Single Cell Analysis of Treatment-Resistant Prostate Cancer: Implications of Cell State Changes for Cell Surface Antigen Targeted Therapies.

Targeting cell surface molecules using radioligand and antibody-based therapies has yielded considerable success across cancers. However, it remains unclear how the expression of putative lineage markers, particularly cell surface molecules, varies in the process of lineage plasticity, wherein tumor cells alter their identity and acquire new oncogenic properties. A notable example of lineage plasticity is the transformation of prostate adenocarcinoma (PRAD) to neuroendocrine prostate cancer (NEPC)--a growing resistance mechanism that results in the loss of responsiveness to androgen blockade and portends dismal patient survival. To understand how lineage markers vary across the evolution of lineage plasticity in prostate cancer, we applied single cell analyses to 21 human prostate tumor biopsies and two genetically engineered mouse models, together with tissue microarray analysis (TMA) on 131 tumor samples. Not only did we observe a higher degree of phenotypic heterogeneity in castrate-resistant PRAD and NEPC than previously anticipated, but also found that the expression of molecules targeted therapeutically, namely PSMA, STEAP1, STEAP2, TROP2, CEACAM5, and DLL3, varied within a subset of gene-regulatory networks (GRNs). We also noted that NEPC and small cell lung cancer (SCLC) subtypes shared a set of GRNs, indicative of conserved biologic pathways that may be exploited therapeutically across tumor types. While this extreme level of transcriptional heterogeneity, particularly in cell surface marker expression, may mitigate the durability of clinical responses to novel antigen-directed therapies, its delineation may yield signatures for patient selection in clinical trials, potentially across distinct cancer types.

Phase 1b study of enzalutamide plus CC-115, a dual mTORC1/2 and DNA-PK inhibitor, in men with metastatic castration-resistant prostate cancer (mCRPC).

BACKGROUND: CC-115, a dual mTORC1/2 and DNA-PK inhibitor, has promising antitumour activity when combined with androgen receptor (AR) inhibition in pre-clinical models. METHODS: Phase 1b multicentre trial evaluating enzalutamide with escalating doses of CC-115 in AR inhibitor-naive mCRPC patients (n = 41). Primary endpoints were safety and RP2D. Secondary endpoints included PSA response, time-to-PSA progression, and radiographic progression. RESULTS: Common adverse effects included rash (31.7% Grades 1-2 (Gr); 31.7% Gr 3), pruritis (43.9% Gr 1-2), diarrhoea (37% Gr 1-2), and hypertension (17% Gr 1-2; 9.8% Gr 3). CC-115 RP2D was 5 mg twice a day. In 40 evaluable patients, 80% achieved ≥50% reduction in PSA (PSA50), and 58% achieved ≥90% reduction in PSA (PSA90) by 12 weeks. Median time-to-PSA progression was 14.7 months and median rPFS was 22.1 months. Stratification by PI3K alterations demonstrated a non-statistically significant trend towards improved PSA50 response (PSA50 of 94% vs. 67%, p = 0.08). Exploratory pre-clinical analysis suggested CC-115 inhibited mTOR pathway strongly, but may be insufficient to inhibit DNA-PK at RP2D. CONCLUSIONS: The combination of enzalutamide and CC-115 was well tolerated. A non-statistically significant trend towards improved PSA response was observed in patients harbouring PI3K pathway alterations, suggesting potential predictive biomarkers of response to a PI3K/AKT/mTOR pathway inhibitor. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02833883.

ETV4 mediates dosage-dependent prostate tumor initiation and cooperates with p53 loss to generate prostate cancer.

The mechanisms underlying ETS-driven prostate cancer initiation and progression remain poorly understood due to a lack of model systems that recapitulate this phenotype. We generated a genetically engineered mouse with prostate-specific expression of the ETS factor, ETV4, at lower and higher protein dosage through mutation of its degron. Lower-level expression of ETV4 caused mild luminal cell expansion without histologic abnormalities, and higher-level expression of stabilized ETV4 caused prostatic intraepithelial neoplasia (mPIN) with 100% penetrance within 1 week. Tumor progression was limited by p53-mediated senescence and Trp53 deletion cooperated with stabilized ETV4. The neoplastic cells expressed differentiation markers such as Nkx3.1 recapitulating luminal gene expression features of untreated human prostate cancer. Single-cell and bulk RNA sequencing showed that stabilized ETV4 induced a previously unidentified luminal-derived expression cluster with signatures of cell cycle, senescence, and epithelial-to-mesenchymal transition. These data suggest that ETS overexpression alone, at sufficient dosage, can initiate prostate neoplasia.

