Distinct signalling properties of insulin receptor substrate (IRS)-1 and IRS-2 in mediating insulin/IGF-1 action

Insulin/IGF-1 action is driven by a complex and highly integrated signalling network. Loss-of-function studies indicate that the major insulin/IGF-1 receptor substrate (IRS) proteins, IRS-1 and IRS-2, mediate different biological functions in vitro and in vivo, suggesting specific signalling properties despite their high degree of homology. To identify mechanisms contributing to the differential signalling properties of IRS-1 and IRS-2 in the mediation of insulin/IGF-1 action, we performed comprehensive mass spectrometry (MS)-based phosphoproteomic profiling of brown preadipocytes from wild type, IRS-1^-/- and IRS-2^-/- mice in the basal and IGF-1-stimulated states. We applied stable isotope labeling by amino acids in cell culture (SILAC) for the accurate quantitation of changes in protein phosphorylation. We found ~10% of the 6262 unique phosphorylation sites detected to be regulated by IGF-1. These regulated sites included previously reported substrates of the insulin/IGF-1 signalling pathway, as well as novel substrates including Nuclear Factor I X and Semaphorin-4B. In silico prediction suggests the protein kinase B (PKB), protein kinase C (PKC), and cyclin-dependent kinase (CDK) as the main mediators of these phosphorylation events. Importantly, we found preferential phosphorylation patterns depending on the presence of either IRS-1 or IRS-2, which was associated with specific sets of kinases involved in signal transduction downstream of these substrates such as PDHK1, MAPK3, and PKD1 for IRS-1, and PIN1 and PKC beta for IRS-2. Overall, by generating a comprehensive phosphoproteomic profile from brown preadipocyte cells in response to IGF-1 stimulation, we reveal both common and distinct insulin/IGF-1 signalling events mediated by specific IRS proteins.

Beneficial effects of dietary restriction in aging brain

Aging is a multifactorial complex process that leads to the deterioration of biological functions wherein its underlying mechanism is not fully elucidated. It affects the organism at the molecular and cellular level that contributes to the deterioration of structural integrity of the organs. The central nervous system is the most vulnerable organ affected by aging and its effect is highly heterogeneous. Aging causes alteration in the structure, metabolism and physiology of the brain leading to impaired cognitive and motor-neural functions. Dietary restriction (DR), a robust mechanism that extends lifespan in various organisms, ameliorates brain aging by reducing oxidative stress, improving mitochondrial function, activating anti-inflammatory responses, promoting neurogenesis and increasing synaptic plasticity. It also protects and prevents age-related structural changes. DR alleviates many age-associated diseases including neurodegeneration and improves cognitive functions. DR inhibits/activates nutrient signaling cascades such as insulin/IGF-1, mTOR, AMPK and sirtuins. Because of its sensitivity to energy status and hormones, AMPK is considered as the global nutrient sensor. This review will present an elucidative potential role of dietary restriction in the prevention of phenotypic features during aging in brain and its diverse mechanisms.

Activated and inactivated immune responses in Caenorhabditis elegans against Photorhabdus luminescens TT01

The Gram-negative bacterium Photorhabdus luminescens which symbiotically associates with the entomopathogenic nematode Heterorhabditis bacteriophora, has a broad insecticidal and nematicidal activity. The virulence of P. luminescens toward the non-mutualistic nematode Caenorhabditis elegans has not been described. We showed that when fed on P. luminescens, the intestinal cells of C. elegans worms become delicate and some crystal-like structure was developed within the intestinal lumen. Next, we examined the requirement of the p38 mitogen-activated protein kinase (MAPK) and insulin/IGF-1 signaling pathway against P. luminescens. Depletion of pmk-1 by RNAi enhances susceptibility to P. luminescens, and numerous downstream targets regulated by the p38 MAPK pathway were induced when fed on P. luminescens. On the other hand, knockdown of daf-16 has no effects on C. elegans lifespan, but knockdown of daf-2 dramatically increased resistance to P. luminescens in a daf-16-dependent manner. We also revealed one of the daf-2 ligands ins-7 was induced and ins-7 deletion mutant survived longer when fed on P. luminescens. These results suggest the p38 MAPK pathway is activated and required for the host defense against P. luminescens. Insulin/IGF-1 signaling pathway is inactivated by P. luminescens through the overexpression of insulin-like gene.

