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

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

Building a laboratory and networks during the COVID-19 pandemic.

The coronavirus disease 2019 (COVID-19) pandemic has created unprecedented obstacles for new investigators to traverse. The pandemic's impact exacerbates inequities for groups historically excluded from science. We provide recommendations to support junior faculty, including women and faculty from groups historically excluded from science, in establishing laboratories during the pandemic and foreseeable future

The Role of Indoleamine 2, 3-Dioxygenase in Immune Suppression and Autoimmunity

Indoleamine 2, 3-dioxygenase (IDO) is the first and rate limiting catabolic enzyme in the degradation pathway of the essential amino acid tryptophan. By cleaving the aromatic indole ring of tryptophan, IDO initiates the production of a variety of tryptophan degradation products called “kynurenines” that are known to exert important immuno-regulatory functions. Because tryptophan must be supplied in the diet, regulation of tryptophan catabolism may exert profound effects by activating or inhibiting metabolism and immune responses. Important for survival, the regulation of IDO biosynthesis and its activity in cells of the immune system can critically alter their responses to immunological insults, such as infection, autoimmunity and cancer. In this review, we assess how IDO-mediated catabolism of tryptophan can modulate the immune system to arrest inflammation, suppress immunity to cancer and inhibit allergy, autoimmunity and the rejection of transplanted tissues. Finally, we examine how vaccines may enhance immune suppression of autoimmunity through the upregulation of IDO biosynthesis in human dendritic cells