Safety of Striatal Infusion of siRNA in a Transgenic Huntington's Disease Mouse Model

Naïve Huntington's disease microglia mount a normal response to inflammatory stimuli but display a partially impaired development of innate immune tolerance that can be counteracted by ganglioside GM1

Chronic activation and dysfunction of microglia have been implicated in the pathogenesis and progression of many neurodegenerative disorders, including Huntington's disease (HD). HD is a genetic condition caused by a mutation that affects the folding and function of huntingtin (HTT). Signs of microglia activation have been observed in HD patients even before the onset of symptoms. It is unclear, however, whether pro-inflammatory microglia activation in HD results from cell-autonomous expression of mutant HTT, is the response of microglia to a diseased brain environment, or both. In this study, we used primary microglia isolated from HD knock-in (Q140) and wild-type (Q7) mice to investigate their response to inflammatory conditions in vitro in the absence of confounding effects arising from brain pathology. We show that naïve Q140 microglia do not undergo spontaneous pro-inflammatory activation and respond to inflammatory triggers, including stimulation of TLR4 and TLR2 and exposure to necrotic cells, with similar kinetics of pro-inflammatory gene expression as wild-type microglia. Upon termination of the inflammatory insult, the transcription of pro-inflammatory cytokines is tapered off in Q140 and wild-type microglia with similar kinetics. However, the ability of Q140 microglia to develop tolerance in response to repeated inflammatory stimulations is partially impaired in vitro and in vivo, potentially contributing to the establishment of chronic neuroinflammation in HD. We further show that ganglioside GM1, a glycosphingolipid with anti-inflammatory effects on wild-type microglia, not only decreases the production of pro-inflammatory cytokines and nitric oxide in activated Q140 microglia, but also dramatically dampen microglia response to re-stimulation with LPS in an experimental model of tolerance. These effects are independent from the expression of interleukin 1 receptor associated kinase 3 (Irak-3), a strong modulator of LPS signaling involved in the development of innate immune tolerance and previously shown to be upregulated by immune cell treatment with gangliosides. Altogether, our data suggest that external triggers are required for HD microglia activation, but a cell-autonomous dysfunction that affects the ability of HD microglia to acquire tolerance might contribute to the establishment of neuroinflammation in HD. Administration of GM1 might be beneficial to attenuate chronic microglia activation and neuroinflammation.

CAG repeat instability in embryonic stem cells and derivative spermatogenic cells of transgenic Huntington's disease monkey

PURPOSE

The expansion of CAG (glutamine; Q) trinucleotide repeats (TNRs) predominantly occurs through male lineage in Huntington's disease (HD). As a result, offspring will have larger CAG repeats compared to their fathers, which causes an earlier onset of the disease called genetic anticipation. This study aims to develop a novel in vitro model to replicate CAG repeat instability in early spermatogenesis and demonstrate the biological process of genetic anticipation by using the HD stem cell model for the first time.

METHODS

HD rhesus monkey embryonic stem cells (rESCs) were cultured in vitro for an extended period. Male rESCs were used to derive spermatogenic cells in vitro with a 10-day differentiation. The assessment of CAG repeat instability was performed by GeneScan and curve fit analysis.

RESULTS

Spermatogenic cells derived from rESCs exhibit progressive expansion of CAG repeats with high daily expansion rates compared to the extended culture of rESCs. The expansion of CAG repeats is cell type-specific and size-dependent.

CONCLUSIONS

Here, we report a novel stem cell model that replicates genome instability and CAG repeat expansion in in vitro derived HD monkey spermatogenic cells. The in vitro spermatogenic cell model opens a new opportunity for studying TNR instability and the underlying mechanism of genetic anticipation, not only in HD but also in other TNR diseases.

