miR-29c regulates neurogliogenesis in the mammalian retina through REST

Epigenetic mechanisms of Müller glial reprogramming mediating retinal regeneration

Retinal degenerative diseases, characterized by retinal neuronal death and severe vision loss, affect millions of people worldwide. One of the most promising treatment methods for retinal degenerative diseases is to reprogram non-neuronal cells into stem or progenitor cells, which then have the potential to re-differentiate to replace the dead neurons, thereby promoting retinal regeneration. Müller glia are the major glial cell type and play an important regulatory role in retinal metabolism and retinal cell regeneration. Müller glia can serve as a source of neurogenic progenitor cells in organisms with the ability to regenerate the nervous system. Current evidence points toward the reprogramming process of Müller glia, involving changes in the expression of pluripotent factors and other key signaling molecules that may be regulated by epigenetic mechanisms. This review summarizes recent knowledge of epigenetic modifications involved in the reprogramming process of Müller glia and the subsequent changes to gene expression and the outcomes. In living organisms, epigenetic mechanisms mainly include DNA methylation, histone modification, and microRNA-mediated miRNA degradation, all of which play a crucial role in the reprogramming process of Müller glia. The information presented in this review will improve the understanding of the mechanisms underlying the Müller glial reprogramming process and provide a research basis for the development of Müller glial reprogramming therapy for retinal degenerative diseases.

Integrative Single-Cell Transcriptomics and Epigenomics Mapping of the Fetal Retina Developmental Dynamics

The underlying mechanisms that determine gene expression and chromatin accessibility in retinogenesis are poorly understood. Herein, single-cell RNA sequencing and single-cell assay for transposase-accessible chromatin sequencing are performed on human embryonic eye samples obtained 9-26 weeks after conception to explore the heterogeneity of retinal progenitor cells (RPCs) and neurogenic RPCs. The differentiation trajectory from RPCs to 7 major types of retinal cells are verified. Subsequently, diverse lineage-determining transcription factors are identified and their gene regulatory networks are refined at the transcriptomic and epigenomic levels. Treatment of retinospheres, with the inhibitor of RE1 silencing transcription factor, X5050, induces more neurogenesis with the regular arrangement, and a decrease in Müller glial cells. The signatures of major retinal cells and their correlation with pathogenic genes associated with multiple ocular diseases, including uveitis and age-related macular degeneration are also described. A framework for the integrated exploration of single-cell developmental dynamics of the human primary retina is provided.

Downregulation of plasma microRNA-29c-3p expression may be a new risk factor for diabetic retinopathy

BACKGROUND

Circulation miRNAs have emerged as new biomarkers for identifying and monitoring the microvascular complications of diabetes. The aim of this study is to evaluate the levels of five candidate miRNAs (miR-29c-3p, miR-18a, miR-31, miR-181 and miR-20a) in patients with diabetic retinopathy (DR) and their relationship with disease severity.

METHODS

The study included 31 diabetes patients without DR (NDR group), 68 patients with DR (DR group) and 30 healthy controls (HC group). Twenty-five of patients with DR were proliferative DR (PDR group) and 43 were non-proliferative DR (NPDR group) patients. Metabolic parameters and serum vascular endothelial growth factor (VEGF) levels of all participants were measured. Circulating miRNAs levels were determined by quantitative real-time PCR. Fundus examinations of all patients were performed by a single ophthalmologist.

RESULTS

VEGF levels were significantly higher in the NDR, and DR groups compared to HC group (P=0.011 and P=0.014, respectively). Plasma miR-29c-3p was downregulated in diabetic patients with retinopathy and without retinopathy. This downregulation was more prominent in diabetic patients without retinopathy compared to those with retinopathy (P=0.016). There was no significant difference in plasma levels of miR-18a, miR-20a, miR-18a and miR-31 between diabetic subjects with and without retinopathy (P>0.05). There was no correlation between DR severity and the levels of miRNAs (P>0.05). In multivariate logistic regression analysis, it was found that changes in plasma miR-29c-3p expression of diabetic patients increased DR risk independent of other risk factors.

