Complex roles of myoglianin in regulating adult performance and lifespan

Myoglianin, the Drosophila homolog of the secreted vertebrate proteins Myostatin and GDF-11, is an important regulator of neuronal modelling, and synapse function and morphology. While Myoglianin suppression during development elicits positive effects on the neuromuscular system, genetic manipulations of myoglianin expression levels have a varied effect on the outcome of performance tests in aging flies. Specifically, Myoglianin preserves jumping ability, has no effect on negative geotaxis, and negatively regulates flight performance in aging flies. In addition, Myoglianin exhibits a tissue-specific effect on longevity, with myoglianin upregulation in glial cells increasing the median lifespan. These findings indicate complex role for this TGF-β-like protein in governing neuromuscular signalling and consequent behavioural outputs and lifespan in adult flies

Reduced insulin signaling maintains electrical transmission in a neural circuit in aging flies

Lowered insulin/insulin-like growth factor (IGF) signaling (IIS) can extend healthy lifespan in worms, flies, and mice, but it can also have adverse effects (the “insulin paradox”). Chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber system (GFS), a simple escape response neuronal circuit, by increasing targeting of the gap junctional protein innexin shaking-B to gap junctions (GJs). Endosomal recycling of GJs was also stimulated in cultured human cells when IIS was reduced. Furthermore, increasing the activity of the recycling small guanosine triphosphatases (GTPases) Rab4 or Rab11 was sufficient to maintain GJs upon elevated IIS in cultured human cells and in flies, and to rescue age-related loss of GJs and of GFS function. Lowered IIS thus elevates endosomal recycling of GJs in neurons and other cell types, pointing to a cellular mechanism for therapeutic intervention into aging-related neuronal disorders

Impact of insulin signaling and proteasomal activity on physiological 2 output of a neuronal circuit in aging D. melanogaster

The insulin family of growth factors plays an important role in development and function of the nervous system. Reduced insulin and insulin-growth-factor signaling (IIS), however, can improve symptoms of neurodegenerative diseases in laboratory model organisms and protect against age-associated decline in neuronal function. Recently, we showed that chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber escape response circuit. Here, we expand our initial findings by demonstrating that reduced functional output in the giant fiber system of aging flies can be prevented by increasing proteasomal activity within the circuit. Manipulations of IIS in neurons can also affect longevity, underscoring the relevance of the nervous system for aging

Reduced insulin signaling maintains electrical transmission in a neural circuit in aging flies

Lowered insulin/insulin-like growth factor (IGF) signaling (IIS) can extend healthy lifespan in worms, flies, and mice, but it can also have adverse effects (the “insulin paradox”). Chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber system (GFS), a simple escape response neuronal circuit, by increasing targeting of the gap junctional protein innexin shaking-B to gap junctions (GJs). Endosomal recycling of GJs was also stimulated in cultured human cells when IIS was reduced. Furthermore, increasing the activity of the recycling small guanosine triphosphatases (GTPases) Rab4 or Rab11 was sufficient to maintain GJs upon elevated IIS in cultured human cells and in flies, and to rescue age-related loss of GJs and of GFS function. Lowered IIS thus elevates endosomal recycling of GJs in neurons and other cell types, pointing to a cellular mechanism for therapeutic intervention into aging-related neuronal disorders

GRAY-SCOTT モデル ニ ミラレル パルス ノ ブンレツ カテイ ニ タイスル リロンテキ アプローチ サンイツケイ ノ スウリ パターン オ ヒョウゲン スル ゼンキンカイ ノ コウセイ

Reduced activity of nutrient-sensing signaling networks can extend organismal lifespan, yet the underlying biology remains unclear. We show that the anti-aging effects of rapamycin and reduced intestinal insulin/insulin growth factor (IGF) signaling (IIS) require the Drosophila FoxA transcription factor homolog Fork Head (FKH). Intestinal FKH induction extends lifespan, highlighting a role for the gut. FKH binds to and is phosphorylated by AKT and Target of Rapamycin. Gut-specific FKH upregulation improves gut barrier function in aged flies. Additionally, it increases the expression of nutrient transporters, as does lowered IIS. Evolutionary conservation of this effect of lowered IIS is suggested by the upregulation of related nutrient transporters in insulin receptor substrate 1 knockout mouse intestine. Our study highlights a critical role played by FKH in the gut in mediating anti-aging effects of reduced IIS. Malnutrition caused by poor intestinal absorption is a major problem in the elderly, and a better understanding of the mechanisms involved will have important therapeutic implications for human aging

Myostatin-like proteins regulate synaptic function and neuronal morphology

Growth factors of the TGFβ superfamily play key roles in regulating neuronal and muscle function. Myostatin (or GDF8) and GDF11 are potent negative regulators of skeletal muscle mass. However, expression of myostatin and its cognate receptors in other tissues, including brain and peripheral nerves, suggests a potential wider biological role. Here, we show that Myoglianin (MYO), the Drosophila homolog of myostatin and GDF11, regulates not only body weight and muscle size, but also inhibits neuromuscular synapse strength and composition in a Smad2-dependent manner. Both myostatin and GDF11 affected synapse formation in isolated rat cortical neuron cultures, suggesting an effect on synaptogenesis beyond neuromuscular junctions. We also show that MYO acts in vivo to inhibit synaptic transmission between neurons in the escape response neural circuit of adult flies. Thus, these anti-myogenic proteins act as important inhibitors of synapse function and neuronal growth

Impact of insulin signaling and proteasomal activity on physiological output of a neuronal circuit in aging Drosophila melanogaster

The insulin family of growth factors plays an important role in development and function of the nervous system. Reduced insulin and insulin-growth-factor signaling (IIS), however, can improve symptoms of neurodegenerative diseases in laboratory model organisms and protect against age-associated decline in neuronal function. Recently, we showed that chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber escape response circuit. Here, we expand our initial findings by demonstrating that reduced functional output in the giant fiber system of aging flies can be prevented by increasing proteasomal activity within the circuit. Manipulations of IIS in neurons can also affect longevity, underscoring the relevance of the nervous system for aging

Over-expression of recycling Rabs rescues age-related loss of gap junctions (GJs) and giant fiber system (GFS) function.