Analysis of BRCA2 Copy Number Loss and Genomic Instability in Circulating Tumor Cells from Patients with Metastatic Castration-resistant Prostate Cancer.

BACKGROUND: BRCA2 alterations predict for a response to poly-ADP-ribose polymerase inhibition in metastatic castration-resistant prostate cancer (mCRPC). However, detection is hindered by insufficient tumor tissue and low sensitivity of cell-free DNA for detecting copy number loss. OBJECTIVE: To evaluate the BRCA2 loss detection using single-cell, shallow whole-genome sequencing (sWGS) of circulating tumor cells (CTCs) in patients with mCRPC. DESIGN, SETTING, AND PARTICIPANTS: We analyzed CTC samples collected concurrently with tumor biopsies intended for clinical sequencing in patients with progressing mCRPC. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Differences in proportions were evaluated using the chi-square test. Correlations between assays were analyzed in linear regression models. Associations between alterations and genomic instability were assessed on the single-cell level using mixed-effect negative binomial models. RESULTS AND LIMITATIONS: We identified 138 patients with concurrent CTC and biopsy samples. CTC sWGS generated copy number profiles in a similar proportion of patients to biopsy samples (83% vs 78%, p = 0.23), but was more effective than bone biopsies (79% vs 50%; p = 0.009). CTC sWGS detected BRCA2 loss in more patients than tissue at the ≥1 (42% vs 16%; p < 0.001) and ≥2 (27% vs 16%; p = 0.028) CTC thresholds. The overall prevalence of BRCA2 loss was not increased in CTCs using sample-level composite z scores (p = 0.4), but was significantly increased compared with a lower-than-expected prevalence in bone samples (21% vs 3%, p = 0.014). Positive/negative predictive values for CTC BRCA2 loss were 89%/96% using the ≥1 CTC threshold and 67%/92% using the composite z score. CTC BRCA2 loss was associated with higher genomic instability in univariate (1.4-fold large-scale transition difference, 95% confidence interval [CI]: 1.2-1.6; p < 0.001) and multivariable analysis (1.4-fold difference, 95% CI: 1.2-1.6; p < 0.001). CONCLUSIONS: Copy number profiles can reliably be generated using CTC sWGS, which detected a majority of tissue-confirmed BRCA2 loss and "CTC-only" losses. BRCA2 losses were supported by increases in genomic instability. PATIENT SUMMARY: Current testing strategies have limitations in their ability to detect BRCA2 loss, a relatively common alteration in prostate cancer that is used to identify patients who may benefit from targeted therapy. In this paper, we evaluated whether we could detect BRCA2 loss in individual tumor cells isolated from patient blood samples and found this method to be suitable for further analysis.

Lineage plasticity in prostate cancer depends on JAK/STAT inflammatory signaling.

Drug resistance in cancer is often linked to changes in tumor cell state or lineage, but the molecular mechanisms driving this plasticity remain unclear. Using murine organoid and genetically engineered mouse models, we investigated the causes of lineage plasticity in prostate cancer and its relationship to antiandrogen resistance. We found that plasticity initiates in an epithelial population defined by mixed luminal-basal phenotype and that it depends on increased Janus kinase (JAK) and fibroblast growth factor receptor (FGFR) activity. Organoid cultures from patients with castration-resistant disease harboring mixed-lineage cells reproduce the dependency observed in mice by up-regulating luminal gene expression upon JAK and FGFR inhibitor treatment. Single-cell analysis confirms the presence of mixed-lineage cells with increased JAK/STAT (signal transducer and activator of transcription) and FGFR signaling in a subset of patients with metastatic disease, with implications for stratifying patients for clinical trials.

Dermatological Adverse Events in Prostate Cancer Patients Treated with the Androgen Receptor Inhibitor Apalutamide.

