Early molecular layer interneuron hyperactivity triggers Purkinje neuron degeneration in SCA1

Toxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using in vivo two-photon imaging in behaving spinocerebellar ataxia type 1 (Sca1) mice, wherein Purkinje neurons (PNs) degenerate, we identify an inhibitory circuit element (molecular layer interneurons [MLINs]) that becomes prematurely hyperexcitable, compromising sensorimotor signals in the cerebellum at early stages. Mutant MLINs express abnormally elevated parvalbumin, harbor high excitatory-to-inhibitory synaptic density, and display more numerous synaptic connections on PNs, indicating an excitation/inhibition imbalance. Chemogenetic inhibition of hyperexcitable MLINs normalizes parvalbumin expression and restores calcium signaling in Sca1 PNs. Chronic inhibition of mutant MLINs delayed PN degeneration, reduced pathology, and ameliorated motor deficits in Sca1 mice. Conserved proteomic signature of Sca1 MLINs, shared with human SCA1 interneurons, involved the higher expression of FRRS1L, implicated in AMPA receptor trafficking. We thus propose that circuit-level deficits upstream of PNs are one of the main disease triggers in SCA1.

Toward the design and development of peptidomimetic inhibitors of the Ataxin-1 aggregation pathway

Spinocerebellar ataxia type 1 is a degenerative disorder caused by polyglutamine expansions and aggregation of Ataxin-1. The interaction between Capicua (CIC) and the AXH domain of Ataxin-1 protein has been suggested as a possible driver of aggregation for the expanded Ataxin-1 protein and the subsequent onset of spinocerebellar ataxia 1. Experimental studies have demonstrated that short constructs of CIC may prevent such aggregation and suggested this as a possible candidate to inspire the rational design of peptidomimetics. In this work, molecular modeling techniques, namely the alchemical mutation and force field-based molecular dynamics, have been employed to propose a pipeline for the rational design of a CIC-inspired inhibitor of the ataxin-1 aggregation pathway. In particular, this study has shown that the alchemical mutation can estimate the affinity between AXH and CIC with good correlation with experimental data, while molecular dynamics shed light on molecular mechanisms that occur for stabilization of the interaction between the CIC-inspired construct and the AXH domain of Ataxin-1. This work lays the foundation for a rational methodology for the in silico screening and design of peptidomimetics, which can expedite and streamline experimental studies to identify strategies for inhibiting the ataxin-1 aggregation pathway.

The Impact of Maternal Fructose Exposure on Angiogenic Activity of Endothelial Progenitor Cells and Blood Flow Recovery After Critical Limb Ischemia in Rat Offspring

Adult metabolic syndrome is considered to be elicited by the developmental programming which is regulated by the prenatal environment. The maternal excess intake of fructose, a wildly used food additive, is found to be associated with developmental programing-associated cardiovascular diseases. To investigate the effect of maternal fructose exposure (MFE) on endothelial function and repair, which participate in the initiation and progress of cardiovascular disease, we applied a rat model with maternal fructose excess intake during gestational and lactational stage and examined the number and function of endothelial progenitor cells (EPCs) in 3-month-old male offspring with induction of critical limb ischemia (CLI). Results showed that the circulating levels of c-Kit+/CD31+ and Sca-1+/KDR+ EPC were reduced by MFE. In vitro angiogenesis analysis indicated the angiogenic activity of bone marrow-derived EPC, including tube formation and cellular migration, was reduced by MFE. Western blots further indicated the phosphorylated levels of ERK1/2, p38-MAPK, and JNK in circulating peripheral blood mononuclear cells were up-regulated by MFE. Fourteen days after CLI, the reduced blood flow recovery, lowered capillary density, and increased fibrotic area in quadriceps were observed in offspring with MFE. Moreover, the aortic endothelium-mediated vasorelaxant response in offspring was impaired by MFE. In conclusion, maternal fructose intake during gestational and lactational stage modulates the number and angiogenic activity of EPCs and results in poor blood flow recovery after ischemic injury.

Decreased expression of glutamate transporter GLAST in Bergmann glia is associated with the loss of Purkinje neurons in the spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease of the cerebellum caused by a polyglutamine-repeat expansion in the protein ATXN1. We have previously demonstrated that astrocytic activation occurs early in pathogenesis, correlates with disease progression, and can occur when mutant ATXN1 expression is limited to Purkinje neurons. We now show that expression of glutamate and aspartate transporter, GLAST, is decreased in cerebellar astrocytes in a mouse model of SCA1. This decrease occurs in non-cell autonomous manner late in disease and correlates well with the loss of Purkinje neurons. Astrogliosis or decreased neuronal activity does not correlate with diminished GLAST expression. In addition, Bergmann glia remain capable of transcriptional upregulation of GLAST in response to improvement in Purkinje neurons supporting the notion of active neuron-glia crosstalk in disease.

Canadian Association of Neurosciences Review: Polyglutamine Expansion Neurodegenerative Diseases

Since the early 1990s, DNA triplet repeat expansions have been found to be the cause in an ever increasing number of genetic neurologic diseases. A subset of this large family of genetic diseases has the expansion of a CAG DNA triplet in the open reading frame of a coding exon. The result of this DNA expansion is the expression of expanded glutamine amino acid repeat tracts in the affected proteins, leading to the term, Polyglutamine Diseases, which is applied to this sub-family of diseases. To date, nine distinct genes are known to be linked to polyglutamine diseases, including Huntington's disease, Machado-Joseph Disease and spinobulbar muscular atrophy or Kennedy's disease. Most of the polyglutamine diseases are characterized clinically as spinocerebellar ataxias. Here we discuss recent successes and advancements in polyglutamine disease research, comparing these different diseases with a common genetic flaw at the level of molecular biology and early drug design for a family of diseases where many new research tools for these genetic disorders have been developed. Polyglutamine disease research has successfully used interdisciplinary collaborative efforts, informative multiple mouse genetic models and advanced tools of pharmaceutical industry research to potentially serve as the prototype model of therapeutic research and development for rare neurodegenerative diseases.

Chemical shift assignment of the ataxin-1 AXH domain in complex with a CIC ligand peptide

Ataxin-1 is the protein responsible for the genetically-inherited neurodegenerative disease spinocerebellar ataxia type-1 linked to the expansion of a polyglutamine tract within the protein sequence. The AXH domain of ataxin-1 is essential for the protein to function as a transcriptional co-repressor and mediates the majority of the interactions of ataxin-1 with cellular partners, mainly transcriptional regulators. One of the best characterized ataxin-1 functional partners is Capicua (CIC), a transcriptional repressor involved in signalling pathways that regulate mammalian development, tumorigenesis and, through the interaction with ataxin-1, also neurodegeneration. Complex formation of ataxin-1 with CIC is important both for the function of the wild-type protein and for pathogenesis as transcriptional disregulation is observed since the early stages of the development of the disease. Here we report the (1)H, (13)C and (15)N backbone and side-chain chemical shift assignments of the human ataxin-1 AXH domain in complex with a CIC ligand-peptide.

Candidate genes and functional noncoding variants identified in a canine model of obsessive-compulsive disorder

BACKGROUND

Obsessive-compulsive disorder (OCD), a severe mental disease manifested in time-consuming repetition of behaviors, affects 1 to 3% of the human population. While highly heritable, complex genetics has hampered attempts to elucidate OCD etiology. Dogs suffer from naturally occurring compulsive disorders that closely model human OCD, manifested as an excessive repetition of normal canine behaviors that only partially responds to drug therapy. The limited diversity within dog breeds makes identifying underlying genetic factors easier.

