Defective germinal center B-cell response and reduced arthritic pathology in microRNA-29a-deficient mice

Understanding the Role of miR-29a in the Regulation of RAG1, a Gene Associated with the Development of the Immune System

The process of Ag receptor diversity is initiated by RAGs consisting of RAG1 and RAG2 in developing lymphocytes. Besides its role as a sequence-specific nuclease during V(D)J recombination, RAGs can also act as a structure-specific nuclease leading to genome instability. Thus, regulation of RAG expression is essential to maintaining genome stability. Previously, the role of miR29c in the regulation of RAG1 was identified. In this article, we report the regulation of RAG1 by miR-29a in the lymphocytes of both mice (Mus musculus) and humans (Homo sapiens). The level of RAG1 could be modulated by overexpression of miR-29a and inhibition using anti-miRs. Argonaute2-immunoprecipitation and high-throughput sequencing of RNA isolated by crosslinking immunoprecipitation studies established the association of miR-29a and RAG1 with Argonaute proteins. We observed a negative correlation between miR-29a and RAG1 levels in mouse B and T cells and leukemia patients. Overexpression of pre-miR-29a in the bone marrow cells of mice led to the generation of mature miR-29a transcripts and reduced RAG1 expression, which led to a significant reduction in V(D)J recombination in pro-B cells. Importantly, our studies are consistent with the phenotype reported in miR-29a knockout mice, which showed impaired immunity and survival defects. Finally, we show that although both miR-29c and miR-29a can regulate RAG1 at mRNA and protein levels, miR-29a substantially impacts immunity and survival. Our results reveal that the repression of RAG1 activity by miR-29a in B cells of mice and humans is essential to maintain Ig diversity and prevent hematological malignancies resulting from aberrant RAG1 expression in lymphocytes.

HIF-2α-dependent induction of miR-29a restrains TH1 activity during T cell dependent colitis

Metabolic imbalance leading to inflammatory hypoxia and stabilization of hypoxia-inducible transcription factors (HIFs) is a hallmark of inflammatory bowel diseases. We hypothesize that HIF could be stabilized in CD4+ T cells during intestinal inflammation and alter the functional responses of T cells via regulation of microRNAs. Our assays reveal markedly increased T cell-intrinsic hypoxia and stabilization of HIF protein during experimental colitis. microRNA screen in primary CD4+ T cells points us towards miR-29a and our subsequent studies identify a selective role for HIF-2α in CD4-cell-intrinsic induction of miR-29a during hypoxia. Mice with T cell-intrinsic HIF-2α deletion display elevated T-bet (target of miR-29a) levels and exacerbated intestinal inflammation. Mice with miR-29a deficiency in T cells show enhanced intestinal inflammation. T cell-intrinsic overexpression of HIF-2α or delivery of miR-29a mimetic dampen TH1-driven colitis. In this work, we show a previously unrecognized function for hypoxia-dependent induction of miR-29a in attenuating TH1-mediated inflammation.

MicroRNAs and human viral diseases: A focus on the role of microRNA-29

The viral replication can impress through cellular miRNAs. Indeed, either the antiviral responses or the viral infection changes through cellular miRNAs resulting in affecting many regulatory signaling pathways. One of the microRNA families that is effective in human cancers, diseases, and viral infections is the miR-29 family. Members of miR-29 family are effective in different viral infections as their roles have appeared in regulation of immunity pathways either in innate immunity including interferon and inflammatory pathways or in adaptive immunity including activation of T-cells and antibodies production. Although miR-29a affects viral replication by suppressing antiviral responses, it can inhibit the expression of viral mRNAs via binding to their 3'UTR. In the present work, we discuss the evidence related to miR-29a and viral infection through host immunity regulation. We also review roles of other miR-29 family members by focusing on their role as biomarkers for diagnosing and targets for viral diseases management.

Thyroid dysfunction in Hashimoto's thyroiditis: a pilot study on the putative role of miR-29a and TGFβ1

PURPOSE

Hashimoto's thyroiditis (HT) is one of the most common causes of thyroid dysfunction in iodine sufficient worldwide areas, but its molecular mechanisms are not completely understood. To this regard, this study aimed to assess serum levels of miRNA-29a (miR-29a) and transforming growth factor beta 1 (TGFβ1) in HT patients with different patterns of thyroid function.

