Suppression of toxicity of the mutant huntingtin protein by its interacting compound, desonide.

Identifying inhibitors of pathogenic proteins is the major strategy of targeted drug discoveries. This strategy meets challenges in targeting neurodegenerative disorders such as Huntington's disease (HD), which is mainly caused by the mutant huntingtin protein (mHTT), an "undruggable" pathogenic protein with unknown functions. We hypothesized that some of the chemical binders of mHTT may change its conformation and/or stability to suppress its downstream toxicity, functioning similarly to an "inhibitor" under a broader definition. We identified 21 potential mHTT selective binders through a small-molecule microarray­based screening. We further tested these compounds using secondary phenotypic screens for their effects on mHTT-induced toxicity and revealed four potential mHTT-binding compounds that may rescue HD-relevant phenotypes. Among them, a Food and Drug Administration­approved drug, desonide, was capable of suppressing mHTT toxicity in HD cellular and animal models by destabilizing mHTT through enhancing its polyubiquitination at the K6 site. Our study reveals the therapeutic potential of desonide for HD treatment and provides the proof of principle for a drug discovery pipeline: target-binder screens followed by phenotypic validation and mechanistic studies.

Long Non-Coding RNA-Cardiac-Inducing RNA 6 Mediates Repair of Infarcted Hearts by Inducing Mesenchymal Stem Cell Differentiation into Cardiogenic Cells through Cyclin-Dependent Kinase 1.

This study aims to investigate the induction effect of LncRNA-CIR6 on MSC differentiation into cardiogenic cells in vitro and in vivo. In addition to pretreatment with Ro-3306 (a CDK1 inhibitor), LncRNA-CIR6 was transfected into BMSCs and hUCMSCs using jetPRIME. LncRNA-CIR6 was further transfected into the hearts of C57BL/6 mice via 100 µL of AAV9-cTnT-LncRNA-CIR6-ZsGreen intravenous injection. After three weeks of transfection followed by AMI surgery, hUCMSCs (5 × 105/100 µL) were injected intravenously one week later. Cardiac function was evaluated using VEVO 2100 and electric mapping nine days after cell injection. Immunofluorescence, Evans blue-TTC, Masson staining, FACS, and Western blotting were employed to determine relevant indicators. LncRNA-CIR6 induced a significant percentage of differentiation in BMSCs (83.00 ± 0.58)% and hUCMSCs (95.43 ± 2.13)% into cardiogenic cells, as determined by the expression of cTnT using immunofluorescence and FACS. High cTNT expression was observed in MSCs after transfection with LncRNA-CIR6 by Western blotting. Compared with the MI group, cardiac contraction and conduction function in MI hearts treated with LncRNA-CIR6 or combined with MSCs injection groups were significantly increased, and the areas of MI and fibrosis were significantly lower. The transcriptional expression region of LncRNA-CIR6 was on Chr17 from 80209290 to 80209536. The functional region of LncRNA-CIR6 was located at nucleotides 0-50/190-255 in the sequence. CDK1, a protein found to be related to the proliferation and differentiation of cardiomyocytes, was located in the functional region of the LncRNA-CIR6 secondary structure (from 0 to 17). Ro-3306 impeded the differentiation of MSCs into cardiogenic cells, while MSCs transfected with LncRNA-CIR6 showed a high expression of CDK1. LncRNA-CIR6 mediates the repair of infarcted hearts by inducing MSC differentiation into cardiogenic cells through CDK1.

A high-throughput-compatible assay to measure the degradation of endogenous Huntingtin proteins.

AIM: The accumulation of disease-causing proteins is a common hallmark of many neurodegenerative disorders. Measuring the degradation of such proteins using high-throughput-compatible assays is highly desired for the identification of genetic and chemical modulators of degradation. For example, Huntington's disease (HD) is an incurable hereditary neurodegenerative disorder caused by the cytotoxicity of mutant huntingtin protein (mHTT). The high-throughput measurement of mHTT degradation is important in HD drug discovery and research. Existing methods for such purposes have limitations due to their dependence on protein tags or pan protein synthesis inhibitors. Here, we report a high-throughput-compatible pulse-chase method (CH-chase) for the measurement of endogenous tag-free huntingtin protein (HTT) degradation based on Click chemistry and Homogeneous Time Resolved Fluorescence (HTRF) technologies. METHODS: The pulsed-labeled proteins were conjugated with biotin using the click reaction strain-promoted alkyne-azide cycloaddition (SPAAC), and the chase signals were calculated by measuring the reduction percentage of the HTT HTRF signals after pull-down with streptavidin beads. RESULTS: We validated that the signals were within the linear detection range and were HTT-specific. We successfully measured the degradation of endogenous HTT in a high-throughput-compatible format using 96-well plates. The predicted changes of HTT degradation by known modifiers were observed, which confirmed that the assay is suitable for the identification of HTT degradation modifiers. CONCLUSION: We have established the first high-throughput-compatible assay capable of measuring endogenous, tag-free HTT degradation, providing a valuable tool for HD research and drug discovery. The method could be applied to other proteins and can facilitate research on other neurodegenerative disorders and proteinopathies.