RESULTS

We use genome-wide association of 87 Doberman Pinscher cases and 63 controls to identify genomic loci associated with OCD and sequence these regions in 8 affected dogs from high-risk breeds and 8 breed-matched controls. We find 119 variants in evolutionarily conserved sites that are specific to dogs with OCD. These case-only variants are significantly more common in high OCD risk breeds compared to breeds with no known psychiatric problems. Four genes, all with synaptic function, have the most case-only variation: neuronal cadherin (CDH2), catenin alpha2 (CTNNA2), ataxin-1 (ATXN1), and plasma glutamate carboxypeptidase (PGCP). In the 2 Mb gene desert between the cadherin genes CDH2 and DSC3, we find two different variants found only in dogs with OCD that disrupt the same highly conserved regulatory element. These variants cause significant changes in gene expression in a human neuroblastoma cell line, likely due to disrupted transcription factor binding.

CONCLUSIONS

The limited genetic diversity of dog breeds facilitates identification of genes, functional variants and regulatory pathways underlying complex psychiatric disorders that are mechanistically similar in dogs and humans.

Silencing neurodegenerative disease: bringing RNA interference to the clinic

RNA interference (RNAi) is a recently described conserved biological pathway where non-coding RNAs suppress the expression of specific genes. Research efforts in the RNAi field aim to gain a better understanding of how its underlying machinery is orchestrated, to define the biological role of this conserved pathway, determine how to effectively manipulate RNAi in the laboratory and to integrate all this knowledge to develop novel therapies for human disease. This review summarizes the advances in the design of therapeutic RNAi for neurodegenerative diseases and discusses some of the experimental steps required to bring this therapy to human clinical trials.

A review on the cause-effect relationship between oxidative stress and toxic proteins in the pathogenesis of neurodegenerative diseases

Protein aggregates are the defining pathological feature of human neurodegenerative diseases. Studies have revealed that mutant huntingtin, polyglutamine-expanded ataxin-1 and ataxin-3 can cause elevated levels of reactive oxygen species in neuronal cells. It has also been indicated that the normal host prion protein behaves as an antioxidant, while the neurotoxic peptide based on the sequence of the scrapie isoform increases hydrogen peroxide toxicity in neuronal cultures. Additionally, not only can oxidative stress contribute to the aggregation of beta-amyloid and alpha-synuclein, but both beta-amyloid and alpha-synuclein can induce oxidative damage. Furthermore, oxidative stressors have been shown to play a critical role in neurofibrillary pathology leading to tau hyperphosphorylation. In conclusion, the present review supports a cause-effect relationship between oxidative stress and toxic proteins in the pathogenesis of neurodegenerative disorders.

Assessing the efficacy of specific cerebellomodulatory drugs for use as therapy for spinocerebellar ataxia type 1

Spinocerebellar ataxias are autosomal dominant diseases, associated in some types with a CAG repeat expansion, and characterised by a progressive loss of motor function. Currently, as there is no cure for most ataxias, treatment predominantly involves physical therapy. Various symptomatic drug treatments have been tried; however, published clinical studies have provided inconsistent results, likely due to small sample sizes, mixed patient populations and insensitive or subjective assessment scales. SCA1(154Q) transgenic mice display motor function impairments and ultimately a reduced number of cerebellar Purkinje neurons-characteristics comparable to most forms of sporadic and hereditary ataxias. We monitored motor function in SCA1(154Q) mice from 5 to 20 weeks of age and assessed the efficacy of four potential cerebellar modulatory drugs in attenuating deficits in rotor-rod performance. The drugs riluzole, amantadine, zolpidem and buspirone were selected based on their different mechanisms of action and their Food and Drug Administration (FDA)/Australian Therapeutic Goods Administration approval for other indications. SCA1(154Q) and C57/Bl6 wild-type mice were administered with four ascending acute doses of each drug, over 2 days. Following each dose, mice were assesed for motor function on the accelerating rotor-rod. None of the four drugs attenuated motor deficts in SCA1(154Q) mice at any dose; at FDA equivalent and higher dose administration of zolpidem and buspirone led to sedation in both strains. Our results suggest that the aforementioned drugs are likely to be ineffective for symptomatic treatment of SCA1 and most other ataxic patients and emphasise the need for comphrehensive drug studies prior to clinical use.

Genome-wide association study of a quantitative disordered gambling trait

Disordered gambling is a moderately heritable trait, but the underlying genetic basis is largely unknown. We performed a genome-wide association study (GWAS) for disordered gambling using a quantitative factor score in 1312 twins from 894 Australian families. Association was conducted for 2 381 914 single-nucleotide polymorphisms (SNPs) using the family-based association test in Merlin followed by gene and pathway enrichment analyses. Although no SNP reached genome-wide significance, six achieved P-values < 1 × 10(-5) with variants in three genes (MT1X, ATXN1 and VLDLR) implicated in disordered gambling. Secondary case-control analyses found two SNPs on chromosome 9 (rs1106076 and rs12305135 near VLDLR) and rs10812227 near FZD10 on chromosome 12 to be significantly associated with lifetime Diagnostic and Statistical Manual of Mental Disorders, fourth edition pathological gambling and South Oaks Gambling Screen classified probable pathological gambling status. Furthermore, several addiction-related pathways were enriched for SNPs associated with disordered gambling. Finally, gene-based analysis of 24 candidate genes for dopamine agonist-induced gambling in individuals with Parkinson's disease suggested an enrichment of SNPs associated with disordered gambling. We report the first GWAS of disordered gambling. While further replication is required, the identification of susceptibility loci and biological pathways will be important in characterizing the biological mechanisms that underpin disordered gambling.

Regulation of ataxin-1 phosphorylation and its impact on biology

Ataxin-1 protein expression is found in the cytoplasm and nucleus of Purkinje cells, the primary site of spinocerebellar ataxia type 1 (SCA1). Phosphorylation at S776 occurs in the cytoplasm and stabilizes the protein through interaction with 14-3-3, allowing it to translocate into the nucleus where disease is initiated. Phosphorylation and stabilization are enhanced when the polyglutamine expansion is present. In this chapter, we present a model of neurodegeneration in SCA1 initiated through phosphorylation at S776 by cAMP-dependent protein kinase (PKA) and enhanced by the presence of the polyglutamine expansion. The biological methods used to uncover SCA1 pathogenesis and phosphorylation at S776 are described.

Identification of human proteins that modify misfolding and proteotoxicity of pathogenic ataxin-1

Proteins with long, pathogenic polyglutamine (polyQ) sequences have an enhanced propensity to spontaneously misfold and self-assemble into insoluble protein aggregates. Here, we have identified 21 human proteins that influence polyQ-induced ataxin-1 misfolding and proteotoxicity in cell model systems. By analyzing the protein sequences of these modifiers, we discovered a recurrent presence of coiled-coil (CC) domains in ataxin-1 toxicity enhancers, while such domains were not present in suppressors. This suggests that CC domains contribute to the aggregation- and toxicity-promoting effects of modifiers in mammalian cells. We found that the ataxin-1-interacting protein MED15, computationally predicted to possess an N-terminal CC domain, enhances spontaneous ataxin-1 aggregation in cell-based assays, while no such effect was observed with the truncated protein MED15ΔCC, lacking such a domain. Studies with recombinant proteins confirmed these results and demonstrated that the N-terminal CC domain of MED15 (MED15CC) per se is sufficient to promote spontaneous ataxin-1 aggregation in vitro. Moreover, we observed that a hybrid Pum1 protein harboring the MED15CC domain promotes ataxin-1 aggregation in cell model systems. In strong contrast, wild-type Pum1 lacking a CC domain did not stimulate ataxin-1 polymerization. These results suggest that proteins with CC domains are potent enhancers of polyQ-mediated protein misfolding and aggregation in vitro and in vivo.

