Fusion of Human Fetal Mesenchymal Stem Cells with "Degenerating" Cerebellar Neurons in Spinocerebellar Ataxia Type 1 Model Mice

Mesenchymal stem cells (MSCs) migrate to damaged tissues, where they participate in tissue repair. Human fetal MSCs (hfMSCs), compared with adult MSCs, have higher proliferation rates, a greater differentiation capacity and longer telomeres with reduced senescence. Therefore, transplantation of quality controlled hfMSCs is a promising therapeutic intervention. Previous studies have shown that intravenous or intracortical injections of MSCs result in the emergence of binucleated cerebellar Purkinje cells (PCs) containing an MSC-derived marker protein in mice, thus suggesting a fusion event. However, transdifferentiation of MSCs into PCs or transfer of a marker protein from an MSC to a PC cannot be ruled out. In this study, we unequivocally demonstrated the fusion of hfMSCs with murine PCs through a tetracycline-regulated (Tet-off) system with or without a Cre-dependent genetic inversion switch (flip-excision; FLEx). In the FLEx-Tet system, we performed intra-cerebellar injection of viral vectors expressing tetracycline transactivator (tTA) and Cre recombinase into either non-symptomatic (4-week-old) or clearly symptomatic (6–8-month-old) spinocerebellar ataxia type 1 (SCA1) mice. Then, the mice received an injection of 50,000 genetically engineered hfMSCs that expressed GFP only in the presence of Cre recombinase and tTA. We observed a significant emergence of GFP-expressing PCs and interneurons in symptomatic, but not non-symptomatic, SCA1 mice 2 weeks after the MSC injection. These results, together with the results obtained using age-matched wild-type mice, led us to conclude that hfMSCs have the potential to preferentially fuse with degenerating PCs and interneurons but not with healthy neurons.

Progressive impairment of cerebellar mGluR signalling and its therapeutic potential for cerebellar ataxia in spinocerebellar ataxia type 1 model mice

KEY POINTS

Spinocerebellar ataxia type 1 (SCA1) is a progressive neurodegenerative disease caused by a gene defect, leading to movement disorder such as cerebellar ataxia. It remains largely unknown which functional defect contributes to the cerebellar ataxic phenotype in SCA1. In this study, we report progressive dysfunction of metabotropic glutamate receptor (mGluR) signalling, which leads to smaller slow synaptic responses, reduced dendritic Ca²⁺ signals and impaired synaptic plasticity at cerebellar synapses, in the early disease stage of SCA1 model mice. We also show that enhancement of mGluR signalling by a clinically available drug, baclofen, leads to improvement of motor performance in SCA1 mice. SCA1 is an incurable disease with no effective treatment, and our results may provide mechanistic grounds for targeting mGluRs and a novel drug therapy with baclofen to treat SCA1 patients in the future.

ABSTRACT

Spinocerebellar ataxia type 1 (SCA1) is a progressive neurodegenerative disease that presents with cerebellar ataxia and motor learning defects. Previous studies have indicated that the pathology of SCA1, as well as other ataxic diseases, is related to signalling pathways mediated by the metabotropic glutamate receptor type 1 (mGluR1), which is indispensable for proper motor coordination and learning. However, the functional contribution of mGluR signalling to SCA1 pathology is unclear. In the present study, we show that SCA1 model mice develop a functional impairment of mGluR signalling which mediates slow synaptic responses, dendritic Ca²⁺ signals, and short- and long-term synaptic plasticity at parallel fibre (PF)-Purkinje cell (PC) synapses in a progressive manner from the early disease stage (5 postnatal weeks) prior to PC death. Notably, impairment of mGluR-mediated dendritic Ca²⁺ signals linearly correlated with a reduction of PC capacitance (cell surface area) in disease progression. Enhancement of mGluR signalling by baclofen, a clinically available GABA_B receptor agonist, led to an improvement of motor performance in SCA1 mice and the improvement lasted ∼1 week after a single application of baclofen. Moreover, the restoration of motor performance in baclofen-treated SCA1 mice matched the functional recovery of mGluR-mediated slow synaptic currents and mGluR-dependent short- and long-term synaptic plasticity. These results suggest that impairment of synaptic mGluR cascades is one of the important contributing factors to cerebellar ataxia in early and middle stages of SCA1 pathology, and that modulation of mGluR signalling by baclofen or other clinical interventions may be therapeutic targets to treat SCA1.