CONCLUSIONS

Plasma miR-29c-3p expression is downregulated in diabetic patients with and without retinopathy, and changes in this miRNA are an independent risk factor for the development of DR.

miR-124-3p regulates the proliferation and differentiation of retinal progenitor cells through SEPT10

Retinal degenerative diseases such as glaucoma, retinitis pigmentosa, and age-related macular degeneration pose serious threats to human visual health due to lack of effective therapeutic approaches. In recent years, the transplantation of retinal progenitor cells (RPCs) has shown increasing promise in the treatment of these diseases; however, the application of RPC transplantation is limited by both their poor proliferation and their differentiation capabilities. Previous studies have shown that microRNAs (miRNA) act as essential mediators in the fate determination of stem/progenitor cells. In this study, we hypothesized that miR-124-3p plays a regulatory role in the fate of RPC determination by targeting Septin10 (SEPT10) in vitro. We observed that the overexpression of miR124-3p downregulates SEPT10 expression in RPCs, leading to reduced RPC proliferation and increased differentiation, specifically towards both neurons and ganglion cells. Conversely, antisense knockdown of miR-124-3p was shown to boost SEPT10 expression, enhance RPC proliferation, and attenuate differentiation. Moreover, overexpression of SEPT10 rescued miR-124-3p-caused proliferation deficiency while weakening the enhancement of miR-124-3p-induced-RPC differentiation. Results from this study show that miR-124-3p regulates RPC proliferation and differentiation by targeting SEPT10. Furthermore, our findings enable a more comprehensive understanding into the mechanisms of proliferation and differentiation of RPC fate determination. Ultimately, this study may be useful for helping researchers and clinicians to develop more promising and effective approaches to optimize the use of RPCs in treating retinal degeneration diseases.

Therapeutic effects of mesenchymal stem cells-derived extracellular vesicles' miRNAs on retinal regeneration: a review

Extracellular vesicles (EVs), which consist of microvesicles and exosomes, are secreted from all cells to transform vital information in the form of lipids, proteins, mRNAs and small RNAs such as microRNAs (miRNAs). Many studies demonstrated that EVs' miRNAs have effects on target cells. Numerous people suffer from the blindness caused by retinal degenerations. The death of retinal neurons is irreversible and creates permanent damage to the retina. In the absence of acceptable cures for retinal degenerative diseases, stem cells and their paracrine agents including EVs have become a promising therapeutic approach. Several studies showed that the therapeutic effects of stem cells are due to the miRNAs of their EVs. Considering the effects of microRNAs in retinal cells development and function and studies which provide the possible roles of mesenchymal stem cells-derived EVs miRNA content on retinal diseases, we focused on the similarities between these two groups of miRNAs that could be helpful for promoting new therapeutic techniques for retinal degenerative diseases.

Neural Stem Cell-Derived Exosomes Regulate Neural Stem Cell Differentiation Through miR-9-Hes1 Axis

Exosomes, a key element of the central nervous system microenvironment, mediate intercellular communication via horizontally transferring bioactive molecules. Emerging evidence has implicated exosomes in the regulation of neurogenesis. Recently, we compared the neurogenic potential of exosomes released from primary mouse embryonic neural stem cells (NSCs) and astrocyte-reprogrammed NSCs, and observed diverse neurogenic potential of those two exosome populations in vitro. However, the roles of NSC-derived exosomes on NSC differentiation and the underlying mechanisms remain largely unknown. In this study, we firstly demonstrated that NSC-derived exosomes facilitate the differentiation of NSCs and the maturation of both neuronal and glial cells in defined conditions. We then identified miR-9, a pro-neural miRNA, as the most abundantly expressed miRNA in NSC-derived exosomes. The silencing of miR-9 in exosomes abrogates the positive effects of NSC-derived exosomes on the differentiation of NSCs. We further identified Hes1 as miR-9 downstream target, as the transfection of Hes1 siRNA restored the differentiation promoting potential of NSC-derived exosomes after knocking down exosomal miR-9. Thus, our data indicate that NSC-derived exosomes facilitate the differentiation of NSCs via transferring miR-9, which sheds light on the development of cell-free therapeutic strategies for treating neurodegeneration.