Conserved signaling pathways genetically associated with longevity across the species

Advanced age is an independent risk factor for natural death and common diseases, such as cardiovascular diseases, dementia, and cancers, which are life-threatening and cause disabilities. On the other hand, individual with healthy longevity is a plausible model for successful aging. Thus, search for longevity-associated genes and pathways likely provides a unique approach to understand the genetic mechanisms underlying aging and healthspan, and emerging evidence from model organisms has highlighted the significance of genetic components in longevity. Here we reviewed the uses of model organisms including yeast, ciliate, nematode, arthropod, fish, rodent, and primate as well as human to identify the genetic determinants of longevity and discussed the genetic contributions of conserved longevity pathways, such as adrenergic system, AMPK, insulin/IGF-1, and mTOR signaling pathways.

Dysregulation of sirtuins and key metabolic genes in skeletal muscle of pigs with spontaneous intrauterine growth restriction is associated with alterations of circulating IGF-1

Prenatal and early postnatal life determines future health, and intrauterine growth restriction (IUGR) - associated low birth weight predisposes to metabolic syndrome in adulthood. We hypothesize here that IUGR might induce hormonal and gene expression alterations predisposing to metabolic disease. Using a porcine model of spontaneous IUGR, we determined in utero (71, 112days post-conception) and early-postnatal (2days post-birth) IGF-1, insulin and leptin levels, and in parallel we investigated, in skeletal muscle, the developmental expression patterns of sirtuins and metabolic and signaling genes IRS1, GLUT4, HK2 and GAPDH. IUGR was associated with impaired IGF-1 plasmatic levels. Gene expression of sirtuin 1, 5, 6, 7, GLUT4 and HK2 exhibited significant correlations with gestational age or body weight. SIRT1 and HK2 expression displayed an age- and weight-dependent downregulation in controls, which was lost in IUGR pigs. Conversely, SIRT2 and GLUT4 were upregulated in IUGR pigs. Within the set of genes studied, we found a significant correlation between IGF-1 levels and gene expression in control, but not IUGR samples, indicating that lower IGF-1 may be a limiting factor in IUGR. IUGR-dependent gene alterations were partly linked to epigenetic changes on histone H3 acetylation and methylation. Overall, our data indicate that several sirtuins and metabolic genes display specific gene expression trajectories during fetal and early postnatal life. Gene expression alterations observed in IUGR are correlated to IGF-1 dysregulation. Given the importance of the genes studied in metabolic control, their perinatal alterations might contribute to the predisposition to metabolic disease of adulthood.

Differential effects of lifespan-extending genetic manipulations in an animal model of MJD/SCA3

Aging is a natural biological process, but evidence suggests that some aspects of aging can be delayed and reduce the prevalence of neurodegenerative diseases, for which aging is a key risk factor. In a neuronal Caenorhabditis elegans model of a Polyglutamine disease-Spinocerebellar Ataxia Type 3 (SCA3), or Machado-Joseph disease (MJD)- we assessed the hypothesis that delaying aging is neuroprotective, investigating the effect of genetically manipulating multiple lifespan-determinant mechanisms. Lifespan-increasing mutations causing insulin/IGF-1 signaling downregulation, mitochondrial dysfunction, germline ablation and dietary restriction/innate immune activation had distinct impacts on MJD/SCA3 phenotypes, suggesting that not all genetic strategies of stalling aging are equally neuroprotective and challenging the idea that delaying aging is a guaranteed therapy for these diseases. Lifespan-extension improved the SCA3/MJD motor phenotype only when induced by altered nutrient-sensing pathways such as those mediated by insulin/IGF-1 and eat-2 signaling, but their effects on neuronal aggregation differed. These pathways exhibited differential proteostasis profiles, but both activated the heat shock response suggesting that they operate through partially independent mechanisms to confer neuroprotection. The therapeutic value of the insulin/IGF-1 downregulation was demonstrated through the chronic treatment of the SCA3/MJD model with an insulin/IGF-1 signaling inhibitor, underscoring the relevance of aging manipulations in guiding therapeutic strategies for these diseases.