METHODS

A total of 29 HT patients, with a median age of 52 years (21-68) were included. Of these, 13 had normal thyroid function (Eu-HT); 8 had non-treated hypothyroidism (Hypo-HT); 8 had hypothyroidism on replacement therapy with LT4 (subst-HT). All patients had serum miR-29a assayed through qRT-PCR and serum TGFβ1 assayed by ELISA.

RESULTS

Serum miR-29a levels were significantly down-regulated in patients with Hypo-HT compared to Eu-HT patients (P < 0.01) and subst-HT patients (P < 0.05). A significant negative correlation was detected between serum miR-29a levels and TSH levels (r = -0.60, P < 0.01). Serum TGFβ1 levels were significantly higher in Hypo-HT than both Eu-HT (P < 0.01) and subst-HT patients (P < 0.05). A negative correlation was observed between serum miR-29a and TGFβ1 (r = -0.75, P < 0.01).

CONCLUSIONS

In conclusion, Hypo-HT patients had lower levels of serum miR-29a and higher levels of TGFβ1 in comparison with Eu-HT patients. Worthy of note, subst-HT patients showed restored serum miR-29a levels compared with Hypo-HT group, associated with lower serum TGFβ1. These novel findings may suggest a possible impact of replacement therapy with levothyroxine on serum miR-29a levels in HT.

The emerging role non-coding RNAs in B cell-related disorders

Long non-coding RNAs and microRNAs have recently attained much attention regarding their role in the development of B cell lineage as well as participation in the lymphomagenesis. These transcripts have a highly cell type specific signature which endows them the potential to be used as biomarkers for clinical situations. Aberrant expression of several non-coding RNAs has been linked with B cell malignancies and immune related disorders such as rheumatoid arthritis, systemic lupus erythematous, asthma and graft-versus-host disease. Moreover, these transcripts can alter response of immune system to infectious conditions. miR-7, miR-16-1, miR-15a, miR-150, miR-146a, miR-155, miR-212 and miR-132 are among microRNAs whose role in the development of B cell-associated disorders has been investigated. Similarly, SNHG14, MALAT1, CRNDE, AL133346.1, NEAT1, SMAD5-AS1, OR3A4 and some other long non-coding RNAs participate in this process. In the current review, we describe the role of non-coding RNAs in B cell malignancies.

MicroRNA regulation of B cell receptor signaling

B lymphocytes play a central role in host immune defense. B cell receptor (BCR) signaling regulates survival, proliferation, and differentiation of B lymphocytes. Signaling through the BCR signalosome is a multi-component cascade that is tightly regulated and is important in the coordination of B cell differentiation and function. At different stages of development, B cells that have BCRs recognizing self are eliminated to prevent autoimmunity. microRNAs (miRNAs) are small single-stranded non-coding RNAs that contribute to post-transcriptional regulation of gene expression and have been shown to orchestrate cell fate decisions through the regulation of lineage-specific transcriptional profiles. Studies have identified miRNAs to be crucial for B cell development in the bone marrow and their subsequent population of the peripheral immune system. In this review, we focus on the role of miRNAs in the regulation of BCR signaling as it pertains to B lymphocyte development and function. In particular, we discuss the most recent studies describing the role of miRNAs in the regulation of both early B cell development and peripheral B cell responses and examine the ways by which miRNAs regulate signal downstream of B cell antigen receptor to prevent aberrant activation and autoimmunity.

IL-23 orchestrating immune cell activation in arthritis

IL-23 is a cytokine member of the IL-12 superfamily. These heterodimeric cytokines offer broad immune regulatory activity with potential effector function in inflammatory arthritis. IL-23 is a pro-inflammatory cytokine secreted by dendritic cells and macrophages. It plays a key role in both innate and adaptive immunity. By promoting and maintaining T cell differentiation into Th17 T cells, IL-23 is a key player in the pathogenesis of rheumatic diseases. Data from pre-clinical IL-23 knockout models show the major importance of IL-23 in development of arthritis. The induction and maintenance of type 17 cells, which secrete IL-17A and other pro-inflammatory cytokines, contributes to local synovial inflammation and skin inflammation in PsA, and perhaps in RA. Commensurate with this, therapeutic strategies targeting IL-23 have proven efficient in PsA in several studies, albeit not yet in RA.

