Mitochondrial Function Is Required for Secretion of DAF-28/Insulin in C. elegans

Abstract

While insulin signaling has been extensively studied in Caenorhabditis elegans in the context of ageing and stress response, less is known about the factors underlying the secretion of insulin ligands upstream of the insulin receptor. Activation of the receptor governs the decision whether to progress through the reproductive lifecycle or to arrest growth and enter hibernation. We find that animals with reduced levels of the mitochondrial outer membrane translocase homologue TOMM-40 arrest growth as larvae and have decreased insulin signaling strength. TOMM-40 acts as a mitochondrial translocase in C. elegans and in its absence animals fail to import a mitochondrial protein reporter across the mitochondrial membrane(s). Inactivation of TOMM-40 evokes the mitochondrial unfolded protein response and causes a collapse of the proton gradient across the inner mitochondrial membrane. Consequently these broadly dysfunctional mitochondria render an inability to couple food abundance to secretion of DAF-28/insulin. The secretion defect is not general in nature since two other neuropeptides, ANF::GFP and INS-22::VENUS, are secreted normally. RNAi against two other putative members of the TOMM complex give similar phenotypes, implying that DAF-28 secretion is sensitive to mitochondrial dysfunction in general. We conclude that mitochondrial function is required for C. elegans to secrete DAF-28/insulin when food is abundant. This modulation of secretion likely represents an additional level of control over DAF-28/insulin function.

A peroxiredoxin,PRDX‐2, is required for insulin secretion and insulin/IIS‐dependent regulation of stress resistance and longevity

“…The effect of loss of PRDX-2 on DAF-28::GFP secretion is comparable to the reported effects of RNAi targeting asna-1 or mitochondrial components, which have previously been shown to be important for insulin secretion (Figs2 and S1) (Kao et al ., 2007; Billing et al ., 2011). However, in contrast to loss of asna-1 or mitochondrial function, for example tomm-20 , there is no larval arrest/constitutive dauer phenotype associated with loss of PRDX-2 function.…”

Complex expression dynamics and robustness in C. elegans insulin networks

“…Third, we did not observe GFP expression in the germline, most likely because of transgene silencing (Kelly et al 1997). Finally, insulins are secreted peptides that may act cellnon-autonomously (Billing et al 2011;Bai et al 2012). Nonetheless, we provide both a first comprehensive data set as well as a set of transgenic strains, both of which enable future studies of the functional dynamics of the entire C. elegans insulin gene family in vivo.…”

Journal of Parkinson’s disease & Alzheimer’s disease

“…Moreover, reducing TOM40 levels in C. elegans retarded growth [41], as did introducing assembly-defective TOM40 mutations in N. crassa [38]. …”

“…The C. elegans RNAi screen showed that reduced TOMM40 levels arrested growth between the 1st and 3rd larval stages; TOMM40 knock-out animals exhibited a phenotype similar to the knock-downs [41]. In neither case were there detectable developmental defects or structural or functional defects in the worms’ feeding apparatus [41], indicating the animals ability to feed was intact and TOMM40 per se was required for continual growth.…”

“…In neither case were there detectable developmental defects or structural or functional defects in the worms’ feeding apparatus [41], indicating the animals ability to feed was intact and TOMM40 per se was required for continual growth. TOMM40 knock-down collapsed the mitochondrial membrane potential, blocked the uptake of mitochondrially targeted proteins and elicited the mitochondrial stress response, but markers of cytoplasmic and endoplasmic reticulum stress were not affected.…”