Scott Q. Harper

RNAi suppresses polyglutamine-induced neurodegeneration in a model of spinocerebellar ataxia

The dominant polyglutamine expansion diseases, which include spinocerebellar ataxia type 1 (SCA1) and Huntington disease, are progressive, untreatable, neurodegenerative disorders. In inducible mouse models of SCA1 and Huntington disease, repression of mutant allele expression improves disease phenotypes. Thus, therapies designed to inhibit expression of the mutant gene would be beneficial. Here we evaluate the ability of RNA interference (RNAi) to inhibit polyglutamine-induced neurodegeneration caused by mutant ataxin-1 in a mouse model of SCA1. Upon intracerebellar injection, recombinant adeno-associated virus (AAV) vectors expressing short hairpin RNAs profoundly improved motor coordination, restored cerebellar morphology and resolved characteristic ataxin-1 inclusions in Purkinje cells of SCA1 mice. Our data demonstrate in vivo the potential use of RNAi as therapy for dominant neurodegenerative disease.

The Bifunctional microRNA miR-9/miR-9* Regulates REST and CoREST and Is Downregulated in Huntington's Disease

The transcription factor REST silences neuronal gene expression in non-neuronal cells. In neurons, the protein is sequestered in the cytoplasm in part through binding to huntingtin. Polyglutamine expansions in huntingtin, which causes Huntingtons disease (HD), abrogates REST-huntingtin binding. Consequently, REST translocates to the nucleus, occupies RE1 repressor sequences and decreases neuronal gene expression. In this work, we found that levels of several microRNAs (miRNAs) with upstream RE1 sites are decreased in HD patient cortices relative to healthy controls. Interestingly, one of these, the bifunctional brain enriched miR-9/miR-9*, targets two components of the REST complex: miR-9 targets REST and miR-9* targets CoREST. These data provide evidence for a double negative feedback loop between the REST silencing complex and the miRNAs it regulates.

Artificial miRNAs mitigate shRNA-mediated toxicity in the brain : Implications for the therapeutic development of RNAi

Huntingtons disease (HD) is a fatal, dominant neurodegenerative disease caused by a polyglutamine repeat expansion in exon 1 of the HD gene, which encodes the huntingtin protein. We and others have shown that RNAi is a candidate therapy for HD because expression of inhibitory RNAs targeting mutant human HD transgenes improved neuropathology and behavioral deficits in HD mouse models. Here, we developed shRNAs targeting conserved sequences in human HD and mouse HD homolog (HDh) mRNAs to initiate preclinical testing in a knockin mouse model of HD. We screened 35 shRNAs in vitro and subsequently narrowed our focus to three candidates for in vivo testing. Unexpectedly, two active shRNAs induced significant neurotoxicity in mouse striatum, although HDh mRNA expression was reduced to similar levels by all three. Additionally, a control shRNA containing mismatches also induced toxicity, although it did not reduce HDh mRNA expression. Interestingly, the toxic shRNAs generated higher antisense RNA levels, compared with the nontoxic shRNA. These results demonstrate that the robust levels of antisense RNAs emerging from shRNA expression systems can be problematic in the mouse brain. Importantly, when sequences that were toxic in the context of shRNAs were placed into artificial microRNA (miRNA) expression systems, molecular and neuropathological readouts of neurotoxicity were significantly attenuated without compromising mouse HDh silencing efficacy. Thus, miRNA-based approaches may provide more appropriate biological tools for expressing inhibitory RNAs in the brain, the implications of which are crucial to the development of RNAi for both basic biological and therapeutic applications.