TAM-derived extracellular vesicles containing microRNA-29a-3p explain the deterioration of ovarian cancer

Extracellular vesicles (EVs) secreted from tumor-associated macrophages (TAMs) are known to generate an immune-suppressive environment conducive to the development of ovarian cancer (OC). We tried to elucidate the role of TAM-derived exosomal microRNA (miR)-29a-3p in OC. miR-29a-3p, forkhead box protein O3 (FOXO3), and programmed death ligand-1 (PD-L1) expression was determined and their interactions evaluated. EVs were isolated, followed by determination of the uptake of EVs by OC cells, after which the proliferation and immune escape facilities of the OC cells were determined. OC xenograft models were constructed with EVs in correspondence with in vivo experiments. Overexpressed miR-29a-3p was detected in OC, and miR-29a-3p promoted OC cell proliferation and immune escape. EVs derived from TAMs enhanced the proliferation of OC cells. miR-29a-3p was enriched in TAM-EVs, and TAM-EVs delivered miR-29a-3p into OC cells. Downregulated FOXO3 was identified in OC, whereas miR-29a-3p targeted FOXO3 to suppress glycogen synthase kinase 3β (GSK3β) activity via the serine/threonine protein kinase (AKT)/GSK3β pathway. Inhibition of TAM-derived exosomal miR-29a-3p decreased PD-L1 to inhibit OC progression through the FOXO3-AKT/GSK3β pathway in vitro and in vivo. Taken together, the current studies highlight the FOXO3-AKT/GSK3β pathway and the mechanism by which TAM-derived exosomal miR-29a-3p enhances the expression of PD-L1 to facilitate OC cell proliferation and immune escape.

Dysregulated translational factors and epigenetic regulations orchestrate in B cells contributing to autoimmune diseases

B cells play a crucial role in antigen presentation, antibody production and pro-/anti-inflammatory cytokine secretion in adaptive immunity. Several translational factors including transcription factors and cytokines participate in the regulation of B cell development, with the cooperation of epigenetic regulations. Autoimmune diseases are generally characterized with autoreactive B cells and high-level pathogenic autoantibodies. The success of B cell depletion therapy in mouse model and clinical trials has proven the role of B cells in pathogenesis of autoimmune diseases. The failure of B cell tolerance in immune checkpoints results in accumulated autoreactive naïve B (B_N) cells with aberrant B cell receptor signaling and dysregulated B cell response, contributing to self-antibody-mediated autoimmune reaction. Dysregulation of translational factors and epigenetic alterations in B cells has been demonstrated to correlate with aberrant B cell compartment in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome, multiple sclerosis, diabetes mellitus and pemphigus. This review is intended to summarize the interaction of translational factors and epigenetic regulations that are involved with development and differentiation of B cells, and the mechanism of dysregulation in the pathogenesis of autoimmune diseases.

The Role of miRNA in the Pathophysiology of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) represent a tumor group that is both rare and heterogeneous. Prognosis is largely determined by the tumor grading and the site of the primary tumor and metastases. Despite intensive research efforts, only modest advances in diagnostic and therapeutic approaches have been achieved in recent years. For patients with non-respectable tumor stages, prognosis is poor. In this context, the development of novel diagnostic tools for early detection of NETs and prediction of tumor response to therapy as well as estimation of the overall prognosis would greatly improve the clinical management of NETs. However, identification of novel diagnostic molecules is hampered by an inadequate understanding of the pathophysiology of neuroendocrine malignancies. It has recently been demonstrated that microRNA (miRNA), a family of small RNA molecules with an established role in the pathophysiology of quite different cancer entities, may also play a role as a biomarker. Here, we summarize the available knowledge on the role of miRNAs in the development of NET and highlight their potential use as serum-based biomarkers in the context of this disease. We discuss important challenges currently preventing their use in clinical routine and give an outlook on future directions of miRNA research in NET.

Aberrant microRNA expression in B lymphocytes from patients with primary warm autoimmune haemolytic anaemia

OBJECTIVE

To screen and analyze the micro-Ribonucleic Acid (miRNA) expression profile in B lymphocytes from patients with autoimmune haemolytic anaemia (AIHA) using high-throughput sequencing.

