A Complex Relationship between Immunity and Metabolism in Drosophila Diet-Induced Insulin Resistance.

Both systemic insulin resistance and tissue-specific insulin resistance have been described in Drosophila and are accompanied by many indicators of metabolic disease. The downstream mediators of insulin-resistant pathophysiology remain unclear. We analyzed insulin signaling in the fat body studying loss and gain of function. When expression of the sole Drosophila insulin receptor (InR) was reduced in larval fat bodies, animals exhibited developmental delay and reduced size in a diet-dependent manner. Fat body InR knockdown also led to reduced survival on high-sugar diets. To look downstream of InR at potential mediators of insulin resistance, transcriptome sequencing (RNA-seq) studies in insulin-resistant fat bodies revealed differential expression of genes, including those involved in innate immunity. Obesity-associated insulin resistance led to increased susceptibility of flies to infection, as in humans. Reduced innate immunity was dependent on fat body InR expression. The peptidoglycan recognition proteins (PGRPs) PGRP-SB2 and PGRP-SC2 were selected for further study based on differential expression studies. Downregulating PGRP-SB2 selectively in the fat body protected animals from the deleterious effects of overnutrition, whereas downregulating PGRP-SC2 produced InR-like phenotypes. These studies extend earlier work linking the immune and insulin signaling pathways and identify new targets of insulin signaling that could serve as potential drug targets to treat type 2 diabetes.

Immune adaptation to chronic intense exercise training: new microarray evidence.

BACKGROUND: Endurance exercise training, especially the high-intensity training, exhibits a strong influence on the immune system. However, the mechanisms underpinning the immune-regulatory effect of exercise remain unclear. Consequently, we chose to investigate the alterations in the transcriptional profile of blood leukocytes in young endurance athletes as compared with healthy sedentary controls, using Affymetrix human gene 1.1 ST array. RESULTS: Group differences in the transcriptome were analyzed using Intensity-based Hierarchical Bayes method followed by a Logistic Regression-based gene set enrichment method. We identified 72 significant transcripts differentially expressed in the leukocyte transcriptome of young endurance athletes as compared with non-athlete controls with a false discovery rate (FDR) < 0.05, comprising mainly the genes encoding ribosomal proteins and the genes involved in mitochondrial oxidative phosphorylation. Gene set enrichment analysis identified three major gene set clusters: two were up-regulated in athletes including gene translation and ribosomal protein production, and mitochondria oxidative phosphorylation and biogenesis; one gene set cluster identified as transcriptionally downregulated in athletes was related to inflammation and immune activity. CONCLUSION: Our data indicates that in young healthy individuals, intense endurance exercise training (exemplifed by athletic training) can chronically induce transcriptional changes in the peripheral blood leukocytes, upregulating genes related to protein production and mitochondrial energetics, and downregulating genes involved in inflammatory response. The findings of the study also provide support for the notion that peripheral blood can be used as a surrogate tissue to study the systemic effect of exercise training.

Longevity Genes Revealed by Integrative Analysis of Isoform-Specific daf-16/FoxO Mutants of Caenorhabditis elegans.

FoxO transcription factors promote longevity across taxa. How they do so is poorly understood. In the nematode Caenorhabditis elegans, the A- and F-isoforms of the FoxO transcription factor DAF-16 extend life span in the context of reduced DAF-2 insulin-like growth factor receptor (IGFR) signaling. To elucidate the mechanistic basis for DAF-16/FoxO-dependent life span extension, we performed an integrative analysis of isoform-specific daf-16/FoxO mutants. In contrast to previous studies suggesting that DAF-16F plays a more prominent role in life span control than DAF-16A, isoform-specific daf-16/FoxO mutant phenotypes and whole transcriptome profiling revealed a predominant role for DAF-16A over DAF-16F in life span control, stress resistance, and target gene regulation. Integration of these datasets enabled the prioritization of a subset of 92 DAF-16/FoxO target genes for functional interrogation. Among 29 genes tested, two DAF-16A-specific target genes significantly influenced longevity. A loss-of-function mutation in the conserved gene gst-20, which is induced by DAF-16A, reduced life span extension in the context of daf-2/IGFR RNAi without influencing longevity in animals subjected to control RNAi. Therefore, gst-20 promotes DAF-16/FoxO-dependent longevity. Conversely, a loss-of-function mutation in srr-4, a gene encoding a seven-transmembrane-domain receptor family member that is repressed by DAF-16A, extended life span in control animals, indicating that DAF-16/FoxO may extend life span at least in part by reducing srr-4 expression. Our discovery of new longevity genes underscores the efficacy of our integrative strategy while providing a general framework for identifying specific downstream gene regulatory events that contribute substantially to transcription factor functions. As FoxO transcription factors have conserved functions in promoting longevity and may be dysregulated in aging-related diseases, these findings promise to illuminate fundamental principles underlying aging in animals.