FMRP Expression Levels in Mouse Central Nervous System Neurons Determine Behavioral Phenotype

Fragile X mental retardation protein (FMRP) is absent or highly reduced in Fragile X Syndrome, a genetic disorder causing cognitive impairment and autistic behaviors. Previous proof-of-principle studies have demonstrated that restoring FMRP in the brain using viral vectors can improve pathological abnormalities in mouse models of fragile X. However, unlike small molecule drugs where the dose can readily be adjusted during treatment, viral vector–based biological therapeutic drugs present challenges in terms of achieving optimal dosing and expression levels. The objective of this study was to investigate the consequences of expressing varying levels of FMRP selectively in neurons of Fmr1 knockout and wild-type (WT) mice. A wide range of neuronal FMRP transgene levels was achieved in individual mice after intra-cerebroventricular administration of adeno-associated viral vectors coding for FMRP. In all treated knockout mice, prominent FMRP transgene expression was observed in forebrain structures, whereas lower levels were present in more caudal regions of the brain. Reduced levels of the synaptic protein PSD-95, elevated levels of the transcriptional modulator MeCP2, and abnormal motor activity, anxiety, and acoustic startle responses in Fmr1 knockout mice were fully or partially rescued after expression of FMRP at about 35–115% of WT expression, depending on the brain region examined. In the WT mouse, moderate FMRP over-expression of up to about twofold had little or no effect on PSD-95 and MeCP2 levels or on behavioral endophenotypes. In contrast, excessive over-expression in the Fmr1 knockout mouse forebrain (approximately 2.5–6-fold over WT) induced pathological motor hyperactivity and suppressed the startle response relative to WT mice. These results delineate a range of FMRP expression levels in the central nervous system that confer phenotypic improvement in fragile X mice. Collectively, these findings are pertinent to the development of long-term curative gene therapy strategies for treating Fragile X Syndrome and other neurodevelopmental disorders.

Viral Vector-Based Dissection of Marmoset GFAP Promoter in Mouse and Marmoset Brains

Adeno-associated virus (AAV) vectors are small in diameter, diffuse easily in the brain, and represent a highly efficient means by which to transfer a transgene to the brain of a large animal. A major demerit of AAV vectors is their limited accommodation capacity for transgenes. Thus, a compact promoter is useful when delivering large transgenes via AAV vectors. In the present study, we aimed to identify the shortest astrocyte-specific GFAP promoter region that could be used for AAV-vector-mediated transgene expression in the marmoset brain. The 2.0-kb promoter region upstream of the GFAP gene was cloned from the marmoset genome, and short promoters (1.6 kb, 1.4 kb, 0.6 kb, 0.3 kb and 0.2 kb) were obtained by progressively deleting the original 2.0-kb promoter from the 5' end. The short promoters were screened in the mouse cerebellum in terms of their strength and astrocyte specificity. We found that the 0.3-kb promoter maintained 40% of the strength of the original 2.0-kb promoter, and approximately 90% of its astrocyte specificity. These properties were superior to those of the 1.4-kb, 0.6-kb (20% promoter strength) and 0.2-kb (70% astrocyte specificity) promoters. Then, we verified whether the 0.3-kb GFAP promoter retained astrocyte specificity in the marmoset cerebral cortex. Injection of viral vectors carrying the 0.3-kb marmoset GFAP promoter specifically transduced astrocytes in both the cerebral cortex and cerebellar cortex of the marmoset. These results suggest that the compact 0.3-kb promoter region serves as an astrocyte-specific promoter in the marmoset brain, which permits us to express a large gene by AAV vectors that have a limited accommodation capacity.