Neuronal Development-Related miRNAs as Biomarkers for Alzheimer's Disease, Depression, Schizophrenia and Ionizing Radiation Exposure

Radiation exposure may induce Alzheimer's disease (AD), depression or schizophrenia. A number of experimental and clinical studies suggest the involvement of miRNA in the development of these diseases, and also in the neuropathological changes after brain radiation exposure. The current literature review indicated the involvement of 65 miRNAs in neuronal development in the brain. In the brain tissue, blood, or cerebral spinal fluid (CSF), 11, 55, or 28 miRNAs are involved in the development of AD respectively, 89, 50, 19 miRNAs in depression, and 102, 35, 8 miRNAs in schizophrenia. We compared miRNAs regulating neuronal development to those involved in the genesis of AD, depression and schizophrenia and also those driving radiation-induced brain neuropathological changes by reviewing the available data. We found that 3, 11, or 8 neuronal developmentrelated miRNAs from the brain tissue, 13, 16 or 14 miRNAs from the blood of patient with AD, depression and schizophrenia respectively were also involved in radiation-induced brain pathological changes, suggesting a possibly specific involvement of these miRNAs in radiation-induced development of AD, depression and schizophrenia respectively. On the other hand, we noted that radiationinduced changes of two miRNAs, i.e., miR-132, miR-29 in the brain tissue, three miRNAs, i.e., miR- 29c-5p, miR-106b-5p, miR-34a-5p in the blood were also involved in the development of AD, depression and schizophrenia, thereby suggesting that these miRNAs may be involved in the common brain neuropathological changes, such as impairment of neurogenesis and reduced learning memory ability observed in these three diseases and also after radiation exposure.

Plasma extracellular microRNAs are related to AIDS/cerebral toxoplasmosis co-infection

This study investigated the potential of five miRNA candidates for cerebral toxoplasmosis/HIV co-infection (CT/HIV) biomarkers. miR-155-5p, miR-146a-5p, miR-21-5p, miR-125b-5p and miR-29c-3p were tested in 79 plasma divided into groups: 32 CT/HIV patients; 27 individuals with asymptomatic toxoplasmosis (AT); and 20 individuals seronegative for toxoplasmosis (NC). From each was collected peripheral blood/EDTA for laboratory diagnosis. Blood cells for DNA extractions (molecular diagnosis), plasma for RNA extractions (gene expression) and ELISA (serological diagnosis). miRNA expression was performed by qPCR, and values were expressed in Relative Quantification (RQ). Among the five miRNAs, miR-21-5p and miR-146a-5p were up-expressed in CT/HIV group when compared with AT and NC groups. RQ means for miR-21-5p and miR-146a-5p in CT/HIV group were 3.829 and 2.500, while in AT group, were 1.815 and 1.661, respectively. Differences between 3 groups were statistically significant (Kruskal-Wallis ANOVA test), as well as CT/HIV and AT groups (Mann-Whitney test). Plasma of CT/HIV and AT groups expressed similar levels of miR-29c-3p, miR-155-5p and miR-125b-5p. As NC group was different of CT/HIV and AT groups, differences between three groups were statistically significant (Kruskal-Wallis ANOVA test). No difference was shown between CT/HIV and AT groups (Mann-Whitney test). These results suggest the host miRNAs modulation by Toxoplasma gondii.

Recapitulating developmental mechanisms for retinal regeneration

Degeneration of specific retinal neurons in diseases like glaucoma, age-related macular degeneration, and retinitis pigmentosa is the leading cause of irreversible blindness. Currently, there is no therapy to modify the disease-associated degenerative changes. With the advancement in our knowledge about the mechanisms that regulate the development of the vertebrate retina, the approach to treat blinding diseases through regenerative medicine appears a near possibility. Recapitulation of developmental mechanisms is critical for reproducibly generating cells in either 2D or 3D culture of pluripotent stem cells for retinal repair and disease modeling. It is the key for unlocking the neurogenic potential of Müller glia in the adult retina for therapeutic regeneration. Here, we examine the current status and potential of the regenerative medicine approach for the retina in the backdrop of developmental mechanisms.