Sirt4 is a mitochondrial regulator of metabolism and lifespan in Drosophila melanogaster.

Sirtuins are an evolutionarily conserved family of NAD+-dependent deacylases that control metabolism, stress response, genomic stability, and longevity. Here, we show the sole mitochondrial sirtuin in Drosophila melanogaster, Sirt4, regulates energy homeostasis and longevity. Sirt4 knockout flies have a short lifespan, with increased sensitivity to starvation and decreased fertility and activity. In contrast, flies overexpressing Sirt4 either ubiquitously or specifically in the fat body are long-lived. Despite rapid starvation, Sirt4 knockout flies paradoxically maintain elevated levels of energy reserves, including lipids, glycogen, and trehalose, while fasting, suggesting an inability to properly catabolize stored energy. Metabolomic analysis indicates several specific pathways are affected in Sirt4 knockout flies, including glycolysis, branched-chain amino acid metabolism, and impaired catabolism of fatty acids with chain length C18 or greater. Together, these phenotypes point to a role for Sirt4 in mediating the organismal response to fasting, and ensuring metabolic homeostasis and longevity.

Chromatin-modifying genetic interventions suppress age-associated transposable element activation and extend life span in Drosophila.

Transposable elements (TEs) are mobile genetic elements, highly enriched in heterochromatin, that constitute a large percentage of the DNA content of eukaryotic genomes. Aging in Drosophila melanogaster is characterized by loss of repressive heterochromatin structure and loss of silencing of reporter genes in constitutive heterochromatin regions. Using next-generation sequencing, we found that transcripts of many genes native to heterochromatic regions and TEs increased with age in fly heads and fat bodies. A dietary restriction regimen, known to extend life span, repressed the age-related increased expression of genes located in heterochromatin, as well as TEs. We also observed a corresponding age-associated increase in TE transposition in fly fat body cells that was delayed by dietary restriction. Furthermore, we found that manipulating genes known to affect heterochromatin structure, including overexpression of Sir2, Su(var)3-9, and Dicer-2, as well as decreased expression of Adar, mitigated age-related increases in expression of TEs. Increasing expression of either Su(var)3-9 or Dicer-2 also led to an increase in life span. Mutation of Dicer-2 led to an increase in DNA double-strand breaks. Treatment with the reverse transcriptase inhibitor 3TC resulted in decreased TE transposition as well as increased life span in TE-sensitized Dicer-2 mutants. Together, these data support the retrotransposon theory of aging, which hypothesizes that epigenetically silenced TEs become deleteriously activated as cellular defense and surveillance mechanisms break down with age. Furthermore, interventions that maintain repressive heterochromatin and preserve TE silencing may prove key to preventing damage caused by TE activation and extending healthy life span.

Increased expression of Drosophila Sir2 extends life span in a dose-dependent manner.

Sir2, a member of the sirtuin family of protein acylases, deacetylates lysine residues within many proteins and is associated with lifespan extension in a variety of model organisms. Recent studies have questioned the positive effects of Sir2 on lifespan inDrosophila. Several studies have shown that increased expression of the Drosophila Sir2 homolog (dSir2) extends life span while other studies have reported no effect on life span or suggested that increased dSir2 expression was cytotoxic. To attempt to reconcile the differences in these observed effects of dSir2 on Drosophila life span, we hypothesized that a critical level of dSir2 may be necessary to mediate life span extension. Using approaches that allow us to titrate dSir2 expression, we describe here a strong dose-dependent effect of dSir2 on life span. Using the two transgenic dSir2 lines that were reported not to extend life span, we are able to show significant life span extension when dSir2 expression is induced between 2 and 5-fold. However, higher levels decrease life span and can induce cellular toxicity, manifested by increased expression of the JNK-signaling molecule Puc phosphatase and induction of dnaJ-H. Our results help to resolve the apparently conflicting reports by demonstrating that the effects of increased dSir2 expression on life span in Drosophila are dependent upon dSir2 dosage.

Genomic and in vivo evidence of synergy of a herbal extract compared to its most active ingredient: Rabdosia rubescens vs. oridonin.

Rabdosia rubescens is a herbal root extract of traditional Chinese medicine (TCM) used to treat inflammatory diseases and oral cancers. A key principle of TCM is that multiple ingredients in a plant extract are more effective and less toxic than a single purified active ingredient or a purified drug derived from a plant product. Rabdosia rubescens extract (RRE) contains terpenoids and flavonoids, but the most active ingredient within the extract attributed to the inhibition of cancer is the kaurene diterpene, oridonin. In order to research synergy with a complete plant extract, the effects of RRE on the inhibition of prostate cancer cell proliferation were compared to the effects of pure oridonin alone in vitro. Three groups of 8 SCID mice bearing human prostate cancer xenografts (LAPC-4) were administered either RRE containing 0.02 mg/g oridonin, pure oridonin at a dose of 0.02 mg/g, or pure oridonin at a dose of 0.1 mg/g, by gavage for 5 days/week for 4 weeks. RRE and pure oridonin at 0.1 mg/g inhibited tumor growth to a similar extent, while oridonin at a dose of 0.02 mg/g did not. Therefore, in comparison to RRE, five times more pure oridonin was required to obtain equivalent prostate xenograft growth inhibition. Since the nuclear factor-κB signaling pathway and inflammation are implicated in prostate carcinogenesis, gene microarray analysis was conducted and demonstrated activation of genes by RRE that was not evident with oridonin treatment alone. This study demonstrated that genomic methods and xenograft studies are capable of demonstrating the benefits of the synergy of whole plant extracts rather than active ingredients isolated and purified as drugs.