The contribution of proteasomal impairment to autophagy activation by C9orf72 poly-GA aggregates.

BACKGROUND: Poly-GA, a dipeptide repeat protein unconventionally translated from GGGGCC (G4C2) repeat expansions in C9orf72, is abundant in C9orf72-related amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9orf72-ALS/FTD). Although the poly-GA aggregates have been identified in C9orf72-ALS/FTD neurons, the effects on UPS (ubiquitin-proteasome system) and autophagy and their exact molecular mechanisms have not been fully elucidated. RESULTS: Herein, our in vivo experiments indicate that the mice expressing ploy-GA with 150 repeats instead of 30 repeats exhibit significant aggregates in cells. Mice expressing 150 repeats ploy-GA shows behavioral deficits and activates autophagy in the brain. In vitro findings suggest that the poly-GA aggregates influence proteasomal by directly binding proteasome subunit PSMD2. Subsequently, the poly-GA aggregates activate phosphorylation and ubiquitination of p62 to recruit autophagosomes. Ultimately, the poly-GA aggregates lead to compensatory activation of autophagy. In vivo studies further reveal that rapamycin (autophagy activator) treatment significantly improves the degenerative symptoms and alleviates neuronal injury in mice expressing 150 repeats poly-GA. Meanwhile, rapamycin administration to mice expressing 150 repeats poly-GA reduces neuroinflammation and aggregates in the brain. CONCLUSION: In summary, we elucidate the relationship between poly-GA in the proteasome and autophagy: when poly-GA forms complexes with the proteasome, it recruits autophagosomes and affects proteasome function. Our study provides support for further promoting the comprehension of the pathogenesis of C9orf72, which may bring a hint for the exploration of rapamycin for the treatment of ALS/FTD.

miR-552-3p modulates transcriptional activities of FXR and LXR to ameliorate hepatic glycolipid metabolism disorder.

BACKGROUND & AIMS: The nuclear location of miRNAs has been known for more than a decade, but the exact function of miRNAs in the nucleus has not been fully elucidated. We previously discovered that intranuclear miR-552-3p has an inhibitory role on gene transcription and contains a particular AGGTCA-like sequence, the cis-elements of the NR1 subfamily of nuclear receptors. Here, we aim to explore the potential effect of miR-552-3p and its AGGTCA-like sequence on NR1s and its possible application in improving hepatic glycolipid metabolism. METHODS: RNA-seq, mass spectrometry, and bioinformatics analysis were used to reveal the possible pathways influenced by miR-552-3p. High fat-high fructose diet-fed mice and db/db mice transfected with AAV2/8-miR-552-3p were established to investigate the in vivo effects of miR-552-3p on hepatic glycolipid metabolism. Fluorescence resonance energy transfer, pull-down, electrophoretic mobility shift, and chromatin immunoprecipitation assays were performed to explore the mechanism by which miR-552-3p regulates NR1s. RT-PCR was conducted to analyse miR-552-3p levels in liver biopsies from patients with NAFLD and normal controls. RESULTS: MiR-552-3p could inhibit metabolic gene expression in vitro and displayed beneficial effects on glycolipid metabolism in vivo. Intranuclear miR-552-3p primarily regulated the LXRα and FXR pathways; this was achieved by its binding to the complementary sequence of AGGTCA to modulate the transcriptional activities of LXRα and FXR. Moreover, LXRα and FXR ligands could restore the effects of miR-552-3p on gene expression and glycolipid metabolism. Additionally, the hepatic miR-552-3p level was significantly decreased in liver samples from patients with NAFLD compared to normal controls. CONCLUSIONS: The mechanism by which miR-552-3p modulates LXRα and FXR has revealed a new method of miRNA-mediated gene regulation. In addition, the beneficial effects in vivo and clinical relevance of miR-552-3p suggest that it might be a potential therapeutic target for the treatment of glycolipid metabolic disease. LAY SUMMARY: Glycolipid metabolic diseases, which have become a major public health concern worldwide, are triggered by abnormalities in lipid and glucose metabolism. Herein, we show that miR-552-3p has the ability to ameliorate hepatic glycolipid metabolic diseases by modulating the transcriptional activities of LXRα and FXR in the nucleus. These findings provide evidence that miR-552-3p may serve as a potential therapeutic target.

