaces display a dense glycan layer often terminated with sialic acids, which have multiple functions due to their location and diverse modifications. The major sialic acids in most mammalian tissues are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), the latter being derived from Neu5Ac via addition of one oxygen atom at the sugar nucleotide level by CMP-Neu5Ac hydroxylase (Cmah). Contrasting with other organs that express various ratios of Neu5Ac and Neu5Gc depending on the variable expression of Cmah, Neu5Gc expression in the brain is extremely low in all vertebrates studied to date, suggesting that neural expression is detrimental to animals. However, physiological exploration of the reasons for this long term evolutionary selection has been lacking. To explore the consequences of forced expression of Neu5Gc in the brain, we have established brain-specific Cmah transgenic mice. Such Neu5Gc overexpression in the brain resulted in abnormal locomotor activity, impaired object recognition memory, and abnormal axon myelination. Brain-specific Cmah transgenic mice were also lethally sensitive to a Neu5Gc-preferring bacterial toxin, even though Neu5Gc was overexpressed only in the brain and other organs maintained endogenous Neu5Gc expression, as in wild-type mice. Therefore, the unusually strict evolutionary suppression of Neu5Gc expression in the vertebrate brain may be explained by evasion of negative effects on neural functions and by selection against pathogens.

Rats overexpressing the dopamine transporter display behavioral and neurobiological abnormalities with relevance to repetitive disorders

The dopamine transporter (DAT) plays a pivotal role in maintaining optimal dopamine signaling. DAT-overactivity has been linked to various neuropsychiatric disorders yet so far the direct pathological consequences of it has not been fully assessed. We here generated a transgenic rat model that via pronuclear microinjection overexpresses the DAT gene. Our results demonstrate that DAT-overexpression induces multiple neurobiological effects that exceeded the expected alterations in the corticostriatal dopamine system. Furthermore, transgenic rats specifically exhibited behavioral and pharmaco-therapeutic profiles phenotypic of repetitive disorders. Together our findings suggest that the DAT rat model will constitute a valuable tool for further investigations into the pathological influence of DAT overexpression on neural systems relevant to neuropsychiatric disorders.

An In Vivo Bioassay for Detecting Antiandrogens Using Humanized Transgenic Mice Coexpressing the Tetracycline-Controlled Transactivator and Human CYP1B1 Gene

The typical strategy used in analysis of antiandrogens involves the morphological changes of a marker in castrated rats Hershberger assay for the prostate, seminal vesicle, levator ani plus bulbocavernosus muscles (LABC), Cowper’s gland, and glans penis. However, there are disadvantages to this approach, such as the time required, and the results may not correspond to those in actual human exposure. To evaluate its ability for detecting antiandrogens, in vivo the dose effect of di-(2-ethylhexyl) phthalate (DEHP) and time effect of five antiandrogens, DEHP, di-n-butyl phthalate (DBP), diethyl phthalate (DEP), linuron (3-(4-dichlorophenyl)-methoxy-1-methylurea), and 2,4′-DDE (1,1-dichloro-2-( p-chlorophenyl)-2-( o-chlorophenyl)ethylene), were investigated using humanized transgenic mice coexpressing tetracycline-controlled transactivator (tTA) and the human cytochrome P450 (CYP) enzyme CYP1B1 (hCYP1B1). Adult transgenic males were treated with each of the five antiandrogens, and their tTA-driven hCYP1B1 expressions analyzed by real-time polymerase chain reaction (PCR) and/or Western blot and for O-debenzylation activity. Herein, the treatments of adult males with the five antiandrogens were shown to affect the increased levels of tTA-driven hCYP1B1 expression in both dose-dependent and repeated experiments. Thus, this novel in vivo bioassay, using humanized transgenic mice, is useful for measuring antiandrogens, and is a means to a more relevant bioas-say relating to actual human exposure.

Systemic Analysis of Atg5-Null Mice Rescued from Neonatal Lethality by Transgenic ATG5 Expression in Neurons

Autophagy is a cytoplasmic degradation system that is important for starvation adaptation and cellular quality control. Previously, we reported that Atg5-null mice are neonatal lethal; however, the exact cause of their death remains unknown. Here, we show that restoration of ATG5 in the brain is sufficient to rescue Atg5-null mice from neonatal lethality. This suggests that neuronal dysfunction, including suckling failure, is the primary cause of the death of Atg5-null neonates, which would further be accelerated by nutrient insufficiency due to a systemic failure in autophagy. The rescued Atg5-null mouse model, as a resource, allows us to investigate the physiological roles of autophagy in the whole body after the neonatal period. These rescued mice demonstrate previously unappreciated abnormalities such as hypogonadism and iron-deficiency anemia. These observations provide new insights into the physiological roles of the autophagy factor ATG5.

Deimmunization for gene therapy: host matching of synthetic zinc finger constructs enables long-term mutant Huntingtin repression in mice

Background

Synthetic zinc finger (ZF) proteins can be targeted to desired DNA sequences and are useful tools for gene therapy. We recently developed a ZF transcription repressor (ZF-KOX1) able to bind to expanded DNA CAG-repeats in the huntingtin (HTT) gene, which are found in Huntington’s disease (HD). This ZF acutely repressed mutant HTT expression in a mouse model of HD and delayed neurological symptoms (clasping) for up to 3 weeks. In the present work, we sought to develop a long-term single-injection gene therapy approach in the brain.