FOX-2 dependent splicing of ataxin-2 transcript is affected by ataxin-1 overexpression

Alternative splicing is a fundamental posttranscriptional mechanism for controlling gene expression, and splicing defects have been linked to various human disorders. The splicing factor FOX-2 is part of a main protein interaction hub in a network related to human inherited ataxias, however, its impact remains to be elucidated. Here, we focused on the reported interaction between FOX-2 and ataxin-1, the disease-causing protein in spinocerebellar ataxia type 1. In this line, we further evaluated this interaction by yeast-2-hybrid analyses and co-immunoprecipitation experiments in mammalian cells. Interestingly, we discovered that FOX-2 localization and splicing activity is affected in the presence of nuclear ataxin-1 inclusions. Moreover, we observed that FOX-2 directly interacts with ataxin-2, a protein modulating spinocerebellar ataxia type 1 pathogenesis. Finally, we provide evidence that splicing of pre-mRNA of ataxin-2 depends on FOX-2 activity, since reduction of FOX-2 levels led to increased skipping of exon 18 in ataxin-2 transcripts. Most striking, we observed that ataxin-1 overexpression has an effect on this splicing event as well. Thus, our results demonstrate that FOX-2 is involved in splicing of ataxin-2 transcripts and that this splicing event is altered by overexpression of ataxin-1.

Eccentric exercise facilitates mesenchymal stem cell appearance in skeletal muscle

Eccentric, or lengthening, contractions result in injury and subsequently stimulate the activation and proliferation of satellite stem cells which are important for skeletal muscle regeneration. The discovery of alternative myogenic progenitors in skeletal muscle raises the question as to whether stem cells other than satellite cells accumulate in muscle in response to exercise and contribute to post-exercise repair and/or growth. In this study, stem cell antigen-1 (Sca-1) positive, non-hematopoetic (CD45^-) cells were evaluated in wild type (WT) and α7 integrin transgenic (α7Tg) mouse muscle, which is resistant to injury yet liable to strain, 24 hr following a single bout of eccentric exercise. Sca-1⁺CD45⁻ stem cells were increased 2-fold in WT muscle post-exercise. The α7 integrin regulated the presence of Sca-1⁺ cells, with expansion occurring in α7Tg muscle and minimal cells present in muscle lacking the α7 integrin. Sca-1⁺CD45⁻ cells isolated from α7Tg muscle following exercise were characterized as mesenchymal-like stem cells (mMSCs), predominantly pericytes. In vitro multiaxial strain upregulated mMSC stem cells markers in the presence of laminin, but not gelatin, identifying a potential mechanistic basis for the accumulation of these cells in muscle following exercise. Transplantation of DiI-labeled mMSCs into WT muscle increased Pax7⁺ cells and facilitated formation of eMHC⁺DiI⁻ fibers. This study provides the first demonstration that mMSCs rapidly appear in skeletal muscle in an α7 integrin dependent manner post-exercise, revealing an early event that may be necessary for effective repair and/or growth following exercise. The results from this study also support a role for the α7 integrin and/or mMSCs in molecular- and cellular-based therapeutic strategies that can effectively combat disuse muscle atrophy.

Transient activation of hematopoietic stem and progenitor cells by IFNγ during acute bacterial infection

How hematopoietic stem cells (HSCs) respond to inflammatory signals during infections is not well understood. Our studies have used a murine model of ehrlichiosis, an emerging tick-born disease, to address how infection impacts hematopoietic function. Infection of C57BL/6 mice with the intracellular bacterium, Ehrlichia muris, results in anemia and thrombocytopenia, similar to what is observed in human ehrlichiosis patients. In the mouse, infection promotes myelopoiesis, a process that is critically dependent on interferon gamma (IFNγ) signaling. In the present study, we demonstrate that E. muris infection also drives the transient proliferation and expansion of bone marrow Lin-negative Sca-1⁺ cKit⁺ (LSK) cells, a population of progenitor cells that contains HSCs. Expansion of the LSK population in the bone marrow was associated with a loss of dormant, long-term repopulating HSCs, reduced engraftment, and a bias towards myeloid lineage differentiation within that population. The reduced engraftment and myeloid bias of the infection-induced LSK cells was transient, and was most pronounced on day 8 post-infection. The infection-induced changes were accompanied by an expansion of more differentiated multipotent progenitor cells, and required IFNγ signaling. Thus, in response to inflammatory signals elicited during acute infection, HSCs can undergo a rapid, IFNγ-dependent, transient shift from dormancy to activity, ostensibly, to provide the host with additional or better-armed innate cells for host defense. Similar changes in hematopoietic function likely underlie many different infections of public health importance.

Xpa deficiency reduces CAG trinucleotide repeat instability in neuronal tissues in a mouse model of SCA1

Expansion of trinucleotide repeats (TNRs) is responsible for a number of human neurodegenerative disorders. The molecular mechanisms that underlie TNR instability in humans are not clear. Based on results from model systems, several mechanisms for instability have been proposed, all of which focus on the ability of TNRs to form alternative structures during normal DNA transactions, including replication, DNA repair and transcription. These abnormal structures are thought to trigger changes in TNR length. We have previously shown that transcription-induced TNR instability in cultured human cells depends on several genes known to be involved in transcription-coupled nucleotide excision repair (NER). We hypothesized that NER normally functions to destabilize expanded TNRs. To test this hypothesis, we bred an Xpa null allele, which eliminates NER, into the TNR mouse model for spinocerebellar ataxia type 1 (SCA1), which carries an expanded CAG repeat tract at the endogenous mouse Sca1 locus. We find that Xpa deficiency does not substantially affect TNR instability in either the male or female germline; however, it dramatically reduces CAG repeat instability in neuronal tissues-striatum, hippocampus and cerebral cortex-but does not alter CAG instability in kidney or liver. The tissue-specific effect of Xpa deficiency represents a novel finding; it suggests that tissue-to-tissue variation in CAG repeat instability arises, in part, by different underlying mechanisms. These results validate our original findings in cultured human cells and suggest that transcription may induce NER-dependent TNR instability in neuronal tissues in humans.

Targeting several CAG expansion diseases by a single antisense oligonucleotide

To date there are 9 known diseases caused by an expanded polyglutamine repeat, with the most prevalent being Huntington's disease. Huntington's disease is a progressive autosomal dominant neurodegenerative disorder for which currently no therapy is available. It is caused by a CAG repeat expansion in the HTT gene, which results in an expansion of a glutamine stretch at the N-terminal end of the huntingtin protein. This polyglutamine expansion plays a central role in the disease and results in the accumulation of cytoplasmic and nuclear aggregates. Here, we make use of modified 2'-O-methyl phosphorothioate (CUG)n triplet-repeat antisense oligonucleotides to effectively reduce mutant huntingtin transcript and protein levels in patient-derived Huntington's disease fibroblasts and lymphoblasts. The most effective antisense oligonucleotide, (CUG)(7), also reduced mutant ataxin-1 and ataxin-3 mRNA levels in spinocerebellar ataxia 1 and 3, respectively, and atrophin-1 in dentatorubral-pallidoluysian atrophy patient derived fibroblasts. This antisense oligonucleotide is not only a promising therapeutic tool to reduce mutant huntingtin levels in Huntington's disease but our results in spinocerebellar ataxia and dentatorubral-pallidoluysian atrophy cells suggest that this could also be applicable to other polyglutamine expansion disorders as well.

Dopamine D2 receptor signaling modulates mutant ataxin-1 S776 phosphorylation and aggregation

Spinocerebellar ataxia 1 (SCA1) is a dominantly inherited neurodegenerative disease associated with progressive ataxia resulting from the loss of cerebellar Purkinje cells (PCs) and neurons in the brainstem. In PCs of SCA1 transgenic mice, the disease causing ataxin-1 protein mediates the formation of S100B containing cytoplasmic vacuoles and further self-aggregates to form intranuclear inclusions. The exact function of the ataxin-1 protein is not fully understood. However, the aggregation and neurotoxicity of the mutant ataxin-1 protein is dependent on the phosphorylation at serine 776 (S776). Although protein kinase A (PKA) has been implicated as the S776 kinase, the mechanism of PKA/ataxin-1 regulation in SCA1 is still not clear. We propose that a dopamine D(2) receptor (D2R)/S100B pathway may be involved in modulating PKA activity in PCs. Using a D2R/S100B HEK stable cell line transiently transfected with GFP-ataxin-1[82Q], we demonstrate that stimulation of the D2R/S100B pathway caused a reduction in mutant ataxin-1 S776 phosphorylation and ataxin-1 aggregation. Activation of PKA by forskolin resulted in an enhanced S776 phosphorylation and increased ataxin-1 nuclear aggregation, which was suppressed by treatment with D2R agonist bromocriptine and PKA inhibitor H89. Furthermore, treating SCA1 transgenic PC slice cultures with forskolin induced neurodegenerative morphological abnormalities in PC dendrites consistent with those observed in vivo. Taken together our data support a mechanism where PKA dependent mutant ataxin-1 phosphorylation and aggregation can be regulated by D2R/S100B signaling.