METHODS

Twelve patients with warm autoimmune haemolytic anaemia (wAIHA) and twelve healthy controls (HCs) were enrolled. CD19⁺ B lymphocytes were isolated and purified using magnetic activated cell sorting (MACS). RNA was subsequently extracted from these cells and a small RNA library was created. The miRNA expression profile was analyzed using Beijing Genomics Institute Sequencing 500 (BGISEQ-500), and stem-loop real-time quantitative PCR (stem-loop qRT-PCR) was used to verify the sequencing results. Downstream target genes of the differentially expressed miRNAs were predicted using miRanda and TargetScan online software, and GO functional enrichment and pathway enrichment analyses were performed on these genes.

RESULTS

Compared with HCs, 178 upregulated and 143 downregulated miRNAs were identified in wAIHA patients, and stem-loop qRT-PCR of four randomly selected differentially expressed miRNAs verified the sequencing results. Ninety-five significantly enriched GO terms and eighty-five significantly enriched pathways were identified. Genes targeted by differentially expressed miRNAs were found to be mainly involved in the regulation of signal transduction, metabolic processes, immune reactions, and neoplastic disease development.

CONCLUSION

The expression of miRNAs in B lymphocytes from patients with primary wAIHA was deregulated, and this phenomenon may be involved in the pathogenesis of wAIHA.

microRNA Fine-Tuning of the Germinal Center Response

Germinal centers (GCs) are complex multicellular structures in which antigen-specific B cells undergo the molecular remodeling that enables the generation of high-affinity antibodies and the differentiation programs that lead to the generation of plasma–antibody-secreting cells and memory B cells. These reactions are tightly controlled by a variety of mechanisms, including the post-transcriptional control of gene expression by microRNAs (miRNAs). Through the development of animal models with B cell-specific modified miRNA expression, we have contributed to the understanding of the role of miRNAs in the regulation of GC responses and in B cell neoplasia. Here, we review recent advances in the understanding of the role of miRNAs in the regulation of B cell and T follicular helper physiology during the GC response and in the diseases associated to GC response dysregulation.

MicroRNAs: Tiny Regulators of Gene Expression with Pivotal Roles in Normal B-Cell Development and B-Cell Chronic Lymphocytic Leukemia

Simple Summary

The involvement of miRNAs in physiological cellular processes has been well documented. The development of B cells, which is dictated by a miRNA-transcription factor regulatory network, suggests a typical process partly orchestrated by miRNAs. Besides their contribution in normal hematopoiesis, miRNAs have been severally reported to be implicated in hematological malignancies, a typical example of which is B-cell chronic lymphocytic leukemia (B-CLL). Numerous studies have attempted to highlight the regulatory role of miRNAs in B-CLL or establish some of them as molecular biomarkers or therapeutic targets. Thus, a critical review summarizing the current knowledge concerning the multifaceted role of miRNAs in normal B-cell development and B-CLL progression, prognosis, and therapy, is urgent. Moreover, this review aims to highlight important miRNAs in both normal B-cell development and B-CLL and discuss future perspectives concerning their regulatory potential and establishment in clinical practice.

Abstract

MicroRNAs (miRNAs) represent a class of small non-coding RNAs bearing regulatory potency. The implication of miRNAs in physiological cellular processes has been well documented so far. A typical process orchestrated by miRNAs is the normal B-cell development. A stage-specific expression pattern of miRNAs has been reported in the developmental procedure, as well as interactions with transcription factors that dictate B-cell development. Besides their involvement in normal hematopoiesis, miRNAs are severally implicated in hematological malignancies, a typical paradigm of which is B-cell chronic lymphocytic leukemia (B-CLL). B-CLL is a highly heterogeneous disease characterized by the accumulation of abnormal B cells in blood, bone marrow, lymph nodes, and spleen. Therefore, timely, specific, and sensitive assessment of the malignancy is vital. Several studies have attempted to highlight the remarkable significance of miRNAs as regulators of gene expression, biomarkers for diagnosis, prognosis, progression, and therapy response prediction, as well as molecules with potential therapeutic utility. This review seeks to outline the linkage between miRNA function in normal and malignant hematopoiesis by demonstrating the main benchmarks of the implication of miRNAs in the regulation of normal B-cell development, and to summarize the key findings about their value as regulators, biomarkers, or therapeutic targets in B-CLL.