PURPOSE: Patients with prostate cancer (PCa) treated with apalutamide frequently develop rash. We aim to characterize apalutamide-related dermatological adverse events (dAEs) and management. MATERIALS AND METHODS: We assessed 303 patients with PCa treated with apalutamide. DAE frequency and time to onset were calculated and clinicopathological features and management described. Associations between dAE occurrence and clinical trial participation, as well as abiraterone/prednisone exposure were detected using logistic regression models. RESULTS: Seventy-one (23.4%) patients had all-grade dAE occurring at a median of 77 (IQR: 30-135) days post-exposure. Twenty (6.6%) dAE-related therapy interruptions included: 8 (2.6%) with dose maintained on rechallenge, 7 (2.3%) with dose reduction and 5 (1.7%) with discontinuation. Common dAEs were maculopapular rashes (33.8%) and xerosis (32.4%). Seven (77.8%) of 9 histological analyses of skin biopsies supported a drug reaction. No significant differences in laboratory hematological, hepatic and renal function were detected between dAE and no dAE cohorts. Most treated grade 1/2 dAEs (29, 40.8%) required topical steroids (14, 19.7%); few required oral steroids (3, 4.2%) ± oral antihistamines. Most grade 3 dAEs (8, 11.3%) required oral/topical steroids (5, 7.0%); few required topical steroids (3, 4.2%) ± oral antihistamines. Clinical trial patients (180, 59.4%) were more likely to report dAEs than those in the off-trial setting (OR=5.1 [95% CI 2.55-10.12]; p <0.001). Of clinical trial patients, concomitant abiraterone/prednisone recipients (109 of 180, 60.6%) were more likely to report dAEs (OR=3.1 [95% CI 1.53-6.17]; p=0.002). CONCLUSIONS: Apalutamide-related dAEs are frequent and can be managed with topical ± oral steroids. With expanded approval of apalutamide, dAE identification and management are essential.

The Effect of Corticosteroids on Prostate Cancer Outcome Following Treatment with Enzalutamide: A Multivariate Analysis of the Phase III AFFIRM Trial.

PURPOSE: The clinical impact of concurrent corticosteroid use (CCU) on enzalutamide-treated patients with metastatic castration-resistant prostate cancer (mCRPC) is unknown. We investigated the association of CCU with overall survival (OS), radiographic progression-free survival (rPFS), and time to prostate-specific antigen progression (TTPP) in post-chemotherapy, enzalutamide-treated patients with mCRPC. PATIENTS AND METHODS: Post hoc analysis of AFFIRM (NCT00974311) with patients (n = 1,199) randomized 2:1 to enzalutamide 160 mg/day or placebo. Treatment group, CCU, and known prognostic factors were evaluated for impact on OS, rPFS, and TTPP using a multivariate Cox proportional hazards model. CCU was defined as "baseline" (use started at baseline) or "on-study" (baseline plus use that was started during the trial). RESULTS: Enzalutamide significantly improved OS, rPFS, and TTPP independent of baseline CCU but was associated with inferior clinical outcomes when compared with no baseline CCU, including a shorter OS [10.8 months vs. not reached (NR); HR for use vs. no use, 2.13; 95% confidence interval (CI), 1.79-2.54], rPFS (5.2 months vs. 8.0 months; HR, 1.49; 95% CI, 1.29-1.72], and TTPP (4.6 months vs. 5.7 months; HR, 1.50; 95% CI, 1.25-1.81). These findings held in a multivariate analysis adjusting for baseline prognostic factors wherein baseline CCU was independently associated with decreased OS (HR, 1.71; 95% CI, 1.43-2.04; P < 0.0001) and rPFS (HR, 1.28; 95% CI, 1.11-1.48; P = 0.0007). CONCLUSIONS: Patients with mCRPC benefited from enzalutamide treatment independent of CCU, but CCU was associated with worse baseline prognostic factors and outcomes.

Circulating Tumor Cell Chromosomal Instability and Neuroendocrine Phenotype by Immunomorphology and Poor Outcomes in Men with mCRPC Treated with Abiraterone or Enzalutamide.