[Simulation of the distribution of spinocerebellar ataxia type 1 in Yakut populations: model parameters and results of simulation]

Demographic and clinical genetic parameters used for simulation modeling of the prevalence of spinocerebellar ataxia type 1 (SCA1) in Yakut populations are described. Demographic parameters of simulated populations and the clinical genetic characteristics of carriers of the SCA1 mutant allele in them have been compared with actual data on Abyisky and Ust-Aldansky uluses of the Republic of Sakha (Yakutia). The results of a series of simulation experiments (without migration or spontaneous mutagenesis) agree with the conclusion that the high prevalence of rate of spinocerebellar ataxia type 1 in Yakut populations may be maintained because of their specific demographic structure. Prediction of the disease prevalence has shown that it will take about 1290 years for natural selection to eliminate the mutation from the population. If medical genetic counseling (MGC) is offered to 1% of the carriers of the mutation, this period will be reduced to 200 years.

Ataxin active site determination using spectral distribution of electron ion interaction potentials of amino acids

Ataxia is a genetic neurological disorder characterised by a neurodegenerative process affecting a motor cortex responsible for balance and coordination. Recently several genes that cause autosomal dominant ataxia development were identified. These abnormal genes share a common ability to produce abnormal ataxin proteins that can affect nerve cells in the cerebellum and spinal cord. Here, using the Resonant Recognition Model (RRM) based on signal processing, we analysed ataxin proteins and identified the characteristic features corresponding to their biological activities. The RRM is a physico-mathematical model developed for analysis of protein interactions. By incorporating Smoothed Pseudo Wigner-Ville distribution (SPWV) in the RRM, we can define the active regions along the protein molecule. The results showed that our computational predictions correspond closely with the experimentally identified locations of the active/binding sites for ataxin-1 and ataxin-3 protein groups. The results obtained provide a valuable insight into the functional performance of ataxin proteins.

Phosphorylation of S776 and 14-3-3 binding modulate ataxin-1 interaction with splicing factors

Ataxin-1 (Atx1), a member of the polyglutamine (polyQ) expanded protein family, is responsible for spinocerebellar ataxia type 1. Requirements for developing the disease are polyQ expansion, nuclear localization and phosphorylation of S776. Using a combination of bioinformatics, cell and structural biology approaches, we have identified a UHM ligand motif (ULM), present in proteins associated with splicing, in the C-terminus of Atx1 and shown that Atx1 interacts with and influences the function of the splicing factor U2AF65 via this motif. ULM comprises S776 of Atx1 and overlaps with a nuclear localization signal and a 14-3-3 binding motif. We demonstrate that phosphorylation of S776 provides the molecular switch which discriminates between 14-3-3 and components of the spliceosome. We also show that an S776D Atx1 mutant previously designed to mimic phosphorylation is unsuitable for this aim because of the different chemical properties of the two groups. Our results indicate that Atx1 is part of a complex network of interactions with splicing factors and suggest that development of the pathology is the consequence of a competition of aggregation with native interactions. Studies of the interactions formed by non-expanded Atx1 thus provide valuable hints for understanding both the function of the non-pathologic protein and the causes of the disease.

Very small embryonic-like stem cells are present in adult murine organs: ImageStream-based morphological analysis and distribution studies

Recently, we purified a population of CXCR4+/Oct-4+/SSEA-1+/Sca-1+/Lin(-)/CD45(-) very small embryonic-like stem cells (VSELs) from adult murine bone marrow (BM). After using flow cytometry, ImageStream analysis, confocal microscopy, and real time RT-PCR, we report that similar cells could be also identified and isolated from several organs in adult mice. The highest total numbers of Oct-4+ VSELs were found in the brain, kidneys, muscles, pancreas, and BM. These observations support our hypothesis that a population of very primitive cells expressing germ line/epiblast markers (Oct-4, SSEA-1) is deposited early during embryogenesis in various organs and survives into adulthood. Further studies are needed to determine whether these cells, after being isolated from various adult human organs similarly to their murine BM-derived counterparts, are endowed with pluripotent stem cell properties.

Expansion of CAG repeats in the spinocerebellar ataxia type 1 (SCA1) gene in idiopathic oligozoospermia patients

PURPOSE

The lengths of CAG repeats in two spinocerebellar ataxia genes, SCA1 and SCA3, were analyzed to determine whether such repeats exist in higher numbers in infertile males.

METHODS

Blood samples were collected from healthy controls, oligozoospermia patients, and azoospermia patients. DNA fragments containing target CAG repeats were amplified by PCR with template DNA purified from the blood samples. CAG repeats in PCR fragments were determined, using ABI PRISM 310 Gene Analyzer.

RESULTS

In SCA1, the distribution of CAG repeats in oligozoospermic males was different from that of the control group: More alleles had a repeat number that exceeded 32. Conversely, for SCA3, the examined oligozoospermia and azoospermia patients exhibited no differences in distribution of CAG repeats in comparison with the control group.

CONCLUSIONS

SCA1 in a subset of oligozoospermia patients has an increased number of CAG repeats.

Molecular pathogenesis of spinocerebellar ataxia type 1 disease

Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 is associated with an elongated polyglutamine tract in ataxin-1, the SCA1 gene product. As summarized in this review, recent studies have clarified the molecular mechanisms of SCA1 pathogenesis and provided direction for future therapeutic approaches. The nucleus is the subcellular site where misfolded mutant ataxin-1 acts to cause SCA1 disease in the cerebellum. The role of these nuclear aggregates is the subject of intensive study. Additional proteins have been identified, whose conformational alterations occurring through interactions with the polyglutamine tract itself or non-polyglutamine regions in ataxin-1 are the cause of SCA-1 cytotoxicity. Therapeutic hope comes from the observations concerning the reduction of nuclear aggregation and alleviation of the pathogenic phenotype by the application of potent inhibitors and RNA interference.

Sox17 promotes cell cycle progression and inhibits TGF-beta/Smad3 signaling to initiate progenitor cell behavior in the respiratory epithelium

The Sry-related high mobility group box transcription factor Sox17 is required for diverse developmental processes including endoderm formation, vascular development, and fetal hematopoietic stem cell maintenance. Expression of Sox17 in mature respiratory epithelial cells causes proliferation and lineage respecification, suggesting that Sox17 can alter adult lung progenitor cell fate. In this paper, we identify mechanisms by which Sox17 influences lung epithelial progenitor cell behavior and reprograms cell fate in the mature respiratory epithelium. Conditional expression of Sox17 in epithelial cells of the adult mouse lung demonstrated that cell cluster formation and respecification of alveolar progenitor cells toward proximal airway lineages were rapidly reversible processes. Prolonged expression of Sox17 caused the ectopic formation of bronchiolar-like structures with diverse respiratory epithelial cell characteristics in alveolar regions of lung. During initiation of progenitor cell behavior, Sox17 induced proliferation and increased the expression of the progenitor cell marker Sca-1 and genes involved in cell cycle progression. Notably, Sox17 enhanced cyclin D1 expression in vivo and activated cyclin D1 promoter activity in vitro. Sox17 decreased the expression of transforming growth factor-beta (TGF-beta)-responsive cell cycle inhibitors in the adult mouse lung, including p15, p21, and p57, and inhibited TGF-beta1-mediated transcriptional responses in vitro. Further, Sox17 interacted with Smad3 and blocked Smad3 DNA binding and transcriptional activity. Together, these data show that a subset of mature respiratory epithelial cells retains remarkable phenotypic plasticity and that Sox17, a gene required for early endoderm formation, activates the cell cycle and reinitiates multipotent progenitor cell behavior in mature lung cells.