Fluorescent-based evaluation of chaperone-mediated autophagy and microautophagy activities in cultured cells

The autophagy-lysosome protein degradation is further classified into macroautophagy (MA), microautophagy (mA), and chaperone-mediated autophagy (CMA). While MA is involved in various functions and disease pathogenesis, little is known about CMA and mA because of the absence of easy methods to assess their activities. We have recently established a method to assess CMA activity using glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a CMA substrate, and HaloTag (HT) system. Another group has recently identified a mammalian mA pathway, in which substrates are delivered to late endosomes in an heat shock cognate protein (Hsc)70-dependent manner. Because Hsc70 is also involved in CMA, our method would detect both CMA and mA activities. In this study, we attempted to assess CMA and mA activities separately through the siRNA-mediated knockdown of CMA- and mA-related proteins. Knockdown of LAMP2A, a CMA-related protein, and TSG101, an mA-related protein, significantly but only partially decreased the punctate accumulation of GAPDH-HT in AD293 cells and primary cultured rat cortical neurons. Compounds that activate CMA significantly increased GAPDH-HT puncta in TSG101-knockdown cells, but not in LAMP2A-knockdown cells, suggesting that punctate accumulation of GAPDH-HT under LAMP2A- and TSG101-knockdown represents mA and CMA activities, respectively. We succeeded in establishing the method to separately evaluate CMA and mA activities by fluorescence observation.

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.

Identification and molecular docking studies for novel inverse agonists of SREB, super conserved receptor expressed in brain

The identification of novel synthetic ligands for G protein-coupled receptors (GPCRs) is important not only for understanding human physiology, but also for the development of novel drugs, especially for orphan GPCRs for which endogenous ligands are unknown. One of the orphan GPCR subfamilies, Super conserved Receptor Expressed in Brain (SREB), consists of GPR27, GPR85 and GPR173 and is expressed in the central nervous system. We report herein the identification of inverse agonists for the SREB family without their agonists. We carried out an in vitro screening of 5472 chemical compounds from the RIKEN NPDepo chemical library. The binding of [(35) S]GTPγS to the GPR173-Gsα fusion protein expressed in Sf9 cells was measured and resulted in the identification of 8 novel GPR173 inverse agonists. The most potent compound showed an IC50 of approximately 8 μm. The identified compounds were also antagonists for other SREB members, GPR27 and GPR85. These results indicated that the SREB family could couple Gs-type G proteins, and SREB-Gsα fusion proteins showed significant constitutive activities. Moreover, a molecular model of GPR173 was constructed using the screening results. The combination of computational and biological methods will provide a unique approach to ligand identification for orphan GPCRs and brain research.

Morphological and Functional Attenuation of Degeneration of Peripheral Neurons by Mesenchymal Stem Cell-Conditioned Medium in Spinocerebellar Ataxia Type 1-Knock-in Mice

AIMS

Spinocerebellar ataxia type 1 (SCA1) is caused by the ataxin-1 protein (ATXN1) with an abnormally expanded polyglutamine tract and is characterized by progressive neurodegeneration. We previously showed that intrathecal injection of mesenchymal stem cells (MSCs) during the nonsymptomatic stage mitigates the degeneration of the peripheral nervous system (PNS) neurons in SCA1-knock-in (SCA1-KI) mice. We tested in this study whether the therapeutic effects of MSCs in SCA1-KI mice could be reproduced with MSC-releasing factor(s).

METHODS

To test the effects of MSC-releasing factor(s), we used MSC-conditioned medium (MSC-CM). MSC-CM was intrathecally and/or intravenously injected into young SCA1-KI mice, and the therapeutic effects were assessed in the PNS at later ages using immunostaining, electrophysiology, and behavioral tests.

RESULTS

MSC-CM attenuated the degeneration of axons and myelin of spinal motor neurons. Consequently, the injected SCA1-KI mice exhibited smaller reductions in nerve conduction velocity in spinal motor neurons and reduced motor incoordination than the untreated mice.

CONCLUSIONS

These results suggest that factors released from MSC mitigate the morphological and functional abnormalities in the PNS that are observed in SCA1-KI mice in a paracrine manner.