Neuronal CRTC-1 governs systemic mitochondrial metabolism and lifespan via a catecholamine signal.

Low energy states delay aging in multiple species, yet mechanisms coordinating energetics and longevity across tissues remain poorly defined. The conserved energy sensor AMP-activated protein kinase (AMPK) and its corresponding phosphatase calcineurin modulate longevity via the CREB regulated transcriptional coactivator (CRTC)-1 in C. elegans. We show that CRTC-1 specifically uncouples AMPK/calcineurin-mediated effects on lifespan from pleiotropic side effects by reprogramming mitochondrial and metabolic function. This pro-longevity metabolic state is regulated cell nonautonomously by CRTC-1 in the nervous system. Neuronal CRTC-1/CREB regulates peripheral metabolism antagonistically with the functional PPARα ortholog, NHR-49, drives mitochondrial fragmentation in distal tissues, and suppresses the effects of AMPK on systemic mitochondrial metabolism and longevity via a cell-nonautonomous catecholamine signal. These results demonstrate that while both local and distal mechanisms combine to modulate aging, distal regulation overrides local contribution. Targeting central perception of energetic state is therefore a potential strategy to promote healthy aging.

HSF-1-mediated cytoskeletal integrity determines thermotolerance and life span.

The conserved heat shock transcription factor-1 (HSF-1) is essential to cellular stress resistance and life-span determination. The canonical function of HSF-1 is to regulate a network of genes encoding molecular chaperones that protect proteins from damage caused by extrinsic environmental stress or intrinsic age-related deterioration. In Caenorhabditis elegans, we engineered a modified HSF-1 strain that increased stress resistance and longevity without enhanced chaperone induction. This health assurance acted through the regulation of the calcium-binding protein PAT-10. Loss of pat-10 caused a collapse of the actin cytoskeleton, stress resistance, and life span. Furthermore, overexpression of pat-10 increased actin filament stability, thermotolerance, and longevity, indicating that in addition to chaperone regulation, HSF-1 has a prominent role in cytoskeletal integrity, ensuring cellular function during stress and aging.

Analysis of DNA methylation reveals a partial reprogramming of the Müller glia genome during retina regeneration.

Upon retinal injury, zebrafish Müller glia (MG) transition from a quiescent supportive cell to a progenitor cell (MGPC). This event is accompanied by the induction of key transcription and pluripotency factors. Because somatic cell reprogramming during induced pluripotent stem cell generation is accompanied by changes in DNA methylation, especially in pluripotency factor gene promoters, we were interested in determining whether DNA methylation changes also underlie MG reprogramming following retinal injury. Consistent with this idea, we found that genes encoding components of the DNA methylation/demethylation machinery were induced in MGPCs and that manipulating MGPC DNA methylation with 5-aza-2'-deoxycytidine altered their properties. A comprehensive analysis of the DNA methylation landscape as MG reprogram to MGPCs revealed that demethylation predominates at early times, whereas levels of de novo methylation increase at later times. We found that these changes in DNA methylation were largely independent of Apobec2 protein expression. A correlation between promoter DNA demethylation and injury-dependent gene induction was noted. In contrast to induced pluripotent stem cell formation, we found that pluripotency factor gene promoters were already hypomethylated in quiescent MG and remained unchanged in MGPCs. Interestingly, these pluripotency factor promoters were also found to be hypomethylated in mouse MG. Our data identify a dynamic DNA methylation landscape as zebrafish MG transition to an MGPC and suggest that DNA methylation changes will complement other regulatory mechanisms to ensure gene expression programs controlling MG reprogramming are appropriately activated during retina regeneration.