PURPOSE: While the detection of AR-V7 in circulating tumor cells (CTC) is associated with resistance to abiraterone or enzalutamide in men with metastatic castration-resistant prostate cancer (mCRPC), it only accounts for a minority of this resistance. Neuroendocrine (NE) differentiation or chromosomal instability (CIN) may be additional mechanisms that mediate resistance. EXPERIMENTAL DESIGN: PROPHECY was a multicenter prospective study of men with high-risk mCRPC starting abiraterone or enzalutamide. A secondary objective was to assess Epic CTC CIN and NE phenotypes before abiraterone or enzalutamide and at progression. The proportional hazards (PH) model was used to investigate the prognostic importance of CIN and NE in predicting progression-free survival and overall survival (OS) adjusting for CTC number (CellSearch), AR-V7, prior therapy, and clinical risk score. The PH model was utilized to validate this association of NE with OS in an external dataset of patients treated similarly at Memorial Sloan Kettering Cancer Center (MSKCC; New York, NY). RESULTS: We enrolled 118 men with mCRPC starting on abiraterone or enzalutamide; 107 were evaluable on the Epic platform. Of these, 36.4% and 8.4% were CIN positive and NE positive, respectively. CIN and NE were independently associated with worse OS [HR, 2.2; 95% confidence interval (CI), 1.2-4.0 and HR 3.8; 95% CI, 1.2-12.3, respectively] when treated with abiraterone/enzalutamide. The prognostic significance of NE positivity for worse OS was confirmed in the MSKCC dataset (n = 173; HR, 5.7; 95% CI, 2.6-12.7). CONCLUSIONS: A high CIN and NE CTC phenotype is independently associated with worse survival in men with mCRPC treated with abiraterone/enzalutamide, warranting further prospective controlled predictive studies to inform treatment decisions.

Morphology-Predicted Large-Scale Transition Number in Circulating Tumor Cells Identifies a Chromosomal Instability Biomarker Associated with Poor Outcome in Castration-Resistant Prostate Cancer.

Chromosomal instability (CIN) increases a tumor cell's ability to acquire chromosomal alterations, a mechanism by which tumor cells evolve, adapt, and resist therapeutics. We sought to develop a biomarker of CIN in circulating tumor cells (CTC) that are more likely to reflect the genetic diversity of patient's disease than a single-site biopsy and be assessed rapidly so as to inform treatment management decisions in real time. Large-scale transitions (LST) are genomic alterations defined as chromosomal breakages that generate chromosomal gains or losses of greater than or equal to10 Mb. Here we studied the relationship between the number of LST in an individual CTC determined by direct sequencing and morphologic features of the cells. This relationship was then used to develop a computer vision algorithm that utilizes CTC image features to predict the presence of a high (9 or more) versus low (8 or fewer) LST number in a single cell. As LSTs are a primary functional component of homologous recombination deficient cellular phenotypes, the image-based algorithm was studied prospectively on 10,240 CTCs in 367 blood samples obtained from 294 patients with progressing metastatic castration-resistant prostate cancer taken prior to starting a standard-of-care approved therapy. The resultant computer vision-based biomarker of CIN in CTCs in a pretreatment sample strongly associated with poor overall survival times in patients treated with androgen receptor signaling inhibitors and taxanes. SIGNIFICANCE: A rapidly assessable biomarker of chromosomal instability in CTC is associated with poor outcomes when detected in men with progressing mCRPC.

Author Correction: An NF-κB-microRNA regulatory network tunes macrophage inflammatory responses.

Li-Fan Lu and Alexander Y. Rudensky, who supplied miR-146a floxed mice used in this study, were inadvertently omitted from the author list in the originally published version of this Article. This has now been corrected in both the PDF and HTML versions of the Article. The generation of the floxed mice has been described in detail by Cho and Lee et al.1.

An NF-κB-microRNA regulatory network tunes macrophage inflammatory responses.

