Loss of Ataxin-1 Potentiates Alzheimer's Pathogenesis by Elevating Cerebral BACE1 Transcription.

Expansion of CAG trinucleotide repeats in ATXN1 causes spinocerebellar ataxia type 1 (SCA1), a neurodegenerative disease that impairs coordination and cognition. While ATXN1 is associated with increased Alzheimer's disease (AD) risk, CAG repeat number in AD patients is not changed. Here, we investigated the consequences of ataxin-1 loss of function and discovered that knockout of Atxn1 reduced CIC-ETV4/5-mediated inhibition of Bace1 transcription, leading to increased BACE1 levels and enhanced amyloidogenic cleavage of APP, selectively in AD-vulnerable brain regions. Elevated BACE1 expression exacerbated Aß deposition and gliosis in AD mouse models and impaired hippocampal neurogenesis and olfactory axonal targeting. In SCA1 mice, polyglutamine-expanded mutant ataxin-1 led to the increase of BACE1 post-transcriptionally, both in cerebrum and cerebellum, and caused axonal-targeting deficit and neurodegeneration in the hippocampal CA2 region. These findings suggest that loss of ataxin-1 elevates BACE1 expression and Aß pathology, rendering it a potential contributor to AD risk and pathogenesis.

Selenocysteine containing analogues of Atx1-based peptides protect cells from copper ion toxicity.

Seleno-substituted model peptides of copper metallochaperone proteins were analyzed for the metal affinity and in vitro anti-oxidative reactivity. An acyclic MTCXXC (X is any amino acid) reference peptide previously analyzed as a potent inhibitor of ROS production underwent substitution of the cysteine residues with selenocysteine to give two singly substituted derivatives C3U and C6U and the doubly substituted analogue C3U/C6U. Presumably due to the softer nature of Se vs. S, all selenocysteine containing peptides demonstrated high affinity to Cu(i), higher than that of the reference peptide, and in the same order of magnitude as that measured for the native protein, Atox1. A stronger impact of residue 3 confirmed previous findings on its more dominant role in metal coordination. In vitro studies on the HT-29 human colon cancer cell line, MEF mice embryonic fibroblasts, and MEF with the knocked-out Atox1 gene (Atox1-/-) consistently identified C3U/C6U as the most potent inhibitor of ROS cellular production based on the 2',7'-dichlorodihydrofluorescin diacetate (H2DCF-DA) assay, also in comparison with known drugs employed in the clinic for Wilson's disease. The selenocysteine containing peptides are thus promising drug candidates for chelation therapy of Wilson's disease and related conditions relevant to excessive copper levels.

Broad distribution of ataxin 1 silencing in rhesus cerebella for spinocerebellar ataxia type 1 therapy.

Spinocerebellar ataxia type 1 is one of nine polyglutamine expansion diseases and is characterized by cerebellar ataxia and neuronal degeneration in the cerebellum and brainstem. Currently, there are no effective therapies for this disease. Previously, we have shown that RNA interference mediated silencing of ATXN1 mRNA provides therapeutic benefit in mouse models of the disease. Adeno-associated viral delivery of an engineered microRNA targeting ATXN1 to the cerebella of well-established mouse models improved motor phenotypes, neuropathy, and transcriptional changes. Here, we test the translatability of this approach in adult rhesus cerebella. Nine adult male and three adult female rhesus macaque were unilaterally injected with our therapeutic vector, a recombinant adeno-associated virus type 1 (rAAV1) expressing our RNAi trigger (miS1) and co-expressing enhanced green fluorescent protein (rAAV1.miS1eGFP) into the deep cerebellar nuclei using magnetic resonance imaging guided techniques combined with a Stealth Navigation system (Medtronics Inc.). Transduction was evident in the deep cerebellar nuclei, cerebellar Purkinje cells, the brainstem and the ventral lateral thalamus. Reduction of endogenous ATXN1 messenger RNA levels were ≥30% in the deep cerebellar nuclei, the cerebellar cortex, inferior olive, and thalamus relative to the uninjected hemisphere. There were no clinical complications, and quantitative and qualitative analyses suggest that this therapeutic intervention strategy and subsequent reduction of ATXN1 is well tolerated. Collectively the data illustrate the biodistribution and tolerability of rAAV1.miS1eGFP administration to the adult rhesus cerebellum and are supportive of clinical application for spinocerebellar ataxia type 1.

