Cloud-based highly parallel execution of t-SNE and SPADE with metaclustering for analysis and visualization of large single-cell datasets

The use of machine learning techniques, in particular unsupervised clustering and dimensionality reduction algorithms, is quickly becoming a standard workflow for identifying and visualizing biological populations from within high-dimensional data. These methods allow researchers to approach data analysis without the bias and subjectivity that has traditionally been standard in the field. Algorithms have context-dependent strengths and weaknesses. Across algorithms, an inability to scale computation to large datasets is a common theme. Most algorithms are designed and distributed to run on individual computers where memory and CPU are quickly exhausted by large datasets. Even when high-performance compute resources are available, algorithms often don't scale to large datasets as a fundamental property of their design. If they do, it might result in an untenable increase in runtime or diminished quality of results. t-SNE and SPADE are two well-published algorithms that suffer problems as discussed above after datasets exceed a number of observations on the order of 1 million. This study introduces an alternative approach to the use of SPADE and t- SNE whereby a dataset is divided and distributed across numerous compute nodes in the cloud to process independently in parallel. The results of each computation are then combined in a metaclustering step for final visualization and analysis. The improvement in execution speed as a function of degree of parallelization is established. The method is validated against a non-parallel analysis of the same dataset to establish concordance of identified populations. The workflow is executed on Cytobank for portability to other researchers

Epithelial cell–derived secreted and transmembrane 1a signals to activated neutrophils during pneumococcal pneumonia

Airway epithelial cell responses are critical to the outcome of lung infection. In this study, we aimed to identify unique contributions of epithelial cells during lung infection. To differentiate genes induced selectively in epithelial cells during pneumonia, we compared genome-wide expression profiles from three sorted cell populations: epithelial cells from uninfected mouse lungs, epithelial cells from mouse lungs with pneumococcal pneumonia, and nonepithelial cells from those same infected lungs. Of 1,166 transcripts that were more abundant in epithelial cells from infected lungs compared with nonepithelial cells from the same lungs or from epithelial cells of uninfected lungs, 32 genes were identified as highly expressed secreted products. Especially strong signals included two related secreted and transmembrane (Sectm) 1 genes, Sectm1a and Sectm1b. Refinement of sorting strategies suggested that both Sectm1 products were induced predominantly in conducting airway epithelial cells. Sectm1 was induced during the early stages of pneumococcal pneumonia, and mutation of NF-kB RelA in epithelial cells did not diminish its expression. Instead, type I IFN signaling was necessary and sufficient for Sectm1 induction in lung epithelial cells, mediated by signal transducer and activator of transcription 1. For target cells, Sectm1a bound to myeloid cells preferentially, in particular Ly6GbrightCD11bbright neutrophils in the infected lung. In contrast, Sectm1a did not bind to neutrophils from uninfected lungs. Sectm1a increased expression of the neutrophil-attracting chemokine CXCL2 by neutrophils from the infected lung. We propose that Sectm1a is an epithelial product that sustains a positive feedback loop amplifying neutrophilic inflammation during pneumococcal pneumonia

14-color flow cytometry to determine the contribution of mitochondrial mass to differences in glycolytic capacity in human immune cell subsets

Mitochondrial metabolism controls immune cell function, but comprehensive tools to assess human primary immune cell metabolic capacity remain rudimentary. We previously demonstrated that CD19+ B cells rely more heavily on anaerobic glycolysis (i.e. are more glycolytic) than CD4+ T cells. Furthermore, both PBMCs and CD4+ T cells from subjects with type 2 diabetes (T2D) are more glycolytic than their counterparts from BMI-matched non-T2D controls. The contribution of mitochondrial mass, an indicator of non-glycolytic metabolism, to the various metabolic phenotypes is untested. To assess the contribution of immune cell subset identity and mitochondrial mass to the enhanced glycolytic capacity of resting B cells and PBMCs from T2D subjects, we designed a 13-color panel based on standard immune cell subset markers and chemokine receptors, and included MitoTracker Green FM (MTG), which quantitatively indicates mitochondrial mass. We used this novel panel to phenotype 63 total samples from BMI-matched subjects in three groups: non-T2D, pre-T2D, and fulminant T2D, as defined by American Diabetes Association guidelines. The panel was built in several iterations to accommodate spillover of MTG fluorescence into neighboring channels and includes, besides MTG and live-dead discriminator, the following surface markers: CD4, CD8, CD19, CD45RA, CD25, CD127, CD14, CCR4, CCR5, CCR6, CXCR3, and CD161. The PBMC samples were run on a 4-laser BD FACSARIA II SORP with pre-established panel-specific PMT voltages tracked using 6-peak Ultrarainbow beads. To normalize MTG fluorescence intensity and thus minimize batch effects, each of 5 total batches included a reference donor PBMC sample that was frozen in multiple aliquots from one blood draw. Using this approach, we quantified the percentages of immune cell populations (CD19+ B cells, CD8+ naïve and memory/effector T cells, and CD4+ cells including Tregs and populations enriched in Th1, Th2 and Th17) along with the relative mitochondrial mass in each subset. We found that CD19+ B cells in PBMCs from both ND and T2D subjects had significantly less mitochondrial mass than CD4+ cells, supporting the demonstration that B cells are more glycolytic than CD4+ T cells. Of all the CD4+ T cell subsets, Th17 cells consistently had the lowest mitochondrial mass, consistent with the interpretation that Th17s are more dependent on glycolysis than previously appreciated. Our results validate the utility of our 13-color panel to simultaneously quantify relative mitochondrial mass in numerous immune cell subsets and thereby provide a new tool to explore metabolism in human primary cells