The role of miR-29 family in disease

MicroRNAs are small noncoding RNAs that can bind to the target sites in the 3’‐untranslated region of messenger RNA to regulate posttranscriptional gene expression. Increasing evidence has identified the miR‐29 family, consisting of miR‐29a, miR‐29b‐1, miR‐29b‐2, and miR‐29c, as key regulators of a number of biological processes. Moreover, their abnormal expression contributes to the etiology of numerous diseases. In the current review, we aimed to summarize the differential expression patterns and functional roles of the miR‐29 family in the etiology of diseases including osteoarthritis, osteoporosis, cardiorenal, and immune disease. Furthermore, we highlight the therapeutic potential of targeting members of miR‐29 family in these diseases. We present miR‐29s as promoters of osteoblast differentiation and apoptosis but suppressors of chondrogenic and osteoclast differentiation, fibrosis, and T cell differentiation, with clear avenues for therapeutic manipulation. Further research will be crucial to identify the precise mechanism of miR‐29 family in these diseases and their full potential in therapeutics.

Decreased expression of miR-29 family associated with autoimmune myasthenia gravis

Background

Myasthenia gravis (MG) is a rare autoimmune disease mainly mediated by autoantibodies against the acetylcholine receptor (AChR) at the neuromuscular junction. The thymus is the effector organ, and its removal alleviates the symptoms of the disease. In the early-onset form of MG, the thymus displays functional and morphological abnormalities such as B cell infiltration leading to follicular hyperplasia, and the production of AChR antibodies. Type-I interferon (IFN-I), especially IFN-β, is the orchestrator of thymic changes observed in MG. As Dicer and miR-29 subtypes play a role in modulating the IFN-I signalization in mouse thymus, we investigated their expression in MG thymus.

Methods

The expression of DICER and miR-29 subtypes were thoroughly investigated by RT-PCR in human control and MG thymuses, and in thymic epithelial cells (TECs). Using miR-29a/b-1-deficient mice, with lower miR-29a/b-1 expression, we investigated their susceptibility to experimental autoimmune MG (EAMG) as compared to wild-type mice.

Results

DICER mRNA and all miR-29 subtypes were down-regulated in the thymus of MG patients and DICER expression was correlated with the lower expression of miR-29a-3p. A decreased expression of miR-29 subtypes was similarly observed in MG TECs; a decrease also induced in TECs upon IFN-β treatment. We demonstrated that miR-29a/b-1-deficient mice were more susceptible to EAMG without higher levels of anti-AChR IgG subtypes. In the thymus, if no B cell infiltration was observed, an increased expression of Ifn-β associated with Baff expression and the differentiation of Th17 cells associated with increased expression of Il-6, Il-17a and Il-21 and decreased Tgf-β1 mRNA were demonstrated in miR-29a/b-1-deficient EAMG mice.

Conclusions

It is not clear if the decreased expression of miR-29 subtypes in human MG is a consequence or a causative factor of thymic inflammation. However, our results from the EAMG mouse model indicated that a reduction in miR-29a/b1 may contribute to the pathophysiological process involved in MG by favoring the increased expression of IFN-β and the emergence of pro-inflammatory Th17 cells.

A20: a master regulator of arthritis

A20, also known as TNF-α-induced protein 3 (TNFAIP3), is an anti-inflammatory protein that plays an important part in both immune responses and cell death. Impaired A20 function is associated with several human inflammatory and autoimmune diseases. Although the role of A20 in mediating inflammation has been frequently discussed, its intrinsic link to arthritis awaits further explanation. Here, we review new findings that further demonstrate the molecular mechanisms through which A20 regulates inflammatory arthritis, and we discuss the regulation of A20 by many factors. We conclude by reviewing the latest A20-associated mouse models that have been applied in related research because they reflect the characteristics of arthritis, the study of which will hopefully cast new light on anti-arthritis treatments.