Glial cell lineage expression of mutant ataxin-1 and huntingtin induces developmental and late-onset neuronal pathologies in Drosophila models

BACKGROUND

In several neurodegenerative disorders, toxic effects of glial cells on neurons are implicated. However the generality of the non-cell autonomous pathologies derived from glial cells has not been established, and the specificity among different neurodegenerative disorders remains unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We newly generated Drosophila models expressing human mutant huntingtin (hHtt103Q) or ataxin-1 (hAtx1-82Q) in the glial cell lineage at different stages of differentiation, and analyzed their morphological and behavioral phenotypes. To express hHtt103Q and hAtx1-82Q, we used 2 different Gal4 drivers, gcm-Gal4 and repo-Gal4. Gcm-Gal4 is known to be a neuroglioblast/glioblast-specific driver whose effect is limited to development. Repo-Gal4 is known to be a pan-glial driver and the expression starts at glioblasts and continues after terminal differentiation. Gcm-Gal4-induced hHtt103Q was more toxic than repo-Gal4-induced hHtt103Q from the aspects of development, locomotive activity and survival of flies. When hAtx1-82Q was expressed by gcm- or repo-Gal4 driver, no fly became adult. Interestingly, the head and brain sizes were markedly reduced in a part of pupae expressing hAtx1-82Q under the control of gcm-Gal4, and these pupae showed extreme destruction of the brain structure. The other pupae expressing hAtx1-82Q also showed brain shrinkage and abnormal connections of neurons. These results suggested that expression of polyQ proteins in neuroglioblasts provided a remarkable effect on the developmental and adult brains, and that glial cell lineage expression of hAtx1-82Q was more toxic than that of hHtt103Q in our assays.

CONCLUSION/SIGNIFICANCE

All these studies suggested that the non-cell autonomous effect of glial cells might be a common pathology shared by multiple neurodegenerative disorders. In addition, the fly models would be available for analyzing molecular pathologies and developing novel therapeutics against the non-cell autonomous polyQ pathology. In conclusion, our novel fly models have extended the non-cell autonomous pathology hypothesis as well as the developmental effect hypothesis to multiple polyQ diseases. The two pathologies might be generally shared in neurodegeneration.

Focal distortion of the nuclear envelope by huntingtin aggregates revealed by lamin immunostaining

Huntington's disease is an autosomal dominant neurodegenerative disorder caused by the expansion of a polyglutamine repeat tract in the huntingtin protein. Polyglutamine-expanded huntingtin forms intranuclear as well as perinuclear inclusion bodies. Perinuclear aggregates formed by polyglutamine-expanded proteins are associated with a characteristic indentation of the nuclear envelope. We examined the nuclear envelope in cells containing huntingtin aggregates using immunostaining for lamin B1, a major component of the nuclear lamina. Laser confocal microscopy analysis revealed that huntingtin aggregates in a juxtanuclear position were associated with a clear focal distortion in the nuclear envelope in cells transfected with polyglutamine-expanded huntingtin. Lamin B1 distribution was not altered by aggregates of polyglutamine-expanded ataxin-1, that are exclusively intranuclear. Thus lamin immunocytochemistry demonstrates clearly the depression of the nuclear envelope resulting from the formation of perinuclear aggregates by polyglutamine-expanded huntingtin. Lamin immunocytochemistry would be of value to monitor the state of the nuclear envelope in experimental paradigms aimed at establishing the significance of perinuclear aggregates of pathogenic proteins.

Use of an alpha-smooth muscle actin GFP reporter to identify an osteoprogenitor population

Identification of a reliable marker of skeletal precursor cells within calcified and soft tissues remains a major challenge for the field. To address this, we used a transgenic model in which osteoblasts can be eliminated by pharmacological treatment. Following osteoblast ablation a dramatic increase in a population of alpha-smooth muscle actin (alpha-SMA) positive cells was observed. During early recovery phase from ablation we have detected cells with the simultaneous expression of alpha-SMA and a preosteoblastic 3.6GFP marker, indicating the potential for transition of alpha-SMA+ cells towards osteoprogenitor lineage. Utilizing alpha-SMAGFP transgene, alpha-SMAGFP+ positive cells were detected in the microvasculature and in the osteoprogenitor population within bone marrow stromal cells. Osteogenic and adipogenic induction stimulated expression of bone and fat markers in the alpha-SMAGFP+ population derived from bone marrow or adipose tissue. In adipose tissue, alpha-SMA+ cells were localized within the smooth muscle cell layer and in pericytes. After in vitro expansion, alpha-SMA+/CD45-/Sca1+ progenitors were highly enriched. Following cell sorting and transplantation of expanded pericyte/myofibroblast populations, donor-derived differentiated osteoblasts and new bone formation was detected. Our results show that cells with a pericyte/myofibroblast phenotype have the potential to differentiate into functional osteoblasts.

Activation of p38MAPK contributes to expanded polyglutamine-induced cytotoxicity

Background

The signaling pathways that may modulate the pathogenesis of diseases induced by expanded polyglutamine proteins are not well understood.

Methodologies/Principal Findings

Herein we demonstrate that expanded polyglutamine protein cytotoxicity is mediated primarily through activation of p38MAPK and that the atypical PKC iota (PKCι) enzyme antagonizes polyglutamine-induced cell death through induction of the ERK signaling pathway. We show that pharmacological blockade of p38MAPK rescues cells from polyglutamine-induced cell death whereas inhibition of ERK recapitulates the sensitivity observed in cells depleted of PKCι by RNA interference. We provide evidence that two unrelated proteins with expanded polyglutamine repeats induce p38MAPK in cultured cells, and demonstrate induction of p38MAPK in an in vivo model of neurodegeneration (spinocerebellar ataxia 1, or SCA-1).

Conclusions/Significance

Taken together, our data implicate activated p38MAPK in disease progression and suggest that its inhibition may represent a rational strategy for therapeutic intervention in the polyglutamine disorders.

UbcH6 interacts with and ubiquitinates the SCA1 gene product ataxin-1

UbcH6 is a member of an evolutionally conserved subfamily of E2 ubiquitin-conjugating enzymes. In this study, we report that UbcH6 interacts with and ubiquitinates ataxin-1, the spinocerebellar ataxia type 1 gene product. UbcH6 was identified as an ataxin-1-interacting protein using a yeast two-hybrid screen. UbcH6 co-immunoprecipitates and co-localizes with the ataxin-1 protein in the nucleus. Our binding assays showed that ataxin-1 interacts with UbcH6 through its AXH domain. Interestingly, UbcH6 could ubiquitinate ataxin-1 in the absence of an E3 ligase. The expression level of UbcH6 regulated the rate of ataxin-1 degradation. This study demonstrates that UbcH6 and ataxin-1 are E2-substrate cognate pairs in the ubiquitin-proteasome system.

[Experimental study on effect of Liuwei Dihuang Pill on HSC from mouse marrow]

OBJECTIVE

To investigate the effect of Liuwei Dihuang Pill on the number, the surface marker, cell cycle and colony formation of HSC from mouse marrow.

METHODS

Old Kunming mice were randomly divided into 4 groups: the control group, low, middle and high dose of Liuwei Dihuang Pill group. Then we separated the HSC from marrow after 7 days fed with saline or Liywei Dihuang Pill respectively, numerated monocyte, detected the surface marker and cell cycle of the HSC by FACS and tested the colony forming by semisolid media culture.

RESULTS

Among the four groups, there was no obvious difference in the number of MNC, suspended cell and colony. The expression of Sca-1 and CD34 increased in the low and middle dosage group, it meant that the number of HSC elevated by low and middle dosage medicine. The ability of cell proliferation was also higher in the three dosage groups.