The innate inflammatory response must be tightly regulated to ensure effective immune protection. NF-κB is a key mediator of the inflammatory response, and its dysregulation has been associated with immune-related malignancies. Here, we describe a miRNA-based regulatory network that enables precise NF-κB activity in mouse macrophages. Elevated miR-155 expression potentiates NF-κB activity in miR-146a-deficient mice, leading to both an overactive acute inflammatory response and chronic inflammation. Enforced miR-155 expression overrides miR-146a-mediated repression of NF-κB activation, thus emphasizing the dominant function of miR-155 in promoting inflammation. Moreover, miR-155-deficient macrophages exhibit a suboptimal inflammatory response when exposed to low levels of inflammatory stimuli. Importantly, we demonstrate a temporal asymmetry between miR-155 and miR-146a expression during macrophage activation, which creates a combined positive and negative feedback network controlling NF-κB activity. This miRNA-based regulatory network enables a robust yet time-limited inflammatory response essential for functional immunity.MicroRNAs (miR) are important regulators of gene transcription, with miR-155 and miR-146a both implicated in macrophage activation. Here the authors show that NF-κB signalling, miR-155 and miR-146a form a complex network of cross-regulations to control gene transcription in macrophages for modulating inflammatory responses.

Absence of miR-146a in Podocytes Increases Risk of Diabetic Glomerulopathy via Up-regulation of ErbB4 and Notch-1.

Podocyte injury is an early event in diabetic kidney disease and is a hallmark of glomerulopathy. MicroRNA-146a (miR-146a) is highly expressed in many cell types under homeostatic conditions, and plays an important anti-inflammatory role in myeloid cells. However, its role in podocytes is unclear. Here, we show that miR-146a expression levels decrease in the glomeruli of patients with type 2 diabetes (T2D), which correlates with increased albuminuria and glomerular damage. miR-146a levels are also significantly reduced in the glomeruli of albuminuric BTBR ob/ob mice, indicating its significant role in maintaining podocyte health. miR-146a-deficient mice (miR-146a-/-) showed accelerated development of glomerulopathy and albuminuria upon streptozotocin (STZ)-induced hyperglycemia. The miR-146a targets, Notch-1 and ErbB4, were also significantly up-regulated in the glomeruli of diabetic patients and mice, suggesting induction of the downstream TGFß signaling. Treatment with a pan-ErbB kinase inhibitor erlotinib with nanomolar activity against ErbB4 significantly suppressed diabetic glomerular injury and albuminuria in both WT and miR-146a-/- animals. Treatment of podocytes in vitro with TGF-ß1 resulted in increased expression of Notch-1, ErbB4, pErbB4, and pEGFR, the heterodimerization partner of ErbB4, suggesting increased ErbB4/EGFR signaling. TGF-ß1 also increased levels of inflammatory cytokine monocyte chemoattractant protein-1 (MCP-1) and MCP-1 induced protein-1 (MCPIP1), a suppressor of miR-146a, suggesting an autocrine loop. Inhibition of ErbB4/EGFR with erlotinib co-treatment of podocytes suppressed this signaling. Our findings suggest a novel role for miR-146a in protecting against diabetic glomerulopathy and podocyte injury. They also point to ErbB4/EGFR as a novel, druggable target for therapeutic intervention, especially because several pan-ErbB inhibitors are clinically available.

The microRNA-212/132 cluster regulates B cell development by targeting Sox4.

MicroRNAs have emerged as key regulators of B cell fate decisions and immune function. Deregulation of several microRNAs in B cells leads to the development of autoimmune disease and cancer in mice. We demonstrate that the microRNA-212/132 cluster (miR-212/132) is induced in B cells in response to B cell receptor signaling. Enforced expression of miR-132 results in a block in early B cell development at the prepro-B cell to pro-B cell transition and induces apoptosis in primary bone marrow B cells. Importantly, loss of miR-212/132 results in accelerated B cell recovery after antibody-mediated B cell depletion. We find that Sox4 is a target of miR-132 in B cells. Co-expression of SOX4 with miR-132 rescues the defect in B cell development from overexpression of miR-132 alone, thus suggesting that miR-132 may regulate B lymphopoiesis through Sox4. In addition, we show that the expression of miR-132 can inhibit cancer development in cells that are prone to B cell cancers, such as B cells expressing the c-Myc oncogene. We have thus uncovered miR-132 as a novel contributor to B cell development.

Regulation of stress-induced hematopoiesis.