Method

Since non-self proteins can elicit immune and inflammatory responses, we designed a host-matched analogue of ZF-KOX1 (called mZF-KRAB), to treat mice more safely in combination with rAAV vector delivery. We also tested a neuron-specific enolase promoter (pNSE), which has been reported as enabling long-term transgene expression, to see whether HTT repression could be observed for up to 6 months after AAV injection in the brain.

Results

After rAAV vector delivery, we found that non-self proteins induce significant inflammatory responses in the brain, in agreement with previous studies. Specifically, microglial cells were activated at 4 and 6 weeks after treatment with non-host-matched ZF-KOX1 or GFP, respectively, and this was accompanied by a moderate neuronal loss. In contrast, the host-matched mZF-KRAB did not provoke these effects. Nonetheless, we found that using a pCAG promoter (CMV early enhancer element and the chicken β-actin promoter) led to a strong reduction in ZF expression by 6 weeks after injection. We therefore tested a new non-viral promoter to see whether the host-adapted ZF expression could be sustained for a longer time. Vectorising mZF-KRAB with a promoter-enhancer from neuron-specific enolase (Eno2, rat) resulted in up to 77 % repression of mutant HTT in whole brain, 3 weeks after bilateral intraventricular injection of 10¹⁰ virions. Importantly, repressions of 48 % and 23 % were still detected after 12 and 24 weeks, respectively, indicating that longer term effects are possible.

Conclusion

Host-adapted ZF-AAV constructs displayed a reduced toxicity and a non-viral pNSE promoter improved long-term ZF protein expression and target gene repression. The optimized constructs presented here have potential for treating HD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0128-x) contains supplementary material, which is available to authorized users.

Disruption of Gpr45 causes reduced hypothalamic POMC expression and obesity

A rise in the occurrence of obesity has driven exploration of its underlying genetic basis and potential targets for intervention. GWAS studies have identified obesity susceptibility pathways involving several neuropeptides that control energy homeostasis, suggesting that variations in the genes that regulate food intake and energy expenditure may contribute to obesity. In this study, we identified 5 additional obesity loci, including a neuronal orphan GPCR called Gpr45, in a forward genetic screen of mutant mice generated by piggyBac insertional mutagenesis. Disruption of Gpr45 led to increased adiposity at the time of weaning and increases in body mass, fat content, glucose intolerance, and hepatic steatosis with advancing age. Mice with disruptions in Gpr45 also displayed a reduction in expression of the metabolic regulator POMC and less energy expenditure prior to the onset of obesity. Mechanistically, we determined that GPR45 regulates POMC expression via the JAK/STAT pathway in a cell-autonomous manner. Consistent with this finding, intraventricular administration of melanotan-2, an analog of the POMC derivative α-MSH, suppressed adult obesity in Gpr45 mutants. These results reveal that GPR45 is a regulator of POMC signaling and energy expenditure, which suggests that it may be a potential intervention target to combat obesity.

Inflammation-induced reversible switch of the neuron-specific enolase promoter from Purkinje neurons to Bergmann glia

Neuron-specific enolase (NSE) is a glycolytic isoenzyme found in mature neurons and cells of neuronal origin. Injecting adeno-associated virus serotype 9 (AAV9) vectors carrying the NSE promoter into the cerebellar cortex is likely to cause the specific transduction of neuronal cells, such as Purkinje cells (PCs) and interneurons, but not Bergmann glia (BG). However, we found BG-predominant transduction without PC transduction along a traumatic needle tract for viral injection. The enhancement of neuroinflammation by the co-application of lipopolysaccharide (LPS) with AAV9 significantly expanded the BG-predominant area concurrently with the potentiated microglial activation. The BG-predominant transduction was gradually replaced by the PC-predominant transduction as the neuroinflammation dissipated. Experiments using glioma cell cultures revealed significant activation of the NSE promoter due to glucose deprivation, suggesting that intracellularly stored glycogen is metabolized through the glycolytic pathway for energy. Activation of the glycolytic enzyme promoter in BG concurrently with inactivation in PC may have pathophysiological significance for the production of lactate in activated BG and the utilization of lactate, which is provided by the BG-PC lactate shuttle, as a primary energy resource in injured PCs.

Long-term consequences of conditional genetic deletion of PTEN in the sensorimotor cortex of neonatal mice

Targeted deletion of the phosphatase and tensin homolog on chromosome ten (PTEN) gene in the sensorimotor cortex of neonatal mice enables robust regeneration of corticospinal tract (CST) axons following spinal cord injury as adults. Here, we assess the consequences of long-term conditional genetic PTEN deletion on cortical structure and neuronal morphology and screen for neuropathology. Mice with a LoxP-flanked exon 5 of the PTEN gene (PTENf/f mice) received AAV-Cre injections into the sensorimotor cortex at postnatal day 1 (P1) and were allowed to survive for up to 18months. As adults, mice were assessed for exploratory activity (open field), and motor coordination using the Rotarod®. Some mice received injections of Fluorogold into the spinal cord to retrogradely label the cells of origin of the CST. Brains were prepared for neurohistology and immunostained for PTEN and phospho-S6, which is a downstream marker of mammalian target of rapamycin (mTOR) activation. Immunostaining revealed a focal area of PTEN deletion affecting neurons in all cortical layers, although in some cases PTEN expression was maintained in many small-medium sized neurons in layers III-IV. Neurons lacking PTEN were robustly stained for pS6. Cortical thickness was significantly increased and cortical lamination was disrupted in the area of PTEN deletion. PTEN-negative layer V neurons that give rise to the CST, identified by retrograde labeling, were larger than neurons with maintained PTEN expression, and the relative area occupied by neuropil vs. cell bodies was increased. There was no evidence of tumor formation or other neuropathology. Mice with PTEN deletion exhibited open field activity comparable to controls and there was a trend for impaired Rotarod performance (not statistically significant). Our findings indicate that early postnatal genetic deletion of PTEN that is sufficient to enable axon regeneration by adult neurons causes neuronal hypertrophy but no other detectable neuropathology.