GADD45ß stabilized by direct interaction with HSP72 ameliorates insulin resistance and lipid accumulation.

Growth arrest and DNA damage-inducible 45ß (GADD45ß) belongs to the GADD45 family which is small acidic proteins in response to cellular stress. GADD45ß has already been reported to have excellent capabilities against cancer, innate immunity and neurological diseases. However, there is little information regard GADD45ß and non-alcoholic fatty liver disease (NAFLD). In the current work, we found that the expression of GADD45ß was markedly decreased in the livers of NAFLD patients via analyzing Gene Expression Omnibus (GEO) dataset and in mouse model through detecting its mRNA in high-fat-high-fructose diet (HFHFr)-fed mice. Moreover, the results from in vivo experiment demonstrated that overexpression of GADD45ß by AAV8-mediated gene transfer in HFHFr-fed mouse model could reduce the level of serum and hepatic triglyceride (TG), and alleviate insulin resistance. Subsequently, by combining immunoprecipitation (IP) and mass spectrometry, we identified that HSP72 directly interacted with GADD45ß to prevent GADD45ß from being degraded by the proteasome pathway. Finally, the benefits of GADD45ß in regulating key factors of TG synthesis and insulin signaling pathway were abolished after HSP72 knockdown. In conclusion, GADD45ß stabilized by the interaction with HSP72 could alleviate the NAFLD-related pathologies, suggested it might be a potential target for the treatment of NAFLD.

Regulatory network of miRNA on its target: coordination between transcriptional and post-transcriptional regulation of gene expression.

MicroRNAs (miRNAs) are a class of endogenous small noncoding RNAs that participate in a majority of biological processes via regulating target gene expression. The post-transcriptional repression through miRNA seed region binding to 3' UTR of target mRNA is considered as the canonical mode of miRNA-mediated gene regulation. However, emerging evidence suggests that other regulatory modes exist beyond the canonical mechanism. In particular, the function of intranuclear miRNA in gene transcriptional regulation is gradually revealed, with evidence showing their contribution to gene silencing or activating. Therefore, miRNA-mediated regulation of gene transcription not only expands our understanding of the molecular mechanism underlying miRNA regulatory function, but also provides new evidence to explain its ability in the sophisticated regulation of many bioprocesses. In this review, mechanisms of miRNA-mediated gene transcriptional and post-transcriptional regulation are summarized, and the synergistic effects among these actions which form a regulatory network of a miRNA on its target are particularly elaborated. With these discussions, we aim to emphasize the importance of miRNA regulatory network on target gene regulation and further highlight the potential application of the network mode in the achievement of a more effective and stable modulation of the target gene expression.

Nucleolar stress and impaired stress granule formation contribute to C9orf72 RAN translation-induced cytotoxicity.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are the two common neurodegenerative diseases that have been associated with the GGGGCC·GGCCCC repeat RNA expansion in a noncoding region of C9orf72. It has been previously reported that unconventional repeat-associated non-ATG (RAN) translation of GGGGCC·GGCCCC repeats produces five types of dipeptide-repeat proteins (referred to as RAN proteins): poly-glycine-alanine (GA), poly-glycine-proline (GP), poly-glycine-arginine (GR), poly-proline-arginine (PR) and poly-proline-alanine (PA). Although protein aggregates of RAN proteins have been found in patients, it is unclear whether RAN protein aggregation induces neurotoxicity. In the present study, we aimed to understand the biological properties of all five types of RAN proteins. Surprisingly, our results showed that none of these RAN proteins was aggregate-prone in our cellular model and that the turnover of these RAN proteins was not affected by the ubiquitin-proteasome system or autophagy. Moreover, poly-GR and poly-PR, but not poly-GA, poly-GP or poly-PA, localized to the nucleolus and induced the translocation of the key nucleolar component nucleophosmin, leading to nucleolar stress and cell death. This poly-GR- and poly-PR-mediated defect in nucleolar function was associated with the suppression of ribosomal RNA synthesis and the impairment of stress granule formation. Taken together, the results of the present study suggest a simple model of the molecular mechanisms underlying RAN translation-mediated cytotoxicity in C9orf72-linked ALS/FTD in which nucleolar stress, but not protein aggregation, is the primary contributor to C9orf72-linked neurodegeneration.