Multivariate Computational Analysis of Gamma Delta T Cell Inhibitory Receptor Signatures Reveals the Divergence of Healthy and ART-Suppressed HIV+ Aging

Even with effective viral control, HIV-infected individuals are at a higher risk for morbidities associated with older age than the general population, and these serious non-AIDS events (SNAEs) track with plasma inflammatory and coagulation markers. The cell subsets driving inflammation in aviremic HIV infection are not yet elucidated. Also, whether ART-suppressed HIV infection causes premature induction of the inflammatory events found in uninfected elderly or if a novel inflammatory network ensues when HIV and older age co-exist is unclear. In this study we measured combinational expression of five inhibitory receptors (IRs) on seven immune cell subsets and 16 plasma markers from peripheral blood mononuclear cells (PBMC) and plasma samples, respectively, from a HIV and Aging cohort comprised of ART-suppressed HIV-infected and uninfected controls stratified by age (≤35 or ≥50 years old). For data analysis, multiple multivariate computational algorithms [cluster identification, characterization, and regression (CITRUS), partial least squares regression (PLSR), and partial least squares-discriminant analysis (PLS-DA)] were used to determine if immune parameter disparities can distinguish the subject groups and to investigate if there is a cross-impact of aviremic HIV and age on immune signatures. IR expression on gamma delta (γδ) T cells exclusively separated HIV+ subjects from controls in CITRUS analyses and secretion of inflammatory cytokines and cytotoxic mediators from γδ T cells tracked with TIGIT expression among HIV+ subjects. Also, plasma markers predicted the percentages of TIGIT+ γδ T cells in subjects with and without HIV in PSLR models, and a PLS-DA model of γδ T cell IR signatures and plasma markers significantly stratified all four of the subject groups (uninfected younger, uninfected older, HIV+ younger, and HIV+ older). These data implicate γδ T cells as an inflammatory driver in ART-suppressed HIV infection and provide evidence of distinct “inflamm-aging” processes with and without ART-suppressed HIV infection

Role of Fas and Treg Cells in Fracture Healing as Characterized in the Fas-Deficient (lpr) Mouse Model of Lupus

Previous studies showed that loss of tumor necrosis factor α (TNFα) signaling delayed fracture healing by delaying chondrocyte apoptosis and cartilage resorption. Mechanistic studies showed that TNFα induced Fas expression within chondrocytes; however, the degree to which chondrocyte apoptosis is mediated by TNFα alone or dependent on the induction of Fas is unclear. This question was addressed by assessing fracture healing in Fas-deficient B6.MRL/Faslpr/J mice. Loss of Fas delayed cartilage resorption but also lowered bone fraction in the calluses. The reduced bone fraction was related to elevated rates of coupled bone turnover in the B6.MRL/Faslpr/J calluses, as evidenced by higher osteoclast numbers and increased osteogenesis. Analysis of the apoptotic marker caspase 3 showed fewer positive chondrocytes and osteoclasts in calluses of B6.MRL/Faslpr/J mice. To determine if an active autoimmune state contributed to increased bone turnover, the levels of activated T cells and Treg cells were assessed. B6.MRL/Faslpr/J mice had elevated Treg cells in both spleens and bones of B6.MRL/Faslpr/J but decreased percentage of activated T cells in bone tissues. Fracture led to ∼30% to 60% systemic increase in Treg cells in both wild-type and B6.MRL/Faslpr/J bone tissues during the period of cartilage formation and resorption but either decreased (wild type) or left unchanged (B6.MRL/Faslpr/J) the numbers of activated T cells in bone. These results show that an active autoimmune state is inhibited during the period of cartilage resorption and suggest that iTreg cells play a functional role in this process. These data show that loss of Fas activity specifically in chondrocytes prolonged the life span of chondrocytes and that Fas synergized with TNFα signaling to mediate chondrocyte apoptosis. Conversely, loss of Fas systemically led to increased osteoclast numbers during later periods of fracture healing and increased osteogenesis. These findings suggest that retention of viable chondrocytes locally inhibits osteoclast activity or matrix proteolysis during cartilage resorption