Sleep and immunomodulatory responses to systemic lipopolysaccharide in mice selectively expressing interleukin-1 receptor 1 on neurons or astrocytes

Sleep-wake behavior is altered in response to immune challenge. Although the precise mechanisms that govern sickness-induced changes in sleep are not fully understood, interleukin-1β (IL-1) is one mediator of these responses. To better understand mechanisms underlying sleep and inflammatory responses to immune challenge, we used two transgenic mouse strains that express IL-1 receptor 1 (IL1R1) only in the central nervous system and selectively on neurons or astrocytes. Electroencephalographic recordings from transgenic and wild-type mice reveal that systemic challenge with lipopolysaccharide (LPS) fragments sleep, suppresses rapid eye movement sleep (REMS), increases non-REMS (NREMS), diminishes NREM delta power, and induces fever in all genotypes. However, the magnitude of REMS suppression is greater in mice expressing IL1R1 on astrocytes compared with mice in which IL1R1 is selectively expressed on neurons. Furthermore, there is a delayed increase in NREM delta power when IL1R1 is expressed on astrocytes. LPS-induced sleep fragmentation is reduced in mice expressing IL1R1 on neurons. Although LPS increases IL-1 and IL-6 in brain of all genotypes, this response is attenuated when IL1R1 is expressed selectively on neurons or on astrocytes. Collectively, these data suggest that in these transgenic mice under the conditions of this study it is neuronal IL1R1 that plays a greater role in LPS-induced suppression of REMS and NREM delta power, whereas astroglial IL1R1 is more important for sleep fragmentation after this immune challenge. Thus, aspects of central responses to LPS are modulated by IL1R1 in a cell type-specific manner.

Stem Cell Monitoring with a Direct or Indirect Labeling Method

The molecular imaging techniques allow monitoring of the transplanted cells in the same individuals over time, from early localization to the survival, migration, and differentiation. Generally, there are two methods of stem cell labeling: direct and indirect labeling methods. The direct labeling method introduces a labeling agent into the cell, which is stably incorporated or attached to the cells prior to transplantation. Direct labeling of cells with radionuclides is a simple method with relatively fewer adverse events related to genetic responses. However, it can only allow short-term distribution of transplanted cells because of the decreasing imaging signal with radiodecay, according to the physical half-lives, or the signal becomes more diffuse with cell division and dispersion. The indirect labeling method is based on the expression of a reporter gene transduced into the cell before transplantation, which is then visualized upon the injection of an appropriate probe or substrate. In this review, various imaging strategies to monitor the survival and behavior change of transplanted stem cells are covered. Taking these new approaches together, the direct and indirect labeling methods may provide new insights on the roles of in vivo stem cell monitoring, from bench to bedside.

Molecular layer interneurons of the cerebellum: developmental and morphological aspects

During the past 25 years, our knowledge on the development of basket and stellate cells (molecular layer interneurons [MLIs]) has completely changed, not only regarding their origin from the ventricular zone, corresponding to the primitive cerebellar neuroepithelium, instead of the external granular layer, but above all by providing an almost complete account of the genetic regulations (transcription factors and other genes) involved in their differentiation and synaptogenesis. Moreover, it has been shown that MLIs' precursors (dividing neuroblasts) and not young postmitotic neurons, as in other germinal neuroepithelia, leave the germinative zone and migrate all along a complex and lengthy path throughout the presumptive cerebellar white matter, which provides suitable niches exerting epigenetic influences on their ultimate neuronal identities. Recent studies carried out on the anatomical-functional properties of adult MLIs emphasize the importance of these interneurons in regulating PC inhibition, and point out the crucial role played by electrical synaptic transmission between MLIs as well as ephaptic interactions between them and Purkinje cells at the pinceaux level, in the regulation of this inhibition.

Host Determinants of Prion Strain Diversity Independent of Prion Protein Genotype

Phenotypic diversity in prion diseases can be specified by prion strains in which biological traits are propagated through an epigenetic mechanism mediated by distinct PrP(Sc) conformations. We investigated the role of host-dependent factors on phenotypic diversity of chronic wasting disease (CWD) in different host species that express the same prion protein gene (Prnp). Two CWD strains that have distinct biological, biochemical, and pathological features were identified in transgenic mice that express the Syrian golden hamster (SGH) Prnp. The CKY strain of CWD had a shorter incubation period than the WST strain of CWD, but after transmission to SGH, the incubation period of CKY CWD was ∼150 days longer than WST CWD. Limited proteinase K digestion revealed strain-specific PrP(Sc) polypeptide patterns that were maintained in both hosts, but the solubility and conformational stability of PrP(Sc) differed for the CWD strains in a host-dependent manner. WST CWD produced PrP(Sc) amyloid plaques in the brain of the SGH that were partially insoluble and stable at a high concentration of protein denaturant. However, in transgenic mice, PrP(Sc) from WST CWD did not assemble into plaques, was highly soluble, and had low conformational stability. Similar studies using the HY and DY strains of transmissible mink encephalopathy resulted in minor differences in prion biological and PrP(Sc) properties between transgenic mice and SGH. These findings indicate that host-specific pathways that are independent of Prnp can alter the PrP(Sc) conformation of certain prion strains, leading to changes in the biophysical properties of PrP(Sc), neuropathology, and clinical prion disease.