Protease Omi cleaving Hax-1 protein contributes to OGD/R-induced mitochondrial damage in neuroblastoma N2a cells and cerebral injury in MCAO mice.

AIM: In the penumbra after focal cerebral ischemia, an increase of protease Omi is linked to a decrease of Hs1-associated protein X-1 (Hax-1), a protein belonging to the Bcl-2 family. In this study we investigated the mechanisms underlying the regulation of Hax-1 by protease Omi in cerebral ischemia/reperfusion (I/R) injury. METHODS: Mouse neuroblastoma N2a cells were subjected to oxygen-glucose deprivation and reoxygenation (OGD/R); cell viability was assessed with MTT assay. Mice underwent 2-h middle cerebral artery occlusion (MCAO) and reperfusion, and the infarct volume was determined with TTC staining. The expression of Omi and Hax-1 was detected using immunoblot and immunofluorescence assays. The mitochondrial membrane potential was measured using TMRM staining. RESULTS: In the brains of MCAO mice, the protein level of Omi was significantly increased, while the protein level of Hax-1 was decreased. Similar changes were observed in OGD/R-treated N2a cells, but the mRNA level of Hax-1 was not changed. Furthermore, in OGD/R-treated N2a cells, knockdown of Omi significantly increased Hax-1 protein level. Immunofluorescence assay showed that Omi and Hax-1 were co-localized in mitochondria of N2a cells. OGD/R caused marked mitochondrial damage and apoptosis in N2a cells, while inhibition of Omi protease activity with UCF-101 (10 µmol/L) or overexpression of Hax-1 could restore the mitochondrial membrane potential and attenuate cell apoptosis. Moreover, pretreatment of MCAO mice with UCF-101 (7.15 mg/kg, ip) could restore Hax-1 expression, inhibit caspase activation, and significantly reduce the infarct volume. CONCLUSION: Protease Omi impairs mitochondrial function by cleaving Hax-1, which induces apoptosis in OGD/R-treated N2a cells and causes I/R injury in MCAO mice.

A novel pathogenic deletion in ISPD causes Walker-Warburg syndrome in a Chinese family.

BACKGROUND: Walker-Warburg syndrome (WWS) is a genetically heterogeneous disease that often presents with complex brain and eye malformations and congenital muscular dystrophy. Mutations of the ISPD gene have been identified as one of the most frequent causes of WWS. OBJECTIVE: The current study aimed to identify the cause of severe congenital hydrocephalus and brain dysplasia in our subject. METHODS: Genomic DNA was extracted from the fetus's umbilical cord blood and peripheral venous blood of the parents. The genetic analysis included whole-exome sequencing and qPCR. Additionally, in silico analysis and cellular experiments were performed. RESULTS: We identified a novel homozygous deletion of exons 7 to 9 in the ISPD gene of the fetus with WWS. In silico analysis revealed a defective domain structure in the C-terminus domain of the ISPD. Analysis of the electrostatic potential energy showed the formation of a new binding pocket formation on the surface of the mutant ISPD gene (ISPD-del ex7-9). Cellular study of the mutant ISPD revealed a significant change in its cellular localization, with the ISPD-del ex7-9 protein translocating from the cytoplasm to the nucleus compared to wild-type ISPD, which is mostly present in the cytoplasm. CONCLUSION: The present study expands the mutational spectrum of WWS caused by ISPD mutations. Importantly, our work suggests that whole-exome sequencing could be considered as a diagnostic option for fetuses with congenital hydrocephalus and brain malformations when karyotype or chromosomal microarray analysis fails to provide a definitive diagnosis.