Safety profile of the intravenous administration of brain-targeted stable nucleic acid lipid particles

In a clinical setting, where multiple administrations of the therapeutic agent are usually required to improve the therapeutic outcome, it is crucial to assess the immunogenicity of the administered nanoparticles. In this data work, we investigated the safety profile of the repeated intravenous administration of brain-targeted stable nucleic acid lipid particles (RVG-9r-targeted SNALPs). To evaluate local activation of the immune system, we performed analysis of mouse tissue homogenates and sections from cerebellum. To investigate peripheral activation of the immune system, we used serum of mice that were intravenously injected with RVG-9r-targeted SNALPs. These data are related and were discussed in the accompanying research article entitled “Intravenous administration of brain-targeted stable nucleic acid lipid particles alleviates Machado–Joseph disease neurological phenotype” (Conceição et al., in press) [1].

Mesenchymal stem cells attenuate peripheral neuronal degeneration in spinocerebellar ataxia type 1 knockin mice

Spinocerebellar ataxia type 1 (SCA1) is a devastating neurodegenerative disorder in which an abnormally expanded polyglutamine tract is inserted into causative ataxin-1 proteins. We have previously shown that SCA1 knockin (SCA1-KI) mice over 6 months of age exhibit a degeneration of motor neuron axons and their encasing myelin sheaths, as reported in SCA1 patients. We examined whether axon degeneration precedes myelin degeneration or vice versa in SCA1-KI mice and then attempted to mitigate motor neuron degeneration by intrathecally administering mesenchymal stem cells (MSCs). Temporal examination of the diameters of motor neuron axons and their myelin sheaths revealed a decrease in diameter of the axon but not of the myelin sheaths in SCA1-KI mice as early as 1 month of age, which suggests secondary degeneration of the myelin sheaths. We injected MSCs into the intrathecal space of SCA1-KI mice at 1 month of age, which resulted in a significant suppression of degeneration of both motor neuron axons and myelin sheaths, even 6 months after the MSC injection. Thus, MSCs effectively suppressed peripheral nervous system degeneration in SCA1-KI mice. It has not yet been clarified how clinically administered MSCs exhibit significant therapeutic effects in patients with SCA1. The morphological evidence presented in this current mouse study might explain the mechanisms that underlie the therapeutic effects of MSCs that are observed in patients with SCA1.

A CDC42EP4/septin-based perisynaptic glial scaffold facilitates glutamate clearance

The small GTPase-effector proteins CDC42EP1-5/BORG1–5 interact reciprocally with CDC42 or the septin cytoskeleton. Here we show that, in the cerebellum, CDC42EP4 is exclusively expressed in Bergmann glia and localizes beneath specific membrane domains enwrapping dendritic spines of Purkinje cells. CDC42EP4 forms complexes with septin hetero-oligomers, which interact with a subset of glutamate transporter GLAST/EAAT1. In Cdc42ep4^−/− mice, GLAST is dissociated from septins and is delocalized away from the parallel fibre-Purkinje cell synapses. The excitatory postsynaptic current exhibits a protracted decay time constant, reduced sensitivity to a competitive inhibitor of the AMPA-type glutamate receptors (γDGG) and excessive baseline inward current in response to a subthreshold dose of a nonselective inhibitor of the glutamate transporters/EAAT1–5 (DL-TBOA). Insufficient glutamate-buffering/clearance capacity in these mice manifests as motor coordination/learning defects, which are aggravated with subthreshold DL-TBOA. We propose that the CDC42EP4/septin-based glial scaffold facilitates perisynaptic localization of GLAST and optimizes the efficiency of glutamate-buffering and clearance.

Glutamate transporters mediate neurotransmitter reuptake at glutamatergic synapses. Here the authors show that CDC42 effector protein CDC42EP4 supports efficient glutamate clearance by promoting the tethering of a glutamate transporter GLAST to perisynaptic clusters of septins in Bergmann glia.

Mesenchymal stem cells as a potential therapeutic tool for spinocerebellar ataxia

Spinocerebellar ataxia (SCA) is a devastating progressive neurodegenerative disorder, for which no effective treatments have been developed. However, some studies have shown that an intracerebellar or intrathecal injection of mesenchymal stem cells (MSCs) was partially effective in some genetic mouse models of cerebellar ataxia such as SCA1 and Lurcher mutant. MSCs likely exert their therapeutic efficacy by secreting innate factors to induce neuronal growth and synaptic connection and reduce apoptosis. In this review, we introduce the therapeutic influence of MSCs on each mouse model for cerebellar ataxia and the possible mechanisms underlying the action of MSCs. We also introduce studies on the safety and effectiveness of umbilical cord MSCs for patients with SCA.

