A role for the metalloprotease invadolysin in insulin signaling and adipogenesis

Abstract

Invadolysin is a novel metalloprotease conserved amongst metazoans that is essential for life in Drosophila. We previously showed that invadolysin was essential for the cell cycle and cell migration, linking to metabolism through a role in lipid storage and interaction with mitochondrial proteins. In this study we demonstrate that invadolysin mutants exhibit increased autophagy and decreased glycogen storage - suggestive of a role for invadolysin in insulin signaling in Drosophila. Consistent with this, effectors of insulin signaling were decreased in invadolysin mutants. In addition, we discovered that invadolysin was deposited on newly synthesized lipid droplets in a PKC-dependent manner. We examined two in vitro models of adipogenesis for the expression and localization of invadolysin. The level of invadolysin increased during both murine 3T3-L1 and human Simpson-Golabi-Behmel syndrome (SGBS), adipogenesis. Invadolysin displayed a dynamic localization to lipid droplets over the course of adipogenesis, which may be due to the differential expression of distinct invadolysin variants. Pharmacological inhibition of adipogenesis abrogated the increase in invadolysin. In summary, our results on in vivo and in vitro systems highlight an important role for invadolysin in insulin signaling and adipogenesis.

The conserved metalloprotease invadolysin is present in invertebrate haemolymph and vertebrate blood

“…Though variant 2 can be detected by RT-PCR, it is not as prevalent as variant 1, and under what conditions it is translated is currently under investigation. We have identified the expression of variant 2 during the later stages of in vitro adipogenesis (Chang et al, 2016). I n silico analysis of invadolysin open reading frames from different species thus suggests the presence of a signal sequence that could target the translation of invadolysin to the secretory pathway.…”

“…invadolysin mutant third instar larvae have reduced fat body thickness and cellular cross-sectional area (Cobbe et al, 2009). Critically, invadolysin mutants also have reduced triglyceride and glycogen levels (Chang et al, 2016; McHugh et al, 2004). To further analyse the role of invadolysin's conserved protease and lipase catalytic motifs in lipid and glycogen storage, transgenic Drosophila strains with mutated motifs were generated by site-directed mutagenesis.…”

“…2F). We propose that the decreased glycogen level observed in invadolysin mutants is likely due to impaired insulin signalling or metabolism of glycogen reserves (Chang et al, 2016). Immunoblotting of ovaries from wild type, a Da-Gal4 driver, and the three invadolysin transgenes suggests that invadolysin is overexpressed perhaps three- to fivefold in the transgenic lines compared to the wild type, and Da-Gal4 driver alone controls (data not shown).…”

“…To date, invadolysin is the only protease shown to localise to lipid droplets, the primary lipid storage organelle of the cell (Cobbe et al, 2009). More recent studies have identified key roles for invadolysin in metabolism including insulin signalling, lipid accumulation and the maintenance of normal mitochondrial function (Chang et al, 2016; Di Cara et al, 2013). Though a fairly conserved lipase motif lies downstream of the highly conserved protease motif, neither of these motifs has been thoroughly examined in invadolysin's function.…”

“…We previously demonstrated that invadolysin plays a crucial role in metabolism and energy storage in Drosophila (Chang et al, 2016; Cobbe et al, 2009). We set about further examining these functions using a number of approaches.…”