Non-coding RNAs: New players in mitophagy and neurodegeneration.

Mitophagy controls mitochondrial quality to maintain cellular homeostasis, while aberrations in this process are responsible for neurodegenerative diseases. Mitophagy is initiated through the recruitment of autophagosomes in a ubiquitin-dependent or ubiquitin-independent manner under different stress conditions. Although the detailed molecular mechanisms of how mitophagy processes influence neurodegeneration remain largely uncharacterized, there is mounting evidence indicating that non-coding RNAs (ncRNAs), a variety of endogenous regulators, including microRNAs and long non-coding RNAs, extensively participate in mitophagy processes and play pivotal roles in the aging process and neurodegenerative diseases. Here, we reviewed the major mitophagy pathways modulated by some classical and newly found ncRNAs and summarized the diverse mechanisms in a regulatory network. We also discussed the generalizability of ncRNAs in the development of common neurodegenerative diseases related to proteotoxicity and the importance of mitophagy in the pathogenesis of these diseases. In summary, we propose that ncRNAs act as linkers between mitophagy and neurodegeneration, showing the potential therapeutic application of mitophagy regulation mediated by ncRNAs in neurodegenerative diseases.

miR-34a-5p regulates PINK1-mediated mitophagy via multiple modes.

AIMS: PTEN induced putative kinase 1 (PINK1)-mediated mitophagy process is tightly associated with various age-dependent diseases in mammals. The roles of miRNAs (miRNAs) in the PINK1-mediated mitophagy process are not fully understood. Here we discovered that miR-34a-5p suppresses PINK1 expression directly though two post-transcriptional non-classical binding modes, resulting in inhibition of PINK1-mediated mitophagy process. MAIN METHODS: For in vivo experiments, brains were dissected from 8 weeks old and 40 weeks old C57BL/6 male mice to measure miR-34a-5p expression and PINK1 expression. For in vitro experiments, overexpression of miR-34a-5p mimics in HEK293 cells was performed to investigate the effect of miR-34a-5p on PINK1 expression and its regulatory mechanism, parkin recruitment and mitophagy process. KEY FINDINGS: The level of miR-34a-5p was upregulated and the level of PINK1 mRNA was downregulated in brains of aged mice. Both the 3'-untranslated region (3'UTR) and the Coding DNA sequence (CDS) of PINK1 mRNA were bound to the non-seed region of miR-34a-5p, rather than the seed region, resulting in a decrease in PINK1 expression. Endogenous miR-34a-5p knockout increased PINK1 expression. Further results indicated that miR-34a-5p inhibits mitophagy process by reduction of PINK1. miR-34a-5p hinders phosphorylated Ser65-ubiquitin (pS65-Ub) accumulation, prevents the mitochondrial recruitment of Parkin, attenuates ubiquitination and delays the clearance of damaged mitochondria. SIGNIFICANCE: We firstly found that miR-34a-5p suppresses PINK1 directly and further regulates mitophagy through non-canonical modes. This finding hints at a crucial role of miR-34a-5p implicated in accelerating the pathogenesis of age-related neurological diseases.

Nuclear miR-30b-5p suppresses TFEB-mediated lysosomal biogenesis and autophagy.