Re-establishing ataxin-2 downregulates translation of mutant ataxin-3 and alleviates Machado-Joseph disease

Machado-Joseph disease is a progressive neurodegenerative disorder associated with the polyQ-expanded ataxin-3 (encoded by ATXN3), for which no therapy is available. With the aim of clarifying the mechanism of neurodegeneration, we hypothesized that the abnormally long polyQ tract would interact aberrantly with ataxin-2 (encoded by ATXN2), another polyQ protein whose function has recently been linked to translational regulation. Using patient's samples and cellular and animal's models we found that in Machado-Joseph disease: (i) ataxin-2 levels are reduced; and (ii) its subcellular localization is changed towards the nucleus. Restoring ataxin-2 levels by lentiviral-mediated overexpression: (i) reduced mutant ataxin-3 levels; and (ii) rescued behaviour defects and neuropathology in a transgenic mouse model of Machado-Joseph disease. Conversely (i) mutating the ataxin-2 motif that enables binding to its natural interactor and translation activator poly(A)-binding protein; or (ii) overexpressing poly(A)-binding protein, had opposite effects, increasing mutant ataxin-3 translation and aggregation. This work suggests that in Machado-Joseph disease, mutant ataxin-3 drives an abnormal reduction of ataxin-2 levels, which overactivates poly(A)-binding protein, increases translation of mutant ataxin-3 and other proteins and aggravates Machado-Joseph disease. Re-establishment of ataxin-2 levels reduces mutant ataxin-3 and alleviates Machado-Joseph disease pathogenesis opening a new avenue for therapeutic intervention in this and potentially other polyQ disorders.

The development of laboratory tests for cancer in Japan with special reference to carcinoembryonic proteins

The present paper describes the present status of clinical tests for cancer in Japan. Since no cancer-specific substance has been found so far the clinical tests for cancer at present are always quantitative but not qualitative. Among these substances, alpha-fetoprotein is one of the most specific substances for cancer and its test is essential for diagnosis of hepatoma beins used worldwide. AFP is a specific product of liver cancer cells. The measurement of carcinoembryonic antigen in patient blood is a hopeful method for cancer diagnosis. This substance is not specifically produced by cancer cells, but the phenomenon of appearance in bloodstream appears to be cancer-specific. This may reflect the invasion of blood vessels in tissues such as colorectum, lung, etc., by infiltration of cancer cell. This is the reason for the appearance of CEA in a wide variety of cancers. There are many other clinical tests at present but these are only secondary aids for the diagnosis of cancer. This is the reason why the description concentrates mostly on AFP and CEA. The companies manufacturing the kits for these tests in Japan are also listed in this paper.

Identification and characterization of PKCγ, a kinase associated with SCA14, as an amyloidogenic protein

Amyloid assemblies are associated with a wide range of human disorders, including Alzheimer's and Parkinson's diseases. Here, we identify protein kinase C (PKC) γ, a serine/threonine kinase mutated in the neurodegenerative disease spinocerebellar ataxia type 14 (SCA14), as a novel amyloidogenic protein with no previously characterized amyloid-prone domains. We found that overexpression of PKCγ in cultured cells, as well as in vitro incubation of PKCγ without heat or chemical denaturants, causes amyloid-like fibril formation of this protein. We also observed that SCA14-associated mutations in PKCγ accelerate the amyloid-like fibril formation both in cultured cells and in vitro. We show that the C1A and kinase domains of PKCγ are involved in its soluble dimer and aggregate formation and that SCA14-associated mutations in the C1 domain cause its misfolding and aggregation. Furthermore, long-term time-lapse imaging indicates that aggregates of mutant PKCγ are highly toxic to neuronal cells. Based on these findings, we propose that PKCγ could form amyloid-like fibrils in physiological and/or pathophysiological conditions such as SCA14. More generally, our results provide novel insights into the mechanism of amyloid-like fibril formation by multi-domain proteins.