Modular flexibility of dystrophin: Implications for gene therapy of Duchenne muscular dystrophy

Attempts to develop gene therapy for Duchenne muscular dystrophy (DMD) have been complicated by the enormous size of the dystrophin gene. We have performed a detailed functional analysis of dystrophin structural domains and show that multiple regions of the protein can be deleted in various combinations to generate highly functional mini- and micro-dystrophins. Studies in transgenic mdx mice, a model for DMD, reveal that a wide variety of functional characteristics of dystrophy are prevented by some of these truncated dystrophins. Muscles expressing the smallest dystrophins are fully protected against damage caused by muscle activity and are not morphologically different from normal muscle. Moreover, injection of adeno-associated viruses carrying micro-dystrophins into dystrophic muscles of immunocompetent mdx mice results in a striking reversal of histopathological features of this disease. These results demonstrate that the dystrophic pathology can be both prevented and reversed by gene therapy using micro-dystrophins.

CHIP Suppresses Polyglutamine Aggregation and Toxicity In Vitro and In Vivo

Huntingtons disease (HD) and other polyglutamine (polyQ) neurodegenerative diseases are characterized by neuronal accumulation of the disease protein, suggesting that the cellular ability to handle abnormal proteins is compromised. As both a cochaperone and ubiquitin ligase, the C-terminal Hsp70 (heat shock protein 70)-interacting protein (CHIP) links the two major arms of protein quality control, molecular chaperones, and the ubiquitin-proteasome system. Here, we demonstrate that CHIP suppresses polyQ aggregation and toxicity in transfected cell lines, primary neurons, and a novel zebrafish model of disease. Suppression by CHIP requires its cochaperone function, suggesting that CHIP acts to facilitate the solubility of mutant polyQ proteins through its interactions with chaperones. Conversely, HD transgenic mice that are haploinsufficient for CHIP display a markedly accelerated disease phenotype. We conclude that CHIP is a critical mediator of the neuronal response to misfolded polyQ protein and represents a potential therapeutic target in this important class of neurodegenerative diseases.

DUX4, a candidate gene for facioscapulohumeral muscular dystrophy, causes p53-dependent myopathy in vivo

Facioscapulohumeral muscular dystrophy (FSHD) is associated with D4Z4 repeat contraction on human chromosome 4q35. This genetic lesion does not result in complete loss or mutation of any gene. Consequently, the pathogenic mechanisms underlying FSHD have been difficult to discern. In leading FSHD pathogenesis models, D4Z4 contractions are proposed to cause epigenetic changes, which ultimately increase expression of genes with myopathic potential. Although no gene has been conclusively linked to FSHD development, recent evidence supports a role for the D4Z4‐encoded DUX4 gene in FSHD. In this study, our objective was to test the in vivo myopathic potential of DUX4.

Microdystrophin Gene Therapy of Cardiomyopathy Restores Dystrophin-Glycoprotein Complex and Improves Sarcolemma Integrity in the Mdx Mouse Heart

Background—More than 90% of Duchenne muscular dystrophy (DMD) patients develop cardiomyopathy, and many die of cardiac failure. Despite tremendous progress in skeletal muscle gene therapy, few attempts have been made to treat cardiomyopathy. Microdystrophin genes are shown to correct skeletal muscle pathological lesions in the mdx mouse model for DMD. Here, we tested the therapeutic potential of adeno-associated virus (AAV)–mediated microdystrophin gene therapy in the mdx mouse heart. Methods and Results—AAV was delivered to the newborn mdx mouse cardiac cavity. The procedure was rapid and well tolerated. Efficient expression was achieved in the inner and the outer layers of the myocardium. The ubiquitous cytomegalovirus promoter resulted in substantially higher expression than the muscle-specific CK6 promoter. The therapeutic effects of microdystrophin were evaluated at 10 months after infection. Immunostaining demonstrated extensive microdystrophin expression and successful restoration of the dystrophin-glycoprotein complex. Importantly, AAV-mediated microdystrophin expression improved the sarcolemma integrity in the mdx heart. Conclusions—We established a simple gene transfer method for efficient and persistent transduction of the mdx mouse heart. AAV-mediated microdystrophin expression restored the critical dystrophin-glycoprotein complex and improved sarcolemma integrity of the mdx heart. Our results revealed the promise of AAV-microdystrophin gene therapy for cardiomyopathy in DMD.

