Autophagy is essential for maintaining both survival and health of cells. Autophagy is normally suppressed by amino acids and insulin. It is unclear what happens to the autophagy activity in the presence of insulin resistance and hyperinsulinemia. In this study, we examined the autophagy activity in the presence of insulin resistance and hyperinsulinemia and the associated mechanism. Insulin resistance and hyperinsulinemia were induced in mice by a high fat diet, followed by measurements of autophagy markers. Our results show that autophagy was suppressed in the livers of mice with insulin resistance and hyperinsulinemia. Transcript levels of some key autophagy genes were also suppressed in the presence of insulin resistance and hyperinsulinemia. Conversely, autophagy activity was increased in the livers of mice with streptozotocin-induced insulin deficiency. Levels of vps34, atg12, and gabarapl1 transcripts were elevated in the livers of mice with insulin deficiency. To study the mechanism, autophagy was induced by nutrient deprivation or glucagon in cultured hepatocytes in the presence or absence of insulin. Autophagy activity and transcript levels of vps34, atg12, and gabarapl1 genes were reduced by insulin. The effect of insulin was largely prevented by overexpression of the constitutive nuclear form of FoxO1. Importantly, autophagy of mitochondria (mitophagy) in cultured cells was suppressed by insulin in the presence of insulin resistance. Together, our results show that autophagy activity and expression of some key autophagy genes were suppressed in the presence of insulin resistance and hyperinsulinemia. Insulin suppression of autophagy involves FoxO1-mediated transcription of key autophagy genes.Macroautophagy (autophagy) is a catabolic process whereby long lived large molecules and cellular organelles, such as mitochondria and endoplasmic reticulum (ER), 3 are degraded by lysosomes for an alternative energy source during starvation (1, 2). Autophagy is normally activated by glucagon or deprivation of amino acids during starvation (1) but inhibited by amino acids and/or insulin through the mTOR-or/and Akt-dependent pathways after food intake (3, 4). Thus, autophagy activity fluctuates with food intakes and fasts. Importantly, autophagy is also essential for maintaining cellular health by removing misfolded large molecules and aged/dysfunctional cellular organelles, such as mitochondria and ER (1, 5). In other words, decreased autophagy will inevitably slow the removal of misfolded large molecules and aged/dysfunctional cellular organelles. Accumulation of these molecules and dysfunctional cellular organelles may not only contribute to the development of cancers (1) but also contribute to the development of metabolic diseases, such as insulin resistance. For example, the accumulation of dysfunctional mitochondria will most likely cause increased mitochondrion-derived oxidative stress, which is known to contribute to the development of insulin resistance (6 -10).Insulin resistance is either a precursor or...
SummaryPutative high-affinity nitrate (NO 3 -) transporter genes, designated Nrt2;1At and Nrt2;2At, were isolated from Arabidopsis thaliana by RT-PCR using degenerate primers. The genes shared 86% and 89% identity at the amino acid and nucleotide levels, respectively, while their proteins shared 30-73% identities with other eukaryotic highaffinity NO 3 -transporters. Both genes were induced by NO 3 -, but Nrt2;1At gene expression was not apparent in 2-and 5-day-old plants. By 10 days, and thereafter, Nrt2; 1At gene expression in roots was substantially higher than for the Nrt2;2At gene. Root Nrt2;1At expression levels were strongly correlated with inducible high-affinity 13 NO 3 -influx into intact roots under several treatment conditions. The use of inhibitors of N assimilation indicated that downregulation of Nrt2;1At expression was mediated by NH 4 ⍣ , gln and other amino acids.
To investigate the regulation of HvNRT2, genes that encode high-affinity NO(3)(-) transporters in barley (Hordeum vulgare) roots, seedlings were treated with 10 mM NO(3)(-) in the presence or absence of amino acids (aspartate, asparagine, glutamate [Glu], and glutamine [Gln]), NH(4)(+), and/or inhibitors of N assimilation. Although all amino acids decreased high-affinity (13)NO(3)(-) influx and HvNRT2 transcript abundance, there was substantial interconversion of administered amino acids, making it impossible to determine which amino acid(s) were responsible for the observed effects. To clarify the role of individual amino acids, plants were separately treated with tungstate, methionine sulfoximine, or azaserine (inhibitors of nitrate reductase, Gln synthetase, and Glu synthase, respectively). Tungstate increased the HvNRT2 transcript by 20% to 30% and decreased NO(3)(-) influx by 50%, indicating that NO(3)(-) itself does not regulate transcript abundance, but may exert post-transcriptional effects. Experiments with methionine sulfoximine suggested that NH(4)(+) may down-regulate HvNRT2 gene expression and high-affinity NO(3)(-) influx by effects operating at the transcriptional and post-transcriptional levels. Azaserine decreased HvNRT2 transcript levels and NO(3)(-) influx by 97% and 95%, respectively, while decreasing Glu and increasing Gln levels. This suggests that Gln (and not Glu) is responsible for down-regulating HvNRT2 expression, although it does not preclude a contributory effect of other amino acids.
Rationale Endothelial progenitor cells (EPCs) contribute to the regeneration of endothelium. Aging-associated senescence results in reduced number and function of EPCs, potentially contributing to increased cardiac risk, reduced angiogenic capacity, and impaired cardiac repair effectiveness. The mechanisms underlying EPC senescence are unknown. Increasing evidence supports the role of microRNAs in regulating cellular senescence. Objective We aimed to determine whether microRNAs regulated EPC senescence and, if so, what the underlying mechanisms are. Methods and Results To map the microRNA/gene expression signatures of EPC senescence, we performed microRNA profiling and microarray analysis in lineage-negative bone marrow cells from young and aged wild-type and apolipoprotein E–deficient mice. We identified 2 microRNAs, microRNA-10A* (miR-10A*), and miR-21, and their common target gene Hmga2 as critical regulators for EPC senescence. Overexpression of miR-10A* and miR-21 in young EPCs suppressed Hmga2 expression, caused EPC senescence, as evidenced by senescence-associated β–galactosidase upregulation, decreased self-renewal potential, increased p16Ink4a/p19Arf expression, and resulted in impaired EPC angiogenesis in vitro and in vivo, resembling EPCs derived from aged mice. In contrast, suppression of miR-10A* and miR-21 in aged EPCs increased Hmga2 expression, rejuvenated EPCs, resulting in decreased senescence-associated β–galactosidase expression, increased self-renewal potential, decreased p16Ink4a/p19Arf expression, and improved EPC angiogenesis in vitro and in vivo. Importantly, these phenotypic changes were rescued by miRNA-resistant Hmga2 cDNA overexpression. Conclusions miR-10A* and miR-21 regulate EPC senescence via suppressing Hmga2 expression and modulation of microRNAs may represent a potential therapeutic intervention in improving EPC-mediated angiogenesis and vascular repair.
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