CONCLUSION

Liuwei Dihuang Pill activates HSC by increasing the number, proliferation and function of more primitive HSC.

Polyglutamine expansion accelerates the dynamics of ataxin-1 and does not result in aggregate formation

BACKGROUND

Polyglutamine expansion disorders are caused by an expansion of the polyglutamine (polyQ) tract in the disease related protein, leading to severe neurodegeneration. All polyQ disorders are hallmarked by the presence of intracellular aggregates containing the expanded protein in affected neurons. The polyQ disorder SpinoCerebellar Ataxia 1 (SCA1) is caused by a polyQ-expansion in the ataxin-1 protein, which is thought to lead to nuclear aggregates.

METHODOLOGY/PRINCIPAL FINDINGS

Using advanced live cell fluorescence microscopy and a filter retardation assay we show that nuclear accumulations formed by polyQ-expanded ataxin-1 do not resemble aggregates of other polyQ-expanded proteins. Instead of being static, insoluble aggregates, nuclear accumulations formed by the polyQ-expanded ataxin-1 showed enhanced intracellular kinetics as compared to wild-type ataxin-1. During mitosis, ataxin-1 accumulations redistributed equally among daughter cells, in contrast to polyQ aggregates. Interestingly, polyQ expansion did not affect the nuclear-cytoplasmic shuttling of ataxin-1 as proposed before.

CONCLUSIONS/SIGNIFICANCE

These results indicate that polyQ expansion does not necessarily lead to aggregate formation, and that the enhanced kinetics may affect the nuclear function of ataxin-1. The unexpected findings for a polyQ-expanded protein and their consequences for ongoing SCA1 research are discussed.

Repopulating activity of ex vivo-expanded murine hematopoietic stem cells resides in the CD48-c-Kit+Sca-1+lineage marker- cell population

A better understanding of the biology of cultured hematopoietic stem cells (HSCs) is required to achieve ex vivo expansion of HSCs. In this study, clonal analysis of the surface phenotype and repopulating activity of ex vivo-expanded murine HSCs was performed. After 7 days of culture with stem cell factor, thrombopoietin, fibroblast growth factor-1, and insulin-like growth factor-2, single CD34-/lowc-Kit+Sca-1+lineage marker- (CD34-KSL) cells gave rise to various numbers of cells. The proportion of KSL cells decreased with increasing number of expanded cells. Transplantation studies revealed that the progeny containing a higher percentage of KSL cells tended to have enhanced repopulating potential. We also found that CD48 was heterogeneously expressed in the KSL cell population after culture. Repopulating activity resided only in the CD48-KSL cell population, which had a relatively long intermitotic interval. Microarray analysis showed surprisingly few differences in gene expression between cultured CD48-KSL cells (cycling HSCs) and CD48+KSL cells (cycling non-HSCs) compared with freshly isolated CD34-KSL cells (quiescent HSCs), suggesting that the maintenance of stem cell activity is controlled by a relatively small number of genes. These findings should lead to a better understanding of ex vivo-expanded HSCs.

Differential effects of polyglutamine proteins on nuclear organization and artificial reporter splicing

Nuclear inclusions formed by proteins with expanded polyglutamine tracts are found in several neurodegenerative diseases. The effect of nuclear inclusions formed by these disease proteins on the functional organization of the nucleus is only partially understood. In particular, it is not known whether polyglutamine disease proteins disrupt the function of Cajal bodies, which are subnuclear domains that play a role in the biogenesis of small nuclear ribonucleoproteins (snRNPs). snRNPs are an integral part of the pre-mRNA splicing machinery, so it is possible that mutant proteins that alter Cajal body activity indirectly affect pre-mRNA splicing. Here, we evaluate three different polyglutamine disease proteins--ataxin-1, ataxin-3, and huntingtin--for their ability to disrupt Cajal body localization and reduce the splicing of an artificial reporter in HeLa cells. Consistent with previous observations, ataxin-1 inclusions do not drastically alter the localization of Cajal bodies. In contrast, ataxin-3 inclusions associate with this structure. Inclusions formed by a fragment of the huntingtin protein do not associate with Cajal bodies or PML bodies, another subnuclear domain. Among the three disease proteins, only ataxin-3 significantly decreases the splicing of an artificial reporter. These results support the hypothesis that different mutant proteins vary in their ability to disrupt nuclear organization and function.

Characterization of adult prostatic progenitor/stem cells exhibiting self-renewal and multilineage differentiation

Demonstration of the hallmarks of stem cells, self-renewal and multilineage differentiation, is a challenge that has not been met for numerous tissues postulated to possess adult stem cells, including prostate tissue. Using a defined medium, we reproducibly isolated and maintained adult mouse prostatic cells with characteristics of progenitor/stem cells. Clonal populations of cells demonstrated tissue-specific multilineage differentiation by their ability to generate organized prostatic ductal structures in vivo, with luminal and basal cell layers, when grafted under the renal capsules of mice in the presence of fetal rat urogenital mesenchyme. Complete differentiation was demonstrated by the expression and secretion of terminally differentiated prostatic secretory products into the lumens. Self-renewal was demonstrated by serial transplantation of clonal populations that generated fully differentiated ductal structures in vivo. In vitro, undifferentiated cells expressed markers associated with prostate stem cells, including Sca 1 and CD49f, as well as basal cell markers (p63 and cytokeratins 5 and 14) and, at a low level, luminal cell markers (androgen receptor and cytokeratins 8 and 18). When grafted and allowed to differentiate in the presence of fetal urogenital mesenchyme, the cells differentiated into luminal cells and basal cells with more restricted protein expression patterns. These studies are the first to report a reproducible system to assess adult prostatic progenitor/stem cells.

dAtaxin-2 mediates expanded Ataxin-1-induced neurodegeneration in a Drosophila model of SCA1

Spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of neurodegenerative disorders sharing atrophy of the cerebellum as a common feature. SCA1 and SCA2 are two ataxias caused by expansion of polyglutamine tracts in Ataxin-1 (ATXN1) and Ataxin-2 (ATXN2), respectively, two proteins that are otherwise unrelated. Here, we use a Drosophila model of SCA1 to unveil molecular mechanisms linking Ataxin-1 with Ataxin-2 during SCA1 pathogenesis. We show that wild-type Drosophila Ataxin-2 (dAtx2) is a major genetic modifier of human expanded Ataxin-1 (Ataxin-1[82Q]) toxicity. Increased dAtx2 levels enhance, and more importantly, decreased dAtx2 levels suppress Ataxin-1[82Q]-induced neurodegeneration, thereby ruling out a pathogenic mechanism by depletion of dAtx2. Although Ataxin-2 is normally cytoplasmic and Ataxin-1 nuclear, we show that both dAtx2 and hAtaxin-2 physically interact with Ataxin-1. Furthermore, we show that expanded Ataxin-1 induces intranuclear accumulation of dAtx2/hAtaxin-2 in both Drosophila and SCA1 postmortem neurons. These observations suggest that nuclear accumulation of Ataxin-2 contributes to expanded Ataxin-1-induced toxicity. We tested this hypothesis engineering dAtx2 transgenes with nuclear localization signal (NLS) and nuclear export signal (NES). We find that NLS-dAtx2, but not NES-dAtx2, mimics the neurodegenerative phenotypes caused by Ataxin-1[82Q], including repression of the proneural factor Senseless. Altogether, these findings reveal a previously unknown functional link between neurodegenerative disorders with common clinical features but different etiology.

SCA 1, SCA 2 & SCA 3/MJD mutations in ataxia syndromes in southern India

BACKGROUND & OBJECTIVE

Spinocerebellar ataxias (SCAs) are often caused by expansions of CTG/ CAG trinucleotide repeat in the genome. Expansions at the SCA1, 2 and 3 loci are the most frequent, but differences in their relative proportion in regions occur across the world. We carried out this study to assess the occurrence of SCA1, 2 and 3, at a tertiary neuro-psychiatric center in Bangalore, Karnataka.