<p>(A and B) Over-expression of Rab4 (wild type [WT]) or Rab11(WT) in the GFS led to increased levels of shaking-B protein (SHAK-B) in the thorax of old flies. Representative confocal images for Rab4(WT) are shown in (A), the quantification in (B) (<i>n</i> = 5–10). (C) Tergotrochanteral muscle pathway (TTM) response latencies from young ([y] days 5–7) and old ([o] days 45–50) flies of various genotypes. WT and constitutively active (CA) construct over-expressed WT or CA forms of Rab4 and Rab11, respectively. Bars with different first letters indicate significant difference (irrespective of the subscript). The letters in the parentheses indicate a lack of significance with the specified bar (<i>n</i> = 4–8). (D) Quantification of the SHAK-B signal intensity in the bilateral tracts of young (7-day-old) flies with silenced Rab4 or Rab11 expression (<i>n</i> = 8–10). (E) Rab11 is indispensable for the effect of reduced signaling on the transmission through the TTM branch of the GF circuit (<i>n</i> = 5–13). Error bars denote SEM.</p

Lowered insulin/insulin-like growth factor signaling (IIS) increases connexin 43 (Cx43) gap junction (GJ) formation in human cells.

<p>(A and B) Confocal pictures of human retinal pigment epithelial (RPE1) cell monolayers upon elevated or reduced IIS, stimulated or not with insulin (1 hour) or insulin receptor (IR)/insulin-like growth factor-1 receptor (IGF1R) dual inhibitor (“IR inhib”), as indicated, and immunostained for Cx43 (green), integrin α3 (ITGA3, red), and DNA (DAPI, blue), images are representative of at least 30 captures from 3 independent experiments). Bar, 10 μm. (C, D, G) Quantification from high-throughput microscopy images of the total levels of Cx43 in RPE1 cells upon elevated or reduced IIS, stimulated or not with insulin, IR/IGF1R dual inhibitor (“IR inhib”), protein kinase C (PKC) activator or inhibitor or lysosomal inhibitors (NH₄Cl or bafilomycin A [BafA]) or transfected with the indicated wild-type (WT), constitutively active (CA) or dominant-negative (DN) Rab constructs, and normalized as indicated. (Data are shown as means ± SEM from 3 independent experiments (over 12,000 Cx43 punctae per condition); <i>n</i>.<i>s</i>., not significant; *<i>P</i> < 0.05, **<i>P</i> < 0.1, ***<i>P</i> < 0.001; 1-way ANOVA and Dunnett test versus “−insulin,” “+insulin,” or enhanced green fluorescent protein [EGFP], as appropriate). (E and H) Percentage of Cx43 colocalizing with ITGA3 (“Surface”), early endosome antigen 1 (EEA1; “Early Endosomes”) or lysosomal-associated membrane protein 1 (Lamp1; “Lysosomes”) in cells treated as indicated (Data are shown as means ± SEM from 3 independent experiments (over 12,000 Cx43 punctae per condition); <i>n</i>.<i>s</i>. = not significant; *<i>P</i> < 0.05, **<i>P</i> < 0.1, ***<i>P</i> < 0.001; 1-way ANOVA and Dunnett test versus “−insulin,” “+insulin,” or EGFP, as appropriate). (F) Transferrin efflux (endosomal recycling) measured by flow cytometry from RPE1 cells upon elevated or reduced IIS, stimulated or not with insulin (1 hour), as indicated. (Data are shown as means ± SEM from 3 independent experiments and normalized to “elevated IIS” at 7.5 minutes. Over 10,000 cells were analyzed per condition and per experiment; <i>n</i>.<i>s</i>., not significant; ***<i>P</i> < 0.001; 1-way ANOVA and Dunnett test.</p

Insulin signaling regulates giant fiber system (GFS) function during aging, and gap junctional density.

<p>(A) GFS-specific over-expression of <i>InR</i>^<i>dn</i> abolished the age-related response latency decline (tergotrochanteral muscle [TTM] pathway age x genotype interaction: <i>P</i> = 0.0004; <i>n</i> = 6–9). (B) Representative images of thoracic shaking-B protein (SHAK-B) staining in 45-day-old control (<i>A307-GAL4/+</i>) flies (left), and 45-day-old <i>A307-GAL4/UAS-InR</i>^<i>dn</i> flies (right). Scale bar: 15 μm. (C) Quantification of SHAK-B signal intensities in the bilateral tracts of the GFS (<i>n</i> = 4–7). (D) Top: Over-expression of <i>SHAK-B(N+16)</i> prevented functional decline in the GFS with age (interaction <i>P</i> = 0.015; <i>n</i> = 6–14 per genotype/age). Bottom: Representative TTM traces from 45-day-old control (left) and <i>SHAK-B(n+16)</i>-over-expressing (right) flies. Red arrows indicate response latency periods. All panels: error bars denote SEM.</p