Lysosome is a crucial organelle in charge of degrading proteins and damaged organelles to maintain cellular homeostasis. Transcription factor EB (TFEB) is the master transcription factor regulating lysosomal biogenesis and autophagy. Under external stimuli such as starvation, dephosphorylated TFEB transports into the nucleus to specifically recognize and bind to the coordinated lysosomal expression and regulation (CLEAR) elements at the promotors of autophagy and lysosomal biogenesis-related genes. The function of TFEB in the nucleus is fine regulated but the molecular mechanism is not fully elucidated. In this study, we discovered that miR-30b-5p, a small RNA which is known to regulate a series of genes through posttranscriptional regulation in the cytoplasm, was translocated into the nucleus, bound to the CLEAR elements, suppressed the transcription of TFEB-dependent downstream genes, and further inhibited the lysosomal biogenesis and the autophagic flux; meanwhile, knocking out the endogenous miR-30b-5p by CRISPR/Cas9 technique significantly increased the TFEB-mediated transactivation, resulting in the increased expression of autophagy and lysosomal biogenesis-related genes. Overexpressing miR-30b-5p in mice livers showed a decrease in lysosomal biogenesis and autophagy. These in vitro and in vivo data indicate that miR-30b-5p may inhibit the TFEB-dependent transactivation by binding to the CLEAR elements in the nucleus to regulate the lysosomal biogenesis and autophagy. This novel mechanism of nuclear miRNA regulating gene transcription is conducive to further elucidating the roles of miRNAs in the lysosomal physiological functions and helps to understand the pathogenesis of abnormal autophagy-related diseases.

Dependence of PINK1 accumulation on mitochondrial redox system.

Accumulation of PINK1 on the outer mitochondrial membrane (OMM) is necessary for PINK-mediated mitophagy. The proton ionophores, like carbonyl cyanide m-chlorophenylhydrazone (CCCP) and carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP), inhibit PINK1 import into mitochondrial matrix and induce PINK1 OMM accumulation. Here, we show that the CHCHD4/GFER disulfide relay system in the mitochondrial intermembrane space (IMS) is required for PINK1 stabilization when mitochondrial membrane potential is lost. Activation of CHCHD4/GFER system by mitochondrial oxidative stress or inhibition of CHCHD4/GFER system with antioxidants can promote or suppress PINK1 accumulation, respectively. Thus data suggest a pivotal role of CHCHD4/GFER system in PINK1 accumulation. The amyotrophic lateral sclerosis-related superoxide dismutase 1 mutants dysregulated redox state and CHCHD4/GFER system in the IMS, leading to inhibitions of PINK1 accumulation and mitophagy. Thus, the redox system in the IMS is involved in PINK1 accumulation and damaged mitochondrial clearance, which may play roles in mitochondrial dysfunction-related neurodegenerative diseases.

C9orf72 associates with inactive Rag GTPases and regulates mTORC1-mediated autophagosomal and lysosomal biogenesis.

GGGGCC repeat expansion in C9orf72 is the most common genetic cause in both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), two neurodegenerative disorders in association with aging. Bidirectional repeat expansions in the noncoding region of C9orf72 have been shown to produce dipeptide repeat (DPR) proteins through repeat-associated non-ATG (RAN) translation and to reduce the expression level of the C9orf72 gene product, C9orf72 protein. Mechanisms underlying C9orf72-linked neurodegeneration include expanded RNA repeat gain of function, DPR toxicity, and C9orf72 protein loss of function. In the current study, we focus on the cellular function of C9orf72 protein. We report that C9orf72 can regulate lysosomal biogenesis and autophagy at the transcriptional level. We show that loss of C9orf72 leads to striking accumulation of lysosomes, autophagosomes, and autolysosomes in cells, which is associated with suppressed mTORC1 activity and enhanced nuclear translocation of MiT/TFE family members MITF, TFE3, and TFEB, three master regulators of lysosomal biogenesis and autophagy. We demonstrate that the DENN domain of C9orf72 specifically binds to inactive Rag GTPases, but not active Rag GTPases, thereby affecting the function of Rag/raptor/mTOR complex and mTORC1 activity. Furthermore, active Rag GTPases, but not inactive Rag GTPases or raptor rescued the impaired activity and lysosomal localization of mTORC1 in C9orf72-deficient cells. Taken together, the present study highlights a key role of C9orf72 in lysosomal and autophagosomal regulation, and demonstrates that Rag GTPases and mTORC1 are involved in C9orf72-mediated autophagy.