METHODS

Probands (N=318) who were diagnosed to have an ataxia syndrome (progressive degenerative ataxia of unknown cause) attending the clinical services of the National Institute of Mental Health and Neuro Sciences (NIMHANS), Bangalore, were evaluated over a period of three years. Standard protocols were used for both clinical and molecular diagnosis.

RESULTS

Genotyping established that SCA1, 2 and 3 accounted for more than one third of the ataxia cases seen in the clinic. In the cases with established family history and autosomal dominant inheritance SCA1 was most prevalent followed by SCA2 and SCA3.

INTERPRETATION & CONCLUSION

Our findings suggested SCA1 rather than SCA2 to be the more common mutation in southern India. Large numbers of SCA3 probands were also identified. Differences in prevalence of these syndromes within India need to be explored further for founder effects, correlations with phenotype, and patterns of outcome. Family history was not apparent in almost a fifth of those tested positive, highlighting the value of testing even in the absence of family history. Molecular testing should be extended to cover the other forms of ataxia, of which a large number are now known. Combined efforts to confirm the presence of these less common forms, as well as family studies to detect novel mutations, are necessary in this context in India.

Inclusion formation by ataxins -1, -2, -3, and -7

The authors studied inclusion formation in vitro using transiently transfected PC12 cells, with epitope-tagged and untagged full-length and truncated wild-type and expanded ataxins -1, -2, -3, and -7. At 72 hours, no inclusions were seen with wild-type full-length or truncated ataxins -2, -3, or -7, and only one with ataxin-1. Truncation abolished nuclear localization of ataxins -1 and -7, and allowed nuclear entry of ataxin-2. Of the expanded ataxins, only -1 and -2 formed inclusions, and those of ataxin-2 were rare and exclusively cytoplasmic. Truncation resulted in inclusion formation by ataxins -3 and -7, increased ataxin-1 inclusions, and enabled formation of nuclear ataxin-2 inclusions. There was no recruitment of wild-type ataxin-1 to expanded ataxin-1 inclusions.

Ataxin-1 fusion partners alter polyQ lethality and aggregation

Intranuclear inclusion bodies (IBs) are the histopathologic markers of multiple protein folding diseases. IB formation has been extensively studied using fluorescent fusion products of pathogenic polyglutamine (polyQ) expressing proteins. These studies have been informative in determining the cellular targets of expanded polyQ protein as well as the methods by which cells rid themselves of IBs. The experimental thrust has been to intervene in the process of polyQ aggregation in an attempt to alleviate cytotoxicity. However new data argues against the notion that polyQ aggregation and cytotoxicity are inextricably linked processes. We reasoned that changing the protein context of a disease causing polyQ protein could accelerate its precipitation as an IB, potentially reducing its cytotoxicity. Our experimental strategy simply exploited the fact that conjoined proteins influence each others folding and aggregation properties. We fused a full-length pathogenic ataxin-1 construct to fluorescent tags (GFP and DsRed1-E5) that exist at different oligomeric states. The spectral properties of the DsRed1-E5-ataxin-1 transfectants had the additional advantage of allowing us to correlate fluorochrome maturation with cytotoxicity. Each fusion protein expressed a distinct cytotoxicity and IB morphology. Flow cytometric analyses of transfectants expressing the greatest fluorescent signals revealed that the DsRed1-E5-ataxin-1 fusion was more toxic than GFP fused ataxin-1 (31.8±4.5% cell death versus 12.85±3%), although co-transfection with the GFP fusion inhibited maturation of the DsRed1-E5 fluorochrome and diminished the toxicity of the DsRed1-E5-ataxin-1 fusion. These data show that polyQ driven aggregation can be influenced by fusion partners to generate species with different toxic properties and provide new opportunities to study IB aggregation, maturation and lethality.

Do stem cells in the heart truly differentiate into cardiomyocytes?

Chronic congestive heart failure (CHF) is a common consequence of heart muscle or valve damage and remains a major cause of morbidity and mortality worldwide. There are increasing interests to treat cardiac failure by stem cell-based therapy. Many types of stem cells or progenitor cells have been suggested for cellular therapy of heart failure. While stem cell-based therapy was initially thought to be achieved by transdifferentiation of stem cells into myocardial cells including cardiomyocytes it has become clear that this may be rather an infrequent event. Instead cardiac regeneration may result from vascular differentiation of stem cells or even from stem cell-mediated reverse remodelling. Thus the term stem cell-mediated cardiac regeneration covers the spectrum from stem cell transdifferentiation into cardiomyocytes to cell-mediated pharmacotherapy. In this review we revise stem cell-based cardiac regeneration both in experimental models and in clinical application. We have limited our discussion on some selected types of stem cells, with particular emphasis on their differentiation potential, current status and perspectives on their future applications.

Expression, localization and tau exon 10 splicing activity of the brain RNA-binding protein TNRC4

Elucidating the mechanisms of alternative splicing in the brain is a prerequisite to the understanding of the pathogenesis of major neurological diseases linked to impairment of pre-mRNA alternative splicing. The gene trinucleotide repeat-containing 4 (TNRC4) is predicted to encode a member of the CELF (CUG-BP- and ETR-3-like factors) family of RNA-binding proteins containing a 15-18-residue polyglutamine sequence. The TNRC4 transcript is selectively expressed in the brain. Using an anti-peptide antibody against the predicted sequence, we establish the presence of TNRC4 as a approximately 50 kDa protein in the brain. Full-length TNRC4 displays nuclear and cytoplasmic localizations in transfected cells, whereas a C-terminally truncated mutant is essentially confined to the cytoplasm. TNRC4 is not recruited into inclusions formed by polyglutamine-expanded ataxin-1 or huntingtin. TNRC4 activates tau exon 10 (E10) inclusion at high efficiency in transfected cells. TNRC4 contains two consecutive N-terminal RNA recognition motifs (RRMs) separated from the C-terminal RRM. Deletion and point mutant analysis show that the activity of TNRC4 on tau E10 splicing is mainly mediated by the RNA-binding activity of the second RRM and involves an intronic element of the tau pre-mRNA. The polyglutamine sequence has no effect on the activity of TNRC4 on tau E10 splicing. This study represents the first characterization of TNRC4 and provides further insight into the mechanisms of brain-specific alternative splicing and their possible pathological implications.

Key developmental regulators change during hyperoxia-induced injury and recovery in adult mouse lung

Developmentally important genes have recently been linked to tissue regeneration and epithelial cell repair in neonatal and adult animals in several organs, including liver, skin, prostate, and musculature. We hypothesized that developmentally important genes play roles in lung injury repair in adult mice. Although there is considerable information known about these processes, the specific molecular pathways that mediate injury and regulate tissue repair are not fully elucidated. Using a hyperoxic injury model to study these mechanisms of lung injury and tissue repair, we selected the following genes based upon their known or putative roles in lung development and organogenesis: TTF-1, FGF9, FGF10, BMP4, PDGF-A, VEGF, Ptc, Shh, Sca-1, BCRP, CD45, and Cyclin-D2. Our findings demonstrate that several developmentally important genes (Sca-1, Shh, PDGF-A, VEGF, BCRP, CD45, BMP4, and Cyclin-D2) change during hyperoxic injury and normoxic recovery in mice, suggesting that adult lung may reactivate key developmental regulatory pathways for tissue repair. The mRNA for one gene (TTF-1), unchanged during hyperoxia, was upregulated late in recovery phase. These novel findings provide the basis for testing the efficacy of post-injury lung repair in animals genetically modified to inactivate or express individual molecules.

