Reduction of DILP2 in Drosophila Triages a Metabolic Phenotype from Lifespan Revealing Redundancy and Compensation among DILPs

Abstract

The insulin/IGF-like signalling (IIS) pathway has diverse functions in all multicellular organisms, including determination of lifespan. The seven insulin-like peptides (DILPs) in Drosophila are expressed in a stage- and tissue-specific manner. Partial ablation of the median neurosecretory cells (mNSCs) in the brain, which produce three DILPs, extends lifespan, reduces fecundity, alters lipid and carbohydrate metabolism and increases oxidative stress resistance. To determine if reduced expression of DILPs is causal in these effects, and to investigate possible functional diversification and redundancy between DILPs, we used RNA interference to lower specifically the transcript and protein levels of dilp2, the most highly expressed of the mNSC-derived DILPs. We found that DILP2 was limiting only for the increased whole-body trehalose content associated with mNSC-ablation. We observed a compensatory increase in dilp3 and 5 mRNA upon dilp2 knock down. By manipulation of dfoxo and dInR, we showed that the increase in dilp3 is regulated via autocrine insulin signaling in the mNSCs. Our study demonstrates that, despite the correlation between reduced dilp2 mRNA levels and lifespan-extension often observed, DILP2 reduction is not sufficient to extend lifespan. Nor is the increased trehalose storage associated with reduced IIS sufficient to extend lifespan. To understand the normal regulation of expression of the dilps and any functional diversification between them will require independent control of the expression of different dilps.

Deletion of Drosophila insulin-like peptides causes growth defects and metabolic abnormalities

“…Based upn genomic sequence and similarity to mammalian insulin, Drosophila have at least seven candidate IIS ligands. Evidence from RNAi experiments in our lab and published by others, while our work was in progress (34), indicate a high degree of redundancy among DILPs, including compensatory upregulation of expression of dilp gene(s), when others are experimentally downregulated. Thus, multiple approaches will be required to assess the functions of this complex multigene family.…”

“…One interpretation of the absence of growth defects is that there is functional redundancy among dilps. In keeping with this, a recent paper reported that expression of dilp2 RNAi resulted in a compensatory increase in dilp3 levels (34). With 7 dilp genes, it is virtually impossible to assess functional redundancy using combinations of individual RNAi lines, which may vary in their effectiveness overall or in different cell types.…”

Long live FOXO: unraveling the role of FOXO proteins in aging and longevity

“…Drosophila has seven genes encoding insulin‐like peptides (dilps), and ablation of the cells expressing only three of the seven dilps in neuroendocrine cells of the brain is sufficient to increase longevity (Broughton et al ., 2008). dFoxO has also been shown to regulate D. melanogaster aging when activated specifically in the adult pericerebral fat body.…”

The hormonal and circadian basis for insect photoperiodic timing

“…In D. melanogaster adults, IPCs produce three out of the seven encoded ILPs (ILP2, ILP3 and ILP5), which are independently regulated [34,37,38]. ILPs signal through the insulin receptor (INR) to regulate metabolism, growth, reproduction and aging [34,[39][40][41][42][43][44] (Fig.…”