RNA Aptamers Rescue Mitochondrial Dysfunction in a Yeast Model of Huntington’s Disease

Abstract

Huntington’s disease (HD) is associated with the misfolding and aggregation of mutant huntingtin harboring an elongated polyglutamine stretch at its N terminus. A distinguishing pathological hallmark of HD is mitochondrial dysfunction. Any strategy that can restore the integrity of the mitochondrial environment should have beneficial consequences for the disease. Specific RNA aptamers were selected that were able to inhibit aggregation of elongated polyglutamine stretch containing mutant huntingtin fragment (103Q-htt). They were successful in reducing the calcium overload, which leads to mitochondrial membrane depolarization in case of HD. In one case, the level of Ca2+ was restored to the level of cells not expressing 103Q-htt, suggesting complete recovery. The presence of aptamers was able to increase mitochondrial mass in cells expressing 103Q-htt, along with rescuing loss of mitochondrial genome. The oxidative damage to the proteome was prevented, which led to increased viability of cells, as monitored by flow cytometry. Thus, the presence of aptamers was able to inhibit aggregation of mutant huntingtin fragment and restore mitochondrial dysfunction in the HD cell model, confirming the advantage of the strategy in a disease-relevant parameter.

Emerging Therapies for Huntington’s Disease – Focus on N-Terminal Huntingtin and Huntingtin Exon 1

“…The Roy lab identified aptamers that bind specifically to mHTT with 51 or 103Q but not wtHTT with 20Q. 86 , 87 The selected aptamers were shown to inhibit aggregation of recombinant mHTT-ex1 in cell-free assays and in yeast, as well as reducing oxidative stress and mitochondrial dysfunction. 86 To our knowledge, this approach has not yet been tested in vivo.…”

Role of RNA Motifs in RNA Interaction with Membrane Lipid Rafts: Implications for Therapeutic Applications of Exosomal RNAs

“…Selected aptamers are extensively studied for diagnostic and therapeutic applications [63,64]. They were reported to be a promising therapeutic agent in such conditions as neurodegenerative diseases [58,65,66] and cancer [67,68]. Moreover, interfering RNAs (iRNA) such as siRNA or miRNA are being investigated for specific gene silencing in the treatment of various diseases [69][70][71].…”

Aptamer Reduces Aggregation of Mutant Huntingtin and Rescues Proteostasis Network in Non-Neuronal and Neuronal Cells

“…Mutant huntingtin aggregates cause increased oxidative stress and impair mitochondrial biogenesis and ROS metabolism. − The binding of mutant huntingtin to the promoter region of peroxisome proliferator-activated receptor-γ coactivator (PGC-1α), a transcription co-regulator of mitochondrial biogenesis, downregulates synthesis of PGC-1α. − In addition, direct interaction of mHTT with PGC-1α reduces its function and affects the synthesis of downstream effectors of the cellular antioxidant system. The growing huntingtin aggregate also sequesters several cellular proteins, including chaperones, so free chaperones are not available to take part in cellular processes. − As molecular chaperones play a vital role in a large number of protein folding processes, sequestration of chaperones in the cells induces proteostasis imbalance, which further alleviates the cytotoxicity due to the accumulation of the aggregated and misfolded protein.…”

“…The selection of aptamers from randomized starting libraries is done via an in vitro , iterative process. , Aptamers can create a variety of secondary and tertiary structures, allowing them to conform to the shape of their targets (proteins, small molecules, and entire cells). Aptamers can potentially function as protein stabilizers in two ways: (1) stabilization of protein monomer and (2) inhibition of protein–protein interaction via steric or electrostatic repulsion. ,, Due to their nonimmunogenic and nontoxic nature, oligonucleotide aptamers are a rational choice for development of therapeutics. , …”

“…We had previously reported the selection of RNA aptamers against N-terminal fragment of huntingtin with expanded glutamine repeat (51Q-htt) . The selected aptamers were able to decrease aggregation of mutant huntingtin in vitro (51Q-htt) and in a yeast cell model of HD (103Q-htt), with concomitant reduction in oxidative stress, proteome and mitochondrial damage, calcium excitotoxicity, restoration of functional properties, and enhanced cell survival. , Yeast cells constitute an excellent first choice for studying different aspects of protein misfolding diseases. − The next step to validate a therapeutic approach would be mammalian cells. In the current work, we have studied the effect of one of the selected RNA aptamers on the aggregation of mutant huntingtin protein (exon 1) in a non-neuronal (HEK293) and neuronal (Neuro 2a) cell model of Huntington’s disease.…”