IMPORTANCE

Prions are misfolded pathogenic proteins that cause neurodegeneration in humans and animals. Transmissible prion diseases exhibit a spectrum of disease phenotypes and the basis of this diversity is encoded in the structure of the pathogenic prion protein and propagated by an epigenetic mechanism. In the present study, we investigated prion diversity in two hosts species that express the same prion protein gene. While prior reports have demonstrated that prion strain properties are stable upon infection of the same host species and prion protein genotype, our findings indicate that certain prion strains can undergo dramatic changes in biological properties that are not dependent on the prion protein. Therefore, host factors independent of the prion protein can affect prion diversity. Understanding how host pathways can modify prion disease phenotypes may provide clues on how to alter prion formation and lead to treatments for prion, and other, human neurodegenerative diseases of protein misfolding.

Selective contributions of neuronal and astroglial interleukin-1 receptor 1 to the regulation of sleep

Interactions between sleep and immune function are bidirectional. Although the mechanisms that govern these interactions are not fully elucidated, the pro-inflammatory cytokine, interleukin-1β (IL-1), is a known regulator of sleep and mediator of immune responses. To further clarify the underlying substrates of sleep and immune interactions, we engineered two transgenic mouse lines that express interleukin-1 receptor 1 (IL1R1) only in the central nervous system (CNS) and selectively on neurons (NSE-IL1R1) or astrocytes (GFAP-IL1R1). During spontaneous sleep, compared to wild type (WT) animals, NSE-IL1R1 and GFAP-IL1R1 mice have more rapid eye movement sleep (REMS) that is characterized by reduced theta power in the electroencephalogram (EEG) spectra. The non-REM sleep (NREMS) EEG of each of the IL1R1 transgenic mouse strains also is characterized by enhanced power in the delta frequency band. In response to 6h of sleep deprivation, sleep of both IL1R1 transgenic mouse strains is more consolidated than that of WT animals. Additionally, the NREMS EEG of NSE-IL1R1 mice contains less delta power after sleep deprivation, suggesting astroglial IL1R1 activity may modulate sleep homeostasis. Intracerebroventricular injection of IL-1 fails to alter sleep or brain temperature of NSE-IL1R1 or GFAP-IL1R1 mice. These data suggest that selective IL1R1 expression on neurons or on astrocytes is not sufficient for centrally-administered IL-1 to induce sleep or fever. Lack of sleep and febrile responses to IL-1 in these IL1R1 transgenic mouse strains may be due to their inability to produce IL-6 in brain. Overall, these studies demonstrate, through the use of novel transgenic mice, that IL1R1 on neurons and astrocytes differentially mediates aspects of sleep under physiological conditions and in response to central IL-1 administration.

HMGB1 facilitates repair of mitochondrial DNA damage and extends the lifespan of mutant ataxin-1 knock-in mice

Mutant ataxin-1 (Atxn1), which causes spinocerebellar ataxia type 1 (SCA1), binds to and impairs the function of high-mobility group box 1 (HMGB1), a crucial nuclear protein that regulates DNA architectural changes essential for DNA damage repair and transcription. In this study, we established that transgenic or virus vector-mediated complementation with HMGB1 ameliorates motor dysfunction and prolongs lifespan in mutant Atxn1 knock-in (Atxn1-KI) mice. We identified mitochondrial DNA damage repair by HMGB1 as a novel molecular basis for this effect, in addition to the mechanisms already associated with HMGB1 function, such as nuclear DNA damage repair and nuclear transcription. The dysfunction and the improvement of mitochondrial DNA damage repair functions are tightly associated with the exacerbation and rescue, respectively, of symptoms, supporting the involvement of mitochondrial DNA quality control by HMGB1 in SCA1 pathology. Moreover, we show that the rescue of Purkinje cell dendrites and dendritic spines by HMGB1 could be downstream effects. Although extracellular HMGB1 triggers inflammation mediated by Toll-like receptor and receptor for advanced glycation end products, upregulation of intracellular HMGB1 does not induce such side effects. Thus, viral delivery of HMGB1 is a candidate approach by which to modify the disease progression of SCA1 even after the onset.

Molecular Genetic Strategies in the Study of Corticohippocampal Circuits

The first reproductively viable genetically modified mice were created in 1982 by Richard Palmiter and Ralph Brinster (Palmiter RD, Brinster RL, Hammer RE, Trumbauer ME, Rosenfeld MG, Birnberg NC, Evans RM. 1982. Dramatic growth of mice that develop from eggs microinjected with metallothionein-growth hormone fusion genes. Nature 300: 611-615). In the subsequent 30 plus years, numerous ground-breaking technical advancements in genetic manipulation have paved the way for improved spatially and temporally targeted research. Molecular genetic studies have been especially useful for probing the molecules and circuits underlying how organisms learn and remember—one of the most interesting and intensively investigated questions in neuroscience research. Here, we discuss selected genetic tools, focusing on corticohippocampal circuits and their implications for understanding learning and memory.