MiR-629-5p promotes the invasion of lung adenocarcinoma via increasing both tumor cell invasion and endothelial cell permeability.

Tumor invasion underlies further metastasis, the leading cause for cancer-related deaths. Deregulation of microRNAs has been identified associated with the malignant behavior of various cancers, including lung adenocarcinoma (LUAD), the major subtype of lung cancer. Here, we showed the significantly positive correlation between miR-629-5p level and tumor invasion in LUAD specimens (n = 49). In a human LUAD metastasis mouse model, H1650 cells (high level of miR-629-5p) were more aggressive than A549 cells (low level of miR-629-5p) in vivo, including higher incidence of vascular invasion and pulmonary colonization. Ectopic expression of miR-629-5p in A549 cells also increased their invasive capability. Then we identified that miR-629-5p promotes LUAD invasion in a mode of dual regulation via tumor cells invasion and endothelial cells permeability, respectively. In tumor cells, miR-629-5p enhanced motility and invasiveness of tumor cells by directly targeting PPWD1 (a cyclophilin), which clinically related to tumor invasion in LUAD specimens. Restoring PPWD1 protein significantly attenuated the invasion-promoting effects of miR-629-5p. Besides, exosomal-miR-629-5p secreted from tumor cells could be transferred to endothelial cells and increased endothelial monolayers permeability by suppressing CELSR1 (a nonclassic-type cadherin), which had a low level in the endothelial cells of invasive LUAD specimens. Activating the expression of CELSR1 in endothelial cells markedly blocked the effect of miR-629-5p. Our study suggests the dual roles of miR-629-5p in tumor cells and endothelial cells for LUAD invasion, implying a therapeutic option to targeting miR-629-5p using the "one stone, two birds" strategy in LUAD.

MiR-4465 directly targets PTEN to inhibit AKT/mTOR pathway-mediated autophagy.

Autophagy plays an important role in maintaining cell function. Abnormal autophagy leads to cell dysfunction and is associated with many diseases such as tumors, immunodeficiency diseases, lysosomal storage disorders, and neurodegenerative diseases. Autophagy is precisely regulated, and PTEN plays an important role in regulating autophagy. As noncoding small RNAs, miRNAs play an important role in the fine regulation of cellular processes. However, the mechanism of the miRNA regulation of PTEN-related autophagy has not been fully elucidated. In this study, our results showed that miR-4465 significantly inhibited the expression of PTEN, upregulated phosphorylated AKT, and thereby inhibited autophagy by activating mTOR in HEK293, HeLa, and SH-SY5Y cells. Further studies indicated that miR-4465 reduced PTEN mRNA levels through posttranscriptional regulation via directly targeting the 3'-UTR. Our novel findings provide useful hints for the comprehensive elucidation of the molecular mechanism of miRNA-regulated PTEN-related autophagy and may also provide some new insights for the exploration of miRNAs in the treatment of PTEN-related diseases.

Motor dysfunction and neurodegeneration in a C9orf72 mouse line expressing poly-PR.

A GGGGCC hexanucleotide repeat expansion in intron 1 of chromosome 9 open reading frame 72 (C9ORF72) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Repeat-associated non-ATG translation of dipeptide repeat proteins (DPRs) contributes to the neuropathological features of c9FTD/ALS. Among the five DPRs, arginine-rich poly-PR are reported to be the most toxic. Here, we generate a transgenic mouse line that expresses poly-PR (GFP-PR28) specifically in neurons. GFP-PR28 homozygous mice show decreased survival time, while the heterozygous mice show motor imbalance, decreased brain weight, loss of Purkinje cells and lower motor neurons, and inflammation in the cerebellum and spinal cord. Transcriptional analysis shows that in the cerebellum, GFP-PR28 heterozygous mice show differential expression of genes related to synaptic transmission. Our findings show that GFP-PR28 transgenic mice partly model neuropathological features of c9FTD/ALS, and show a role for poly-PR in neurodegeneration.