The miR-17 similar to 92a Cluster of MicroRNAs Is Required for the Fitness of Foxp3(+) Regulatory T Cells

By genetic inactivation of key microRNA biogenesis enzymes, we and others have previously demonstrated the critical requirement of the microRNA pathway for the differentiation and function of Foxp3(+) regulatory T cells. In this study, we identified members of the miR-17 ∼ 92a cluster of microRNAs to be enriched in regulatory T cells. To investigate the function of this microRNA cluster, we deleted the gene specifically in Foxp3(+) cells in mice. We found that miR-17 ∼ 92a is required for the fitness of regulatory T cells, and deficiency impacted at the level of apoptosis and proliferation of these cells. This led to a loss of Foxp3(+) cells over time, particularly in competitive settings, and culminated in a range of immunologic perturbations. Thus, miR-17 ∼ 92a-target interactions are part of the essential microRNA networks that safeguard the regulatory T cell lineage

MicroRNA-independent roles of the RNase III enzymes Drosha and Dicer

The ribonuclease III enzymes Drosha and Dicer are renowned for their central roles in the biogenesis of microRNAs (miRNAs). For many years, this has overshadowed the true versatility and importance of these enzymes in the processing of other RNA substrates. For example, Drosha also recognizes and cleaves messenger RNAs (mRNAs), and potentially ribosomal RNA. The cleavage of mRNAs occurs via recognition of secondary stem-loop structures similar to miRNA precursors, and is an important mechanism of repressing gene expression, particularly in progenitor/stem cell populations. On the other hand, Dicer also has critical roles in genome regulation and surveillance. These include the production of endogenous small interfering RNAs from many sources, and the degradation of potentially harmful short interspersed element and viral RNAs. These findings have sparked a renewed interest in these enzymes, and their diverse functions in biology

Runx-CBFbeta complexes control expression of the transcription factor Foxp3 in regulatory T cells.

The transcription factor Foxp3 has an indispensable role in establishing stable transcriptional and functional programs of regulatory T cells (T(reg) cells). Loss of Foxp3 expression in mature T(reg) cells results in a failure of suppressor function, yet the molecular mechanisms that ensure steady, heritable Foxp3 expression in the T(reg) cell lineage remain unknown. Using T(reg) cell-specific gene targeting, we found that complexes of the transcription factors Runx and CBFbeta were required for maintenance of Foxp3 mRNA and protein expression in T(reg) cells. Consequently, mice lacking CBFbetab exclusively in the T(reg) cell lineage had a moderate lymphoproliferative syndrome. Thus, Runx-CBFbeta complexes maintain stable high expression of Foxp3 and serve as an essential determinant of T(reg) cell lineage stability

A Role for the Mitochondrial Protein Mrpl44 in Maintaining OXPHOS Capacity

We identified Mrpl44 in a search for mammalian proteins that contain RNase III domains. This protein was previously found in association with the mitochondrial ribosome of bovine liver extracts. However, the precise Mrpl44 localization had been unclear. Here, we show by immunofluorescence microscopy and subcellular fractionation that Mrpl44 is localized to the matrix of the mitochondria. We found that it can form multimers, and confirm that it is part of the large subunit of the mitochondrial ribosome. By manipulating its expression, we show that Mrpl44 may be important for regulating the expression of mtDNA-encoded genes. This was at the level of RNA expression and protein translation. This ultimately impacted ATP synthesis capability and respiratory capacity of cells. These findings indicate that Mrpl44 plays an important role in the regulation of the mitochondrial OXPHOS capacity

Suppressor of cytokine signaling-1 is a critical regulator of interleukin-7-dependent CD8(+) T cell differentiation

C1 - Journal Articles RefereedTo determine the tissue-specific functions of SOCS-1, mice were generated in which the SOCS-1 gene could be deleted in individual tissues. A reporter gene of SOCS-1 promoter activity was also inserted. Using the reporter, high SOCS-1 expression was found at the CD4(+)CD8(+) stage in thymocyte development. To investigate the function of this expression, the SOCS-1 gene was specifically deleted throughout the thymocyte/T/NKT cell compartment. Unlike SOCS-1(-/-) mice, these mice did not develop lethal multiorgan inflammation but developed multiple lymphoid abnormalities, including enhanced differentiation of thymocytes toward CD8(+) T cells and very high percentages of peripheral CD8(+) T cells with a memory phenotype (CD44(hi)CD25(lo)CD69(lo)). These phenotypes were found to correlate with hypersensitivity to the gamma-common family of cytokines

Biologically active constituents of the secretome of human W8B2+ cardiac stem cells

The benefits of adult stem cells for repair of the heart have been attributed to the repertoire of salutary paracrine activities they appear to exert. We previously isolated human W8B2+ cardiac stem cells (CSCs) and found they powerfully influence cardiomyocytes and endothelial cells to collectively promote cardiac repair and regeneration. Here, the complexity of the W8B2+ CSC secretomes was characterised and examined in more detail. Using ion exchange chromatography to separate soluble proteins based on their net surface charge, the secreted factors responsible for the pro-survival activity of W8B2+ CSCs were found within the low and medium cation fractions. In addition to the soluble proteins, extracellular vesicles generated from W8B2+ CSCs not only exhibited pro-survival and pro-angiogenic activities, but also promoted proliferation of neonatal cardiomyocytes. These extracellular vesicles contain a cargo of proteins, mRNA and primary microRNA precursors that are enriched in exosomes and are capable of modulating collectively many of the cellular pathways involved in protein metabolism, cell growth, as well as cellular responses to stress and organisation of the extracellular matrix. Thus the W8B2+ CSC secretome contains a multitude of bioactive paracrine factors we have now characterised, that might well be harnessed for therapeutic application for cardiac repair and regeneration. © 2018 The Author(s)

DICER1 deficit induces Alu RNA toxicity in age-related macular degeneration.

Geographic atrophy (GA), an untreatable advanced form of age-related macular degeneration, results from retinal pigmented epithelium (RPE) cell degeneration. Here we show that the microRNA (miRNA)-processing enzyme DICER1 is reduced in the RPE of humans with GA, and that conditional ablation of Dicer1, but not seven other miRNA-processing enzymes, induces RPE degeneration in mice. DICER1 knockdown induces accumulation of Alu RNA in human RPE cells and Alu-like B1 and B2 RNAs in mouse RPE. Alu RNA is increased in the RPE of humans with GA, and this pathogenic RNA induces human RPE cytotoxicity and RPE degeneration in mice. Antisense oligonucleotides targeting Alu/B1/B2 RNAs prevent DICER1 depletion-induced RPE degeneration despite global miRNA downregulation. DICER1 degrades Alu RNA, and this digested Alu RNA cannot induce RPE degeneration in mice. These findings reveal a miRNA-independent cell survival function for DICER1 involving retrotransposon transcript degradation, show that Alu RNA can directly cause human pathology, and identify new targets for a major cause of blindness