Heterogeneity In Metabolic Activity Research Articles

In silico single-cell metabolism analysis unravels a new transition stage of CD8 T cells 4 days post-infection

CD8 T cell proper differentiation during antiviral responses relies on metabolic adaptations. Herein, we investigated global metabolic activity in single CD8 T cells along an in vivo response by estimating metabolic fluxes from single-cell RNA-sequencing data. The approach was validated by the observation of metabolic variations known from experimental studies on global cell populations, while adding temporally detailed information and unravelling yet undescribed sections of CD8 T cell metabolism that are affected by cellular differentiation. Furthermore, inter-cellular variability in gene expression level, highlighted by single cell data, and heterogeneity of metabolic activity 4 days post-infection, revealed a new transition stage accompanied by a metabolic switch in activated cells differentiating into full-blown effectors.

2006 – STEM CELL BASED HETEROGENEITY OF INTERFERON SIGNALING DURING HEMATOPOIETIC DEVELOPMENT

Inflammation has a great impact on an organism. In order to protect the hematopoietic system from exhaustion during pathogenic insult, heterogeneity in metabolic activity, gene expression patterns, and responsiveness to cytokines such as interferons (IFN) have been revealed. Yet, how this diversity in the system is generated and maintained remains poorly understood. Here, we show that intra-cell type heterogeneity in expression of IFN-stimulated genes (ISGs) is already established at the level of the hematopoietic stem cell (HSC). Transplantation experiments using different reporter mouse models indicated stable inheritance of the ISG expression to downstream progeny. Single cell transplantation experiments of wild type (WT) HSCs supported these findings, proposing a stable inheritance of IFN signaling heterogeneity from HSCs to mature blood cells. Next, we investigated the origin of ISG heterogeneity. From a first streak of primitive hematopoiesis early in embryonal development to the expansion of definitive HSCs in the fetal liver, HSCs pass through a number of embryonal sites. Fetal liver HSCs at E13.5 already showed ISG expression heterogeneity, comparable to the adult stem cells. Yet, at earlier time points during development the degree of ISG expression was depending on the time point and organ the cells were isolated from. In both WT and reporter mice the highest degree of ISG expression was found in the placenta. These data suggest an important role for the placenta during establishment of the heterogeneity. Thus, our data suggest that heterogeneity of IFN signaling in the hematopoietic system, stably inherited from stem cells to progeny, is already established early during hematopoietic development. Uncovering the origin and function of the heterogeneity will have far-reaching implications for HSC biology in health, disease, and upon infection.

Adaptation to sustained nitrogen starvation by Escherichia coli requires the eukaryote-like serine/threonine kinase YeaG.

The Escherichia coli eukaryote-like serine/threonine kinase, encoded by yeaG, is expressed in response to diverse stresses, including nitrogen (N) starvation. A role for yeaG in bacterial stress response is unknown. Here we reveal for the first time that wild-type E. coli displays metabolic heterogeneity following sustained periods of N starvation, with the metabolically active population displaying compromised viability. In contrast, such heterogeneity in metabolic activity is not observed in an E. coli ∆yeaG mutant, which continues to exist as a single and metabolically active population and thus displays an overall compromised ability to survive sustained periods of N starvation. The mechanism by which yeaG acts, involves the transcriptional repression of two toxin/antitoxin modules, mqsR/mqsA and dinJ/yafQ. This, consequently, has a positive effect on the expression of rpoS, the master regulator of the general bacterial stress response. Overall, results indicate that yeaG is required to fully execute the rpoS-dependent gene expression program to allow E. coli to adapt to sustained N starvation and unravels a novel facet to the regulatory basis that underpins adaptive response to N stress.

Heterogeneity of metabolic activity in the canine parasternal intercostals during breathing.