TNF-α-elicited miR-29b potentiates resistance to apoptosis in peripheral blood monocytes from patients with rheumatoid arthritis

CD14-positive monocytes from patients with rheumatoid arthritis (RA) are more resistant to apoptosis, which promotes their persistence at the inflammatory site and thereby contributes crucially to immunopathology. We sought to elucidate one mechanism underlying this unique pathogenesis: resistance to apoptosis and the potential involvement of miR-29b in this process. CD14-positive peripheral blood monocytes (PBMs) from RA patients were observed to be resistant to spontaneous apoptosis compared to PBMs from healthy volunteers. Intriguingly, expression of miR-29b was significantly upregulated in PBMs from RA patients than those from healthy volunteers, and this upregulation was correlated with RA disease activity. Functionally, forced expression of the exogenous miR-29b in CD14-positive Ctrl PBMs conferred resistance to spontaneous apoptosis and Fas-induced death, thereafter enhancing the production of major proinflammatory cytokines in there cells. Following identification of the potential miR-29b target transcripts using bioinformatic algorithms, we showed that miR-29b could directly bind to the 3'-UTR of the high-mobility group box-containing protein 1 (HBP1) and inhibited its transcription in PBMs. Importantly, stable expression of the exogenous HBP1 in differentiated THP-1 monocytes effectively abolished miR-29b-elicited resistance to Fas-induced apoptosis. Finally, among patients with RA and good clinical responses to immunotherapy, expression levels of miR-29b were significantly compromised in those treated with infliximab (a TNF-α inhibitor) but not in those treated with tocilizumab (a humanized mAb against the IL-6 receptor), pointing to a potential association between miR-29b activation and TNF-α induction. The available data collectively suggest that TNF-α-elicited miR-29b potentiates resistance to apoptosis in PBMs from RA patients via inhibition of HBP1 signaling, and testing patients for miR-29b/HBP1 expression ratios may provide more accurate prognostic information and could influence the recommended course of immunotherapy.

Epigenetic Regulation of Skeletal Tissue Integrity and Osteoporosis Development

Bone turnover is sophisticatedly balanced by a dynamic coupling of bone formation and resorption at various rates. The orchestration of this continuous remodeling of the skeleton further affects other skeletal tissues through organ crosstalk. Chronic excessive bone resorption compromises bone mass and its porous microstructure as well as proper biomechanics. This accelerates the development of osteoporotic disorders, a leading cause of skeletal degeneration-associated disability and premature death. Bone-forming cells play important roles in maintaining bone deposit and osteoclastic resorption. A poor organelle machinery, such as mitochondrial dysfunction, endoplasmic reticulum stress, and defective autophagy, etc., dysregulates growth factor secretion, mineralization matrix production, or osteoclast-regulatory capacity in osteoblastic cells. A plethora of epigenetic pathways regulate bone formation, skeletal integrity, and the development of osteoporosis. MicroRNAs inhibit protein translation by binding the 3'-untranslated region of mRNAs or promote translation through post-transcriptional pathways. DNA methylation and post-translational modification of histones alter the chromatin structure, hindering histone enrichment in promoter regions. MicroRNA-processing enzymes and DNA as well as histone modification enzymes catalyze these modifying reactions. Gain and loss of these epigenetic modifiers in bone-forming cells affect their epigenetic landscapes, influencing bone homeostasis, microarchitectural integrity, and osteoporotic changes. This article conveys productive insights into biological roles of DNA methylation, microRNA, and histone modification and highlights their interactions during skeletal development and bone loss under physiological and pathological conditions.

Micro-RNAs in inflammatory arthritis: From physiopathology to diagnosis, prognosis and therapeutic opportunities

Micro-RNAs are an area of research exponentially expanding over the past years. These small sequences of 20-22 nucleotides have a strong role as post-transcriptional regulators of gene expression. Inflammatory arthritis pathophysiology involves various key players from innate to adaptive immunity, as well as various signalling pathways of inflammation. In this review, we discuss how micro-RNAs are involved in rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis and juvenile inflammatory arthritis, from pre-clinical phases to established diseases. We describe mi-RNAs key roles in fibroblast like synoviocytes migration, proliferation, apoptosis and cytokine production, in macrophages polarization, as well as in B cells and T cell proliferation and differentiation, with a special emphasis on Treg/Th17 imbalance. We finally discuss the application of these findings in pre-clinical models and highlight opportunities and limits of a therapeutic approach using mi-RNAs agonists or antagonists.

Molecular regulation of peripheral B cells and their progeny in immunity

In this review, Boothby et al. summarize some salient advances toward elucidation of the molecular programming of the fate choices and function of B cells in the periphery. They also note unanswered questions that pertain to differences among subsets of B lymphocytes and plasma cells.