Gene therapy and immunotherapy as promising strategies to combat Huntington's disease-associated neurodegeneration: emphasis on recent updates and future perspectives

INTRODUCTION

Modulation of gene expression using gene therapy as well as modulation of immune activation using immunotherapy has attracted considerable attention as rapidly emerging potential therapeutic intervention for the treatment of HD. Several preclinical and clinical trials for gene-based therapy and immunotherapy/antibody-based have been conducted.

AREAS COVERED

This review focused on the potential use of gene therapy and immuno-based therapies to treat HD, including the current status, the rationale for these approaches as well as preclinical and clinical data supporting it. Growing knowledge of HD pathogenesis has resulted in the discovery of new therapeutic targets, some of which are now in clinical trials. Focus has been allocated to RNA and DNA-based gene therapies for the reduction of mutant huntingtin (mHTT), using Immuno/antibody-based therapies.

EXPERT OPINION

While safety and efficacy of gene therapy and immunotherapy has been well demonstrated for HD, therefore much focus has now been shifted to disease-modifying therapies. This review defines the current status and future directions of gene therapy and immunotherapies. The review summarizes by what means HD genetic root cause modification and functional restoration of mHtt protein could be achieved by using targeted multimodality gene therapy and immunotherapy to target intracellular and extracellular mHtt.

Safe and Efficient Silencing with a Pol II, but Not a Pol lII, Promoter Expressing an Artificial miRNA Targeting Human Huntingtin

Huntington's disease is a devastating, incurable neurodegenerative disease affecting up to 12 per 100,000 patients worldwide. The disease is caused by a mutation in the Huntingtin (Htt) gene. There is interest in reducing mutant Huntingtin by targeting it at the mRNA level, but the maximum tolerable dose and long-term effects of such a treatment are unknown. Using a self-complementary AAV9 vector, we delivered a mir-155-based artificial miRNA under the control of the chicken β-actin or human U6 promoter. In mouse brain, the artificial miRNA reduced the human huntingtin mRNA by 50%. The U6, but not the CβA promoter, produced the artificial miRNA at supraphysiologic levels. Embedding the antisense strand in a U6-mir-30 scaffold reduced expression of the antisense strand but increased the sense strand. In mice treated with scAAV9-U6-mir-155-HTT or scAAV9-CβA-mir-155-HTT, activated microglia were present around the injection site 1 month post-injection. Six months post-injection, mice treated with scAAV9-CβA-mir-155-HTT were indistinguishable from controls. Those that received scAAV9-U6-mir-155-HTT showed behavioral abnormalities and striatal damage. In conclusion, miRNA backbone and promoter can be used together to modulate expression levels and strand selection of artificial miRNAs, and in brain, the CβA promoter can provide an effective and safe dose of a human huntingtin miRNA.

Nanoparticulate strategies for the treatment of polyglutamine diseases by halting the protein aggregation process

Polyglutamine (polyQ) diseases are a class of neurodegenerative disorders that cause cellular dysfunction and, eventually, neuronal death in specific regions of the brain. Neurodegeneration is linked to the misfolding and aggregation of expanded polyQ-containing proteins, and their inhibition is one of major therapeutic strategies used commonly. However, successful treatment has been limited to date because of the intrinsic properties of therapeutic agents (poor water solubility, low bioavailability, poor pharmacokinetic properties), and difficulty in crossing physiological barriers, including the blood-brain barrier (BBB). In order to solve these problems, nanoparticulate systems with dimensions of 1-1000 nm able to incorporate small and macromolecules with therapeutic value, to protect and deliver them directly to the brain, have recently been developed, but their use for targeting polyQ disease-mediated protein misfolding and aggregation remains scarce. This review provides an update of the polyQ protein aggregation process and the development of therapeutic strategies for halting it. The main features that a nanoparticulate system should possess in order to enhance brain delivery are discussed, as well as the different types of materials utilized to produce them. The final part of this review focuses on the potential application of nanoparticulate system strategies to improve the specific and efficient delivery of therapeutic agents to the brain for the treatment of polyQ diseases.