PURPOSE OF REVIEW: Hematopoietic stem cells can self-renew and also give rise to the entire repertoire of hematopoietic cells. During acute infectious and inflammatory stresses, the hematopoietic system can quickly adapt to demand by increasing output of innate immune cells many-fold, often at the expense of lymphopoiesis and erythropoiesis. We review recent advances in understanding the regulation of stress-induced hematopoiesis with a specific focus on the direct effects of inflammatory signaling on hematopoietic stem and progenitor cells (HSPCs). RECENT FINDINGS: Recent studies have highlighted several areas of exciting new developments in the field, including the complex interaction and crosstalk within HSPCs and between bone marrow mesenchymal stem cells and endothelial cells needed to achieve regulated myelopoiesis, identification of increased number of inflammatory and infectious molecules with direct effects on HSPCs, the critical role of inflammatory signaling on embryonic specification of hematopoietic stem cells, and the ability of cytokines to instruct lineage choice at the HSPC level. SUMMARY: These exciting new findings will shape our fundamental understanding of how inflammatory signaling regulates hematopoiesis in health and disease, and facilitate the development of potential interventions to treat hematologic diseases associated with altered inflammatory signaling.

The MicroRNA-132 and MicroRNA-212 Cluster Regulates Hematopoietic Stem Cell Maintenance and Survival with Age by Buffering FOXO3 Expression.

MicroRNAs are critical post-transcriptional regulators of hematopoietic cell-fate decisions, though little remains known about their role in aging hematopoietic stem cells (HSCs). We found that the microRNA-212/132 cluster (Mirc19) is enriched in HSCs and is upregulated during aging. Both overexpression and deletion of microRNAs in this cluster leads to inappropriate hematopoiesis with age. Enforced expression of miR-132 in the bone marrow of mice led to rapid HSC cycling and depletion. A genetic deletion of Mirc19 in mice resulted in HSCs that had altered cycling, function, and survival in response to growth factor starvation. We found that miR-132 exerted its effect on aging HSCs by targeting the transcription factor FOXO3, a known aging associated gene. Our data demonstrate that Mirc19 plays a role in maintaining balanced hematopoietic output by buffering FOXO3 expression. We have thus identified it as a potential target that might play a role in age-related hematopoietic defects.

MicroRNA-146a regulates ICOS-ICOSL signalling to limit accumulation of T follicular helper cells and germinal centres.

Tight control of T follicular helper (Tfh) cells is required for optimal maturation of the germinal centre (GC) response. The molecular mechanisms controlling Tfh-cell differentiation remain incompletely understood. Here we show that microRNA-146a (miR-146a) is highly expressed in Tfh cells and peak miR-146a expression marks the decline of the Tfh response after immunization. Loss of miR-146a causes cell-intrinsic accumulation of Tfh and GC B cells. MiR-146a represses several Tfh-cell-expressed messenger RNAs, and of these, ICOS is the most strongly cell autonomously upregulated target in miR-146a-deficient T cells. In addition, miR-146a deficiency leads to increased ICOSL expression on GC B cells and antigen-presenting cells. Partial blockade of ICOS signalling, either by injections of low dose of ICOSL blocking antibody or by halving the gene dose of Icos in miR-146a-deficient T cells, prevents the Tfh and GC B-cell accumulation. Collectively, miR-146a emerges as a post-transcriptional brake to limit Tfh cells and GC responses.

Transcriptomics identified a critical role for Th2 cell-intrinsic miR-155 in mediating allergy and antihelminth immunity.

Allergic diseases, orchestrated by hyperactive CD4(+) Th2 cells, are some of the most common global chronic diseases. Therapeutic intervention relies upon broad-scale corticosteroids with indiscriminate impact. To identify targets in pathogenic Th2 cells, we took a comprehensive approach to identify the microRNA (miRNA) and mRNA transcriptome of highly purified cytokine-expressing Th1, Th2, Th9, Th17, and Treg cells both generated in vitro and isolated ex vivo from allergy, infection, and autoimmune disease models. We report here that distinct regulatory miRNA networks operate to regulate Th2 cells in house dust mite-allergic or helminth-infected animals and in vitro Th2 cells, which are distinguishable from other T cells. We validated several miRNA (miR) candidates (miR-15a, miR-20b, miR-146a, miR-155, and miR-200c), which targeted a suite of dynamically regulated genes in Th2 cells. Through in-depth studies using miR-155(-/-) or miR-146a(-/-) T cells, we identified that T-cell-intrinsic miR-155 was required for type-2 immunity, in part through regulation of S1pr1, whereas T-cell-intrinsic miR-146a was required to prevent overt Th1/Th17 skewing. These data identify miR-155, but not miR-146a, as a potential therapeutic target to alleviate Th2-medited inflammation and allergy.