Mature B lymphocytes are crucial components of adaptive immunity, a system essential for the evolutionary fitness of mammals. Adaptive lymphocyte function requires an initially naïve cell to proliferate extensively and its progeny to have the capacity to assume a variety of fates. These include either terminal differentiation (the long-lived plasma cell) or metastable transcriptional reprogramming (germinal center and memory B cells). In this review, we focus principally on the regulation of differentiation and functional diversification of the “B2” subset. An overview is combined with an account of more recent advances, including initial work on mechanisms that eliminate DNA methylation and potential links between intracellular metabolites and chromatin editing.

The microRNA-29/PGC1α regulatory axis is critical for metabolic control of cardiac function

Different microRNAs (miRNAs), including miR-29 family, may play a role in the development of heart failure (HF), but the underlying molecular mechanisms in HF pathogenesis remain unclear. We aimed at characterizing mice deficient in miR-29 in order to address the functional relevance of this family of miRNAs in the cardiovascular system and its contribution to heart disease. In this work, we show that mice deficient in miR-29a/b1 develop vascular remodeling and systemic hypertension, as well as HF with preserved ejection fraction (HFpEF) characterized by myocardial fibrosis, diastolic dysfunction, and pulmonary congestion, and die prematurely. We also found evidence that the absence of miR-29 triggers the up-regulation of its target, the master metabolic regulator PGC1α, which in turn generates profound alterations in mitochondrial biogenesis, leading to a pathological accumulation of small mitochondria in mutant animals that contribute to cardiac disease. Notably, we demonstrate that systemic hypertension and HFpEF caused by miR-29 deficiency can be rescued by PGC1α haploinsufficiency, which reduces cardiac mitochondrial accumulation and extends longevity of miR-29–mutant mice. In addition, PGC1α is overexpressed in hearts from patients with HF. Collectively, our findings demonstrate the in vivo role of miR-29 in cardiovascular homeostasis and unveil a novel miR-29/PGC1α regulatory circuitry of functional relevance for cell metabolism under normal and pathological conditions.

To combat diseases, we first need to gain knowledge on how cells function at the molecular level to maintain normal physiology. One great scientific achievement of the last decade was the identification of thousands of small regulatory RNA molecules, called microRNAs. Strikingly, each microRNA has the potential to fine-tune the expression of hundreds of target genes depending on the spatiotemporal context. Therefore, defects in key microRNAs can contribute to the development of diseases. In the present work, we characterize the role for miR-29 in cardiac function in a mouse model. We found that mice deficient for miR-29 develop life-threatening cardiometabolic alterations that subsequently cause heart failure with diastolic dysfunction and systemic hypertension. We also demonstrate that these pathological phenotypes originate in part by the anomalous up-regulation of the transcriptional coactivator PGC1α, which can lead to mitochondrial hyperplasia in the heart. Genetic removal of one copy of PGC1α significantly attenuated the severity of the cardiovascular phenotype observed in miR-29–deficient mice. In addition, we show that PGC1α expression is misregulated in heart failure patients, suggesting that the implementation of miR-29 replacement therapy could potentially be used to treat these fatal pathologies.

miR-29b directly targets activation-induced cytidine deaminase in human B cells and can limit its inappropriate expression in naïve B cells

Class-switch recombination (CSR) is an essential B cell process that alters the isotype of antibody produced by the B cell, tailoring the immune response to the nature of the invading pathogen. CSR requires the activity of the mutagenic enzyme AID (encoded by AICDA) to generate chromosomal lesions within the immunoglobulin genes that initiate the class switching recombination event. These AID-mediated mutations also participate in somatic-hypermutation of the immunoglobulin variable region, driving affinity maturation. As such, AID poses a significant oncogenic threat if it functions outside of the immunoglobulin locus. We found that expression of the microRNA, miR-29b, was repressed in B cells isolated from tonsil tissue, relative to circulating naïve B cells. Further investigation revealed that miR-29b was able to directly initiate the degradation of AID mRNA. Enforced overexpression of miR-29b in human B cells precipitated a reduction in overall AID protein and a corresponding diminution in CSR to IgE. Given miR-29b's ability to potently target AID, a mutagenic molecule that can initiate chromosomal translocations and "off-target" mutations, we propose that miR-29b acts to silence premature AID expression in naïve B cells, thus reducing the likelihood of inappropriate and potentially dangerous deamination activity.