Seeing stem cells at work in vivo

Stem cell based-therapies are novel therapeutic strategies that hold key for developing new treatments for diseases conditions with very few or no cures. Although there has been an increase in the number of clinical trials involving stem cell-based therapies in the last few years, the long-term risks and benefits of these therapies are still unknown. Detailed in vivo studies are needed to monitor the fate of transplanted cells, including their distribution, differentiation, and longevity over time. Advancements in non-invasive cellular imaging techniques to track engrafted cells in real-time present a powerful tool for determining the efficacy of stem cell-based therapies. In this review, we describe the latest approaches to stem cell labeling and tracking using different imaging modalities.

Possible involvement of iron-induced oxidative insults in neurodegeneration

Involvement of iron in the development of neurodegenerative disorders has long been suggested, and iron that cannot be stored properly is suggested to induce iron toxicity. To enhance iron uptake and suppress iron storage in neurons, we generated transgenic (Tg) mice expressing iron regulatory protein 2 (IRP2), a major regulator of iron metabolism, in a neuron-specific manner. Although very subtle, IRP2 was expressed in all regions of brain examined. In the Tg mice, mitochondrial oxidative insults were observed including generation of 4-hydroxynonenal modified proteins, which appeared to be removed by a mitochondrial quality control protein Parkin. Inter-crossing of the Tg mice to Parkin knockout mice perturbed the integrity of neurons in the substantia nigra and provoked motor symptoms. These results suggest that a subtle, but chronic increase in IRP2 induces mitochondrial oxidative insults and accelerates neurodegeneration in a mouse model of Parkinson's disease. Thus, the IRP2 Tg may be a useful tool to probe the roles of iron-induced mitochondrial damages in neurodegeraration research.

Compartmental organization of synaptic inputs to parvalbumin-expressing GABAergic neurons in mouse primary somatosensory cortex

Parvalbumin (PV)-positive fast-spiking cells in the neocortex are known to generate gamma oscillations by mutual chemical and electrical connections. Recent findings suggest that this rhythm might be responsible for higher-order brain functions, and related to psychiatric disorders. To elucidate the precise structural rules of the connections of PV neurons, we first produced genetic tools. Using a lentiviral expression system, we developed neuron-specific promoters and a new reporter protein that labels the somatodendritic membrane of neurons. We applied the reporter protein to the generation of transgenic mice, and succeeded in visualizing the dendrites and cell bodies of PV neurons efficiently. Then we analyzed excitatory and inhibitory inputs to PV neurons in the primary somatosensory cortex using the mice. Corticocortical glutamatergic inputs were more frequently found on the distal dendrites than on the soma, whereas thalamocortical inputs did not differ between the proximal and distal portions. Corticocortical inhibitory inputs were more densely distributed on the soma than on the dendrites. We further investigated which types of neocortical GABAergic neurons preferred the PV soma over their dendrites. We revealed that the somatic and dendritic compartments principally received GABAergic inputs from vasoactive intestinal polypeptide (VIP)-positive and PV neurons, respectively. This compartmental organization suggests that PV neurons communicate with each other mainly via the dendrites, and that their activity is effectively controlled by the somatic inputs of VIP neurons. These findings provide new insights into the neuronal circuits involving PV neurons, and contribute to a better understanding of brain functions and mental disorders.

Abcd2 is a strong modifier of the metabolic impairments in peritoneal macrophages of ABCD1-deficient mice

The inherited peroxisomal disorder X-linked adrenoleukodystrophy (X-ALD), associated with neurodegeneration and inflammatory cerebral demyelination, is caused by mutations in the ABCD1 gene encoding the peroxisomal ATP-binding cassette (ABC) transporter ABCD1 (ALDP). ABCD1 transports CoA-esters of very long-chain fatty acids (VLCFA) into peroxisomes for degradation by β-oxidation; thus, ABCD1 deficiency results in VLCFA accumulation. The closest homologue, ABCD2 (ALDRP), when overexpressed, compensates for ABCD1 deficiency in X-ALD fibroblasts and in Abcd1-deficient mice. Microglia/macrophages have emerged as important players in the progression of neuroinflammation. Human monocytes, lacking significant expression of ABCD2, display severely impaired VLCFA metabolism in X-ALD. Here, we used thioglycollate-elicited primary mouse peritoneal macrophages (MPMΦ) from Abcd1 and Abcd2 single- and double-deficient mice to establish how these mutations affect VLCFA metabolism. By quantitative RT-PCR, Abcd2 mRNA was about half as abundant as Abcd1 mRNA in wild-type and similarly abundant in Abcd1-deficient MPMΦ. VLCFA (C26∶0) accumulated about twofold in Abcd1-deficient MPMΦ compared with wild-type controls, as measured by gas chromatography-mass spectrometry. In Abcd2-deficient macrophages VLCFA levels were normal. However, upon Abcd1/Abcd2 double-deficiency, VLCFA accumulation was markedly increased (sixfold) compared with Abcd1-deficient MPMΦ. Elovl1 mRNA, encoding the rate-limiting enzyme for elongation of VLCFA, was equally abundant across all genotypes. Peroxisomal β-oxidation of C26∶0 amounted to 62% of wild-type activity in Abcd1-deficient MPMΦ and was significantly more impaired (29% residual activity) upon Abcd1/Abcd2 double-deficiency. Single Abcd2 deficiency did not significantly compromise β-oxidation of C26∶0. Thus, the striking accumulation of VLCFA in double-deficient MPMΦ compared with single Abcd1 deficiency was due to the loss of ABCD2-mediated, compensatory transport of VLCFA into peroxisomes. We propose that moderate endogenous expression of Abcd2 in Abcd1-deficient murine macrophages prevents the severe metabolic phenotype observed in human X-ALD monocytes, which lack appreciable expression of ABCD2. This supports upregulation of ABCD2 as a therapeutic concept in X-ALD.