Role of microRNA-146a in normal and malignant hematopoietic stem cell function.

Regulation of hematopoiesis is controlled by microRNAs (miRNAs). In this review, we focus on miR-146a, and its role in regulating normal and malignant hematopoiesis. miR-146a is a negative regulator of immune cell activation by repressing two targets, TRAF6 and IRAK1. Genetic deletion of miR-146a confirmed a role of miR-146a during innate immune signaling as well as for hematopoietic stem cell function. miR-146a is also implicated in the pathogenesis of human myelodysplastic syndromes (MDSs) as it is located within a commonly deleted region on chromosome 5, and miR-146a-deficient mice exhibit features of an MDS-like disease. With new insight into miR-146a through genetic and expression analyses, we highlight and discuss the recent advances in the understanding of miR-146a in physiological hematopoiesis during steady-state and inflammation, as well as in MDS.

MicroRNA-146a provides feedback regulation of lyme arthritis but not carditis during infection with Borrelia burgdorferi.

MicroRNAs have been shown to be important regulators of inflammatory and immune responses and are implicated in several immune disorders including systemic lupus erythematosus and rheumatoid arthritis, but their role in Lyme borreliosis remains unknown. We performed a microarray screen for expression of miRNAs in joint tissue from three mouse strains infected with Borrelia burgdorferi. This screen identified upregulation of miR-146a, a key negative regulator of NF-κB signaling, in all three strains, suggesting it plays an important role in the in vivo response to B. burgdorferi. Infection of B6 miR-146a-/- mice with B. burgdorferi revealed a critical nonredundant role of miR-146a in modulating Lyme arthritis without compromising host immune response or heart inflammation. The impact of miR-146a was specifically localized to the joint, and did not impact lesion development or inflammation in the heart. Furthermore, B6 miR-146a-/- mice had elevated levels of NF-κB-regulated products in joint tissue and serum late in infection. Flow cytometry analysis of various lineages isolated from infected joint tissue of mice showed that myeloid cell infiltration was significantly greater in B6 miR-146a-/- mice, compared to B6, during B. burgdorferi infection. Using bone marrow-derived macrophages, we found that TRAF6, a known target of miR-146a involved in NF-κB activation, was dysregulated in resting and B. burgdorferi-stimulated B6 miR-146a-/- macrophages, and corresponded to elevated IL-1ß, IL-6 and CXCL1 production. This dysregulated protein production was also observed in macrophages treated with IL-10 prior to B. burgdorferi stimulation. Peritoneal macrophages from B6 miR-146a-/- mice also showed enhanced phagocytosis of B. burgdorferi. Together, these data show that miR-146a-mediated regulation of TRAF6 and NF-κB, and downstream targets such as IL-1ß, IL-6 and CXCL1, are critical for modulation of Lyme arthritis during chronic infection with B. burgdorferi.

Conversion of danger signals into cytokine signals by hematopoietic stem and progenitor cells for regulation of stress-induced hematopoiesis.

During an infection, the body increases the output of mature immune cells in order to fight off the pathogen. Despite convincing evidence that hematopoietic stem and progenitor cells (HSPCs) can sense pathogens directly, how this contributes to hematopoietic cell output remains unknown. Here, we have combined mouse models with a single-cell proteomics platform to show that, in response to Toll-like receptor stimulation, short-term HSCs and multipotent progenitor cells produce copious amounts of diverse cytokines through nuclear factor κB (NF-κB) signaling. Interestingly, the cytokine production ability of HSPCs trumps mature immune cells in both magnitude and breadth. Among cytokines produced by HSPCs, IL-6 is a particularly important regulator of myeloid differentiation and HSPC proliferation in a paracrine manner and in mediating rapid myeloid cell recovery during neutropenia. This study has uncovered an important property of HSPCs that enables them to convert danger signals into versatile cytokine signals for the regulation of stress hematopoiesis.