Expression of lipid storage droplet protein-1 may define the role of AKH as a lipid mobilizing hormone in Manduca sexta

Abstract

Adipokinetic hormone (AKH) is the main hormone involved in the acute regulation of hemolymph lipid levels in several insects. In adult Manduca sexta AKH promotes a rapid phosphorylation of “Lipid storage protein-1”, Lsd1, and a concomitant activation of the rate of hydrolysis of triglycerides by the main fat body lipase. In contrast, in the larval stage AKH modulates hemolymph trehalose levels. The present study describes the sequence of a full length Lsd1 cDNA obtained from M. sexta fat body and investigates a possible link between Lsd1 expression and the distinct effects of AKH in larva and adult insects. The deduced protein sequence showed a high degree of conservation compared to other insect Lsd1s, particularly in the central region of the protein (amino acids 211–276) in which the predicted lipid binding helices are found. Lsd1 was absent in feeding larva and its abundance progressively increased as the insect develops from the non-feeding larva to adult. Contrasting with the levels of protein, Lsd1 transcripts were maximal during the feeding larval stages. The subcellular distribution of Lsd1 showed that the protein exclusively localizes in the lipid droplets. Lsd1 was found in the fat body but it was undetectable in lipid droplets isolated from oocytes or embryos. The present study suggests a link between AKH-stimulated lipolysis in the fat body and the expression of Lsd1.

Multifaceted biological insights from a draft genome sequence of the tobacco hornworm moth, Manduca sexta

“…The concerted study of the three lipases, ATGL, TGL and HSL, and the role of the lipid droplet proteins, PLIN1 (Msex2.00753) and PLIN2 (Msex2.00753), previously named Lsd1 and Lsd2, should lead to advances in the biochemistry of lipid mobilization. PLIN proteins are lipid droplet resident proteins that play a major role in the regulation of storage of TG and DG production and secretion (Arrese et al, 2008a; Bi et al, 2012; Gronke et al, 2003; Patel et al, 2005; Teixeira et al, 2003). Studies in M. sexta demonstrated that AKH induces PKA-mediated phosphorylation of PLIN1 which activates the hydrolysis of TG (Arrese et al, 2008b; Patel et al, 2005).…”

Developmental changes in the protein composition of Manduca sexta lipid droplets

“…The total protein associated with purified LDs accounted for approximately 1.7% of total protein in the fat body homogenate. Lsd1, a protein that is found mostly associated with lipid droplets in Manduca sexta fat body (Arrese et al, 2008a), was used as fat body lipid droplet marker. As expected, the LDs fraction was enriched in this protein.…”

“…The higher abundance of Lsd1 in LDs from adult insects, as compared to LDs of larval fat body and ovaries, is consistent with the physiological state of adult insects, which are mobilizing FA from the fat body to the ovaries. Previous studies have linked the expression levels of Lsd1 (Arrese et al, 2008a) with the ability of M. sexta fat body to mobilize FA. Moreover, since adult insects are kept without food, they are also mobilizing and oxidizing FA to support basal metabolism.…”

A comparative perspective on lipid storage in animals

“…Although these proteins are localized on the LD surface, they have both opposing and redundant functions (Bi et al, 2012). Lsd-1 modulates the accessibility of lipases, such as Drosophila hormone sensitive lipase (Hsl), to the LD and stabilizes the structure of the LD (Arrese et al, 2008;Beller et al, 2010). Lsd-1 mutant flies are hyperphagic and obese (Beller et al, 2010).…”