Generation and characterization of an Nse-CreERT2 transgenic line suitable for inducible gene manipulation in cerebellar granule cells

We created an Nse-CreER^T2 mouse line expressing the tamoxifen-inducible CreER^T2 recombinase under the control of the neuron-specific enolase (Nse) promoter. By using Cre reporter lines we could show that this Nse-CreER^T2 line has recombination activity in the granule cells of all cerebellar lobules as well as in postmitotic granule cell precursors in the external granular layer of the developing cerebellum. A few hippocampal dentate gyrus granule cells showed Cre-mediated recombination as well. Cre activity could be induced in both the developing and adult mouse brain. The established mouse line constitutes a valuable tool to study the function of genes expressed by cerebellar granule cells in the developing and adult brain. In combination with reporter lines it is a useful model to analyze the development and maintenance of the cerebellar architecture including granule cell distribution, migration, and the extension of granule cell fibers in vivo.

In vivo characterization of the role of tissue-specific translation elongation factor 1A2 in protein synthesis reveals insights into muscle atrophy

Translation elongation factor 1A2 (eEF1A2), uniquely among translation factors, is expressed specifically in neurons and muscle. eEF1A2‐null mutant wasted mice develop an aggressive, early‐onset form of neurodegeneration, but it is unknown whether the wasting results from denervation of the muscles, or whether the mice have a primary myopathy resulting from loss of translation activity in muscle. We set out to establish the relative contributions of loss of eEF1A2 in the different tissues to this postnatal lethal phenotype. We used tissue‐specific transgenesis to show that correction of eEF1A2 levels in muscle fails to ameliorate the overt phenotypic abnormalities or time of death of wasted mice. Molecular markers of muscle atrophy such as Fbxo32 were dramatically upregulated at the RNA level in wasted mice, both in the presence and in the absence of muscle‐specific expression of eEF1A2, but the degree of upregulation at the protein level was significantly lower in those wasted mice without transgene‐derived expression of eEF1A2 in muscle. This provides the first in vivo confirmation that eEF1A2 plays an important role in translation. In spite of the inability of the nontransgenic wasted mice to upregulate key atrogenes at the protein level in response to denervation to the same degree as their transgenic counterparts, there were no measurable differences between transgenic and nontransgenic wasted mice in terms of weight loss, grip strength, or muscle pathology. This suggests that a compromised ability fully to execute the atrogene pathway in denervated muscle does not affect the process of muscle atrophy in the short term.

Regulator of calcineurin 1 modulates expression of innate anxiety and anxiogenic responses to selective serotonin reuptake inhibitor treatment

Regulator of calcineurin 1 (RCAN1) controls the activity of calcium/calmodulin-dependent phosphatase calcineurin (CaN), which has been implicated in human anxiety disorders. Previously, we reported that RCAN1 functioned as an inhibitor of CaN activity in the brain. However, we now find enhanced phosphorylation of a CaN substrate, cAMP response element-binding protein (CREB), in the brains of Rcan1 knock-out (KO) mice. Consistent with enhanced CREB activation, we also observe enhanced expression of a CREB transcriptional target, brain-derived neurotrophic factor (BDNF) in Rcan1 KO mice. We also discovered that RCAN1 deletion or blockade of RCAN1-CaN interaction reduced CaN and protein phosphatase-1 localization to nuclear-enriched protein fractions and promoted CREB activation. Because of the potential links between CREB, BDNF, and anxiety, we examined the role of RCAN1 in the expression of innate anxiety. Rcan1 KO mice displayed reduced anxiety in several tests of unconditioned anxiety. Acute pharmacological inhibition of CaN rescued these deficits while transgenic overexpression of human RCAN1 increased anxiety. Finally, we found that Rcan1 KO mice lacked the early anxiogenic response to the selective serotonin reuptake inhibitor (SSRI) fluoxetine and had improved latency for its therapeutic anxiolytic effects. Together, our study suggests that RCAN1 plays an important role in the expression of anxiety-related and SSRI-related behaviors through CaN-dependent signaling pathways. These results identify RCAN1 as a mediator of innate emotional states and possible therapeutic target for anxiety.

Reporter gene imaging

OBJECTIVE

The purposes of this article are to summarize the basic concept and the strategies of reporter imaging; introduce reporter genes frequently used in optical imaging, nuclear medicine, and MRI for in vivo application; and show typical examples of reporter gene imaging.

CONCLUSION

In molecular biology, many reporter genes have been developed for monitoring cellular processes. Development of controlled gene delivery systems promotes construction of various types of reporter genes for monitoring the level of a gene expression, promoter activity, and protein-protein interaction. When an imaging reporter gene is placed under the control of a promoter, the amount of reporter protein can be dynamically visualized in vivo. Instrumental advances in molecular imaging have increased the sensitivity and resolution of in vivo reporter imaging. Though several types of reporters and multimodal imaging instruments are currently available, more efficient multimodal reporter gene systems and detectors compatible with several imaging modalities are needed.