Cardioprotective effect of the secretome of Sca-1+ and Sca-1- cells in heart failure: not equal, but equally important?

AIMS: Both progenitor and differentiated cells were previously shown to secrete cardioprotective substances, but so far there has been no direct comparison of the paracrine effects of the two cell types on heart failure. The study sought to compare the paracrine effect of selected progenitors and the corresponding non-progenitor mononuclear cardiac cells on the cardiac function of transgenic heart failure mice. In addition, we aimed to further enhance the paracrine effect of the cells via pretreatment with the heart failure mediator aldosterone. METHODS AND RESULTS: Transgenic heart failure mice were injected with the supernatant of murine cardiac stem cell antigen-1 positive (Sca-1+) and negative (Sca-1-) cells with or without aldosterone pretreatment. Cardiac function was determined using small animal magnetic resonance imaging. In addition, heart failure markers were determined using enzyme-linked immunosorbent assay, RT-PCR, and bead-based multiplexing assay. While only the secretome of aldosterone pretreated Sca-1+ cells led to a significant improvement in cardiac function, N-terminal pro brain natriuretic peptide plasma levels were significantly lower and galectin-1 levels significantly higher in mice that were treated with either kind of secretome compared with untreated controls. CONCLUSION: In this first direct comparison of the paracrine effects of progenitor cells and a heterogeneous population of mononuclear cardiac cells the supernatants of both cell types showed cardioprotective properties which might be of great relevance for endogenous repair. During heart failure raised aldosterone levels might further increase the paracrine effect of progenitor cells.

ATXN1-CIC Complex Is the Primary Driver of Cerebellar Pathology in Spinocerebellar Ataxia Type 1 through a Gain-of-Function Mechanism.

Polyglutamine (polyQ) diseases are caused by expansion of translated CAG repeats in distinct genes leading to altered protein function. In spinocerebellar ataxia type 1 (SCA1), a gain of function of polyQ-expanded ataxin-1 (ATXN1) contributes to cerebellar pathology. The extent to which cerebellar toxicity depends on its cognate partner capicua (CIC), versus other interactors, remains unclear. It is also not established whether loss of the ATXN1-CIC complex in the cerebellum contributes to disease pathogenesis. In this study, we exclusively disrupt the ATXN1-CIC interaction in vivo and show that it is at the crux of cerebellar toxicity in SCA1. Importantly, loss of CIC in the cerebellum does not cause ataxia or Purkinje cell degeneration. Expression profiling of these gain- and loss-of-function models, coupled with data from iPSC-derived neurons from SCA1 patients, supports a mechanism in which gain of function of the ATXN1-CIC complex is the major driver of toxicity.

Systemic Mesenchymal Stromal Cell Transplantation Prevents Functional Bone Loss in a Mouse Model of Age-Related Osteoporosis.

UNLABELLED: Age-related osteoporosis is driven by defects in the tissue-resident mesenchymal stromal cells (MSCs), a heterogeneous population of musculoskeletal progenitors that includes skeletal stem cells. MSC decline leads to reduced bone formation, causing loss of bone volume and the breakdown of bony microarchitecture crucial to trabecular strength. Furthermore, the low-turnover state precipitated by MSC loss leads to low-quality bone that is unable to perform remodeling-mediated maintenance--replacing old damaged bone with new healthy tissue. Using minimally expanded exogenous MSCs injected systemically into a mouse model of human age-related osteoporosis, we show long-term engraftment and markedly increased bone formation. This led to improved bone quality and turnover and, importantly, sustained microarchitectural competence. These data establish proof of concept that MSC transplantation may be used to prevent or treat human age-related osteoporosis. SIGNIFICANCE: This study shows that a single dose of minimally expanded mesenchymal stromal cells (MSCs) injected systemically into a mouse model of human age-related osteoporosis display long-term engraftment and prevent the decline in bone formation, bone quality, and microarchitectural competence. This work adds to a growing body of evidence suggesting that the decline of MSCs associated with age-related osteoporosis is a major transformative event in the progression of the disease. Furthermore, it establishes proof of concept that MSC transplantation may be a viable therapeutic strategy to treat or prevent human age-related osteoporosis.