Fatty Acid Metabolites Combine with Reduced β Oxidation to Activate Th17 Inflammation in Human Type 2 Diabetes

Mechanisms that regulate metabolites and downstream energy generation are key determinants of T cell cytokine production, but the processes underlying the Th17 profile that predicts the metabolic status of people with obesity are untested. Th17 function requires fatty acid uptake, and our new data show that blockade of CPT1A inhibits Th17-associated cytokine production by cells from people with type 2 diabetes (T2D). A low CACT:CPT1A ratio in immune cells from T2D subjects indicates altered mitochondrial function and coincides with the preference of these cells to generate ATP through glycolysis rather than fatty acid oxidation. However, glycolysis was not critical for Th17 cytokines. Instead, β oxidation blockade or CACT knockdown in T cells from lean subjects to mimic characteristics of T2D causes cells to utilize 16C-fatty acylcarnitine to support Th17 cytokines. These data show long-chain acylcarnitine combines with compromised β oxidation to promote disease-predictive inflammation in human T2D. Although glycolysis generally fuels inflammation, Nicholas, Proctor, and Agrawal et al. report that PBMCs from subjects with type 2 diabetes use a different mechanism to support chronic inflammation largely independent of fuel utilization. Loss- and gain-of-function experiments in cells from healthy subjects show mitochondrial alterations combine with increases in fatty acid metabolites to drive chronic T2D-like inflammation

Metformin Enhances Autophagy and Normalizes Mitochondrial Function to Alleviate Aging-Associated Inflammation

Age is a non-modifiable risk factor for the inflammation that underlies age-associated diseases; thus, anti-inflammaging drugs hold promise for increasing health span. Cytokine profiling and bioinformatic analyses showed that Th17 cytokine production differentiates CD4+ T cells from lean, normoglycemic older and younger subjects, and mimics a diabetes-associated Th17 profile. T cells from older compared to younger subjects also had defects in autophagy and mitochondrial bioenergetics that associate with redox imbalance. Metformin ameliorated the Th17 inflammaging profile by increasing autophagy and improving mitochondrial bioenergetics. By contrast, autophagy-targeting siRNA disrupted redox balance in T cells from young subjects and activated the Th17 profile by activating the Th17 master regulator, STAT3, which in turn bound IL-17A and F promoters. Mitophagy-targeting siRNA failed to activate the Th17 profile. We conclude that metformin improves autophagy and mitochondrial function largely in parallel to ameliorate a newly defined inflammaging profile that echoes inflammation in diabetes

Metformin Enhances Autophagy and Normalizes Mitochondrial Function to Alleviate Aging-Associated Inflammation

Age is a non-modifiable risk factor for the inflammation that underlies age-associated diseases; thus, anti-inflammaging drugs hold promise for increasing health span. Cytokine profiling and bioinformatic analyses showed that Th17 cytokine production differentiates CD4+ T cells from lean, normoglycemic older and younger subjects, and mimics a diabetes-associated Th17 profile. T cells from older compared to younger subjects also had defects in autophagy and mitochondrial bioenergetics that associate with redox imbalance. Metformin ameliorated the Th17 inflammaging profile by increasing autophagy and improving mitochondrial bioenergetics. By contrast, autophagy-targeting siRNA disrupted redox balance in T cells from young subjects and activated the Th17 profile by activating the Th17 master regulator, STAT3, which in turn bound IL-17A and F promoters. Mitophagy-targeting siRNA failed to activate the Th17 profile. We conclude that metformin improves autophagy and mitochondrial function largely in parallel to ameliorate a newly defined inflammaging profile that echoes inflammation in diabetes

Inhibition of Ubc13-mediated ubiquitination by GPS2 regulates multiple stages of B cell development