Metazoan MicroRNAs

MicroRNAs (miRNAs) are ∼22 nt RNAs that direct posttranscriptional repression of mRNA targets in diverse eukaryotic lineages. In humans and other mammals, these small RNAs help sculpt the expression of most mRNAs. This article reviews advances in our understanding of the defining features of metazoan miRNAs and their biogenesis, genomics, and evolution. It then reviews how metazoan miRNAs are regulated, how they recognize and cause repression of their targets, and the biological functions of this repression, with a compilation of knockout phenotypes that shows that important biological functions have been identified for most of the broadly conserved miRNAs of mammals.

Epigenetic regulation in B-cell maturation and its dysregulation in autoimmunity

B cells have a critical role in the initiation and acceleration of autoimmune diseases, especially those mediated by autoantibodies. In the peripheral lymphoid system, mature B cells are activated by self or/and foreign antigens and signals from helper T cells for differentiating into either memory B cells or antibody-producing plasma cells. Accumulating evidence has shown that epigenetic regulations modulate somatic hypermutation and class switch DNA recombination during B-cell activation and differentiation. Any abnormalities in these complex regulatory processes may contribute to aberrant antibody production, resulting in autoimmune pathogenesis such as systemic lupus erythematosus. Newly generated knowledge from advanced modern technologies such as next-generation sequencing, single-cell sequencing and DNA methylation sequencing has enabled us to better understand B-cell biology and its role in autoimmune development. Thus this review aims to summarize current research progress in epigenetic modifications contributing to B-cell activation and differentiation, especially under autoimmune conditions such as lupus, rheumatoid arthritis and type 1 diabetes.

Germinal Center B Cells Are Essential for Collagen-Induced Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is considered to be a prototypical autoimmune disorder. Several mechanisms have been proposed for the known pathologic function of B cells in RA, including antigen presentation, cytokine secretion, and humoral immunity. The aim of this study was to address the function of B lymphocytes in experimental arthritis.

METHODS

We mapped the adaptive immune response following collagen-induced arthritis (CIA). We subsequently monitored these responses and disease outcomes in genetically modified mouse strains that lack mature B cell or germinal center (GC) functionality in a B cell-intrinsic manner.

RESULTS

Following primary immunization, the draining lymph nodes broadly reacted against type II collagen (CII) with the formation of GCs and T cell activation. Mice that lacked mature B cell function were fully protected against CIA and had a severely attenuated ability to mount isotype-switched humoral immune responses against CII. Almost identical results were observed in mice that were selectively deficient in GC responses. Importantly, GC-deficient mice were fully susceptible to collagen antibody-induced arthritis.

CONCLUSION

We identified GC formation and anticollagen antibody production as the key pathogenic functions of B cells in CIA. The role of B cells in RA is likely to be more complex. However, targeting the GC reaction could allow for therapeutic interventions that are more refined than general B cell depletion.

MicroRNA-29a Counteracts Synovitis in Knee Osteoarthritis Pathogenesis by Targeting VEGF

Synovitis contributes to the development of osteoarthritis (OA) of the knee. MicroRNAs regulate joint microenvironment homeostasis and deterioration. This study was undertaken to characterize the actions of microRNA-29a (miR-29a) to synovial remodeling in OA joints. Synovial specimens isolated from patients with end-stage OA knees showed abundant fibrotic matrix and vessel histopathology concomitant with weak miR-29a expression. In vitro, miR-29a knockdown caused synovial fibroblasts to exhibit high expressions of collagen III, TGF-β1, MMP9, MMP13, and ADAMTS5, whereas miR-29a overexpression diminished these joint-deleterious factors. In collagenase-mediated OA pathogenesis, miR-29a-overexpressing transgenic mice showed minor responses to hyperplasia, macrophage infiltration, fibrosis, hyperangiogenesis, and VEGF expression in synovial lesions. These effects mitigated articular cartilage loss and gait aberrance of injured joints. Intra-articular administration of miR-29a precursor lessened the collagenase aggravation of excessive synovial remodeling reactions and thereby sustained joint tissue integrity. miR-29a lowered VEGF production and angiogenic activities in synovial fibroblasts through targeting the 3′-UTR of VEGF. Taken together, miR-29a deficiency exacerbated synovitis pathogenesis in the end-stage OA knees. miR-29a signaling fends off excessive synovial angiogenesis and fibrosis, which delays joint destruction. This study sheds new light on the protective effects against synovial deterioration and the therapeutic advantage of miR-29a in OA knees.