The neurodegenerative disease protein ataxin-1 antagonizes the neuronal survival function of myocyte enhancer factor-2

Ataxin-1 is a neurodegenerative disorder protein whose mutant form causes spinocerebellar ataxia type-1 (SCA1). Evidence suggests that ataxin-1 may function as a transcription repressor. However, neither the importance of this putative transcriptional repression activity in neural cytotoxicity nor the transcriptional targets of ataxin-1 are known. Here we identify the MEF2-HDAC4 transcriptional complex involved in neuron survival as a target of ataxin-1. We show that ataxin-1 binds specifically to histone deacetylase-4 (HDAC4) and MEF2 and colocalizes with them in nuclear inclusion bodies. Significantly, these interactions are greatly reduced by the S776A mutation, which largely abrogates the cytotoxicity of ataxin-1. Supporting the importance of these interactions, we show that wild type ataxin-1 represses MEF2-dependent transcription, whereas the S776A mutant is less potent. Furthermore, overexpression of MEF2 can partially reverse cytotoxicity caused by ataxin-1. Our results identify the MEF2-HDAC4 complex as a target for ataxin-1 transcriptional repression activity and suggest a novel pathogenic mechanism whereby ataxin-1 sequesters and inhibits the neuronal survival factor MEF2.

Non-canonical Wnt signaling enhances differentiation of Sca1+/c-kit+ adipose-derived murine stromal vascular cells into spontaneously beating cardiac myocytes

Recent reports have described a stem cell population termed stromal vascular cells (SVCs) derived from the stromal vascular fraction of adipose tissue, which are capable of intrinsic differentiation into spontaneously beating cardiomyocytes in vitro. The objective of this study was to further define the cardiac lineage differentiation potential of SVCs in vitro and to establish methods for enriching SVC-derived beating cardiac myocytes. SVCs were isolated from the stromal vascular fraction of murine adipose tissue. Cells were cultured in methylcellulose-based murine stem cell media. Analysis of SVC-derived beating myocytes included Western blot and calcium imaging. Enrichment of acutely isolated SVCs was carried out using antibody-tagged magnetic nanoparticles, and pharmacologic manipulation of Wnt and cytokine signaling. Under initial media conditions, spontaneously beating SVCs expressed both cardiac developmental and adult protein isoforms. Functionally, this specialized population can spontaneously contract and pace under field stimulation and shows the presence of coordinated calcium transients. Importantly, this study provides evidence for two independent mechanisms of enriching the cardiac differentiation of SVCs. First, this study shows that differentiation of SVCs into cardiac myocytes is augmented by non-canonical Wnt agonists, canonical Wnt antagonists, and cytokines. Second, SVCs capable of cardiac lineage differentiation can be enriched by selection for stem cell-specific membrane markers Sca1 and c-kit. Adipose-derived SVCs are a unique population of stem cells that show evidence of cardiac lineage development making them a potential source for stem cell-based cardiac regeneration studies.

Modulating mtDNA heteroplasmy by mitochondria-targeted restriction endonucleases in a 'differential multiple cleavage-site' model

The ability to manipulate mitochondrial DNA (mtDNA) heteroplasmy would provide a powerful tool to treat mitochondrial diseases. Recent studies showed that mitochondria-targeted restriction endonucleases can modify mtDNA heteroplasmy in a predictable and efficient manner if it recognizes a single site in the mutant mtDNA. However, the applicability of such model is limited to mutations that create a novel cleavage site, not present in the wild-type mtDNA. We attempted to extend this approach to a 'differential multiple cleavage site' model, where an mtDNA mutation creates an extra restriction site to the ones normally present in the wild-type mtDNA. Taking advantage of a heteroplasmic mouse model harboring two haplotypes of mtDNA (NZB/BALB) and using adenovirus as a gene vector, we delivered a mitochondria-targeted Scal restriction endonuclease to different mouse tissues. Scal recognizes five sites in the NZB mtDNA but only three in BALB mtDNA. Our results showed that changes in mtDNA heteroplasmy were obtained by the expression of mitochondria-targeted ScaI in both liver, after intravenous injection, and in skeletal muscle, after intramuscular injection. Although mtDNA depletion was an undesirable side effect, our data suggest that under a regulated expression system, mtDNA depletion could be minimized and restriction endonucleases recognizing multiple sites could have a potential for therapeutic use.

Down-regulation of the dopamine receptor D2 in mice lacking ataxin 1

Ataxin 1 (Atxn1) is a protein of unknown function associated with spinocerebellar ataxia type 1 (SCA1), a neurodegenerative disease of late onset with variable degrees of cerebellar ataxia, ophthalmoplegia and neuropathy. SCA1 is caused by the toxic effects triggered by an expanded polyglutamine (polyQ) within Atxn1 resulting in neurodegeneration in the cerebellum, brain stem and spinocerebellar tracts. To gain insights into Atxn1 function, we have analysed the cerebellar gene expression profiles by microarray analysis in Atxn1-null mice, and identified alterations in expression of genes regulated by Sp1-dependent transcription, including the dopamine receptor D2 (Drd2), retinoic acid/thyroid hormone and Wnt-signalling. Interestingly, Drd2 expression levels are reduced in both Atxn1-null and transgenic mice expressing a pathogenic human Atxn1 with an expanded polyglutamine in cerebellar Purkinje cells. Our co-transfection experiments in human neuroblastoma SH-SY5Y cells and luciferase assays provide evidence for transcriptional regulation of Drd2 by Atxn1 and its AXH module. We show that Atxn1 occupies at the Drd2 promoter in vivo, and interacts and functions synergistically with the zinc-finger transcription factor Sp1 to co-regulate Drd2 expression. The interaction and transcriptional effects are mediated by the AXH domain within Atxn1 and are abrogated by the expanded polyQ within Atxn1. Therefore, this study identifies novel molecular targets that are regulated by Atxn1 which might contribute to the motor deficits in SCA1, and provides new insights into the mechanisms by which Atxn1 co-regulates transcription.

LYVE-1-positive macrophages are present in normal murine eyes

PURPOSE

A functioning lymphatic system is necessary not only to permit the organism to mount a rapid and effective immune response but, even more so, to maintain tissue fluid homeostasis. However, no clear evidence of lymphatic vessels draining intraocular and orbital tissues--retina, choroid, sclera, and extraocular muscles--exists.

METHODS

Ocular tissue flatmounts from normal or enhanced green fluorescence protein (EGFP) chimeric mice were immunostained for lymphatic endothelium hyaluronan receptor (LYVE-1, a routinely used lymphatic endothelial marker), podoplanin, Flt4/VEGFR3, Sca-1, CD11b, or F4/80 and were observed by confocal microscopy. Single-cell suspensions from ocular tissues were also prepared and were analyzed by flow cytometry.

RESULTS

Lymphatic vessels were detected in the posterior regions of the extraocular muscles and the connective tissues of the extraocular muscle cones in the normal mouse. No typical lymphatic vessels were found within the eye. A large population of LYVE-1(+) nonendothelial cells, distributed as single cells, was detected in all ocular tissues except the central cornea. These cells also express another lymphatic endothelial cell marker, Flt4/VEGFR3, but not podoplanin, and they have hyaluronan-binding ability. Bone marrow chimerism studies indicated that the LYVE-1(+) cell populations are bone marrow derived and have a slow turnover in ocular tissues (3-6 months). Phenotype analysis revealed that nonendothelial LYVE-1(+)cells in the sclera, choroid, and iris included CD11b(+)F4/80(+) macrophages, CD11b(+)F4/80(-) macrophages, and CD11b(-)F4/80(-) bone marrow-derived cells. All LYVE-1(+) cells in the retina were CD11b(+)F4/80(+) macrophages. Cells in the limbus and the iris root also express Sca-1, suggesting that they are hematopoietic lymphatic vessel progenitor cells.

CONCLUSIONS

These observations suggest that a lymphatic system exists for the transport of immune cells and fluids from the posterior segment of the eye, that ocular tissues are rich in bone marrow-derived LYVE-1(+) macrophages under normal physiological conditions, and that a subpopulation of these cells may represent resident precursor cells necessary for the de novo formation of ocular/orbital lymphatic vessels in pathologic conditions.