Effects of liraglutide on ANP secretion and cardiac dynamics.

To observe the effects of liraglutide (analog of glucagon-like peptide 1 (GLP-1)) on atrial natriuretic peptide (ANP) secretion and atrial dynamics, an ex vivo isolated rat atrial perfusion model was used to determine atrial ANP secretion and pulse pressure. DPP-4-/- mice were also established in vivo. ANP levels were determined by radioimmunoassay; GLP-1 content was determined by Elisa. The expression levels of GLP-1 receptor (GLP-1R), PI3K/AKT/mTOR, piezo 1, and cathepsin K were analyzed by Western blot. In the clinical study, patients with acute coronary syndrome (ACS) had low levels of plasma GLP-1 but relatively high levels of plasma ANP. In ex vivo (3.2 nmol/L) and in vivo (30 µg/kg) models, liraglutide significantly decreased ANP levels and atrial pulse pressure. Exendin9-39 alone (GLP-1R antagonist) reversibly significantly increased ANP secretion, and the reduction effect of liraglutide on the secretion of ANP was significantly alleviated by Exendin9-39. Exendin9-39 demonstrated slightly decreased atrial pulse pressure; however, combined liraglutide and Exendin9-39 significantly decreased atrial pulse pressure. Ly294002 (PI3K/AKT inhibitor) inhibited the increase of ANP secretion by liraglutide for a short time, while Ly294002 didn't counteract the decrease in pulse pressure by liraglutide in atrial dynamics studies. Liraglutide increased the expression of GLP-1R and PI3K/AKT/mTOR in isolated rat atria and the hearts of mice in vivo, whereas Exendin9-39 reversibly reduced the expression of GLP-1R and PI3K/AKT/mTOR. Piezo 1 was significantly decreased in wild type and DPP-4-/- mouse heart or isolated rat atria after being treated with liraglutide. Cathepsin K expression was only decreased in in vivo model hearts. Liraglutide can inhibit ANP secretion while decreasing atrial pulse pressure mediated by GLP-1R. Liraglutide probably plays a role in the reduction of ANP secretion via the PI3K/AKT/mTOR signaling pathway. Piezo 1 and cathepsin K may be involved in the liraglutide mechanism of reduction.

A striatal-enriched intronic GPCR modulates huntingtin levels and toxicity.

Huntington's disease (HD) represents an important model for neurodegenerative disorders and proteinopathies. It is mainly caused by cytotoxicity of the mutant huntingtin protein (Htt) with an expanded polyQ stretch. While Htt is ubiquitously expressed, HD is characterized by selective neurodegeneration of the striatum. Here we report a striatal-enriched orphan G protein-coupled receptor(GPCR) Gpr52 as a stabilizer of Htt in vitro and in vivo. Gpr52 modulates Htt via cAMP-dependent but PKA independent mechanisms. Gpr52 is located within an intron of Rabgap1l, which exhibits epistatic effects on Gpr52-mediated modulation of Htt levels by inhibiting its substrate Rab39B, which co-localizes with Htt and translocates Htt to the endoplasmic reticulum. Finally, reducing Gpr52 suppresses HD phenotypes in both patient iPS-derived neurons and in vivo Drosophila HD models. Thus, our discovery reveals modulation of Htt levels by a striatal-enriched GPCR via its GPCR function, providing insights into the selective neurodegeneration and potential treatment strategies.

TR-FRET assays of Huntingtin protein fragments reveal temperature and polyQ length-dependent conformational changes.

Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) technology is a widely used immunoassay that enables high-throughput quantitative measurements of proteins of interest. One of the well established examples is the TR-FRET assay for mutant huntingtin protein (HTT), which is the major cause of the neurodegenerative Huntington's disease (HD). To measure the mutant HTT protein, the published assays utilize a polyQ antibody, MW1, paired with HTT N-terminal antibodies. MW1 has much higher apparent affinity to mutant HTT with expanded polyQ stretch than to wild-type HTT with shorter polyQ, and thus the assays detect mutant HTT preferentially. Here we report a reversible temperature dependent change of TR-FRET signals for HTT N-terminal fragments: the signals become higher when the temperature is lowered from room temperature to 4°C. Interestingly, the temperature sensitivity of the TR-FRET signals is much higher for the Q25 (wild-type) than for the Q72 (mutant) protein. We further revealed that it is likely due to a temperature and polyQ length-dependent structural or spatial change of HTT, which is potentially useful for understanding polyQ structure and toxicity.