In the dog, the inspiratory mechanical advantage of the parasternal intercostals shows a marked spatial heterogeneity, whereas the expiratory mechanical advantage of the triangularis sterni is relatively uniform. The contribution of a particular respiratory muscle to lung volume expansion during breathing, however, depends both on the mechanical advantage of the muscle and on its neural input. To evaluate the distribution of neural input across the canine parasternal intercostals and triangularis sterni, we have examined the distribution of metabolic activity among these muscles in seven spontaneously breathing animals by measuring the uptake of the glucose tracer analog [(18)F]fluorodeoxyglucose (FDG). FDG uptake in any given parasternal intercostal was greatest in the medial bundles and decreased rapidly toward the costochondral junctions. In addition, FDG uptake in the medial parasternal bundles increased from the first to the second interspace, plateaued in the second through fifth interspaces, and then decreased progressively toward the eighth interspace. In contrast, uptake in the triangularis sterni showed no significant rostrocaudal gradient. These results overall strengthen the idea that the spatial distribution of neural input within a particular set of respiratory muscles is closely matched with the spatial distribution of mechanical advantage.

Metabolic activity and proliferation of CHO cells in hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) microcapsules.

To better understand encapsulated cell behaviour, Chinese Hamster Ovary (CHO) fibroblasts were encapsulated in HEMA-MMA microcapsules and short-term (<2 wks) proliferation and changes in metabolic activity were investigated in vitro. CHO cells were observed to undergo rapid proliferation in the first week following encapsulation after which a growth arrest was obtained at approximately 3500 cells/capsule. The cell growth was localized in aggregates in the capsule core, resulting in high local cell density but low cell density in the whole capsule interior (approximately 10(7) cells/mL). The total metabolic activity, as determined by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium) assay, within the microcapsules increased in the first week, with no significant change afterwards. A broad variation in metabolic activity among the individual capsules was obtained. Supplementing the cell suspension with 20% Ficoll 400 during the encapsulation process resulted in significantly higher morphological uniformity among the individual capsules (with reduced capsule wall thickness and eccentricity); however, this did not change the extent of heterogeneity in metabolic activity. We conclude that viability and proliferation ability (at least to a limited extent) of CHO cells are maintained in HEMA-MMA microcapsules. The local cell growth and subsequent growth arrest remain issues to be addressed in order to obtain better utilization of the microcapsule core volume. Alternatively, small diameter (< 400 microns as opposed to the present approximately 750 microns diameter) capsules are necessary.

Local blood flow and glucose uptake within resting and exercising rabbit skeletal muscle

A marked regional heterogeneity in blood flow at the level of large arterioles or small arteries is present within single skeletal muscles both in the dog and in the rabbit. A corresponding regional heterogeneity in metabolic activity could explain this phenomenon. We studied the correlation between regional blood flow and regional uptake of glucose within single muscles. Blood flow and glucose uptake were measured using the microsphere technique and the deoxyglucose method, respectively. Blood flow and glucose uptake were determined in 0.25-g regions from resting and stimulated muscles in anesthetized rabbits. Under resting conditions, no correlation between regional blood flow and regional glucose uptake (P greater than 0.05, 12 muscles) was observed. During stimulation, regional blood flow was positively correlated (0.4 less than r less than 0.6, P less than 0.05, 12 muscles) with regional glucose uptake. The coefficients of variation for regional blood flow and regional glucose uptake averaged approximately 0.35 and 0.23, respectively, both at rest and during stimulation. Specific fiber type distributions could not explain either the regional heterogeneity in blood flow or in glucose uptake. We conclude that regional blood flow within single skeletal muscles is not strongly linked to regional uptake of glucose. Both variables show considerable heterogeneity.

Glucose metabolism in renal tubular function

Heterogeneity of metabolic activity along the nephron points to a very varied relationship between glucose metabolism and ion transport. Glycolysis is linked closely to free-water clearance and possibly to sodium, potassium, and hydrogen ion transport. Glucose oxidation, while not the major source of renal energy, is crucial in sodium, potassium, and phosphate reabsorption. Gluconeogenesis recovers carbon compounds generated during the process of renal ammoniagenesis. Glucose synthesis and active sodium transport appear to compete for renal ATP, although no regulatory function for this competition has been identified. Glucose formed in the proximal tubule may support free-water clearance in adjacent distal tubule, but is not thought to contribute to any medullary function. The complex network of biosynthetic and catabolic pathways of glucose metabolism may have evolved in the kidney to protect the organism against wide variations in glucose demand which would otherwise be unavoidable during the course of rapidly fluctuating renal electrolyte loads.