Non-proteolytic ubiquitin signaling mediated by Lys63 ubiquitin chains plays a critical role in multiple pathways that are key to the development and activation of immune cells. Our previous work indicates that GPS2 (G-protein Pathway Suppressor 2) is a multifunctional protein regulating TNF signaling and lipid metabolism in the adipose tissue through modulation of Lys63 ubiquitination events. However, the full extent of GPS2-mediated regulation of ubiquitination and the underlying molecular mechanisms are unknown. Here, we report that GPS2 is required for restricting the activation of TLR and BCR signaling pathways and the AKT/FOXO1 pathway in immune cells based on direct inhibition of Ubc13 enzymatic activity. Relevance of this regulatory strategy is confirmed in vivo by B cell-targeted deletion of GPS2, resulting in developmental defects at multiple stages of B cell differentiation. Together, these findings reveal that GPS2 genomic and non-genomic functions are critical for the development and cellular homeostasis of B cells

BET Protein Function Is Required for Inflammation: Brd2 Genetic Disruption and BET Inhibitor JQ1 Impair Mouse Macrophage Inflammatory Responses

Histone acetylation regulates activation and repression of multiple inflammatory genes known to play critical roles in chronic inflammatory diseases. However, proteins responsible for translating the histone acetylation code into an orchestrated proinflammatory cytokine response remain poorly characterized. Bromodomain and extraterminal (BET) proteins are "readers" of histone acetylation marks, with demonstrated roles in gene transcription, but the ability of BET proteins to coordinate the response of inflammatory cytokine genes through translation of histone marks is unknown. We hypothesize that members of the BET family of dual bromodomain-containing transcriptional regulators directly control inflammatory genes. We examined the genetic model of brd2 lo mice, a BET protein hypomorph, to show that Brd2 is essential for proinflammatory cytokine production in macrophages. Studies that use small interfering RNA knockdown and a small-molecule inhibitor of BET protein binding, JQ1, independently demonstrate BET proteins are critical for macrophage inflammatory responses. Furthermore, we show that Brd2 and Brd4 physically associate with the promoters of inflammatory cytokine genes in macrophages. This association is absent in the presence of BET inhibition by JQ1. Finally, we demonstrate that JQ1 ablates cytokine production in vitro and blunts the "cytokine storm" in endotoxemic mice by reducing levels of IL-6 and TNF-a while rescuing mice from LPS-induced death. We propose that targeting BET proteins with small-molecule inhibitors will benefit hyperinflammatory conditions associated with high levels of cytokine production. The Journal of Immunology, 2013, 190: 000-000. R egulation of inflammatory gene expression is tightly controlled through chromatin "readers" that specifically bind histone posttranslational modifications and provide a scaffold, which, in addition to sequence-specific transcription factors, is an integral component of the transcriptional activation complex (1). The biological effects of chromatin-dependent, multiprotein complexes include both transcriptional coactivation and corepression of inflammatory genes in differentiated adult cells (2); thus chromatin readers play critical roles in exquisitely tuned inflammatory responses to a variety of immune system stimuli. Proinflammatory stimuli such as bacterial endotoxin (LPS) arouse extensive transcriptional reprogramming through their ability to activate acetylation of ε-amino groups of nucleosomal histone lysines, a general mark of gene activation (3-5). The acetylated lysine residues are recognized by chromatin readers, many of which contain a conserved structure designated the bromodomain. Bromodomains are highly conserved, left-twisted bundles of four a-helices, with a hydrophobic cleft between two conserved loops that connect the helices (6). The motif uses hydrogen bonding, often at asparagine residues, to bind to acetylated histones (7). In humans, there are at least 40 bromodomain proteins (8, 9), which include histone acetyltransferases, helicases, scaffolding proteins, and other cofactors that control gene transcription. These findings raise the possibility that bromodomain proteins regulate acetylated, histone-packaged inflammatory genes through multiple downstream mechanisms to significantly contribute to outcomes from proinflammatory stimuli. The bromodomain and extraterminal domain (BET) family is a distinct group of bromodomain proteins that in mammals includes Brd2, Brd3, and Brd4, all of which are ubiquitously expressed in mammalian tissues (10-13). Brd2 and Brd4 have been extensively studied in the context of cell-cycle control (14-18) and transcription elongation (19-21), but potential roles in inflammatory responses have not been explored well. Establishing links between BET proteins and inflammation has become clinically critical owing in part to recent drug development efforts, which have shown that drugs able to interrupt interactions between Brd4 and thienodiazepines (22) have efficacy in BET protein-related cancers (23, 24). JQ1 was the first drug developed that specifically interacts with the hydrophobic pocket of the BET bromodomain to block interaction between multiple BET proteins (Brd2/3/4) and acetylated histones (9). JQ1 effectively prompted squamous differentiation and reduced tumor volume of Brd4-dependent, human NUT midline carcinoma xenografts in mice (9), and was proved efficient to block growth of various leukemic cell