Estrogen mediates neuroprotection and anti-inflammatory effects during EAE through ERα signaling on astrocytes but not through ERβ signaling on astrocytes or neurons

Estrogens can signal through either estrogen receptor α (ERα) or β (ERβ) to ameliorate experimental autoimmune encephalomyelitis (EAE), the most widely used mouse model of multiple sclerosis (MS). Cellular targets of estrogen-mediated neuroprotection are still being elucidated. Previously, we demonstrated that ERα on astrocytes, but not neurons, was critical for ERα ligand-mediated neuroprotection in EAE, including decreased T-cell and macrophage inflammation and decreased axonal loss. Here, we determined whether ERβ on astrocytes or neurons could mediate neuroprotection in EAE, by selectively removing ERβ from either of these cell types using Cre-loxP gene deletion. Our results demonstrated that, even though ERβ ligand treatment was neuroprotective in EAE, this neuroprotection was not mediated through ERβ on either astrocytes or neurons and did not involve a reduction in levels of CNS inflammation. Given the differential neuroprotective and anti-inflammatory effects mediated via ERα versus ERβ on astrocytes, we looked for molecules within astrocytes that were affected by signaling through ERα, but not ERβ. We found that ERα ligand treatment, but not ERβ ligand treatment, decreased expression of the chemokines CCL2 and CCL7 by astrocytes in EAE. Together, our data show that neuroprotection in EAE mediated via ERβ signaling does not require ERβ on either astrocytes or neurons, whereas neuroprotection in EAE mediated via ERα signaling requires ERα on astrocytes and reduces astrocyte expression of proinflammatory chemokines. These findings reveal important cellular differences in the neuroprotective mechanisms of estrogen signaling through ERα and ERβ in EAE.

Mouse models of age-related mitochondrial neurosensory hearing loss

Hearing loss is the most common sensory disorder in the elderly population. Overall, 10% of the population has a hearing loss in the US, and this age-related hearing disorder is projected to afflict more than 28 million Americans by 2030. Age-related hearing loss is associated with loss of sensory hair cells (sensory hearing loss) and/or spiral ganglion neurons (neuronal hearing loss) in the cochlea of the inner ear. Many lines of evidence indicate that oxidative stress and associated mitochondrial dysfunction play a central role in age-related neurodegenerative diseases and are a cause of age-related neurosensory hearing loss. Yet, the molecular mechanisms of how oxidative stress and/or mitochondrial dysfunction lead to hearing loss during aging remain unclear, and currently there is no treatment for this age-dependent disorder. Several mouse models of aging and age-related diseases have been linked to age-related mitochondrial neurosensory hearing loss. Evaluation of these animal models has offered basic knowledge of the mechanism underlying hearing loss associated with oxidative stress, mitochondrial dysfunction, and aging. Here we review the evidence that specific mutations in the mitochondrial DNA or nuclear DNA that affect mitochondrial function result in increased oxidative damage and associated loss of sensory hair cells and/or spiral ganglion neurons in the cochlea during aging, thereby causing hearing loss in these mouse models. Future studies comparing these models will provide further insight into fundamental knowledge about the disordered process of hearing and treatments to improve the lives of individuals with communication disorders. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Nicastrin overexpression in transgenic mice induces aberrant behavior and APP processing

Nicastrin (NCT) is a component of the presenilin protein complex, which is involved in the cleavage of β-amyloid precursor protein (βAPP) and Notch. The aim of this study was to determine the manner in which overexpression of wild-type human nicastrin (hNCTw) or mutant human nicastrin (hNCTm, D336A/Y337A) regulates brain functions and amyloid precusor protein (APP) processing. For this, we created transgenic (Tg) mice expressing neuron-specific enolase (NSE)-controlled hNCTw or hNCTm and measured their phenotypes as time passed. The NSE/hNCTw and NSE/hNCTm Tg groups exhibited greater behavioral dysfunction from 10 months of age than the non-Tg group, although their severities differed. Further, activity and component levels of the γ-secretase complex were significantly elevated in NSE/hNCTw Tg mice, expect for PEN-2. These alterations induced stimulation of APP processing, resulting in overproduction of Aβ-42 peptide in the NSE/hNCTw Tg group, whereas the NSE/hNCTm Tg group showed a comparatively weaker effect. Furthermore, the highest expression levels of β-secretase and NICD were observed in the NSE/hNCTw Tg group, similar to other phenotypes. Especially, a significances interference on the interaction between NCT and γ-secretase substrates was detected in NSE/hNCTm Tg groups compare with NSE/hNCTw Tg group. These results indicate that hNCTw overexpression in Tg mice promoted active assembly of the γ-secretase complex through modulation of APP processing and behavior, whereas the lesser effect in NSE/hNCTm Tg mice was due to reduced expression of hNCTm. These Tg mice could be useful for the development and application of therapeutic drugs in an animal model of Alzheimer's disease.