RNA Interference Inhibits DUX4-induced Muscle Toxicity In Vivo: Implications for a Targeted FSHD Therapy

No treatment exists for facioscapulohumeral muscular dystrophy (FSHD), one of the most common inherited muscle diseases. Although FSHD can be debilitating, little effort has been made to develop targeted therapies. This lack of focus on targeted FSHD therapy perpetuated because the genes and pathways involved in the disorder were not understood. Now, more than 2 decades after efforts to decipher the root cause of FSHD began, this barrier to translation is finally lowering. Specifically, several recent studies support an FSHD pathogenesis model involving overexpression of the myopathic DUX4 gene. DUX4 inhibition has therefore emerged as a promising therapeutic strategy for FSHD. In this study, we tested a preclinical RNA interference (RNAi)-based DUX4 gene silencing approach as a prospective treatment for FSHD. We found that adeno-associated viral (AAV) vector-delivered therapeutic microRNAs corrected DUX4-associated myopathy in mouse muscle. These results provide proof-of-principle for RNAi therapy of FSHD through DUX4 inhibition.

Connecdenn, A Novel DENN Domain-Containing Protein of Neuronal Clathrin-Coated Vesicles Functioning in Synaptic Vesicle Endocytosis

Clathrin-coated vesicles (CCVs) are responsible for the endocytosis of multiple cargo, including synaptic vesicle membranes. We now describe a new CCV protein, termed connecdenn, that contains an N-terminal DENN (differentially expressed in neoplastic versus normal cells) domain, a poorly characterized protein module found in multiple proteins of unrelated function and a C-terminal peptide motif domain harboring three distinct motifs for binding the α-ear of the clathrin adaptor protein 2 (AP-2). Connecdenn coimmunoprecipitates and partially colocalizes with AP-2, and nuclear magnetic resonance and peptide competition studies reveal that all three α-ear-binding motifs contribute to AP-2 interactions. In addition, connecdenn contains multiple Src homology 3 (SH3) domain-binding motifs and coimmunoprecipitates with the synaptic SH3 domain proteins intersectin and endophilin A1. Interestingly, connecdenn is enriched on neuronal CCVs and is present in the presynaptic compartment of neurons. Moreover, connecdenn has a uniquely stable association with CCV membranes because it resists extraction with Tris and high-salt buffers, unlike most other CCV proteins, but it is not detected on purified synaptic vesicles. Together, these observations suggest that connecdenn functions on the endocytic limb of the synaptic vesicle cycle. Accordingly, disruption of connecdenn interactions with its binding partners through overexpression of the C-terminal peptide motif domain or knock down of connecdenn through lentiviral delivery of small hairpin RNA both lead to defects in synaptic vesicle endocytosis in cultured hippocampal neurons. Thus, we identified connecdenn as a component of the endocytic machinery functioning in synaptic vesicle endocytosis, providing the first evidence of a role for a DENN domain-containing protein in endocytosis.

Viral Delivery of Recombinant Short Hairpin RNAs

Recent work demonstrates that RNA interference (RNAi) can coordinate protein expression. Inhibitory RNAs are expressed naturally in cells as microRNAs (miRNAs) or introduced into cells as small interfering RNAs (siRNAs). Both types of small RNAs can be used at the bench to silence mRNA expression. For many researchers, transfection of siRNAs synthesized in vitro or purchased from commercial sources is impractical for the cellular system under study. As an alternative to transfection-based methods, we provide a practical approach to accomplish siRNA-mediated gene silencing through the generation and introduction of recombinant viral vectors expressing short hairpin RNAs (shRNAs). shRNAs are subsequently processed to siRNAs in vivo, leading to efficient, and, in some cases, long-term silencing.