Inducible gene expression in postmitotic neurons by an in vivo electroporation-based tetracycline system

In vivo electroporation has been widely used to transfect foreign genes into neural progenitors and analyze the function of genes of interest in the developing nervous system. However, it has not been thoroughly examined in the conditional regulation of exogenous genes in postmitotic neurons. Here we show that the combination of in vivo electroporation and the newest version of the tetracycline (Tet)-controlled gene regulatory (Tet-On) system efficiently induced gene expression in various types of neurons in mouse embryonic and postnatal tissues. In pyramidal neurons of the cerebral cortex, tetracycline-responsive element (TRE)-driven gene expression was induced in the presence of doxycycline (Dox). The induction occurred in a dose-dependent manner. The Dox-dependent induction was also observed in cerebellar Purkinje cells and spinal cord neurons. Moreover, the TRE-driven inducible expression of mammalian Barh1 (Mbh1) mimicked the phenotype of the ubiquitous expression of Mbh1 in the spinal cord. These results indicate that the combination of the Tet-On system and in vivo electroporation is useful for analyzing gene function specifically in postmitotic neurons.

In vivo non invasive molecular imaging for immune cell tracking in small animals

Clinical and preclinical in vivo immune cell imaging approaches have been used to study immune cell proliferation, apoptosis and interaction at the microscopic (intra-vital imaging) and macroscopic (whole-body imaging) level by use of ex vivo or in vivo labeling method. A series of imaging techniques ranging from non-radiation based techniques such as optical imaging, MRI, and ultrasound to radiation based CT/nuclear imaging can be used for in vivo immune cell tracking. These imaging modalities highlight the intrinsic behavior of different immune cell populations in physiological context. Fluorescent, radioactive or paramagnetic probes can be used in direct labeling protocols to monitor the specific cell population. Reporter genes can also be used for genetic, indirect labeling protocols to track the fate of a given cell subpopulation in vivo. In this review, we summarized several methods dealing with dendritic cell, macrophage, and T lymphocyte specifically labeled for different macroscopic wholebody imaging techniques both for the study of their physiological function and in the context of immunotherapy to exploit imaging-derived information and immune-based treatments.

Restricted transgene expression in the brain with cell-type specific neuronal promoters

Tissue-targeted expression is of major interest for studying the contribution of cellular subpopulations to neurodegenerative diseases. However, in vivo methods to investigate this issue are limited. Here, we report an analysis of the cell specificity of expression of fluorescent reporter genes driven by six neuronal promoters, with the ubiquitous phosphoglycerate kinase 1 (PGK) promoter used as a reference. Quantitative analysis of AcGFPnuc expression in the striatum and hippocampus of rodents showed that all lentiviral vectors (LV) exhibited a neuronal tropism; however, there was substantial diversity of transcriptional activity and cell-type specificity of expression. The promoters with the highest activity were those of the 67 kDa glutamic acid decarboxylase (GAD67), homeobox Dlx5/6, glutamate receptor 1 (GluR1), and preprotachykinin 1 (Tac1) genes. Neuron-specific enolase (NSE) and dopaminergic receptor 1 (Drd1a) promoters showed weak activity, but the integration of an amplification system into the LV overcame this limitation. In the striatum, the expression profiles of Tac1 and Drd1a were not limited to the striatonigral pathway, whereas in the hippocampus, Drd1a and Dlx5/6 showed the expected restricted pattern of expression. Regulation of the Dlx5/6 promoter was observed in a disease condition, whereas Tac1 activity was unaffected. These vectors provide safe tools that are more selective than others available, for the administration of therapeutic molecules in the central nervous system (CNS). Nevertheless, additional characterization of regulatory elements in neuronal promoters is still required.

Transgenic models of spinocerebellar ataxia type 10: modeling a repeat expansion disorder

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurodegenerative disease with a spectrum of phenotypes. SCA10 is caused by a pentanucleotide repeat expansion of the ATTCT motif within intron 9 of ATAXIN 10 (ATXN10). Patients present with cerebellar ataxia; however, a subset also develops epileptic seizures which significantly contribute to the morbidity and mortality of the disease. Past research from our lab has demonstrated that epileptic SCA10 patients predominantly originate from or have ancestral ties to Mexico. In addition, a large proportion of epileptic SCA10 patients carry repeat interruptions within their SCA10 expansion. This paper outlines the variability in SCA10 phenotypes and our attempts to model these phenotypes using transgenic mouse models and highlights the benefits of using a transgenic model organism to understand the pathological mechanisms of a human disease.

Overexpression of parkin ameliorates dopaminergic neurodegeneration induced by 1- methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice

Mutations in the parkin gene are currently thought to be the most common cause of recessive familial Parkinsonism. Parkin functions as an E3 ligase to regulate protein turnover, and its function in mitochondrial quality control has been reported recently. Overexpression of parkin has been found to prevent neuronal degeneration under various conditions both in vivo and in vitro. Here, we generated a transgenic mouse model in which expression of wild type parkin was driven by neuron-specific enolase (NSE) promoter. We reported that both young and old parkin transgenic mice exhibited less reduction of striatal TH protein and number of TH positive neurons in the substantia nigra induced by 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP), compared to wild type littermates. MPTP-induced mitochondrial impairment in the substantia nigra was improved in young parkin transgenic mice. Decreased striatal α-synuclein was demonstrated in old parkin transgenic mice. These results provide reliable evidence from the transgenic mouse model for parkin that overexpression of parkin may attenuate dopaminergic neurodegeneration induced by MPTP through protection of mitochondria and reduction of α-synuclein in the nigrostriatal pathway.